Selective flocculation of synthetic mineral mixtures using modified polymers

International Journal of Mineral Processing, 6 (1980) 303--320 © Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands

303

SELECTIVE FLOCCULATION OF SYNTHETIC MINERAL MIXTURES USING MODIFIED POLYMERS

G.C. SRESTY* and P. SOMASUNDARAN Henry Krumb School of Mines, Columbia University, New York, N.Y. 10027 (U.S.A.) (Received February 6, 1979; revised version accepted September 11, 1979)

ABSTRACT Sresty, G.C. and Somasundaran, P., 1980. Selective flocculation of synthetic mineral mixtures using modified polymers. Int. J. Miner. Process., 6: 303--320. The role of the presence of active groups in polymers and operating variables such as conditioning time in producing flocculation in single and mixed mineral slimes made of hematite, quartz and chalcopyrite is examined at different conditions of pH. Selective flocculation was achieved on the basis of results obtained for single mineral systems as, for example, in the case of hematite--quartz mixtures using sulfonated polymer. Flocculation was found to go through a maximum as the mineral was conditioned with the polymer solution. Interestingly, the times of maximum flocculation for various minerals were sufficiently different from each other so that it could be considered as a potential factor for achieving selectivity. Also, cleaning of the selectively flocculated product by simple redispersion in water improved the separation. Electrokinetic studies conducted to study the mechanisms involved provided indication for the shift of shear plane.

INTRODUCTION In the case o f n u m b e r o f c u r r e n t l y available ores, mineral values are m o r e finely dispersed t h a n in the past. C o n v e n t i o n a l b e n e f i c i a t i o n t e c h n i q u e s are in general r a t h e r inefficient in the sub-sieve size range and hence, it has bec o m e necessary t o develop n e w or m o d i f i e d processes. A m o n g the t e c h n i q u e s t h a t are being c o n s i d e r e d at p r e s e n t f o r fine particle beneficiation, selective f l o c c u l a t i o n appears t o be o n e o f m o s t promising. Ideally this s h o u l d involve aggregation o f either the desired mineral species or the gangue particles into flocs leaving the o t h e r s in suspension. S e p a r a t i o n o f the u n f l o c c u l a t e d material b y processes such as f l o t a t i o n or e l u t r i a t i o n results in the desired beneficiation. F l o c c u l a t i o n i n d u c e d b y dissolved p o l y m e r m o l e c u l e s can be a t t r i b u t e d t o charge n e u t r a l i z a t i o n a n d / o r interparticle bridging. Selectivity in flocculation requires selective a d s o r p t i o n o f t h e p o l y m e r m o l e c u l e s o n t h e desired *Present address: IIT Research Institute, 10 West 35th Street, Chicago, Ill. 60616 (U.S.A.)

304 mineral particles. A majority of the commercially available polymers are, however, bulk flocculants with insufficient selectivity. In such cases, selectivity can be achieved either by altering the interfacial potential of the mineral to create the desired electrical interactions between the polymer molecules and the mineral surface or by incorporating suitable functional groups into the polymer which, by formation of complexes, can make flocculation selective, h c o r p o r a t i o n of xanthate groups into cellulose has, for example, enabled Attia and Kitchener (1975) to obtain selective flocculation of copper minerals from a copper ore. Similarly modification of starches for selective flocculation of hematite from low-grade iron ore and use of commercial polymers containing various ionic groups for selective flocculation of mineral mixtures have been successfully attempted in the past (Frommer, 1968; Usoni et al., 1968; Read, 1972). This paper will deal with selective flocculation of two systems: hematite-quartz and chalcopyrite--quartz. Effects of time of conditioning with polymer solution of flocculation behavior of minerals, and the role of cleaning the selectively flocculated product are described. Mechanisms involved are discussed with the help of the above data and the results obtained for electrokinetic properties of a selected mineral/polymer system. EXPERIMENTAL Natural minerals used in this study (quartz, hematite and chalcopyrite) were obtained from Wards Natural Sciences Establishment. Synthetic silica (Biosil-A) used was of reagent grade powder. Quartz and chalcopyrite were wet ground at 50% solids in a porcelain ball mill and the hematite was ground in steel ball mill. The minus 20 micron fractions were then separated by wet screening and stored in distilled water. Commercial polymers used are listed in Table I. The hydroxypropylcellulose xanthate sample was made in the laboratory by reacting one mole of Klucel H F with three moles of potassium hydroxide and three moles of carbondisulfide. All the flocculants, except for starch, had an approximate average molecular weight of one million. Flocculation experiments were done in 2 cm diameter and 15 cm long test tubes at a solid content of approximately 5%. The pH of the suspensions was adjusted when required by addition of standard solutions of HNO3 or KOH, and ionic strength by addition of KNO3 solution. The flocculation response of the minerals is expressed as the percentage of suspended materials settling into the b o t t o m one-third volume fraction in the test tube during a settling time of 45 sec. One-third of the mineral that will be naturally distributed in the b o t t o m layer is excluded so that what is measured will correspond to that settling into the layer. The flocculation of mineral/polymer systems was studied as a function of flocculant concentration and time of conditioning of the mineral with flocculant. Selective flocculation experiments were conducted using synthetic mixtures of hematite--quartz and chalcopyrite--quartz prepared by addition

