Sulfur: New Sources and Uses - American Chemical Society

7 Sulfur from the Hydrometallurgical Processing of Sulfide Materials

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A . T. W I L S O N Duval Corporation, Tucson, AZ 81502

In the classical pyrometallurgical smelting of metal sulphide concentrates most of the sulphur is driven off as sulphur dioxide. This process is becoming increasingly unacceptable from an environmental point of view. An alternative is to process the concentrates using hydrometallurgical techniques. In these processes the metal sulphides are reacted with a saline acid solution containing f e r r i c or cupric chlorides or sulphates. This results in the solubilization of the metal as a complex ion while the sulphide sulphur is converted to elemental sulphur. The sulphur remains in the leach residue mixed with pyrite and siliceous material which were the contaminants of the original metal sulphide flotation concentrate. As the nonferrous smelting industry changes from pyrometallurgy, large quantities of hydrometallurgical sulphur w i l l become available from the processing of copper, lead and zinc sulphide concentrates. The sulphur produced from hydrometallurgical processes w i l l be more impure than Frasch sulphur but in some cases it can be upgraded for use in sulphur burning acid plants. In i t s impure state it could also find a use in sulphur extended asphalt highway or sulphur concrete construction. The c l a s s i c a l p y r o m e t a l l u r g i c a l method of p r o c e s s i n g metal s u l p h i d e concentrate is to heat the m a t e r i a l in a i r and d r i v e o f f the sulphur as sulphur d i o x i d e . T h i s process is becoming i n c r e a s i n g l y unacceptable from an environmental p o i n t of view. An a l t e r n a t i v e that is r a p i d l y emerging is to process the conc e n t r a t e using h y d r o m e t a l l u r g i c a l techniques. Aqueous s o l u t i o n s of c e r t a i n metal s a l t s w i l l c h e m i c a l l y attack most metal s u l phides, t a k i n g i n t o s o l u t i o n the c o n s t i t u e n t metals and l e a v i n g behind a residue of elemental sulphur. Because of the l a r g e 0097-6156/82/0183-0101$05.00/0 © 1982 American Chemical Society

In Sulfur: New Sources and Uses; Raymont, M.; ACS Symposium Series; American Chemical Society: Washington, DC, 1982.

SULFUR: NEW SOURCES A N D USES


102

tonnages o f metal sulphides processed each year one might expect by-product sulphur from t h i s source t o make a s i g n i f i c a n t c o n t r i b u t i o n t o the t o t a l sulphur a v a i l a b l e in the f u t u r e . The present development o f h y d r o m e t a l l u r g i c a l processing of metal sulphides not only stems from the d i f f i c u l t y p y r o m e t a l l u r g i c a l smelters have in meeting c u r r e n t environmental l i m i t s on sulphur d i o x i d e emissions but a l s o the f a c t t h a t it is only r e l a t i v e l y r e c e n t l y that s u i t a b l e c o r r o s i o n r e s i s t a n t m a t e r i a l s such as p l a s t i c s and metals (e.g. t i t a n i u m ) have been a v a i l a b l e to make such hydrom e t a l l u r g i c a l processing t e c h n i c a l l y f e a s i b l e . H y d r o m e t a l l u r g i c a l Processes The most l i k e l y minerals t o be processed using hydrometallurg i c a l techniques would probably be s p h a l e r i t e (ZnS) and c h a l c o p y r i t e (CuFeS ). Duval C o r p o r a t i o n in Tucson already has a 40,000 t o n (of copper per year) h y d r o m e t a l l u r g i c a l p l a n t produci n g about 38,000 tons/year o f h y d r o m e t a l l u r g i c a l by-product sulphur ( 1 ) . Since about 2x10 tons o f copper as s u l p h i d e minera l a r e smelted each year in the United States and Canada there is the p o t e n t i a l f o r 2x10 tons/year o f sulphur produced as the byproduct o f such p r o c e s s i n g i f a t o t a l conversion is made t o hydrom e t a l l u r g i c a l p r o c e s s i n g . The impact would be e s p e c i a l l y great in the copper producing areas o f the world such as Western U.S. and Canada, C h i l e and A f r i c a . Of course the development o f a nonp o l l u t i n g process such as Duval's CLEAR process could move the s m e l t i n g o p e r a t i o n away from the mining areas and nearer t o the centers o f p o p u l a t i o n . Lead s u l p h i d e (galena - PbS) is another l i k e l y candidate f o r h y d r o m e t a l l u r g i c a l p r o c e s s i n g p a r t i c u l a r l y in the United States where, apart from the problems of the sulphur d i o x i d e emissions, the l e a d t o x i c i t y problem is making it very d i f f i c u l t f o r the l e a d smelters t o operate t h e i r c o n v e n t i o n a l p y r o m e t a l l u r g i c a l process and comply w i t h EPA and OSHA standards. The t o t a l amount of l e a d mined in the United States is about 600,000 tons per year which, i f f u l l y converted, would y i e l d about 100,000 tons per year o f by-product sulphur. The Bureau of Mines in Reno, Nevada, have an a c t i v e p i l o t p l a n t study to produce l e a d v i a a hydrometall u r i g a l process (2). I n t h i s process the common l e a d m i n e r a l galena is d i s s o l v e d in an a c i d b r i n e s o l u t i o n o f f e r r i c c h l o r i d e . 2

