ABSTRACT
C h r o m i u m a n d c h r o m i u m ( V I ) [1] h a v e b e e n p r e c o n c e n t r a t e d b y p r o c e d u r e s b a s e d o n c o p r e c i p i t a t i o n w i t h fe r r ic h y d r o x i d e . T h e m e c h a n i s m of the s o r p t i o n of chromate ions onto a m o r p h o u s ferric h y d r o x i d e , ferr ic o x i d e a n d magnet i te par t ic les has been e x a m i n e d a n d the effects of severa l va r iab les i n c l u d i n g the p H of the s o l u t i o n a n d the presence of c o m p e t i n g ions (ch lor ide , su lphate , m o l y b d a t e ) d e t e r m i n e d . The so rp t i on of hexava len t c h r o m i u m onto h y d r o u s ferric o x i d e can be e x p l a i n e d i n te rms of l i g a n d exchange, h y d r o x y l ions b e i n g released f r o m the surface of the h y d r a t e d o x i d e par t ic les . F o r magne t i c par t ic les , however , the s o r p t i o n effect w a s e x p l a i n e d b y the r e d u c t i o n of traces of hexava len t c h r o m i u m at the m a g n e t i t e / w a t e r interface, as a resul t of w h i c h a v e r y f ine ferric h y d r o x i d e / c h r o m i u m h y d r o x i d e coa t ing w a s p r o d u c e d w h i c h e x c l u d e d further r e d u c t i o n of hexava len t c h r o m i u m .