305 TABLE I APPROXIMATE MOLECULAR

FLOCCULANT

DESCRIPTION

WEIGHT CATIONIC POLYACRYLAMIDE NALCOLYTE-610 Nalco

Chemical

SEPEARAN-AP 30 Dow

Chemical

106

~CH2_~H ~ L CONH2

106

ANION; C POLYACRYLAMIDE

Comp.

~

Comp.

~H,-CH----I--~ +~--CH^-CH--~

/ L .

~ ! . ~ . 7

L

L-

z I

CONH2

--'-J'~

COOH

I

POLYSTYRENE SULFONATE (Sodium Polysciences

Salt)

106

, Inc.

ANIONIC r~ -~CH2CH-C6H5SO3Na~ L J NONIONIC

KLUCEL HF Hercules, Inc.

106

~ LI

z

,

,

~

~

o

.

o

~

~

o

2

~.;~., '~oc,,.~2icsc~] oH

3

J

ocx2~al 3 ca

CORN STARCH National Starch and Chemical Comp.

5000

NONIONIC

,../~-I~k~ ~ ~ a

oH

of equal amounts of single minerals and equilibrating the mixed fines for one hour. These tests were conducted in 4 cm diameter and 15 cm long test tubes at 5% solids. The pulp was first conditioned with the floccculant for 30 sec and then, after allowing it to settle for 45 sec, the supernatant (top 67% of the total volume) was siphoned out using vacuum. For the purpose of cleaning, the floc portion was rediluted to the original volume with distilled water, conditioned for 30 sec (without further addition of flocculant} and then after 45 sec, the supernatant was again siphoned off. The supernatant product (wash), the material initially siphoned (tailing) and the final floc product (concentrate) were all analyzed for the ifidividual minerals. Electrokinetic measurements were made using a Zetameter. Towards this purpose, a fraction of the flocculated slurry was brought to a 0.1% solids concentration by the addition of electrolyte that resulted from centrifugation of the slurry from the s a m e test.

