Applied Science, Faculty of
Mining Engineering, Keevil Institute of
DSpace
UBCV
Moreno Chavez, Jose Ricardo
Master of Applied Science - MASc
University of British Columbia
The effect of electrolyte concentration and potential determining ions on the coagulation and flocculation of illite, dolomite, and illite-dolomite mixture suspensions was investigated. Electrokinetic measurements, settling rate tests, and viscosity measurements were performed to examine the stability of these mineral suspensions and to characterize flocculants under various physico-chemical conditions. Two flocculants: A-100 anionic polyacrylamide (PAM) and polyethylene oxide (PEO) were used in the flocculation tests and viscosity measurements. The settling rate tests confirmed the polyacrylamide flocculant’s wide range of functionality in solid-liquid separation unit operations by flocculating mineral suspensions under nearly all tested conditions. The tests revealed that polyethylene oxide does not flocculate dolomite under any tested conditions. The obtained viscosity results corroborated that the conformation of PAM macromolecules in water is very sensitive to electrolyte concentration; on the other hand, the conformational state of PEO macromolecules is not affected by ionic strength. The intrinsic viscosity measurements suggest that the unattainable flocculation of dolomite suspensions with PEO must result from poor adsorption of this flocculant onto the carbonate. In both tested cases, with PAM and PEO, the relationship between coagulation and flocculation was not confirmed.
EFFECT OF ELECTROLYTE CONCENTRATION IN PROCESS WATER ON FLOCCULATION by Jose Ricardo Moreno Chavez B. Eng., Escuela Superior Politecnica del Litoral, 2015 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE in The Faculty of Graduate and Postdoctoral Studies (Mining Engineering) THE UNIVERSITY OF BRITISH COLUMBIA (Vancouver) August 2018 © Jose Ricardo Moreno Chavez, 2018 ii The following individuals certify that they have read, and recommend to the Faculty of Graduate and Postdoctoral Studies for acceptance, a thesis/dissertation entitled: Effect of electrolyte concentration in process water on flocculation submitted by Jose Ricardo Moreno Chavez in partial fulfillment of the requirements for the degree of Master of Applied Science in Mining Engineering Examining Committee: Dr. Janusz Laskowski, Mining Engineering Supervisor Dr. Marek Pawlik, Mining Engineering Supervisory Committee Member Dr. Maria Holuszko, Mining Engineering Supervisory Committee Member Additional Examiner Additional Supervisory Committee Members: Supervisory Committee Member Supervisory Committee Member iii Abstract The effect of electrolyte concentration and potential determining ions on the coagulation and flocculation of illite, dolomite, and illite-dolomite mixture suspensions was investigated. Electrokinetic measurements, settling rate tests, and viscosity measurements were performed to examine the stability of these mineral suspensions and to characterize flocculants under various physico-chemical conditions Two flocculants: A-100 anionic polyacrylamide (PAM) and polyethylene oxide (PEO) were used in the flocculation tests and viscosity measurements. The settling rate tests confirmed the polyacrylamide flocculant’s wide range of functionality in solid-liquid separation unit operations by flocculating mineral suspensions under nearly all tested conditions. The tests revealed that polyethylene oxide does not flocculate dolomite under any tested conditions. The obtained viscosity results corroborated that the conformation of PAM macromolecules in water is very sensitive to electrolyte concentration; on the other hand, the conformational state of PEO macromolecules is not affected by ionic strength. The intrinsic viscosity measurements suggest that the unattainable flocculation of dolomite suspensions with PEO must result from poor adsorption of this flocculant onto the carbonate. In both tested cases, with PAM and PEO, the relationship between coagulation and flocculation was not confirmed. iv Lay Summary Flocculation is used in solid/liquid separation unit operations in the mining industry. Polymeric compounds are used to cause aggregation of fine particles, the process that improves these particles separation in thickening and filtration. Water utilized in mineral processing circuits is recycled, and this “process water” carries ions and fine mineral particles. Illite and dolomite were employed and two flocculants: A-100 anionic polyacrylamide (PAM) and polyethylene oxide (PEO). The purpose of this research is to test the stability of the selected suspensions, to characterize both flocculants under various physico-chemical conditions, and to probe a possible relationship between coagulation and flocculation. Experimental results confirmed the PAM’s wide range of functionality in solid-liquid separation unit circuits by flocculating mineral suspensions under nearly all tested conditions. PEO turned out to be very different. The results suggest that poor flocculation of dolomite by PEO is a consequence of poor adsorption of PEO onto the mineral. v Preface This dissertation is original, unpublished and an independent work by the author, Jose R. Moreno Chavez. Although the main ideas behind this research are his own, this project would be impossible without the continuous dialogue that took place between the author and his supervisor, Dr. Janusz Laskowski. Quantitative X-ray analysis of the mineral samples are the only tests in this thesis which were not conducted by the author. They were carried out by personnel from the Electron Microbeam & X-Ray Diffraction Facility at the Department of Earth, Ocean and Atmospheric Sciences at the University of British Columbia (UBC). Chapters 1, 2, and 3 present respectively an introduction to the research, literature review, and experimental program designed for this study by the author. Chapter 4 involves the results of four different series of tests performed by the author to study the effect of electrolyte concentration and pH on particle aggregation and conformation of polymer macromolecules. These tests include electrokinetic measurements, settling rate tests and intrinsic viscosity measurements. Chapter 5 includes the analysis of the research data. vi Table of Contents Abstract .................................................................................................................................... iii Lay Summary........................................................................................................................... iv Preface ...................................................................................................................................... v Table of Contents ..................................................................................................................... vi List of Tables ......................................................................................................................... viii List of Figures .......................................................................................................................... ix Acknowledgements.................................................................................................................. xi Dedication ................................................................................................................................ xi 1. Introduction ....................................................................................................................... 1 1.1 Coagulation and Flocculation ................................................................................................. 1 1.2 Project Objectives .................................................................................................................. 4 2. Literature Review .............................................................................................................. 5 2.1 Effect of electrolyte concentration on flotation. ................................................................... 5 2.2 Electrokinetic behaviour of dolomite and illite in aqueous solutions.................................... 6 2.3 Effect of electrolyte concentration on flocculation. ............................................................ 11 2.4 Characterization of flocculants via dilute solution viscometry. ........................................... 12 3. Experimental Program ..................................................................................................... 15 3.1 Methodology ........................................................................................................................ 15 3.2 Statistical Tools..................................................................................................................... 18 3.3 Zeta potential measurements .............................................................................................. 19 3.4 Coagulation tests .................................................................................................................. 20 3.5 Flocculation tests ................................................................................................................. 21 3.6 Viscosity measurements ...................................................................................................... 23 4. Results and Discussion .................................................................................................... 25 4.1 Zeta potential measurements .............................................................................................. 25 4.2 Coagulation results ............................................................................................................... 27 4.3 Flocculation results .............................................................................................................. 30 4.4 Intrinsic viscosity measurements ......................................................................................... 39 5. Conclusions ..................................................................................................................... 45 6. Recommendations for future work .................................................................................. 47 Bibliography ........................................................................................................................... 48 vii Appendix I: Glassware cleaning method ................................................................................ 54 Appendix II: Quantitative phase analysis of two powder samples using the Rietveld method and x-ray powder diffraction data........................................................................................... 55 Appendix III: Viscosity data of PEO and PAM in distilled water, 0.01 M NaCl and 1 M NaCl solutions at different pH and at 25 °C. ................................................................................... 59 Appendix IV: Intrinsic Viscosities of PEO and PAM in distilled water, 0.01 M NaCl and 1 M NaCl solutions at different pH and at 25 °C. .......................................................................... 66 viii List of Tables Table 1 Forces and mechanism that exist in flocculated systems. ........................................... 2 Table 2 The main components of the tested minerals (wt. %). .............................................. 17 Table 3 Linear fit (Eq. (6)) parameters for 0.01M NaCl solutions. ........................................ 43 Table 4 Viscosity data of PEO in different background solutions at natural pH and 25 °C. . 59 Table 5 Viscosity data of PEO in different background solutions at pH 11 and 25 °C. ........ 60 Table 6 Viscosity data of PAM in different background solutions at natural pH and 25 °C. 61 Table 7 Viscosity data of PAM in different background solutions at pH 11 and 25 °C. ....... 