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The effects of polyacrylamide flocculants on sulphide flotation and flotation tailings Vreugde, Morris Johannes Aloysius 1973

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THE EFFECTS OF POLYACRYLAMIDE FLOCCULANTS ON SULPHIDE FLOTATION AND FLOTATION TAILINGS by MORRIS JOHN ALOYSIUS VREUGDE B.A.Sc., U n i v e r s i t y o f B r i t i s h C o l u m b i a , 1971 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE i n t h e Department o f MINERAL ENGINEERING We a c c e p t t h i s t h e s i s as c o n f o r m i n g t o t h e r e q u i r e d s t a n d a r d THE UNIVERSITY OF BRITISH COLUMBIA June, 1973 In p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t of the requirements f o r an advanced degree at the U n i v e r s i t y o f B r i t i s h Columbia, I agree t h a t the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and study. I f u r t h e r agree t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y purposes may be gran t e d by the Head o f my Department or by h i s r e p r e s e n t a t i v e s . I t i s understood t h a t c o p y i n g or p u b l i c a t i o n of t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l not be allowed without my w r i t t e n p e r m i s s i o n . Department o f MINERAL ENGINEERING The U n i v e r s i t y o f B r i t i s h Columbia Vancouver 8, Canada Date J IAME . Z S , fll 5 ( i ) ABSTRACT The r e l a t i v e e f f e c t i v e n e s s o f a n i o n i c and n o n i o n i c p o l y a c r y l a m i d e i n e n h a n c i n g t h e s e t t l i n g r a t e o f f l o t a t i o n t a i l i n g s was s t u d i e d by p e r f o r m i n g b a t c h s e t t l i n g t e s t s . A n i o n i c p o l y a c r y l a m i d e was found t o be more e f f e c t i v e t h a n n o n i o n i c p o l y a c r y l a m i d e . A l i q u i d f l o c c u l a n t was f o u n d t o g i v e l o w e r s e t t l i n g r a t e s t h a n d r y f l o c c u l a n t s due t o a l o w e r p o l y a c r y l a m i d e c o n t e n t . The a g i n g o f t a i l i n g s r e s u l t e d i n i n c r e a s e d s e t t l i n g r a t e s . R e s i d u a l p o l y a c r y l a m i d e was d e t e c t e d i n t h e s u p e r n a t a n t w a t e r even a t low f l o c c u l a n t a d d i t i o n r a t e s and r e a c h e d s i g n i f i c a n t c o n c e n t r a t i o n s b e f o r e t h e optimum a d d i t i o n r a t e was a t t a i n e d . The e f f e c t o f p o l y a c r y l a m i d e on f l o t a t i o n o f a copper-molybdenum o r e was i n v e s t i g a t e d i n a s e r i e s o f b a t c h f l o t a t i o n t e s t s . F l o c c u l a n t c o n c e n t r a t i o n s up t o 10 p a r t s p e r m i l l i o n d i d n o t l o w e r e i t h e r c o n c e n t r a t e grade or r e c o v e r y . The p r e s e n c e o f an o i l phase from t h e l i q u i d f l o c c u l a n t a l s o had no n o t i c e a b l e e f f e c t on f l o t a t i o n . ( i i ) TABLE OF CONTENTS Page CHAPTER.1. INTRODUCTION 1 1.1 The Problem o f M i n e r a l P r o c e s s i n g Wastewater .. < 1 1.2 P l a n t E x p e r i e n c e i n Use o f R e c l a i m Water 2 1.3 The Use o f A d d i t i v e s t o Enhance S o l i d -L i q u i d S e p a r a t i o n 7 1.4 The Use o f P o l y a c r y l a m i d e F l o c c u l a n t s i n S o l i d - L i q u i d S e p a r a t i o n 9 1.5 Mechanism o f P o l y a c r y l a m i d e A ttachment t o S o l i d s 12 1.6 S e l e c t i v e A c t i o n o f F l o c c u l a n t s 16 1.7 D e l e t e r i o u s E f f e c t s o f R e s i d u a l P o l y a c r y l a m i d e i n R e c l a i m Water 19 1.8 O b j e c t i v e s o f t h e R e s e a r c h Undertaken ... 22 1.9 Summary o f F i n d i n g s 2k CHAPTER 2. EXPERIMENTAL MATERIALS 25 2.1 F l o c c u l a n t s 25 2.2 Ore Used i n F l o t a t i o n S t u d i e s 25 2.3 C o n c e n t r a t o r T a i l i n g s 26 2.4- Seawater 28 CHAPTER 3; EXPERIMENTAL AND ANALYTICAL PROCEDURES .. 29 3.1 G r i n d i n g 29 3.2 F l o t a t i o n 29 ( i i i ) Page 3.3 Size Analysis ....... ..«..<,...... 29 3.3.1 Coulter Counter 30 3.4 S e t t l i n g Tests 32 3.5 Zeta P o t e n t i a l 32 3.6 Residual Flocculant Determination ........ 33 3.7 Chemical Analysis o . . . 37 CHAPTER 4. RESULTS 38 4.1 S e t t l i n g Tests 38 4.1.1 Comparative S e t t l i n g Tests 38 4.1.2 Residual Polyacrylamide i n Supernatant Water 45 4.2 F l o t a t i o n Tests 50 CHAPTER 5, 5.1 5.2 5.3 DISCUSSION 62 Comparative Evaluation of Flocculants .... 62 Residual Polyacrylamide i n Supernatant Water 6 4 E f f e c t of Residual Flocculants on F l o t a t i o n 6 6 5.3.I E f f e c t of Flocculant Impurities on F l o t a t i o n 68 SUMMARY AND CONCLUSIONS 69 BIBLIOGRAPHY . . 71 APPENDIX I 75 APPENDIX II 76 APPENDIX III 77 (iv) LIST OF TABLES Table Page 1 S e l e c t i v e F l o c c u l a t i o n Separations of Various Mineral Mixtures 18 2 Flocculants Employed f o r Testwork 25 3 Ionic Composition of Synthetic Seawater .... 28 k V a r i a t i o n of S e t t l i n g Rate and Residual Flocculant Concentration with Nalco 8863 Addition 50 5 Results of Fresh Water F l o t a t i o n Tests ..... 51 6. Results of Tests Employing Reclaim Water from T a i l i n g s Settled with Various Superfloc 21k Additions 53 7 Results of Tests Employing Controlled Superfloc 21^  Additions to Grind 55 8 Results of Tests Employing Controlled Superfloc 21^  Additions to Grind and to Make-up Water 57 9 Results of Five Cycle F l o t a t i o n Test Using Nalco 8863 f o r S e t t l i n g of T a i l i n g s .. 60 (v) LIST OF FIGURES Figure Page 1 Structure of Polyacrylamide .«..«..... 10 2 E f f e c t of Polymer Molecular Weight on S e t t l i n g Rate 11 3 Model of S i l i c a Surface 13 4 Occurrence of Polymer on S o l i d and i n Solution 20 5 Size Analysis of Concentrator T a i l i n g s ..... 27 6 Elements of E l e c t r i c a l Zone Sensing P a r t i c l e Size Analyzer . . . . . » . o . • < > » . . • . 31 7 Turbidimetric T i t r a t i o n of 100 ml. 10 ppm Solution Superfloc 214 . 35 8 Batch S e t t l i n g Curves f o r T a i l i n g s with Flocculant Additions 40 9 Batch S e t t l i n g Curves f o r Comparison of Flocculants 42 10 Batch S e t t l i n g Curves with Constant Additions to Observe Aging of Pulp ......... 44 11 V a r i a t i o n of S e t t l i n g Rate and Residual Flocculant Concentration with Superfloc 214 Addition 47 12 Tests with Superfloc 214 Additions i n Progress 49 ( v i ) ACKNOWLEDGEMENTS The c o n t i n u e d a d v i c e and s u p p o r t o f Dr. G. W. P o l i n g i s g r a t e f u l l y acknowledged. A p p r e c i a t i o n i s e x p r e s s e d t o th e Department o f Energy, Mines and R e s o u r c e s f o r f i n a n c i a l s u p p o r t and t o I s l a n d Copper L t d . f o r s u p p l y i n g t h e t a i l i n g s and o re samples. A p p r e c i a t i o n i s a l s o e x p r e s s e d t o my w i f e f o r h e r c o n s t a n t encouragement and h e l p i n p r e p a r a t i o n o f t h i s t h e s i s . CHAPTER 1  INTRODUCTION 1*1 The Problem of Mineral Processing Wastewater. Concentrator t a i l i n g s are generally discharged to a na t u r a l l y occurring depression or s p e c i a l l y constructed t a i l i n g s pond. The residence time i n these ponds allows suspended material to s e t t l e out and e s s e n t i a l l y c l e a r water i s removed by decantation. The overflow i s either permitted to enter l o c a l waterways or i s reclaimed and reused i n the process. P r i o r to the recent increase i n environmental concern, the dissolved species i n water discharged to waterways were i n most cases not considered. The possible e f f e c t s of dissolved species, p a r t i c u l a r l y r e s i d u a l reagents, on the f l o t a t i o n process has necessitated that the occurrence of these dissolved species i n reclaim water be investigated. Increased l e g i s l a t i o n against the p o l l u t i o n of waterways (1, 2) has forced operators to monitor c l o s e l y the q u a l i t y of wastewater discharges. Oko (3) and Evans et a l (4) outline monitoring programs which have been implemented f o r t a i l i n g s discharges. Schmidt and Conn (5) and McArthur (6) outline studies which have been performed to elucidate the c h a r a c t e r i s t i c s of wastewaters r e s u l t i n g from mineral processing operations. Acid mine drainage and radioactive drainages have "been thoroughly studied, p a r t i c u l a r l y i n Ontario (7, 8). (2) Rivett and Oko (9) have summarized operations at Falconbridge's Moose Lake n e u t r a l i z a t i o n plant where wastewater has to be treated p r i o r to discharge. At the same time as being faced with increased l e g i s l a t i o n against p o l l u t i o n of waterways, the industry has encountered increasing water requirements and diminishing water supplies. The exp l o i t a t i o n of increasingly lower grade orebodies has necessitated the construction of plants capable of t r e a t i n g tens of thousands of tons per day. These operations commonly involve plant flows of tens of m i l l i o n s of gallons of water per day. Since water supplies are l i m i t e d , the increasing water requirements faced by the mining industry has made i t aware of the need f o r water conservation and has resulted i n considerable reuse of processing wastewaters (10). Recent examples are Brenda Mines Ltd., which treats 24,000 tons per day of copper-molybdenum ore and recycles 100 per cent of i t s process water (11), and the International Nickel Company of Canada at Sudbury, which uses 100 m i l l i o n gallons of reclaim water out of a t o t a l requirement of 133 m i l l i o n gallons of water per day (12). 1.2 Plant Experience i n Use of Reclaim Water. A recent survey by Pickett (13) gives figures f o r water reuse at a number of Canadian concentrators. The ( 3 ) operations surveyed dealt with a v a r i e t y of minerals and diverse flowsheets. While some operations s t i l l r e l y e n t i r e l y on fresh water, the majority use at l e a s t some recycled water. Many plants i n other countries as well as Canada have employed reclaim water f o r a number of years and a c e r t a i n amount of t h e i r experience with the use of reclaim water has been published. Shakhmatova (14) reported on the use of reclaim water i n p i l o t t e sts on a copper-lead-zinc-pyrite ore. Thickeners employing polyacrylamide additions to enhance s e t t l i n g were used to reclaim water from t a i l i n g s and concentrates. Reclaim water from each stage of the operation was reused only i n the same stage. He concludes that a t the same time as maintaining recovery and grade of each concentrate, a sub s t a n t i a l reduction i n reagent consumption was r e a l i z e d . Yonezawa ( 4 3 ) reported on a series of tests performed on a copper bearing i r o n sulphide ore to determine the e f f e c t of r e s i d u a l reagents i n reclaim water on f l o t a t i o n . He concludes that the use of reclaim water could r e s u l t i n lowered reagent additions being required with no apparent deleterious e f f e c t s on f l o t a t i o n . Browne and Butler (15) present a comprehensive report of the experience the International Nickel Company, (4) (INCO), at Sudbury has had with the use of reclaim water. This operation has employed reclaim water from thickeners and t a i l i n g s ponds since 1933 i n producing n i c k e l and copper concentrates. Their experience indicates that water reclaimed from t h e i r t a i l i n g s ponds has a s l i g h t l y a c i d i c pH. Minor quantities of sulphides are oxidized during f l