Direct Leaching of sulfides: Chemistry and applications
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Direct Leaching of Sulfides: Chemistry and Applications
ERNEST PETERS
The sulfide minerals associated with copper, nickel, zinc, lead, and molybdenum concentrates are described according to their thermodynamic stability zones on Eh-pH diagrams. From these zones, the chemistry associated with various thermodynamically feasible decomposition paths is discussed, and process developments associated with the most favorable decomposition paths are briefly reviewed.
I . ~ X T R A C T I V E m e t a l l u r g y c o n s i s t s of t h e s c i e n c e a n d a r t of o b t a i n i n g c o m m e r c i a l g r a d e s of m e t a l f r o m o r e material mined from the earth's crust. For reasons of m a r k e t a b i l i t y , t h e f i n a l m e t a l s a r e a l m o s t a l w a y s standardized products; on the other hand, the ores from which extraction starts are enormously diverse. How does a metallurgist devise a process and design a plant around a newly discovered ore body (or, for that matter, a new plant for an old ore body) that will produce standard metal products in such a way as to justify the investment ? T h e m o s t c u s t o m a r y a n s w e r t o t h i s q u e s t i o n i s to c o n c e n t r a t e t h e o r e b y m e a n s of a s t a n d a r d m i n e r a l d r e s s i n g o p e r a t i o n , a n d t h e n to s m e l t t h e c o n c e n trates, again, in a relatively standard way. A refining process completes the route to marketable grades of m e t a l . T h i s a n s w e r w o r k s p a r t i c u l a r l y w e l l f o r those metals found in nature as sulfide minerals, bec a u s e a) t h e y a r e r e l a t i v e l y e a s y t o c o n c e n t r a t e , a n d b) t h e s u l f u r s u p p l i e s p a r t of t h e f u e l e n e r g y r e quired in the smelting operation. Furthermore, at smelting temperatures, the ore minerals lose their
identity in a molten mass, and the technical and scientific problems are limited to choosing operating conditions dictated by thermodynamics, mass transfer kinetics, and phase separations. There is now an excellent body of scientific knowledge and engineering experience in these areas, and so this processing problem responds with good reliability and predictability to a rather mature science and technology. However, two new problems have confronted us in t h i s l a s t q u a r t e r of t h e t w e n t i e t h c e n t u r y , r e l a t e d t o the exponentially increasing density of human settlements on a finite planet. These are environmental pollution and energy shortages. The metal extraction i n d u s t r y h a s b e c o m e a n e a r l y v i c t i m of t h e p u b l i c concern for these problems; the tall stack is a highly v i s i b l e s o u r c e of a i r p o l l u t i o n , a n d t h e h u n g e r f o r energy by the metal extraction industry appears to be well known. Environmental restrictions may make it uneconomic to use sulfur for fuel, and the metallurgist must consider the conflicting rumours that hydrometallurgy offers pollution-free processes, or that it cons
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