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Comminution circuit design and simulation for the development of a novel high pressure grinding roll… Rosario, Persio Pellegrini 2010

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Comminution Circuit Design and Simulation for the Development of a Novel High Pressure Grinding Roll Circuit by  Persio Pellegrini Rosario  A thesis submitted in partial fulfillment of the requirements for the degree of  Doctor of Philosophy in  The Faculty of Graduate Studies (Mining Engineering)  The University of British Columbia (Vancouver) November 2010  © Persio Pellegrini Rosario, 2010  ABSTRACT  The application of High Pressure Grinding Roll (HPGR) in comminution circuits is well established in processing cement, diamonds and iron ore. Recently, the application of HPGR has been extended to high-tonnage precious and base metals operations with hard ore. This is due to the HPGR: being more energy-efficient than grinding mills, not requiring steel grinding media, and providing higher throughputs than cone crushers. Although HPGR circuits are being used in high-tonnage precious and base metals, there is limited quantitative knowledge to indicate the true benefits or drawbacks of HPGR compared to Semi-autogenous mill (SAG). This lack of knowledge restricts the ability of designers to determine the optimal circuit.  To address this lack of knowledge the  research in this thesis:  •  Reviews the basics of the HPGR machine, its benefits and shortcomings.  •  Details the development of the SAG circuits and explains how the new generation of crushing circuits, with HPGR for tertiary crushing, are starting to replace SAG circuits in hard-rock mining.  •  Presents a structured methodology for comparison of the energy requirements for HPGR versus SAG complete circuits. The process is based on industrial best practices and advanced modelling tools, and is demonstrated through the evaluation of two hypothetical mining projects (based on real ore data).  •  Investigates the feasibility of a novel AG-Crusher-HPGR circuit using rock samples from a large copper-gold mining project. The approach was to develop and evaluate the circuit design for high-tonnage operations with mixed hardness  ii  ores containing clay. Previously, HPGR was considered only suitable for very hard ores and the technology was rejected for other cases. A unique pilot-plant test program was developed as a basis for experimental simulation. As a result the suitability of the circuit was demonstrated. The development of this novel circuit along with the findings of this research have the potential to improve future mining operations dealing with similar orebodies that, in fact, are major sources of base metals worldwide. The potential for significant savings in energy and steel media have been demonstrated. This may also lead to the selection of more sustainable circuits for a broader range of orebodies.  iii  PREFACE  Prof. Robert Hall is my PhD program supervisor and co-authored two manuscripts (Chapters 3 and 4).  Prof. Hall provided feedback on manuscript preparations and  contributed to the identification and design of my research program. Prof. Bern Klein is my PhD program co-supervisor and co-authored the third manuscript (Chapter 4). Prof. Klein provided input on the design of the testwork program applied in this research as well as participated in the identification and design of the research program. Mr. Mike Grundy was a co-author of two manuscripts (Chapters 2 and 4). Being a senior metallurgist with vast experience in AG/SAG mill application, he assisted me in the clarification of parts of the manuscript, especially the ones covering the history and recent applications of SAG circuit.  In addition, he provided feedback during the  development of the novel HPGR circuit, verifying a number of my assumptions and assisting me in specific engineering details for the operation of a circuit. Mr. Ken Boyd was a co-author of the first manuscript (Chapter 2).  Being a senior  mechanical engineer specialized in material handling systems he contributed with information regarding the application of pebble crushers in recent SAG mill circuits. The contributions of all the people above mentioned was important and very much appreciated. However, the vast majority of the research and writing was conducted or developed and directed solely by the author, i.e. more than 95% of the work. This included the following:  •  Development of the research objectives, methodology and testing programs.  iv  •  Performance of all simulation analysis.  •  Performance of all test work with support from laboratory personnel for some manual labour and specialized tasks.  •  Review of the current state of the art as presented in the thesis.  •  Rewriting and integration of the papers into the current form in the thesis with revisions based feedback from my supervisory committee.  v  TABLE OF CONTENTS  Abstract ................................................................................................................................. ii Preface................................................................................................................................. iv Table of Contents ................................................................................................................. vi List of Tables........................................................................................................................ ix List of Figures........................................................................................................................ x Acknowledgements .............................................................................................................. xi 1  Introduction ................................................................................................................ 1 1.1 Comminution .................................................................................................. 1 1.2 Modern Metal Mining ...................................................................................... 3 1.3 HPGR in Hard Rock Mining ............................................................................ 5 1.4 Thesis Objectives ........................................................................................... 7 1.5 Thesis Outline ................................................................................................ 9  2  Comminution Circuits - Literature review ................................................................. 10 2.1 Introduction .................................................................................................. 10 2.2 Recent History of Comminution .................................................................... 11 2.3 SAG Mill Background ................................................................................... 13 2.3.1 AG/SAG Mill Machines ..................................................................... 13 2.3.2 SAG Operational Parameters ........................................................... 14 2.3.3 SAG Mill Original Circuit ................................................................... 15 2.3.4 Pebble Crushing for AG/SAG Circuits............................................... 17 2.3.5 SAG Feed Preparation ..................................................................... 21 2.3.6 Steel Wear........................................................................................ 22 2.4 HPGR Background....................................................................................... 25 2.4.1 HPGR Machine................................................................................. 25 2.4.2 HPGR Terminology and Operational Parameters ............................. 28 2.4.3 HPGR Original Circuits ..................................................................... 31 2.4.4 HPGR Precious/Base Metal Recent Circuits..................................... 35 2.4.5 Energy Savings ................................................................................ 37 2.4.6 Metallurgical Extraction Advantages ................................................. 40 2.4.7 HPGR Feed and Product Specifics ................................................... 41 2.4.8 Limitations and Disadvantages ......................................................... 42 2.5 Other Developments .................................................................................... 43 2.5.1 Increasing Machine Sizes ................................................................. 43 2.5.2 Stirred Mills ....................................................................................... 43 2.5.3 Fully Autogenous Grinding................................................................ 44 2.6 Summary of Current State ............................................................................ 46  3  Guidelines for Energy Requirement Comparisons between HPGR and SAG Mill Circuits in High-Tonnage Hard Rock Mining ...................................................... 47 3.1 Introduction .................................................................................................. 47 3.2 Modelling and Simulation Background ......................................................... 49 3.3 Case Studies................................................................................................ 51 3.4 Design Criteria Development........................................................................ 52 3.5 Flowsheet Development ............................................................................... 54  vi  3.6 3.7 3.8  3.9  Developed Models ....................................................................................... 56 Equipment Sizing ......................................................................................... 61 Results and Discussions .............................................................................. 62 3.8.1 Pure Comminution Energy ................................................................ 62 3.8.2 Complete Circuit Comminution Energy ............................................. 63 3.8.3 Steel Usage ...................................................................................... 64 3.8.4 Ore Variability ................................................................................... 65 3.8.5 Heating and Ventilation..................................................................... 66 3.8.6 Availability and Maintainability .......................................................... 66 3.8.7 Additional HPGR Benefits................................................................. 67 3.8.8 HPGR Circuit Drawbacks.................................................................. 67 Summary...................................................................................................... 69  4  Testwork Program for the Evaluation of a Novel HPGR-Based Circuit to Treat Mixed Hardness Ores Containing Clays .................................................................. 71 4.1 Introduction .................................................................................................. 71 4.2 Novel HPGR Circuit for Ores Containing Clayish Material ............................ 75 4.3 Testwork ...................................................................................................... 77 4.3.1 Sample ............................................................................................. 77 4.3.2 Testwork Design ............................................................................... 77 4.3.3 Test Equipment ................................................................................ 79 4.4 Results and Discussion ................................................................................ 81 4.4.1 Sample Properties ............................................................................ 81 4.4.2 Tumbling Test ................................................................................... 81 4.4.3 HPGR Feed PSD.............................................................................. 83 4.4.4 HPGR Feed Moisture Content .......................................................... 88 4.4.5 HPGR Tests ..................................................................................... 91 4.4.6 HPGR Product Cakes ..................................................................... 102 4.4.7 Bond Ball Mill Work Indices ............................................................ 106 4.5 Summary.................................................................................................... 108  5  Feasibility Assessment of the AG-Crusher-HPGR Circuit to Treat Clayish and/or Mixed Hardness Ores ................................................................................. 109 5.1 Introduction ................................................................................................ 109 5.2 Modelling and Simulation ........................................................................... 110 5.3 Energy Requirements................................................................................. 115 5.3.1 Ball Mill Energy ............................................................................... 115 5.3.2 Pure Comminution Energy .............................................................. 117 5.3.3 Complete Circuit Comminution Energy ........................................... 119 5.4 Operating and Capital Costs ...................................................................... 122 5.4.1 Operating Cost ............................................................................... 122 5.4.2 Capital Cost .................................................................................... 122 5.5 Discussions ................................................................................................ 124  6  Conclusions ........................................................................................................... 126 6.1 Main Research Contributions ..................................................................... 126 6.2 Future Research Opportunities .................................................................. 128  References........................................................................................................................ 131 Appendix – A: Inputs Used for the JKSimMet® Models .................................................... 142 Appendix – B: SMC and MinnovEX SPI Test Results ....................................................... 145  vii  Appendix – C: Sample Preparation and Test Flowsheet................................................... 146 Appendix – D: HPGR Feed Test Blend – Linear Programing ............................................ 148 Appendix – E: HPGR Tests – Complete Data................................................................... 150 Appendix – F: AG-Crusher-HPGR Plant Layout ............................................................... 158 Appendix – G: SABC Plant Layout ................................................................................... 160 Appendix – H: Power Consumption Comparison .............................................................. 162  viii  LIST OF TABLES  Table 3-1: Table 3-2: Table 3-3: Table 3-4: Table 4-1: Table 4-2: Table 4-3: Table 4-4: Table 4-5 Table 5-1: Table 5-2: Table 5-3:  Summary of Design Criteria ......................................................................... 53 Pure Comminution Energy ........................................................................... 62 Complete Circuit Comminution Energy......................................................... 64 SAG Mill Steel Ball Consumption ................................................................. 65 Pilot-Scale HPGR Specifications .................................................................. 79 Summary of Parameters and Calculated Results for Moisture Content ........ 91 HPGR Tests Quick Reference Legend ......................................................... 92 Summary of the Main Parameters and Results for All HPGR Pilot Tests...... 93 Average Dimensions of Cakes Produced by the HPGR Tests .................... 104 Simulation Results – Pure Comminution Energy Requirements ................. 118 Energy Requirements for the Complete Circuits ......................................... 121 Capital Cost Summary ............................................................................... 123  ix  LIST OF FIGURES  Figure 2-1: Figure 2-2: Figure 2-3: Figure 2-4: Figure 2-5: Figure 2-6: Figure 2-7: Figure 2-8: Figure 2-9: Figure 2-10: Figure 2-11: Figure 2-12: Figure 2-13: Figure 3-1: Figure 3-2: Figure 3-3: Figure 4-1: Figure 4-2: Figure 4-3: Figure 4-4: Figure 4-5: Figure 4-6: Figure 4-7: Figure 4-8: Figure 4-9: Figure 4-10: Figure 4-11: Figure 4-12: Figure 4-13: Figure 4-14: Figure 4-15: Figure 4-16: Figure 4-17: Figure 4-18: Figure 4-19: Figure 4-20: Figure 5-1: Figure 5-2: Figure 5-3: Figure 5-4: Figure 5-5: Figure 5-6:  Three Stages of Crushing, Rod Mill, Ball Mill ................................................ 16 SAG-Ball Mill Circuit ..................................................................................... 17 SABC Circuit ................................................................................................ 18 Open-Circuit SABC ...................................................................................... 19 SABC with HPGR......................................................................................... 20 Pre-Crushing in an SABC Circuit.................................................................. 22 Schematic of a HPGR (Napier-Munn et al, 1996) ......................................... 26 Open Circuit HPGR – Closed-Circuit Ball Mill (Aydogan et al, 2006) ............ 32 HPGR Applied for Pebble Re-Crush at Empire Iron (Kawatra et al, 2003) .... 33 Re-Crush Circuit at Argyle Diamond Mines (KHD, 2008).............................. 34 Boddington HPGR (Dunne et al 2007) ......................................................... 35 Cerro Verde (Vanderbeek 2006) .................................................................. 36 Pebble Extraction and Milling ....................................................................... 45 Simplified SABC and HPGR Flowsheets ...................................................... 55 JKSimMet® Screen Snapshot of Case A – SABC ......................................... 57 JKSimMet® Screen Snapshot of Case A – HPGR ........................................ 58 Cerro Verde Flowsheet (Vanderbeek 2006) ................................................. 72 Hardness Distribution of the Deposit Based on Jk A*b Parameters .............. 74 Proposed HPGR Flowsheet for Clayish Ore ................................................. 75 UBC Pilot HPGR .......................................................................................... 79 Particle Size Distribution for the Samples as Received ................................ 81 Tumbling Test Feed and Product Size Distributions ..................................... 83 Lab-Scale Circuit to Prepare the Feed to the Pilot HPGR (open-circuit) ....... 84 PSDs for Fresh and Crushed Laboratory Screen O/S Material ..................... 85 PSDs from the Preliminary Simulation.......................................................... 86 PSDs for the Optimum Blend, Original Products and Simulated Product ...... 87 Lab-Scale Circuits Used for the Tests .......................................................... 88 Specific Throughput as a Function of Pressing Force................................... 95 Influence in Energy Consumption due to Pressing Force ............................. 96 Pressure Sensitivity Tests – Feed and Product PSDs .................................. 96 F80/P80 and F50/P50 Reduction Ratios ...................................................... 97 Feed and Product PSDs for Closed-Circuit Tests ......................................... 98 Feed and Product PSDs for Full Feed and Tumbled-Screened OpenCircuit HPGR Tests .................................................................................... 100 HPGR Test #1 Product Cake Samples....................................................... 103 Screen Oversize PSDs from the Tests for Assessment of HPGR Product Cake Competency...................................................................................... 105 Bond Ball Mill Index Results in Different Points of the Circuit ..................... 108 Feed PSD for Circuit Modelling and Simulations ........................................ 111 JKSimMet® Screen Snapshot of the SABC Circuit Simulation .................... 113 JKSimMet® Screen Snapshot of the Final AG-Crusher-HPGR Circuit Simulation .................................................................................................. 114 Ball Mill Cyclone Feed PSD from AG-Crusher-HPGR and SABC Circuits .. 116 AG Mill Feed (Combined) and Product PSDs ............................................. 117 AG-Crusher-HPGR Circuit Simplified Flowsheet ........................................ 120  x  ACKNOWLEDGEMENTS  I would like to express my gratitude to AMEC Mining & Metals, Vancouver, B.C., for the generous support during the research period for his Doctoral Thesis. I would like to extend a special thank you to my current and former managers, Alexandra Kozak and Joseph Milbourne (respectively), for allowing me the significant amount of time required to complete my research. I also would like to sincerely thank my friend and co-worker Mike Grundy for his invaluable support and advice. I am deeply thankful to my thesis supervisors, Prof. Robert Hall and Prof. Bern Klein, for their guidance and patience.  Members of the supervisory committee for valuable  advice. I would also like to thank the B.C. Mining Research, Koppern and the University of British Columbia for providing the excellent research facilities needed for my work. Of course, without my wife’s encouragement, support and patience, and the love shown by her and my three sons, this thesis would not be completed. I would also like to acknowledge the support of the (anonymous) mining company for supplying the sample used in experimental simulation and for co-sponsoring the investigation of the feasibility of the novel HPGR circuit.  xi  1 INTRODUCTION  1.1  Comminution  The dictionary definition (source: Merriam-Webster Dictionary) of the verb comminute is: to reduce to minute particles. In the mining and mineral processing industry, the term comminution mainly refers to crushing and grinding processes, although the size reduction of rocks starts in the blasting phase of mining. Comminution is an essential phase in mineral processing as it is required to liberate the valuable minerals from the gangue.  The breakage action is also described as the  creation of new mineral surface. Increasing mineral surface is essential for metallurgical extraction processes such as leaching and flotation. The energy requirement in comminution is a function of the reduction ratio, product size, and the hardness characteristics of the material, i.e. its breakage resistance.  The  relationship between required comminution energy, reduction ratio, product size, and material properties has been the object of research for more than a century.  The  theoretical and empirical formulas derived from this previous work and are summarized by Jankovic et al. (2010). Comminution in mining operations usually comprises the reduction of large rocks with sizes around 1 meter or larger to minute particles of 25 microns or smaller. However, most of the energy is used by the industry (89%) during the reduction from approximately 20 mm to 100 microns (Powell, 2010). Currently, the comminution process is energy intensive and highly energy inefficient. It is estimated that comminution accounts for 65% to 80% of all energy usage in mining 1  operations and that only 1% to 2% of the applied energy is effectively translated in the production of new surface area (Tromans and Meech, 2002).  This expensive and  inefficient process also represents a significant fraction of the world electric power consumption, e.g. in 1981, comminution processing accounted for approximately 2% of the total U.S.A. electric power usage (Kawatra and Eisele, 2005). The combination of the energy intensive and inefficient characteristics of comminution implies that there is a great opportunity for significant energy and economic savings by the improvement of this process (Kawatra and Eisele, 2005).  2  1.2  Modern Metal Mining  In the recent few decades, there has been a shift from the mining of high-grade, nearsurface, and relatively soft orebodies to low-grade, deeper and harder ores.  The  depletion of high-grade ores and the increasing demand for metals have stimulated the development of large-scale operations. These large-scale mining operations extract the valuable minerals from massive orebodies and are the main source for many base and precious metals. For instance, the twenty largest copper mines around the globe were responsible for more than 60% of all copper production from mines in 2008 (International Copper Study Group, 2009). The advent of large tumbling mills has facilitated the development of these high-tonnage deposits for the last three to four decades. These high capacity mills, specifically the autogenous (AG) and semi-autogenous mills (SAG), have progressively replaced crusher-based circuits due to their simpler flowsheets with fewer pieces of equipment. In addition, these circuits do not utilize washing plants.  Washing plants are usually  required ahead of a crushing circuit when dealing with orebodies that contain a high level of weathered material (regions with high-clay content) or high moisture content (not rare characteristics in these large orebodies). Even though SAG-based comminution circuits are dominant in the industry, they do present some challenges for the treatment of several types of large orebodies. If the orebody contains significant hard ore, the SAG mill becomes extremely energy inefficient as its capacity is highly reduced (Morley and Staples, 2010). High hardness variability throughout the orebody produces significant SAG capacity variation and thus provides an adverse overall throughput fluctuation (Burger et al, 2006). Similar fluctuations occur  3  when the SAG feed size distribution cannot be maintained relatively uniform through time (Morrell and Valery, 2001). Usually, the larger these low-grade deposits are, the larger the variance in rock properties such as hardness levels. For instance, large porphyry copper ore deposits (currently the largest source of copper ore) can present highly variable hardness and some examples of such orebodies are Freeport-McMoRan’s Chino Mine in New Mexico (Amelunxen et al, 2001) and Newmont’s Batu Hijau operation in Indonesia (Burger et al, 2006).  4  1.3  HPGR in Hard Rock Mining  In recent years efforts to improve the comminution process have led to the integration of the High Pressure Grinding Roll (HPGR) into non conventional applications.  