306 RESULTS AND DISCUSSIONS

Flocculation of single mineral suspensions Flocculation refers to the process of aggregation involving interparticle bridging (La Met, 1964; Kane and La Mer, 1964). Ability of polymers to brdige particles together arises partly from the conformational properties of the adsorbed polymer species. Polymer molecules are considered to adsorb on mineral particles by attachment at a few sites with tangling loops and loose segments projected into the suspending meditun (Silberberg, 1972; Eirich, 1977). Interparticle bridging follows such adsorption of polymers either due to adsorption of these projected polymer segments on uncovered surfaces of other particles or due to intertwining of the projected polymer segments from different particles. As a result, individual particles grow into three-dimensional networks called flocs. Such flocculation can be expected to depend on both the structure of adsorbed polymer species and the availability of uncovered particle surface for bridging. Time of reagentization of the mineral with polymer solution can affect bo~h of the above mentioned parameters governing flocculation (Botham and Thies, 1969). Increased reagentization can result in an increase in the adsorption density and therefore in an increase in the fraction of surface covered by polymer molecules. Also, a redistribution of the adsorbed polymer segments among the suspending medium and particle surface can occur at the same time and this may l e a d t o further increase in surface coverage even at constant adsorption density. At a certain initial polymer concentration, surface coverage of particles at any given time is determined by the kinetics of adsorption of the polymer (Lipatov and Sergeeva, 1972). Role of these factors in governing flocculation was examined for the present system with the help of results obtained for flocculation of hematite as a function of conditioning time with polymer solution. Such data for hematite/Separan AP-30 (hydrolyzed polyacrylamide) system is given in Fig. 1 where the percentage solids settled in 45 sec is plotted as a function of conditioning time. Results given in this figure indicate that maximum flocculation is reached within short periods of conditioning and prolonged conditioning causes some redispersion of the flocculated material. Conditioning times corresponding to maximum flocculation for the system in Fig. 1 are about 60 sec at pH 7.8 and 120 sec at pH 4. These results suggest slower kinetics of adsorption of polymer and flocculation at pH 4 than at pH 7.8. The active group of the polymer used in this study was carboxylate with a pH value of 4.7 (Aplan and Fuerstenau, 1962). These groups will be in fully associated form at pH 4 whereas, at pH 7.8, they will be fully dissociated. Absence of sufficient number of anionic groups on the polymer at pH 4 can indeed cause retardation of its adsorption on the hematite particles that are positively charged. Flocculation response of quartz as a function of conditioning time with Separan AP-30 is shown in Fig. 2. Good flocculation of quartz was observed using the anionic polymer at pH 7 where quartz is negatively changed.

307 75

"i" pH : 4 0

POLYMER DOSAGE =30 PPM

} 600

0

l

I

~200

~BO0

240O

CONDITIONING I"IME, SECONDS

Fig. 1. Percentage of hematite fines settled as a function of time of reagentizing with Separan AP-30; settling time, 45 sec.

95

o

85

J

-

-J o u~

I)H = 7 0

75

POLYME)~ DOSAGE = 30 F'PM

65

0

I 400

I BOO

I 1200

CONDITIONING TIME, SECONDS

Fig. 2. Percentage of quartz fines settled as a function of time of reagentizing with Separan AP-30; settling time, 45 sec.

308 Flocculation of negatively charged quartz by this anionic polymer is probably due to hydrogen bonding or contamination of quartz during its grinding in porcelain mill. However, maximum in flocculation was not as sharp in this case as in the case of hematite and conditioning time corresponding to the maximum is at about 600 sec. The relatively slow flocculation is probably due to the weak forces of adsorption between the anionic polymer and similarly charged quartz particles. The large difference observed here between the optimum reagentization times for hematite and quartz suggests the possibility of using times of conditioning of mineral with polymer solution for achieving a limited selectivity in flocculation. Adsorption of polymer molecules on mineral particles is governed mainly by three types of bonding, namely, electrostatic, hydrogen and covalent bonding. The predominance of any of the above three bonding mechanisms over other depends on the particular mineral/polymer system and properties of the suspending medium. A combination of the above mechanisms can also be operative under favourable conditions. The role of electrostatic forces in controlling adsorption of polymers and flocculation is further discussed in this section. Electrostatic bonding is the predominant mechanism by which ionic polymers can adsorb on mineral particles that are usually charged in solutions. Polymer molecules, by adsorption on oppositely charged particles, can neutralize the charge on particle surface and decrease the interparticle repulsive forces that prevent aggregation of particles (Ries and Meyers, 1968). Adsorption of ionic polymers on similarly charged particles is not 100J-

__

[50 0

•

It •

I 60

I 120

180

POLYMER CONC., PPM (DRY SOLIDS BASIS)

Fig. 3. P e r c e n t a g e o f s y n t h e t i c silica s e t t l e d as a f u n c t i o n o f c o n c e n t r a t i o n of Nalcolyte-

610 and Separan AP-30; reagentizingtime, 30 sec; settling time, 45 sec.