62 Table 8 Intrinsic viscosity data of PEO in different background solutions at natural pH and pH 11 and at 25 °C. ................................................................................................................ 66 Table 9 Intrinsic viscosity data of PAM in different background solutions at natural pH and pH 11 and at 25 °C. ................................................................................................................ 66 ix List of Figures Figure 1. Closed water circuit in the modern mineral processing plant. .................................. 1 Figure 2. Crystallographic structure of kaolinite (1:1 layer aluminosilicate) (J. S. Laskowski, 2012); reproduced by the permission of the Canadian Institute of Mining, Metallurgy and Petroleum. ................................................................................................................................. 7 Figure 3. Crystallographic structure of talc (2:1 layer magnesium silicate) (J. S. Laskowski, 2012); reproduced by the permission of the Canadian Institute of Mining, Metallurgy and Petroleum. ................................................................................................................................. 8 Figure 4. Potentiometric titration curve for talc that identifies the point-of-zero charge for talc (Burdukova et al., 2007); reproduced by the permission of Elsevier. ............................... 9 Figure 5. Casson yield stress curve for talc aqueous suspensions as function of pH (Burdukova et al., 2007); reproduced by the permission of Elsevier. ...................................... 9 Figure 6. Proposed charge distribution on the surface of talc particles (Burdukova et al., 2007); reproduced by the permission of Elsevier. .................................................................. 10 Figure 7. Effect of electrolyte concentration on lyophobic and lyophilic systems (Laskowski, 2016). ...................................................................................................................................... 12 Figure 8. Experimental program flowsheet. ........................................................................... 15 Figure 9. Schematic illustration of the mixing tank used for coagulation and flocculation tests. ........................................................................................................................................ 20 Figure 10. Zeta potential-pH behavior of dolomite suspensions in distilled water, at 0.001 M NaCl and 0.01 M NaCl. .......................................................................................................... 25 Figure 11. pH-dependent sensitivity of fine fraction of kaolinite sols to indifferent electrolyte (Tombácz & Szekeres, 2006); reproduced by the permission of Elsevier. ............................ 28 Figure 12. Effect of pH on settling rate of (A) illite, (B) dolomite and (C) 50:50 illite-dolomite suspensions in distilled water and at 1 M NaCl. ..................................................... 29 Figure 13. Visual appearance of flocculated mineral suspensions (schematic): A. Clear mudline, B. Undetectable mudline. ........................................................................................ 30 Figure 14. Effect of “A100” polyacrylamide flocculant dosage on settling rate of the (A) illite, (B) dolomite and (C) illite-dolomite suspensions in distilled water and at 1 M NaCl and varying pH. ............................................................................................................................. 33 Figure 15. Effect of polyethylene oxide flocculant dosage on settling rate of illite (A), dolomite (B) and illite-dolomite mixture (C) in distilled water and at 1 M NaCl and varying pH. .......................................................................................................................................... 34 Figure 16. Effect of concentration of potential determining ions (pH) in distilled water on flocculation by PAM and PEO at 20mg/L dosage.................................................................. 36 Figure 17. Effect of concentration of potential determining ions (pH) in 1 M NaCl solutions on flocculation by PAM and PEO at 20mg/L dosage. ............................................................ 37 Figure 18. Effect of potential determining ions (pH) on the flocculation of illite suspensions by PEO (20 mg/L) with and without Sodium Hexametaphosphate (1g/L). ........................... 38 Figure 19. Effect of pH and electrolyte concentration on the intrinsic viscosity of nonionic flocculant (PEO) at 25 °C. ...................................................................................................... 39 x Figure 20. Effect of pH and electrolyte concentration on the intrinsic viscosity of anionic polyacrylamide flocculant (PAM) at 25 °C. ........................................................................... 40 Figure 21 Reduced viscosity vs PAM concentration for different sodium chloride solutions and pH at 25°C. ...................................................................................................................... 42 Figure 22. Rietveld refinement plot of sample Illite Shale (blue line - observed intensity at each step; red line - calculated pattern; solid grey line below - difference between observed and calculated intensities; vertical bars - positions of all Bragg reflections). Coloured lines are individual diffraction patterns of all phases. ..................................................................... 57 Figure 23. Rietveld refinement plot of sample Dolomite (blue line - observed intensity at each step; red line - calculated pattern; solid grey line below - difference between observed and calculated intensities; vertical bars - positions of all Bragg reflections). Coloured lines are individual diffraction patterns of all phases. ..................................................................... 58 Figure 24. Fedors representation of viscosity data of polyacrylamide flocculant (PAM) and polyethylene oxide flocculant (PEO) in distilled water at 25 °C and varying pH. ................. 63 Figure 25. Fedors representation of viscosity data of polyacrylamide flocculant (PAM) and polyethylene oxide flocculant (PEO) in 0.01 M NaCl solution at 25 °C and varying pH. .... 64 Figure 26. Fedors representation of viscosity data of polyacrylamide flocculant (PAM) and polyethylene oxide flocculant (PEO) in 1 M NaCl solution at 25 °C and varying pH. ......... 65 xi Acknowledgements I wish to sincerely express my thanks to Dr. Janusz Laskowski for his supervision of this study. His patience and willingness to discuss ideas and to reply to my emails with endless questions even on the weekends motivated me to complete this work. I wish to extend my appreciation and deepest gratitude to Mr. Aaron Hope for providing laboratory assistance and to Ms. Sally Finora for her invaluable support and editing wizardry to ensure this document was ready in both digital and printed formats. To my committee, Dr. Marek Pawlik and Dr. Maria Holuszko, I am extremely grateful for your assistance and suggestions throughout my project. I would also like to acknowledge the financial support provided by Becas SENESCYT and to thank the Escuela Superior Politecnica del Litoral, Ecuador under whose auspices I was able to come to Canada for pursuing a master’s degree. Thanks to all individuals who supported me in one way or another. I close by acknowledging the constant support and encouragement from my family in Ecuador. Dedication xii To my parents and Valeria 1 1. Introduction 1.1 Coagulation and Flocculation Recycled WaterROMOreProducts Figure 1. Closed water circuit in the modern mineral processing plant. The mineral processing plant flowsheet includes four distinct unit operations (Figure 1): comminution (crushing and grinding) & classification, separation (flotation), product dewatering (solid/liquid separation), and water clarification. To improve solid/liquid separation operations (both thickening & filtration) the industry applies flocculants. These are water-soluble polyelectrolytes. Since the process water that is used in flotation, before its reuse, is treated in the product dewatering and water clarification unit operations, the use of seawater in flotation also requires the same treatment in which flocculants are applied. The effect of the salt concentration on flocculation is as important as on flotation. In the solid/liquid separation unit operations, a flocculation process is used to aid particle settling and filtration. Polymeric flocculants are hydrophilic colloids with high 2 molecular weight, their solubility in water is owing to solvation of the polar (ionic and non-ionic) groups being strong enough to prevail over the van der Waals cohesive forces between the polymer segments (Laskowski, 2001). Forces and mechanisms that generally are present in flocculated systems are summarized in Table 1. Table 1 Forces and mechanism that exist in flocculated systems. Attractive Forces Attractive Mechanism Repulsive Forces Van der Waals Polymer bridging Electrostatic Hydrophobic Hydration It is generally accepted that aggregation caused by polymeric flocculants results from bridging mechanism (Michaels, 1954). It is important to ascertain that adsorption and flocculation are not separate sequential processes, but occur simultaneously (Hogg, 1999). Polymeric flocculants can be classified based on one or more of their properties, such as molecular weight, functional group, charge, chemical structure, or origin (Attia, 1992). It is known that different polyacrylamide flocculants have different molecular weights and different degrees of anionicity (Arinaitwe & Pawlik, 2009). Several studies have shown that high molecular weight anionic polymers, such as polyacrylamide, are commonly used to flocculate negatively charged clays (Mpofu et al., 2003; Nasser and James, 2006; Addai-Mensah, 2007). As indicated by Kitchener (1972), polymeric flocculants have the ability to produce larger, stronger flocs than those aggregates obtained by inorganic coagulants. They may be applied either after destabilizing the suspension via coagulation, or without prior destabilization: 3 (a) Stable suspension → coagulation → flocculant addition → flocculation (b) Stable suspension → flocculant addition → flocculation Nevertheless, method (a) is always better since flocculants are not very effective in treating stable suspensions (Hogg, 1987). Consequently, destabilization of a fine particle suspension can be accomplished by supressing the electrical repulsion by double layer compression (coagulation), the treatment that improves flocculation. A recent study by Onen and Gocer (2018) has shown that coagulation plus flocculation results in better sedimentation efficiency rather than single methods. However, there are also studies that contradict the previous statements. As indicated by Rubio (1981), coagulation of the particles before flocculation is not always a sufficient condition for obtaining effective flocculation. In modern processing plants water is recycled and reused. The recycled process water is a high electrolyte concentration medium. Concentration of these solutions may be as high as 1 M NaCl (e.g. Mount Keith plant in Australia) (Laskowski & Castro, 2015). Furthermore, in arid regions, the need to save water is necessary and the use of seawater in mineral processing plants is the only sustainable solution in many parts of the world. Sea water is a concentrated solution of NaCl (about 0.6 M) with high content of Ca2+ (0.4 g/L), Mg2+(1.3 g/L) and sulfate ions (2.7 g/L). When seawater is utilized not only the effect of seawater on flotation but also on solid/liquid separation unit operations must be studied. Since flocculation of mineral suspensions—as was pointed out by Kitchener—is more efficient when the suspension is first destabilized by coagulation, the main thesis of this research project is that testing coagulation may serve as a convenient method of studying flocculation. 