Until  recently this relatively new type of crusher was used in the cement, diamond and iron industries. Over the last few years HPGR has expanded its application to base and precious metals high-tonnage hard rock processing. With the application of HPGR to new types of ores there has been debate as to their suitability compared to the more traditional AG/SAG circuits (Morley and Staples, 2010). One area that the HPGR manufacturers emphasize is the energy efficiency advantages of the HPGR when compared to tumble milling.  The HPGR manufacturers claim  substantial energy savings (up to 40% savings) when the HPGR circuit is compared to conventional crushing and grinding circuits (KHD, 2002; von Seebach and Knobloch, 1987; Koppern, 2006). There have also been indications by comminution consultants outside HPGR manufacturing field that significant energy savings may be achieved on very hard ores (Morley, 2006; Morrell, 2008) and research are research confirming this trend (Napier et al, 1996; Shi et al, 2006). The recognition of these possible advantages added to the recent developments in HPGR roll surface wear resistance trigged the adoption of HPGR circuits for recent high-tonnage projects dealing with relatively homogenous, hard to extremely hard rock orebodies and with limited clay content (Vanderbeek, 2006; Seidel et al, 2006). These recent applications have in common the application of the HPGR for tertiary crushing. Their circuits are very similar to the 3-stage crushing circuits that were vastly  5  applied until the 1960s. Now, in high-tonnage mining these circuits are restricted to extremely hard ores or in processes where throughput stability is of primary importance. In other words, at the time of this research the HPGR was only replacing tertiary cone crushers in a very limited niche for base/precious metal mining. As a matter of fact, the research community seems to be now realizing this limitation. Very recently, Prof. Powell presented a paper at the Comminution’10 conference, and confirmed that although the great potential of HPGR is starting to be recognized, a better understanding of the technology and development of different HPGR flowsheets are required to ensure that this technology is fully exploited (Powell, 2010). There are still many unknowns with respect to the types of applications in which HPGR can be used and as of yet there has been little work done to develop a comprehensive approach to evaluate the overall efficacy of HPGR circuits versus other circuits. This research focuses on high-tonnage, base/precious metal operations, the most recent area where HPGR has been applied. As with any new technology, there is limited knowledge about it and its true benefits.  This research aims to improve the  understanding of the potential benefits and applications of HPGR circuits, and address some current uncertainties, such as:  •  Whether a complete HPGR comminution circuit is still able to provide substantial net energy savings when compared to a SAG-based circuit.  •  Will the HPGR bring the same benefits when applied on orebodies with mixed hardness and/or orebodies with high clay content, which are characteristics of various large copper ore deposits in the world?  6  1.4  Thesis Objectives  The current energy inefficient comminution circuits that are applied in base/precious metal mining present considerable opportunity for significant energy and economic savings.  In addition, the application of HPGR has demonstrated energy benefits in  comparable applications such as in cement and diamond processing. Recently, similar benefits are being claimed through the replacement of cone crushers by the HPGR in conventional 3-stage crushing circuits for some specific hard rock metal mining cases. However, to take fully advantage of their benefits and to broader their applications improved understandings of their technology as well as the development of different HPGR flowsheets are required. This research focuses on high-tonnage, base/precious metal comminution circuits and the primary objective of this work is to improve the understanding of the potential benefits and applications of the HPGR in such circuits.  In pursuit of the primary  objective the following secondary objectives are targeted:  •  Expand on current work to develop a structured methodology for the evaluation of the energy requirements of the complete HPGR circuits by the application of circuit design best practices and advanced modelling techniques.  •  Evaluate and demonstrate the applicability of the structured methodology for the comparison of SAG and HPGR overall circuit energy requirements through case studies.  •  Develop an innovative HPGR flowsheet to treat mixed hardness ores and/or weathered ores with a high proportion of clays and moisture.  7  •  Through a case study assess the suitability and the potential benefits of the novel circuit for the comminution of hard, weathered ores containing clayish material.  •  Develop a rigorous approach for testing HPGR circuits by the application of a unique pilot-plant test program as a basis for experimental simulation.  8  1.5  Thesis Outline  This Thesis is divided into five sections: The first section (Chapter 2) covers the history of comminution circuits and basic concepts related to grinding mills and the HPGR. The second section (Chapter 3) presents the developed structured process for the design and energy requirement evaluation of comminution circuits.  In addition, two  trade-off case studies, based on real ore data, are detailed to demonstrate the applicability of the procedures. The third section (Chapter 4) introduces the novel HPGR flowsheet and details the testwork program used for its evaluation.  Also in this section, testwork results are  presented and discussed. The fourth section (Chapter 5) described the design of a comminution circuit utilizing the novel HPGR flowsheet for an existing copper-gold orebody. Analyses of the expected outcomes are given as well as a comparison between the proposed circuit and the conventional circuit that was previously proposed for the development of the same orebody. The final section (Chapter 6) covers the research main contributions and future research opportunities.  9  2 COMMINUTION CIRCUITS1 - LITERATURE REVIEW  2.1  Introduction  Some facts are self-evident: commodities prices fluctuate; high-grade, large deposits with easy-to-process ore are uncommon; and energy efficiency is a public matter. However, mineral processors adapt as well as most to the changing economic environment, especially in the field of comminution. Comminution is the largest energy consumer in mineral processing, and, if the ore is hard, requires the largest capital and operating cost. In modern low-grade mining operations, the scale of the use of energy and other consumables is unprecedented (Charles and Gallagher, 1982; Abouzeid and Fuerstenau, 2009). Proper design of the comminution circuit is a critical task, especially for large-scale hardrock projects.  Today, several options are analyzed when designing such a circuit.  Some are based on long-established technologies, and others are based on more recently developed technologies, or technologies that have been adapted from other types of projects. Selecting the most appropriate circuit is of paramount importance, not only in deciding the equipment, but also how it is configured. The design task can be quite different in greenfields projects than in expansions, or in modifications of existing circuits (Barratt and Sherman 2002).  1  A version of this chapter has been published. Rosario P.P., Boyd K. and Grundy M. (2009). “Recent Trends in the Design of Comminution Circuits for High Tonnage Hard Rock Mining”. Recent Advances in Mineral Processing Plant Design, eds. Malhotra D., Taylor P.R., Spiller E., and LeVier M., Society for Mining, Metallurgy, and Exploration, Inc. (SME), pp. 347-355  10  2.2  Recent History of Comminution  From the 1920s to 1950s, most comminution circuits were designed with several stages of crushing, followed by rod and ball mills.  During the 1960s, the use of rod mills  declined, as larger diameter ball mills, accepting coarser feeds, became available. The 1960s also saw the advent of autogenous, and, later, semiautogenous mills, and by the early 1970s, large-diameter autogenous grinding mills (AG), and semiautogenous grinding mills (SAG), often together with ball mills, became the accepted norm. Although the power consumption was generally higher, the simpler circuits with fewer components and smaller footprints made the overall economics of SAG mills superior to three-stage crushing in most cases (Bond 1985). These SAG circuits opened the door to the hightonnage, low-grade operations that have characterized the base metal industry for the past 40 years. The application of these large tumbling mills increased in such a way that from the early 1980s to the early 2000s most new or expansion mining projects have selected some circuit configuration that includes either an AG or a SAG mill (Barratt and Sherman 2002). More recently, two factors have driven a change in this trend, especially in hard ore operations. Firstly, the wish to reduce energy consumption intensified, driven not only by economics, but also by public interest in climate change, greenhouse gas emissions and carbon footprint.  Secondly, high-pressure grinding rolls (HPGR) became more  attractive as their manufacturers developed roll-wear protection systems to better deal with hard and abrasive ores. As HPGRs are more energy-efficient than conventional grinding mills, and because large HPGRs can deliver higher unit throughput at higher reduction ratios than tertiary cone crushers, some projects are now using HPGRs in combination with secondary cone crushers instead of SAG mills.  11  Stirred milling technology was developed in the 1950s but has only been applied for mineral processing during the last couple of decades. There are a few different models of stirred mill machines on the market and they have been mostly used for regrind applications. The stirred mill presents better energy efficiency than ball mills for fine grinding and during the last few years there has been an increasing interest in applying this technology to coarser grinding ranges (Valery and Jankovic 2002).  12  2.3 2.3.1  SAG Mill Background AG/SAG Mill Machines  A SAG or AG mill, as with any other type of tumbling mill, is a metallic drum of cylindrical or in most cases cylindro-conical shape which rotates on its horizontal axis. Raw material and water are fed through an opening at one end of the mill and discharge through the other end.  The interior surface is lined with resistant material such as  rubber, steel or a combination of them to provide wear protection. In addition, lifters, i.e. raised sections of the liners, are used to lift and direct the fall of the charge during rotation. AG and SAG mills are usually characterized by their large diameter dimension and their aspect ratio (diameter to length relation) which, differently than the ball and rod mills, is a high ratio in the order of 1.5 to 3 (Napier-Munn et al, 1996). Another difference is related to the discharge design, AG and SAG mills are usually equipped with grated discharge ends to hold back large pieces of rock and steel balls (in SAG mills) and to allow the flow of the slurry containing the fines (usually a portion of the feed and obviously the ground material). These mills can be either shell or trunion bearing supported and most of them are electric motor-gear driven with single or twin-double pinion arrangements. However, as currently the limit of power transmission through a pinion is around 7,500 kW (Evans et al, 2001), the large mills with 11 m diameter (36 ft) and higher and requiring 15,000 kW and more, are equipped with gearless electric drives. Currently the largest mill in operation has a diameter of 12.2 m (40 ft) and is equipped with a gearless drive with 22,000 kW. Based on mill vendors information, the largest mill that could be currently engineered would be limited to 13.4 m (44 ft) diameter (Vanderbeek, 2004). 13  Three breakage mechanisms occur inside a SAG or AG mill, they are: abrasion, attrition and impact (Napier-Munn et al, 1996). Impact breakage is achieved by the cataracting of the load (steel media and slurry – raw material plus water) due to the high speed rotation; cataracting action meaning the free fall of the load above itself. Abrasion and attrition are generated by the rolling movement of the load as the material lifts and slips together.  The balance of the energy applied in the comminution of the rocks is  dissipated in the form of heat, noise and the wear of the grinding balls and the mill liners (Norman and Decker, 1985). The control of raw material and water feed-rates, and mill speed (for mills equipped with variable feed drives) is essential for smooth operation and minimum comminution of media and liners. For example, if the property of the feed rapidly changes and softer and finer than normal feed is present, the operator (or automated control system) may need to decrease the feed-rate of the raw material and lower the speed of the mill to avoid a decrease in the mill load level and thus an increase in the frequency of mediamedia and media-liner impacts. 2.3.2  SAG Operational Parameters  Steel ball charges range from 0% (AG mill) up to 20% by volume, and a typical value for SAG is 12%. The total charge (balls plus slurry) is usually between 20% and 35%, and the slurry is usually between 65% to 75% solids. The most frequent ball size for large mills is 127 mm diameter, but it can vary from around 90 mm to a maximum of 152 mm (Sepulveda 2008). The recent trend has been to operate at increasingly high ball loads, and at increasingly low total loading—it has been observed that a lower total charge improves capacity. Today some operations operate with ball charges up to 20%.  Total mill volumetric 14  loading has decreased from around 35% in the early days to as low as 24% or below (Sepulveda 2008). High ball charges have only been made possible by the advent of the variable-speed drive, one of the most significant advances in SAG milling. The variable-speed drive was first installed on a SAG mill at Afton (1977) (Thomas 1989) and is now almost universally used. An early example of the advantage of variable-speed drives was at Lornex (now Highland Valley Copper), where a variable-speed mill installed in 1981 was operated at up to 19% ball load, compared to 12% for fixed-speed mills in parallel circuits. The operators could drive the new mill harder, confident that if the ore suddenly became softer, they could slow the mill down to protect the shell. 2.3.3  SAG Mill Original Circuit  Before SAG milling entered the scene, large grinding plants consisted of many trains of two or three stages of crushing, rod milling, ball milling, and the associated conveyors, screens and surge bins (Figure 2-1). The SAG mill gained its leading status in large mill operations because of its ability, in a single unit, to receive coarse primary crusher product and deliver adequate ball mill feed at high operational availability (approximately 93%) (Figure 2-2). Development since the early days has centered on increasing the amount of ball mill feed that a single unit produces.  15  Figure 2-1:  Three Stages of Crushing, Rod Mill, Ball Mill  Process Water Coarse Ore  Secondary Crushers  Flotation Tertiary Crushers  Fine Ore Bin Rod Mills  Secondary Screens  Ball Mills  Tertiary Screens  Since their appearance in the 1970s, SAG mills have increased in size and power, their drive systems are more advanced, they are equipped with better control systems, and their benefits and shortcomings are better understood. These developments resulted in new circuit configurations and programs to improve the quality of feed. Many of the more significant advances were made by operators determined to extract more from what they were given. Large diameter SAG mills have been selected for new hard rock projects and expansions (Los Bronces Development Project, Phoenix Project, San Cristobal) which indicates that, depending on the ore type and project specifics, a SAG circuit may still be the preferred choice.  16  Figure 2-2:  SAG-Ball Mill Circuit  Process Water  Flotation  SAG Mill Discharge Screen  Coarse Ore  Ball Mills  SAG Mill  2.3.4  Pebble Crushing for AG/SAG Circuits  Competent rocks in the 12 mm to 75 mm range (critical size) present reduced breakage rates in autogenous (AG) mills. A significant contribution of grinding media in a SAG mill is to accelerate the breakage of critical size material to reduce its tendency to accumulate in the mill. Another, nowadays less common, method of preventing the build-up is the Autogenous Mill-Ball Mill-Crusher (ABC) circuit, where the critical size material is extracted from the mill, crushed, and returned to the mill.  These two  techniques were combined during the 1980s, when there were several successful attempts by operating mines, to improve their SAG mill performance by using pebble crushers—the Semiautogenous-Ball Mill-Crusher (SABC) circuit.  Examples are Los  Bronces, Similkameen (Major and Wells 2001) and Chino (Vanderbeek 1989). Inclusion of a pebble circuit has become almost standard in the design of grinding circuits (Figure 2-3). Even if it is not thought appropriate to install pebble crushers at the outset, it is usually considered prudent to leave space should circumstances require pebble crushing later in the operation.  17  Figure 2-3:  SABC Circuit  Process Water  Flotation Pebble Bin  Pebble Crushers  SAG Mill Discharge Screen  Coarse Ore  Ball Mills  SAG Mill  For hard and very hard ores (JK Axb values below 40 and Bond Work indices above 16 kWh/t), correct forecasting of the production of critical-size material, and of its extraction rate through the mill grates, is still difficult.  There have been reports of  operations that spent great effort to achieve the designed pebble extraction, and therefore the design throughput, for quite some time after startup—for example Cadia Hill (Hart et al 2001) and Sossego (Delboni et al 2006). Until recently, AG mill and SAG mill circuits were invariably designed in closed circuit with the screen and pebble crusher, with the screen oversize portion being crushed and completely recycled to the mill feed. Recently, however, some SABC installations have been operated in open circuit by having the screened crusher product report to the ball mill circuit (Figure 2-4). The effect of opening the circuit is to pass more tonnage at coarser size to the ball mill circuit. Consequently in most cases it has been used to increase throughput of an existing operation which had extra ball mill capacity or could tolerate a coarser grinding-circuit product size. There are also new installations (most at the planning stage) where the largest available SAG mill could not reach desired  18  capacity with the pebble crusher in closed circuit.  Thus an open-circuit SABC was  chosen. An example is the El Teniente Colon Concentrator with an 11.6m diameter SAG and four parallel pebble crushers in SAG open circuit configuration (Spann and Ottergren 2004). Figure 2-4:  Open-Circuit SABC Flotation  Process Water  Pebble Crushers  Pebble Bin  Crushed Pebble Screen Ball Mills SAG Mill Discharge Screen  Coarse Ore  SAG Mill  A design where the pebble crusher can either be used or bypassed provides the operator with some external operating control of the SABC circuit. The ability to open or close the circuit during operation provides additional flexibility. The authors recently completed a study for a property where the run-of-mine ore had zones of greatly fractured ore, and zones of very competent ore, both with high ball-mill work indices. It was proposed to lay the plant out so that the operator could bypass the crushers and operate the SAG mill in closed circuit when receiving fractured ore (to maximize SAG mill power) and, when the ore was competent, use the pebble crushers and even open the circuit, to pass more of the work to the ball mills.  19  Another recent development in pebble crushing is the addition of HPGRs to treat the pebble crusher product (Figure 2-5). The pebbles are reduced to a much finer product thereby decreasing ball mill power requirements.  Depending on the original circuit,  opening the SABC circuit and adding an HPGR stage may achieve a significant capacity increase, without increasing the ball mill duty requirement (Dixon et al, 2010). This concept can also be applied to a circuit that will ramp-up after startup. For example the Peñasquito project has started up with a single SAG line in mid 2009, a second SAG line was added in mid 2010, and later one HPGR will be added (Goldcorp 2009). Figure 2-5:  SABC with HPGR  Process Water Flotation  Pebble Bin  HPGR Storage Bin  Pebble Crushers HPGR Crushed Pebble  SAG Mill  SAG Mill Trommel Screen  Ball Mills  HPGR Screen  Coarse Ore  Pebble Washing Screen  Screens Early designs for the screens closing the AG/SAG mill circuit were either trommel screens with water jets returning pebbles through the discharge end of the mill, or vibrating screens with a series of conveyors returning the oversize to the feed end of the mill. Some (such as Lornex and Copperton), used a combination of trommel screens, pumps and vibrating screens. Since pebble crushing circuits have become common, the  20  trommel screen/water jet has become less so. Some companies (e.g. Alumbrera and Antamina) have later added recycle conveyors and pebble crushers to their trommel screen system, and keep the water off when the pebble crushers are in use. More recent large operations employ trommel screens to remove most of the slurry, followed by vibrating screens to wash the pebbles before discharging them onto the recycle conveyors. Pebble Surge Capacity Early SABC circuits incorporated crushers retrofit into SAG mill recycle conveyor systems, and often had no surge capacity. Surge capacity is highly desirable, enabling the crushers to be choke fed by controlling the feed rate. Thus pebble bins are now included in circuits as a matter of course. The scale of many recycle operations is now at the point where a pebble stockpile is more economic than a pebble bin. 2.3.5  SAG Feed Preparation  In the early years after the advent of the SAG mill, typical ball charges were in the range of 3% to 7% of mill volume, and the general consensus was that large rocks in the feed were always necessary to assist in breakage. Under present operating conditions of high ball load and low total loads, the contribution of large rocks as grinding media is insignificant. It is now realized that improving the blasting and primary crushing phases to deliver a consistently fine feed to the mill are cost-effective contributions to the overall comminution system. Several operations have demonstrated substantial improvement in SAG production by feed preparation programs (mine-to-mill), improving production by a factor of up to 15% (Lam et al 2001). SAG throughput is very susceptible to changes in the hardness of the ore and this should be assessed at early stages of design. In cases where the orebody presents a 21  high variability of friability, provision for blending may be an option to minimize high fluctuation in production (Dance 2004). If a well defined plan to maintain reasonably uniform ore hardness is not possible, the operation should be prepared to sustain fluctuations in tonnage. In some cases, pre-crushing—scalping off and crushing coarse material in the SAG mill feed—has been applied to manage the SAG feed size distribution (Figure 2-6). Pre-crushing can be used where there is limited scope to optimize blasting and primary crushing, as in block-caving underground mines. In addition, pre-crushing has been applied to maintain designed production levels at mines where the ore hardness has increased over time or to expand production (Sylvestre et al 2001). Figure 2-6:  Pre-Crushing in an SABC Circuit  Process Water Coarse Ore  Coarse Ore Screens  Secondary Crushers  Pebble Crushers  Pebble Bin  Crushed Pebble Screen SAG Mill Discharge Screen  SAG Mill  2.3.6  To Ball Mills  Steel Wear  In comminution circuits, steel is used in the form of steel balls as media for the tumbling mills, both for the SAG and the ball mills. Steel is also used in many other components such as: mill liners, HPGR rolls, crusher liners, chute liners, bin liners, etc. The total consumption of steel is usually a high operational cost (Charles and Gallagher, 1982). In 22  addition, the consumed steel requires energy for its mining, refinement, manufacturing and transportation phases and represents a significant indirect (or embedded) energy consumption even when compared to the amount of direct comminution energy (Radziszewski, 2002; Pokrajcic and Morrison, 2008; Musa and Morrison, 2009). Although the precise estimation of the steel ball consumption is not a straightforward task, it is common during the design phase of the projects to estimate the wear rate through a combination of ore abrasiveness test work, empirical models and historical data. The empirical model most commonly used is based on the work by Bond for small diameter ball mills with some reduction in the magnitude of its constants, as suggested by Norman and Decker. (Bond, 1964; Norman and Decker, 1985). This model utilizes the Bond Abrasion index (Ai) as input to determine the wear in grams relative to the specific power applied. The original equation formulated by Bond for wet ball mills, is as follows: Ball-wear in lb/kW-h = 0.35 (Ai - 0.015)1/3 There are two main deficiencies of this model:  •  the Ai is determined in a dry test and the differences in chemical characteristics of the pulp in wet milling are not taken into consideration, and,  •  steel quality differences are not included in the model and metal quality has significantly improved since the development of the model in 1963.  Halbe and Smolik (2002) state: “Unpublished data indicates that for current high quality metallurgical steel these calculated values [of ball wear] could be reduced [by] as much  23  as 50%.  A good procedure is to conduct Ai tests to determine how the sample  evaluated compares with others [ores].  With Ai information it is possible to review  operating data from other plants with similar conditions and Ai’s, and make a reasonable estimate of expected wear. Generally the lab performing the tests will have a data base of this sort of information. Engineers at the test lab or consulting engineers with extensive experience in grinding circuit [design] can be very useful here.” Radziszewski and his associates at McGill University are developing a comprehensive mathematical model of steel media wear as a function of mill operating parameters as well as a set of test procedures to simulate the effect of both, corrosion and abrasion wear mechanisms (Radziszewski, 1997; Radziszewski et al, 2005). Unfortunately, as per his last known publication on this matter in 2005, the model seems to be still in the development phase.  