309

possible if the interfacial potential is sufficiently high to introduce electrostatic repulsion. For example, results shown in Fig. 3 indicate that synthetic silica (Biosil-A) can be flocculated with the cationic polyacrylamide, Nalcolyte-610, but not with the anionic polyacrylamide, Separan AP-30. Addition of Separan AP-30 did not result in any increase in the fraction of silica settled in 45 sec. Since the silica particles are highly negatively charged in the pH range tested, electrostatic forces can evidently be considered as responsible for controlling their flocculation. It is to be noted, however, from Fig. 4, that good flocculation of hematite was obtained with both of these polymers eventhough anionic Separan was slightly more effective than cationic Nalcolyte. Figure 5 shows the flocculation response of hematite at various concentrations of sodium polystyrenesulfonate as a function of pH. Anionic polystyrenesulfonate flocculates hematite better at lower pH values where the mineral is positively charged than at higher pH values where it is negatively charged. These results indicate the complex nature of mechanisms involved in flocculation of mineral suspensions. Though electrostatic forces are observed to govern flocculation of some of the above systems, observed flocculation cannot be explained on the basis of electrostatic bonding alone for all cases. For the present systems, it is suggested that flocculation is dependent on a number of mechanisms, the predominance of any one mechanism being dependent on the particular mineral/polymer combination and physicochemical properties of the suspending medium.

loo

~

~.

J.

I

=7;:°0

o 75 w J

dm • 5o

25

I 0

1

I

50 I00 150 POLYMER CONC., PPM (DRY SOLIDS BASIS)

I ~lO

Fig. 4. Percentage of hematite fines settled as a f u n c t i o n of c o n c e n t r a t i o n of Nalcolyte610 and Separan AP-30; reagentizing time, 30 see; settling time, 45 s e c .

310 100

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-

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% SOLIDS SETTLED

so q l i ~ o

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POLYSTYRENESULFONATE --~-200 ppm - - 1 1 - - 5 0 ppm --0~4 pprn - - dl~-.- 0 ppm I I I I 1 3 5 7 pH

•

I 9

i I1

13

F i g . 5. P e r c e n t a g e o f h e m a t i t e f i n e s s e t t l e d as a f u n c t i o n o f p H a n d e o n e e n t r a t i o n sodium polystyrenesulf0nate; r e a g e n t i z i n g t i m e , 3 0 see; s e t t l i n g t i m e , 4 5 see.

of

Selective flocculation of synthetic mineral mixtures Preferential flocculation of a single or a group of mineral particulates from a suspension containing more than one mineral is referred to as selective flocculation. Success of the selective flocculation technique in beneficiating heterogeneous natural ores will depend on a number of factors, some of which include: (a) good dispersion of the fine particles in suspension; (b) preferential adsorption of the dissolved polymer molecules on particles and subsequent flocculation; and (c) effective separation of the flocs from the suspension. Results of the tests on selective flocculation of hematite and chalcopyrite from their mixtures with quartz; and effect of the above mentioned parameters on the separation are discussed in this section.

Hematite--quartz mixture using sodium polystyrenesulfonate Preferential adsorption of long-chain alkyl sulfonates on iron oxide minerals is well known in flotation. Chemical aspects of flotation collectors and polymeric flocculants are similar in several ways. Experiments were conducted to determine whether such selectivity can be obtained with sulfonate

311

,ij./< i

o

60

4)- QUARTZ pH=6.9 ~Ir HEMATITE pH=7.8

40

2O

o

0

I

L

L

50 I00 150 POLYMER CONC.,PPM(DRY SOLIDSBASIS)

I

210

Fig. 6. P e r c e n t a g e o f h e m a t i t e fines a n d q u a r t z fines s e t t l e d as a f u n c t i o n o f c o n c e n t r a t i o n of s o d i u m p o l y s t y r e n e s u l f o n a t e ; r e a g e n t i z i n g time, 30 sec; settling time, 4 5 sec.