o t a t i o n and are further oxidized i n the t a i l i n g s area according to the following equation i hydrolysis S 2 ° 3 > Sn°6 " > S3°6 — > H 2 S 0 4 1 " 1 Thiosulphate Polythionate T r i t h i o n a t e Sulphuric Acid This mechanism was proposed by Schmidt and Conn (5) i n t h e i r study of acid generation from mining operations. Laboratory tests by INCO have indicated that the use of reclaim water from t a i l i n g s would not impair the m e t a l l u r g i c a l performance of the plant. | I INCO*s experience also indicates that the maintenance i of c l e a r joverflow from thickeners i s imperative i f the water ! i s being reused i n the m i l l . The presence of slimes i n reclaim water i n h i b i t s d i f f e r e n t i a l f l o t a t i o n and may lower the met a l l u r g i c a l e f f i c i e n c y of the plant. Excessive suspended s o l i d s and the p r e c i p i t a t i o n of calcium carbonate - calcium sulphate may also r e s u l t i n water piping systems becoming r e s t r i c t e d by the formation of scale deposits. (5) The problem of carbonate p r e c i p i t a t e s i n reclaim water systems was studied by Beasley and McKinney (16). Carbon dioxide from the a i r dissolves i n water and leads to the formation of bicarbonate ion. The addition of lime i n the m i l l c i r c u i t to increase pH r e s u l t s i n the conversion of bicarbonate to carbonate HCO^" + OH ^ ± C0^ = + H 20 1-2 and also increases the Ca ion concentration r e s u l t i n g i n the p r e c i p i t a t i o n of calcium carbonate* C a + + + C 0 3 = CaCO^ 1-3 By the use of inorganic molecularly dehydrated phosphonates or organic phosphonates the problem of valve and pi p e l i n e r e s t r i c t i o n by p r e c i p i t a t e s can be l a r g e l y c o n t r o l l e d . The experiences of several operations i n the new lead b e l t of Southeast Missouri with the use of recycled m i l l water have been summarized by Sharp and C l i f f o r d (17) • They found l i t t l e basic information on the eff e c t s of reclaim water on f l o t a t i o n i n the l i t e r a t u r e . The major problems that these operations have experienced with the use of reclaim water have been associated with f r o t h i n g problems r e s u l t i n g from recycled f r o t h e r s . They have attempted to use chemical oxygen demand f o r monitoring the buildup of frother i n recycled water and (6) thereby regulate new froth e r additions. The control of f r o t h i n the c i r c u i t i s more d i f f i c u l t when using water reclaimed from the thickeners than from t a i l i n g s ponds. The t a i l i n g s ponds have s u f f i c i e n t residence time so that some degradation of frother i s able to take place. When using reclaim water from the thickeners, the plant can frequently be run with no make-up frother additions. Some of the lead b e l t ores contain considerable gangue sulphides such as marcasite. Oxidation of these sulphides i n the t a i l i n g s system can lead to high sulphate and ferrous i r o n concentrations. The buildup of ferrous i r o n may r e s u l t i n p r e c i p i t a t i o n of f e r r i c hydroxide on mineral surfaces, p a r t i c u l a r l y chalcopyrite, and thus impair f l o t a t i o n . Likewise, the high sulphate content may r e s u l t i n slime p r e c i p i t a t i o n on mineral surfaces thereby impairing f l o t a t i o n . The same authors also report on d i f f i c u l t y i n separating copper and lead due to the presence of o i l y substances. O i l can r e s u l t from s p i l l s within the mining area or from o i l y -type oxidation products of the chemicals used i n the m i l l i n g process. This type of o i l y material can r e a d i l y b u i l d up i n reclaim water, p a r t i c u l a r l y when employing thickeners to reclaim water from t a i l i n g s . (7) 1.3 The Use of Additives to Enhance S o l i d - L i q u i d Separation. Where thickeners are employed f o r reclaiming water from concentrates or t a i l i n g s , chemical additions are frequently made to give increased s e t t l i n g rates and to ensure a c l e a r overflow. In discussing the e f f e c t s of additives and the mechanisms by which they act, the d i v i s i o n s used by La Mer and Healy (18) w i l l be followed throughout t h i s t h e s i s : (a) "Coagulation - s h a l l r e f e r to those processes whereby c o l l o i d a l p a r t i c l e s are driven together p r i m a r i l y by a reduction of the repulsive p o t e n t i a l of the e l e c t r i c a l double layer, as suggested by Derjaguin, Landau, Verwey and Overbeek. " (b) "Flocculation - s h a l l be considered to be brought about by the action of materials of high molecular weight, (potato starch or p o l y e l e c t r o l y t e ) a c t i n g as l i n e a r polymers which bridge and thus unite the s o l i d p a r t i c l e s into a random structure that i s three dimensional, loose and porous. " (8) The most widely used coagulant i n mineral processing operations i s lime, added as Ca(0H) 2 or CaO. Adsorption of the divalent calcium cation on mineral surfaces decreases the zeta p o t e n t i a l of the p a r t i c l e s and r e s u l t s i n coagulation. A paper by Mackenzie ( 1 9 ) reviews the concept of zeta p o t e n t i a l and i t s a p p l i c a t i o n to mineral processing operations. Other coagulants used are CaCl^ (21) and NaCl. Recently Poling (20) has used seawater additions to enhance s o l i d - l i q u i d separations. The f l o c c u l a n t s which found early use i n the mineral industry were potato s t a r c h p tapioca starch and corn starch. Alum (A1 2(S0^)^»18 HgO) was long believed to cause coagulation +3 through adsorption of the A l ion but was l a t e r recognized to b r i n g about f l o c c u l a t i o n through the formation of a long, often l i n e a r , A l hydroxide bridging complex. It appears l i k e l y that both charge n e u t r a l i z a t i o n and bridging play.a r o l e i n the formation of p a r t i c l e aggregates by A l + ^ additions. This mechanism i s discussed by La Mer (22) who also discusses the action of starches. The f l o c c u l a n t s which today are probably the most widely used i n the minerals industry are the synthetic p o l y e l e c t r o l y t e s , p a r t i c u l a r l y the polyacrylamides. (9) 1„4 The Use of Polyacrylamide Flocculants i n S o l i d -Liquid Separation. Polyacrylamide f l o c c u l a n t s have been widely used as s e t t l i n g aids i n mineral processing operations since the introduction of the Separan series of fl o c c u l a n t s i n the early 1950's. Figure 1 shows a s i m p l i f i e d molecular structure of polyacrylamide as well as the anionic and c a t i o n i c v a r i a t i o n s of the polyacrylamide type f l o c c u l a n t s . Polyacrylamide i s prepared by s o l u t i o n polymerization of acrylamide i n aqueous medium i n the presence of an i n i t i a t o r and a basic a c t i v a t o r (44). Anionic nature i s attained by copolymerizing acrylamide with a c r y l i c acid or by t r e a t i n g polyacrylamide with c a u s t i c . Cationic nature r e s u l t s from copolymerizing acrylamide with quaternary amines. Addition rates of these f l o c c u l a n t s vary from 0.0001 to 0.1 pounds of f l o c c u l a n t per ton of s o l i d s treated (23). McCarty and Olson (24) summarized early experience, within the mining industry, with the use of polyacrylamides. They give several examples of increased f i l t e r and thickener capacity brought about by the use of f l o c c u l a n t s but -also indicate that where fl o c c u l a n t s are added p r i o r to f l o t a t i o n , reductions i n concentrate grade or recovery may be encountered. They also discuss the proper manner of a p p l i c a t i o n of f l o c c u l a n t s to s l u r r i e s . (10) - CH - CH, - CH - CH, - CH - CH, -I * | * \ d CO CO CO I I I NHo NH0 NH0 (a) - CH - CH, - CH I 2 I CO CO I I NH„ . NH, CH2 "* CH — CH2 — CO I OH (b) - CH - CH 0 - CH. - CH, - CH - CH, -I CO I NH, CH, I 2 R-N-R 111 R-^Cl CO I NH, (c) Figure 1. Structure of (a) polyacrylamide (b) anionic polyacrylamide (c) c a t i o n i c polyacrylamide. (11) A comprehensive l i t e r a t u r e review by Warren Spring Laboratory (25) summarizes t h e o r e t i c a l considerations and p r a c t i c a l applications of organic polymers. 0.7 0.6 6 0.5 o E u UJ OA i 0.3 to 0.2 0.1 -* 5,000,000 1 / ^^M.W.'2,030,000. • 1 / / 1 / / '/ / M.W.'1,000,000 * -/i / <y r / / yJ / M.W \ b / -500.000 If/ II1 / 1 t 1 —1 1 1 i ! i 1 0 . 0.1 02 0.3 P O L Y M E R ADDED, L B S . / T O N Figure 2. E f f e c t of Polymer Molecular Weight on S e t t l i n g Rate. (26) 0.4 The increase i n s e t t l i n g rate attained with f l o c c u l a n t additions i s dependent on the molecular weight of the polymer as well as the additi o n rate. Factors such as degree of mixing and coagulant additions also play a r o l e i n the enhancement of s e t t l i n g rate with f l o c c u l a n t additions. Figure 2 presents the r e s u l t s of Linke and Booth (26) of (12) f l o c c u l a t i o n of s i l i c a by polyacrylamide. This figure also i l l u s t r a t e s the optimum addition rate of polymer, beyond which the s e t t l i n g rate decreases with further polymer addition. The optimum r a t i o corresponds to p a r t i a l surface coverage and further adsorption of polymer reduces the area a v a i l a b l e f o r multi-p a r t i c l e bridging. In the past, polyacrylamides have generally been introduced i n a powder form. D i f f i c u l t i e s were frequently encountered i n d i s s o l v i n g these polymers and undissolved lumps of the material resulted i n lowered e f f i c i e n c y when using these f l o c c u l a n t s . Polymers i n the l i q u i d form have recently been introduced and these promise to a l l e v i a t e the problem of f l o c c u l a n t mixing (27). The Alchem l i q u i d f l o c c u l a n t employs an a c t i v a t o r to disperse the polymer i n s o l u t i o n . 1.5 Mechanism of Polyacrylamide Attachment to S o l i d s . Linke and Booth (26) proposed three possible mechanisms by which polyacrylamide may attach to mineral surfaces: 1. Hydrogen bonding - between the hydrogen of the amide group and oxygen on the mineral surfaces. 