4 1.2 Project Objectives The overall objective of the project is better understanding of the effect of electrolyte concentration (NaCl), and the effect of potential determining ions (pH), on flocculation in solid/liquid separation. In particular, this project is designed to: - test stability of the suspensions of two selected minerals, dolomite and illite, varying pH and NaCl concentration to determine the conditions required for coagulation; - compare how important it is for two different flocculants, anionic polyacrylamide and non-ionic polyethylene oxide, that the coagulation stage precedes flocculation; - verify the effect of concentration of potential determining ions (pH) in highly concentrated electrolyte solutions on flocculation; - characterize two different flocculants through intrinsic viscosity measurements under various physico-chemical conditions of pH and ionic strength. 5 2. Literature Review 2.1 Effect of electrolyte concentration on flotation. Use of seawater in mining/metallurgical operations is the only sustainable solution in zones where fresh water is limited. Fundamental aspects of flotation in aqueous solutions with high concentration of inorganic electrolytes comparable with concentration of seawater that is to the range up to 1 M NaCl were discussed by Castro and Laskowski (2011) and Laskowski and Castro (2015). In the so-called salt flotation, the inherently hydrophobic solids are floated in NaCl solutions without any other flotation reagents. As it was recently concluded (Laskowski et al., 2018) the salt flotation meets all the following flotation process requirements: (i) the solid particles are hydrophobic; (ii) in the environment of high ionic strength, the energy barrier opposing attachment of the hydrophobic particles to bubbles is reduced making attachment possible; (iii) at the same time, fine bubbles are generated under such conditions. Laskowski and Castro (2015) highlighted that in flotation in highly concentrated electrolyte solutions not only ionic strength but also pH and chemical composition of the process water are crucial. In the classification of the flotation processes carried out the most important variable turned out to be not ionic strength but concentration of hydrolyzable cations like Mg2+ and Ca2+ (Yousef et al., 2003; Laskowski et al., 2018). While there are quite a few publications on the use of seawater in flotation (Castro et al., 2010; Ozdemir, 2013; Laskowski and Castro, 2015), the literature on flocculation under 6 such conditions is limited. Since it cannot be expected that polymeric compounds, i.e. flocculants, will respond similarly to an increased ionic strength of the pulp as the flotation process does, it is important that such project is carried out. 2.2 Electrokinetic behaviour of dolomite and illite in aqueous solutions. Dolomite is a common gangue mineral in many ores and properties of this mineral have been widely studied. Ding and Laskowski (2006) presented results on zeta potential of calcite and dolomite. Both measured zeta potential values were positive but small over a broad pH range. Since colloidal systems coagulate around the point of zero charge (Pugh, 1974; Mewis and Wagner, 2012) dolomite (and calcite) aqueous suspensions should not be very stable. Another selected mineral for this project, illite, is an anisotropic mineral. The properties of such minerals have been widely discussed (Johnson et al., 2000; Wan & Tokunaga, 2002; Tombácz & Szekeres, 2006; Laskowski, 2012). These minerals have different electrical charges on different sides of the crystal; for instance, kaolinite, a 1:1 layer silicate, has one tetrahedral sheet of silica (Si-O) and one octahedral sheet of Al-OH. The former carries negative electric charge at all pH values due to isomorphous substitution of some Si4+ by Al3+ and the latter, as well as its edges, carries a charge that depends on solution pH. Differences between zeta potential measurements of the two basal planes of kaolinite were also studied by Gupta and Miller (2010). Figure 2 shows the layered structure of kaolinite, pointing out the chemical structure of the basal planes and edges. 7 Figure 2. Crystallographic structure of kaolinite (1:1 layer aluminosilicate) (J. S. Laskowski, 2012); reproduced by the permission of the Canadian Institute of Mining, Metallurgy and Petroleum. While clays are very different from other anisotropic minerals such as graphite, molybdenite and talc, what they have in common is a laminar crystal structure. Talc, an inherently hydrophobic mineral, is a layered silicate mineral that consists of octahedral magnesium hydroxide structures sandwiched between sheets of silicon-oxygen tetrahedra (Figure 3). The basal planes exhibit negative electrical charge due to substitution of Al3+ and Ti3+ for Si4+ ions in talc tetrahedral layers. However, the charge at the edges depends on pH. 8 Figure 3. Crystallographic structure of talc (2:1 layer magnesium silicate) (J. S. Laskowski, 2012); reproduced by the permission of the Canadian Institute of Mining, Metallurgy and Petroleum. The apparent electrophoretic isoelectric point of talc lies at approximately pH 2.5 (Fuerstenau & Huang, 2003). Results obtained using the titration technique, as shown in Figure 4, indicate that the point-of-zero charge talc falls at approximately pH 7.7 and this is very different from the iep for talc (Burdukova, et al., 2007). Results of rheological experiments reveal that the maximum coagulation of talc aqueous suspensions occurs at approximately pH 5.5 (Figure 5). This indicate that there exists an attractive force between particles other than the attractive van der Waals and it could be an attractive electrostatic force between oppositely charge particle planes which brings about heterocoagulation (Burdukova et al., 2007). From these results, a model describing electrical charge distribution on talc edges and faces was derived (Figure 6). 9 Figure 4. Potentiometric titration curve for talc that identifies the point-of-zero charge for talc (Burdukova et al., 2007); reproduced by the permission of Elsevier. Figure 5. Casson yield stress curve for talc aqueous suspensions as function of pH (Burdukova et al., 2007); reproduced by the permission of Elsevier. 10 Figure 6. Proposed charge distribution on the surface of talc particles (Burdukova et al., 2007); reproduced by the permission of Elsevier. Hence, it is expected that suspensions of illite, a 2:1 layer alumino-silicate, where the octahedral Al-OH layer is sandwiched between two silica tetrahedral layers, will be showing coagulation over a pH range of 4-6 at which the differences between the electrical charges of the faces and the edges of illite platelets are the largest. Furthermore, illite suspensions can be expected to be stable in water at pH values larger than 9. 11 2.3 Effect of electrolyte concentration on flocculation. The effect of electrolyte concentration on flocculation has not yet been fully studied. Pawlik and Laskowski (2006) tested the flocculation of illite and dolomite by guar gum—a nonionic polysaccharide—in high electrolyte concentration solutions and reported clear correlations between the polysaccharide adsorption process on illite and dolomite and the stability of suspensions of these minerals. The flocculation of illite by guar gum was very efficient in concentrated electrolytes, and the suspensions of both minerals were stable against flocculation when excessive dosages of guar gum were used. Pawlik et al. (2003) studied flocculation of illite and dolomite suspensions by anionic carboxymethyl cellulose (CMC), also in NaCl-KCl brine. They reported that at low CMC concentrations both illite and dolomite suspensions were strongly aggregated irrespective of the electrolyte concentration. At higher CMC concentrations both dispersions were redispersed and this effect did not depend on the electrolyte concentration either. Huang et al.’s (2013) results showed the typical bell-shaped curve for a settling rate of illite-dolomite suspensions vs polyacrylamide dosage plot in distilled water, indicating a clear optimum flocculant dosage due to bridging mechanism. Since the macromolecules of polyacrylamide are hydrophilic, at higher polymer concentrations the repulsion between the macromolecules becomes a dominant factor and stabilizes the suspension (steric stabilization). In contrast, at increased ionic strength, better results of flocculation were obtained even in higher concentrations of flocculant. Friend and Kitchener (1973) described a peculiar type of flocculation in which calcite, with almost all available flocculant adsorbed, formed bridges in the flocs between deficiently flocculating species. This could be an 12 explanation for the good flocculation results obtained by Huang et al. (2013) using illite-dolomite mixture at high electrolyte concentration. 2.4 Characterization of flocculants via dilute solution viscometry. When a flocculant acts efficiently on one mineral suspension but not on another one in a similar aqueous medium, this could be the result of lower adsorption of the flocculant on the latter; conversely, changes of efficiency with one flocculant and the same mineral suspension but with alteration in the medium may arise from changes of strength of adsorption or from changes of effective length of the polymer molecules (Slater & Kitchener, 1966). Figure 7. Effect of electrolyte concentration on lyophobic and lyophilic systems (Laskowski, 2016). 13 As shown in Figure 7, increasing electrolyte concentration affects not only the suspension of mineral particles (lyophobic system), but also the properties of aqueous solutions of flocculant macromolecules (lyophilic system). While solid particles tend to coagulate at a given concentration of electrolyte, the flocculant macromolecules start coiling and finally may be entirely salted out. Both these phenomena affect the outcome of the flocculation process. While coagulation may be improving flocculation, coiling of the flocculant macromolecules may reduce the flocculant’s ability to flocculate. The conformation of flocculant macromolecules in solution can be studied through intrinsic viscosity measurements. Viscosity measurements may be reported in several forms such as dynamic viscosity 𝜂, relative viscosity 𝜂𝑟 = 𝜂 𝜂𝑠⁄ , specific viscosity 𝜂𝑠𝑝 =𝜂−𝜂𝑠𝜂𝑠=𝜂𝑟 − 1, reduced viscosity 𝜂𝑟𝑒𝑑(𝑐) = 𝜂𝑠𝑝 𝑐⁄ and intrinsic viscosity [𝜂]. In these expressions 𝜂𝑠 is the solvent viscosity, 𝑐 is the polymer solution concentration. The intrinsic viscosity is defined as the reduced viscosity when the concentration 𝑐 tends to zero and its unit is [𝑐−1] , usually given as [100 ml/g=dL/g]. The behaviour of polymers in salt solutions is commonly analyzed using the macromolecule-solvent interaction χ parameter usually referred to as the Flory-Huggins parameter. Perhaps one of the simplest way of assessing the χ parameter is via intrinsic viscosity measurements (Pawlik et al., 2003). With the use of a capillary viscometer, the time it takes a volume of the dilute solution to flow between two fixed marks in a capillary tube is measured. This time is compared to the time it takes the same volume of solvent to flow between the two marks on the capillary. The flow time, t, for the solution and the solvent is inversely proportional to the density, ρ, and proportional to the viscosity, η (Kulicke & Clasen, 2004). 