polymers in the flocculation of hematite. The flocculation responses for single mineral suspensions of hematite and quartz are shown in Fig. 6 as a function of concentration of sodium polystyrenesulfonate. The percentage of hematite settling in 45 sec is higher thamthat for quartz and the results suggest that separation of hematite from quartz b y selective flocculation should be possible unless there are strong interactions between these t w o minerals. The results obtained for selective flocculation tests are shown in Fig. 7. The recovery and grade in terms of % Fe2 Oa in the settled portion are shown in this figure as a function of flocculant concentration. Grade of the settled portion is observed to increase marginally with flocculant concentration, attain a maximum and then decrease in the higher concentration range. However, the recovery of iron oxide is found to increase sharply with increase in flocculant concentration and reach a constant value of a b o u t 75%. The decrease in the grade of the settled,portion at higher flocculant concentration indicates commencement of flocculation on entrapment of quartz particles in this concentration range. The settled portion was cleaned by redispersing in water to remove the weakly flocculated and mechanically entrained quartz particles. The grade and recovery obtained after one cleaning operation are also given in Fig. 7. Cleaning of the settled portion has improved the grade with a simultaneous decrease in recovery of iron oxide.

312

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i~lO0

7o ~

2

" ~

I ~o

~ o+ RECOVERY ,N F,RST F OC

L~

50~-- / I/ /

40~0

S

-O- Fez 0 3 RECOVERY AFTER ONE CLEANING

-O- ASSAY,AFTER ONECLEANING -Q- ASSAY,FIRSTFLOC pH = 77 TO 7.8

I 6o

I ]20

1 Ie0

234!5

POLYMER CONC., PPM (DRY SOLIDS BASIS)

Fig. 7. Recovery and grade of the concentrate from selective/loeculation of hematite-quartz m i x t u r e as a function of c o n c e n t r a t i o n of sodium p o l y s t y r e n e s u l f o n a t e ; reagentizing time, 30 sec; settling time, 45 sec.

In order to evaluate the performance of flocculation, and in particular, cleaning, both grade and recovery will have to be considered. Separation index incorporates b o t h of these variables and is defined as "(percentage of value mineral recovered in the concentrate + percentage of gangue rejected in the tailing - 100)/100". A value of either plus or minus unity for separation index refers to complete separation of the minerals and a value close to zero refers to failure of the process. Calculated values, of separation index for the results shown in Fig. 7 are given in Fig. 8. These results indicate that cleaning of the flocculated product has improved the separation significantly. The importance of cleaning the flocculated slurry has been discussed earlier by Friend et al. (1973) and Clauss et al. (1976). In order to elucidate the mechanisms by which such polymers act, zetapotential measurements of hematite particles were made as a function of concentration of the flocculant. Measurements were done under variable and constant ionic strength conditions at two pH values, i.e., 7.8 where the hematite particles are negatively charged and 4 where the hematite particles are positively charged*. The results obtained are given in Fig. 9a, b. At pH 4, adsorption of the anionic polymer on the positively charged hematite particles is found to produce a decrease in the zeta potential and even make the surface negatively charged. Tests could not be continued at pH 4 and ionic • Point of zero charge for the massive red h e m a t i t e (95% pure) used in this study is at pH 5 (Sresty, 1977)

313 1.00

AFTER ONE CLEANING FIRST FLOC 0.75 -

Z

z

05C

02~

o .o( o

I Ioo

l 200

300

POLYMER CONC., PPM(DRY SOLIDS BASIS)

Fig. 8. Separation index achieved f r o m selective flocculation of h e m a t i t e - - q u a r t z mixture as a f u n c t i o n of c o n c e n t r a t i o n of sodium polystyrenesulfonate; reagentizing time, 30 sec; settling time, 45 sec.

strength of 10 -2 M above a polymer concentration of 100 ppm as there was excessive flocculation making the measurements difficult. Excellent flocculation was observed even after the charge reversal of hematite particles. Similar results were earlier obtained by Somasundaran et al. (1966) for aggregation of alumina using sodium dodecylsulfonate. Such charge reversal normally suggests specific adsorption of the polymer molecules due to forces that are non-electrical in nature. In this case, however, it is most interesting to note that polymer adsorption has also caused a decrease in zeta potential of similarly charged particles at pH 7.8. Under constant ionic strength conditions, adsorption of negatively charged molecules cannot normally be expected to make the mineral particles less negative. The observed results clearly suggest a significant shift in the shear plane due to adsorption of the massive polymer molecules. In fact, under these conditions, the zeta potential obtained can be considered to be a good measure of the adsorbed polymer layer rather than that of the original mineral particles themselves.