2. S p e c i f i c , e l e c t r o s t a t i c site-bonding - between the carboxylate group i n anionic polyacrylamides and metal ions such as calcium i n the mineral l a t t i c e . (13) 3. Nonspecific, double layer i n t e r a c t i o n - which i s an e l e c t r o s t a t i c i n t e r a c t i o n due to d i s s i m i l a r charges on the polymer and mineral surface. Due to the high charge density on the polymer, i t w i l l displace simple s a l t ions and be highly e f f e c t i v e i n lowering the zeta p o t e n t i a l . Of the s o l i d s which are treated by polyacrylamides the greatest proportion consists of the plant t a i l i n g s which are mainly s i l i c a t e and alumi n o s i l i c a t e minerals. The fundamental study of polymer-mineral attachment has therefore been la r g e l y a study of the c l o s e l y s i m i l a r polymer-silica system. Fontana and Thomas (28) used infrared spectroscopy to study the adsorption of a l k y l methacrylate onto s i l i c a . They used the model depicted i n Figure 3 f o r the surface of the s i l i c a . Hydroxyl groups are covalently bonded to s i l i c o n , forming surface s i l a n o l groups. Use was made of a s h i f t i n the carbonyl frequency at 1740 cm"1 to determine adsorption by hydrogen bonding. H H H 0 0 0 - S i - 0 S i - 0 - S i - S i - 0 - S i -Figure 3« Model of S i l i c a Surface With Hydroxyl Groups, Both Free And Hydrogen Bonded. (14) Griot and Kitchener (29) studied the adsorption of polyacrylamide onto s i l i c a by i n f r a r e d techniques. Peaks at 339° cm"1 corresponding to hydrogen bonded OH groups and at 3642 cm"1 corresponding to free hydroxyl groups were observed. The disappearance of the 3642 band was associated with hydrogen bonding between polyacrylamide and surface s i l a n o l groups. The surface changes of s i l i c a on aging was also studied and i t was found that a f t e r long immersion i n water, s i l i c a l o s t i t s a b i l i t y to be f l o c c u l a t e d by polyacrylamide whereas the alumino-s i l i c a t e s , k a o l i n and bentonite, retained t h e i r capacity f o r polyacrylamide adsorption. I t was proposed that while the •Si - OH s i t e s on the s i l i c a surface disappear with time, due to surface hydration, the »A1 - OH groups remain a c t i v e . Michaels and Morelos (30) concluded that polyacrylamide adsorbed on k a o l i n i t e through hydrogen bonding between un-ionized carboxyl or amide groups on the polymer and oxygen at the mineral surface. At high pH where polymer adsorption by k a o l i n i t e does not occur, anionic p o l y e l e c t r o l y t e s can cause f l o c c u l a t i o n through reduction of zeta p o t e n t i a l of the clays. Iwasaki and Lipp (21) considered that c a t i o n i c polymers would be highly attracted to the negative s i l i c a surface but would not be stretched out enough f o r e f f e c t i v e polymer bridging. Calcium ion i n solution "activates" the quartz surface f o r adsorption of anionic polyacrylamides. ( 1 5 ) Adsorbed anionic polymer remains f u l l y stretched out and polymer bridging r e s u l t s even at low l e v e l s of addition. I l e r (41) also considered that p a r t i c u l a r l y f o r large p a r t i c l e s , c a t i o n i c polymers would l i e with t h e i r side groups on the s o l i d surfaces g i v i n g a high degree of surface coverage. The process whereby polyacrylamides ac|t to bring p a r t i c l e s together has been the source of considerable i disagreement. Kuzkin et a l ( 3 1 ) consider charge n e u t r a l i z a t i o n i to be the primary f a c t o r i n the a c t i o n of polymeric f l o c c u l a n t s . Healy ( 3 2 ) sought to r e l a t e v a r i a t i o n s i n zeta p o t e n t i a l to polymer adsorption on quartz and concluded that decreases i n zeta p o t e n t i a l were of secondary importance with the bridging mechanism being the more s i g n i f i c a n t feature. La Mer ( 3 3 ) also supports the b e l i e f that the bridging mechanism i s the main feature i n polymer f l o c c u l a t i o n . Gregory ( 3 4 ) , i n studying the f l o c c u l a t i o n of polystyrene p a r t i c l e s with c a t i o n i c poly-e l e c t r o l y t e s , concluded that low molecular weight polymer ( 1 . 5 -4v 2.5 x 10 ) was e f f e c t i v e mainly as a r e s u l t of charge neut r a l -i z a t i o n while polymer bridging i s the more s i g n i f i c a n t mechanism f o r high molecular weight f l o c c u l a n t (M.W. greater than 1 0 ^ ) . At present the bridging mechanism appears to be generally favoured as the primary f a c t o r i n f l o c c u l a t i o n with high molecular weight polymers. ( 1 6 ) To date, the majority of experimental work with polyacrylamide adsorption has involved s i l i c a or s i l i c a t e minerals. Read (35) however, has proposed that the adsorption of anionic polyacrylamide on hematite could involve carboxylate groups i n the f l o c c u l a n t and iron-hydroxy complexes on the hematite. In general however, the mechanism of i n t e r a c t i o n of polyacrylamides and heavy metal oxides and sulphides has received l i t t l e study. 1,6 Selective Action of Flocculants. The concept of s e l e c t i v e f l o c c u l a t i o n of minerals i n a s l u r r y was developed by the U.S. Bureau of Mines under the leadership of Frommer (36). He investigated the s e l e c t i v e f l o c c u l a t i o n of iron ore slimes, modified by additions of e l e c t r o l y t e and dispersant, by starches. Balajee and Iwasaki (37) studied the adsorption mechanism of starches on s i l i c a and on hematite. They concluded that adsorption occurred v i a e l e c t r o s t a t i c a t t r a c t i o n and hydrogen bonding and that s e l e c t i v i t y resulted from variations i n the electronegative character of starches and mineral surfaces. Yarar and Kitchener (38) present basic p r i n c i p l e s and an experimental i n v e s t i g a t i o n of s e l e c t i v e f l o c c u l a t i o n of quartz, c a l c i t e and galena by polyacrylamides. They note (17) that metal cations such as Ca , Cu , Co , Fe^ are capable of " a c t i v a t i n g " minerals i n a suspension so that the minerals are f l o c c u l a t e d under conditions when they normally would not be. A notable example i s the a c t i v a t i o n of s i l i c a by calcium so that i t i s f l o c c u l a t e d by both non-ionic and anionic polyacrylamide i n a l k a l i n e medium. They also show by zeta p o t e n t i a l studies that polyacrylamide i s removed from f l o c c u l a t e d galena by addition of Na 2S. A s i g n i f i c a n t feature which they observed was that when the major constituent was f l o c c u l a t e d , l i t t l e s e l e c t i v i t y was attained due to entrapment of the minor constituent within the f l o e s . Read (35) noted that depending on the anionic character of the polyacrylamide, hematite or s i l i c a could be s e l e c t i v e l y f l o c c u l a t e d . The s l u r r y was modified with additions of e l e c t r o l y t e and dispersant to enhance s e l e c t i v i t y . Considerable v a r i a t i o n i n s e l e c t i v i t y with hematite was observed from one grind to the next and was also impaired when minerals were ground together. Usoni et a l (39) investigated the s e l e c t i v i t y of several f l o c c u l a n t s including Separan NP 10, a polyacrylamide. Their study was performed on a v a r i e t y of minerals and i n additio n to determining the p o s s i b i l i t y of separation by s e l e c t i v e f l o c c u l a t i o n followed by sedimentation, they determined the (18) f l o t a t i o n behaviour of f i n e minerals i n the presence of fl o c c u l a n t s . They found that fl o c c u l a n t s did not a f f e c t the f l o t a t i o n behaviour of galena and p y r i t e either with regard to improving recovery or lowering i t , provided extremely high concentrations were not employed. The recovery of zinc minerals by f l o t a t i o n was improved by low additions of fl o c c u l a n t . When additions of f l o c c u l a n t exceeded 10 ppm to 100 ppm, recovery was diminished, p a r t i c u l a r l y with the higher molecular weight Separan NP 10. Their tests were performed with a low shear f l o t a t i o n device to prevent break up of the f l o e s . Selective flocculation of mineral A from Solids mixture v/ith mineral B Ancillary content A B Flocculant reagents 7. Hematite Silicate Strongly hydrolysed polyacrylamide Calgon+ NaFor NaCl 17 Silicate Hematite Weakly hydrolysed polyacrylamide Calgon + NaF or NaCl 11-22 Hematite Quartz Anionic starch or tapioca flour Sodium silicate Tetrasodium pyrophosphate 17 Dilatant Thixotropic Manno-galactan Calgon 25 clay clay . . Pyrite Quartz Polyacrylamide or polyacrylonitrile 4 Sphalerite Quartz Polyacrylamide or polyacrylonitrile 4 Smithsonite Quartz Polyacrylamide or polyacrylonitrile 4 Calcite Quartz Hydrolysed polyacrylamide 1-5 Galena Quartz Hydrolysed polyacrylamide 2-10 Galena Calcite Weakly hydrolysed polyacrylamide Na";S + sodium polyacrylate 5 Apatite Quartz clay Starch NaOH 5 Talc Pyrite Polyethylene Frother -. Limonite (+10/;m)J oxide Gangue Chromite Carboxymethyl NaOH, sodium . IS (unspecified) cellulose silicate Coal Shale Polyacrylamide (unspecified) Tetrasodium pyrophosphate + Ca salt Kaolin Unspecified impurity Polyacrylamide Ammonia, sodium hexametaphosphate 10 Table 1. Selec t i v e F l o c c u l a t i o n Separations of Various Mineral Mixtures (40). (19) Table 1 presents a summary prepared by Read and Whitehead (40) of s e l e c t i v e f l o c c u l a t i o n separations. The process used f o r separation i n the majority of cases involves a sedimentation operation although several f l o t a t i o n schemes have also been considered. The above investigations would seem to indicate that rather than being a natural feature of mineral suspensions, p a r t i c u l a r l y under normal f l o t a t i o n conditions, s e l e c t i v e f l o c c u l a t i o n can generally only be attained under controlled conditions. 1.7 Deleterious E f f e c t s of Residual Polyacrylamide In Reclaim Water. Although operators of mineral processing plants have at times indicated that r e s i d u a l f l o c c u l a n t i n reclaim water was adversely a f f e c t i n g plant e f f i c i e n c y , l i t t l e work has been performed to determine whether r e s i d u a l polyacrylamide was present i n reclaim water and i f so, what the e f f e c t on f l o t a t i o n would be. The r e s u l t s of Linke and Booth (26) presented i n Figure 4 indicate that r e s i d u a l polyacrylamide does not occur i n s o l u t i o n u n t i l the optimum r a t i o has been exceeded. The present range of economic usage i s i n general considerably (20) below the optimum r a t i o . Increasing competition i n the manufacture of polyacrylamide f l o c c u l a n t s could lead to lowered cost however, and r e s u l t i n higher addition rates. Linke and Booth observed that the degree of mixing affected the amount of polymer remaining i n s o l u t i o n . Their r e s u l t s are f o r a -325 mesh s i l i c a slime and comparable r e s u l t s f o r a coarser s i z e d i s t r i b u t i o n are not presented. O 2 4 6 8 10 T O T A L P O L Y M E R A D D E D , m g . / I O g m . S i 0 2 12 Figure 4. Occurrence of Polymer on S o l i d and i n Solution (26) . Dashed l i n e s indicate e f f e c t of increased a g i t a t i o n . (21) The r e l a t i o n of p a r t i c l e s i z e of s i l i c a to the amount of polymer required f o r f l o c c u l a t i o n and surface coverage was studied by I l e r (41). While s i l i c a with a diameter of 4 x 10"*-^  micron required 9.5 - 10.5$ polymer (percentage by weight of s o l i d polymer based on s i l i c a ) to fl o c c u l a t e a l l the s i l i c a present and 35 - 37-5$ polymer to saturate the s i l i c a surface, s i l i c a with a diameter of 0.22 micron required only 0.03 - 0.04$ polymer f o r complete f l o c c u l a t i o n and 0.2 - 0.3$ to saturate the surface. The assumption made i n saturation determinations i s that r e s i d u a l f l o c c u l a n t does not occur i n sol u t i o n u n t i l complete surface coverage has been achieved. Michaels and Morelos (30) determined that at maximum f l o c c u l a t i o n of k a o l i n i t e by polyacrylamide only 37$ of polymer added was adsorbed, Clement and Bahr (42) observed that when f l o a t i n g pure sph a l e r i t e (activated with CuSO^) increasing additions of separan led to decreasing recovery. At 50 mg./l. of Separan NP 10, recovery was e s s e n t i a l l y n i l . When 480 grams of gangue was added to 120 grams of sp h a l e r i t e , f l o c c u l a t e d with 50 mg./l. Separan NP 10 and conditioned 2 to 3 minutes, recovery was equal to that attained i n unflocculated material. They considered separan to be p r e f e r e n t i a l l y adsorbed on s i l i c a t e and gangue minerals even i f i t has f i r s t adsorbed on (22) sulphides. I t was proposed that when separan has adsorbed on sulphide mineral surfaces, xanthate adsorption i s decreased because s i t e s a v a i l a b l e f o r adsorption are decreased. 