14 𝑡𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛 = 𝑐𝑜𝑛𝑠𝑡𝑎𝑛𝑡 ×η𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛ρ𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛 ; 𝑡𝑠𝑜𝑙𝑣𝑒𝑛𝑡 = 𝑐𝑜𝑛𝑠𝑡𝑎𝑛𝑡 ×η𝑠𝑜𝑙𝑣𝑒𝑛𝑡ρ𝑠𝑜𝑙𝑣𝑒𝑛𝑡 (1) The relative viscosity (ηr) is defined as the ratio η𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛η𝑠𝑜𝑙𝑣𝑒𝑛𝑡. For very small polymer concentrations, the assumption is that the density of the dilute polymer solution ρ𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛 equals the density of the pure solvent ρ𝑠𝑜𝑙𝑣𝑒𝑛𝑡 .Therefore, the relative viscosity is a simple ratio: η𝑟 =t𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛t𝑠𝑜𝑙𝑣𝑒𝑛𝑡 (2) The intrinsic viscosity [η] is a measure of the inherent ability of a polymer to increase solution viscosity. It is evaluated by extrapolation of experimental data to zero concentration —to eliminate polymer intermolecular interactions—and can also be estimated from the reciprocal of the slope of the line of best fit to the experimental data using Fedors’ equation. According to Fedors (1979) for uncharged polymers: 12(η𝑟1/2 − 1)=1[η]c−1[η]c𝑚 (3) where ηr is the relative viscosity at c (polymer concentration) and cm is a polymer concentration parameter. A plot of the quantity 12(η𝑟1/2−1) versus 1c should result in linear response with slope equal to 1[η] and intercept 1[η]c𝑚. 15 Rao (1993), Ghimici and Popescu (1998) and Arinaitwe (2008) concluded that Fedors equation can be used to describe also the viscosity of some polyelectrolyte solutions over a wide concentration range, it yielded excellent fits to all raw viscosity data . 3. Experimental Program 3.1 Methodology The tests on stability/flocculation of mineral suspensions in simulated process water were carried out in the laboratories of N.B. Keevil Institute of Mining Engineering at the University of British Columbia. The main structure of the test methodology is shown in Figure 8. Figure 8. Experimental program flowsheet. 16 “Superfloc-A100” polyacrylamide flocculant was provided by CYTEC and polyethylene oxide was acquired from SIGMA-ALDRICH. The viscosity-average molecular weight (MV) was 3,900,000 for A100 (as measured by Ferrera et al., (2009)) and 5,000,000 for PEO (provided by the manufacturer). Both flocculants were received as dry, white granules and no further treatment or purification was used. According to Arinaitwe & Pawlik (2009) the degree of anionicity of the A-100 flocculant is 10.2%. Sodium hexametaphosphate was provided by VWR International – Canada. Two minerals, namely dolomite and illite, were chosen for the experiments. These two minerals were selected following the information provided by Friend and Kitchener (1973) and the preliminary tests in the Mining Engineering Department at UBC carried out by Huang et al. (2013) and by Yu (2015). The tests include mineral samples (pure minerals) which were acquired from VWR International - Canada, and sample preparation by crushing in a laboratory jaw crusher and dry grinding to below 38 µm in a vibratory disc mill. In the next stage, the particle size distribution of the ground material was determined. The volume-average particle size for illite and dolomite were 4.43 µm and 4.67 µm, respectively (Malvern 2000 Mastersizer). The mineralogical composition of the samples, as analyzed by X-ray diffraction is shown in Table 2. X-ray diffraction analysis of a dolomite mineral confirmed that it was pure dolomite. On the other hand, XRD analysis of illite mineral showed that it was a mid-grade illite sample. 17 Table 2 The main components of the tested minerals (wt. %). Illite Dolomite Illite 66.8% Dolomite 99.1% Quartz 24.2% Quartz 0.9% Dolomite 3.7% Clinochlore 2.4% Kaolinite 1.3% Pyrite 0.7% Rutile 0.5% Anatase 0.4% It is to be pointed out that while the dolomite sample obtained from VWR International was high quality, the sample of illite contained only 67% of illite and 24 % of quartz. The tests were performed with single minerals, but also with 50:50 mixtures of these two minerals. The settling experiments were executed under controlled hydrodynamic conditions following the procedure described by Hogg (1987). Polymer was added continuously over a period of vigorous mixing after which agitation was ceased entirely. Very rapid polymer addition results to some extent in large floc sizes, but such flocs tend to be weaker than those produced at lower addition rates. Transferring the flocculated suspension to a graduate cylinder permits more precise settling rate measurements but brings about additional disturbance to the system. The initial settling tests were performed using prepared suspensions versus concentration of electrolytes and pH. To determine coagulation/stability zones the results of the settling experiments of dolomite suspensions (isotropic mineral) were correlated with the values of the electrokinetic potential (zeta potential). The polymers were characterized using viscosity measurements following the procedures described by Arinaitwe (2008) in which a PVS1 Lauda photo-timing and processing system interfaced with a computer and Cannon–Fenske capillary viscometers 18 were employed. Dilute solutions of flocculants were prepared at varying pH and ionic strength (sodium chloride solutions). To ensure repeatability of the results, a cleaning procedure with nitric acid and ethanol was adopted for removing any organics from the glassware. Differences in reproducibility from previous studies may arise due to differences in mineral composition and particle sizes, also from differences in experimental conditions such as impeller speed, conditioning time, and geometry of mixing tank. 3.2 Statistical Tools A statistic that could be used for describing the spread or variability of the data values is the sample variance (s2) (Ross, 2014). The sample variance of the data set x1, …, xn is defined by 𝑠2 = ∑(𝑥𝑖 − 𝑥)2(𝑛 − 1)𝑛𝑖=1 (4) n -number of observed values 𝑥𝑖 -ith observed value 𝑥 -average of all observed values The positive square root of the sample variance is called the sample standard deviation. To use the same units as the data values, the sample standard deviation (s) was employed in the analysis of the experimental data of this study and it is defined by 𝑠 = √∑(𝑥𝑖 − 𝑥)2(𝑛 − 1)𝑛𝑖=1 (5) Standard deviations are displayed as error bars in the plots of zeta potential, coagulation and flocculation tests. Although it appears that there are no error bars on some 19 curves, it does not mean that standard deviation was not calculated. In this case, this statistic is very small, showing high reproducibility of the results. 3.3 Zeta potential measurements Dolomite samples were used and the required solid concentration in distilled water, 0.001 M NaCl and 0.01 M NaCl solutions was 0.00005 wt% of solids (5 mg of mineral in 100 g of solution). The beaker, containing the suspension and a magnetic stirring bar, was put on a magnetic stirrer for conditioning at room temperature for 10 minutes. The pH of the suspension was measured (natural pH) or it was adjusted by the addition of a few drops of NaOH solutions (0.1 M or 1M). The equilibration time while stirring was 5 minutes to ensure a stable pH reading before the measurements. An aliquot was carefully removed by a syringe without disturbing the settled particles at the bottom of the beaker. The cell of the Zeta View PMX 100 instrument was filled with the sample removed from the beaker. This equipment measures the electrophoretic mobility of the particles in suspensions, and zeta potential is calculated using Smoluchowski’s equation. Each measurement in the instrument was done in triplicate, and each test was duplicated. Thus, mean zeta values were produced and displayed in the zeta potential plot; the largest standard deviation was 3.5 mV. 20 3.4 Coagulation tests The mineral suspensions (12.5 g of solids) were prepared by mixing with 175 ml of distilled water or background electrolyte solution at different pH by a four-bladed flat paddle in a mixing tank for 7 minutes at an impeller speed of 400 rpm using a Lightnin Labmaster mixer. This mixing tank was made of a Plexiglas cylinder and equipped with four baffles, as illustrated in Figure 9. Figure 9. Schematic illustration of the mixing tank used for coagulation and flocculation tests. 21 The partly coagulated slurry was then rapidly transferred to a 250-ml graduated cylinder, and the cylinder was inverted once to homogenize the suspension. The mudline was recorded for 5 minutes with the use of a digital camera. The interface settling rate (cm/s) was calculated from the linear portion of the interface position vs time curve. All settling tests were conducted in duplicate, thus the results presented in this study are average values. 3.5 Flocculation tests Stock solutions of polymer at concentrations of 0.5 g/L were prepared by weighing 0.125 g of the flocculant in a weighing dish. Distilled water (250 ml) was then added into a 500-ml beaker at room temperature and a magnetic stirrer was used to create a deep vortex. The flocculant granules were carefully added into the sides of the vortex. The top of the beaker was then covered with parafilm. The flocculant solution was left mixing overnight to achieve complete dissolution of the flocculant. To avoid the aging effect, the stock solution was used within 24 hours. It has to be mentioned, an anionic polymer gradually changes its conformation with time from a stretched one to coiled (Arinaitwe, 2008). The mineral suspensions (12.5 g of solids) were prepared by mixing with 175 ml of distilled water or background electrolyte solution at different pH’s in a mixing tank at 400 rpm for 3 minutes. The pH was adjusted using sodium hydroxide (1 M) and hydrochloric acid (1M). After conditioning, flocculant solution (25 ml) in a burette was added slowly over 4 minutes at a constant rate to the mixing tank and the mixture was stirred at 400 rpm to 22 provide adequate mixing for polymer solution (polyacrylamide or polyethylene oxide flocculant) and mineral suspension. When polymer addition was complete, agitation was immediately stopped. Flocculant performance was evaluated through batch settling tests in 250-ml graduated cylinders. The partly flocculated slurry was transferred to a graduated cylinder. The calculation of interface settling rates is the same as used in the coagulation tests. All settling tests were conducted in duplicate, thus the results presented in this study are average values, with the largest standard deviation for flocculation rates of mineral suspensions by PAM and PEO being 0.77 cm/s and 0.79 cm/s, respectively. In addition, some tests with hexametaphosphate were also conducted. Illite suspensions in distilled water and at 1M NaCl were mixed with dispersant, sodium hexametaphosphate (NaHMP). Then, polyethylene flocculant was added to observe the effect of the dispersant on flocculation. The settling tests were duplicated, and the standard deviations of the averages of settling rates were not higher than 1.01 cm/s. 23 3.6 Viscosity measurements Kinematic viscosity measurements of nonionic and anionic flocculant solutions in distilled water and NaCl solutions were performed at natural pH and pH 11. PEO flocculant was evaluated in the concentration range from 140 – 260 mg/L while PAM flocculant was tested in the concentration range from 10 – 115 mg/L. These ranges were selected to be below the critical concentration limit - c* = 2.5/[η] proposed for PAM by Kulicke el al. (1982), and also to assure an exact analysis, relative viscosities were between 1.2 and 2.5 as was recommended by Kulicke and Clasen (2004). Stock flocculant solutions were prepared and left overnight and then diluted the next day. These solutions were used within 24 hours. The measurements were made using three Canon-Fenske capillary viscometers (diameter 0.54mm) of different calibration constants. The capillary constant, K, is a specific factor for each capillary. The constants (0.007475, 0.007356 and 0.007551) that were provided by the manufacturer were recalculated using the literature value of the kinematic viscosity of water at 25°C, 0.8926 mm2/s (Lide, 2007). These tests were carried out with distilled water at 25°C and the new constants were 0.007332, 0.007143 and 0.007330, respectively. The viscometers were cleaned with a 15% hydrogen peroxide (H2O2) solution and then with a 15% HCl solution as recommended by the manufacturer. When pH 11 was needed to be reached, to minimize dilution of the already dilute polymer solutions, the pH adjustment was effected by the addition of a few drops of 1 M NaOH solution. 