314 3O pH

= 3.7

-&- pH = 7.8 >

15

w

~

-15

-30 o

30

L

1

,

50

IO0

150

200

POLYSTYRENE SULFONATE CONC., PPM (DRY SOLIDS BASIS)

: pH=3.B TO4O

@

£0 pH

o -I0 Q_

~

7.8

-

- 20

-30'

0 b

I

I

I

50

ICO

150

200

POLYSTYRENE SULFONATE CONC., PPM (DRYSOLIDS BASIS)

Fig. 9a. Zeta potential of hematite fines as a function of concentration of sodium polystyrenesulfonate, natural ionic strength, b. Zeta potential of hematite fines as a function of concentration of sodium polystyrenesulfonate; ionic strength 10 .2 M KNO3.

Hematite--quartz mixture using causticized corn starch Selectivity o f corn starch in depressing iron o x i d e during anionic flotation o f silica and in selectively flocculating iron oxides are well k n o w n ( C o o k e et al., 1 9 5 2 ; Iwasaki et al., 1 9 6 9 ) . The selectivity of starch in depressing iron oxides during flotation o f silica from iron ores depends to a large e x t e n t on the f u n c t i o n a l groups present in the starch m o l e c u l e (Iwasaki et al., 1 9 6 9 ) . Chang ( 1 9 5 2 ) has reported o x i d i z e d starch to p r o d u c e m o s t preferential adsorption o n hematite particles than other types.

315

Flocculation responses of hematite and quartz fines in the presence of causticized corn starch are shown in Fig. 10. Increase in settling of hematite due to flocculation is larger than that of quartz. Also, the difference between the flocculation response of these two minerals in the presence of causticized corn starch is greater than that in the presence of sodium polystyrenesulfonate suggesting better selectivity with starch than with the latter. Results of the selective flocculation experiments using hematite-quartz mixtures are given in Fig. 11. In this case, a satisfactory separation index of 0.7 was in fact obtained after a one-stage cleaning of the flocculated product. A single stage cleaning of the flocculated product has produced significant improvement in the separation index for both of the above mentioned systems. The effect of multiple-st,age cleaning of the flocculated product on both grade and recovery was determined at two concentrations of starch. Multiple-stage cleaning of the flocculated slurry produced significant improvement in the grade owing to further removal of entrained quartz. As expected, recovery, however, decreased during each stage of cleaning. The effect of multiple-stage cleaning on the separation index obtained for selective flocculations are shown in Figs. 12 and 13. Due to the existence of an apparent upper limit of grade that can be obtained in this case, improvement in separation index occurred only during the first few stages of the cleaning. Under these conditions, scaverging of the tailings might be necessary to obtain economically acceptable separation levels. These results also 1(:)0

JL

JL

80

.J w 60 U)

N 40

2C

0

l 50

I I00

I 150

I 210

STARCH CONC., PPM (DRY SOLIDS BASIS) F i g . 1 0 . P e r c e n t a g e o f h e m a t i t e f i n e s a n d q u a r t z f i n e s s e t t l e d as a f u n c t i o n t i o n o f s t a r c h ; r e a g e n t i z i n g t i m e , 3 0 s e e ; s e t t l i n g t i m e , 4 5 see.

of concentra-

316 ]00

x/0

75

z

z

o o5o

0251UI4-/

~ AFTER ONE CLEANING

/

FIRST FLOC

0. O0 0

lO0 2 O0 STARCH CONC., PPM (DRY SOLIDS BASIS)

300

Fig. 11. Separation index achieved from selective flocculation of h e m a t i t e - - q u a r t z mixture as a f u n c t i o n of c o n c e n t r a t i o n of starch; reagentizing time, 30 sec; settling time, 45 sec 100

08

\\

o7

90

(~

/

u~

/

"I" °I° FezO' RECOVERY

~

u~

"Jr ASSAY% Fe203

~

9.4

•I-SEPARATION INDEX STARCH CONC. =BO PPM, pH =7.7 7C

0

I

l

I

I

I

1

2

3

4

5

3.3

NUMBER OF CLEANINGS

Fig. 12. R e c o v e r y and grade of the concentrate, and separation index achieved f r o m selective flocculation of h e m a t i t e - - q u a r t z m i x t u r e s using starch as a f u n c t i o n of n u m b e r of cleaning stages; reagentizing time, 30 sec; settling time, 45 sec.

