A model of the dump leaching process that incorporates oxygen balance, heat balance, and air convection
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AND
J. A. APPS
A one d i m e n s i o n a l , n o n s t e a d y - s t a t e m o d e l of the copper w ast e dump l e a c h i n g p r o c e s s has been d e v e l o p e d which i n c o r p o r a t e s both c h e m i s t r y and p h y s i c s . The m o d el is b a s e d upon t h r e e equations r e l a t i n g oxygen balance, heat balance, and a i r convection. It a s s u m e s that the dump is c o m p o s e d of an a g g r e g a t e of r o c k p a r t i c l e s containing nonsulfide copper m i n e r a l s and the s u lf i d e s , c h a l c o p y r i t e and p y r i t e . Leaching o c c u r s through c h e m i c a l and d i f fusion c o n t r o l l e d p r o c e s s e s in which p y r i t e and c h a l c o p y r i t e a r e oxidized by f e r r i c ions in the l i x i v i a n t . Oxygen, the p r i m a r y oxidant, is t r a n s p o r t e d into the dump by m e a n s of ai r convection and o x i d i z e s f e r r o u s ion through b a c t e r i a l c a t a l y s i s . The heat g e n e r a t e d by the oxidation of the sulfides p r o m o t e s a i r convection. The m o d el was used to s i m u l a t e the l e a c h i n g of c o p p e r f r o m a s m a l l t e s t dump, and e x c e l l e n t a g r e e m e n t with field m e a s u r e m e n t s was obtained. The m o d e l p r e d i c t s that the m o s t i m p o r t a n t v a r i a b l e s a f f e c t i n g copp e r r e c o v e r y f r o m the t e s t dump a r e dump height, p y r i t e c o n c e n t r a t i o n , copper grade, and l i x i v i a n t ap p l i c a ti o n r a t e . T H E l e a c h i n g of l o w - g r a d e c o p p e r - b e a r i n g w a s t e has been p r a c t i c e d e i t h e r by accident or through design for s e v e r a l hundred y e a r s . During the l a s t fifty y e a r s , i n c r e a s i n g attention has been paid to the s y s t e m a t i c l e a c h i n g of l o w - g r a d e w a s t e r e s u l t i n g f r o m the open pit m i n i n g of p o r p h y r y copper d e p o s i t s in the w e s t e r n United States. By now, this a c t i v i t y is yielding an i m p o r t a n t s e c o n d a r y s o u r c e of d o m e s t i c copper, t Indeed, s o m e mining o p e r a t i o n s have been planned and a r e o p e r a t i n g e x c l u s i v e l y f r o m the production of copper obtained f r o m l each i n g . Many of t h e s e o p e r a t i o n s a r e exploiting oxide c o p p e r d e p o s i t s w h e r e copper is r e a d ily l e a c h e d by the a p p l i c a t i o n of dilute s u l f u r i c acid. L o w - g r a d e was t e d i s c a r d e d as a r e s u l t of open pit m i n i n g of p o r p h y r y c o p p e r d e p o s i t s is dumped in gull i e s s u r r o u n d i n g the d e p o s i t . The d i s p o s a l site is d e t e r m i n e d p r i m a r i l y by the convenience of the site to the m i n i n g o p e r a t i o n , and is not u s u a l l y b a s e d on c o n s i d e r a t i o n s n e c e s s a r y f o r o p t i m u m l e a c h in g . In the w e s t e r n United States s e v e r a l billion tons of waste has a c c u m u l a t e d in th
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