24  2.4 2.4.1  HPGR Background HPGR Machine  The origin of HPGR can be linked to coal briquetting equipment developed in the early 1900s (Morley, 2006). However, HPGR as a comminution machine was developed in the early 1980s and is a product of fundamental and applied research on fracture phenomena conducted by Professor Klaus Schonert (Bearman, 2006). The HPGR was first introduced around 1985 to treat relatively soft material in the cement industry. Comminution in a HPGR is achieved by the high pressure compression of a bed of material which results in high interparticle stresses, i.e., the crushing principle could be viewed as having rocks compressed in a piston press.  The retention time for the  material in a HPGR is very short. The interparticle breakage mechanism enables a low level of consumed energy and results in a high proportion of fines in the HPGR product (Tavares, 2005; Gunter et al, 1996). The HPGR machine has two counter-rotating rolls mounted in a sturdy frame as shown in Figure 2-7.  One roll rotates on a fixed axis and the other one, the floating or  moveable roll, is allowed to move linearly on rails and is positioned by the action of a hydro-pneumatic system. The material is fed through a shaft feeder creating a forced feeding action by gravity. The use of the rotating rolls enables a continuous pressing process instead of a batch process that would be achieved by a limited throughput piston press type of machine.  25  Figure 2-7:  Schematic of a HPGR (Napier-Munn et al, 1996)  Nitrogen cylinder Oil cylinders  Feed Moveable roll  Fixed roll  Product  HPGR should not be confused with conventional crushing rolls. Klymowsky et al (2006) detailed the distinctive characteristics between them, as summarized next:  •  the HPGR is equipped with a hydro-pneumatic system to apply and maintain a high pressure condition within the crushing region  •  they are operated at much lower speeds than crushing rolls (around 20 rpm, approximately one third of the crushing rolls speed)  •  HPGR has a unique feed system to maintain constant choke feed conditions,  •  and, the surfaces of their rolls are made of highly wear resistant materials.  There are three manufacturers of the HPGR machines, all with headquarters in Germany, they are:  •  ThyssenKrupp Polysius  •  Koeppern (or Köppern in German)  •  KHD Humboldt Wedag AG  26  There are a few differences in the design of the machines depending on the manufacturer. Polysius machines usually have a high aspect ratio roll design, i.e., the ratio between the diameter and the length of the roll. An example of a currently largesize Polysius machine would be one with 2400 mm roll diameter and 1600 mm roll length. The other two makers favour a low aspect roll design, and an example of a KHD standard construction machine size would be one with 1700 mm roll diameter and 1400 mm roll length. In order to minimize roll surface wear when treating abrasive materials, all manufacturers are able to provide some kind of protection layer for the rolls. Tires with tungsten carbide studs are used to create an autogenous layer on the roll surface, i.e. material builds up on the surface area in between the studs to create an ore layer on the roll.  This technology is offered by KHD and Polysius. Koppern has developed  Hexadur®, a hard surface layer consisting of ceramic hard phases embedded in a hardenable steel matrix (Gardula et al, 2005). The application of HPGR in comminution circuits has increased over the past two decades and is well established in processing cement, diamonds and iron ore (Broeckmann and Gardula, 2005).  In the last few years HPGR plants to process  precious and base metals from hard ores have been designed and started up. The main examples are:  •  SM Cerro Verde, copper, Peru  •  Boddington, gold, Australia  •  Mogalakwena North, platinum, South Africa  •  PT Freeport Indonesia, copper-gold, Indonesia  27  •  Zapadnoe, gold, Irkutsk-Russia  •  Bendigo, gold, Australia  2.4.2  HPGR Terminology and Operational Parameters  A number of terms and operational parameters are particular to the HPGR and the most relevant ones are listed as following:  •  HPGR product “cake” or “flake”  •  specific throughput, m-dot  •  operating gap, Xg  •  specific pressing force, FSP  •  specific energy consumption, ESP  HPGR product “cake” or “flake” The HPGR product generally contains a blend of loose particles and agglomerated “cakes” or “flakes”, in different proportions and sizes, depending upon ore characteristics and machine operational parameters; such as feed PSD and moisture content, applied pressure, and gap width. Cake strength or competency is usually low, and commonly these brittle lumps can be easily broken by hand. (Gruendken et al, 2008). To the best of the author’s knowledge there are no standard procedures to evaluate cake competency. Specific throughput The specific throughput, m-dot, is a factor that is regularly obtained from a laboratory- or pilot-scale HPGR test and is calculated by dividing the value of the measured throughput (t/h) by the testing machine roll diameter (m), roll width (m) and the peripheral roll speed  28  (m/s).  The m-dot consequently is expressed in ts/hm3 units and indicates what  throughput would be achieved from a machine with 1 m x 1 m rolls operated at 1 m/s for the tested material. If the testwork is properly conducted to closely simulate expected industrial-scale conditions, such as: moisture content, operating pressure, and roll surface properties, the m-dot can be assumed to be constant and directly used for throughput estimation of different size machines (Bearman, 2006).  ݉ሶ ‫݉ ݎ݋‬-݀‫ ݐ݋‬ൌ  ‫ܯ‬ ‫ ܦ‬ൈ‫ܮ‬ൈߥ  where: m-dot = specific throughput (ts/hm3) M = throughput rate (tph) D = roll diameter (m) L = roll width (m) ν = peripheral roll speed (m/s) Operating gap The operating gap is the minimum distance between the rolls.  The HPGR gap,  differently than the close side setting (CSS) in the crushers, is not the determining factor for size reduction but just an indication of the top size in the product. The inter-particle comminution mechanism enables high levels of size reduction and fines production even with apparent large gaps (Gruendken et al, 2008). The gap is a function of the roll diameter and the friction between the feed material and the roll surface. Larger diameters and/or higher friction factors provide larger gaps and thus higher throughputs. The friction is affected by feed material proprieties (such as  29  moisture and particle size distribution) and roll surface properties, e.g. studded rolls with their substantial autogenous layer provide higher friction than hard-faced smooth rolls (Klymowsky et al, 2006). The operating gap, together with the roll speed, can also be used for throughput calculations by the use of the continuity equation, as follows: ‫ ܯ‬ൌ ܺ௚ ൈ ߥ ൈ ‫ ܮ‬ൈ ‫ݎ‬௖ ൈ 3.6 where: M = throughput rate (tph) Xg = operating gap (mm) ν = peripheral roll speed (m/s) L = roll width (m) rc = density of the product cake (t/m3) Specific pressing force The specific pressing (or grinding) force corresponds to the total hydraulic force exerted on the rolls divided by the roll surface area, i.e. it is the total force divided by the roll diameter and width and is expressed in N/mm2 (Klymowsky et al, 2006).  ‫ܨ‬௦௣ ൌ  ‫ܨ‬ 1000 ൈ ‫ ܦ‬ൈ ‫ܮ‬  where: Fsp = specific pressing force (N/mm2) F = applied pressing force (kN)  30  D = roll diameter (m) L = roll width (m)  The specific pressing force is a useful parameter for machine scale-up and its value is usually in the range of 1 to 9 N/mm2 (Bearman, 2006). Specific energy consumption The specific energy consumption (or specific energy input) corresponds to the machine power input (kW) divided by throughput rate (tph), and thus is expressed in kWh/t. For machine scale-up and performance comparisons the net specific energy consumption is more appropriate whereas the calculation is performed with the total net power input, i.e., the idle power draw is discounted. Usually the value of the specific energy consumption ranges from 1 to 3 kWh/t. The specific energy is directly proportional to the specific pressing force and, similarly to other comminution machines, harder ores require higher values of specific energy when compared to softer ores to achieve similar size reductions (Bearman, 2006). 2.4.3  HPGR Original Circuits  Cement HPGR was first introduced in 1985. industry.  Since then it has found usage in the cement  Cement production usually involves three phases.  In the first phase raw  materials, such as limestone, are ground. In the second phase, the ground components are mixed and undergo a chemical reaction in a rotary kiln at high temperatures producing the cement clinker. The third phase is a final grinding phase to reduce the clinker nodules to 100% passing 90 microns size.  Both the pre-treatment of raw  31  materials and the final clinker grinding phases are performed dry. Ball mills, usually twocompartment mills divided by a diaphragm and using different steel ball sizes in each compartment, are generally used for clinker grinding (Jankovic et al, 2004). The first applications of HPGR in cement were in manufacturing plant retrofits. This was done by the addition of the machine upstream of the clinker grinding mill. With time, different circuit configurations have been applied and the HPGR has been able to provide 10% to 50% energy savings in cement grinding (Patzelt, 1992).  Figure 2-8  shows one type of circuit that is applied for the precrushing of clinker. Figure 2-8:  Open Circuit HPGR – Closed-Circuit Ball Mill (Aydogan et al, 2006)  Iron Ore In the iron industry, the HPGR was first introduced in 1995 and its application has been growing since then. For iron ore the HPGR has been applied either as a standalone stage or ahead of ball mills to improve the efficiency of the grinding required in pellet feed production. In addition, the machine has been installed in AG-mill circuits (primary  32  grinding of the ore) to re-crush pebble crusher product (KHD, 2008). The HPGR product is either returned to the AG mill feed or directed to the downstream processes. An example of the application of the HPGR for re-crushing and being in closed circuit with the AG mill is shown in Figure 2-9. This type of circuit enhances the mill capacity by releasing the AG from pebbles which have a limited breakage rate and may build up the charge volume inside the mill unless the feed rate is reduced. It is noteworthy that most of the comminution energy is still applied by the conventional AG mills and that the crusher and HPGR act mostly as auxiliary equipment. Figure 2-9:  HPGR Applied for Pebble Re-Crush at Empire Iron (Kawatra et al, 2003)  Maybe the initial success of the application of HPGR in iron ore AG pebble re-crush motivated Krupp-Polysius to patent several circuit configurations with HPGR for pebble crushing. The patent was issued in 1999 and covers the application of the HPGR as a  33  standalone unit for AG/SAG circuit pebble crushing (Knecht, 1999) but the author is not aware of any industrial application to date. Diamonds In diamond ore processing, the main drive for the utilization of the HPGR is the selective grinding capability that enables the crushing of kimberlite-diamond ore while preserving the relative large diamond gems. extracting the large gems.  The circuit design correlates to the objective of  Thus, common circuits are built with quite complex  classification systems, such as combination of multi-deck screens and density media separators (DMS), and scrubbers. Figure 2-10 shows a portion of the circuit (re-crush stage) applied for Argyle Diamond Mines in Australia. (KHD, 2008) Figure 2-10: Re-Crush Circuit at Argyle Diamond Mines (KHD, 2008)  34  2.4.4  HPGR Precious/Base Metal Recent Circuits  In the last few years HPGR-based plants processing hard ore in high-tonnage precious and base metals operations have started production. The two main examples in hightonnage operations are SM Cerro Verde (start-up in 2006) and Boddington (start-up in 2009). It is claimed that of the many possible flowsheets that have been proposed for HPGR, those using HPGR as tertiary crushers, in closed circuit with fine screens, are expected to provide maximum energy efficiency in hard-rock applications (Morley 2006a).  In  addition, the secondary crushing product is screened before feeding the HPGR to avoid oversized material damaging the rolls. This configuration is illustrated by the Boddington and Cerro Verde flowsheets (Figure 2-11 and Figure 2-12). Figure 2-11: Boddington HPGR (Dunne et al 2007) Gravity Separation  Process Water Secondary Crushers (5) Coarse Screens Primary Crushers (2)  Coarse Ore Stockpile  HPGR (4)  Flotation  Fine Ore Stockpile  Ball Mills (4)  Fine Screens (8) (Wet) Flash Flotation  35  Figure 2-12: Cerro Verde (Vanderbeek 2006) Process Water  Flotation  Screens  Fine Ore Surge Bin  HPGR (4) Primary Crushing  Coarse Ore Surge Bin  Ball Mill Feed Surge Bin  Ball Mill Feed Screens ( Wet)  Ball Mills (4)  Secondary Crushers (4)  In a variation of these flowsheets (with the HPGR in closed circuit with screens), the HPGR can be equipped with a dividing chute; the product from the centre of the rolls is directed to the ball mill, and the material produced at the edges of the rolls, which is coarser, is returned to the HPGR feed. This form of HPGR product recirculation has already been applied in iron ore projects and has been recently developed for some base metals projects (Gruendken et al 2008). The Boddington project has a design capacity of 35Mtpa (approximately 96,000 t/d) and processes two very hard gold ores with average Bond ball mill work indices (BWi) of 15.1 and 16.6 kWh/t, Bond rod mill work indices (RWi) of 22.8 and 24.2 kWh/t, and JK Axb values of 27.9 and 25.5. The circuit is comprised of: five 746 kW cone crushers, four 2.4 m diameter(D) x 1.65 m length(L) 5.5 MW HPGRs, and four 7.9 m D x 11.9 m L (26 x 39 ft) 15.6 MW ball mills (Dunne et al 2007). The projected roll surface wear life was estimated at 4,250 hours. A 2006 trade-off study showed that a preliminary SABC circuit would have 7% lower capital costs than the HPGR circuit, and that the HPGR circuit provided 12% savings in comminution operational costs. Furthermore, the study concluded that the lower operational costs of the HPGR circuit offset its higher capital costs (Seidel et al 2006).  36  Cerro Verde has a design capacity of 108,000 t/d of hard copper-molybdenum ore (average BWi 15.3 kWh/t). The circuit is comprised of: four 746 kW cone crushers; four 2.4 m D x 1.65 m L 5.0 MW HPGRs; and four 7.3 m D x 10.7 m L (24 x 35 ft) 12 MW ball mills. The projected roll surface wear life is 6,000 hours. In 2006, just prior to startup, it was reported that although estimated capital costs were higher for the HPGR circuit than an equivalent SAG circuit, the estimated total comminution operational costs were 1.33 US$/t and 1.70 US$/t for the HPGR and SAG circuits respectively.  The main  contributors for this difference are the costs of power and grinding media. The estimated total comminution circuit specific energy for the SAG circuit was 20.1 kWh/t and for the HPGR circuit 15.9 kWh/t. In addition, risk analysis results and internal rate of return factors were responsible for the decision to build an HPGR circuit instead of SAG circuit (Vanderbeek 2006). AG circuits are notoriously sensitive to changes not only in ore hardness, as previously noted, but also in feed size. SAG mill circuits are more stable, and SABC circuits eeven more stable. However, SAG-based circuits are still very sensitive to feed variations (Vanderbeek 2006; Morrell and Valery 2001). Anglo Platinum, at the Mogalakwena North concentrator, selected crushing technology in large part because it gave stability in feed rate and product size. HPGR was selected in particular, because of its economic advantages over tertiary and quaternary crushing (Rule 2006). 2.4.5  Energy Savings  As described in section 2.4.1, breakage in the HPGR is associated with high interparticle stresses in the machine’s compression zone and occurs relatively fast. This breakage mechanism enables a low level of consumed energy and creates a high proportion of fines in the HPGR product, thus providing a high level of comminution energy efficiency  37  (Tavares, 2005), (Gunter et al, 1996). For tumbling mills, such as the SAG mill, the comminution energy efficiency is lower than the HPGR. This is due to their breakage system that behaves as an unconfined system (loose bed), i.e., a great portion of the applied energy is lost through several non-breakage dynamics that are inherent from the machine design and interparticle interaction effects (Fuerstenau and Abouzeid, 1998). The HPGR manufacturers emphasize the energy efficiency advantages of the HPGR when compared to tumbling mills. In one of KHD’s brochures it is claimed that: “For most ores, the specific energy consumption lies at around 0.8 – 3.0 kWh/t. Especially when coupled with subsequent downstream processes or high efficiency classifiers, overall grinding energy reductions as high as 40% have been observed.” (KHD, 2002). Polysius declare that the HPGR “allows for lower operating and maintenance costs due to energy savings of up to 20% and reduction of wear to less than 1% for dry and less than 0.1% for wet milling.” (von Seebach and Knobloch, 1987). Koppern reports that “operating experiences and collected data indicate substantial advantages in energy savings, material throughput capacities and product quality of HPGR technology versus traditional crushing and grinding equipment.” (Koppern, 2006). Some researchers and consultants in the mineral industry also discuss the HPGR energy benefits, but usually less emphatically. Napier et al (1996) commented that savings between 15% to 50% had been reported but cautioned that many of these reports were based on small-scale machines. Morley asserts that the HPGR is “the most energy-efficient comminution technology available” (Morley, 2006). Morrell also believes in overall energy benefits for the circuit but highlights that the benefits may be achieved on very hard ores and in circuits where a large portion of the work shifts from milling to crushing and HPGR (Morrell, 2008). In 2006, Shi et al observed 8% to 29%  38  savings in total energy in a HPGR study treating platinum ores. The comparison were made between two lab-scale circuits, one comprised of a jaw crusher, conventional crushing rolls and ball mill, and the other comprised of a HPGR and ball mill. This study also indicated that the benefits are more pronounced in harder ores and with coarser ball mill targeted products. Although no full-scale operational results have been released yet, estimates of energy consumption calculated during the design phases of the Boddington and Cerro Verde projects are available. For the Boddington project, a 2006 trade-off study showed that a preliminary HPGR circuit would provide approximately 5% savings in comminution power (Seidel et al, 2006). For Cerro Verde, in 2006 it was estimated that the total comminution circuit specific energy for the SAG circuit was 20.1 kWh/t and for the HPGR circuit 15.9 kWh/t, approximately a 21% savings (Vanderbeek, 2006). Energy savings in comminution at downstream grinding phases, usually ball milling, are expected through the reduction of the Bond ball mill work index (BWi) of the HPGR product. This reduction in the hardness of the ore, particle weakening, is due to the production of microfractures in the high pressure process. In addition to this particle weakening phenomenon, the HPGR produces a high proportion of fines that further decrease energy requirements in the subsequent mill (Tavares, 2005; Patzelt et al, 1995). Tests performed by Polysius on siliceous gold ores resulted in 5 to 20% BWi reduction (Patzelt et al, 1995).  Tests performed in a lab-scale HPGR at Anglo Research on  several different ores resulted in BWi reductions between 3% to 7% (van Drunick and Smit, 2006). Differences in the evaluation of this reduction factor are common. The author has observed significant differences between testwork performed on the same  39  ore through different HPGR vendors. This may be related to different test procedures. Some procedures may combine the results of particle weakening with fine product and others may report the particle weakening factor alone. 2.4.6  Metallurgical Extraction Advantages  The enhanced extraction in processes, such as flotation and leaching following HPGR, is credited to the generation of micro-cracked rocks during high pressure process, and by the theory that these micro-cracks are formed predominantly at grain boundaries; which consequently increases mineral liberation and reagent penetration rate (von Michaelis, 2005; Morley, 2006). There are a number of studies linking the application of the HPGR to real benefits in gold leaching, especially at coarse fractions as applied in heap leaching (Klingmann, 2005; Baum et al, 1997; Dunne et al, 1996; Gardula and Sheriff, 2005).  Polysius conducted laboratory tests on copper oxide ores suitable for heap  leaching and reported encouraging results (Baum et al, 1996) and von Michaels (2005) described the kinetics of copper heap leaching and concluded that the better permeability of the HPGR product may in fact bring benefits in copper leaching. There have also been reports of significant improvements in gravity recovery of ores containing coarse gold (Johansen et al, 2005; Dunne et al, 1996). In addition, filtering and thickening benefits can be expected if a reduction of slimes production is achieved with a HPGR circuit (von Michaels, 2005). In the case of flotation, research that demonstrates the flotation benefits on HPGR products seems to be more limited. In the late 1990s, a few papers written by Mr W. Baum from Pittsburg Mineral & Environmental Technology and coauthored by two professionals from Polysius, claimed flotation benefits. One of these papers reports that rougher flotation on copper sulphide ore improved between 3% to 5% and final overall 40  recovery was up to 7%, but no details of the experimental approach is given (Baum et al, 1997). Flotation studies conduct with copper ore in a lab-scale HPGR and ball mill were not very conclusive (van Drunick and Smit, 2006). On platinum ores, a similar study with a lab-scale HPGR and a Ball mill found some benefits at coarse size fractions flotation feeds but not at finer fractions (Shi et al, 2006). Another study indicates doubts about the potential HPGR benefits in flotation, as in most cases the HPGR product is subjected to ball milling ahead of the flotation phase. In this recent research, HPGR products were subjected to the JKMRC mineralogical analysis (MLA) and the images confirmed the production of micro-cracks. However, it was also observed that these cracks were destroyed when subjected to ball milling. In addition, “no evidence was found of any significant alteration in the characteristics of the liberation distribution of the valuable minerals within the size distributions studied. This however should be confirmed with flotation tests for example.” (Daniel, 2008) 2.4.7  HPGR Feed and Product Specifics  Like other crushers, the HPGR operation will present challenges when fed with a high proportion of very fine material (clayish material), ores with elastic properties, or significantly soft ores (Morley, 2006b). These substances tend to cushion the crushing action and make the process inefficient.  High moisture in the HPGR feed is also  problematic as it may cause slippage of the material on the roll surface, accelerating wear. Tramp metal can severely damage the roll surface and means for its removal from the HPGR feed are necessary (Klymowsky et al., 2006).  41  Both Boddington and Cerro Verde ores produce a moderately friable HPGR cake product that is de-agglomerated in wet screening by the action of water sprays and vibration. However, if an ore has the tendency to create competent product cakes it may be necessary to have a more powerful process to break it down prior to sending it to downstream processes. Scrubbers are standard in the diamond industry, not only to wash out the clay prior to the HPGR feed, but also after each HPGR stage. Flowsheets incorporating low-speed tooth roll sizers (MMD sizers) used as de-agglomerators downstream of the HPGR have been developed (Valery and Jankovic, 2002). 2.4.8  Limitations and Disadvantages  The main disadvantages of a crushing circuit, with the HPGR as its tertiary phase, are the increased dust generation that requires dust suppression/collection systems, the complexity of the circuit especially on material handling systems with a large number of conveyor belts and stockpiles/bins, and possible higher capital cost (Morley, 2006, Vanderbeek, 2006). At the start of this research, the industry consensus was that HPGR are not recommended to treat high weathered ores, very soft ores or a feed that contains high level of moisture (Morley, 2006). In addition, capital costs for HPGR circuits are higher than the costs for a similar SABC circuit, as was observed during the Cerro Verde design phases (Vanderbeek, 2006). The simplicity and the high availability of SAG circuits seem to be hard to achieve with HPGR circuits. The HPGR machine can provide high availability alone, however the complete circuit, which has a cone crusher and the required screens and conveyors can only provide a high circuit availability when redundancy is added to the circuit.  42  2.5 2.5.1  Other Developments Increasing Machine Sizes  Over the past four decades, tumbling mill sizes increased considerably; the largest mills were 6,750 kW in the early 1970s, and now there are mills operating at 23,000 kW. The increase appears to have stalled somewhat, not because of a lack of need for larger units, or that the mills have reached a manufacturing limit, but seemingly because of a lack of confidence in the industry that motor manufacturers can produce reliable drives in larger sizes.  On the other hand, crusher sizes are increasing; recently crusher  manufacturers launched larger machines than were previously available. For example, Metso has a new heavy duty cone crusher with 932 kW.  Both Polysius and KHD  produce HPGR up to 6.6 MW. The increasing sizes of crushing units mean fewer units and a simpler, less costly, plant; thus reducing the chief advantage of the SAG mill. 2.5.2  Stirred Mills  The stirred mill presents better energy efficiency than ball mills for fine grinding. One of the reasons being that it can operate with smaller media and provide a better match between the particles and the media. It has been demonstrated that media sizing is a key factor for ball mill comminution efficiency (McIvor 1997). The Metso Vertimill® has been used in tertiary grinding for many years, for example, at Red Dog and Chino (Vanderbeek 1997) and has now been successfully used in secondary milling (Valery and Jankovic 2002; Jankovic and Valery 2004). A large scale secondary grinding circuit is now being built and the manufacturer has recently launched a higher capacity machine equipped with a 2,240 kW motor, claiming that this mill can handle 6mm top size in the feed (Metso 2009).  