1.8 Objectives of the Research Undertaken.-The foregoing l i t e r a t u r e review indicates that polyacrylamide fl o c c u l a n t s have not been studied s p e c i f i c a l l y f o r t h e i r i n t e r a c t i o n with f l o t a t i o n t a i l i n g s . It has also revealed contradictions as to the occurrence of r e s i d u a l polyacrylamide i n supernatant water from s o l i d - l i q u i d separations enhanced by polyacrylamide additions. The effects of poly-acrylamides on f l o t a t i o n of sulphide minerals has not been extensively studied. Those references dealing with the problem of the e f f e c t of r e s i d u a l f l o c c u l a n t s i n reclaim water on f l o t a t i o n presented contradicting conclusions as to possible deleterious e f f e c t s . The aims of the work undertaken i n t h i s project weres to investigate the i n t e r a c t i o n of polyacrylamide and f l o t a t i o n t a i l i n g s , to determine whether r e s i d u a l polyacrylamide. could be expected i n reclaim water from t a i l i n g s thickeners and, to investigate the effects of r e s i d u a l polyacrylamide i n reclaimed water on the f l o t a t i o n of sulphide minerals. (23) The study was performed i n several stages t 1. Batch s e t t l i n g tests were performed on t a i l i n g s with various coagulant and f l o c c u l a n t additions to es t a b l i s h the s e t t l i n g behaviour of actual t a i l i n g s , as opposed to pure s i l i c a , with f l o c c u l a n t additions. Flocculants to be used i n further work were also selected during t h i s stage. 2. The occurrence of r e s i d u a l polyacrylamide i n reclaim water was determined by performing a se r i e s of batch s e t t l i n g t ests with increasing f l o c c u l a n t additions and analyzing the r e s u l t i n g supernatant water. 3. To determine v/hether r e s i d u a l polyacrylamide present i n reclaim water would a f f e c t the f l o t a t i o n of sulphides, a series of batch f l o t a t i o n t ests with f l o c c u l a n t additions were performed. A low grade disseminated - type copper-molybdenum ore was selected f o r the study so that entrap-ment of the sulphides as well as prevention of c o l l e c t o r adsorption by previously adsorbed polyacrylamide could be considered. 4. A t e s t c o n s i s t i n g of f i v e cycles of f l o t a t i o n with water reclaimed from the previous cycle was performed. The t a i l i n g s i n each case were s e t t l e d with additions of l i q u i d f l o c c u l a n t . The purpose of these tests was to determine whether the o i l phase present i n the l i q u i d f l o c c u l a n t would b u i l d up and have a deleterious e f f e c t on f l o t a t i o n . Possible (24) effects of the o i l phase were that the f r o t h could become unstable or that the o i l could carry slimes or polyacrylamide back from the thickener to the f l o t a t i o n c i r c u i t . 1.9 Summary of Findings. I t was found that anionic polyacrylamides gave greater s e t t l i n g rates with t a i l i n g s than non-ionic polyacrylamides. L i q u i d f l o c c u l a n t s gave lower s e t t l i n g rates than comparable dry f l o c c u l a n t s at equivalent addition rates due to a lower polyacrylamide content. The aging of t a i l i n g s was found to r e s u l t i n increased s e t t l i n g rates compared to fresh t a i l i n g s . Residual polyacrylamides were encountered i n the supernatant water of s e t t l i n g tests well before the optimum addition rate was attained. i The a d d i t i o n of polyacrylamides to f l o t a t i o n did not s i g n i f i c a n t l y a f f e c t e i t h e r concentrate grade or recovery. The o i l i n the l i q u i d f l o c c u l a n t was not observed to impair f l o t a t i o n with reclaimed water. (25) CHAPTER 2 EXPERIMENTAL MATERIALS 2.1 Flocculants* The f l o c c u l a n t s used i n t h i s study were commercially a v a i l a b l e f l o c c u l a n t s produced by Dow, Cyanaraid and Alchem. The various f l o c c u l a n t s employed are l i s t e d i n Table 2. Table 2. Flocculants Employed f o r Testwork. Designation Approx, Mole Wt. x 10° Description Superfloc 127 12-15 polyacrylamide 210 12-15 carboxylated polyacrylamide 214 12-15 highly carboxylated polyacrylamide 310 12-15 polyamine ( l i q u i d ) Nalco 4153 15 carboxylated polyacrylamide 8863 15 l i q u i d equivalent of 4153 S eparan NP 10 1 polyacrylamide 2.2 Ore Used i n F l o t a t i o n Studies. The ore used f o r f l o t a t i o n t ests was a s i l i c i f i e d andesite obtained from Island Copper Mines Ltd., on Vancouver Island. A quartz-monzonite porphyry ore from the same deposit was (26) employed i n preliminary work but was found to give inconsistent recoveries and concentrate grades due to excessive slime production during grinding. The andesite ore was found to contain approximately 0.5f° copper as disseminated chalcopyrite grains up to 0.5 mm i n s i z e and 0.013^ Mo as f i n e l y disseminated molybdenite. A trace of magnetite and up to several percent p y r i t e was present. 2.3 Concentrator T a i l i n g s . T a i l i n g s supplied by Island Copper Mines Ltd., were a i r freighted to the laboratory f o r study, but were at l e a s t several days old when used f o r testwork. The feed to the m i l l at the time the t a i l i n g s were taken consisted both of s i l i c i f i e d andesite and quartz-raonzonite porphyry. The s i z e analysis of t a i l i n g s used for the comparison of f l o c c u l a n t s i s shown i n Figure 5« The material consisted of rougher t a i l i n g s at pH = 10.4 I when shipped. The plant f l o t a t i o n was performed with xanthate j and f u e l joil additions and employed lime f o r adjusting pH. Analysis of the t a i l i n g s indicated approximately 0.1$ Cu and 4$ Fe, believed to be mainly present as sulphides. Concentrator t a i l i n g s were only used f o r evaluation of f l o c c u l a n t s . Laboratory produced t a i l i n g s were used f o r r e s i d u a l f l o c c u l a n t t e s t s . 1 0 0 CD z CO CO < Q_ z UJ o cc UJ CL u i > h-< O 6 0 0 PARTICLE SIZE (microns) Figure 5. Size Analysis of Concentrator T a i l i n g s . Screen Analysis Above 7^  Microns, Coulter Counter Below 7^  Microns. (28) 2.4 Seawater. Seawater employed i n the s e t t l i n g tests was synthetic seawater made with "Instant Ocean Synthetic Sea S a l t s " . The water was adjusted to a s a l i n i t y of Jkfio and had the io n i c composition given i n Table 3« Table 3. Ionic Composition of Synthetic Seawater (57) (parts per m i l l i o n ) C l 18400 Br 20 Rb .1 Na 10200 Sr 8 I .07 so^ 2500 S i 3 EDTA .05 Mg 1200 P°4 1 A l .04 K 370 Mn 1 Zn .02 Ca 370 MoO^ .7 V ,02 HCO-j 140 s2°3 .4 Co .01 H^BO^ 25 L i .2 Fe .01 Cu .003 (29) CHAPTER 3 EXPERIMENTAL AND ANALYTICAL PROCEDURES 3.1 Grinding. Grinding was performed i n a 10.1 inch by 11.4 inch s t e e l m i l l . The rod charge of 80 pounds s t e e l roils consisted of two 1 1/2 inch rods and the remainder 3/4 inchj rods. The ore charge consisted of 2500 grams minus 10 mesh material at 6ofo i s o l i d s by weight. The ore was ground f o r 20 minutes at 80% c r i t i c a l speed. An addition of 1.2 lbs./ton lime was made to the grind. 3.2 F l o t a t i o n . A 2000 gram A g i t a i r f l o t a t i o n c e l l was employed with an i n i t i a l pulp density of 34.8% s o l i d s by weight. F l o t a t i o n was performed with 0.004 lbs./ton potassium amyl xanthate and 0.02 lbs./ton Aerofroth 71. Lime was used to adjust pH. F l o t a t i o n was performed i n three stages and the concentrates were combined to form a bulk concentrate. 3.3 Size Analysis. A l l s i z e analyses were performed both wet and dry. The material was f i r s t washed on a 200 mesh (74 micron) screen (30) and the minus 200 mesh material was c o l l e c t e d and d r i e d . The plus 200 mesh material was dried and screened ©n a set of screens with a Ro-Tap. Where a s i z e analysis was d e s i r e d below 200 mesh, use was made of a Warman Cyclosizer which gave f i v e a d d i t i o n a l s i z e f r a c t i o n s down to 11 to 12 microns. In the case of the concentrator t a i l i n g s , a s i z e analysis below 10 microns was desired and a Coulter Counter was employed f o r t h i s purpose, 3.3.1 Coulter Counter. described by U l l r i c h ( 4 6 ) . The material to be analyzed i s placed as a \% suspension i n an e l e c t r o l y t e s o l u t i o n . The material i s agitated to prevent sedimentation and frequently a dispersing agent i s added as w e l l . An e l e c t r i c current between two chambers separated by an o r i f i c e i s monitored. As a unit volume of the suspension i s drawn from one chamber to the other, the resistance of the o r i f i c e i s changed by the p a r t i c l e s . The basic elements of the e l e c t r i c a l sensing zone are pictured i n Figure 6 . current through the o r i f i c e and t h i s i s detected. The r e l a t i o n between change i n resistance and p a r t i c l e volume i s as follows: The operation of the Coulter Counter has been The change i n resistance causes a pulse i n the AR = x 1 3-1 1- A (3D the e l e c t r o l y t e r e s i s t i v i t y V = the p a r t i c l e volume A = the o r i f i c e area normal to the axis ; = the e f f e c t i v e p a r t i c l e r e s i s t i v i t y a = projected area of p a r t i c l e Figure 6 . Elements of E l e c t r i c a l Zone Sensing P a r t i c l e Size Analyzer ( 4 6 ) . The s e n s i t i v i t y of the pulse-detection c i r c u i t i s gradually increased so that a cumulative count of p a r t i c l e s l a r g e r than a given s i z e i s made over the entire range covered by the instrument. The instrument i s c a l i b r a t e d with monodisperse p a r t i c l e s having a known volume. Accuracy i s maintained by using d i f f e r e n t sizes of aperture f o r d i f f e r e n t p a r t i c l e s i z e s . (32) 3A S e t t l i n g Tests. A l l s e t t l i n g tests were performed i n 1000 ml. stoppered graduated cyl i n d e r s . The t a i l i n g s s l u r r y was placed i n the cylinde r up to the 700 ml. mark. In the tests employing seawater additions, f i l t e r e d t a i l i n g s were employed and the volume was adjusted with the appropriate seawater and d i s t i l l e d water additions. Where pH adjustments were made, t h i s was done p r i o r to f l o c c u l a n t addition. The f l o c c u l a n t s were prepared as 0.1% stock solutions. The required amount f o r each te s t was then mixed with 300 ml. water. Flocculant additions were made to the t a i l i n g s s l u r r y i n three stages. Afte r each addition the cyl i n d e r was inverted s i x times to allow the f l o c c u l a n t and s o l i d s to i n t e r a c t . A f t e r the f i n a l addition and mixing, the column was turned upright and the rate of descent of the int e r f a c e between supernatant water and s l u r r y was recorded. * Where analysis of the supernatant was desired, a vacuum pump was used to draw o f f the water. 