7-ml aliquots of the final dilute flocculant solution were transferred to the capillary viscometer reservoir. The remaining diluted samples were used for measuring pH. 24 Thereafter the viscometer was placed in a water bath whose temperature was maintained constant at 25 °C for an equilibration time of 30 minutes. The kinematic viscosity was then determined by allowing the flocculant solution to flow down the capillary under gravity. A PVS1 Lauda photo-timing and processing system interfaced with a computer was employed to measure three flow times and the average of these values was used to calculate the kinematic viscosity (in mm2/s). The standard deviation of flow times was always less than 1 second. From the flow times, relative viscosities of the flocculants in distilled water and NaCl were calculated at each concentration and pH. The equation suggested by Fedors (1979) for application to intrinsic viscosity determination of dilute to moderately concentrated solutions was used to fit the data and obtain the intrinsic viscosity values. The effect of pH and increased electrolyte concentration on the solution viscosities was assessed by determining the intrinsic viscosity of the flocculants in the tested solutions by calculating the inverse of the slope of the 12(η𝑟1/2−1) versus 1c graph. A linear interpolation was used to obtain the slope of each plot and R-squared (R2) values were above 0.90 meaning good linear fits. 25 4. Results and Discussion 4.1 Zeta potential measurements Figure 10. Zeta potential-pH behavior of dolomite suspensions in distilled water, at 0.001 M NaCl and 0.01 M NaCl. Zeta potential of dolomite particles was measured in distilled water, 10-3 M NaCl and 10-2 M NaCl solutions as a function of pH (Figure 10). The reason of the lack of data in an acidic environment is to prevent reaction of this carbonate mineral with the acid (HCl) used to adjust pH. The particles have moderately negative charge in all solutions, as determined by micro-electrophoresis, and no isoelectric point was observed. Similar electrokinetic measurements were reported by Moudgil et al. (1995) for three dolomite samples from three 26 different suppliers. Some works, as that of Somasundaran and Agar (1967), reported that the principal potential determining species for calcite, another carbonate, are Ca2+, HCO3-, H+, and OH. They suggested that the negative zeta potential of dolomite is mainly attributed to the high concentration of negatively charged species such as HCO3-. There is a slight decrease in the magnitude of zeta potential values when ionic strength is increased. Similarly to the electrokinetic results obtained in this study, the zeta potential measurements of dolomite in distilled water have been reported and values varied from 0 to -20 mV (Marouf et al., 2009). Some researchers have reported values of pHiep of pure dolomite around 6 (Gence and Ozbay, 2006; Marouf et al., 2009) and 8 (Pokrovsky et al., 1999), and even in several studies all zeta potential values were found to be positive as a function of pH (Liu and Liu, 2004; Ding & Laskowski, 2006; Kasha et al., 2015). What is important here is that, generally, it is considered that for the zeta potential greater than +20 mV or more negative than -20 mV the electrostatic repulsion between the particles is larger than the attractive energy and, consequently, such a mineral suspension is stable. Therefore, since the measured zeta potential values for the tested dolomite were smaller than -20 mV these particles should form slowly coagulating suspensions. With respect to the electrokinetic measurements of illite (anisotropic mineral), Johnson et al., (2000) reported the lack of correlation between the rheological measurements and the electrokinetic measurements for kaolinite suspensions. This discrepancy questions the applicability of Smoluchowski’s equation to the calculation of zeta potential from the measured electrophoretic mobility for plate-like anisotropic minerals (Laskowski, 2012). For this reason, zeta potential measurements were not performed for illite in this project. 27 4.2 Coagulation results As expected dolomite suspensions in water were found to be unstable (Figure 12B); this is especially visible when compared with the stability of illite (Figure 12A). The coagulation results for illite suspensions varying in ionic strength and pH indicate that these suspensions were stable in distilled water over the pH range from 6.5 to 11. The coagulation was becoming visible when ionic strength was increased. This agrees with Tombácz and Szekeres (2006), who highlighted that the positive edge – negative face interactions lead to coagulation of kaolinite suspensions only above a threshold of electrolyte concentration as shown in Figure 11. A high electrolyte concentration needed to initiate kaolinite coagulation indicates dramatically increased stability of these suspensions in alkaline environment. The stability ratio (w) in Figure 11 was calculated from the initial slopes of kinetic curves belonging to the slow and fast coagulation as suggested in literature (Holthoff et al., 1996). While the effect of increased concentration of NaCl on stability of the tested suspensions was as expected for illite, it turned out to be the opposite for dolomite. These suspensions were found to be more stable in 1M NaCl solution than in distilled water. While illite suspensions were expected to coagulate in acidic solutions and be stable in alkaline environment this was not confirmed by the experiments. 28 Figure 11. pH-dependent sensitivity of fine fraction of kaolinite sols to indifferent electrolyte (Tombácz & Szekeres, 2006); reproduced by the permission of Elsevier. 29 Figure 12. Effect of pH on settling rate of (A) illite, (B) dolomite and (C) 50:50 illite-dolomite suspensions in distilled water and at 1 M NaCl. 30 4.3 Flocculation results Figure 13. Visual appearance of flocculated mineral suspensions (schematic): A. Clear mudline, B. Undetectable mudline. As was observed in the flocculation tests, flocculating suspensions followed two patterns (A and B) illustrated in Figure 13. In the case of A, a clear layer develops after a while, with a definite boundary below it, which is the “mudline”. The boundary falls rapidly and then more slowly approaching a limiting sediment volume. This provides reproducible settling rates. On the other hand, in the case of B., the fragments built from flocculating particles sediment faster than the non-flocculating fine particles, leading a haze at the top of the settling column. The settling rate results obtained under such conditions are not very reliable and highly irreproducible. 31 Mineral suspensions flocculated by polyacrylamide flocculant emulates case A (Figure 13), but illite suspensions in distilled water at pH 11 displayed a peculiar behavior (similar to case B) which is explained subsequently. Flocculation in an acidic environment is not good for both illite and dolomite. A bell-shaped curve with settling rate vs dosage of PAM is obtained for flocculated illite suspensions in distilled water at pH 9 (Figure 14A). This confirms that for the hydrophilic macromolecules when they are well extended in a good solvent, at some flocculant dosages, the bridging mechanism is possible and is indicated by a clear optimum on the flocculation curve. At higher polymer concentrations, the polymer-polymer interactions are preferred to polymer-solvent interactions and repulsion appears which stabilizes the suspension. At the pH range from 9-11, the effect of ionic strength in illite suspensions eliminates the optimum visible in distilled water at pH 9, and flocculation become possible even at higher dosages of the polyacrylamide flocculant where the steric stabilization is observed in distilled water at pH 9. Moreover, illite suspensions in distilled water at pH 11 showed high settling rates accompanied by a turbid supernatant. It is usually associated with the bimodal floc size distribution obtained by “poor flocculation” (R. Hogg, 2000). This effect may be a consequence of the repulsion between the high negative charges (at high pH) on the different sides of illite particles and the anionic flocculant. Furthermore, other minerals such as quartz are present in the illite samples tested in this study and these silicone oxide particles also carry highly negative charges in alkaline environments. 32 The dolomite and 50:50 illite-dolomite suspensions are to some extent unstable toward particle size enlargement with polyacrylamide flocculant, as shown in Figure 14. At pH of 11 in distilled water, illite does not flocculate with PAM, dolomite does. Consequently, addition of the flocculating dolomite to non-flocculating illite makes the illite-dolomite mixture flocculate. According to settling rate results, the illite-dolomite mixture suspensions demonstrate great dependence on pH, as presented in coagulation results. In all cases the flocculation with PEO at pH 6.5 is poor. The flocculation of clay suspensions by polyethylene flocculant reported higher settling rates in distilled water than those obtained at 1 M NaCl both at pH 9 and 11 (Figure 15A). Scheiner and Wilemon (1987) reported that PEO is effective in flocculating wastes that contain clay materials. As shown in Figure 15, polyethylene oxide does not flocculate dolomite suspensions under the tested conditions (pH, ionic strength and flocculant dosages). At pH 11, addition of flocculating illite to non-flocculating dolomite forces the illite-dolomite mixture to flocculate. At high dosage of the flocculant (30 mg/L) the flocculation of the mixture can be quite good. However, it was observed that the mixture suspensions flocculated by PEO at the highest flocculant dosage used in this study exhibited significantly high turbidity and this is explained by the case B displayed in Figure 13. Particularly, it suggests that PEO selectively flocculated illite, and non-flocculating dolomite particles remained localized in the supernatant. 33 Figure 14. Effect of “A100” polyacrylamide flocculant dosage on settling rate of the (A) illite, (B) dolomite and (C) illite-dolomite suspensions in distilled water and at 1 M NaCl and varying pH. 34 Figure 15. Effect of polyethylene oxide flocculant dosage on settling rate of illite (A), dolomite (B) and illite-dolomite mixture (C) in distilled water and at 1 M NaCl and varying pH. 35 The effect of pH and NaCl concentration on flocculation of illite and dolomite suspensions by PAM and PEO is shown in Figure 16 and Figure 17. Comparison of these two figures indicates that PAM is a much better flocculant, in that it flocculates both tested minerals and their mixture. Effectiveness of PAM significantly decreases in acidic conditions both in distilled water and in 1 M NaCl solution; moreover, this happens despite the extended configuration of PAM macromolecules in acidic solutions (as suggested by the intrinsic viscosity measurements). In the case of illite at pH 11, the particles are negatively charged, and this may stabilize illite suspension against coagulation but also may affect PAM adsorption. As reported by Sworska et al. (2000), the presence of Mg2+ and Ca2+ ions can significantly improve flocculation of kaolinite in alkaline solutions. The two discussed figures also show that dolomite is not flocculating with PEO at all. The poor flocculation of dolomite suspensions was observed both in acidic and alkaline solutions, and both in distilled water and 1 M NaCl solution. That indicates that conformation of the PEO macromolecules is not the reason in this case. The likely reason is poor adsorption of PEO onto dolomite. Rubio and Kitchener (1976) suggested that adsorption of PEO on silica may be due to isolated silanol groups and/or hydrophobic sites on silica. Moudgil and Chanchani (1985) floated dolomite as a function of oleate concentration. For this reason, in this work, several experiments with addition of sodium oleate to render dolomite surface hydrophobic were carried out but no improvement in the flocculation rate of this carbonate with PEO was observed, these results are not included in this thesis. Moudgil et al. (1995) determined that the flocculation of a dolomite sample by PEO was associated with the presence of minor amounts of palygorskite—a Mg-rich clay— which modifies the surface chemical behavior of the dolomite sample. The isolated -OH 36 groups hydrogen-bond with the ether oxygen of PEO and result in flocculation of palygorskite and dolomite. Mathur and Moudgil's (1998) study revealed that the simple presence of isolated hydroxyls on oxide surfaces does not necessarily result in adsorption of PEO. Figure 16. Effect of concentration of potential determining ions (pH) in distilled water on flocculation by PAM and PEO at 20mg/L dosage. 