317 100

0.9

~

o 9('

,,..Q~ ' ~ ~~/

-

"

0.8

r,~ " " - 4 . H

,,~ o~

sc ~

/?

LL

//'~

~ % Fe20~, RECOVERY

,//

-a,-ASSAY % Fe~03

i

~

0.6

SEPARATION INDEX

STARCH CONC.= 220 PPM

/

0.5

pH = 7.7

7C 0

1 1

I

I

2

3

I 4

I 5

0.4

NUMBER OF CLEANINGS

Fig. 13. Recovery and grade of the concentrate, and separation index achieved from selective flocculation of hematite--quartz mixture using starch as a function of number of cleaning stages; reagentizing time, 30 sec; settling time, 45 sec.

show that optimum amount of cleaning depends on the concentration of polymer added. In the present case, use of higher polymer concentrations are found to require a larger number of cleaning stages. Chalcopyrite--quartz mix ture using xan thate Selective adsorption of xanthates on heavy minerals such as chalcopyrite, galena and sphalerite in preference to quartz and calcite has resulted in its extensive use as collectors in the flotation of sulfide minerals. An ideally selective flocculant can be made for separating these minerals from gangue by incorporating the sulfhydryl group into long chain polymers. Hydroxypropylcellulose supplied by Hercules, Inc., under the name "Klucel H F " is a high-molecular weight surface-active polymer with foaming tendency. This polymer also possesses a long flexible chain which can be helpful for flocculation. Hydroxypropylcellulose xanthate was prepared by reacting this polymer with three moles of potassium hydroxide and three moles of carbondisulfide. FloccMation responses of both chalcopyrite and quartz fines as a function of concentration of hydroxypropylcellulose xanthate at the corresponding natural pH values for these systems is illustrated in Fig. 14. It is seen that this polymer can be effective in flocculating chalcopyrite with practically no effect on quartz. The results obtained for the selective flocculation of chalcopyrite from chalcopyrite--quartz mixture are given in Fig. 15. An excellent separation index of 0.75 was obtained after a one-stage cleaning operation.

Z5

5C

0

CHALCOPYRITE pH =3.61

I 200

XANTHATE CONC., PPM (DRY SOLIDS BASIS)

I00

~

-I'QUARTZ=pH =7.0

3OO

x

~

Z I.--I

f-..-..8--

•A- FIRST FLOC

o.oc O

,_.__----I

XANTHATE CONC., PPM (DRY SOLIDS BASIS)

I 500

I I000

"1-AFTER ONE CLEANING

O25 ~"~'~"'~"'----.~

0.5C

0.75

1.OC

Fig. 15. Separation index achieved f r o m selective flocculation o f chalcopyrite--quartz mixture as a function o f concentration o f h y d r o x y p r o p y l c e l l u l o s e xanthate; reagentizing time, 30 sec; settling time, 45 sec.

Fig. 14. Percentage of chalcopyrite fines and quartz fines settled as a f u n c t i o n of concentration of h y d r o x y p r o p y l c e l l u l o s e xanthate; reagentizing time, 30 sec; settling time, 45 sec.