3.5 Zeta P o t e n t i a l . Electrophoretic mobility was determined with a Zeta-Meter. Zeta potentials were derived from electrophoretic data by the Helmholtz-Smoluchowski formula (ZP = 12.8 EM) (58). ( 3 3 ) 3.6 Residual Flocculant Determination.. The determination of r e s i d u a l polyacrylamide i n supernatant water i s based on the p r i n c i p l e that polyanions react with f a t t y cations or c a t i o n i c p o l y e l e c t r o l y t e s to produce insoluble complexes. The complexes remain c o l l o i d a l l y suspended i and give r i s e to t u r b i d i t y . Variations i n t u r b i d i t y are detected by l i g h t s c a t t e r i n g techniques and are r e l a t e d to polyacrylamide concentration. The i n t e r a c t i o n of p o l y e l e c t r o l y t e s was f i r s t discussed by Fuoss and Sadek (47) who studied the turbidimetric t i t r a t i o n of polyvinyl-butyl-pyridonium bromide with sodium polyacrylate. Michaels and Morelos ( 3 0 ) l a t e r used the same p r i n c i p l e to study the adsorption of p o l y e l e c t r o l y t e s on k a o l i n i t e . In the present study the r a t i o of 90° s c a t t e r i n g i n t e n s i t y to 0 ° , transmitted i n t e n s i t y was employed to detect variat i o n s i n complex concentration. P r i n c i p l e s governing the use of turbidimetric and nephelometric t i t r a t i o n s have been discussed by Meehan and Chiu (48) and by Hochgesang (49). A model 2000 Brice-Phoenix Light Scattering Photometer employing a 40 x 40 mm semi octagonal c e l l was used f o r the determinations. The operation of t h i s instrument i s described by Yang ( 5 0 ) . The s c a t t e r i n g r a t i o i s proportional to the (34) absolute t u r b i d i t y (X) according tot X = K 3-2 where G g/G w i s the observed r a t i o of galvanometer d e f l e c t i o n f o r l i g h t scattered at 90° to transmitted l i g h t at 0°, and K i s a constant depending on the geometry of the instrument. For the present determinations the machine constant K was ignored and a c a l i b r a t i o n curve f o r G /G,u versus f l o c c u l a n t concentration s w was employed. A blue f i l t e r was employed, g i v i n g l i g h t of wavelength 436 raju. The t i t r a t i o n curve f o r a 10 ppm s o l u t i o n of Superfloc 214 was prepared to determine the addition of t i t r a t i n g s o l u t i o n required f o r maximum s e n s i t i v i t y . A 1% s o l u t i o n of Superfloc 3 1 0 , a c a t i o n i c polyacrylamide, was employed as the t i t r a n t . The r e s u l t s are presented i n Figure 7. The t u r b i d i t y increased with c a t i o n i c additions up to the equivalence point. Beyond the equivalence point there was a sharp increase i n t u r b i d i t y which decreased with time, becoming stable a f t e r approximately 20 minutes. Addit i o n a l c a t i o n i c additions resulted i n a s l i g h t decrease i n t u r b i d i t y which then remained at a constant value. Up to 2 ml. of c a t i o n i c s o l u t i o n was added with no e f f e c t on f i n a l t u r b i d i t y . Solutions of varying Superfloc 214 concentration were prepared and 1 ml. of 1% Superfloc 310 was added to each one. A 1 ml. a d d i t i o n was f e l t to be r e l i a b l e f o r solutions up to 10 ppm Superfloc 214 and could give answers to 20 ppm. In the 0 3 0.4 0.5 0.6 mis. of 1% S u p e r f l o c 310 Figure 7 . 0.7 0.8 0.9 1.0 T i t r a t i o n Curve f o r 10 ppm Solution of Superfloc 23.4. (36) case of Nalco 8863, the lower polyacrylamide content of the fl o c c u l a n t made a 0.5 ml. additi o n of 1% Superfloc 310 adequate f o r r e s i d u a l determinations. A curve f o r t u r b i d i t y versus f l o c c u l a n t concentration was prepared f o r each f l o c c u l a n t and t h i s was used to determine r e s i d u a l f l o c c u l a n t i n supernatant water. It should be noted that r e s i d u a l concentrations are reported i n terras of parts per m i l l i o n f l o c c u l a n t rather than polyacrylamide. In the case of Superfloc 214, polyacrylamide concentration i s not s i g n i f i c a n t l y d i f f e r e n t from f l o c c u l a n t concentration while f o r Nalco 8863 the polyacrylamide comprises l e s s than one t h i r d of the f l o c c u l a n t . The polyacrylamide content of Nalco 8863 was determined by f i r s t c e n t r i f u g i n g to remove the o i l f r a c t i o n and then evaporating the water to y i e l d a s o l i d residue. The f l o c c u l a n t was determined to consist of 16% o i l , 53*5$ water and 30.5% s o l i d s . The inf r a r e d spectrum of the s o l i d f r a c t i o n was obtained and showed i t to be almost e n t i r e l y polyacrylamide. The inf r a r e d spectra of polyacrylamide f l o c c u l a n t s are more f u l l y discussed i n Appendix I I I . T i t r a t i o n curves of 10 parts per m i l l i o n solutions of both Superfloc 214 and Nalco 8863 were prepared. By comparison of the equivalence points i t was determined that the Superfloc 214 (37) contained three times the concentration of polyacrylamide that Nalco 8863 contained. It was found that f l o c c u l a n t concentrations down to 1 part per m i l l i o n could be r e l i a b l y determined. Concentrations down to 0.2 ppm were detected but could not be accurately reproduced unless s o l u t i o n c l a r i t y was very high. Comparative tests were performed on centrifuged and turbid samples. The r e s u l t s of the two tests were comparable with a larger c o r r e c t i o n f a c t o r having to be applied to the u n c l a r i f i e d samples. In none of the s e t t l i n g tests performed was the supernatant extremely tu r b i d . Comparative tests run on r e p l i c a t e samples gave r e s u l t s to within 0.2 ppm. 3.7 Chemical Analysis. The analysis of concentrates and t a i l i n g s f o r Cu and Mo were made by d i s s o l v i n g the sample i n aqua r e g i a and analyzing the sol u t i o n with a Perkin Elmer 306 Atomic Absorption Spectrophotometer. (38) CHAPTER 4  RESULTS 4.1 S e t t l i n g Tests. S e t t l i n g tests were f i r s t run with actual m i l l t a i l i n g s , employing a v a r i e t y of f l o c c u l a n t additions. The purpose of these tests was to investigate the s e t t l i n g behaviour of actual concentrator t a i l i n g s with f l o c c u l a n t additions. A second objective of these tests was to esta b l i s h acceptable reagent additions and t e s t conditions and to evaluate the l i q u i d f l o c c u l a n t , Nalco 8863. A second series of tests were performed to e s t a b l i s h r e s i d u a l polyacrylamide concentrations r e s u l t i n g from f l o c c u l a n t additions made to enhance sedimentation of t a i l i n g s . 4.1.1 Comparative S e t t l i n g Tests. In evaluating the f l o c c u l a n t s by batch s e t t l i n g t e s t s , the sedimentation rate was employed as the primary c r i t e r i o n f o r comparison. Dollimore and Horridge (51) have shown that the maxima f o r s e t t l e d volume, l i g h t transmission, sedimentation rate and f i l t r a t i o n rate do not occur at an equal polyacrylamide concentration. In the present work, c l a r i t y was q u a l i t a t i v e l y evaluated and when unacceptable, appropriate additions were made. Preliminary tests employing m i l l t a i l i n g s were performed with varying additions. The t a i l i n g s were at 30% (39) s o l i d s by weight when the f l o c c u l a n t had been added. Although f l o c c u l a t i o n occurred and s e t t l i n g was observed i n the column, the supernatant was highly t u r b i d . It appears that with a heterogeneous s i z e d i s t r i b u t i o n , such as that of the t a i l i n g s , the coarse f r a c t i o n can become f l o c c u l a t e d and s e t t l e while the f i n e f r a c t i o n i s not included i n the f l o e s and remains suspended. The zeta p o t e n t i a l of the t a i l i n g s was determined to be -27 mV. and t h i s value i s adequate to keep the f i n e material dispersed. Several a d d i t i o n a l tests were performed with the use of lime to adjust the pH to 11.5 p r i o r to f l o c c u l a n t addition. The super-natant i n these tests became completely c l e a r but the material was into compressive s e t t l i n g from the outset and s e t t l i n g rates were so low as to make comparison of the various f l o c c u l a n t s impractical. Figure 8 shows the r e s u l t s of tests performed at 30$ s o l i d s but employing seawater additions i n place of lime to a t t a i n a c l e a r supernatant. The use of seawater additions as j • an a i d i n thickening of t a i l i n g s has previously been discussed by Poling (20). The v a r i a t i o n of zeta p o t e n t i a l of the t a i l i n g s I with increasing seawater addition i s presented i n Appendix I. The s e t t l i n g rate i n Figure 8 i s seen to increase with time i n i t i a l l y . Similar behaviour was observed by Scott (52) i n dealing with pulps of intermediate concentration i n the absence of s t i r r i n g . Although the curves are not well suited to the comparative evaluation of f l o c c u l a n t s , i t appears that the (40) I I I 1 J 1 I I 10 2 0 3 0 4 0 50 6 0 70 8 0 T I M E (min.) Figure 8. Batch S e t t l i n g Curves for T a i l i n g s with Flocculant Additions. (41) f l o c c u l a n t s tested are e f f e c t i v e i n the order i Superfloc 210^ Nalco 8863 > Nalco 4153. Figure 9 presents the r e s u l t s of tests performed at 10$ s o l i d s by weight. The m i l l t a i l i n g s had been f i l t e r e d and the s l u r r y was prepared by mixing the s o l i d s with s i n g l e d i s t i l l e d water. It can be seen i n Figure 9 thatj at equivalent additions of the various f l o c c u l a n t s , the s e t t l i n g rates decrease i i n the order 1 Superfloc 210 — Superfloc 12? — Nalco 8863 — 1 Nalco 4l53« These r e s u l t s agree with those of Figure 8, performed at a higher s o l i d s concentration. In addition to producing a lower s e t t l i n g rate than the Superfloc additions, the Nalco 8863 was q u a l i t a t i v e l y determined to produce a more turbid supernatant. A t e s t was performed with a 5$ seawater addition p r i o r to f l o c c u l a n t addition to determine whether i n c l u s i o n of the previously suspended f i n e material i n the f l o e s would r e s u l t i n lowered s e t t l i n g rates. The r e s u l t s of t h i s t e s t are also included i n Figure 9 and are seen to not d i f f e r greatly from those with no seawater present. > The t e s t with Superfloc 210, a s l i g h t l y anionic polyacrylamide i s seen to have given a greater s e t t l i n g rate than the t e s t with Superfloc 127, a non-ionic polyacrylamide. Both 210 and 127 have the same molecular weight. I t was also observed during the t e s t that the Superfloc 127 f l o e s broke (42) 3 5 28 E u U J 21 o z < co CD 2 14] - J U J C O Co =10% so l ids F l o c c u l a n t =0.09 Ib./ton O Super f loc 210 A 127 O N a l c o 8 8 6 3 • •« II a 2 % S.W. V » 4153 10 2 0 3 0 4 0 5 0 6 0 7 0 Figure 9« T I M E ( s e c o n d s ) Batch S e t t l i n g Curves f o r Comparison of Flocculants. (43) down when the s e t t l i n g column was inverted a f t e r complete s e t t l i n g had occurred while the Superfloc 210 f l o e s remained i n t a c t . Although the addition of seawater offers i t s e l f as a p o s s i b i l i t y to those operations located on or near ocean waters, the majority of operations must r e l y on chemical additions | and lime appears to be favoured. A f i n a l set of tests were i therefore performed with lime additions to pH =11.5 as a coagulant. With t h i s addition the supernatant was found to be completely c l e a r . The tests were c a r r i e d out at an i n i t i a l concentration of 1?.8$ s o l i d s by weight and t h i s