37 Figure 17. Effect of concentration of potential determining ions (pH) in 1 M NaCl solutions on flocculation by PAM and PEO at 20mg/L dosage. Figure 18 confirms the effect of sodium hexametaphosphate (NaHMP) as a dispersant of clay minerals. It is shown there that addition of NaHMP decreases the flocculation rates of illite suspensions over the pH range from 9 to 11. Ramirez et al., 2018 evaluated the effect of sodium hexametaphosphate in the flotation of chalcopyrite in the presence of kaolinite in sea water over the pH range from 7 to 11 and reported that this clay dispersant depresses kaolinite under such conditions. The preceding statement corroborates the results obtained in this work. According to Andreola et al., (2006), NaHMP accomplishes its dispersing action through a combined mechanism: (i) by increasing the overall negative surface charge, 38 especially at the edges of the clay mineral particles; (ii) by increasing the thickness of the electrical double layer. Despite sodium hexametaphosphate’s functionality as a clay dispersant, NaHMP unexpectedly improved settling rates of illite suspensions flocculated by PEO at pH 6.5 and this fact can not be explained at this stage. Figure 18. Effect of potential determining ions (pH) on the flocculation of illite suspensions by PEO (20 mg/L) with and without Sodium Hexametaphosphate (1g/L). 39 4.4 Intrinsic viscosity measurements Figure 19. Effect of pH and electrolyte concentration on the intrinsic viscosity of nonionic flocculant (PEO) at 25 °C. 40 Figure 20. Effect of pH and electrolyte concentration on the intrinsic viscosity of anionic polyacrylamide flocculant (PAM) at 25 °C. As pointed out by Gochin et al., (1985) for non-ionic polymers electrolyte concentration does not change the conformational state of the macromolecules and this entirely agrees with the results shown in Figure 19. The solubility of this polymer in water results from hydrogen bonding and these macromolecules are always in the extended form provided that the temperature is kept constant (increased temperature reduces hydrogen bonding between the polymer macromolecules and water and decreases PEO solubility) (Mpofu et al., 2004). The situation of anionic PAM is very different; it is in the extended state in distilled water and any increase in ionic strength causes coiling of the PAM macromolecules (as shown by decreasing intrinsic viscosity–Figure 20). It indicates that the carboxylic groups seem to be sufficiently dissociated at natural pH, as shown by the highest 41 intrinsic viscosities. The results also indicate excellent solvation of the polymer chains by water and this makes possible chain extension. When the pH is increased to approximately 11 in distilled water, there is a pronounced decrease in the intrinsic viscosity for anionic flocculant. Therefore, the most likely explanation for this reduction is that at high pH due to NaOH addition the charge on the ionized carboxylic groups is neutralized by the counterions. When the anionic polyacrylamide flocculant is tested in NaCl solutions (0.01mol/L and 1mol/L) there is a coiling of the macromolecules which is reflected in a marked decrease in intrinsic viscosity values. An interesting observation is the one-fold increase of the intrinsic viscosity of A100 when the electrolyte concentration is increased from 0.01 M to 1 M NaCl. Due to the polyectrolyte effect, Huggins equation which was originally derived for dilute solutions of nonionic polymers can not be used to measure intrinsic viscosities of anionic polymers. However, this equation was employed to illustrate the effects of solvency of sodium chloride solutions for polyacrylamide macromolecules. According to the Huggins equation (Huggins, 1942): 𝜂𝑟𝑒𝑑 = [𝜂] + 𝑘 [𝜂2]𝑐 (6) where ηred is the reduced viscosity ((ηr-1)/c), [η] is the intrinsic viscosity, c is the polymer concentration, and k is the Huggins coefficient which is dimensionless. A plot of ηred vs c should yield a straight line with the intercept equal to [η]. Therefore, the Huggins coefficient can be calculated from the slope values. 42 Sakai, (1968) have reported that the values of k may vary between 0.5 and 0.7 for a polymer under theta-conditions which promotes polymer-polymer interactions over polymer-solvent interactions. This is the transition from a good solvent to a poor solvent. Generally, a polymer exhibits a higher value of k in a poor solvent than in a good solvent. Furthermore, this coefficient is very sensitive to the formation of molecular aggregates. In a few words, the solvency power of the solvents plays an important role with coil dimensions being the largest in good solvents; in addition, intrinsic viscosity measurements are a convenient way of estimating solvency effects. Figure 21 Reduced viscosity vs PAM concentration for different sodium chloride solutions and pH at 25°C. 43 Table 3 Linear fit (Eq. (6)) parameters for 0.01M NaCl solutions. pH Slope, 𝒌[𝜼𝟐] [𝒅𝑳𝟐𝒈𝟐] Intercept, [𝜼] [𝒅𝑳𝒈] Huggins coefficient, 𝒌 6 709.57 24.34 1.20 11 741.81 21.78 1.56 The solid lines of Figure 16 are trend lines, while the dashed lines show the linear fits (Huggins equation) to the experimental data in 0.01M NaCl solutions over the tested polyacrylamide concentration range at pH 6 and 11 (Table 3). The intrinsic viscosity results of A100 PAM in 0.01M NaCl solutions at pH 6 and 11 and at 25°C agree with the already published values by Arinaitwe and Pawlik (2013). As Figure 21 and Table 3 indicate, 0.01M NaCl solutions seem to be a worse-than-theta solvent (k is greater than 0.5-0.7) for the anionic polyacrylamide flocculant. Unexpectedly the overall relationship between the reduced viscosity and PAM concentration in 1M NaCl solutions assumes a polynomial function with respect to the polymer concentration c. As reported by Napper, (1977), the simplest way to bring about instability in sterically stabilized dispersions is to reduce the solvency of the dispersing medium for the stabilizing species. It is reasonable to expect that high concentrations of hydrated Na+ ions bind large amounts of water molecules leaving no free water for the anionic polyacrylamide hydration and dissolution (Ma & Pawlik, 2007). Hence, it induces intermolecular association between coiling PAM macromolecules which may increase the intrinsic viscosity as shown in Figure 20 in which there is a one-fold increase of the intrinsic viscosity of A100 when the electrolyte concentration is increased from 0.01M to 1M NaCl. Consequently, it may lead to 44 “incipient flocculation” where adsorbed layers of polyacrylamide are aggregated, and this is supported by the quite good results obtained in the flocculation of illite suspensions with PAM in 1M NaCl solutions over the pH range from 9 to 11 (as shown in Figure 14A). The effect of pH on the intrinsic viscosities at constant ionic strength is not dramatic. The presence of background ions rather than pH seems to be the prevailing factor in determining the conformation of PAM, as reported by Arinaitwe (2008). In addition, the anionic flocculant seems to be more flexible than the nonionic flocculant in terms of its ability to coil or stretch as shown by the significant decrease of PAM’s intrinsic viscosity when tested at increased ionic strength. The results of intrinsic viscosities using Fedors equation are in agreement with those reported by Rao (1993), Ghimici and Popescu (1998) and Arinaitwe (2008) which indicate the applicability of this equation for describing not only the viscosity of nonionic flocculants but also the viscosity of polyelectrolyte solutions. 45 5. Conclusions For a polymeric flocculant to bring about bridging flocculation, it is necessary for its macromolecules not only to adsorb onto the surface of the particles, but also for the loops and tails of the adsorbed chains to extend or stretch further into the dispersing medium. This is possible if the macromolecules adopt an extended configuration. This is determined not only by the molecular weight but also by electrical charge and hydration of the macromolecules. In the case of ionic flocculants at high ionic strength, shielding of the charge produces a more compact configuration; hence, reducing the possibility of bridging. It is worth mentioning that at very high salt concentrations, the medium would tend to become a “worse solvent” for polymeric compounds and may tend to salt out the polymer. In this work two flocculants have been used: A-100 anionic polyacrylamide (PAM) and non-ionic polyethylene oxide (PEO). As viscosity tests demonstrate, while conformational properties of PAM macromolecules are very sensitive to ionic strength (Figure 20), the conformation state of PEO is not influenced by electrolyte concentration. These macromolecules adopt rather coiled configuration irrespective of pH and concentration of NaCl (Figure 19). Furthermore, as the intrinsic viscosity results show, polyacrylamide is coiled at high salt concentrations, and this conformation should prevent bridging flocculation. As the same time, high pH (9-11) promotes strong dispersion of illite particles. In other words, flocculation of illite by PAM at high pH and high salt concentrations should be very difficult. However, it is obvious that flocculation of illite under those conditions is the most pronounced of all the tested conditions (Figure 14A). In this case, attraction between coiled polyacrylamide molecules adsorbed on individual mineral particles seems to 46 drive the flocculation process at high salt concentrations. This process differs from flocculation by bridging. In bridging flocculation, extended flocculant chains adsorb on several particles at the same time and, since the bridging flocculation process takes place in good solvent conditions, attraction between extended flocculant chains is very weak. Bridging by adsorbed polymer chains should be the prevailing mechanism at low salt concentrations and under good solvent conditions. Moreover, the results of flocculation tests with PEO, shown in Figure 15, demonstrate that illite is flocculated very well at pH 9 and 11 but not at pH of 6.5. Illite-dolomite mixture behaves correspondingly; in addition, its flocculation is negligible at slightly acidic conditions. Dolomite is not flocculated by PEO under any tested conditions. Since these differences cannot be explained by different conformation of PEO in distilled water or salt solutions, the reason for very poor flocculation of this carbonate must result from poor adsorption of PEO onto dolomite particles. Additionally, Figure 15C seems to indicate that the flocculation of the illite-dolomite mixture is predominantly by flocculating illite and may be selective. The PAM flocculant, in comparison with PEO, appears to be less selective and flocculates very well both tested minerals (including the mixture). It flocculates dolomite better than illite. Both minerals flocculate better in alkaline solutions and exhibit less efficient flocculation at pH 6.5; thus, the illite-dolomite mixture presents the same effect as the individual mineral suspensions. In general, dolomite suspensions are less stable than illite and it is confirmed via electrokinetic measurements and coagulation tests; however, their higher stability in 1M NaCl solutions cannot be explained at this stage. It is difficult—in both tested cases with PAM and PEO—to determine any relationship between coagulation and flocculation. 