Recovery of Metals from Electroplating Wastes

1 . Concent ra t ion changes i n s o l u t i o n dur ing a d d i t i o n of HIYO. waste t o 2 . Concent ra t ion changes i n s o l u t i o n du r ing a d d i t i o n of HNO, waste t o 3 . Concent ra t ion changes i n s o l u t i o n du r ing a d d i t i o n of C r waste t o 4 . Concent ra t ion changes i n s o l u t i o n dur ing a d d i t i o n of C r waste t o 5 . Concent ra t ion changes i n s o l u t i o n du r ing a d d i t i o n of C r waste t o NB-A waste ........................................................ 4 NB-B waste ........................................................ 5 NB-A .Jaste ........................................................ 6 ~ NB-Ag .Jaste ....................................................... 7 NB-B TJaste ........................................................ 7 TABLES 1 . Annual l o s s of meta l v a l u e s from two i n d u s t r i a l e l e c t r o p l a t i n g companies ......................................................... 2 2 . Composition ranges of i n d u s t r i a l e l e c t r o p l a t i n g wastes .............. 3 RECOVERY OF METALS FROM ELECTROPLATING WASTES BY THE WASTE-PLUS-WASTE METHOD L. C, George ‘ and Andrew A, Cochranz ABSTRACT Addi t ion of an a c i d waste t o an a l k a l i n e cyanide was te w a s i n v e s t i g a t e d f o r f i v e d i f f e r e n t combinat ions of e l e c t r o p l a t i n g was te s . A t t h e optimum f i n a l pH va lues of t h e mixtures , meta ls and cyanides were almost q u a n t i t a t i v e l y p r e c i p i t a t e d . No e v o l u t i o n of hydrogen cyanide was d e t e c t e d . By a few a d d i t i o n a l p rocess ing s t e p s , s i g n i f i c a n t amounts of v a l u a b l e meta ls were recovered f o r r e c y c l i n g . The waste-plus-waste s t e p i s a t t r a c t i v e because no r e a g e n t s a r e r e q u i r e d , me ta l s a r e concent ra ted , and a r e l a t i v e l y harmless e f f l u e n t t h a t meets most wa te r q u a l i t y s t anda rds f o r cyanide con ten t i s produced. LNTRODUCTIONAddi t ion of an a c i d waste t o an a l k a l i n e cyanide was te w a s i n v e s t i g a t e d f o r f i v e d i f f e r e n t combinat ions of e l e c t r o p l a t i n g was te s . A t t h e optimum f i n a l pH va lues of t h e mixtures , meta ls and cyanides were almost q u a n t i t a t i v e l y p r e c i p i t a t e d . No e v o l u t i o n of hydrogen cyanide was d e t e c t e d . By a few a d d i t i o n a l p rocess ing s t e p s , s i g n i f i c a n t amounts of v a l u a b l e meta ls were recovered f o r r e c y c l i n g . The waste-plus-waste s t e p i s a t t r a c t i v e because no r e a g e n t s a r e r e q u i r e d , me ta l s a r e concent ra ted , and a r e l a t i v e l y harmless e f f l u e n t t h a t meets most wa te r q u a l i t y s t anda rds f o r cyanide con ten t i s produced. LNTRODUCTION A s p a r t of i t s s o l i d was te r e sea rch program the Bureau of Mines i s engaged i n s t u d i e s t o develop t e c h n i c a l l y f e a s i b l e , low-cost processes f o r r ecove r ing v a l u a b l e m a t e r i a l s from a wide v a r i e t y of i n d u s t r i a l p l a t i n g was te s , S i g n i f i c a n t tonnages of v a l u a b l e meta ls and chemicals can be recovered from t h e s e wastes , which a r e r i c h e r i n meta l conten t t han many o r e s p r e s e n t l y being p rocessed , An a d d i t i o n a l b e n e f i t i s t h e a l l e v i a t i o n of t h e s t ream and ground water p o l l u t i o n t o which t h e s e wastes c o n t r i b u t e . Many of t h e waste t rea tment p rocesses developed i n t h e pas t have one o r more of t h e fo l lowing f a u l t s : (1) The t rea tment produces a new waste t h a t a l s o c o n s t i t u t e s a d i s p o s a l problem, ( 2 ) t h e t r ea tmen t process does not i nc lude t h e recovery and r euse of t h e m e t a l and o t h e r v a l u e s , o r (3) t h e t rea tment process i s s o c o s t l y t h a t volunt a r y adopt ion by i n d u s t r y i s u n l i k e l y . The r e s e a r c h desc r ibed he re in d e s c r i b e s an i n n o v a t i v e t r ea tmen t process f o r p l a t i n g was tes t h a t does n o t have t h e s e shortcomings. ~ ~~ ~~~ ~ -~ ~~~ ~ ~ ~~ ~ ~~~ ~~ ~ ~~ ~ ~~ ~ The t r ea tmen t of cyanide wastes t o render them innocuous has rece ived e x t e n s i v e coverage i n r e c e n t yea r s , and t h e s e methods have been adequate ly IResearch chemist , Ro l l a Metal lurgy Research Center , Bureau of Mines, “Superv isory r e s e a r c h chemist , Ra l l a Metal lurgy Research Center , Bureau of Rol la , Mo.