was found to give an i n i t i a l period of constant s e t t l i n g . One t e s t was conducted with 10 day old t a i l i n g s and two more with 27 day old t a i l i n g s . As seen i n Figure 10, the two tests performed at the same time gave i d e n t i c a l s e t t l i n g rates while the e a r l i e r t e s t gave a lower s e t t l i n g rate. The t a i l i n g s pH had also been observed to drop from 10.5 to 8.3 while they were shipped from the plant to the' laboratory. At t h i s point several disadvantages' were seen i n using actual concentrator t a i l i n g s and i t was decided to employ laboratory produced t a i l i n g s f o r further work. The main problem with using the concentrator t a i l i n g s which were av a i l a b l e was that they had to be d i l u t e d to get a l i n e a r s e t t l i n g zone and ( W 2 4 6 8 10 12 14 T I M E (min.) Figure 10. Batch S e t t l i n g Curves with Constant Additions to Observe Aging of Pulp. (45) t h i s d i l u t i o n resulted i n u n r e a l i s t i c s o l i d s concentrations. A second problem with the t a i l i n g s used so f a r was the v a r i a t i o n of s e t t l i n g rate as the t a i l i n g s aged, suggesting that aging of the surfaces of the s o l i d s could be altered with time. Since the e f f e c t of aged surfaces on further work could not be predicted,, i t was decided to use fresh t a i l i n g s f o r further work. 4.1.2 Residual Polyacrylamide i n Supernatant Water. S e t t l i n g tests were performed with various additions of Superfloc 214 and Nalco 8863 and the supernatant water i n each case was analyzed f o r r e s i d u a l polyacrylamide. Superfloc 214 was employed i n t h i s t e s t although i t had not been previously tested. The reason Superfloc 214 was used was that i n es t a b l i s h i n g the procedure f o r r e s i d u a l f l o c c u l a n t determination, i t was found that the more ioni c polyacrylamide was more r e a d i l y detected. T a i l i n g s used i n these tests were produced by laboratory grinding and f l o t a t i o n . The s i z e analysis of the t a i l i n g s used i n the tests i s given i n Appendix I I . The tests were run with an i n i t i a l concentration of 26$ s o l i d s by weight. Coagulants were not required i n these tests as s e t t l i n g with f l o c c u l a n t s produced an e s s e n t i a l l y c l e a r supernatant. ( 4 6 ) The v a r i a t i o n i n s e t t l i n g rate and r e s i d u a l f l o c c u l a n t concentration with increasing Superfloc 214 additions i s presented i n Figure 11. The r e s i d u a l f l o c c u l a n t appears i n solu t i o n even at low addition rates and becomes greater than 20 ppm well before the optimum addition rate i s reached. The surface area of the t a i l i n g s used i n t h i s t e s t was calculated by the formula: K V D " 1 AW b p £ AW ' where: S = s p e c i f i c surface, sq. cm. / gm. K g = s p e c i f i c surface f a c t o r , AD / V f = density of material, gm. / cc &W = incremental weight, gm. D„ = mean s i z e of increment, cm. m The s i z e analysis presented i n Appendix II was used to c a l c u l a t e the surface area and gave a value of 0.016 m. /gm. Considering an addition rate of 0.03 lb./ton and a molecular weight of 15 x 10^, t h i s would correspond to 1 molecule per 2.66 x 10^ A ° 2 . I f one carboxyl group per f i v e monomer units i s assumed and the molecule consists of a l i n e a r chain of C-C bonds, the length would be i n the order of 65 x 10^ A° . This would therefore correspond to a high degree of surface coverage ( 4 7 ) S U P E R F L O C 214 ADDIT ION ( l b s . / t o n ) Figure 11. Var i a t i o n of S e t t l i n g Rate and Residual Flocculant Concentration with Superfloc 214 Addition. (48) i f the molecules were assumed to be l y i n g down. Since the configuration of the adsorbed molecules i s not known however, not too much can be made o f t h i s . I t can be seen i n Figure 11 that at an addition of 0.17 lbs./ton which corresponds to 30 parts per m i l l i o n on a l i q u i d basis, a r e s i d u a l concentration of 10 parts per m i l l i o n was found. This corresponds to an adsorption of only 67$ of the f l o c c u l a n t added although the maximum s e t t l i n g rate has not yet been reached. Figure 12 shows the te s t with Superfloc 214 i n progress. The s e t t l i n g rack which allowed s i x s e t t l i n g tests to be performed simultaneously was employed so that the degree of mixing would be the same i n each case. A duplicate set of tests were performed with Superfloc 214 but with the cylinders i n d i v i d u a l l y shaken. The same trends i n s e t t l i n g rate and r e s i d u a l f l o c c u l a n t concentration were observed but the points were more scattered than when the s e t t l i n g rack was employed. A s i m i l a r set of tests were performed with Nalco 8863. Again r e s i d u a l f l o c c u l a n t was detected well before the optimum addition rate was reached. The r e s u l t s of these tests are summarized i n Table 4, S e t t l i n g rates of the Superfloc 214 tests and Nalco 8863 tests can not r e a d i l y be compared since the tests were performed on separate grinds having d i f f e r e n t (49) > F i g u r e 12. T e s t s w i t h S u p e r f l o c 214 A d d i t i o n s i n P r o g r e s s (a) a f t e r 6 min. 40 s e c . (b) a f t e r 5 5 n i i n . (50) s i z e analysis and also since the fl o c c u l a n t s d i f f e r i n anionic character. Table 4. V a r i a t i o n of S e t t l i n g Rate and Residual Flocculant Concentration with Nalco 8863 Addition. Addition lbs./ton S e t t l i n g Rate cm./min. Residual Flocculant ppm 0 .26 -.05 .72 o .13 1.53 <1 .21 2.76 <1 .41 3.75 <1 4.2 F l o t a t i o n Tests. In order to e s t a b l i s h the l e v e l of Recovery and grade which could be attained using fresh water f o r grinding and f l o t a t i o n , eight tests employing fresh water were performed. The r e s u l t s of these tests are presented i n Table 5» The weight percent minus 200 mesh f o r each test i s also presented. Each grind was performed under i d e n t i c a l conditions and f o r the same length of time so that the grind i n each case should have been the same. I t would also be expected that the recovery or concentrate grade would have been dependent on the fineness of Table 5. Results of Fresh Water F l o t a t i o n Tests. Test No. Weight Cu Mo Cu Mo Weight % % % f0 Recovery Recovery - 2 0 0 # 1 concentrate t a i l i n g 4 . 3 95-7 9 . 1 0 . 0 9 .225 . 0 0 2 8 2 . 1 1 7 . 9 8 3 . 6 1 6 . 4 6 1 . 4 2 concentrate t a i l i n g 5 . 4 9 4 . 6 7.60 . 0 9 .18 0 . 0 0 2 8 3 . 8 16 .2 8 3 . 7 1 6 . 3 5 8 . 2 3 concentrate t a i l i n g 7 .3 9 2 . 7 5 . 7 0 . 0 9 .131 . 0 0 2 8 3 . 3 I 6 . 7 8 3 . 8 1 6 . 2 6 2 . 9 4 coneentrate t a i l i n g 6 . 6 9 3 . 4 6 . 7 0 .08 . 1 5 2 . 0 0 2 8 5 . 6 1 4 . 4 84 .3 15 .7 7 4 . 4 5 concentrate t a i l i n g 5.5 9 4 . 5 7 . 7 0 .08 .186 . 0 0 2 84. 9 15 . 1 84 .5 15.5 7 4 . 5 6 concentrate t a i l i n g . 6.4 9 3 . 6 6 .50 . 0 6 .166 . 0 0 2 8 8 . 2 1 1 . 8 8 5 . 1 1 4 . 9 7 3 . 1 7 concentrate t a i l i n g 6 . 0 9 4 . 0 7 . 1 0 . 0 8 5 .155 . 0 0 2 84. 0 1 6 . 0 8 3 . 1 I 6 . 9 55 .0 8 concentrate t a i l i n g 5 . 4 9 4 . 6 7 . 0 0 . 1 1 . 1 8 3 .004 7 8 . 5 2 1 . 5 7 2 . 3 2 7 . 7 5 6 . 5 Average concentrate 5 . 9 7 . 2 0 cr = 1 . 0 . 1 7 2 8 3 . 8 cr = 2 . 8 8 4 . 0 (52) grind. No systematic v a r i a t i o n in recovery or grade with fineness of grind i s apparent however, and i t can only be assumed that, over the range encountered, the degree of l i b e r a t i o n attained was not dependent on the grind. The concentrate from several tests was examined under a binocular microscope and was determined to consist l a r g e l y of chalcopyrite-gangue middlings. The Mo recovery i n t e s t 8 was s i g n i f i c a n t l y lower than i n the other tests but no explanation f o r t h i s could be determined. A t e s t was performed wherein the t a i l i n g s from one t e s t were allowed to s e t t l e and the r e s u l t i n g supernatant was used f o r a second t e s t . It was observed that considerable recovery could be achieved with no reagent additions, there seemingly being adequate r e s i d u a l reagents in the reused water. Tests performed with reclaimed water but reagent additions as i n the fresh water tests showed no loss of grade or recovery. Three tests were performed with varying Superfloc 214 additions to the t a i l i n g s of one t e s t and with the r e s u l t i n g supernatant water being used f o r a second test. The r e s u l t s are presented i n Table 6. The water r e s u l t i n g from the f i r s t t e s t i n each case was analyzed f o r r e s i d u a l f l o c c u l a n t and these concentrations are included i n Table 6. The f l o c c u l a n t i n these tests was mixed with the t a i l i n g s by means of a plunger which Table 6. Results of Tests Employing Reclaim Water from T a i l i n g s Settled with Various Superfloc 214 Additions. 214 Addition Residual 214 Weight Cu Mo Cu Mo lbs./ton 1 ppm % fo % Recovery Recovery .03 .70 cone. 5.4 7.40 .185 80.2 83.4 t a i l 94.6 .103 .002 19.8 I6.5 .10 .95 cone. 6.5 6.00 .150 79.9 83.5 t a i l 93.5 .104 .002 20.1 15.3 .20 .82 cone. 5 .4 7.50 .183 81.2 84. 0 t a i l 94.6 .10 .002 18.8 15.9 (54) introduced high shear into the s l u r r y . This resulted i n a breakdown of flo e s into smaller units and resulted i n lower r e s i d u a l f l o c c u l a n t concentration than had previously been indicated by s e t t l i n g t e s t s . Inconsistent r e s i d u a l concentrations were also p a r t i a l l y due to problems encountered with introducing the polyacrylamide s o l u t i o n into the s l u r r y . - In order to study the ef f e c t of increasing polyacrylamide ! concentration on f l o t a t i o n i t appeared necessary to make additions j d i r e c t l y to the ore. The r e s u l t s of four tests performed with cont r o l l e d additions of Superfloc 214 to the grinding stage are presented i n Table 7. Considerable f l o c c u l a t i o n of the fi n e s present i n the ore was observed to occur when f l o c c u l a n t s o l u t i o n was added to the ore i n the m i l l , p a r t i c u l a r l y i n the case of the 10 ppm addition. When the material was removed from the m i l l a f t e r grinding no evidence of f l o c c u l a t i o n was observed. Fresh water was used to bring the f l o t a t i o n c e l l to volume and f l o t a t i o n proceeded as normal. No change i n the nature of the fr o t h or material f l o a t e d was observed i n these tests compared with fresh water t e s t s . The r e s u l t s indicate no s i g n i f i c a n t loss of recovery or grade-resulted from up to 10 ppm Superfloc 214 i n water to the grinding stage. It was considered that the grinding broke up a l l the previously formed f l o e s and resulted i n no ef f e c t on f l o t a t i o n . Table 7. Results of Tests Employing Controlled Superfloc 214 Additions to Grind. 214 Concentration Weight Cu Mo Cu Mo ppm % io % Recovery Recovery 0.9 cone, t a i l 6.1 93.9 6.95 .085 .140 .002 84.0 15.9 81.9 18.1 2 cone. t a i l 6.2 93.8 7.05 .075 .150 .002 86. 0 14.0 83.1 I6.9 5 cone, t a i l 6.2 93.8 6.90 .075 .135 .002 85.9 . 