6

6

PbS + 2 F e C l

3

+ PbCl

2

+ 2FeCl

2

+ S°

A l i q u i d / s o l i d s e p a r a t i o n y i e l d s a r e s i d u e and a s o l u t i o n . The s o l u t i o n is cooled t o produce c r y s t a l l i n e P b C l which is l a t e r e l e c t r o l y z e d t o l e a d metal and c h l o r i n e in a fused s a l t c e l l . The r e s i d u e c o n s i s t s o f elemental sulphur, p y r i t e and gangue. The s o l u t i o n is r e o x i d i z e d t o convert the f e r r o u s i r o n back to f e r r i c i r o n . 2


7.

WILSON

Hydrometallurgical Processing of Sulfide Materials

103

S p h a l e r i t e ( z i n c s u l p h i d e ) is a s t r o n g contender f o r hydrom e t a l l u r g i c a l p r o c e s s i n g . North America mines 2 x 1 0 tons of z i n c per year as z i n c s u l p h i d e which represents a p o t e n t i a l of 6 0 0 , 0 0 0 tons of by-product sulphur per year. S h e r r i t t - G o r d o n and Cominco are a c t i v e in developing a h y d r o m e t a l l u r g i c a l process f o r processing z i n c ores (3)(4)(5), and Cominco has c o n s t r u c t e d a 6 5 , 0 0 0 ton/ year Zn ( 2 0 , 0 0 0 tons/year S°) p l a n t in T r a i l , B r i t i s h Columbia. The z i n c pressure sulphate l e a c h system has the o v e r a l l reaction: Downloaded by UNIV OF CALIFORNIA SANTA BARBARA on August 24, 2015 | http://pubs.acs.org Publication Date: March 29, 1982 | doi: 10.1021/bk-1982-0183.ch007

6

+ Fe (S0i»)3 + ZnSOi, + 2FeS0i* +

(A)

ZnS

(B)

2FeS0

2

lt

+ H2SO4 + ^ 0

2

+ Fe (S0i*) 2

3

+

S° H 0 2

The r e s i d u e from t h i s r e a c t i o n c o n s i s t s of two e a s i l y separated types of s o l i d s , one b e i n g an elemental sulphur-metal s u l p h i d e - p y r i t e f r a c t i o n , the other being an i r o n o x i d e - l e a d sulphate (or j a r o s i t e ) - g a n g u e f r a c t i o n . The sulphur in the T r a i l p l a n t is recovered from a s e p a r a t i o n autoclave by continuous décantation of the aqueous z i n c sulphate phase along w i t h the oxide-gangue p o r t i o n of the s o l i d s , and continuous or p e r i o d i c removal of the molten elemental sulphur from the bottom of the v e s s e l . The molten sulphur c o n t a i n s p y r i t e and a s m a l l amount of metal s u l p h i d e s , and so is f i l t e r e d to produce e s s e n t i a l l y pure sulphur. The z i n c sulphate s o l u t i o n is processed through the normal p u r i f i c a t i o n and e l e c t r o w i n n i n g c i r c u i t s to produce element a l z i n c and spent l i q u o r which is r e t u r n e d to the pressure l e a c h ing step. The sulphur produced in the Cominco p l a n t is c u r r e n t l y burnt in t h e i r s u l p h u r i c a c i d p l a n t . Although the p r o d u c t i o n of by-product sulphur from hydrom e t a l l u r g i c a l p r o c e s s i n g of s u l p h i d e m i n e r a l s would appear to have a p o t e n t i a l l y l a r g e impact on sulphur p r o d u c t i o n , it probably w i l l not always compete d i r e c t l y w i t h c o n v e n t i o n a l sulphur but w i l l probably generate i t s own end uses. For example, Duval's CLEAR P l a n t near Tucson in A r i z o n a c u r r e n t l y produces 3 8 , 0 0 0 tons/ year of by-product sulphur which might be compared w i t h A r i z o n a ' s c u r r e n t consumption of o n l y 6 , 0 0 0 tons/year. Only a p a r t of Duval's c h a l c o p y r i t e p r o d u c t i o n is processed in t h i s p l a n t and Duval is o n l y one of many copper mines in the Tucson area. To put the problem in p e r s p e c t i v e and to i l l u s t r a t e the type of product produced, Duval's CLEAR process is d e s c r i b e d below although g e n e r a l l y the same c o n s i d e r a t i o n s would apply to any hydrometall u r g i c a l treatment of a metal s u l p h i d e concentrate. Duval's CLEAR Process The CLEAR process is designed to completely l e a c h the copper v a l u e s from a copper concentrate c o n s i s t i n g of any combination of copper s u l p h i d e or copper i r o n s u l p h i d e m i n e r a l i z a t i o n . The most abundant copper m i n e r a l is c h a l c o p y r i t e whose composition is