47 6. Recommendations for future work A. The work presented in this thesis should be extended to include high quality illite samples. B. The experiment revealed one case: i) with the use of PEO, dolomite suspensions did not flocculate at all, illite suspensions did, and the dolomite-illite mixture seemed to be flocculating selectively. This system should be studied further as this may provide a new insight into the mechanism of selective flocculation. C. Turbidity measurements should be included in the tests as this may be very useful in following the selective flocculation cases. 48 Bibliography Addai-Mensah, J. (2007). Enhanced flocculation and dewatering of clay mineral dispersions. Powder Technology, 179(1–2), 73–78. https://doi.org/10.1016/j.powtec.2006.11.008 Andreola, F., Castellini, E., Ferreira, J. M. F., Olhero, S., & Romagnoli, M. (2006). Effect of sodium hexametaphosphate and ageing on the rheological behaviour of kaolin dispersions. Applied Clay Science, 31(1–2), 56–64. https://doi.org/10.1016/j.clay.2005.08.004 Arinaitwe, E. (2008). Characterization of Industrial Flocculants Through Intrinsic Viscosity Measurements. MASc Thesis, The University of British Columbia, Canada. https://doi.org/10.14288/1.0066521 Arinaitwe, E., & Pawlik, M. (2009). A method for measuring the degree of anionicity of polyacrylamide-based flocculants. International Journal of Mineral Processing, 91(1–2), 50–54. https://doi.org/10.1016/j.minpro.2008.12.002 Arinaitwe, E., & Pawlik, M. (2013). A role of flocculant chain flexibility in flocculation of fine quartz . Part I . Intrinsic viscosities of polyacrylamide-based flocculants. International Journal of Mineral Processing, 124, 50–57. Attia, Y. A. (1992). Flocculation. In J. S. Laskowski & J. Ralston (Eds.), Colloid chemistry in mineral processing (pp. 277–308). Elsevier Science Publishers B.V. Burdukova, E., Becker, M., Bradshaw, D. J., & Laskowski, J. S. (2007). Presence of negative charge on the basal planes of New York talc. Journal of Colloid and Interface Science, 315(1), 337–342. https://doi.org/10.1016/j.jcis.2007.06.067 Castro, S., & Laskowski, J. S. (2011). Froth flotation in saline water. KONA, 29(29), 4–15. Castro, S., Venegas, I., Landero, A., & Laskowski, J. (2010). Frothing in seawater flotation systems. XXV International Mineral Processing Congress 2010, IMPC 2010, 5(September), 4039–4047. Ding, K., & Laskowski, J. S. (2006). Application of a Modified Water Glass in a Cationic Flotation of Calcite and Dolomite. Canadian Metallurgical Quarterly, 45(2), 199–206. https://doi.org/10.1179/cmq.2006.45.2.199 Fedors, R. F. (1979). An equation suitable for describing the viscosity of dilute to moderately concentrated polymer solutions. Polymer, 20(2), 225–228. https://doi.org/10.1016/0032-3861(79)90226-X Ferrera, V., Arinaitwe, E., & Pawlik, M. (2009). A Role of Flocculant Conformation in the Flocculation Process. In C. O. Gomez, J. E. Nesset, & S. R. Rao (Eds.), Proceedings of the 7th UBC-McGill-UA Symposium on Fundamentals of Mineral Processing (pp. 397–408). Montreal. Friend, J. P., & Kitchener, J. A. (1973). Some physico-chemical aspects of the separation of 49 finely-divided minerals by selective flocculation. Chemical Engineering Science, 28(4), 1071–1080. https://doi.org/10.1016/0009-2509(73)80010-7 Fuerstenau, D. W., & Huang, P. (2003). Interfacial phenomena involved in talc flotation and depression. In XXII International Mineral Processing Congress (pp. 1034–1043). Gence, N., & Ozbay, N. (2006). pH dependence of electrokinetic behavior of dolomite and magnesite in aqueous electrolyte solutions. Applied Surface Science, 252(23), 8057–8061. https://doi.org/10.1016/j.apsusc.2005.10.015 Ghimici, L., & Popescu, F. (1998). Determination of intrinsic viscosity for some cationic polyelectrolytes by Fedors method. European Polymer Journal, 34(1), 13–16. https://doi.org/10.1016/S0014-3057(97)00072-4 Gochin, R. J., Leklll, M., & Shergold, H. L. (1985). The mechanism of flocculation of coal particles by polyethyleneoxide. Coal Preparation, 2(May 2012), 19–33. https://doi.org/10.1080/07349348508905150 Gupta, V., & Miller, J. D. (2010). Surface force measurements at the basal planes of ordered kaolinite particles. Journal of Colloid and Interface Science, 344(2), 362–371. https://doi.org/10.1016/j.jcis.2010.01.012 Hogg, R. (1987). Flotation in highly concentrated electrolyte solutions/seawater. In Fine Coal Processing. Noyes Publications. Hogg, R. (1999). Polymer adsorption and flocculation. In J. S. Laskowski (Ed.), Polymers in Mineral Processing - Proc. of the Third UBC-McGill International Symposium on Fundamentals of Mineral Processing (pp. 3–18). Quebec City: Metallurgical Society of CIM. Hogg, R. (2000). Flocculation and dewatering. International Journal of Mineral Processing, 58(1–4), 223–236. https://doi.org/10.1016/S0301-7516(99)00023-X Holthoff, H., Egelhaaf, S. U., Borkovec, M., Schurtenberger, P., & Sticher, H. (1996). Coagulation Rate Measurements of Colloidal Particles by Simultaneous Static and Dynamic Light Scattering. Langmuir, 12(23), 5541–5549. https://doi.org/10.1021/la960326e Huang, P., Laskowski, J. S., Zeng, H., & Lu, Q. (2013). Use of Flocculants in High Ionic Strength Process Waters. In 9th UBC-McGill-UA Int. Symposium. Huggins, M. L. (1942). The Viscosity of Dilute Solutions of Long-Chain Molecules. IV. Dependence on Concentration. Journal of the American Chemical Society, 64(11), 2716–2718. https://doi.org/10.1021/ja01263a056 Johnson, S. B., Franks, G. V., Scales, P. J., Boger, D. V., & Healy, T. W. (2000). Surface chemistry-rheology relationships in concentrated mineral suspensions. International Journal of Mineral Processing, 58(1–4), 267–304. https://doi.org/10.1016/S0301-7516(99)00041-1 Kasha, A., Al-Hashim, H., Abdallah, W., Taherian, R., & Sauerer, B. (2015). Effect of Ca2+, Mg2+ and SO<inf>4</inf>2- ions on the zeta potential of calcite and dolomite particles 50 aged with stearic acid. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 482, 290–299. https://doi.org/10.1016/j.colsurfa.2015.05.043 Kitchener, J. A. (1972). Principles of Action of Polymeric Flocculants. British Polymer Journal, 4(September 1971), 217–229. https://doi.org/10.1002/pi.4980040307 Kulicke, W.-M., & Clasen, C. (2004). Viscosimetry of Polymers and Polyelectrolytes. https://doi.org/10.1002/pi.1722 Kulicke, W.-M., Kniewske, R., & Klein, J. (1982). Preparation, characterization, solution properties and rheological behaviour of polyacrylamide. Progress in Polymer Science, 8, 373–468. Laskowski, J., & Castro, S. (2015). Flotation in concentrated electrolyte solutions. International Journal of Mineral Processing, 144, 50–55. https://doi.org/10.1016/j.minpro.2015.09.017 Laskowski, J. S. (2001). Particle Size Enlargement. Coal Flotation and Fine Coal Utilization. Elsevier Science B.V. Laskowski, J. S. (2012). Anisotropic minerals in flotation circuits. CIM Journal, 3(4), 203–214. Laskowski, J. S. (2016). High electrolyte concentration process water in mineral processing circuits. In II International Congress of Mineral Flotation. Lima. Laskowski, J. S., Castro, S., & Gutierrez, L. (2018). Flotation in highly concentrated electrolyte solutions/seawater. In 29th Int. Mineral Processing Congress. Moscow: Submitted. Lide, D. R. (2007). CRC Handbook of Chemistry and Physics (88th ed.). CRC Press. https://doi.org/10.4324/9781410610348 Liu, Y., & Liu, Q. (2004). Flotation separation of carbonate from sulfide minerals, II: Mechanisms of flotation depression of sulfide minerals by thioglycollic acid and citric acid. Minerals Engineering, 17(7–8), 865–878. https://doi.org/10.1016/j.mineng.2004.03.007 Ma, X., & Pawlik, M. (2007). Adsorption of Guar Gum on Potash Slimes. Canadian Metallurgical Quarterly, 46(3), 321–327. https://doi.org/10.1179/cmq.2007.46.3.321 Marouf, R., Marouf-Khelifa, K., Schott, J., & Khelifa, A. (2009). Zeta potential study of thermally treated dolomite samples in electrolyte solutions. Microporous and Mesoporous Materials, 122(1–3), 99–104. https://doi.org/10.1016/j.micromeso.2009.02.021 Mathur, S., & Moudgil, B. (1998). Mechanisms of nonionic polymer adsorption on oxide surfaces. Minerals & Metallurgical Processing, 15(2), 24–28. Retrieved from http://apps.webofknowledge.com/full_record.do?product=UA&search_mode=CitingArticles&qid=14&SID=S2LFwYXFsCbLPtiwfIh&page=6&doc=55 Mewis, J., & Wagner, N. J. (2012). Colloidal Suspension Rheology. Cambridge University 51 Press. Michaels, A. S. (1954). Aggregation of Suspensions by Poly electrolytes. Industrial and Engnineering Chemistry, 46(7), 1485–1490. https://doi.org/10.1021/ie50538a053 Moudgil, B. M., & Chanchani, R. (1985). Flotation of Apatite and Dolomite Using Sodium Oleate As the Collector. Transactions of the American Institute of Mining, Metallurgical, and Petroleum Engineers, 278(March 1983), 13–19. Moudgil, B. M., Mathur, S., & Behl, S. (1995). Flocculation behavior of dolomite with poly(ethylene oxide). Minerals and Metallurgical Processing, 12(4), 219–224. Moudgil, B. M., Mathur, S., & Hehl, S. (1995). Dolomite-dolomite separation by a selective flocculation technique. Minerals and Metallurgical Processing, 24–27. Mpofu, P., Addai-mensah, J., & Ralston, J. (2003). Investigation of the effect of polymer structure type on flocculation , rheology and dewatering behaviour of kaolinite dispersions. International Journal of Mineral Processing, 71, 247–268. https://doi.org/10.1016/S0301-7516(03)00062-0 Mpofu, P., Addai-Mensah, J., & Ralston, J. (2004). Temperature influence of nonionic polyethylene oxide and anionic polyacrylamide on flocculation and dewatering behavior of kaolinite dispersions. Journal of Colloid and Interface Science, 271(1), 145–156. https://doi.org/10.1016/j.jcis.2003.09.042 Napper, D. H. (1977). Steric stabilization. Journal of Colloid And Interface Science, 58(2), 390–407. https://doi.org/10.1016/0021-9797(77)90150-3 Nasser, M. S., & James, A. E. (2006). The effect of polyacrylamide charge density and molecular weight on the flocculation and sedimentation behaviour of kaolinite suspensions. Separation and Purification Technology, 52(2), 241–252. https://doi.org/10.1016/j.seppur.2006.04.005 Onen, V., & Gocer, M. (2018). The effect of single and combined coagulation / flocculation methods on the sedimentation behavior and conductivity of bentonite suspensions with different swelling potentials. Particulate Science and Technology, 0(0), 1–8. https://doi.org/10.1080/02726351.2018.1454993 Ozdemir, O. (2013). Specific ion effect of chloride salts on collectorless flotation of coal. Physicochemical Problems of Mineral Processing, 49(2), 511–524. https://doi.org/10.5277/ppmp130212 Pawlik, M., & Laskowski, J. S. (2006). Stabilization of Mineral Suspensions by Guar Gum in Potash Ore Flotation Systems. Canadian Journal of Chemical Engineering, 84(5), 532–538. Pawlik, M., Laskowski, J. S., & Ansari, A. (2003). Effect of carboxymethyl cellulose and ionic strength on stability of mineral suspensions in potash ore flotation systems. Journal of Colloid and Interface Science, 260(2), 251–258. https://doi.org/10.1016/S0021-9797(02)00225-4 Pokrovsky, O. S., Schott, J., & Thomas, F. (1999). Dolomite surface speciation and reactivity 52 in aquatic systems. Geochimica et Cosmochimica Acta, 63(19–20), 3133–3143. https://doi.org/10.1016/S0016-7037(99)00240-9 Pugh, B. R. J. (1974). Selective coagulation in quartz-hematite and quartz-rutile suspensions. Colloid