14.1 81.7 18.3 10 cone. t a i l 6.1 93.9 6.93 .075 .156 .002 85.8 14.2 83.6 16.4 (56) In actual operations," reclaim water i s generally added a f t e r as well as before grinding. A series of tests were therefore performed with co n t r o l l e d f l o c c u l a n t (Superfloc 214) additions to the grinding stage as well as to a l l make-up and wash water during the te s t . In these tests the use of water containing 2 ppm Superfloc 214 was observed to cause f l o c c u l a t i o n i n the f l o t a t i o n c e l l and at 10 ppm the f l o c c u l a t i o n was very intense. The a c t i o n of the impeller created high shear conditions i n the c e l l and served to destroy the f l o e s . By the end of the f l o t a t i o n the flo e s were very minute and led to only s l i g h t l y enhanced s e t t l i n g when the machine was stopped. No e f f e c t on f l o t a t i o n was observed other than the f r o t h appeared s l i g h t l y more f r a g i l e towards the end of the t e s t . The r e s u l t s presented i n Table 8 show no s i g n i f i c a n t loss i n recovery or grade with increasing f l o c c u l a n t concentration. Flocculant was added with the water at varying concentrations but amounts are also shown on a pound per ton of f l o t a t i o n feed basis. The Mo recovery i n these tests was s i g n i f i c a n t l y lower than i n previous t e s t s . Since the recovery was lower f o r a fresh water t e s t performed at the same time and did not worsen with increasing f l o c c u l a n t concentration, the lowered recovery i s not believed to be re l a t e d to the presence of polyacrylamide. There appeared to be several possible explanations as to why the presence of polyacrylamide did not i n t e r f e r e Table 8. Results of Tests Employing Controlled Superfloc 214 Additions to Grind and to Make-Up Water. 214 Cone. ppm 214 Addition lbs./ton Weight % Cu % Mo % Cu Recovery Mo Recovery N i l N i l cone. t a i l 5.4 94.6 7.04 .11 .183 .004 78.5 21.5 72. 3 27. 7 0.9 .003 cone. t a i l 9^4 7.03 .09 .18 0 .004 82. 2 17. 8 72. 7 27.3 2 .007 cone. t a i l ?'5 94.5 7.20 .09 .18 0 .004 82.3 17-7 72.4 27.6 5 .019 cone. t a i l 5.9 94.1 6.20 .11 .162 .004 78.0 22. 0 71.8 28.2 10 .038 cone. t a i l 5-5 94.5 7.35 .09 .185 .004 82.6 17.3 72.9 27.0 (58) with the f l o t a t i o n of sulphides. One p o s s i b i l i t y was that the polyacrylamide had adsorbed only on the s i l i c a minerals and thus not affected c o l l e c t o r adsorption on the sulphides« This also required that the sulphides were not entrapped within the gangue f l o e s . Another p o s s i b i l i t y was that f l o c c u l a t i o n of the sulphides had occurred but that the action of the f l o t a t i o n c e l l had broken up the f l o e s . To v e r i f y that polyacrylamide does adsorb on copper sulphides but does not make the surface hydrophilic and thereby prevent f l o t a t i o n , a series of bubble pick-up tests (45) were performed on pure chalcopyrite. The addition of 2 ppm poly-acrylamide s o l u t i o n to -270 mesh material resulted i n complete f l o c c u l a t i o n and confirmed that adsorption of the polymer on chalcopyrite was occurring. Larger p a r t i c l e s (-150 +270 mesh) were employed fo r the pick-up tests so that v a r i a t i o n s i n pick-up could be more r e a d i l y detected. I t was found that with additions of Superfloc 214 or Separan NP 10 up to 100 parts per m i l l i o n with 0.5 gm. chalcopyrite i n 100 ml. s o l u t i o n no q u a l i t a t i v e v a r i a t i o n i n pick-up occurred. It was observed that when the Superfloc 214 concentration was 10 ppm or greater, the v i s c o s i t y on the s o l u t i o n was greatly increased. Apparently the chalcopyrite surface had become • covered and considerable r e s i d u a l polyacrylamide remained i n s o l u t i o n . The e f f e c t of increased s o l u t i o n v i s c o s i t y was that (59) i t r e sulted i n p a r t i c l e s being sheared o f f as the bubble was l i f t e d . The e f f e c t was less pronounced when Separan NP 10 was employed. The Nalco 8863 f l o c c u l a n t i s supplied by the manufacturing company as an emulsion. An analysis of the material supplied showed that i t consisted of 16% o i l , 53•5$ water and 30.5$ polyacrylamide. In order to evaluate whether the o i l present i n Nalco 8863 could be expected to b u i l d up and cause problems i n f l o t a t i o n , a tes t c o n s i s t i n g of f i v e cycles was performed i n which the t a i l i n g s from each cycle were s e t t l e d with an addition of 0.2 pounds per ton Nalco 8863. Considering the o i l content of 8863 to be 16$ by weight, i f a l l the o i l reported to the supernatant the f i f t h cycle would have had 0.19 gm. of o i l (.15 l b / t present. I t was considered that the presence of the o i l could r e s u l t i n the f r o t h becoming unstable (53)• .Another possible e f f e c t was that the o i l returning with the water could carry s i g n i f i c a n t slimes and these slimes could lead to det e r i o r a t i o n of f l o t a t i o n . No adverse effects were observed and t h i s i s v e r i f i e d by the r e s u l t s presented i n Table 9« Although the copper recovery appears to be somewhat lower than that obtained with fresh water, a s t a t i s t i c a l t - t e s t with c<=.05 was performed on the copper recoveries and th i s rejected the hypothesis that Table 9. Results of Five Cycle Test Using 0.2 Pounds/Ton Nalco 8863 f o r S e t t l i n g of T a i l i n g s . Cycle No. Weight fo Cu . Mo fo Cu Recovery Mo Recovery 1 cone. t a i l 5.1 94.9 7.70 .10 .184 .002 80.4 19.6 83. 0 17. 0 2 cone. t a i l 4.4 95.6 8.30 .10 .200 .002 79.2 20.8 82. 1 17. 9 3 cone, t a i l 4.6 95.4 8.50 .10 .200 .002 80.6 19.4 83. 0 17. 0 4 cone. t a i l 4.1 95.9 9.40 .105 .230 .002 79.3 20.7 83. 1 16. 9 5 cone. t a i l 4.8 95.2 7.50 .095 .186 .002 80.0 20.0 82. 5 17.5 ( 6 1 ) the values were s i g n i f i c a n t l y lower. The p o s s i b i l i t y of polyacrylamide remaining i n the o i l droplets and thereby returning to f l o t a t i o n was considered. I t was found that i n preparing the f l o c c u l a n t solution, consider ably more a c t i v a t o r had to be used than recommended by the manufacturer, or the polyacrylamide would not go into s o l u t i o n . I t appears l i k e l y that when using l i q u i d f l o c c u l a n t s i n practice polyacrylamide would end up i n reclaim water i n t h i s manner. Considering the r e s u l t s of tests with Superfloc 214 added to f l o t a t i o n , no deleterious effects r e s u l t i n g from recycled polyacrylamide would be expected. (62) CHAPTER 6  DISCUSSION Where thickeners are employed i n mineral processing operations to reclaim water, additions of coagulants and floc c u l a n t s are frequently made to enhance s o l i d - l i q u i d separations. The polyacrylamide f l o c c u l a n t s i n p a r t i c u l a r are f i n d i n g wide-spread use i n s o l i d - l i q u i d separations. Previous studies have been la r g e l y concerned with the i n t e r a c t i o n between polyacrylamides and pure minerals of high surface area. Various authors have arrived at opposing conclusions with regard to the occurrence of r e s i d u a l polyacrylamide i n s o l u t i o n i n the presence of s o l i d s . The present study may contribute to the understanding of polyacrylamide i n t e r a c t i o n with actual t a i l i n g s and the possible effects of r e s i d u a l polyacrylamide on f l o t a t i o n as discussed i n the following sections. 5.1 Comparative Evaluation of Flocculants. Nonionic polyacrylamide f l o c c u l a n t s are believed to adsorb on s i l i c a through hydrogen bonding between amide groups on the poiymer and surface s i l a n o l groups on s i l i c a . At high pH the f l o c c u l a t i o n of s i l i c a by polyacrylamide and p a r t i c u l a r l y anionic polyacrylamide, i s hindered because the increased negative charge on the s i l i c a keeps the s o l i d s dispersed. The (63) ++ presence of Ca ions serves to reduce the charge on the s o l i d s and activates the s o l i d s f o r polyacrylamide adsorption through the carboxylate groups. In sulphide f l o t a t i o n systems, C a + + ions are frequently introduced i n the form of CaO or Ca(0H) 2 f o r pH adjustment. In the present study with equal weight!additions, i the effectiveness of f l o c c u l a n t s was found to decrease i n the order Superfloc 210 - Superfloc 127 - Nalco 8863 - Nalco 4153. ' l This can be seen i n Figures 8 and 9. I t i s believed that the lower effectiveness of the Nalco f l o c c u l a n t s i s due to a lower concentration of polyacrylamide i n these f l o c c u l a n t s . Equivalent additions of Superfloc and Nalco f l o c c u l a n t s does not indicate equivalent additions of polyacrylamide. In Figure 9 i t i s observed that the anionic 210 gave greater enhancement of s e t t l i n g than the nonionic 127. The lime used i n the f l o t a t i o n of the ore has seemingly activated the s i l i c a so that adsorption v i a the carboxylate groups could occur. The anionic chain remains extended from the surface however, and i s therefore more e f f e c t i v e for i n t e r p a r t i c l e bridging than the nonionic chain. In performing batch s e t t l i n g tests f o r the comparison of enhanced s e t t l i n g due to polyacrylamides, the i n i t i a l s o l i d s concentration must be low enough that a region of constant s e t t l i n g rate i s encountered. I f the i n i t i a l s o l i d s concentration i s too high the formation of channels i n the pulp r e s u l t s i n ( 6 4 ) increasing s e t t l i n g rate with time as seen i n Figure 8. The aging of t a i l i n g s r e s u l t s i n variat i o n s i n s e t t l i n g "behaviour as seen i n Figure 10. I t appears that as the s i l i c a t e s age, polyacrylamide does not adsorb as r e a d i l y and the chains remain extended into s o l u t i o n , r e s u l t i n g i n greater i n t e r p a r t i c l e bridging. In actual thickening operations, t a i l i n g s ' are s e t t l e d immediately a f t e r f l o t a t i o n and the aging e f f e c t can be disregarded. Where s e t t l i n g t ests are to be used i f o r designing t a i l i n g s thickeners, fresh t a i l i n g s should be employed. If aged t a i l i n g s are used, the enhancement of f l o c c u l a t i o n upon aging could r e s u l t i n thickeners being designed with too low a capacity. 5 . 2 Residual Polyacrylamide i n Supernatant Water. Although previous work with polyacrylamides had shown that r e s i d u a l polymer did not appear i n s o l u t i o n u n t i l the optimum addition rate had been exceeded, the present work has shown t h i s to be untrue when dealing with t a i l i n g s . The r e s u l t s presented i n Figure 11 and Table 4 indicate that r e s i d u a l polyacrylamide appears i n s o l u t i o n even at very low additions and has reached a s i g n i f i c a n t concentration by the time the optimum addition rate has been reached. The Nalco 8863 r e s u l t s presented i n Table 4 are s i g n i f i c a n t l y lower than those of the (65) Superfloc 214 t e s t presented i n Figure 11. This i s likely-due to the f a c t that the Nalco f l o c c u l a n t contains less than one t h i r d as much polyacrylamide as the Superfloc and was also observed to go into s o l u t i o n very poorly. The Nalco f l o c c u l a n t also has less anionic character than the Superfloc 214 and i s therefore more completely adsorbed on the s o l i d s . I This would r e s u l t i n both lower s e t t l i n g rates and lower r e s i d u a l concentrations. Two reasons are seen f o r the difference i n r e s u l t s obtained with s i l i c a powders and the t a i l i n g s employed i n the present study. One reason i s that previous studies employed powders having a high surface area which require a greater amount of polyacrylamide f o r f l o c c u l a t i o n and surface coverage. The other reason f o r the difference i n r e s u l t s i s that previous testwork generally involved severe a g i t a t i o n of the solid-polymer s o l u t i o n mixture. Present testwork involved only the turbulence due to inversion of the s e t t l i n g column to achieve mixing. In actual thickeners there i s considerable turbulence i n the feed-well but t h i s i s of short duration and the remainder of the separation takes place under r e l a t i v e l y quiescent conditions. It i s believed that the conditions i n the s e t t l i n g column are more r e a l i s t i c than those obtained with a high rate of a g i t a t i o n of the s l u r r y . (66) Considering that r e s i d u a l polyacrylamides can be expected i n reclaim water i t was of i n t e r e s t to determine the possible effects of residuals on f l o t a t i o n . 