43  The horizontal stirred mill IsaMill™, manufactured by Xstrata Technology is also now available in a larger scale unit equipped with a 3,000 kW motor (Isamill 2009). This type of mill has been tested in the platinum industry as a primary mill receiving the product of two HPGRs in series.  In addition to the high energy efficiency, this experimental  flowsheet is also aiming at metallurgical efficiencies by having a comminution circuit free of metal media. This is achieved by the HPGR rolls being built to hold a layer of ore and by the IsaMill™ utilizing ceramic grinding media (Ayers et al 2008). 2.5.3  Fully Autogenous Grinding  The same economic and social factors that have driven the inclusion of HPGR into the realm once almost exclusive to SAG mills, have driven the reversion of some operations to two-stage fully autogenous milling (Koivistoinen and Levanaho 2006). It may be that the current high cost of steel will persist or strengthen, in which case the replacement of ball milling with pebble mills may become a trend. Provided that the ore is reasonably competent, pebbles may be obtained from the feed to either ABC or HPGR circuits. Figure 2-13 shows one of the circuits in the now defunct Bethlehem Copper mill. This use of pebble mills was commonly practiced in the Canadian iron ore and uranium operations.  44  Figure 2-13: Pebble Extraction and Milling Primary Crushed Ore Primary Screens  -125mm+75mm Pebbles Pebble Bins  Secondary Crushers  Secondary Screens  Process Water  Flotation  Tertiary Crushers  Tertiary Screens  Pebble Mills  45  2.6  Summary of Current State  The high capacities and simple circuits of AG and SAG mills opened the door to the high-tonnage, low-grade operations that predominate in today’s mining industry. From the early 1980s to the early 2000s, the use of SAG mills prevailed in high-tonnage hard rock operations throughout the world. The SAG technology has improved over time and currently their main features and limitations are well understood. More recently, crushing circuits using high pressure grinding rolls (HPGR) as their tertiary stage have been also applied to the treatment of hard and very hard ores in base/precious metal mining applications. The HPGR technology presents promising benefits especially for energy savings and the elimination of grinding steel media. The use of steel media represents indirect energy consumption and in some cases is detrimental for downstream processes.  Currently there are other developments in  parallel to the HPGR application to free the comminution circuits from steel media aiming at completely autogenous grinding. The HPGR technology has been considered one of the best innovations to tackle the inefficiencies of the current comminution circuits. However, a better understanding of this technology along with the development of different circuits is required to fully exploit their benefits in metal mining. Areas of particular need for additional understanding include the evaluation of energy requirements of complete HPGR circuits and the development of different HPGR flowsheets for non conventional ores such as ores with high clay content.  46  3 GUIDELINES FOR ENERGY REQUIREMENT COMPARISONS BETWEEN HPGR AND SAG MILL CIRCUITS IN HIGH-TONNAGE HARD ROCK MINING2  3.1  Introduction  Climate change, energy efficiency, greenhouse gas emissions and carbon footprint have gained a high priority status in the public interest (Sullivan and Oliva, 2007). Electricity costs have been rapidly increasing in response to record fuel costs for power generation. Moreover, several countries, such as the Southern African countries, are now facing a shortage of electric power.  Chile, the world leader in copper production, may face  electricity rationing in the near future (Walsh, 2008). The mining industry has realized the high importance of energy-efficiency and is currently placing this issue at high priority level (Bearman, 2006). Comminution processes account for the largest portion of energy consumption in mining operations, and it has been demonstrated that significant energy savings can be realized by their optimization (Valery and Jankovic, 2002). Fundamental and applied research on fracture phenomena demonstrates that interparticle comminution at high pressure consumes substantially less energy than conventional grinding processes, and served as the origin for the development of the HPGR (Schonert, 1988 and 1991). An important additional benefit in replacing the SAG mill with HPGR circuits in hard rock mining is the reduction is grinding media. The reduction in steel ball consumption not only has direct economic impacts, it also provides savings in indirect energy, i.e. the  2  A version of this chapter has been published. Rosario, P.P., and Hall, R.A. (2010). “A Structured Approach to the Evaluation of the Energy Requirements of HPGR and SAG Mill Circuits in Hard Ore Applications”. The Journal of the Southern African Institute of Mining & Metallurgy, vol. 110, pp. 117-123  47  energy that would be used in the fabrication and transportation of the balls (Pokrajcic and Morrison, 2008). Although the development of recent HPGR-based plants to process precious and base metals from hard ores indicates a greater acceptance of their application, there is still uncertainty as to the extension of its benefits. Among them is the net circuit energy savings when comparing complete SAG circuits to complete HPGR circuits, since extra equipment is required when using the HPGR. With the aim to improve the understanding of the direct and indirect energy requirement differences between complete comminution circuits using SAG mill and HPGR technologies, a methodology was developed based on comminution circuit design best practices. This structured methodology involves modern modelling and simulation tools among other more traditional design tasks, as summarized in the following:  48  3.2  Modelling and Simulation Background  One of the principal application areas of process simulation is in the design and optimization of comminution circuits.  Process modelling and simulation are well  recognized and important tools in mineral process engineering (Herbst et al, 2002) Modelling and simulation packages provide a reliable way to evaluate different flowsheets with different types of equipment in a reasonable time. This facilitates the determination of an optimum choice of circuit (Urrejola et al, 2008; Morrell et al, 2001). There are three main simulation packages for the AG/SAG milling that are commonly used to assist engineers in the development of a new comminution circuit or its optimization; they are JKSimMet®, SGS CEET®, and Millpower 2000 (Barratt and Doll, 2008). The best known and most readily available simulation package is the JKSimMet®, this package includes several comminution models that have been developed at the Julius Kruttschnitt Mineral Research Centre (JKMRC) in Brisbane, Australia. The AG/SAG mill model utilizes impact and abrasion breakage parameters derived from specific test procedures. The model is capable of simulating product size distributions and energy requirements for AG/SAG mills (Morrell, 1992).  In addition, the package contains  several additional models for classification, such as cycloning, and other comminution processes, such as cone crushing. The JKSimMet® package has been used for design and optimization of several hightonnage hard rock operations, such as: Cadia Hill (Hart et al, 2001), Sossego (Delboni et al, 2006), and Candelaria (Muňoz et al, 2008). It is a powerful tool for analysing the effect of ore characteristics and machine operating parameters on crushing and grinding  49  circuits. It is generally well accepted in the industry after 20 years of successful use. Although this simulator has been used predominantly for SAG mill circuits it has been increasingly applied for HPGR circuits.  In addition, JKSimMet® to the best of the  author’s knowledge is the only commercially available package that incorporates HPGR modelling capabilities. The HPGR model embedded in the package was developed at the JKMRC at the University of Queensland, Australia (Morrell et al, 1997). The model has been verified against data collected from industrial units operating at different diamond mines (Daniel and Morrell, 2004), and the results indicate that the model is robust enough for the evaluation of new and optimization of existing comminution circuits.  As a recent  example, this model was applied for the flowsheet design by Anglo Platinum, at the Mogalakwena North concentrator project (Rule et al, 2008). The ore parameters for the HPGR model in the JKSimMet® come from the JK dropweight and compressed-bed breakage tests in a piston press3. The remaining model parameters are derived from laboratory or pilot-scale HPGR tests, and they include: dimensions and operating conditions of the testing machine, experimental size distributions of the feed and the product, bulk density of the feed and the product flake, experimental power draw, and throughput rate. There are indications that the accuracy of the model, and therefore the scaled-up simulation results, improves if the tests are conducted in a pilot-scale testing machine (Rule et al, 2008). In addition, all HPGR manufacturers conduct pilot-scale testing to recommend machine sizes for design purposes (Klymowsky et al, 2006).  3 JKTech are not currently conducting these piston press tests as this information can be derived from the drop-weight tests accompanied by lab/pilot scale HPGR test results.  50  3.3  Case Studies  To better describe and demonstrate the applicability of the proposed comparison methodology, two case studies were used in this research. The hypothetical cases used for this study are two mines each with the option of SABC (SAG mill-ball mill-crusher) or 3-stage crushing with HPGR comminution circuits for the processing of precious or base metals hard ores. These hypothetical projects are assumed to be located in very distinct regions of the world. One project would be located in a very remote area subjected to harsh winters, with plant heating requirements, and relying on electricity from the power grid. The other project is assumed to be located in a semi-arid region subjected to very mild winters, with no heating requirements, and connected to the power grid. Both cases are typical of new projects for precious and base metals mining operations. The physical and grindability parameters of the ore were based on real ore data from two different sites from previous work. HPGR modeling parameters came from pilot test results conducted with the same ores (Appendix A).  51  3.4  Design Criteria Development  The battery limits for this comminution circuit evaluation are the primary crusher product as the feed to the circuit and the Ball mill product (i.e. ball mill cyclone overflow). The primary crusher product size distribution can be estimated based on survey data from similar operations, blasting fragmentation and primary crusher modelling (requires comprehensive testing), or based on a correlation between the abrasion breakage parameter ta and the crusher P80 as recommended by JKTech (Bailey et al, 2009). For the proposed case studies, based on survey data from hard rock operations and taking a simplified and rather conservative approach a primary crusher product with a 125 mm P80 was assumed for both cases. And the complete particle size distribution utilized as the feed for all circuits is shown in detail in Appendix A. For each mine, the values for daily production and final grinding were estimated based on the author’s personal experience and historical information. As previously stated, test results from real ore were used for the physical and grindability parameters such as S.G. and Bond Ball Mill Work indices. HPGR testing results which are key components of the design criteria and major inputs for model construction were based on the same ores (Appendix A lists the complete dataset). The HPGR lab/pilot tests indicated that product cakes are moderately competent and can be de-agglomerated by the application of wet screening. It was assumed that the two orebodies that are used for this study contain a low percentage of clays and are formed of non stick rocks, i.e., ores that are amenable to crushing and high pressure grinding.  52  The daily production, final grinding values, physical and grindability parameters of the ore, and the HPGR modeling parameters were grouped to generate the core process design criteria for the two mines as shown in Table 3-1. Table 3-1:  Summary of Design Criteria Case A  Case B  Design Criteria (summary)  SABC  HPGR  SABC  HPGR  Feed rate (t/d)  55,000 2.60 125 0.32 12.5 50.4 0.46 14.1 N/A N/A N/A 140 -25/+14  55,000 2.60 125 0.32 12.5 50.4 0.46 13.2 6.3% 1.68 261 140 -25/+14  40,000 2.73 125 0.22 14.4 28.7 0.38 16.5 N/A N/A N/A 180 +17/+22  40,000 2.73 125 0.22 14.4 28.7 0.38 16.0 3.0% 1.85 237 180 +17/+22  Solids SG Circuit F80 (mm) Bond Abrasion Index (g) Crusher (Impact) Work Index (kWh/t) JK Parameter A x b JK Parameter ta Ball Mill Work Index (kWh/t) Ball Mill Work Index Reduction HPGR Net Spec. Energy Req. (kWh/t) HPGR Specific Throughput rate (ts/hm3) Final Product P80 (µm) Climate – Mean Temp. Winter/Sum. (°C)  Other ore parameters that were used in the design process were the complete crusher table parameters from the JK drop-weight tests and HPGR test results including the feed and product size distributions. This information is shown in Appendix A.  53  3.5  Flowsheet Development  Currently, after many years of SAG application, it has been recognized and demonstrated that the inclusion of pebble crushing in hard ore SAG circuits results in substantial energy savings (Vanderbeek, 2004). Since for this research the JK A*b parameters and their positions in JKTech’s database indicate both ores are hard, SABC circuits will be use for the comparisons. For the HPGR plant design there are several possible flowsheet arrangements. However, it has been demonstrated that having the HPGR in closed circuit with fine screens for the tertiary crushing stage provides maximum energy efficiency. For hard ore the secondary crushing product should be screened before feeding the HPGR to avoid over size material damaging the rolls (Morley, 2006). Figure 3-1 shows the simplified flowsheets for the two types of circuits used in this research. The SABC circuit is very typical and the HPGR circuit has great similarities to the one applied at Cerro Verde (Vanderbeek, 2006). The only modification is that the order of the material being fed at the fine ore conveyor is inverted to minimize problems in the transport of the moderately wet material.  54  Figure 3-1:  Simplified SABC and HPGR Flowsheets  HPGR Circuit  SABC Circuit Coarse Ore (C.O.)  Coarse Ore (C.O.) C.O. Bin  Screen  Pebble Crusher  SAG  O/S  Sec. Crusher  Trommel Screen  O/S  U/S  HPGR  Cyclones  O/S wet  O/F to Flotatio n  U/F F.O. Screen  Ball Mill  O/F to Flotatio Cyclones n  Ball Mill  U/F  55  3.6  Developed Models  Complete comminution circuit models were developed using JKSimMet® simulator. Figure 3-2 is a screen snapshot of one SABC model developed with JKSimMet® (ASABC case) and Figure 3-3 shows a HPGR case (A-HPGR case). As shown in these figures, the simulation produces a comprehensive set of information, among them the stream values of solids, the power draw per equipment, and size distribution details.  56  Figure 3-2:  JKSimMet® Screen Snapshot of Case A – SABC  57  Figure 3-3:  JKSimMet® Screen Snapshot of Case A – HPGR  58  For this study, the SAG mill simulations utilized breakage constant parameters based on a comparable size mill that had been surveyed in the past (Appendix A), and the ore characteristics from grindability testwork as listed in Table 3-1. Usually, several tests are conducted from samples collected in different parts of the orebody and an analysis of the hardness variability is conducted. Thus, a number of simulations are conducted to refine the sizing of the mill and usually one test result is selected for final design and the nominal material balance is derived from there. This final design test result usually represents the medium hardness or a certain percentile of the hardness, depending on the variability throughout the orebody, the mining schedule or other particular characteristics of the project. For this work, as only one set of tests per case was utilized, it is assumed that this was the test result that would be selected for the actual final design (i.e., the 75th percentile of hardness value from a vast database of grindability tests showing modest variability). Crusher modelling was developed based on Andersen’s model (Andersen, 1988) and the necessary constant parameters were determined using the JKSimMet® Model-Fit capability, i.e., inputting information from test work or plant survey, (such as feed and product size distributions, lab machine dimensions and operating parameters), to the model and running a special simulation that back-calculates the constants several times until the best fit is found (JKSimMet®, 2004). For the model-fit of the crushers the information required consisted of results from drop-weight tests and feed and product size distributions.  Since no crusher pilot test was available for this work, the size  distributions were assumed based on simulations performed with Metso Bruno® crushing and screening simulation software (Kaja, 2002). The ore properties are from the real ore testing results and are listed in Table 3-1.  59  Ball Mill energy requirements were based on Bond’s third theory of comminution and the adjustment of the Ball Mill feed rate and F80 by the application of the “phantom” cyclone method (Napier-Munn et al, 1996). Screens and hydrocyclones were modelled with the JKSimMet® standard efficiency curve model (Kavetsky, 1979). The required parameters for this model were based on manufacturer’s recommendation for the cyclones and screens. Development of the HPGR models was based on the pilot scale testwork results and the Model-Fit process. Model fitting was considered adequate for both cases by analysing the correlation between the experimentally measured product size distribution from the pilot tests and the simulation predictions based on the model-fitted parameters. This methodology was described by Daniel and Morrell in 2004.  60  3.7  Equipment Sizing  The selection of the comminution equipment to be used in the circuit involved several simulation iterations and a number of corresponding ball mill energy requirement calculations.  During this process, different values for SAG mill machine/operational  parameters, such as ball load, total grate open area and speed, and HPGR parameters, such as roll dimensions and speed, were tried. In addition, for this systematic procedure it was taken into consideration equipment vendor information, and information gathered from past projects. The four final refined JKSimMet® models were used for the specification of the main pieces of equipment for the comminution plants.  With the information from these  models, preliminary general arrangement drawings were developed.  These layouts,  along with resulting material balances, were used for the material handling system design.  The  design  of  the  conveyors,  surge  bins,  feeders  and  dust  collection/suppression systems, was performed with the assistance of AMEC’s Material Handling department to assure a prefeasibility level of accuracy.  61  3.8  Results and Discussions  3.8.1  Pure Comminution Energy  The simulation work produced an estimation of the instantaneous energy draw of the mills, crushers and HPGRs. These data were corrected based on the circuit availability to estimate the average power draw per hour as reported in Table 3-2. The availability factors were assumed based on historical information from operations and current industrial practice. Table 3-2:  Pure Comminution Energy Unit Power Qt.  Inst. (kW)  Simu. (kW)  Avai. Factor  Total Power (kW)  Specific Energy (kWh/t)  1 1 2  19,985 597 10,000  18,007 307.9 9,193  0.92 0.92 0.92  16,566 283 16,915  7.23 0.12 7.38  33,765  14.73  1,198 7,661 16,428  0.52 3.34 7.17  Totals  25,286  11.03  Energy Savings HPGR Circuit – Case A  25.1%  Description  SABC – Case A SAG Mill – 11.6m D x 7m L ( 38 x 23 ft ) Pebble Crusher MP 800 Ball Mill – 6.7m D x 11.1m L ( 22 x 36.5 ft ) Totals HPGR – Case A Sec. Crusher MP 1000 Tert. HPGR – 2.2 D x 1.7 W m Ball Mill – 6.7m D x 11.1m L ( 22 x 36.5 ft )  SABC – Case B SAG Mill – 11.6m D x 5.5m L ( 38 x 18 ft ) Pebble Crusher MP 1000 Ball Mill – 7.6m D x 11.6m L ( 25 x 38 ft )  2 2 2  1 1 1  746 5,000 10,000  15,000 746 14,500  672.9 4304 8,928  13,766 736.2 13,323  0.89 0.89 0.92  0.92 0.92 0.92  12,665 677 12,257  7.60 0.41 7.35  25,599  15.36  994 5,440 11,447  0.60 3.26 6.87  Totals  17,881  10.73  Energy Savings HPGR Circuit – Case B  30.2%  Totals HPGR – Case B Sec. Crusher MP 800 Tert. HPGR – 1.9 D x 1.55 W m Ball Mill – 7.6m D x 11.0m L ( 25 x 36 ft )  2 2 1  597 3,700 13,500  558.6 3056 12,442  0.89 0.89 0.92  62  As shown in Table 3-2, the HPGR circuit provides savings in comminution energy in the order of 25% and 30% for cases A and B respectively. From these results the potential for energy savings provided by the application of HPGRs in these types of ores becomes apparent. This fact has already been reported by a number of authors (Morrell et al., 1996; Vanderbeek, 2006) some of them working for HPGR suppliers (Gunter et al., 1996; Broeckmann and Gardula, 2005; Klymowsky et al., 2006) and was in some extent expected at the beginning of this study. 3.8.2  Complete Circuit Comminution Energy  Following the same methodology described above, the hourly average power draw values were calculated for all significant systems and pieces of equipment included in the design of the four concentration plants, as shown in Table 3-3. As presented in the table, the HPGR energy savings for the complete circuit decreased substantially from 25% to 7.7% in case A, and from 30% to 18% in case B. Although the magnitude of the savings decreased, the amounts of reduction are still significant since it is related to the highest energy consumption portion of any mining operation.  63  Table 3-3:  Complete Circuit Comminution Energy Case A  Case B  Total Power (kW)  Spec. Energy (kWh/t)  Total Power (kW)  Spec. Energy (kWh/t)  Comminution Equip Conveyors & feeders Pumps Dust & Heating Systems & Extras  33,765 610 1,649 2,346  14.73 0.27 0.72 1.02  25,599 575 1,199 28  15.36 0.34 0.72 0.02  Total  38,370  16.74  27,402  16.44  Comminution Equip Conveyors & feeders Screens Pumps Dust & Heating Systems & Extras  25,286 3,660 300 1,731 4,454  11.03 1.60 0.13 0.76 1.94  17,881 2,388 195 1,259 634  10.73 1.43 0.12 0.76 0.38  Total  35,432  15.46  22,357  13.41  Description SABC Circuit  HPGR Circuit  Energy Savings HPGR Circuit  3.8.3  7.7%  18.4%  Steel Usage  As detailed in section 2.3.6, steel is used in different forms in the comminution circuits. The SAG and the Ball mills grinding media, their liners, crusher liners, HPGR rolls, and the liners for bins and chutes are consumed over time and are an important component in operational costs. In section 2.3.6 there is also information about the methods for testing and estimating steel consumption. For this study, it was assumed that the HPGR circuits and the SAG mill circuits would have similar steel consumption for liners (including HPGR roll surfaces and SAG mill liners, grates and pulp lifter bars) and ball mill media. In other words, it is assumed that the main difference in steel consumption lies in the SAG mill balls. Therefore, the HPGR circuit benefit would be the value corresponding to the wear of SAG steel balls of the corresponding SABC circuit.  64  In order to estimate this potential savings in steel consumption, the SAG mill ball wear rates were calculated based on Bond abrasion index results, Bond’s wet ball mill equation, and a correction factor of 65% (based on the author’s experience) and the results are shown in Table 3-4. Table 3-4:  SAG Mill Steel Ball Consumption Case A  Description  Consumption of SAG steel balls  Case B  SAG Balls (kg/t)  SAG Balls (t/h)  SAG Balls (kg/t)  SAG Balls (t/h)  0.504  1.16  0.465  0.78  The estimate savings in SAG steel ball consumption for both cases are significant. Assuming a cost of Can$ 1,000 per ton of SAG steel ball, the operating cost savings in steel grinding media for the HPGR-circuit would be 0.50 Can$/t and 0.47 Can$/t, for cases A and B respectively. Moreover these savings represent approximately Can$ 28,000 and Can$ 19,000 per day for cases A and B respectively. 3.8.4  Ore Variability  Since the objectives of this research were only the description and demonstration of the applicability of the proposed comparison methodology, the ore variability of the studied deposits was not taken into account. However, it should be noted that ore properties will vary through project life and that this work provides two points in a possible large spectrum. Therefore the results here presented should not be seen as two precise estimations for two very specific cases but should be interpreted as an indication of the potential energy savings for projects dealing with average ore hardness between these two points. Additionally, the extension of the ore variability through the orebody needs to be considered when comparing the SABC to the HPGR circuit.  Research, testing and 65  modeling has indicated that the application of SABC brings higher risk of production variability than HPGR circuits when dealing with highly variable ores (Humphries et al., 2006; Vanderbeek, 2006). 3.8.5  Heating and Ventilation  For case A, the energy required for heating systems in a project located in an area with harsh winters was taken into consideration. The estimated energy requirement had a considerable effect on the total energy consumption. The total energy value for the SABC circuit increased from 36 MW to 38.4 approximately, and for the HPGR circuit from 31.8 to 35.4 when the heating requirements were included in the analyses. The HPGR circuit requires significantly more energy than the SABC circuit because it has a separate building for the secondary crushers and there are numerous conveyor belt galleries that have to be maintained at a minimum of +5°C. The 7.7% reduction in total energy requirements represents a considerable reduction and if heating requirements where not present in this case the savings would raise to 11.7%. This result indicates that heating energy requirements have an effect in the comparison between HPGR and SAG circuits if the project is located in a cold climate area. However, for this specific case, it was assumed that the power would not be generated at site, which may not be the case for a number of operations at very cold and remote areas. In such cases, the fact that the energy can be easily recovered from fuel power generators may give the HPGR case a greater advantage. 