-J ~'-

75

I00

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319 CONCLUSIONS Flocculation o f mineral suspensions is sensitive to m a n y operating variables and the effect of some of these variables such as the t y p e of active group present in the p o l y m e r molecules is very significant. Results obtained in this study have indicated the existence of an o p t i m u m reagentizing time o f the mineral with the p o l y m e r solution, which was d e p e n d e n t on the particular min er a l / pol ym er system and the electrolytic properties of the suspending medium. Conditions t hat permit favourable electrostatic forces between mineral particles and p o l y m e r molecules do induce flocculation, but all of the results obtained could n o t be explained on the basis of an electrostatic mechanism alone. Selective flocculation experiments c o n d u c t e d with mixed mineral systems under conditions selected on the basis of the results obtained for single mineral suspensions f ur t her confirms selective flocculation to be a feasible process. Selectivity of the polymers towards flocculation can be improved significantly by the incorporation of suitable functional groups into the polymeric chains. Cleaning of the flocculated p r o d u c t is observed to be essential for obtaining satisfactory separation. Electrokinetic tests c o n d u c t e d for h e m a t i t e / p o l y s t y r e n e s u l f o n a t e system at different pH values gave indications for a shift of the shear plane. In the case of a polymer-coated particle, the results suggest t hat the value o f the zeta potential obtained to be characteristic of the adsorbed p o l y m e r layer itself rather than t hat of the original particle. ACKNOWLEDGEMENT The s u p p o r t of the Particulate and Multiphase Processes Program of the National Science F o u n d a t i o n and the International Nickel C o m p a n y is gratefully acknowledged.

REFERENCES Aplan, F.F. and Fuerstenau, D.W., 1962. Principles of non-metallic mineral flotation. In: D.W. Fuerstenau (Editor}, Froth Flotation. 50th Anniversary volume, AIME, p. 170. Attia, Y.A.I. and Kitchener, J.A., 1975. Development of complexing polymers for the selective flocculation of copper minerals. In: M. Carta (Editor}, Proc. XIth Int. Congr. Miner. Process. Universata di Cagliari, p. 1233. Botham, R. and Thies, C., 1969. The effect of stereoregularity upon the adsorption behavior of high molecular weight poly (isopropylacrylate). J. Colloid Interface Sci., 31: 1. Chang, C.C., 1952. Substituted starches in amine flotation of iron ores. Trans. AIME, 199: 922. Clauss, C.R.A., Appleton, E.A. and Vink, J.J., 1976. Flocculation of cassiterite in mixtures with quartz using a modified polyacrylamide flocculant. Int. J. Miner. Process., 3: 27.

320 Cooke, S.R.B., Schulz, N.F. and Lindross, E.W., 1952. The effect of certain starches on hematite and quartz suspensions. Trans. AIME, 193: 697. Einrich, E.F., 1977. The conformational states of macromolecules adsorbed at solidliquid interfaces. J. Colloid Interface Sci., 58: 423. Friend, J.P., Iskra, J. and Kitchener, J.A., 1973. Cleaning a selectively flocculated mineral slurry. Trans. IMM, 833: C235. Frommer, D.W., 1968. Preparation of nonmagnetic taconites for flotation by selective flocculation. Proc. VIIIth Int. Congr. Miner. Process., Leningrad, Paper D-9. Iwasaki, I., Carlson, W.J. and Parmerter, S.M., 1969. The use of starches and starch derivatives as depressants and flocculants in iron ore beneficiation. Trans. AIME, 244: 88. Kane, J.C. and La Mer, V.K., 1964. The effect of solid content on the adsorption and flocculation behavior of silica suspensions. J. Phys. Chem., 68: 3539. La Mer, V.K., 1964. Introduction to colloid symposium. J. Colloid Sci., 19: 191. Lipatov, Yu. S. and Sergeeva, L.M., 1972. Adsorption of Polymers. Wiley, New York, N.Y. Read, A.D., 1972. The use of high molecular weight polyacrylamides in the selective flocculation separation of a mineral mixture. Br. Polym. J., 4: 253. Ries, H.E., Jr. and Meyers, B.L., 1968. Flocculation mechanism: Charge neutralization and bridging. Science, 160: 1149. Silberberg, A., 1972. Multilayer adsorption of macromolecules. J. Colloid Interface Sci., 38: 217. Somasundaran, P., Healy, T.W. and Fuerstenau, D.W., 1966. The aggregation of colloidal alumina dispersions by adsorbed surfactant ions. J. Colloid Interface Sci., 22: 599. Sresty, G.C., 1977. Beneficiation of Mineral Slimes: Flocculation and Selective Flocculation. M.S. Thesis, Columbia Univ., New York, N.Y. Usoni, L., Rinelli, G., Marabini, A.M. and Ghigi, G., 1968. Selective properties of flocculants and possibilities of their use in flotation of fine minerals. Proc. VIIIth Int. Congr Miner. Process., Leningrad, Paper D-13.k