and Polymer Science, 252(5), 400–406. Ramirez, A., Rojas, A., Gutierrez, L., & Laskowski, J. S. (2018). Sodium hexametaphosphate and sodium silicate as dispersants to reduce the negative e ff ect of kaolinite on the fl otation of chalcopyrite in seawater. Minerals Engineering, 125(November 2017), 10–14. https://doi.org/10.1016/j.mineng.2018.05.008 Rao, M. V. S. (1993). Viscosity of dilute to moderately concentrated polymer solutions. Polymer, 34(3), 592–596. https://doi.org/10.1016/0032-3861(93)90555-O Ross, S. M. (2014). Introduction to probability and statistics for engineers and scientists. Academic Press. Rubio, J. (1981). The flocculation properties of poly (ethylene oxide). Colloids and Surfaces, 3(1), 79–95. https://doi.org/10.1016/0166-6622(81)80035-2 Rubio, J., & Kitchener, J. A. (1976). The mechanism of adsorption of poly(ethylene oxide) flocculant on silica. Journal of Colloid And Interface Science, 57(1), 132–142. https://doi.org/10.1016/0021-9797(76)90182-X Sakai, T. (1968). Huggins Constant k’ for Flexible Chain Polymers. Journal of Polymer Science, 6, 1535–1549. Scheiner, B. J., & Wilemon, G. M. (1987). Applied flocculation efficiency: a comparison of polyethylene oxide and polyacrylamides. In Y. A. Attia (Ed.), Flocculation in Biotechnology and Separation Systems (Vol. 4, pp. 175–185). Amsterdam: Elsevier Science Publishers B.V. Slater, R. W., & Kitchener, J. A. (1966). Characteristics of flocculation of mineral suspensions by polymers. Discussions of the Faraday Society, 42, 267. https://doi.org/10.1039/df9664200267 Somasundaran, P., & Agar, G. E. E. (1967). The zero point of charge of calcite. Journal of Colloid and Interface Science, 24(4), 433–440. https://doi.org/10.1016/0021-9797(67)90241-X. Sworska, A., Laskowski, J. S., & Cymerman, G. (2000). Flocculation of the Syncrude fine tailings Part I. Effect of pH, polymer dosage and Mg2+ and Ca2+ cations. International Journal of Mineral Processing, 60(2), 143–152. https://doi.org/10.1016/S0301-7516(00)00012-0 Tombácz, E., & Szekeres, M. (2006). Surface charge heterogeneity of kaolinite in aqueous suspension in comparison with montmorillonite. Applied Clay Science, 34(1–4), 105–124. https://doi.org/10.1016/j.clay.2006.05.009 Wan, J., & Tokunaga, T. K. (2002). Partitioning of clay colloids at air-water interfaces. Journal of Colloid and Interface Science, 247(1), 54–61. https://doi.org/10.1006/jcis.2001.8132 53 Yousef, A. A., Arafa, M. A., Ibrahim, S. S., & Abdel Khalek, M. A. (2003). Seawater Usage in Flotation for Mnerals Beneficiation in Arid Regions (Arab Countries) (Simulation and Application). In XXII International Mineral Processing Congress (pp. 1023–1033). Cape Town. Yu, K. (2015). Lab report: Flocculation with the use of polyacrylamide as a flocculant in NaCl solutions. In Mining Engineering Department, UBC. 54 Appendix I: Glassware cleaning method Nitric acid and ethanol together produce strong fumes capable of removing any organics in the glassware. Due to the explosion hazard, mix very small amounts. Procedure: 1. Wear full face shield. Either use good gloves or have wet hands and arms and frequently wash them. Work in a properly ventilated fume hood. 2. Pour 2-3 mL of concentrated nitric acid into glassware. 3. Add 3-4 drops of concentrated ethanol. 4. Leave to stand until brown fumes have been generated and completely disappear. 5. Rinse glassware well with copious distilled water (avoid the use of soap). Note: In case of accidental spattering, remove contaminated clothing and rinse affected area thoroughly for 10 minutes. Get medical attention if necessary. 55 Appendix II: Quantitative phase analysis of two powder samples using the Rietveld method and x-ray powder diffraction data Experimental method The samples were reduced to the optimum grain-size range for quantitative X-ray analysis (<10 m) by grinding under ethanol in a vibratory McCrone Micronizing Mill for 10 minutes. Step-scan X-ray powder-diffraction data were collected over a range 3-80°2 with CoKα radiation on a Bruker D8 Advance Bragg-Brentano diffractometer equipped with an Fe monochromator foil, 0.6 mm (0.3°) divergence slit, incident- and diffracted-beam Soller slits and a LynxEye-XE detector. The long fine-focus Co X-ray tube was operated at 35 kV and 40 mA, using a take-off angle of 6°. Results The X-ray diffractogram was analyzed using the International Centre for Diffraction Database PDF-4 using Search-Match software by Bruker. X-ray powder-diffraction data of the samples were refined with Rietveld program Topas 4.2 (Bruker AXS). The results of quantitative phase analysis by Rietveld refinements are given in Table 2. These amounts represent the relative amounts of crystalline phases normalized to 100%. The Rietveld refinement plots are shown below. For the Illite Shale sample, the illite/muscovite phases are structurally disordered which hamper fitting the peaks. Also, the X-ray pattern for this sample (Figure 22) shows the 56 presence of some amorphous or nanoscale material that was accounted for by fitting the pattern with a broad calculated peak at about 31º2θ. Also, note that the X-ray pattern for the Dolomite sample shows a broad peak from unknown clay minerals (see hump at about 5-10º2θ in Figure 23). Therefore, all the results should be considered approximate. 57 Figure 22. Rietveld refinement plot of sample Illite Shale (blue line - observed intensity at each step; red line - calculated pattern; solid grey line below - difference between observed and calculated intensities; vertical bars - positions of all Bragg reflections). Coloured lines are individual diffraction patterns of all phases. 2Th Degrees8075706560555045403530252015105Sqrt(Counts)1501005001JM_Illite Shale.raw Quartz low 24.20 %Dolomite 3.67 %Illite/Muscovite 1M 10.46 %Rutile 0.55 %Pyrite 0.69 %Clinochlore IIb-4 68942 2.37 %Illite/Muscovite 2M1 56.34 %Kaolinite 1A 1.30 %Anatase 0.41 %58 Figure 23. Rietveld refinement plot of sample Dolomite (blue line - observed intensity at each step; red line - calculated pattern; solid grey line below - difference between observed and calculated intensities; vertical bars - positions of all Bragg reflections). Coloured lines are individual diffraction patterns of all phases. 2Th Degrees8075706560555045403530252015105Sqrt(Counts)1501005002JM_Dolomite.raw Dolomite 99.09 %Quartz low 0.91 %59 Appendix III: Viscosity data of PEO and PAM in distilled water, 0.01 M NaCl and 1 M NaCl solutions at different pH and at 25 °C. Polyethylene oxide flocculant, natural pH (5.4-6.1) Table 4 Viscosity data of PEO in different background solutions at natural pH and 25 °C. Distilled water Concentration [g/dL] Kinematic viscosity [mm2/s] Relative viscosity Specific viscosity Reduced viscosity [dL/g] 0.0258 1.20 1.35 0.35 13.49 0.0230 1.16 1.30 0.30 13.09 0.0201 1.12 1.26 0.26 13.00 0.0171 1.09 1.22 0.22 12.81 0.0146 1.06 1.19 0.19 13.03 0.01 M NaCl Concentration [g/dL] Kinematic viscosity [mm2/s] Relative viscosity Specific viscosity Reduced viscosity [dL/g] 0.0258 1.24 1.39 0.39 15.22 0.0241 1.20 1.35 0.35 14.61 0.0200 1.15 1.29 0.29 14.40 0.0171 1.10 1.24 0.24 14.03 0.0145 1.07 1.20 0.20 13.61 1 M NaCl Concentration [g/dL] Kinematic viscosity [mm2/s] Relative viscosity Specific viscosity Reduced viscosity [dL/g] 0.0267 1.28 1.43 0.43 16.26 0.0238 1.23 1.38 0.38 15.95 0.0207 1.18 1.33 0.33 15.92 0.0178 1.14 1.29 0.29 16.06 0.0149 1.11 1.24 0.24 16.17 60 Polyethylene oxide flocculant, pH 10.5-11.1 Table 5 Viscosity data of PEO in different background solutions at pH 11 and 25 °C. Distilled water Concentration [g/dL] Kinematic viscosity [mm2/s] Relative viscosity Specific viscosity Reduced viscosity [dL/g] 0.0259 1.20 1.35 0.35 13.58 0.0229 1.16 1.30 0.30 13.28 0.0201 1.13 1.27 0.27 13.29 0.0172 1.09 1.22 0.22 12.99 0.0144 1.05 1.18 0.18 12.50 0.01 M NaCl Concentration [g/dL] Kinematic viscosity [mm2/s] Relative viscosity Specific viscosity Reduced viscosity [dL/g] 0.0258 1.23 1.38 0.38 14.59 0.0231 1.18 1.33 0.33 14.09 0.0202 1.14 1.28 0.28 13.94 0.0172 1.10 1.23 0.23 13.66 0.0143 1.06 1.19 0.19 13.01 1 M NaCl Concentration [g/dL] Kinematic viscosity [mm2/s] Relative viscosity Specific viscosity Reduced viscosity [dL/g] 0.0267 1.26 1.42 0.42 15.72 0.0237 1.22 1.37 0.37 15.55 0.0207 1.18 1.32 0.32 15.64 0.0178 1.14 1.28 0.28 15.64 0.0148 1.09 1.23 0.23 15.55 61 Polyacrylamide flocculant, natural pH (4.8-6.1) Table 6 Viscosity data of PAM in different background solutions at natural pH and 25 °C. Distilled water Concentration [g/dL] Kinematic viscosity [mm2/s] Relative viscosity Specific viscosity Reduced viscosity [dL/g] 0.0115 2.07 2.33 1.33 115.66 0.0087 1.82 2.03 1.03 118.56 0.0057 1.54 1.73 0.73 128.18 0.0030 1.25 1.40 0.40 134.50 0.0014 1.07 1.20 0.20 143.24 0.01 M NaCl Concentration [g/dL] Kinematic viscosity [mm2/s] Relative viscosity Specific viscosity Reduced viscosity [dL/g] 0.0114 1.22 1.37 0.37 32.39 0.0087 1.13 1.27 0.27 30.36 0.0058 1.04 1.17 0.17 29.27 0.0030 0.96 1.07 0.07 25.00 0.0018 0.93 1.05 0.05 26.42 1 M NaCl Concentration [g/dL] Kinematic viscosity [mm2/s] Relative viscosity Specific viscosity Reduced viscosity [dL/g] 0.0119 1.06 1.19 0.19 15.83 0.0091 1.02 1.15 0.15 16.37 0.0060 0.99 1.12 0.12 19.48 0.0031 0.96 1.08 0.08 25.94 0.0016 0.95 1.06 0.06 40.95 62 Polyacrylamide flocculant, pH 10.5-10.9 Table 7 Viscosity data of PAM in different background solutions at pH 11 and 25 °C. Distilled water Concentration [g/dL] Kinematic viscosity [mm2/s] Relative viscosity Specific viscosity Reduced viscosity [dL/g] 0.0114 1.64 1.84 0.84 73.13 0.0087 1.43 1.60 0.60 69.15 0.0058 1.23 1.38 0.38 64.52 0.0031 1.08 1.22 0.22 68.76 0.0015 0.98 1.10 0.10 65.59 0.01 M NaCl Concentration [g/dL] Kinematic viscosity [mm2/s] Relative viscosity Specific viscosity Reduced viscosity [dL/g] 0.0115 1.20 1.35 0.35 30.07 0.0088 1.11 1.25 0.25 27.93 0.0060 1.04 1.16 0.16 27.24 0.0031 0.96 1.08 0.08 24.51 0.0016 0.92 1.04 0.04 22.19 1 M NaCl Concentration [g/dL] Kinematic viscosity [mm2/s] Relative viscosity Specific viscosity Reduced viscosity [dL/g] 0.0118 1.05 1.18 0.18 15.37 0.0089 1.02 1.14 0.14 16.02 0.0060 0.99 1.11 0.11 18.36 0.0030 0.96 1.08 0.08 26.97 0.0015 0.95 1.07 0.07 42.47 63 Figure 24. Fedors representation of viscosity data of polyacrylamide flocculant (PAM) and polyethylene oxide flocculant (PEO) in distilled water at 25 °C and varying pH. 64 Figure 25. Fedors representation of viscosity data of polyacrylamide flocculant (PAM) and polyethylene oxide flocculant (PEO) in 0.01 M NaCl solution at 25 °C and varying pH. 65 Figure 26. Fedors representation of viscosity data of polyacrylamide flocculant (PAM) and polyethylene oxide flocculant (PEO) in 1 M NaCl solution at 25 °C and varying pH. 66 Appendix IV: Intrinsic Viscosities of PEO and PAM in distilled water, 0.01 M NaCl and 1 M NaCl solutions at different pH and at 25 °C. Table 8 and Table 9 show intrinsic viscosity data of the two tested flocculants obtained from Fedors representation of viscosity data of PEO and PAM presented in Figure 24, Figure 25 and Figure 26. Table 8 Intrinsic viscosity data of PEO in different background solutions at natural pH and pH 11 and at 25 °C. Natural pH (5.4-6.1) pH 11 Background solution Intrinsic viscosity [dL/g] Background solution Intrinsic viscosity [dL/g] Distilled water 12.44 Distilled water 11.42 0.01M NaCl 12.13 0.01M NaCl 11.57 1M NaCl 16.13 1M NaCl 15.37 Table 9 Intrinsic viscosity data of PAM in different background solutions at natural pH and pH 11 and at 25 °C. Natural pH (4.8-6.1) pH 11 Background solution Intrinsic viscosity [dL/g] Background solution Intrinsic viscosity [dL/g] Distilled water 147.22 Distilled water 64.92 0.01M NaCl 25.15 0.01M NaCl 21.21 1M NaCl 56.41 1M NaCl 60.95
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Mining Engineering
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Effect of electrolyte concentration in process water on flocculation
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