3.8.6  Availability and Maintainability  Since only a small number of precious and base metal HPGR plants are being operated at present, the assumptions for circuit availability should be further explored to increase the confidence in the findings of this research. However, the major problem of short life 66  of rolls reported at early trials with HPGR treating hard abrasive ores resulted in the development of superior design for these components. Substantial improvements in this area are claimed by all three HPGR manufacturers. A good example is the application of tungsten studded roll tyres to provide an autogenous layer on the roll surface minimizing its wear rate. Ore abrasiveness is an important factor that has not been included in this study. This parameter can not only influence the wear rate of HPGR rolls, but also the consumption of mill liners and steel balls. Future analyses should be conducted in this area. 3.8.7  Additional HPGR Benefits  Additional benefits in downstream processes are not addressed in this work but it should be recognized that benefits such as improved flotation performance through preferential liberation and reduced levels of ore oxidation through the reduction of steel usage as grinding media have the potential to decrease overall energy consumption. It can be expected that improved flotation equals to fewer/smaller flotation mechanical cells and therefore less power. These benefits are being assessed by other researchers (Humphries et al., 2006) and more information is expected to emerge in the future. 3.8.8  HPGR Circuit Drawbacks  The HPGR circuit selected for the comparisons is basically the former 3-stage crushing circuit and thus may suffer from the same deficiencies or issues. As described in the section 2.4.7, the HPGR will present challenges when dealing with high moisture and/or a high proportion of fine material. For this research it was assumed hard rock homogenous orebodies with limited clay content similar to what is reported for Cerro Verde and Boddington (Vanderbeek, 2006; Seidel et al, 2006). These specific  67  conditions may not be always encountered in every application and in many cases the application of this type of circuit may become detrimental due to frequent operational problems especially in the crusher and HPGR systems. Such problems will impact the overall circuit maintainability and availability negating any economic benefits. The higher number of pieces of equipment and the additional requirements for surge bins, conveyors, transfer points, dust suppression/collection systems, and feeders certainly turn the HPGR circuit into a more complex circuit when compared to the SAG circuit. Complexity increases the risk for design and construction errors that may delay the achievement of design targets and/or disturb operations.  The complexity and  possible deficiencies in the final circuit may increase labour requirements in both operational and maintenance departments. Currently, a crushing-HPGR circuit as used in the comparisons generally represents a higher capital cost investment than the corresponding SABC circuit. Although the two case studies demonstrated the potential for significant savings in operational costs to offset the capital cost disadvantage, that may be not the case for other deposits. In addition, junior or mid-tier mining companies may face challenges in raising capital for project development which would then favour the SAG mill option. The HPGR-based circuits studied here present a considerable overall circuit footprint. The crusher and HPGR embedded close circuits, the bins and feeding requirements for these machines, along with the application of conventional conveyor belts make the overall plant layout larger than the SAG-based one.  This large footprint and the  corresponding additional building requirements not only effect capital and operational costs but may be a limiting factor for projects with restricted room for plant allocation what is the case in some mountainous regions.  68  3.9  Summary  In this chapter the development and application of a methodology for evaluating the total energy requirements of HPGR and SAG comminution plants were presented. This systematic methodology is based on current industry best practices and involves flowsheet development, modelling and simulation, equipment sizing and selection, plant layout development, and power and steel media consumption calculations. Based on the proposed methodology, comparisons between the total energy usage for HPGR and SABC circuits for two metal deposits have been conducted. The analysis included detailed design of four complete comminution circuits. The work produced an estimation of the real energy savings that can be achieved in the treatment of similar precious and base metal hard ores. It has demonstrated that these savings are within the range of 7.7% and 18.4%.  In addition, it has shown that a  significant reduction in steel consumption could be achieved based on the elimination of the SAG mill steel media.  As well, this lower steel usage reduces the energy  requirements and or carbon footprint of external suppliers. The limitations of this work relate to assumptions regarding clay contents, heating and ventilation requirements and ore hardness variability. These were discussed along with potential benefits and drawbacks of the selected HPGR circuit. The work demonstrated the potential benefits of HPGR in energy and carbon footprint reduction and may serve as an incentive for similar trade-off studies at early stages of project design evaluations. In addition, the demonstration of these potential benefits may also serve as incentive for the development of alternative HPGR circuits for a broader application of this technology 69  by the mining industry. And in the next chapters the development and evaluation of an innovative HPGR flowsheet to treat mixed hardness ores and/or weathered ores with a high proportion of clays and moisture are covered.  70  4 TESTWORK PROGRAM FOR THE EVALUATION OF A NOVEL HPGR-BASED CIRCUIT TO TREAT MIXED HARDNESS ORES CONTAINING CLAYS 4  4.1  Introduction  Recently HPGR-based plants processing hard ore in high-tonnage precious and base metals operations have also entered operation. One of the major drivers for using HPGR in hard-rock operations is that HPGR are found to have better energy efficiency and savings in grinding media than the circuits based on autogenous mills (AG) or semiautogenous mills that have been prevalent over the past four decades (Rosario et al, 2009). A number of base metal operations treating unusually hard ore have determined that the operating cost savings of the HPGR outweigh the capital cost disadvantage. The capital cost is generally higher than in a SAG-based circuit (Seidel et al, 2006). Examples are SM Cerro Verde (Vanderbeek, 2006), which was started up in 2007, and Boddington (Dunne et al, 2007), commissioned in 2009. Another significant driver is the relative stability in throughput rate and product size achieved by crusher-based circuits. AG circuits are notoriously sensitive to changes not only in ore hardness but also in feed size; SAG mill circuits are more stable, and SABC circuits more stable still, but SAG-based circuits are still very sensitive to feed variations (Morrell and Valery, 2001). Anglo Platinum, at the Mogalakwena North concentrator, selected crushing technology in large part because it gave stability in feed rate and product size, and HPGR in particular because of its economic advantages over tertiary and quaternary crushing (Rule, 2006).  4 A version of this chapter has been accepted for publication. Rosario, P.P., and Hall, R.A., Grundy M., Klein B. (2010). “A Preliminary Investigation into the Feasibility of a Novel HPGR-based Circuit for Hard, Weathered Ores Containing Clayish Material”. Minerals Engineering, Special Issue: Comminution ‘10  71  Finally, HPGR are known to produce more micro-fractures in the crushed ore, improving the power efficiency of a subsequent ball-milling operation or the metal recovery in a subsequent heap leach (von Michaelis, 2005). Of the many possible flowsheets that have been proposed for HPGR, those using HPGR as tertiary crushers, in closed-circuit with fine screens, are expected to provide maximum energy efficiency. The fine screens are also applied to ensure an acceptable top-size for the downstream process such as ball milling.  A safety coarse-screen  preceding the HPGR prevents oversized material from damaging the rolls (Morley, 2006a). This flowsheet configuration was selected for both the Cerro Verde (Figure 4-1) and Boddington projects. Figure 4-1:  Cerro Verde Flowsheet (Vanderbeek 2006)  Process Water  Flotation  Screens  Primary Crushing  Fine Ore Surge Bin  HPGR (4) Coarse Ore Surge Bin  Ball Mill Feed Surge Bin  Ball Mill Feed Screens ( Wet)  Ball Mills (4)  Secondary Crushers (4)  However, although significant benefits are derived from their present applications, HPGR still present some shortcomings which currently limit broader application. Like other crushers, the HPGR is challenged by ore with a high proportion of very fine material (clayish material), by wet feed, or by feed likely to contain tramp metal. Fine material (or material with elastic properties) cushions the crushing action, reducing process efficiency. Wet feed may cause slippage of the material on the roll surface, accelerating  72  wear.  And tramp metal can damage the roll surface, creating serious maintenance  issues (Morley, 2006b). Some base metal ore bodies contain a mixture of very hard rocks, softer material, and clays, in proportions that can vary greatly throughout the deposit.  The author was  involved in such a base metal project through participation in a prefeasibility assessment conducted by AMEC. The project is a low-grade copper-gold porphyry deposit, requiring a high-tonnage operation to take advantage of economies of scale. The current plan calls for an 180,000 t/d processing plant. Early testwork and economic pre-assessments had already recognized that a significant portion of this orebody contains high proportions of sericite (clays) and that this portion of the orebody would be processed in the early years of the project. Based on this fact, all the work conducted prior and during the prefeasibility assessment was based on a comminution circuit consisting of SAG mills, ball mills and pebble crushing (SABC). Conventional three-stage crushing circuits, with or without HPGR for tertiary crushing, were ruled out because of the high clay content of the orebody.  Reinforcing this  decision was the position of SAG-based comminution as the standard for porphyry deposits (Barratt and Sherman, 2002).  As a result, no HPGR testwork had been  conducted. A comprehensive body of grindability testwork has been conducted on the ore at this property over the past few years and it indicates that the two mineral zones in this property contain a mixture of very hard rocks, softer material, and clays in proportions that will vary throughout the life of the mine.  Figure 4-2 represents the hardness  distribution of 371 samples that were tested, by the mining company’s contracted laboratory, for impact breakage, either by JK full drop-weight tests or by SMC tests.  73  Figure 4-2:  Hardness Distribution of the Deposit Based on Jk A*b Parameters  Soft 12%  Very Soft Very Hard 1% 8% Hard 16%  Mod. Soft 16%  Mod. Hard 15% Medium 32%  Figure 4-2 illustrates the high variability of hardness and implies that an SABC circuit will result in substantial fluctuations in tonnage and product size unless a very effective ore blending program is in place.  However, the considerable amount of material in the  moderately soft to very soft classes along with the presence of high clays suggest that a conventional crushing or crushing-HPGR circuit will present operational challenges. This combination of facts prompted the author to develop a research project to investigate the applicability of an innovative HPGR-based flowsheet.  74  4.2  Novel HPGR Circuit for Ores Containing Clayish Material  The novel HPGR flowsheet was developed to take advantage of the potential operating cost savings in processing hard rocks, stabilize production, and mitigate issues caused by the soft and clayish materials. The proposed flowsheet is shown in Figure 4-3 and evaluating its capabilities is the object of this research. Figure 4-3:  Proposed HPGR Flowsheet for Clayish Ore  Crusher Feed Bin HPGR Cone Crusher  Diverter  Coarse Ore  Trommel Screen Washing Screen Autogenous Mill/Scrubber To Ball Mills  In this circuit, the primary-crushed ore is slurried in a low-power autogenous mill, where weaknesses in the fresh rock are immediately exploited and hard material is scrubbed. The autogenous mill has a non-conventional design with an overflow type of discharge. The mill product is screened in two stages. The first stage is a trommel screen, which removes the bulk of the fine product. The trommel screen oversize is then washed on a vibrating screen and now free from fines it is conveyed to a cone crushing stage followed by an HPGR. An automatic bypass arrangement protects the HPGR when the cone crushers release coarse material to relieve jams. The HPGR product is recycled to the autogenous mill, where it is scrubbed, slurried and screened with the fresh feed.  75  The potential advantages of this circuit over conventional SAG-based or crusher-based circuits are:  •  the production rate is less sensitive to variations in ore hardness than a SAGbased circuit  •  the autogenous mill deals with any clays and obviates possible issues with highcapacity, wet, fine screening  •  competent HPGR cakes are de-agglomerated in the autogenous mill before screening  •  dust generation is less than in conventional crushing circuits  •  no SAG steel media consumption  •  no potential for steel ball scats to report to the crusher (as in SAG-based circuits).  To evaluate this circuit, it was simulated using pilot plant data obtained from tests run at the University of British Columbia (UBC). Pilot testing was conducted rather than less costly bench-scale tests as there are indications that the accuracy of simulations improves if the tests are conducted in a pilot-scale testing machine (Rule et al, 2008). A sample of ore from the deposit previously discussed was sent to the mineral processing laboratory at the University of British Columbia, Vancouver (UBC), and a test program was developed to represent a full-scale circuit. These tests (including HPGR pilot-scale) provided inputs to a modelling program in which the circuit was compared to conventional SABC technology. In parallel, a single HPGR test was conducted on the same ore for a preliminary evaluation of HPGR performance in a conventional tertiarycrushing application.  76  4.3  Testwork  4.3.1  Sample  An ore sample for the test program was obtained from the mining company. The sample was a blend of material remaining from an extensive comminution characterization testwork program conducted on several HQ and PQ drill-cores from the main mineral zone of the property. These samples had been coarsely (-32 mm) crushed using a jaw crusher, blended, homogenized and stored by the laboratory for an eventual HPGR testing program. The total weight of the material available was approximately 9,300 kg. This composite sample was expected to provide a good representation of the mineralized zone.  The characterization drilling program had integrated all the main  mineralized zones of the complete orebody, including the regions containing high proportions of sericite (clays). The mining company extracted two sub-samples from the composite, and had their contracted laboratory perform one SAG Mill Comminution (SMC) test and one MinnovEX SPI test (these results are shown in Appendix B). A further sub-sample weighing approximately 3,300 kg was shipped to UBC for the research described herein. (Appendix C details the sample preparation). 4.3.2  Testwork Design  The testwork was designed to represent the full scale process as much as possible. As part of this, effort was taken to generate a feed for the HPGR that approximated the feed that it would receive in the actual processing plant. The test flowsheet is shown in Appendix C, and is summarized as follows: 1. Conduct a preliminary circuit simulation, using JKSimMet, to obtain a target screen analysis of the cone crusher product. 77  2. Tumble and screen the sample to scrub and remove the clays and very soft material, to simulate the effect of the autogenous mill in the full circuit. 3. Crush a portion of the tumbled sample in the laboratory crusher. 4. Run the synthesised sample through the HPGR, at three different pressing forces. 5. Repeat the procedure twice; at each repetition, before the tumbling stage, mix the product from the previous stage with a calculated quantity of the fresh ore sample, to simulate the recycle in the plant (approximately 85%). (Note: four tests were planned, but after three tests the results (HPGR product screen analysis) converged, and the last cycle was not required.)  Following the HPGR tests, a series of tests was done to determine the effect, in terms of screening efficiency, of passing the HPGR product through the autogenous mill/scrubber.  First, product cake from the closed-cycle tests was scrubbed in the  tumbling mill, then washed on a screen with high-pressure water for one minute, and the screen efficiency determined.  Second, a standard HPGR test on the unscrubbed  sample, “full feed”, was conducted, following which the product, still unscrubbed, was washed on a screen with high-pressure water for one minute, and the screen efficiency determined. Third, a standard HPGR test on the full feed sample was conducted, then the product was scrubbed in the tumbling mill, followed by washing on a screen with high-pressure water for one minute, and the screen efficiency determined.  78  4.3.3  Test Equipment  High-Pressure Grinding Rolls The HPGR at the University of British Columbia was manufactured specifically for pilot plant work. The test unit, shown in Figure 4-4, is fitted with 0.75 m diameter rollers; test machines of this size require minimal scale-up factors.  Table 4-1 summarizes the  HPGR specifications. Figure 4-4:  UBC Pilot HPGR  Table 4-1:  Pilot-Scale HPGR Specifications  Item  Scale  Roller diameter Roller width Press frame Wear surface Main motor power  750 mm 220 mm Hinged design Hexadur® WTII 200 kW  Maximum specific pressing force Variable speed drive  8.5 N/mm2 up to 40 rpm (1.55 m/s) 79  The unit was designed to provide test data for sizing and selection of commercial units and to improve knowledge of the HPGR process and applications. The press is fitted with Koeppern’s patented Hexadur® wear lining with profiled surface (hexagonal tiles with different heights) and is capable of crushing at specific pressing forces (FSP) of up to 8.5 N/mm2. Tumbling Mill The tumbling mill used to scrub and de-agglomerate the ore is a 60mm diameter x 1m long smooth-lined vessel. It rotates at 22 rpm, providing mixing and tumbling action in the longitudinal direction. Screen A vibrating screen, Sweco® Vibro-Energy® Separator model ZS40 with 40" diameter screen panel with steel-wire mesh was used as the process screen for the pilot-scale work. Other equipment Additional equipment used for the tests were laboratory-scale gyratory and cone crushers, standard Bond ball mill, and dry and wet screen shaking apparatuses.  80  4.4  Results and Discussion  4.4.1  Sample Properties  The samples were blended and homogenized at the laboratory contracted by the mining company before shipment; this previous homogenization was checked by preparing samples from two drums randomly selected from among the twelve received, and determining their particle size distributions (PSDs) and Bond ball mill work indices. The Bond ball mill work indices (BWIs) were quite similar, 16.4 and 16.6 kWh/t. The particle size distributions also proved to be quite similar with 80% passing size (P80) of 21.8 and 21.3 mm. Figure 4-5 shows the complete particle size distribution curves. Figure 4-5:  Particle Size Distribution for the Samples as Received Particle Size Distributions - Original Samples  100% 90%  Cumulative Passing [%]  80% Sample A  70%  Sample B  60% 50% 40% 30% 20% 10% 0% 0.01  4.4.2  0.1  1 Particle Size [m m ]  10  100  Tumbling Test  Tumbling is the first step of the AG-HPGR circuit and therefore the first test conducted in the program. The laboratory tumbling mill provides mild autogenous grinding action and  81  is appropriate for the pilot tests. The AG-Scrubber in a full scale circuit is primarily used to scrub the clays and de-agglomerate cakes produced by the HPGR. As well, some of the coarse material coming from the primary crusher (large rocks in the range of 120 to 280 mm) is expected to be broken by the action of a large diameter tumbling mill. However, this can not be properly simulated by pilot testing. Thus, as in the case of AG/SAG milling, modelling and simulation are used to forecast commercial scale results. The tumbling tests were conducted wet, with the addition of water to reach 70% solids by weight. Batch tests were conducted for 7 minutes with loads of approximately 70 kg. The graph in Figure 4-6 gives an indication of the grinding action as both the feed and the product particle size distributions are plotted for one of several tests conducted. As can be observed on the graph, very little size reduction occurs on material larger than 10 mm but there is a significant increase in the fine portion. The -1 mm fraction changed from approximately 10% to 14.5% and the very fine minus 45 microns fraction increased from approximately 2% to 7%.  82  Figure 4-6:  Pre and Post Tumbling PSD Analysis  100 90  Feed PSD  80 Cumulative Passing [%]  Tumbling Test Feed and Product Size Distributions  Tumbling Product PSD  70 60 50 40 30 20 10 0 0.01  0.1  1 Particle Size [m m ]  10  100  Even though the full-scale circuit is designed with the application of a non-conventional AG mill with a deliberately low applied power, the mild breakage action achieved by this tumbling test is probably lower than what would be seen in the full-scale mill. This difference is acceptable for two reasons. First, the assessment of the full-scale AG mill performance will be conducted through modelling and simulation (details are given in chapter 5) based on material hardness characteristics (assessed by other tests) and a very distinct feed size distribution.  Secondly, the main purpose of the laboratory  tumbling test is to simply scrub off the clays as a first phase in the preparation of an adequate feed for the HPGR test. 4.4.3  HPGR Feed PSD  In the full-scale circuit the product of the tumbling mill is wet screened and the oversize portion reports to the cone crushers. At full scale the mesh to be used in the trommel and wet screens is expected to be in the range of 9 to 15 mm, similar to AG/SAG 83  conventional operations.  For this research full scale simulations assumed 12.7 mm  screen apertures. For the pilot tests the screen selected had a 6.35 mm aperture based on the fact that the sample is finer than what will be seen in the full scale plant and because the pilot HPGR operational gap would be around half that of the size of a fullscale unit. Figure 4-7 shows a schematic of the lab-scale circuit used to prepare the feed for the pilot HPGR (open-circuit). Figure 4-7:  Lab-Scale Circuit to Prepare the Feed to the Pilot HPGR (open-circuit)  Tumbling Mill  Wet Vibratory Screen +6.35 mm -6.35 mm  Pilot HPGR Laboratory Crusher  In the full-scale circuit, the oversize material from the screen reports to the cone crushers and their product in turn feeds the HPGR. For the laboratory testwork, there was a concern regarding the crushing action provided by the small scale crushers, as the available laboratory crushers would produce too fine a product which would not represent what would happen at a full-scale operation. However, if no crushing was applied, the HPGR feed could also be misleading, as no fines would be present and the size distribution would be significantly truncated at larger than 6.35 mm material. Figure 4-8 shows the particle size distributions for the screen oversize material with and without laboratory crushing.  84  Figure 4-8:  PSDs for Fresh and Crushed Laboratory Screen O/S Material Particle Size Distributions  100% 90%  Cumulative Passing [%]  80% 70%  100% crushed material Non-crushed (100% screen O/S)  60% 50% 40% 30% 20% 10% 0% 0.01  0.1  1  10 100 Particle Size [m m ]  To get a better understanding of the PSD in a full-scale operation, a preliminary simulation was conducted in JKSimMet using standard and benchmarked parameters previously gathered for different projects (Rosario and Hall, 2010). Figure 4-9 shows the PSDs for the screen oversize and the cone crusher product from the simulation.  85  Figure 4-9:  PSDs from the Preliminary Simulation  Particle Size Distributions - Preliminary Circuit Simulation  Cumulative Passing [%]  100% 90%  JK Cone Prod  80%  JK - Screen O/S  70% 60% 50% 40% 30% 20% 10% 0% 0.01  0.1  1  10 100 Particle Size [m m ]  1000  The preliminary simulation predicted that some fines will be generated from the cone crusher and provided an indication of the PSD curve shape that may be expected. Having this information and the laboratory testing results it was decided to investigate what would be the optimum blend between the screen oversize and laboratory crushed material to obtain a PSD with the approximate shape of the full scale circuit and with minimum size reduction. With the use of linear programming it was calculated that approximately 20% of the screen oversize material should be crushed for an optimum blend (Appendix D provides details on the linear programming calculation). Figure 4-10 shows the final blend PSD as well as the original products and the full-scale simulated cone crusher product. Figure 4-11 shows a schematic of the refined lab-scale circuit for the tests.  86  Figure 4-10: PSDs for the Optimum Blend, Original Products and Simulated Product  Particle Size Distributions 100% 90%  Cumulative Passing [%]  80% 70%  Pre-simulated HPGR feed 100% crushed material Non-crushed (100% screen O/S) Optimum blend (~1/5 crushed)  60% 50% 40% 30% 20% 10% 0% 0.01  0.1  1  10 100 Particle Size [mm ]  87  Figure 4-11: Lab-Scale Circuits Used for the Tests FULL FEED  CLOSED CIRCUIT (CYCLES 2 & 3)  Open Circuit (Cycle 1) Tumbling Mill  Sample Pilot HPGR  Wet Vibratory Screen ~14% -6mm (~30%)  ~70%  Laboratory Gyratory Crusher  Pilot HPGR  Split ~56%  4.4.4  HPGR Feed Moisture Content  As describe in section 2.4.2, the moisture content in the HPGR feed is an important operational parameter. Moisture content has an effect on the friction between the feed material and the roll surface and thus in the operating gap dimension. Consequently the moisture content affects the machine throughput as well as the energy consumption. Furthermore, feed moisture has an effect on the characteristics of the cakes produced. In “conventional” crusher-HPGR circuits, such as Cerro Verde and Boddington, the HPGR feed moisture content is driven directly by the fresh feed moisture and the moisture content of the recirculation stream (wet fine screen oversize). As the fresh feed moisture usually varies based on regions or depths being mining as well as local weather, it is difficult to properly estimate the moisture for the HPGR feed. For the test of this type of circuit it is usually assumed a feed moisture range and a number of tests are conducted to evaluate its effects.  