104

SULFUR:

NEW

SOURCES

AND

USES

CuFeS . The r e a c t i o n is c a r r i e d out in a n e a r l y s a t u r a t e d s o l u t i o n c o n t a i n i n g copper, potassium and i r o n as a c t i v e e s s e n t i a l c o n s t i t u t e n t s together w i t h sodium and magnesium as n o n - r e a c t i v e c a t i o n s to m a i n t a i n the h i g h c h l o r i n i t y . 2

The d i g e s t i o n r e a c t i o n is c a r r i e d out in two steps: (A)

The r e d u c t i o n r e a c t i o n : -


H

+

2CuFeS + 3Cu~ " -> 4 C u + Fe* 2

+ 2S° + CuFeS

2

In p r a c t i c e it is d i f f i c u l t to d i s s o l v e a l l the c h a l c o p y r i t e in a reasonable time as i n d i c a t e d in the above r e a c t i o n so the s o l i d s from the r e a c t i o n are separated and passed to another r e a c t i o n v e s s e l where o x i d i z i n g c o n d i t i o n s are maintained. (B)

The o x i d i z i n g r e a c t i o n : -

CuFeS + 2 C u 2

+ +

+ Fe"*"*" + % ) + 3H 0 •> 3Cu~*~*" + 2Fe(0H) 2

2

3

+ 2S°

The l i q u o r from the f i r s t r e a c t i o n is used as a pregnant l i q u o r to be f e d to e l e c t r o w i n n i n g c e l l s . An important e l e c t r i c a l current b e n e f i t is r e a l i z e d in that it is o n l y necessary to con v e r t cuprous copper (Cu ) to copper r a t h e r than the c o n v e n t i o n a l e l e c t r o w i n n i n g process where c u p r i c copper (Cu* *) is converted to copper. In an a l t e r n a t i v e process developed by Cymet ( 6 ) , the cuprous c h l o r i d e is c r y s t a l l i z e d from t h i s l i q u o r by c o o l i n g . The cuprous c h l o r i d e is l a t e r reduced to copper in a furnace u s i n g hydrogen. In the o x i d i z i n g r e a c t i o n v e s s e l the p a r t i a l l y r e a c t e d con c e n t r a t e from the f i r s t stage is completely r e a c t e d in an oxygen enriched atmosphere. The i r o n is produced as b e t a - f e r r i c hydro x i d e or hematite ( F e 0 ) depending on the r e a c t i o n temperature. In the preceeding r e a c t i o n s a l l the sulphur is produced as elemen t a l sulphur; in p r a c t i c e a s m a l l amount is o x i d i z e d to sulphate which must be purged from the c i r c u i t . I n the Duval process t h i s is done by having potassium in the s o l u t i o n which, together w i t h i r o n and s u l p h a t e , leads to the p r e c i p i t a t i o n of potassium j a r o s i t e (ΚΡ€ (80θ (0Η) ). T h i s m a t e r i a l is an i n e r t i n s o l u b l e m a t e r i a l s i m i l a r to the m i n e r a l of the same name found in nature. The corresponding aluminum m i n e r a l a l u n i t e (KA1 (SOΟ (0H)s) is perhaps b e t t e r known. The i r o n , t h e r e f o r e , is produced from the o v e r a l l process as a mixture of potassium j a r o s i t e and b e t a - f e r r i c hydroxide which mixed w i t h sulphur can be r e a d i l y f i l t e r e d forming a s o l i d , r e l a t i v e l y dry, cake. +

-

2

3

2

3

6

3

2

H y d r o m e t a l l u r g i c a l By-Product Sulphur The m i n e r a l concentrate feed to any h y d r o m e t a l l u r g i c a l pro cess is u s u a l l y the product of a f l o t a t i o n process. T h i s process



7.

