Oxygenation of Ferrous Iron in Mine Drainage Waters

P r e v i o u s s t u d i e s of t h e o x i d a t i o n of i r o n p y r i t e and t h e subsequent r e l e a s e of a c i d i t y i n t o mine d r a i n a g e w a t e r s have provided no c o n c l u s i v e r e su l t s i n a s c e r t a i n i n g which of t h e s t e p s i n t h e o v e r a l l r e a c t i o n i s r a t e d e t e r m i n i n g . Although microorganisms have f r e q u e n t l y been i m p l i c a t e d a s t h e c a u s a t i v e a g e n t s i n t h e p r o d u c t i o n of a c i d i c mine d r a i n a g e , t h e a c t i v i t y o f t h e s e microorganisms i n n a t u r a l sys tems h a s r a r e l y been e v a l u a t e d . F u r t h e r more, f e w s t u d i e s have been conducted i n o r d e r t o a s s e s s t h e c a t a l y t i c i n f l u e n c e of s e v e r a l c h e m i c a l a g e n t s which are indigenous t o mine d r a i n a g e w a t e r s and v h i c h have been c i t e d i n t h e l i t e r a t u r e , i n v a r i o u s c i rcumstances , as e x h i b i t i n g c a t a l y t i c p r o p e r t i e s i n t h e o x i d a t i o n o f f e r r o u s i r o n . T h i s paper r e p r e s e n t s a q u a n t i t a t i v e e v a l u a t i o n of t h e i n d i v i d u a l f a c t o r s cont r o l l i n g the o x i d a t i o n of i r o n p y r i t e ; t h e r e l a t i v e rates o f t h e v a r i o u s c o n s e c u t i v e r e a c t i o n s have been c o n s i d e r e d i n o r d e r t o e l u c i d a t e t h e r a t e d e t e r m i n i n g r e a c t i o n . The l a b o r a t o r y r e s u l t s are complemented by r e s u l t s of a f i e l d i n v e s t i g a t i o n of i r o n ( I 1 ) o x i d a t i o n i n n a t u r a l mine waters. The mine-water s y s t e m can be c h a r a c t e r i z e d by t h e f o l l o w i n g s t o i c h i o metric r e a c t i o n s : FeS2(s) + 7 /2 O2 + H20 = Fe+2 + 2 S04-2 + 2 H+ Pe+* + 114 O2 + H+ = Fe+3 + 112 H20 (1)