88  In the proposed AG-Crusher-HPGR circuit, the fresh feed moisture has no effect as all material reporting to the HPGR is first slurried in the AG mill and then screened through a combination of trommel and wet vibrating screens for high efficiency. Due to the importance of the HPGR feed moisture content in the machine performance, an investigation was conducted to determine the expected moisture content at full scale operation and thus the most appropriate moisture value to be used in the HPGR tests. The approach taken for this research was to estimate the full-scale HPGR feed moisture based on two main parameters. First, the tested material surface moisture, i.e. the amount of water that remains retained on the rock surface subsequent to tumbling and screening.  Second, the full-scale vibrating screen oversize PSD based on the  preliminary simulation as described in section 4.4.3. The procedure utilized for this research involved testing phases and calculations described as follows: 1. tumbling a sub-sample through the laboratory mill; 2. screening the tumbled material on the laboratory vibrating screen (9.25 mm aperture panel) with abundant water spray; 3. determining the amount of water retained on the screened oversize material by weighing it soon after the screening, drying it, and weighing it again; 4. determining the PSD of the screen oversize material; 5. calculating the total surface area of this material by: a. assuming that the rocks, or particles, have perfect cubical shape,  89  b. assuming that all rocks remained in each PSD screen are cubes with an edge-length value equals to the average of the screen apertures they passed and were retained. For example, the material that passed the 32 mm screen and was retained on the 25 mm screen was assumed to be formed by 38.5 mm edge-length rock cubes, c. converting the PSD weights in volumes using the S.G. value of 2.70 (value from the tests conducted by the contracted laboratory), d. calculating the number of rocks per size fraction through the division of the PSD volume by the corresponding rock unit-volume (the assumed edge-length raised to the 3rd power), e. having the number of rocks and their dimensions, the total surface area of the material is calculated by the sum of the rock surface areas for the entire size distribution; 6. dividing the amount of water retained (step 3) by the calculated total surface area (step 5), the surface moisture for the tested material is determined; 7. calculating the total surface area of the  AG-Crusher-HPGR circuit screen  oversize material (same moisture content as the HPGR feed) by repeating step 5 with the full-scale vibrating screen oversize PSD (based on the preliminary simulation); 8. assuming that the tested surface moisture would be the same at full-scale operation; and,  90  9. determine the full-scale HPGR feed moisture content based on the calculated total surface area for the full-scale material and the tested surface moisture. Table 4-2 lists the main observed values for the test parameters along with the assumed and calculated values for the full-scale operation. Based on the 3.5% moisture content observed on the tests, it was calculated that the moisture content for full-scale operation would be approximately 1.7%.  Table 4-2:  Summary of Parameters and Calculated Results for Moisture Content  Description Screen aperture (mm) Oversize P80 (mm) Oversize P50 (mm) Total surface area (dm2) Solids weight (g) Water weight (g) Liquid content (%) Surface moisture (g/dm2)  Test  Full-Scale  9.35 22.5 16.8 164.4** 8718 315 3.49 1.92**  12.7 98.2 45.2 78.3** 8718* 150** 1.69** 1.92*  Note: *assumed, **calculated  4.4.5  HPGR Tests  In total, seven pilot-HPGR tests were conducted during the period of this research. Table 4-3 is a quick reference legend for the tests and detailed test results and operational parameters are listed in Table 4-4. The schematic of the lab-scale circuits for the tests is shown in Figure 4-11 (page 88). Moreover, the test results and details regarding feed preparation and operational parameters are given in the sections that follow.  91  Table 4-3:  HPGR Tests Quick Reference Legend  Test  Tag  Circuit  FSP**  Feed  #01 #02 #03 #04* #05 #06 #07  Cycle 1 Cycle 1 Cycle 1 Full Feed Cycle 2 Cycle 3 Full Feed  Open Open Open Open Closed Closed Open  4.0 3.0 3.5 3.5 3.5 3.4 3.4  Tumbled & screened (T-S) Tumbled & screened (T-S) Tumbled & screened (T-S) Original (as received) T-S plus Test #03 product T-S plus Test #05 product Original (as received)  Note: *Test disregarded due to operational problems, **Specific Pressing Force (N/mm2)  92  Table 4-4:  Summary of the Main Parameters and Results for All HPGR Pilot Tests  Item Speed Specific Pressing Force Average Actual Speed Actual Roller gap (average) Actual Hydraulic Pressure (average) Actual Pressing Force (average) Total Specific Energy Consumption Net Specific Energy Consumption Specific Throughput Constant Average Cake Density Cake Thickness Average Feed Moisture Particle Size Distribution 90% Center & 10% Edge: 80% Passing Size 90% Center & 10% Edge: 50% Passing Size Reduction Ratio F80/P80 (Centre & Edge) Reduction Ratio F50/P50 (Centre & Edge) Percentage Passing 6.35 mm (Centre & Edge)  Test Number: Symbol Unit  #02 #03 #01 Pressure Tests – Cycle 1  #05 Cycle 2  #06 Cycle 3  #07 Full Feed  m/s  0.75  0.75  0.75  0.75  0.75  0.75  rpm N/mm2  19.1 3.0  19.1 3.5  19.10 4.0  19.1 3.5  19.1 3.4  19.1 3.4  wAV XgAV PAV FAV ESP ESP net m-dot rC Xc  m/s mm Bar kN kWh/t kWh/t ts/hm3 t/m3 mm %  0.76 18.9 61.3 493 1.89 1.57 217.6 2.30 20.5 1.6%  0.75 18.5 71.6 576 2.14 1.79 215.3 2.30 20.4 1.6%  0.75 17.6 81.4 655 2.35 1.99 210.8 2.33 20.0 1.6%  0.73 17.5 71.1 572 2.23 1.82 216.2 2.29 21.8 1.5%  0.75 17.8 69.5 559 2.09 1.68 209.4 2.32 19.8 1.2%  0.74 20.6 69.9 562 2.05 1.68 246.9 2.30 24.0 1.7%  P80 P50  mm mm  6.5 2.6 3.2 5.5 79%  6.2 2.6 3.4 5.5 81%  5.4 2.3 3.9 6.3 85%  5.4 2.3 3.7 5.0 85%  5.7 2.4 3.2 4.4 83%  5.9 2.5 3.6 5.2 81%  ν n FSP  %  93  Cycle 1 – Open-Circuit Pressure Sensitivity Tests After four drums of material (approximately 1,200 kg) were tumbled, screened, partially crushed, blended, moisture corrected, and homogenized, they were split into three samples for HPGR testing. Three tests were performed at different specific grinding forces of 3.0, 3.5 and 4.0 N/mm²; the rotational speed was set at 19.1 rpm (circular velocity of 0.75 m/s) for all tests. These tests resulted in specific throughput constants (m-dot) of approx. 218, 215, and 211 ts/hm3, respectively (Figure 4-12). The net specific energy consumption values were 1.6, 1.8, and 2.0 kWh/t, respectively (Figure 4-13). The product P80s were 6.5, 6.2, and 5.4 mm for an adjusted product containing 90% of centre material and 10% edge material5. For a better visualization of the level of size reduction, the feed and product PSDs are provided in Figure 4-14, and F80/P80 and F50/P50 ratios are given in Figure 4-15. In addition, a summary of the main parameters and results for all HPGR pilot tests is shown in Table 4-4. The complete data for all tests is shown in Appendix E. These pressure-sensitivity tests provided an indication of how the product can get finer at higher pressure levels, which may be advantageous in full-scale operations. On the other hand, the tests also indicated the usual negative trends with increased pressure, such as the decrease in specific throughput and the increase in energy consumption. These test results did not indicate any anomaly in the application of HPGR for this type of material with this partially truncated feed (very limited amount of fines). Reasonable product fineness and moderate specific throughput were achieved at all pressure levels. At this preliminary assessment phase, with a single composite sample and without  5 The pilot HPGR is fitted with rolls with a large aspect ratio, i.e. the ratio between the diameter  and the length of the roll is 3.4. An excessive amount of edge material is generated during the tests and thus the product dividing chute is set to get approx. 70%center-30%edge split. In fullscale machines the normal split is approx. 90%-10% and it is common procedure to report testproduct PSDs with a calculated final product at this split to plot a single PSD curve  94  proper HPGR roll wear tests conducted, it would be premature to recommend an optimum specific grinding force for full-scale operations. Based on these initial results, the subsequent closed circuit and full feed tests were conducted at 3.5 N/mm2.  Figure 4-12: Specific Throughput as a Function of Pressing Force Assessment of Specific Pressing Force: Specific Throughput  Specific Throughput Mdot [ts/hm³]  300 280 260 Full Feed #7  240 Cycle 1  220  Cycle 2  Cycle 3 200 180 160 2.0  2.5  3.0  3.5  4.0  4.5  5.0  Specific Pressing Force [N/m m ²] Cycle 1  Cycle 2  Cycle 3  Full Feed #7  95  Figure 4-13: Influence in Energy Consumption due to Pressing Force Assessment of Spec. Press. Force: Net Specific Energy Consumption  Net Specific Energy Consumption [kwh/t]  2.4  2.1 #1 - Low Press  1.9  #5 - cycle 2 # 3 Medium Press  #6 - cycle 3  Test #7 - full feed  1.6 # 2 -High Press  1.4  1.1 2.5  3.0  3.5  4.0  4.5  Specific Pressing Force [N/mm²]  Figure 4-14: Pressure Sensitivity Tests – Feed and Product PSDs Particle Size Distributions -Test #1 to #3 100% 90%  Cumulative Passing [%]  80% 70%  HPGR Feed #1 to#3 HPGR Prod #1 (Fsp=4.0) 90%C-10%E HPGR Prod #2 (Fsp=3.0) 90%C-10%E HPGR Prod #3 (Fsp=3.5) 90%C-10%E  60% 50% 40% 30% 20% 10% 0% 0.01  0.1  1  10  100 Particle Size [m m ]  96  Figure 4-15: F80/P80 and F50/P50 Reduction Ratios Assessment of Spec. Press. Force: Reduction Ratio P80 & P50  Reduction Ratio  8  6  Test 07 (Full feed) 4  2 2.0  2.5 F80 / P80  3.0 F50 / P50  3.5  4.0  4.5  5.0  Specific Pressing Force [N/m m ²]  Cycles 2 and 3 – Closed-Circuit Tests To investigate the effects of closed-circuit operation on the HPGR’s performance, the test procedure was repeated twice; at each repetition, before the tumbling stage, the product from the previous stage was mixed with a calculated amount of fresh sample, to simulate the recirculation expected in the plant (Figure 4-11 on page 88, note the dashed line). The plan was to repeat the closed-circuit tests for three or more times to achieve a good convergence, but after two iterations the results showed an acceptable level of convergence and the third cycle was not required. The m–dot showed very little variation in the first repetition, Cycle 2, and a slight decrease in Cycle 3 (Table 4-4). The convergence in feed and product size distributions can be observed in Figure 4-16. From Cycle 1 to 2, the HPGR feed becomes moderately finer, especially below 20 mm, and the product is just slightly finer. From Cycle 2 to 3, the HPGR feed becomes slightly finer (small difference in the plus 6 mm portion) and the product is practically the same.  97  Figure 4-16: Feed and Product PSDs for Closed-Circuit Tests  Particle Size Distributions - Cycles 1 to 3 (close-circuit tests) 100% 90%  Cumulative Passing [%]  80% 70% 60%  Feed test #3 (1st cycle) HPGR Prod #3 (Fsp=3.5) 90%C-10%E Feed test #5 (2nd cycle) HPGR Prod #5 90%Cen 10%Edg Feed test #6 (3rd cycle) HPGR Prod #6 90%Cen 10%Edg  50% 40% 30% 20% 10% 0% 0.01  0.1  1  10  100 Particle Size [m m]  98  Full Feed Open-Circuit Test To assess the differences on HPGR performance between the proposed circuit (based on the developed testwork program) and a conventional HPGR circuit, an additional HPGR test was performed (Test 7 – full feed). This test was the type of test that is commonly used for conventional HPGR circuit assessment, i.e., the entire (full) feed is processed through the pilot-HPGR without any tumbling or scalping of fines or clays (a sketch of the test procedure is shown in Figure 4-11). The first observation during the test execution was the difference in the cakes produced. Visually, the product cakes from the full-feed test were large, approximately double the size of the cakes produced in the previous tests (refer to Table 4-5 on page 104). Subsequently, when handling this product through the rotary splitter, the chute ahead of the vibrating feeder plugged a number of times, which gives an indication of the kind of problems that may occur in full scale production. Problems related to material-handling in crushing plants dealing with clayish or high-fines material are expected and the same is expected for HPGR application (Morley, 2006a). The full-feed test (Test 7) product PSD revealed a significant correlation to the product obtained from Test 3 (tumbled and screened) as shown in Figure 4-17 (along with feed PSDs). The comparison is done with Test 3 as it is also an open-circuit test performed at the FSP of 3.5 N/mm² but with the prepared feed. Interestingly, although Test 7 feed presents considerably finer feed than Test 3 (31.4% and 9.4% -6.35 mm, respectively), the HPGR product size distribution is almost the same. The author suspects that the observed higher performance, i.e. increased size reduction, for the Test 3 (tumbled and screened) occurred because its feed had most of the softer and very fine material scalped off and thus was comprised of almost entirely hard 99  material. Similar observations have been recently reported by researchers that indicate a higher HPGR performance when treating a homogenous feed of hard material if compared to a blended feed containing the same hard material plus some other softer component(s) (Abouzeid and Fuerstenau, 2009; Benzer et al, 2010). Figure 4-17: Feed and Product PSDs for Full Feed and Tumbled-Screened Open-Circuit HPGR Tests PSDs HPGR Open Circ. Tests: Standard & Tumbled-Screened  Cumulative Passing [%]  100% 90%  Tumbled-Screened Feed  80%  Tumbled-Screened Product  70% 60%  Standard Feed Standard Product  50% 40% 30% 20% 10% 0% 0.01  0.1  1  10 Particle Size [m m ] Measured 68-32% Center-Edge - Calculated 90-10% C-E  100  As shown in Table 4-4, the Net Specific Energy Consumption (ESP net) result for Test 7 was 1.68kWh/t which presents an approximate 6% reduction when compared to Test 3 ESP net (1.79 kWh/t). In addition, there is a gain of approximately 15% in the value for Specific Throughput Constant (m-dot) from 215.3 ts/hm3 in Test 3 to 246.9 ts/hm3 in Test 7. These results appear to concur with the findings of other researchers (van der Meer and Gruendken, 2009; Morley, 2006a) which advise against the use of HPGR for the treatment of truncated feeds.  100  However, the full-feed case has 15% higher specific throughput, but the tumbled-andscreened case only includes 70% of the ore, because 30% (fine material) bypasses the circuit. Therefore the total plant throughput of the tumbled-and-screened case is actually 24% higher. The calculation follows:  ݉ሶ ‫݉ ݎ݋‬-݀‫ ݐ݋‬ൌ M⁄ሺD ൈ L ൈ ߥሻ  (1) ( Bearman, 2006)  where: M = throughput rate (tph) D = roll diameter (m) L = roll width (m) ߥ = roll speed (m/s)  Assuming similar machine sizes and at similar speed: ‫்ܯ‬௢௧௔௟ ଻ ⁄‫ܯ‬ு௉ீோ ଷ ൌ ݉ሶ 7 ⁄݉ሶ 3 ‫்ܯ‬௢௧௔௟ ଻ ⁄‫ܯ‬ு௉ீோ ଷ ൌ 1.15  (2)  ‫்ܯ‬௢௧௔௟ ଷ ൌ ‫ܯ‬ு௉ீோ ଷ ⁄0.7  (3)  and,  and combining equations 2 and 3,  ‫்ܯ‬௢௧௔௟ ଷ ൌ ‫ܯ‬ு௉ீோ ଷ ൈ 1.24  101  Similarly, the 6% specific power reduction refers only to the feed to the HPGR; the specific power applied to the total fresh feed is actually less, even when taking into account the minimal extra power required for screening and partial crushing. The difference between these findings and those of the earlier research is that the feed to the HPGR is only partially truncated, because a portion of the feed to the HPGR was crushed using a laboratory crusher (as previously described in the HPGR Feed section). In a full scale operation, the entire feed to HPGR will be crushed upstream. This analysis indicates that the removal of a portion of fines from the feed proved to be beneficial. Therefore, in this case a partially truncated feed can be effectively processed by the HPGR. 4.4.6  HPGR Product Cakes  The HPGR product generally contains a blend of loose particles and agglomerated “cakes”, in different proportions (0% to 80%) and cake sizes, depending upon ore and machine characteristics. These characteristics include: feed PSD and moisture content; applied pressure; and gap width. Cake strength or competency is usually low, and commonly these brittle lumps can be easily broken by hand. The agglomerated nature of the HPGR product influences the selection and performance of downstream processes, and even the performance of the HPGR itself when part of the product is circulated back to the machine. In hard ore applications, the current perception is that no, or only mild, de-agglomeration action is required for product “fine” (usually 6 to 9 mm) wet screening in closed-circuit HPGR (van der Meer and Gruendken, 2009). This is the case for both the Boddington and the Cerro Verde projects.  102  During the development of the AG-HPGR circuit, it was anticipated that, even with the tumbling and screening phases ahead of the HPGR, its product could still contain competent cakes due to the clayish nature of the ore, which prompted the concept of having the HPGR product re-circulated through the AG mill. Efforts were made to assess the properties of the cakes produced during the testwork. First, it was acknowledged that the cakes produced for all HPGR tests could be broken with similar pressure. Second, an attempt was made to gauge the compressive strength with the use of the Point Load Test and Brazilian Test apparatus available at the rock mechanics laboratory at UBC, but with no success (these types of tests and apparatus are designed for at least one order of magnitude greater strengths). Finally, it was decided to develop a test based on a wet-screening application, since this is usual in full scale processes. In addition, standard cake density and dimensional measurements were performed on samples from all HPGR test products. Figure 4-18 shows cake samples produced in Test 1 and Table 4-5 lists the average dimensions for the cakes produced by the tests. As shown in this table, the full feed test (Test 7) produced significantly larger cakes in the HPGR centre product than the tests conducted with prepared feed (tumbled and screened). Figure 4-18: HPGR Test #1 Product Cake Samples  103  Table 4-5  Average Dimensions of Cakes Produced by the HPGR Tests  Tests  Length Ave. (mm)  Width Ave. (mm)  Thickness Ave. (mm)  1 to 3 5&6 7  59 58 75  44 45 73  22 21 24  Volume 3 (mm )  56,290 55,494 132,168  The wet-screening test was developed to assess the behaviour of the HPGR test product when screening on the laboratory wet-screen and to give an indication of possible screening efficiencies at full-scale circuits. The test protocol is summarized as follows: 1. An HPGR centre-product sample, weighing approximately 10 kg, is collected through the standard procedure of splitting the mass through a rotary splitter. 2. The laboratory screen oversize discharge is blanked off. 3. The sample is gently fed onto the vibrating screen panel and left there for one minute under a controlled water spray (fixed flow rate and pressure). 4. At the end of one minute, the oversized material is collected, dried, weighed, and its PSD determined. 5. The amount of undersized material in the oversize is determined and the original PSD of the center-product is also determined (standard HPGR procedure on a parallel sample) allowing the test screening efficiency to be calculated. This procedure was used in a number of tests and some of the resulting oversize PSDs are shown in Figure 4-19. Through these tests, it was possible to observe a significant difference in screening efficiency between HPGR products from the test with prepared  104  feed and the one with the full feed, with the former producing a substantially higher efficiency than the latter (90% vs. 77%). In order to assess the tumbling effect on the HPGR product, tests were also performed with the HPGR product being tumbled prior to the developed screening test. Figure 4-19 shows the substantial benefit that is achieved with this procedure for both the prepared and full feed HPGR tests (94% and 96% respectively). Figure 4-19: Screen Oversize PSDs from the Tests for Assessment of HPGR Product Cake Competency Particle Size Distributions 100% 90%  Cumulative Passing [%]  80% 70%  Prepared f eed HPGR prod - test screen o/s Full feed HPGR prod - test screen o/s Prep. feed HPGR prod tumbled - test scr. o/s Full feed HPGR prod tumbled - test scr. o/s  60% 50% 40% 30% 20% 10% 0% 0.01  0.1  1  10 100 Particle Size [m m ]  A poor screening efficiency of the HPGR product may seriously degrade the performance of a closed-circuit HPGR system.  In such a case, there will be an  unproductive return of fine material which otherwise would report directly to the downstream process. The fine material compromises the HPGR performance in two ways. First, the fresh feed throughput is decreased due to excessive return.  Second, the returning fine  105  material carries back additional water to the HPGR increasing the total feed moisture content which will further degrade the machine performance. High levels of moisture represent a reduction in the friction between the feed material and the roll surface which decreases the specific throughput and increases the energy consumption. In addition, excessive moisture may cause slippage of the material on the rolls surface, accelerating roll surface wear. (Klymowsky et al., 2006). The tests confirmed the benefit of a scrubbing phase in the HPGR circuit. The scrubbing increases screening efficiency and reduces moisture in the recycle stream, even following a wet processing step. 4.4.7  Bond Ball Mill Work Indices  Energy savings in comminution in downstream grinding phases (usually ball milling), are expected through the reduction of the Bond ball mill work index (BWi) of the HPGR product.  This reduction in the hardness of the ore is due to the production of  microfractures in the high-pressure process.  In addition to this particle-weakening  phenomenon, the HPGR produces a high proportion of fines that further decrease energy requirements in the subsequent mill (Tavares, 2005; Patzelt et al, 1995). Tests performed by Patzelt et al (1995) on siliceous gold ores resulted in 5% to 20% BWi reduction. Tested performed in a lab-scale HPGR by van Drunick and Smit (2006) on several different ores resulted in BWi reductions between 3% and 7%. Differences in the evaluation of this reduction factor are not rare; the authors have observed significant differences between testwork performed on the same ore through different HPGR vendors and that may be related to different test procedures. Some procedures may combine the results of particle weakening with fine product and others may report the particle weakening factor alone. 106  The HPGR effect in reducing the Bond ball mill work index was assessed in this research and the methodology was based on the standard Bond ball mill test procedure. On one occasion, following the routine Bond test on the feed and product of one HPGR test (Test 6 with 19.3 and 17.4 kWh/t, respectively), the test on the product was repeated with a PSD artificially adjusted to that of the HPGR feed. This was done to investigate if the high amount of fines in such a product was affecting the work-index result. The new WIBM result for the product was virtually the same (17.5 kWh/t). It is suspected that because of the nature of the Bond test, (several cycles and makeup of the feed based on the production of fines in the product until test convergence), it is only marginally affected by the fines, and may turn out to be the proper test to investigate the particle weakening effect alone. Figure 4-20 summarizes the WIBM results in different points of the circuit. Both the full and prepared feed HPGR products showed a sizeable reduction in the index (12.7% and 9.3% respectively). A higher WIBM for the screen oversize portion than for the feed was observed (19.3 and 16.6 kWh/t, respectively) which may indicate that the softer material does constitute the finer fractions of the sample, as one would expect. Due to practical limitations, the WIBM of the whole screen undersize product (minus 6 mm portion and approximately 30% of the feed) was not determined. This material was subjected to fine wet screening for PSD analysis and only the plus 45 microns portion was used for WIBM testing. Consequently, this WIBM result of 16.9 kWh/t is higher than what would be expected for the whole screen underflow portion.  107  Figure 4-20: Bond Ball Mill Index Results in Different Points of the Circuit FULL FEED  CLOSED CIRCUIT (CYCLES 2 & 3)  WIBM 16.6 kWh/t Sample (2% -45 µm)  WIBM 16.6 kWh/t  WIBM 19.3 kWh/t  Sample (2% -45 µm)  Pilot HPGR  Tumbling Mill  Wet Vibratory Screen ~14%  Pilot HPGR  -6mm (~30%) ~70% + 45 µm ~23%  - 45 µm Laboratory Screen  Split ~56%  Laboratory Gyratory Crusher  ~7% WIBM 17.5 kWh/t (9.3% Reduction)  WIBM 14.5 kWh/t (12.7% Reduction) WIBM 16.9 kWh/t  4.5  Summary  This chapter has demonstrated the complete procedure for pilot testing a proposed HPGR circuit for the treatment of mixed hardness ors containing clays. The testing program resulted in important observations indicating the suitability and potential benefits of this novel flowsheet. In addition, a comprehensive testing results dataset was produced, which includes the pilot HPGR operational parameters and the feed and product characteristics. These results enabled the design, simulation and evaluation of the proposed novel AG-Crusher-HPGR circuit which are detailed in the next chapter.  108  5 FEASIBILITY ASSESSMENT OF THE AG-CRUSHER-HPGR CIRCUIT TO TREAT CLAYISH AND/OR MIXED HARDNESS ORES  5.1  Introduction  As explained in Chapter 4, the author has been involved in the assessment of a SAGbased comminution circuit originally proposed for a high-tonnage copper-gold porphyry deposit. This deposit is heterogeneous in rock hardness and present regions with high clay content.  In addition, a sample from this deposit was made available for this  research and has been used for tests at UBC for the development of an innovative HPGR-based circuit for such ores. Based on the test results from Chapter 4 and using the methodology proposed in Chapter 3, the original SABC circuit and the proposed novel-HPGR circuit are evaluated and their benefits and disadvantages discussed.  