WILSON


105

i n v o l v e s t r e a t i n g the f i n e l y ground o r e in a f l o t a t i o n c e l l t o which s u i t a b l e chemicals are added and bubbles o f a i r a r e blown through the suspension. The chemicals and c o n d i t i o n s (e.g. pH) are arranged such that the m i n e r a l d e s i r e d is rended a e r o p h y l i c and attaches i t s e l f t o the bubbles and is c a r r i e d o f f in the f r o t h l e a v i n g the rock gangue behind in the m i n e r a l suspension. There is, however, always a s m a l l amount o f s i l i c e o u s m a t e r i a l locked t o the m i n e r a l p a r t i c l e s and t h i s is c a r r i e d through the process t o end in the r e s i d u e . F u r t h e r in p r a c t i c e most m i n e r a l o r e contains some p y r i t e (FeSa) and although t h i s is i n t e n t i o n a l l y suppressed during the f l o t a t i o n process a s m a l l amount is c a r r i e d forward w i t h the d e s i r e d metal s u l p h i d e . P y r i t e is r e f r a c t o r y t o hydrom e t a l l u r g i c a l s o l u t i o n s and l a r g e l y s u r v i v e s the CLEAR process to end w i t h the r e s i d u e . Thus the sulphur from the h y d r o m e t a l l u r g i c a l process is produced mixed w i t h f e r r i c hydroxide, j a r o s i t e , s i l i c e o u s gangue and p y r i t e . The residue from any h y d r o m e t a l l u r g i c a l process would be s i m i l a r . C l e a r l y , i f i r o n was not a p a r t of the s t a r t i n g m a t e r i a l some would u s u a l l y be added t o remove the sulphate e i t h e r as sodium or potassium j a r o s i t e and there would be l e s s f e r r i c hydrox i d e and a greater p r o p o r t i o n of sulphur. Uses of H y d r o m e t a l l u r g i c a l

Sulphur

One p o s s i b l e approach t o the use of h y d r o m e t a l l u r g i c a l byproduct sulphur would be t o separate the sulphur by f r o t h f l o t a t i o n . I t is p o s s i b l e t o e n r i c h the sulphur w i t h respect to the b e t a - f e r r i c hydroxide, j a r o s i t e and s i l i c e o u s gangue but d i f f i c u l t to completely separate it from the sulphides which are r e f r a c t o r y to the h y d r o m e t a l l u r g i c a l s o l u t i o n s [e.g., p y r i t e (FeS2> and molybdenite (MoS )]. The sulphur could always be s o l v e n t e x t r a c t ed a t a cost to produce pure sulphur but being o f m i n e r a l o r i g i n w i l l always be more impure than Frasch sulphur which is of microb i o l o g i c a l o r i g i n . I t might, t h e r e f o r e , not be s u i t a b l e f o r modern c a t a l y t i c s u l p h u r i c a c i d p l a n t s because o f a r s e n i c and other i m p u r i t i e s which would poison the c a t a l y s t . There w i l l be an i n c e n t i v e t o use the h y d r o m e t a l l u r g i c a l by-product sulphur in i t s impure s t a t e o r p a r t l y enriched s t a t e . The most obvious use would be to use the sulphur e i t h e r as is, or c h e m i c a l l y modified as a p a r t i a l replacement f o r a s p h a l t in highway c o n s t r u c t i o n . Asphalt is expected t o become not only more expensive b u t in short supply e s p e c i a l l y as the petroleum i n d u s t r y b u i l d s hydrocracking f a c i l i t i e s t o convert more o f the a s p h a l t i c f r a c t i o n o f the crude oil i n t o other more v a l u a b l e products. The h y d r o m e t a l l u r g i c a l by-product sulphur could be used c l o s e t o i t s p o i n t of production which would most o f t e n be remote from the sources o f asphalt and hence have a t r a n s p o r t cost advantage. Recent work by the Southwest Research I n s t i t u t e in San Antonio, Texas, has produced a s y n t h e t i c asphalt type m a t e r i a l from sulphur [ c a l l e d Sulphlex (J)]. This a s p h a l t replacement contains no asphalt and is made 2