5 . 3 E f f e c t of Residual Flocculants on F l o t a t i o n . The r e s u l t s of s e l e c t i v e f l o c c u l a t i o n studies indicate I i that unless s p e c i a l additions are made, polyacrylamide w i l l i cause f l o c c u l a t i o n of both sulphides and gangue. When a 1 f l o t a t i o n stage i s preceded by a f l o c c u l a t i o n operation or i s performed with water containing r e s i d u a l polyacrylamides, two possible reasons f o r n o n - f l o t a b i l i t y are seen. Either previously adsorbed polyacrylamide prevents the adsorption of c o l l e c t o r , or the sulphides become entrapped within gangue f l o e s and cannot contact a bubble. Bubble pick-up tests were performed and these indicated that the adsorption of polyacrylamide should not prevent f l o t a t i o n . I t was observed that an i n i t i a l concentration of 10 ppm polyacrylamide resulted i n increased v i s c o s i t y of the s o l u t i o n even a f t e r mixing with s o l i d s had occurred. As would be expected, the v i s c o s i t y was q u a l i t a t i v e l y observed to increase with increasing polyacrylamide concentration. I t i s believed that i n previous work performed with sulphides alone or a high r a t i o of sulphide to gangue, lowered recoveries were achieved with increasing polyacrylamide concentration due to t h i s (67) v i s c o s i t y e f f e c t and not due to polyacrylamide adsorption or to f l o c c u l a t i o n of the sulphides. The e f f e c t of v i s c o s i t y on the p r o b a b i l i t y of bubble - p a r t i c l e c o l l i s i o n has been discussed by Gaudin ( 5 4 ) . The r e s u l t s of a series of f l o t a t i o n tests performed i n the presence of polyacrylamide are presented i n Tables 6, 7 and 8. The ore used f o r the study was a low grade disseminated type ore and since f l o e s were observed to form, entrapment of the sulphides within f l o e s almost c e r t a i n l y occurred. The chance of entrapment i s even greater because the concentrate was observed to consist l a r g e l y of s i l i c a t e - s u l p h i d e middlings. The s i l i c a t e portion of these middlings could be expected to p a r t i c i p a t e f r e e l y i n f l o e formation. Since the r e s u l t s of the tests performed with polyacrylamide addition a f t e r grinding (Table 8) show no loss of grade or recovery, i t appears that the shear forces within the f l o t a t i o n c e l l were s u f f i c i e n t to destroy the f l o e s . In the present study, polyacrylamide concentrations i n excess of 10 ppm were not used f o r f l o t a t i o n studies although r e s i d u a l determinations i n s e t t l i n g tests indicated that such concentrations could be expected i f addition rates were increased from t h e i r present l e v e l s . Such high r e s i d u a l concentrations represent a low e f f i c i e n c y of reagent usage. It i s believed that should such large residuals occur, more (68) e f f i c i e n t systems such as perhaps counter-current t h i c k e n i n g would be investigated and thus keep residuals to a r e a s o n a b l e l e v e l . 5.3•1 E f f e c t of Flocculant Impurities on F l o t a t i o n . The r e s u l t s of Table 9 indicate that within f i v e cycles, no impurities became concentrated i n thejwater t o the extent that they affected f l o t a t i o n . The o i l phase present j i n the l i q u i d f l o c c u l a n t tested was the primary concern i n these t e s t s . Although the present tests show no e f f e c t due to these o i l impurities i t i s believed that i n actual operations where water i s continually recycled, a greater build-up could be experienced and lead to deleterious e f f e c t s . It s h o u l d also be noted that although the build-up of o i l was possible, no analyses were performed to determine whether the o i l d i d i n f a c t b u i l d up i n reclaim water. ( 6 9 ) SUMMARY AND CONCLUSIONS A study was made of the f l o c c u l a t i o n of f l o t a t i o n t a i l i n g s by polyacrylamides and possible effects of r e s i d u a l polyacrylamides i n reclaim water on f l o t a t i o n . The s i g n i f i c a n t r e s u l t s pf t h i s study are summarized as follows i 1. Anionic polyacrylamide (Superfloc 210) was more e f f e c t i v e than nonionic polyacrylamide i n f l o c c u l a t i o n of sulphide f l o t a t i o n t a i l i n g s when lime was used f o r pH control i n the f l o t a t i o n stage. 2. At equal weight additions, the l i q u i d f l o c c u l a n t Nalco 8 8 6 3 was found to be less e f f e c t i v e than the dry Superfloc f l o c c u l a n t s . This i s apparently due to a lower polyacrylamide content i n the Nalco f l o c c u l a n t . 3 . The aging of t a i l i n g s resulted i n enhancement of s e t t l i n g r a t e . That polyacrylamide adsorption i s less e f f e c t i v e upon aging, r e s u l t i n g i n chain segments remaining extended from the surfaces and leading to greater i n t e r p a r t i c l e bridging, i s seen as a possible explanation"for t h i s enhancement. 4. Residual polyacrylamide can be expected i n reclaim water from t a i l i n g s thickeners well before the optimum weight additi o n of f l o c c u l a n t i s reached. Highly anionic polyacrylamides can be expected to r e s u l t i n higher residuals than nonionic polyacrylamides. (?o) 5. Residual polyacrylamide i n reclaim water does not adversely a f f e c t the f l o t a t i o n of sulphides as long as the shear forces i n the f l o t a t i o n c e l l are adequate to cause f l o e degradation. 6. 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Usoni, L., R i n e l l i , G., Marabini, A. M. and Ghigi, G., Proceedings of VIII International Mineral Processing Congress, Leningrad, I968, 40. Read, A. D. and Whitehead, A.,, preprint, International Mineral Processing Congress London, 1973. 4 1 . H e r , R. K., J. C o l l . Int. S c i . , 22:2, pp. 364 - 373 (197D. 42. Clement, M. and Bahr, A., Freiberger Forschungshefte, Reine A. (German) 25P. A» PP- i 2 5 - 136 (1965). 43. Yonezawa, T., Jour. Min. Inst. Japan (Japanese), 706. PP. 55 - 59 (1944). • 4 4 . Schildknecht, C. E., CH. V. i n "Polymer Processes", Vol. X, editor C. E. Schildknecht, Interscience, New York, pp. 191 - 194 (1956). 45. Sun, S. and T r o x e l l , R. C , EM J, July 1957, p. 79. 4 6 . U l l r i c h , 0. A., presented at Instrument Society of America Conference, New York C i t y , New York, September 26, i960. 47. Fuoss, R. M. and Sadek, H., Science 110. pp. 552 - 554 (1949). 4 8 . Meehan, E. J . and Chiu, G., A n a l y t i c a l Chemistry, 2 £ « 3 > pp. 536 - 5 4 0 (1964). ( 7 4 ) 4-9. Hochgesang, F. P., "Nephelometry and T u r b i d i t y " CH. 63, T r e a t i s e on A n a l y t i c a l C h e m i s t r y , P a r t I , Volume 5, I n t e r s c i e n c e , New York (1964). 50. Yang, J . T., Ame r i c a n V i s c o s e C o r p o r a t i o n , T e c h n i c a l R e p o r t No. R.D.D., I958 - 33 (1958). 51. D o l l i m o r e , D. and H o r r i d g e , T. A., Water R e s e a r c h , 6, pp. 703 - 710 (1972). 52. S c o t t , K. J . , T r a n s . IMM, 2Z» C 85 - 97. 53« G l e r a b o t s k i i , V. A., D m i t r i e v a , G, M. and S o r o k i n , M. M., CH. IV i n "Nonpolar F l o t a t i o n A g e n t s " , ! I s r a e l - Program f o r S c i e n t i f i c T r a n s l a t i o n s , J e r u s a l e m 1970. i 54. Gaudin, A. M., " F l o t a t i o n " , M c G r a w - H i l l , New Yo r k , 1957, pp. 3 4 0 - 355. I i 55» M a n u f a c t u r i n g C h e m i s t s A s s o c i a t i o n , R e s e a r c h P r o j e c t Spectrum No. 82 (i960). 56. I b o n a i r , M., P u r a s u c h i k k u s u (Japanese) 22:1, pp. 1 4 2 -1 4 5 , (1971). 57« P r o d u c t I n f o r m a t i o n S h e e t , Aquarium Systems I n c . , E a s t l a k e , Ohio. 58. Z e t a Meter I n s t r u c t i o n Manual. S P E C I F I C C O N D U C T I V I T Y ( ^ m h o - c m . - 1 ) VARIATION OF ZETA POTENTIAL WITH SEAWATER CONCENTRATION. 100 C2> " Z w CO < CL I— z UJ o or U J Q _ U J > < _J ID 2 3 O 10 4 i i i i i Jl I 1 L O N a l c o 8 8 6 3 t e s t • S u p e r f l o c 214 t e s t > w 2! a f—i x 10 Jl I I I t I ON 100 1 0 0 0 PARTICLE S IZE ( m i c r o n s ) SIZE ANALYSES OF TAILINGS USED IN SECTION 4.1 .2. / t f ( 7 7 ) APPENDIX I I I INFRARED SPECTRA OF POLYACRYLAMIDE FLOCCULANTS The i n f r a r e d s p e c t r u m o f p o l y a c r y l a m i d e i s p r e s e n t e d i n F i g u r e 1. By p r e p a r i n g the s p e c t r a f o r t h e v a r i o u s c o m m e r c i a l f l o c c u l a n t s , t h e number o f c a r b o x y l a t e groups on t h e c h a i n and hence t h e degree o f i o n i c n a t u r e o f t h e f l o c c u l a n t s c o u l d be e v a l u a t e d . T a b l e 1 p r e s e n t s t h e band a s s i g n m e n t s a c c o r d i n g t o I b o n a i r (56). T a b l e 1. I n f r a r e d Band A s s i g n m e n t s f o r P o l y a c r y l a m i d e . Assignment Wavenumber (cm"'*") N - H 3500 - 3300 - c V 2940 - 2915 c=o 1690 - 1670 N - H 1650 - 1580. - C H 2 - 1480 - 1440 - C H - 1340 - C - N 1340 - 1250 0' • ' L 4 0 0 0 3 0 0 0 2 0 0 0 1800 1600 1 4 0 0 1 2 0 0 1 0 0 0 8 0 0 W A V E NU 1$ B E R ( c m : ' ) Figure 1. Polyacrylamide Reference Spectrum (55). (79) In preparing the KBr p e l l e t s of the various f l o c c u l a n t s , considerable problems were encountered i n that the f l o c c u l a n t p a r t i c l e s could not be ground up and dispersed i n the p e l l e t . The r e s u l t i n g spectra were therefore of a poor q u a l i t y . A representative spectrum (Superfloc 214) i s presented i n Figure 2. I t can be seen i n Figure 2 that the bands i n the regions 3500 - 3300 and 1650 - 1580, corresponding to the amide groups, have become diminished. This would be consistent with the anionic nature of Superfloc 214. At the same time a band has emerged i n the region 1200 - 1100. It was considered that t h i s could be due to dissociated carboxylate -C00~ groups but i t was also noted that the presence of CaSO^ i n the f l o c c u l a n t , as a binding agent, could account f o r the bands. In the end the problem of preparing high q u a l i t y spectra resulted i n t h i s work being abandoned and the e f f e c t of r e s i d u a l f l o c c u l a n t s on f l o t a t i o n was studied. With some e f f o r t , i t should be possible to prepare samples sui t a b l e f o r i n f r a r e d a n a l y s i s . A systematic study of the f l o c c u l a n t s supplied by various manufacturers could be performed and would be very useful f o r s e l e c t i n g f l o c c u l a n t s . ( 8 0 ) 

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