109  5.2  Modelling and Simulation  A JKSimMet® model was developed for the proposed AG-Crusher-HPGR circuit. The main inputs were:  •  data derived from results obtained through the SMC test (A=62.9, b=0.55, and ta=0.33 and specific comminution energy)  •  Bond ball-mill work index (16.6 kWh/t)  •  appearance function from a previously performed JK full drop-weight test on material from the same project with similar A and b parameters  •  specific gravity tests (S.G.=2.70)  •  HPGR pilot machine physical parameters(diameter, length, rpm of rolls)  •  HPGR pilot machine operational parameters (e.g. speed, power)  •  The results from the HPGR Test 7, Closed-Circuit Cycle 3 (m-dot, PSD of feed and product). Some HPGR model parameters were calibrated using the model fitting capability embedded in JKSimMet® (Daniel and Morrell, 2004).  Additional details regarding JKSimMet® model construction are described in Chapter 3. The primary crusher product PSD was estimated from survey data from different operations with similar hardness and also on the correlation with the ta parameter recommended by JKTech (Bailey et al, 2009). Figure 5-1 shows the developed PSD of the feed with a F80 of approximately 125 mm.  110  Figure 5-1:  Feed PSD for Circuit Modelling and Simulations Feed Size Distribution used for the AG-Crusher-HPGR and SABC Circuits  100 SABC & ACH Feed  90 80 70  Cumulative passing (%)  60 50 40 30 20 10 0 0.01  0.1  1  10  Particle Size (mm)  100  1000  During the prefeasibility assessment, the original project equipment (SABC circuit) was selected to provide a life-of-mine average throughput in the order of 180,000 t/d. Consequently, the AG-Crusher-HPGR circuit was designed and its model developed to provide a throughput of approximately 180,000 t/d for the sample provided by the mining company. The SABC circuit was simulated using the previously developed JKSimMet model, the same feed PSD, and the grindability characteristics of the sample utilized in the research (based on the SMC test and Bond ball-mill work index). This simulation estimated that the SABC circuit would deliver 139,000 t/d when fed with this ore. The screen snapshot of the model given in Figure 5-2 shows the mass balance, the P80 of the streams, the simulated power for the various pieces of equipment, and some machine operational parameters.  111  Several simulation iterations were performed for the refinement of the AG-CrusherHPGR circuit. During this process, different values for full-scale machine/operational parameters, such as HPGR roll dimensions and speed, were tried. In addition, this finetuning process took into consideration equipment vendor information, and the provision for parallel systems to increase the availability of the circuit. The screen snapshot of the model given in Figure 5-3 shows the mass balance, the P80 of the streams, the simulated power for the various pieces of equipment, and some machine operational parameters.  112  Figure 5-2:  ®  JKSimMet Screen Snapshot of the SABC Circuit Simulation  113  Figure 5-3:  ®  JKSimMet Screen Snapshot of the Final AG-Crusher-HPGR Circuit Simulation  114  5.3  Energy Requirements  5.3.1  Ball Mill Energy  The Ball Mill energy requirement for both circuits were based on Bond’s third theory of comminution, the application of the “phantom” cyclone method (Chapter 3; Napier-Munn et al, 1996), and the value of 16.6 kWh/t for the WIBM as per the test results conducted on the sample. Although a reduction on the WIBM was observed for the HPGR product, no discount was applied for the Ball Mill power requirement for the HPGR circuit. This decision may have added some conservatism to the design but seems appropriated due to the difficulty in precisely estimate the WIBM for the effective Ball Mill feed. As discussed in section 4.4.7, although a reduction in the HPGR product WIBM was observed, the HPGR feed is expected to have a higher WIBM than the fresh feed as per the screen oversize test results.  In addition, the WIBM test result for the undersize portion was deemed  inconclusive. For the required final product P80 of 200 microns, the calculation for the Ball Mill specific energy resulted in 7.78 and 8.21 KWh/t for the AG-HPGR-Crusher and the SABC circuits respectively. This difference is mainly due to the higher amount of fines in the Ball Mill feed for the HPGR circuit as shown in Figure 5-4.  115  Figure 5-4:  Ball Mill Cyclone Feed PSD from AG-Crusher-HPGR and SABC Circuits Simulated Size Distributions: AG-Crusher-HPGR and SABC Circuits  100 AG-Cr-HPGR - Balll Mill Cyclone Feed  90  SABC - Ball Mill Cyclone Feed  80 70  Cumulative passing (%)  60 50 40 30 20 10 0 0.01  0.1  1  Particle Size (mm)  10  100  There are a number of reasons for the coarser Ball Mill feed in the SABC circuit. This circuit was design to cope with the hard and extremely hard ores that are part of the orebody and to minimize a decrease in the overall circuit capacity. Consequently the SAG mill is designed to operate at significant high ball load and speed which implies a coarser SAG product. In addition, the SAG mill discharge screen is designed with a fairly large aperture of 15.9 mm thus further coarsening the material that reports to the Ball Mill. On the other hand, the HPGR circuit is designed with a smaller aperture for the AG discharge screen (12.7 mm) and the AG mill, though at low applied power, may produce extra fines. This mill acts on both the fresh feed and the HPGR product and provides moderate abrasion breakage to these materials as can be observed in Figure 5-5. The graph shows the simulated AG combined feed and product and indicates that moderate  116  breakage is achieved especially in the fine and extra coarse portions of the feed. The simulated results are in agreement with the usual reduced breakage in the size range between 12 mm to 75 mm that is a characteristic of AG milling (Napier-Munn et al, 1996).  Figure 5-5:  AG Mill Feed (Combined) and Product PSDs Simulated Size Distributions: AG-Crusher-HPGR and SABC Circuits  100 AG Combined Feed  90  AG Product  80 70  Cumulative passing (%)  60 50 40 30 20 10 0 0.01  5.3.2  0.1  1  10  Particle Size (mm)  100  1000  Pure Comminution Energy  Based on the simulations results and the ball mill energy requirement calculations, the total energy applied by the comminution equipment was assessed. Table 5-1 shows the description of the selected machine sizes and energy simulation results for the comminution equipment for both circuits.  117  Table 5-1:  Simulation Results – Pure Comminution Energy Requirements  Description  Unit Power  Average Consumption  Specific Energy  Qt.  Inst. (kW)  Sim. (kW)  Total (kW)  kWh/t  AG Mills - 10.4 m D x 6.1m EGL (34 x 20 ft)  2  8,000  7,411  13,636  1.85  Sec. Crushers XL-1100 (8 - 6 oper. 2 stdby)  6  820  807  4,455  0.61  AG-Crusher-HPGR Option (2 lines)  4,000 t/h per line (simulated instantaneous) 176,640 t/d @ 92% Availability Comminution equipment  Tert. HPGR - 2.4m D x 1.7m W  4  5,000  3,665  13,487  1.83  Ball Mill - 7.9m D x 12.8m L ( 26 x 42 ft )  4  18,000  15,563  57,272  7.78  88,850  12.07  112,920  Totals SABC Option  (2 lines)  3,080 t/h per line (simulated instantaneous) 138,970 t/d @ 94% Availability Comminution equipment  SAG Mills - 12.2 m D x 6.7m EGL (40 x 22 ft)  2  25,000  23,279  43,764  7.56  Pebble Crusher XL-1100  4  820  361.4  1,359  0.24  Ball Mill - 7.9m D x 12.8m L ( 26 x 42 ft )  4  18,000  12,636  Totals  125,279  Difference in Specific Energy  47,511  8.21  92,634  16.00 24.50%  Even though the ore provided by the mining company for the research was harder than previously estimated for the life-of-mine average, the two circuits were simulated using the same ore parameters. Therefore any energy requirement comparison should be focused on specific energy values (last column of the table), as the installed equipment may be larger than necessary for the AG-Crusher-HPGR circuit. As shown in the table, the proposed HPGR circuit provides savings in pure comminution energy in the order of 24.5%. However, as discussed in Chapter 3, most HPGR circuits add a level of complexity, as more auxiliary equipment is usually required. Although, the proposed circuit targets simpler operation than “conventional” HPGR circuits, the  118  determination of the real difference in the energy savings for the complete circuit involves a higher level of circuit detail. 5.3.3  Complete Circuit Comminution Energy  For the complete circuit energy requirement comparison, auxiliary equipment was sized and added to the HPGR flowsheet. This refined flowsheet was arranged in parallel to the development of a preliminary plant layout. Figure 5-6 is the resulted AG-CrusherHPGR circuit flowsheet which includes the main additional equipment. The developed plant layout is shown in Appendix F. And in Appendix G, the original SABC circuit plant layout is reproduced.  119  Figure 5-6:  Process Water  Magnet  AG-Crusher-HPGR Circuit Simplified Flowsheet  Crusher Bin Feed Conveyor  Crusher Bin Feeder Crusher Feed Bin  HPGR Feed Bin  HPGR Bin Feed Conveyor  Belt Feeder To Ball Mills Belt Feeder  HPGR Scrubber  Feeders HPGR Cone Crushers Diverters  Coarse Ore  Magnet  Metal Detector  Trommel Screen  HPGR Disharge Conveyor  Washing Screen  Tramp Material Bypass Conveyor  Magnet  Autogenous Mill/Scrubber Tramp Material Pile  Screen Discharge Conveyor To Ball Mills  120  Once the circuit was detailed, the estimation of the energy usage of the complete circuit was also performed and the complete set of results is shown in Appendix H. Table 5-2 summarized the findings and shows that the complete circuit energy savings are in the order of 22.7%. Table 5-2:  Energy Requirements for the Complete Circuits Connected Power  Sim. Average Consumption  Specific Energy  kW  kW  kWh/t  Comminution equipment  112,920  88,850  12.07  Conveyors and feeders  5,108  3,468  0.47  Pumps  12,080  8,562  1.16  Screens  119  82  0.01  Comm. Eq. Lube and Cooling systems  1,537  1,092  0.15  Dust and metal collection requirements  651  466  0.06  Heat & Ventilation Systems  325  299  0.04  132,740  102,819  13.97  Comminution equipment  125,279  92,634  16.00  Conveyors and feeders  2,554  1,809  0.31  Pumps  11,968  8,664  1.50  Screens  60  42  0.01  Comm. Eq. Lube and Cooling systems  1,476  1,089  0.19  Dust and metal collection requirements  204  148  0.03  Heat & Ventilation Systems  274  258  0.04  141,815  104,645  18.07  Description  AG-Crusher-HPGR Option (2 lines)  4,000 t/h per line (simulated instantaneous) 176,640 t/d @ 92% Availability  Totals SABC Option  (2 lines)  3,080 t/h per line (simulated instantaneous) 138,970 t/d @ 94% Availability  Totals Difference in Specific Energy  22.71%  121  5.4 5.4.1  Operating and Capital Costs Operating Cost  For the comparison of operating costs, it was assumed that the HPGR circuits and the SAG mill circuits would have similar steel consumption for liners (including HPGR roll surfaces and SAG mill liners, grates and pulp lifter bars) and ball mill media. In other words, it is assumed that the main difference in steel consumption lies in the SAG mill balls. For the SAG steel media consumption the same methodology as described in Chapter 3 was used and resulted in 480 grams of steel per processed ton. Assuming a cost of Can$ 1,000 per ton of SAG steel ball and assuming 180,000 t/d, the operating cost savings in steel grinding media for the HPGR-circuit would be Can$ 86,400 per day. Assuming the unit power cost of Can$ 0.08 kWh, and having the specific energy difference of 4.1 kWh/t, it is estimated that the energy savings with the HPGR circuit are Can$ 59,000 per day. Thus the total estimated savings including steel grinding media is Can$ 145,400 per day. 5.4.2  Capital Cost  For the purposes of this research, a rigorous materials take-off was not undertaken. To arrive at an order-of-magnitude capital cost for the AG-Crusher-HPGR circuit, the total area cost was factored from the cost of the installed equipment, using the ratio of the area cost to installed equipment cost for the SABC circuit. The SABC circuit costs were generated during the original pre-feasibility study and are summarized in Table 5-3. This table also shows the summary of the calculated costs for AG-Crusher-HPGR circuit.  122  Table 5-3:  Capital Cost Summary  Item  Cost (USD)  SABC Circuit SAG Area Total Cost from Pre-feasibility Study Pebble Crushing Area Total Cost from Pre-feasibility Study Total SABC Area Cost Installed Major Process Equipment (SABC) Factor, SABC Area Cost: Process Equipment Cost  225,943,408 54,484,696 280,428,104 123,835,917  Ratio  2.26  AG-Crusher-HPGR Circuit Installed Major Process Equipment Factor (Area Cost: Process Equipment Cost) Total AG-Crusher-HPGR Area Direct Cost  345,657,373  Difference (AG-Crusher-HPGR vs. SABC) Indirects Cost @ 43% Contingency at 20% of Direct plus Indirect Total Cost Difference AG-Crusher- HPGR > SABC  65,229,269 28,048,586 18,655,571 111,933,426  152,640,899 2.26  23%  Based on the difference in the operating costs, the payout period for the additional capital cost for the HPGR-circuit is estimated in approximately 2.1 years. The simulation results and the cost analyses demonstrate that the novel circuit presents the potential for significant energy savings and reduced grinding media consumption.  123  5.5  Discussions  Copper porphyry deposits are a major source of global copper production and, in several cases, present quite heterogeneous orebodies (in terms of rock hardness) which present challenges to SAG mill operation. Based on the promising results from this application of the novel circuit for heterogeneous, hard ore with high clay content, it is possible that this circuit, or one derived from it, may become an important alternative for SAG-based circuits for processing of copper porphyry deposits. An example of a property where this circuit might have had an application is the Batu Hijau operation in Indonesia, with an orebody with high variability of hardness (JK Axb results ranging from 23 to 107) and the consequent highly variable throughput rates for SABC circuits—daily variation ranging from 4,500 to 7,300 tph total for two parallel circuits—(Burger et al, 2006). This may disturb the flotation stage and compromise metal recovery. This work has demonstrated that the change in energy savings using the novel circuit when additional equipment is added is much lower (from 24.5% to 22.7%) than those calculated in Chapter 3 (from 25.1% to 7.7% in case A, and from 30.2% to 18.4% in case B). It is believed this is due to some unique characteristics of the proposed circuit, such as the circuit simplicity and the scalping of the softer components of the ore prior to the crushers-HPGR portion of the circuit. The circuit emphasises simplicity; compared to current HPGR-based circuit designs, the amount and complexity of ancillary equipment is reduced by the elimination of the nested closed circuits.  In addition, the use of high-angle conveyors (“sandwich  conveyor”) reduces overall circuit footprint and thus building requirements.  124  As described in Chapter 2, crushers and HPGR are considerably more energy-efficient than AG or SAG mills. For this circuit, the gain in efficiency is augmented by the fact that the crusher-HPGR portion of the circuit deals with the harder component of the feed only. Recent research in the application of HPGR for mixtures indicates that machine performance might be enhanced if treating the hard component of the mixture separately (Abouzeid and Fuerstenau, 2009; Benzer et al, 2010).  Moreover, this circuit fully  exploits the AG mill’s strong point, i.e. its ability to scalp the softer components of the fresh feed and the clays. In the proposed AG-Crusher-HPGR circuit design, a single AG mill per line is used. This mill has some non-conventional features.  The AG is designed with unusual limited  power to perform the scrubbing action of conventional scrubbers and to provide limited breakage on the soft portions of the ore. This will be achieved with a higher applied power than conventional scrubbers provided by the higher diameter-length aspect ratio and the proportionally high internal load inherent to the AG. However, one potential risk of this design is the required high volumetric flow of slurry (flux) through the mill. To deal with this, an overflow-discharge type of mill is proposed. Another option would be a discharge mechanism with modern pulp lift design such as the kind proposed by Latchireddi in 2009, in combination with larger than usual grate openings (slots) positioned at the far circular periphery region of the mill. As detailed in the introduction, the sample utilized in this research was a carefully prepared composite for proper correlation with the average properties of the orebody. However, as a single sample was used for the evaluations, the results are quite specific for the corresponding grindability parameters of this sample.  125  6  CONCLUSIONS  6.1  Main Research Contributions  This thesis has contributed to the understanding of HPGR technology, especially for its application in comminution circuits for high-tonnage, base/precious metal mining. This research led to some specific contributions, as follows:  •  The development of a structured methodology for the evaluation of energy requirements of complete HPGR and SAG mill circuits. This work involved using advanced modelling tools and the demonstration of the methodology through case studies.  •  The development of an innovative HPGR flowsheet with an AG mill/scrubber and parallel trains of crusher-HPGR to treat mixed-hardness ores and/or ores with a high proportion of clays and moisture.  •  The development of a systematic testing program for the design and evaluation of HPGR circuits with the application of a unique pilot-plant test program as a basis for experimental simulation. The method includes the pre-assessment of HPGR feed properties in full-scale operations as well as corresponding procedures to prepare the sample, and may serve as incentive to the improvement of HPGR circuit design protocol.  •  The demonstration of the suitability and the potential benefits of the novel circuit for the comminution of hard, weathered ores containing clayish material. This 126  was achieved through the use of the testing protocol, and of the methodology for energy evaluation, in the assessment of a full-scale mining project.  This research has unveiled the potential for innovative HPGR-based circuits, and may serve as incentive for the future use of HPGR in other applications currently labelled as ideal for different technologies.  127  6.2  Future Research Opportunities  The AG-Crusher-HPGR pilot-plant test program results, as detailed in section 4.4.5, demonstrated the advantage of scalping the fine particles ahead of the crusher and the HPGR. It was demonstrated that required HPGR capacity, size and power decreases and the HPGR product is similar to the one achieved with full feed. It is speculated that the fine/soft material cushions the breakage action (provide by the high pressure) on the hard portion of the feed. In cement applications, recent research involving plant surveys and laboratory piston-die tests provided results in agreement with the observations from this research (Benzer et al, 2010). In addition, research based on limestone and quartz mixtures, feeding a laboratory-scale HPGR, suggests that the breakage level of the hard component is related to the mixture composition and that the presence of hard components in a mixture enhances HPGR energy efficiency (Abouzeid and Fuerstenau, 2009). This research did not investigate this phenomenon further but follow-up research in this area will add significant value in the understanding of the HPGR for base/precious metal application. More should also be done to create a suitable protocol for analysis of the weakening effect provided by the HPGR. This research demonstrated a different level of reduction when treating the scalped feed and the full feed, and indicated the difference in the Bond Work indices for different size fractions in the sample received from the mining company. For the energy calculations and comparisons to the SAG-circuit presented in Chapter 5, a conservative approach was taken by not using any hardness reduction factor for the Ball Mill power requirements. This seems to be the current consensus for design and trade-off studies of comminution circuits involving HPGR (Vanderbeek, 2006; Morley and Staples, 2009). However, the benefit seems to be quite significant, and in some cases may play a critical role in trade-off studies and/or circuit evaluations, thus the sooner a 128  better understanding of this phenomenon is achieved, and proper testing protocols accepted by the industry; the better.  Tavares (2005) and Daniel (2008), developed  invaluable work in this area but more is needed. The author recognizes that the “low-power” AG mill proposed for the AG-Crusher-HPGR may present some challenges regarding the required high volumetric flow of slurry (flux) through the mill. To mitigate the problem two alternative but unconventional designs are proposed. Both the overflow-discharge option and the application of an enhanced grate discharge system could be the object of future investigation. Probably by the application of DEM modelling, such as the work being conducted by Cleary and his associates at CSIRO (Cleary et al, 2008), the effect of different discharge arrangements and the simulated level of breakage provided by this AG mill could be verified. Higher precision in equipment and plant availability factors through a more elaborated assessment would be advantageous for this research.  This could be achieved if  dynamic simulation was conducted, such as that done during the feasibility studies for the Cerro Verde project (Vanderbeek, 2006).  Unfortunately, the lack of reliable  maintenance data for HPGR operation (especially in base/precious metal mining) prevents this from being done at present. The disclosure of current maintenance data from HPGR operations, especially from Cerro Verde and Boddington, would be of great value for the industry. If such data was available, the accuracy of dynamic simulations would be increased and their outcomes would facilitate design and engineering of conventional and/or novel HPGR plants. For the two case studies presented in Chapter 3, single samples were used for the evaluations, and therefore the results are quite specific for the corresponding grindability parameters of those samples. It was advised that the findings from those case studies  129  be interpreted as an indication of potential HPGR-circuit benefits for projects dealing with average ore hardness between those two points. For the evaluation of the innovative HPGR circuit, the sample utilized in the research was a carefully prepared composite which is expected to correlate well with average properties of the original project’s orebody.  However, the grindability parameters  obtained during the test program indicated that the composite may be harder than the average, and this should be investigated further. This fact does not compromise the findings of this research but it is recommended that a number of samples, collected from different parts of the orebody, be tested, and that the program is repeated. Of special value would be the comparison between the two circuits when treating ores softer than the average, and the prediction of throughput values based on the mine plan. The assessment of the ore variability and its effect in the overall AG-Crusher-HPGR circuit performance may also determine if this preliminary design is appropriate. For instance, the crusher-HPGR portion of the circuit may receive substantially less material when dealing with softer than tested ores and changes to the circuit may be required. For the preliminary design, it was anticipated that the feed rate to this sub-system will fluctuate and that there will be occasions requiring the shutdown of one or more units. In addition, the design incorporates some features for improved operational flexibility such as: crusher and HPGR feed bins, variable frequency drives for the feeders and machines. Nevertheless, future analysis may still indicate that the application of more units at lower capacities will be preferable, e.g. four 600 kW operating crushers instead of three 820 kW units along with three smaller HPGR units.  130  REFERENCES  Abouzeid A.-Z.M. and Fuerstenau D.W. (2009). “Grinding of Mixtures in High-Pressure Grinding Rolls”. Int. J. Miner. Process, vol. 93, pp. 59-65 Amelunxen P., Bennett C., Garretson P., and Mertig H. 2001. 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(2005). “Real and Potential Metallurgical Benefits of HPGR in Hard Rock Ore Processing”. Proceedings of the Randol Innovative Metallurgy Forum held in Perth, W.A., Australia, 21-24 August 2005, pp. 31-39  140  von Seebach, M. and Knobloch, O.R. (1987). High-Pressure Grinding Rolls in Industrial Application”. Presentation at the SME Annual Meeting, Denver, Colorado – 24-27 February 1987. SME Preprint number 87-99 Walsh H. (2008). “Chile Power Crunch May Cut Copper Output”. Spur Record (Update2). Bloomberg.com: Energy, 9 April 2008, URL.  http://www.bloomberg.com/apps/news?pid=20601086&sid=aJlEuFVIVRbs&refer=ne ws  141  APPENDIX – A: INPUTS USED FOR THE JKSIMMET® MODELS  HPGR Pilot Test Scaling Data Case A  Case B  Rolls Diameter (mm)  800.0  710.0  Rolls Length (mm)  250.0  210.0  Working Gap (mm)  22.00  22.00  Speed (m/s)  0.670  0.290  Specific Comm. Energy (kWh/t)  1.680  1.726  Flake Density (t/m3)  2.620  2.360  Feed Bulk Density (t/m3)  1.700  1.604  HPGR Modelling Parameters - Pilot Test PSDs Case A  Case B  Particle Size  Feed Cum. Pas.  Product Cum. Pas.  Particle Size  Feed Cum. Pas.  Product Cum. Pas.  [mm]  [%]  [%]  [mm]  [%]  [%]  45  100.00%  100.00%  45  100.00%  100.00%  31.5  100.00%  100.00%  31.5  100.00%  100.00%  22.4  93.31%  99.56%  22.4  91.10%  100.00%  16  84.64%  96.03%  16  81.90%  98.40%  11.2  77.67%  93.49%  11.2  68.70%  94.40%  8  66.24%  88.14%  8  57.60%  87.20%  5.6  49.55%  81.01%  4  39.70%  70.80%  2.8  22.04%  62.15%  2  28.20%  57.00%  1  12.75%  43.36%  1  18.80%  45.30%  0.5  9.87%  34.48%  0.5  13.60%  37.70%  0.315  8.40%  29.66%  0.2  8.40%  29.70%  0.2  7.01%  25.01%  0.09  5.60%  21.90%  0.125  5.77%  20.80%  0.045  4.00%  16.40%  142  Feed PSDs for the Circuits (Cases A & B)  Particle Size  Feed Cum. Pass.  [mm] 270.2 254 203.2 152.4 127 101.6 76.2 50.8 25.4 19.05 12.7 9.51 6.35 4.76 3.36 2.38 1.68 1.19 0.841 0.595 0.42 0.297 0.21 0.149 0.105 0.074 0.053 0.037  [%] 100.00% 99.14% 95.56% 86.64% 80.61% 73.31% 62.26% 46.45% 30.65% 26.15% 21.13% 18.54% 15.38% 13.37% 11.23% 9.30% 7.71% 6.54% 5.39% 4.28% 3.56% 3.08% 2.65% 2.19% 1.79% 1.57% 1.46% 1.33%  143  Crusher/HPGR Parameters from JK Drop-weight Tests Case A - Appearance Function Value of t10 10 20 30 50  t75 3.64 6.89 10.35 17.03  t50 4.27 8.22 12.51 20.70  t25 5.86 11.37 17.20 28.48  t4 20.64 39.83 55.60 70.45  t2 44.06 67.74 82.17 99.70  Case B - Appearance Function Value of t10 10 20 30  t75 2.50 5.10 8.00  t50 3.20 6.50 10.10  t25 5.00 10.10 15.60  t4 24.40 46.30 64.80  t2 60.50 90.50 100.00  50  14.05  16.95  26.13  81.82  100.00  Case A - Breakage ECS Data Value of t10 10 20 30  14.53 0.19 0.41 0.70  20.63 0.18 0.40 0.68  28.89 0.18 0.39 0.66  50  1.72  1.67  1.63  Initial part. Size (mm) ECS (kWh/t)  Case B - Breakage ECS Data Value of t10 10 20 30  14.53 0.56 1.18 1.89  20.63 0.45 0.96 1.54  28.89 0.36 0.76 1.25  50  4.13  3.43  2.82  Initial part. Size (mm) ECS (kWh/t)  SAG Breakage Rate Constant Parameters (Cases A & B) Knot  Size (mm)  Constant  1 2 3 4 5  0.250 4.000 16.00 44.80 128.0  1.160 -0.910 0.750 -0.030 0.330  144  APPENDIX – B: SMC AND MINNOVEX SPI TEST RESULTS  JKTech - SMC Drop-weight Test Results  Sample Name W3 HPGR Feed  A  b  Axb  ta  DWI (kWh/m3)  Mia (kWh/t)  Mih (kWh/t)  Mic (kWh/t)  Relative Density  62.9  0.55  34.6  0.33  7.81  22.0  16.8  8.7  2.70  Specific Comminution Energy  particle size (mm) 14.5 14.5 14.5 28.9 28.9 28.9 57.8 57.8 57.8 t10 10 20 30 10 20 30 10 20 30 kWh/t kWh/t kWh/t kWh/t kWh/t kWh/t kWh/t kWh/t kWh/t 0.41 0.89 1.46 0.31 0.65 1.05 0.23 0.49 0.76  MinnovEX SPI® Test Results Sample Name W3 HPGR Feed  CEET Crusher Index (Ci) 41.8  SPI (minute)  Hardness Percentile  94.4  65  145  APPENDIX – C: SAMPLE PREPARATION AND TEST FLOWSHEET  146  147  APPENDIX – D: HPGR FEED TEST BLEND – LINEAR PROGRAMING  The calculation procedure for the determination of the optimum blend between the laboratory screen oversize material and the crusher product is described through the applied calculation sequence and the corresponding table of results, as follows: 1. The full-scale simulated cone crusher product PSD was scaled down by a constant 81% factor to reduce the top size from 71 mm to 50 mm and the P80 from 28 mm to 22 mm (assumed for the lab-scale procedure) and to preserve the PSD shape. 2.  Based on the PSDs of the crusher product and the screen oversize material, which were determined through the laboratory tests, the size distribution for 100 kg of each product were estimated.  3. Having the ideal distribution determined as well as the distributions of the two components, a linear objective function was set and executed (using the Excel’s Solver add-in functionality) to determined the proportion of the parts (a and b) that would generate a blend that best approximate the ideal distribution. The objective function was set to find the blend that minimizes the sum of the standard deviation values calculated for all size fractions of the ideal and the possible blends, as following expressed: Minimize  ∑σ  Subject to:  0 ≤ a ≥1 0 ≤ b ≥1 a + b =1  148  Table of Results – HPGR Feed Test Blend Determination  1 Full-scale Preliminary Simulation PSD Factors  Simul. Sizes [mm] 70.71 50 35.36 32 25 19 16 12.5 8 5.6 4 2 1 0.5 0.25 0.125 0.045  C. Pas. (simul.) [%] 100% 99.9% 96.3% 89.4% 74.8% 56.6% 45.7% 33.0% 17.1% 12.5% 10.0% 6.8% 5.0% 3.7% 2.8% 2.1% 1.4%  Totals  2  Scaled-down Particle Size Distribution Constant 0.81 New Sizes [mm] 57.3 40.5 28.6 25.9 20.3 15.4 13.0 10.1 6.5 4.5 3.2 1.6 0.810 0.405 0.203 0.101 0.036  C. Pas. (same) [%] 100% 100% 96.3% 89.4% 74.8% 56.6% 45.7% 33.0% 17.1% 12.5% 10.0% 6.8% 5.0% 3.7% 2.8% 2.1% 1.4%  Stand. Sizes [mm] 50 35.36 32 25 19 16 12.5 8 5.6 4 2 1 0.5 0.25 0.125 0.045 0.02  C. Pas. adjusted [%] 100% 98.4% 97.3% 87.1% 71.6% 58.8% 43.7% 23.8% 15.0% 11.4% 7.6% 5.4% 4.0% 3.0% 2.3% 1.5% 1.2%  Weight Perc. [%] 0.00% 1.63% 1.05% 10.19% 15.54% 12.73% 15.17% 19.92% 8.73% 3.59% 3.87% 2.15% 1.39% 1.00% 0.75% 0.79% 0.28%  Ideal Distrib.  Crushed Prod.  3 Screen O/S Prod.  Crushed Prod.  Screen O/S Prod.  Targeted Blend  Standard Deviations (ideal-target)  a 0.214  b 0.786  a+b 1.000  Objective Minimum Sum  Screen Weight [kg] 0.00 1.65 1.07 10.31 15.73 12.89 15.36 20.16 8.84 3.63 3.92 2.18 1.40 1.01 0.76 0.80 0.28  Screen Weight [kg] 0.00 0.00 0.00 0.00 0.09 1.60 8.56 39.91 20.75 9.69 8.34 4.06 2.18 1.46 1.11 1.06 1.19  Screen Weight [kg] 0.00 0.00 2.28 10.65 32.35 11.66 9.99 14.78 11.45 3.25 1.45 0.86 0.47 0.27 0.17 0.17 0.21  [kg] 0.00 0.00 0.00 0.00 0.02 0.34 1.83 8.55 4.45 2.08 1.79 0.87 0.47 0.31 0.24 0.23 0.25  [kg] 0.00 0.00 1.79 8.36 25.42 9.16 7.85 11.61 9.00 2.55 1.14 0.67 0.37 0.21 0.14 0.13 0.16  [kg] 0.00 0.00 1.79 8.36 25.44 9.50 9.68 20.16 13.45 4.63 2.93 1.54 0.83 0.53 0.37 0.36 0.42  [kg] 0.00 1.17 0.51 1.38 6.86 2.39 4.01 0.00 3.26 0.71 0.70 0.45 0.40 0.34 0.27 0.32 0.09  100  100  100  21.43  78.57  100  22.87  149  APPENDIX – E: HPGR TESTS – COMPLETE DATA  Roller Diameter (D) Roller Width (W)  Data  Description  Process Set Points  HPGR  0.750 0.220  Test Number:  #001  #002  #003  #006  #007  Cycle 2 0.75 19.10 9.0 72 577.0 3.5  Cycle 3 0.75 19.10 9.0 72 577.0 3.5  Full Feed 0.75 19.10 9.0 72 577.0 3.5  Static Gap Hydraulic Pressure Pressing Force Specific Pressing Force  Unit [m/s] [rpm] [mm] [bar] [kN] [N/mm2]  Test Time  t  [s]  19.59  23.80  20.60  20.40  20.20  19.59  Average Actual Speed:  ωAV  [m/s]  0.75  0.76  0.75  0.73  0.75  0.74  Standard Deviation  σω  0.10  0.22  0.08  0.11  0.09  0.07  Actual Roller gap (average)  XgAV  17.61  18.95  18.51  17.49  17.81  20.62  0.50  0.37  0.51  0.52  0.58  0.54  61.3 1.5 492.7  71.6 1.7 575.7  71.1 0.7 571.7  69.5 2.4 558.9  69.9 1.0 562.3  Speed  Actual Hydraulic Pressure (average) Standard Deviation Actual Pressing Force (average)  σX PAV  [mm] [bar]  Pressure Tests - Cycle 1 0.75 0.75 0.75 19.10 19.10 19.10 9.0 9.0 9.0 82 62 72 659.5 494.6 577.0 4 3 3.5  #005  Symbol ν n X0 P F FSP  Standard Deviation Process Data  [m] [m]  FAV  [kN]  81.4 0.6 654.7  Actual Specific Pressure (average) Idle Power Draw Power Draw  FSPAV Pi P  [kN/m2] [kW] [kW]  4.0 9.39 61.3  3.0 8.73 51.4  3.50 9.70 58.0  3.5 9.64 56.1  3.4 10.61 54.6  3.42 10.96 61.1  Total Specific Energy Consumption  ESP  [kWh/t]  2.35  1.89  2.14  2.23  2.09  2.05  Net Specific Energy Consumption Press throughput Specific Throughput Constant  ESP net W m dot  [kWh/t] [t/h] [ts/hm3]  1.99 26.02 210.78  1.57 27.19 217.63  1.79 27.04 215.25  1.82 25.50 216.24  1.68 26.12 209.37  1.68 29.77 246.93  150  Material Data  Data  Description  Cycle No. Average Cake Density Cake Thickness Average Feed Moisture Feed Bulk Density Feed: 80% Passing Size Feed: 50% Passing Size Centre: 80% Passing Size Centre: 50% Passing Size Edge: 80% Passing Size Edge: 50% Passing Size 90% Center & 10% Edge: 80% Passing Size 90% Center & 10% Edge: 50% Passing Size Reduction Ratio F80/P80 (Centre & Edge) Reduction Ratio F50/P50 (Centre & Edge) Percentage Passing 6.35 mm (Centre & Edge) Total Feed Material Total Centre Product Centre Product % of Centre & Edge Material Total Edge Product Edge Product % of Centre & Edge Material Edge Product % of Centre Product Total Waste Product Waste Product % of Total Feed Total Recovered Product Mass Reconciliation (+ "gain; - "loss") Throughput (Continuity Formula - Based on Op Gap) Mdot - Coninuity Formula (Based on Op Gap) Throughput (Continuity For.- Based on Cake Thick.) Mdot - Coninuity Formula (Based on Cake Thickness) Mdot (Cont. For. Average: oper. gap & cake thick. ) Mdot (Calculated based on test reporting data)  Test Number: Symbol Unit  rC XC  F80 F80 P80 P50 P80 P50 P80 P50  MF MC MCE% ME MEF% MEC% MW MWF% MP MPF% m-dot m-dot m-dot m-dot  [t/m3] [mm] [%] [t/m3] [mm] [mm] [mm] [mm] [mm] [mm] [mm] [mm]  [%] [kg] [kg] [%] [kg] [%] [%] [kg] [%] [kg] [%] [t / h] [ts/hm3] [t/h] [ts/hm3] [ts/hm3] [ts/hm3]  #001  #002  #003  2.33 20.0 1.63% 1.68 21.00 14.44 5.16 2.13 8.96 4.17 5.40 2.28 3.89 6.34 84.5% 297 96.4 68.1% 45.2 31.9% 46.9% 152.1 51.2% 294 -1.1% 24.39 197.17 27.75 224.39 210.78 210.90  2.30 20.5 1.63% 1.68 21.00 14.44 6.02 2.47 10.09 4.64 6.48 2.62 3.24 5.50 79.4% 296 120 67.9% 56.8 32.1% 47.3% 116.8 39.5% 294 -0.8% 26.31 208.91 28.51 226.36 217.63 216.51  1 2.30 20.4 1.63% 1.68 21.00 14.44 5.66 2.46 9.75 4.75 6.18 2.63 3.40 5.48 80.7% 297 102.9 67.8% 48.8 32.2% 47.4% 145.3 48.9% 297 0.0% 25.36 204.67 27.98 225.83 215.25 218.86  #005 Cycles 2 2.29 21.8 1.56% 1.68 20.08 11.59 4.59 2.17 8.83 4.26 5.42 2.32 3.71 4.99 84.7% 266 98.5 68.2% 46.0 31.8% 46.7% 118.7 44.6% 263 -1.1% 23.10 192.29 28.85 240.18 216.24 212.85  #006 3 2.32 19.8 1.23% 1.68 18.41 10.72 5.43 2.27 8.71 4.23 5.70 2.42 3.23 4.43 82.8% 254.3 99.9 68.1% 46.7 31.9% 46.7% 103.8 40.8% 250 -1.5% 24.63 198.37 27.36 220.37 209.37 210.94  #007 Full Feed  2.30 24.0 1.72% 1.87 21.26 12.83 5.52 2.34 10.15 4.03 5.93 2.46 3.59 5.22 81.5% 224 110.9 68.8% 50.2 31.2% 45.3% 56.7 25.3% 218 -2.8% 27.95 228.01 32.58 265.85 246.93 243.55  151  HPGR Test #1 Pressure:  4.0  N/mm2  Weight (Kg) Feed  297  Waste Center Edge Moisture BOND BMWi  152.1 96.4 45.2 1.63% 19.3  HPGR Center Product 31.9%  kw-hr/tonne  HPGR Feed #1 to#3 Screen Size [mm] -35.5 to +32 -32 to +25 -25 to +19 -19 to +16 -16 to +12.5 -12.5 to +8 -8 to +5.6 -5.6 to +4 -4 to +2 -2 to +1 -1 to +0.5 -0.5 to +0.25 -.25 to +.125 -.125 to +.045 -0.045 Total  Particle Size [mm] 32 25 19 16 12.5 8 5.6 4 2 1 0.5 0.25 0.125 0.045 Pan  Particle Size [mm] 32 25 Feed  Screen Weight [g] 0.0 0.0  Weight Perc. [%] 0.0% 0.0%  HPGR Edge Product Cum. Pass. [%] 100.0% 100.0%  Screen Weight [g] 0.0 0.0  Weight Perc. [%] 0.0% 0.0%  Cum. Pass. [%] 100.0% 100.0%  19  7.6  0.1%  99.9%  22.7  0.2%  99.8%  16 12.5 8 5.6 4 2.8 2 1.4 1 0.71 0.5 0.355 0.25 0.18 0.125 0.09 0.063 0.045 Pan  8.4 107.4 772.3 920.7 1646.4 1302.6 1067.8 976.3 733.6 609.7 504.9 420.2 369.7 306.9 285.8 181.1 210.8 134.1 756.1 11322.4  0.1% 0.9% 6.8% 8.1% 14.5% 11.5% 9.4% 8.6% 6.5% 5.4% 4.5% 3.7% 3.3% 2.7% 2.5% 1.6% 1.9% 1.2% 6.7% 100.0%  99.9% 98.9% 92.1% 84.0% 69.4% 57.9% 48.5% 39.9% 33.4% 28.0% 23.5% 19.8% 16.6% 13.8% 11.3% 9.7% 7.9% 6.7% 0.0%  153.3 460.1 2072.7 1572.4 1549.4 1083.4 830.0 637.7 515.8 436.4 344.6 280.2 228.0 200.7 167.5 113.8 122.9 73.9 463.5 11329.0  1.4% 4.1% 18.3% 13.9% 13.7% 9.6% 7.3% 5.6% 4.6% 3.9% 3.0% 2.5% 2.0% 1.8% 1.5% 1.0% 1.1% 0.7% 4.1% 100.0%  98.4% 94.4% 76.1% 62.2% 48.5% 39.0% 31.6% 26.0% 21.5% 17.6% 14.6% 12.1% 10.1% 8.3% 6.8% 5.8% 4.7% 4.1% 0.0%  Screen Weight [g] 0.0 347.0 2842.5 1716.8 1566.3 2811.4 1211.9 349.2 175.6 60.2 28.7 24.7 23.0 24.9 27.8 11210.0  Weight Perc. [%] 0.0% 3.1% 25.4% 15.3% 14.0% 25.1% 10.8% 3.1% 1.6% 0.5% 0.3% 0.2% 0.2% 0.2% 0.2% 100.0%  Cum. Pass. [%] 100.0% 96.9% 71.5% 56.2% 42.3% 17.2% 6.4% 3.3% 1.7% 1.2% 0.9% 0.7% 0.5% 0.2% 0.0%  Calc. P80 Calc. P50 -6.35mm  [mm] [mm] %  21.00 14.44 9.7%  Calc. P80 Calc. P50 -6.35mm  [mm] [mm] %  5.16 2.13 86.5%  Calc. P80 Calc. P50 -6.35mm  [mm] [mm] %  8.96 4.17 66.5%  -1.0 mm  %  1.2%  -1.0 mm  %  28.0%  -1.0 mm  %  17.6%  152  HPGR Test #2 Pressure:  3.0  N/mm2  Weight (Kg) Feed  296  Waste Center Edge  116.8 120 56.8  Moisture BOND BMWi  1.63% 19.3  HPGR Center Product 32.1%  kw-hr/tonne  HPGR Feed Screen Size [mm] -35.5 to +32 -32 to +25 -25 to +19 -19 to +16 -16 to +12.5 -12.5 to +8 -8 to +5.6 -5.6 to +4 -4 to +2 -2 to +1 -1 to +0.5 -0.5 to +0.25 -.25 to +.125 -.125 to +.045 -0.045 Total  Particle Size [mm] 32 25 19 16 12.5 8 5.6 4 2 1 0.5 0.25 0.125 0.045 Pan  Particle Size [mm] 32 25 Feed  Screen Weight [g] 0.0 0.0  HPGR Edge Product  Weight Perc. [%] 0.0% 0.0%  Cum. Pass. [%] 100.0% 100.0%  Screen Weight [g] 0.0 18.9  Weight Perc. [%] 0.0% 0.2%  Cum. Pass. [%] 100.0% 99.8%  19  0.0  0.0%  100.0%  71.8  0.7%  99.1%  16 12.5 8 5.6 4 2.8 2 1.4 1 0.71 0.5 0.355 0.25 0.18 0.125 0.09 0.063 0.045 Pan  82.9 197.5 928.7 1012.6 1375.6 1139.7 909.5 817.2 617.8 524.7 440.2 342.0 313.3 251.6 237.5 156.4 180.1 104.7 596.6 10228.6  0.8% 1.9% 9.1% 9.9% 13.4% 11.1% 8.9% 8.0% 6.0% 5.1% 4.3% 3.3% 3.1% 2.5% 2.3% 1.5% 1.8% 1.0% 5.8% 100.0%  99.2% 97.3% 88.2% 78.3% 64.8% 53.7% 44.8% 36.8% 30.8% 25.6% 21.3% 18.0% 14.9% 12.5% 10.1% 8.6% 6.9% 5.8% 0.0%  209.8 701.1 1937.1 1380.1 1310.0 928.8 654.1 589.2 453.7 276.3 287.3 235.1 199.3 156.2 146.7 101.7 96.3 73.2 376.8 10203.5  2.1% 6.9% 19.0% 13.5% 12.8% 9.1% 6.4% 5.8% 4.4% 2.7% 2.8% 2.3% 2.0% 1.5% 1.4% 1.0% 0.9% 0.7% 3.7% 100.0%  97.1% 90.2% 71.2% 57.7% 44.8% 35.7% 29.3% 23.5% 19.1% 16.4% 13.6% 11.3% 9.3% 7.8% 6.4% 5.4% 4.4% 3.7% 0.0%  Screen Weight [g] 0.0 347.0 2842.5 1716.8 1566.3 2811.4 1211.9 349.2 175.6 60.2 28.7 24.7 23.0 24.9 27.8 11210.0  Weight Perc. [%] 0.0% 3.1% 25.4% 15.3% 14.0% 25.1% 10.8% 3.1% 1.6% 0.5% 0.3% 0.2% 0.2% 0.2% 0.2% 100.0%  Cum. Pass. [%] 100.0% 96.9% 71.5% 56.2% 42.3% 17.2% 6.4% 3.3% 1.7% 1.2% 0.9% 0.7% 0.5% 0.2% 0.0%  Calc. P80 Calc. P50 -6.35mm  [mm] [mm] %  21.00 14.44 9.7%  Calc. P80 Calc. P50 -6.35mm  [mm] [mm] %  6.02 2.47 81.4%  Calc. P80 Calc. P50 -6.35mm  [mm] [mm] %  10.09 4.64 61.9%  -1.0 mm  %  1.2%  -1.0 mm  %  25.6%  -1.0 mm  %  16.4%  153  HPGR Test #3 Pressure:  3.5  N/mm2  Weight (Kg) Feed Waste Center Edge Moisture BOND BMWi  297 145.3 102.9 48.8  32.2%  1.63% 19.3  kw-hr/tonne  HPGR Center Product  Feed test #3 (1st cycle) Screen Size [mm] -35.5 to +32 -32 to +25 -25 to +19 -19 to +16 -16 to +12.5 -12.5 to +8 -8 to +5.6 -5.6 to +4 -4 to +2 -2 to +1 -1 to +0.5 -0.5 to +0.25 -.25 to +.125 -.125 to +.045 -0.045 Total  Particle Size [mm] 32 25 19 16 12.5 8 5.6 4 2 1 0.5 0.25 0.125 0.045 Pan  Particle Size [mm] 32 25 Feed  Screen Weight [g] 0.0 0.0  Weight Perc. [%] 0.0% 0.0%  HPGR Edge Product Cum. Pass. [%] 100.0% 100.0%  Screen Weight [g] 0.0 0.0  Weight Perc. [%] 0.0% 0.0%  Cum. Pass. [%] 100.0% 100.0%  19  11.1  0.1%  99.9%  0.0  0.0%  100.0%  16 12.5 8 5.6 4 2.8 2 1.4 1 0.71 0.5 0.355 0.25 0.18 0.125 0.09 0.063 0.045 Pan  24.6 145.2 833.0 966.0 1391.9 1139.5 883.8 800.7 580.4 434.8 432.8 334.0 319.2 247.0 232.6 148.5 168.3 107.2 572.2 9772.8  0.3% 1.5% 8.5% 9.9% 14.2% 11.7% 9.0% 8.2% 5.9% 4.4% 4.4% 3.4% 3.3% 2.5% 2.4% 1.5% 1.7% 1.1% 5.9% 100.0%  99.6% 98.1% 89.6% 79.7% 65.5% 53.8% 44.8% 36.6% 30.7% 26.2% 21.8% 18.4% 15.1% 12.6% 10.2% 8.7% 7.0% 5.9% 0.0%  168.4 467.1 1822.0 1277.8 1196.9 850.3 596.7 429.9 359.4 246.9 245.1 197.4 173.3 139.1 129.3 189.0 85.9 55.2 119.3 8749.0  1.9% 5.3% 20.8% 14.6% 13.7% 9.7% 6.8% 4.9% 4.1% 2.8% 2.8% 2.3% 2.0% 1.6% 1.5% 2.2% 1.0% 0.6% 1.4% 100.0%  98.1% 92.7% 71.9% 57.3% 43.6% 33.9% 27.1% 22.2% 18.1% 15.2% 12.4% 10.2% 8.2% 6.6% 5.1% 3.0% 2.0% 1.4% 0.0%  Screen Weight [g] 0.0 347.0 2842.5 1716.8 1566.3 2811.4 1211.9 349.2 175.6 60.2 28.7 24.7 23.0 24.9 27.8 11210.0  Weight Perc. [%] 0.0% 3.1% 25.4% 15.3% 14.0% 25.1% 10.8% 3.1% 1.6% 0.5% 0.3% 0.2% 0.2% 0.2% 0.2% 100.0%  Cum. Pass. [%] 100.0% 96.9% 71.5% 56.2% 42.3% 17.2% 6.4% 3.3% 1.7% 1.2% 0.9% 0.7% 0.5% 0.2% 0.0%  Calc. P80 Calc. P50 -6.35mm  [mm] [mm] %  21.00 14.44 9.7%  Calc. P80 Calc. P50 -6.35mm  [mm] [mm] %  5.66 2.46 82.8%  Calc. P80 Calc. P50 -6.35mm  [mm] [mm] %  9.75 4.75 61.9%  -1.0 mm  %  1.2%  -710um  %  26.2%  -710um  %  15.2%  154  HPGR Test #5 (1st Recirculation) Pressure: 3.5 N/mm2 Weight (Kg) Feed 266 Waste 118.7 Center 98.5 Edge 46 Moisture 1.56%  31.8%  Feed test #5 (2nd cycle) Screen Size Particle Size [mm] -35.5 to +32 -32 to +25 -25 to +19 -19 to +16 -16 to +12.5 -12.5 to +8 -8 to +5.6 -5.6 to +4 -4 to +2.8 -2.8 to +2 -2 to +1.4 -1.4 to +1 -1 to +.71 -.71 to +.5 -.5 to +.355 -.355 to +.25 -.25 to +.18 -.18 to +.125 -.125 to +.09 -.09 to +.063 -.063 to +.045 -0.045 Total  [mm] 32 25 19 16 12.5 8 5.6 4 2.8 2 1.4 1 0.71 0.5 0.355 0.25 0.18 0.125 0.09 0.063 0.045 Pan  Feed  HPGR Center Product  Screen Weight [g] 0.0 549.3 2399.6 1254.3 1380.9 3510.3 2083.9 713.8 187.0 108.8 82.6 72.2 45.1 47.8 38.0 31.6 23.0 1.6 7.6 6.3 9.9 40.8 12594.5 Calc. P80 Calc. P50 -6.35mm  Weight Perc. [%] 0.0% 4.4% 19.1% 10.0% 11.0% 27.9% 16.5% 5.7% 1.5% 0.9% 0.7% 0.6% 0.4% 0.4% 0.3% 0.3% 0.2% 0.0% 0.1% 0.1% 0.1% 0.3% 100.0% [mm] [mm] %  Cum. Pass. [%] 100.0% 95.6% 76.6% 66.6% 55.7% 27.8% 11.2% 5.6% 4.1% 3.2% 2.6% 2.0% 1.6% 1.3% 1.0% 0.7% 0.5% 0.5% 0.5% 0.4% 0.3% 0.0%  -1.0mm -710um  Particle Size [mm] 32 25 19 16 12.5 8 5.6 4 2.8 2 1.4 1 0.71 0.5 0.355 0.25 0.18 0.125 0.09 0.063 0.045 Pan  HPGR Edge Product  Weight Perc. [%] 0.0% 0.0% 0.0% 0.1% 0.8% 6.3% 9.1% 14.5% 12.0% 9.3% 8.7% 6.4% 5.6% 4.5% 3.7% 3.3% 2.7% 2.4% 1.6% 1.8% 1.1% 6.3% 100.0% [mm] [mm] %  Cum. Pass. [%] 100.0% 100.0% 100.0% 99.9% 99.1% 92.9% 83.8% 69.3% 57.4% 48.1% 39.3% 32.9% 27.4% 22.8% 19.2% 15.9% 13.2% 10.8% 9.2% 7.4% 6.3% 0.0%  20.08 11.59 16.4%  Screen Weight [g] 0.0 0.0 0.0 7.7 83.6 668.8 967.3 1547.6 1277.2 990.6 933.0 685.2 594.5 482.1 392.6 348.7 283.8 261.2 167.0 193.6 119.1 673.1 10676.7 Calc. P80 Calc. P50 -6.35mm  Weight Perc. [%] 0.0% 0.0% 0.0% 1.5% 3.9% 17.9% 14.6% 14.4% 9.9% 6.8% 6.4% 4.3% 3.5% 2.9% 2.3% 2.0% 1.6% 1.4% 1.0% 0.9% 0.7% 3.7% 100.0% [mm] [mm] %  Cum. Pass. [%] 100.0% 100.0% 100.0% 98.5% 94.6% 76.7% 62.1% 47.6% 37.7% 30.9% 24.5% 20.2% 16.6% 13.7% 11.4% 9.4% 7.7% 6.3% 5.3% 4.4% 3.7% 0.0%  4.59 2.17 86.7%  Screen Weight [g] 0.0 0.0 0.0 163.7 419.0 1948.5 1590.5 1568.2 1077.1 741.8 697.1 468.0 385.4 315.0 252.8 218.6 177.6 154.1 110.7 97.8 75.4 402.7 10864.0 Calc. P80 Calc. P50 -6.35mm  %  2.0%  -710um  %  %  1.6%  27.4%  -710um  %  16.6%  8.83 4.26 66.6%  155  HPGR Test #6 (2nd Recirculation) Pressure: 3.5 N/mm2 Weight (Kg) Feed Waste Center Edge Moisture  254.3 103.8 99.9 46.7  Particle Size [mm] 32 25  31.9%  1.23%  Feed test #6 (3rd cycle) Screen Size Particle Size [µm] -35.5 to +32 -32 to +25 -25 to +19 -19 to +16 -16 to +12.5 -12.5 to +8 -8 to +5.6 -5.6 to +4 -4 to +2 -2 to +1 -1 to +0.5 -0.5 to +0.25 -.25 to +.125 -.125 to +.045 -0.045 Total  HPGR Center Product  [mm] 32 25 19 16 12.5 8 5.6 4 2 1 0.5 0.25 0.125 0.045 Pan  Screen Weight [g] 0.0 0.0  Weight Perc. [%] 0.0% 0.0%  Cum. Pass. [%] 100.0% 100.0%  Screen Weight [g] 0.0 0.0  Weight Perc. [%] 0.0% 0.0%  Cum. Pass. [%] 100.0% 100.0%  19  0.0  0.0%  100.0%  9.3  0.1%  99.9%  16 12.5 8 5.6 4 2.8 2 1.4 1 0.71 0.5 0.355 0.25 0.18 0.125 0.09 0.063 0.045 Pan  0.1% 1.4% 7.1% 9.9% 13.8% 11.5% 9.2% 8.5% 6.0% 5.3% 4.5% 3.6% 3.2% 2.6% 2.4% 1.5% 1.8% 1.1% 6.3% 100.0% [mm] [mm] %  99.9% 98.4% 91.3% 81.4% 67.6% 56.1% 46.9% 38.4% 32.4% 27.1% 22.6% 19.0% 15.8% 13.2% 10.8% 9.3% 7.4% 6.3% 0.0%  1.2% 4.0% 17.5% 14.8% 14.5% 10.0% 6.8% 6.3% 4.4% 3.7% 2.9% 2.3% 2.0% 1.6% 1.5% 1.0% 1.0% 0.7% 3.9% 100.0% [mm] [mm] %  98.7% 94.8% 77.2% 62.5% 48.0% 38.0% 31.2% 24.9% 20.5% 16.9% 14.0% 11.7% 9.7% 8.1% 6.6% 5.6% 4.6% 3.9% 0.0%  5.43 2.27 84.5%  134.8 456.3 2005.9 1691.1 1661.1 1143.2 774.7 717.1 503.3 422.8 332.4 260.4 229.3 184.7 169.9 115.0 115.5 76.1 446.4 11449.3 Calc. P80 Calc. P50 -6.35mm  8.71 4.23 67.1%  %  27.1%  -710um  %  16.9%  Screen Weight  Feed Weight %.  [g] 0.0 362.8 1859.8 1250.6 1317.1 3485.3 2392.3 885.9 357.8 161.3 85.6 54.1 42.8 45.8 44.3 12345.5 Calc. P80 Calc. P50 -6.35mm  [%] 0.0% 2.9% 15.1% 10.1% 10.7% 28.2% 19.4% 7.2% 2.9% 1.3% 0.7% 0.4% 0.3% 0.4% 0.4% 100.0% [mm] [mm] %  [%] 100.0% 97.1% 82.0% 71.9% 61.2% 33.0% 13.6% 6.4% 3.5% 2.2% 1.5% 1.1% 0.7% 0.4% 0.0% 18.41 10.72 19.6%  14.3 178.3 879.1 1220.6 1707.0 1423.1 1140.6 1048.6 743.2 657.1 554.1 440.6 399.5 315.6 300.9 189.4 226.4 138.7 780.3 12357.4 Calc. P80 Calc. P50 -6.35mm  -1.0 mm  %  2.2%  -710um  C. Pass.  HPGR Edge Product  156  HPGR Test #7 (Fresh Feed) Pressure: 3.5 Weight (Kg) Feed 224 Waste 56.7 Center 110.9 Edge 50.2 Moisture 1.72% BOND BMWi  16.6  N/mm2  31.2% kw-hr/tonne  HPGR Feed #7 (FF Drum4) Screen Size [µm] -35.5 to +32 -32 to +25 -25 to +19 -19 to +16 -16 to +12.5 -12.5 to +8 -8 to +5.6 -5.6 to +4 -4 to +2.8 -2.8 to +2 -2 to +1.4 -1.4 to +1 -1 to +.71 -.71 to +.5 -.5 to +.355 -.355 to +.25 -.25 to +.18 -.18 to +.125 -.125 to +.09 -.09 to +.063 -.063 to +.045 -0.045 Total  Particle Size [mm] 32 25 19 16 12.5 8 5.6 4 2.8 2 1.4 1 0.71 0.5 0.355 0.25 0.18 0.125 0.09 0.063 0.045 Pan  Feed  HPGR Center Product  Screen Weight [g] 0.0 645.8 1776.3 1187.8 856.4 1100.5 655.8 472.8 399.1 263.8 256.3 204.6 156.2 135.3 113.9 91.6 78.5 69.4 42.7 52.6 24.3 187.1 8770.8 Calc. P80 Calc. P50 -6.35mm  Weight Perc. [%] 0.0% 7.4% 20.3% 13.5% 9.8% 12.5% 7.5% 5.4% 4.6% 3.0% 2.9% 2.3% 1.8% 1.5% 1.3% 1.0% 0.9% 0.8% 0.5% 0.6% 0.3% 2.1% 100.0% [mm] [mm] %  Cum. Pass. [%] 100.0% 92.6% 72.4% 58.8% 49.1% 36.5% 29.1% 23.7% 19.1% 16.1% 13.2% 10.8% 9.1% 7.5% 6.2% 5.2% 4.3% 3.5% 3.0% 2.4% 2.1% 0.0%  -1.0mm  %  Particle Size [mm] 32 25 19 16 12.5 8 5.6 4 2.8 2 1.4 1 0.71 0.5 0.355 0.25 0.18 0.125 0.09 0.063 0.045 Pan  HPGR Edge Product  Weight Perc. [%] 0.0% 0.0% 0.4% 0.9% 2.1% 7.9% 8.0% 13.7% 11.7% 9.3% 8.6% 6.1% 5.4% 4.4% 3.5% 3.2% 2.6% 2.4% 1.5% 1.8% 1.1% 5.4% 100.0% [mm] [mm] %  Cum. Pass. [%] 100.0% 100.0% 99.6% 98.7% 96.6% 88.7% 80.7% 67.0% 55.3% 46.0% 37.5% 31.4% 26.0% 21.6% 18.1% 14.9% 12.3% 9.9% 8.4% 6.6% 5.4% 0.0%  21.26 12.83 31.4%  Screen Weight [g] 0.0 0.0 51.8 104.7 259.4 963.6 980.9 1680.2 1427.9 1138.2 1048.8 743.1 656.1 538.7 433.1 392.1 313.6 296.2 185.3 223.4 135.8 666.6 12239.5 Calc. P80 Calc. P50 -6.35mm  Weight Perc. [%] 0.0% 0.0% 1.3% 3.0% 7.5% 15.6% 10.2% 12.6% 9.1% 7.2% 5.3% 4.5% 4.6% 3.4% 2.7% 2.3% 1.8% 1.7% 1.1% 1.2% 0.8% 4.2% 100.0% [mm] [mm] %  Cum. Pass. [%] 100.0% 100.0% 98.7% 95.7% 88.1% 72.6% 62.3% 49.8% 40.7% 33.5% 28.3% 23.7% 19.1% 15.7% 13.1% 10.8% 9.0% 7.3% 6.2% 5.0% 4.2% 0.0%  5.52 2.34 83.2%  Screen Weight [g] 0.0 0.0 162.6 376.8 938.3 1933.6 1271.3 1563.3 1126.7 890.5 655.6 565.0 573.3 421.1 330.1 281.7 227.8 212.5 133.7 151.4 97.6 520.0 12432.9 Calc. P80 Calc. P50 -6.35mm  10.8%  -710um  %  26.0%  -710um  %  19.1%  10.15 4.03 65.5%  157  APPENDIX – F: AG-CRUSHER-HPGR PLANT LAYOUT  158  159  APPENDIX – G: SABC PLANT LAYOUT  160  161  APPENDIX – H: POWER CONSUMPTION COMPARISON  Unit Power Qt. Description  Average Consumption  Specific  Inst.  Simu.  Load  Unit  Total  Energy  kW  kW  Factor  kW  kW  kWh/t  AG-Cr-HPGR Option (2 lines) 4,000 tph per line (simulated instantaneous) 92% Circuit Overall Availability - 176,640 t/d Comminution equipment AG Mills - 10.4 m D x 6.1m EGL (34 x 20 ft)  2  8,000  7,411  1  6,818.1  13,636.2  1.853  Sec. Crushers XL-1100 (8 - 6 oper. 2 stdby)  6  820  807  1  742.4  4,454.6  0.605  Tert. HPGR - 2.4 D x 1.7 W m  4  5,000  3,665  1  3,371.8  13,487.2  1.833  Ball Mill - 7.9m D x 12.8m L ( 26 x 42 ft )  4  18,000  15,563  1  14,318.0  57,271.8  7.782  88,850  12.07  43,764.1  7.558  96576 SABC Option  (2 lines)  3,080 tph (simulated instantaneous rate) 94% Circuit Overall Availability - 138,970 t/d Comminution equipment SAG Mills - 12.2 m D x 6.7m EGL (40 x 22 ft)  2  25,000  23,279  1  21,882.1  Pebble Crusher XL-1100  4  820  361.4  1  339.7  1,358.9  0.235  Ball Mill - 7.9m D x 12.8m L ( 26 x 42 ft )  4  18,000  12,636  1  11,877.8  47,511.4  8.205  92,634  16.00  98547  24.5% AG-Cr-HPGR Option (2 lines) Comminution equipment AG Mills - 10.4 m D x 6.1m EGL (34 x 20 ft)  2  Sec. Crushers XL-1100 (8 - 6 oper. 2 stdby)  6  Tert. HPGR - 2.4 D x 1.7 W m  4 4  18,000  Ball Mill - 7.9m D x 12.8m L ( 26 x 42 ft )  8,000  7,411  1  820  807  1  742.4  4,454.6  0.605  5,000  3,665  1  3,371.8  13,487.2  1.833  15,563  1  14,318.0  57,271.8  7.782  88,850  12.07  Sub-total  6,818.1  96576  13,636.2  1.853  Conveyors and feeders AG Mill Feed Conveyors  2  857  857  0.75  591.5  1,183.1  0.161  AG Screen Discharge Conveyors  2  149  149  0.75  102.9  205.8  0.028  Sc Crushers Bin Feed Conveyor  2  298  298  0.75  205.8  411.6  0.056  Sec. Crusher Bin Feeder  2  56  56  0.75  38.6  77.2  0.010  Sec. Crusher Feeders No.1 to 8 (2 on standby)  6  56  56  0.75  38.6  231.5  0.031  Crusher prod. to HPGR bin - High Lift Conveyor  2  373  373  0.75  257.3  514.5  0.070  Crusher tramp material by-pass conveyor  2  56  56  0.20  10.3  20.6  0.003  HPGR Feeders No.1 to 4  4  112  112  0.75  77.2  308.7  0.042  HPGRs Discharge - High Lift Conveyor  2  373  373  0.75  257.3  514.5  0.070  3,468  0.47  Sub-total  5108  Pumps Ball Mill Cyclone Feed Pumps  4  2,983  2983  0.77  2,113.0  8,452.1  1.148  Peb.Cr Area -Scrubber Effluent Return pump  4  37  37  0.8  27.4  109.8  0.015  162  Sub-total  12080  8,562  1.16  82.3  0.011  82  0.01  Screens SAG Discharge vibrating screens  4  30  Sub-total  30  0.75  20.6  119  Comminution Eq. - Lube and Cooling systems Crusher Lube units  6  75  75  0.75  51.5  308.7  0.042  Crusher Lube cooling units  6  37  37  0.75  25.7  154.4  0.021  HPGR Lube units  4  15  15  0.75  10.4  41.4  0.006  HPGR Lube cooling units  4  30  30  0.75  20.7  82.8  0.011  Ball Mill Motor Cooling Systems  4  75  75  0.8  54.9  219.5  0.030  Ball Mill Cycloconv. Cooling Systems  4  75  75  0.8  54.9  219.5  0.030  Ball Mill Lube Cooling Systems  4  22  22  0.8  16.5  65.9  0.009  1,092  0.15  Sub-total  328  Dust and metal collection requirements Peb.Cr Area -Scrubber Fan  4  89  89  0.80  65.9  263.4  0.036  AG Screen Discharge Conveyor Magnet  2  30  30  0.75  20.6  41.2  0.006  Crusher system self cleaning Magnet  2  30  30  0.75  20.6  41.2  0.006  HPGR system self cleaning Magnet  2  30  30  0.75  20.6  41.2  0.006  Metal detectors  4  10  10  0.75  6.9  27.6  0.004  Ball Mill Trunion Magnets  4  19  19  0.75  12.9  51.5  0.007  466  0.06  299.4  0.041  299  0.04  102,819  13.97  Sub-total  208 1  Heat & Ventilation Systems  325  325  1  299.4  Sub-total TOTAL SABC Option  (2 lines)  Comminution equipment SAG Mills - 12.2 m D x 6.7m EGL (40 x 22 ft)  2  25,000  23,279  1  21,882.1  43,764.1  7.558  Pebble Crusher XL-1100  4  820  361.4  1  339.7  1,358.9  0.235  Ball Mill - 7.9m D x 12.8m L ( 26 x 42 ft )  4  18,000  12,636  1  11,877.8  47,511.4  8.205  92,634  16.00  1,051.4  0.182  98547 Conveyors and feeders SAG Mill Feed Conveyors  2  746  746  0.75  525.7  SAG Screen Discharge Conveyor  1  261  261  0.75  184.0  184.0  0.032  Pebble Bin Feed Conveyor No. 1  1  186  186  0.80  140.2  140.2  0.024  Pebble Crusher Bypass Conveyor  1  112  112  0.75  78.9  78.9  0.014  Pebble Bin Feed Conveyor No. 2  1  19  19  0.75  13.1  13.1  0.002  Pebble Crusher Discharge Conveyor No. 1  1  112  112  0.75  78.9  78.9  0.014  Pebble Crusher Discharge Conveyor No. 2  1  149  149  0.75  105.1  105.1  0.018  4  56  56  0.75  39.4  157.7  0.027  1,809  0.31  8,635.8  1.491  Pebble Crusher Feeders No.1 to 4 Sub-total  2554  Pumps Ball Mill Cyclone Feed Pumps Peb.Cr Area -Scrubber Effluent Return pump  4  2,983  1  37  Sub-total  2983  0.77  2,159.0  37  0.8  28.0  11968  28.0  0.005  8,664  1.50  42.1  0.007  42  0.01  Screens SAG Discharge vibrating screens  2 Sub-total  30  30 60  0.75  21.0  Comminution Eq. - Lube and Cooling systems  163  Crusher Lube units  4  75  75  0.75  52.6  210.3  0.036  Crusher Lube cooling units  4  37  37  0.75  26.3  105.1  0.018  SAG Lube Cooling Systems  2  22  22  0.8  16.8  33.6  0.006  SAG Cycloconv. Cooling Systems  2  75  75  0.8  56.1  112.2  0.019  SAG Motor Cooling Systems  2  75  75  0.8  56.1  112.2  0.019  Ball Mill Motor Cooling Systems  4  75  75  0.8  56.1  224.3  0.039  Ball Mill Cycloconv. Cooling Systems  4  75  75  0.8  56.1  224.3  0.039  4  22  22  0.8  16.8  67.3  0.012  1,089  0.19  Ball Mill Lube Cooling Systems Sub-total  1476  Dust and metal collection requirements Peb.Cr Area -Scrubber Fan  1  89  89  0.80  67.3  67.3  0.012  SAG Screen Discharge Conveyor Magnet  1  30  30  0.75  21.0  21.0  0.004  Metal detectors  1  10  10  0.75  7.1  7.1  0.001  Ball Mill Trunion Magnets  4  19  19  0.75  13.1  52.6  0.009  148  0.03  257.9  0.045  258  0.04  104,645  18.07  Sub-total  204  1  Heat & Ventilation Systems Sub-total TOTAL  274  274 274  1  257.9  Total Com. Circ. Specific Energy Difference  22.7%  164  

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