106

SULFUR:

NEW

SOURCES

AND

USES

from elemental sulphur, c h e m i c a l l y cross l i n k e d w i t h organic m a t e r i a l s such as cyclopentadiene. Manufacture of m a t e r i a l s of the Sulphlex type may be a p o s s i b l e use f o r the impure hydrom e t a l l u r g i c a l by-product sulphur. Another a t t r a c t i v e use f o r the sulphur-siliceous-ganguep y r i t e - f e r r i c h y d r o x i d e - j a r o s i t e product might be in sulphur concrete type m a t e r i a l s . Sulphur concrete is e s s e n t i a l l y rock aggregate where the voids are f i l l e d w i t h elemental sulphur which has been c h e m i c a l l y modified by r e a c t i o n w i t h a p l a s t i c i z e r such as dicyclopentadiene. For an account of sulphur concrete see the e x c e l l e n t review by M.E.D. Raymont ( 8 ) . Sulphur concrete possesses many u s e f u l f e a t u r e s e x h i b i t e d by other aggregatec o n t a i n i n g m a t e r i a l s as w e l l as some unique p r o p e r t i e s such as speed and ease of f a b r i c a t i o n and low cost. For example, curbs and g u t t e r s can be l a i d continuously using sulphur concrete. Extensive use has already been made in Canada of sulphur concrete f o r median b a r r i e r s , bumper b a r s , and in f a c t almost any use f o r which conventional concrete can be used where the object is not l i k e l y to be subjected to temperatures above the m e l t i n g p o i n t of sulphur and where the l i k e l i h o o d of a f i r e hazard is s m a l l . Conclusion H y d r o m e t a l l u r g i c a l processing of s u l p h i d e minerals may in the f u t u r e provide an important source of sulphur. This sulphur even when p u r i f i e d w i l l be more impure than Frasch sulphur. As produced from the h y d r o m e t a l l u r g i c a l process the sulphur w i l l always be contaminated w i t h s i l i c e o u s gangue and p y r i t e . In some cases, it w i l l be upgraded f o r use in sulphur burning a c i d p l a n t s , but there w i l l be a strong i n c e n t i v e to use the m a t e r i a l in i t s impure s t a t e f o r sulphur extended asphalt highway c o n s t r u c t i o n and sulphur concrete a p p l i c a t i o n s . Literature Cited 1.

2.

3.

4.

Atwood, G. E., L i v i n g s t o n , R. W., "The CLEAR Process, a Duval Corporation Development", E r z m e t a l l 33 (1980), 5, 251-255. Haver, F. P., Won, Μ. Μ., " F e r r i c C h l o r i d e - B r i n e Leaching of Galena Concentrate", U.S. Bureau of Mines Rep. I n v e s t . , 1976, 1805. Veltman, H., B o l t o n , G. L., " D i r e c t Pressure Leaching of Zinc Blende w i t h Simultaneous P r o d u c t i o n of Elemental Sulphur. A S t a t e - o f - t h e - a r t Review", E r z m e t a l l 33, 1980, 2, 76-84. Parker, E. G., and Romanchuk, S., "Pilot P l a n t Demonstration of Z i n c Sulphide Pressure Leaching", Lead-Zinc-Tin '80, Proceedings of World Symposium, 109 AIME Annual Meeting, Feb. 24-28, 1980, Las Vegas.


7. 5.

6.

7.


8.

WILSON


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Parker, E.G., " O x i d a t i v e Pressure Leaching o f Zinc Concentrates", Fifth Annual District S i x Meeting o f CIMM, Kimberley, B.C., Oct. 23-25, 1980. Goens, D.N., K r u e s i , P.R., "Process f o r the Recovery of Cuprous C h l o r i d e in the Presence of M e t a l I m p u r i t i e s " , U.S. Patent No. 4,013,457, Mar. 22, 1977. "Test Road Paved w i t h Plasticized S u l f u r " , Chemical and Engineeri n g News, (1980), 58 (35), 25. Raymont, M.E.D., "Sulphur Concretes and Coatings", Sulphur Development I n s t i t u t e of Canada, Calgary, 1978, New Uses for Sulphur Technology S e r i e s Number Four.

RECEIVED

October 5, 1981.


Sulfur: New Sources and Uses - American Chemical Society

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