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The r e d u c t i o n of synthetic i l m e n i t e with graphite in the s o l i d state h a s been studied by t h e r m o g r a v i m e t r i c a n a l y s i s . The r e a c t i o n has b e e n o b s e r v e d to i n i t i a t e n e a r 860~ at the c o n t a c t points b e t w e e n the r e a c t a n t s . Up to 1020~ solid state r e d u c t i o n a p p e a r s to be the m a i n r e a c tion m e c h a n i s m , while above this t e m p e r a t u r e a r a t e i n c r e a s e has b e e n o b s e r v e d and h a s b e e n a t t r i b u t e d to a change of m e c h a n i s m to g a s e o u s r e d u c t i o n of i l m e n i t e by r e g e n e r a t e d CO. M i c r o s c o p i c e x a m i n a t i o n and e l e c t r o n probe a n a l y s i s of the r e d u c e d p a r t i c l e s have i n d i c a t e d a tendency toward s e g r e g a t i o n of the p r o d u c t s i r o n and TiO2. I r o n p a r t i c l e s as l a r g e as 80 can be obtained by keeping the r e d u c e d s a m p l e at 1025 ~ to 1075~ for s e v e r a l h o u r s . Reduction r a t e data u n d e r i s o t h e r m a l conditions were fitted to d i f f e r e n t rate equations and have b e e n found to be well r e p r e s e n t e d by the e q u a t i o n . 1 - 2x/3-

(1 - x ) 2/3 = K ' t

T h i s equation is b a s e d upon diffusion of r e a c t a n t s through a product l a y e r . CO is s u g g e s t e d as the diffusing s p e c i e s . The activation e n e r g y for the r e a c t i o n in the t e m p e r a t u r e r a n g e 1075 ~ to 1140~ h a s b e e n c a l c u l a t e d to be 64 + 6 kcal per m o l e . Jt~ECENTLY, c o n s i d e r a b l e attention has b e e n given to s t u d i e s of solid state m e t a l l u r g i c a l p r o c e s s e s for r e c o v e r i n g m e t a l s from o r e s . T h e s e p r o c e s s e s a r e i m p o r t a n t as potential r e p l a c e m e n t s for c o n v e n t i o n a l s m e l t i n g and wet c h e m i s t r y s y s t e m s . An i n d u s t r i a l l y i m p o r t a n t p r o c e s s r e c e i v i n g a g r e a t deal of a t t e n t i o n i s the solid state s e p a r a t i o n of TiOz and i r o n p r e s e n t in i l m e n i t e . Most of the a v a i l a b l e l i t e r a t u r e , h o w e v e r , d e s c r i b e s studies on n a t u r a l l y o c c u r r i n g o r e s u s i n g H2, CO, or c a r b o n as r e d u c t a n t s . 1-~ F r o m a kinetic v i e w point, r e s u l t s of such s t u d i e s a r e difficult to i n t e r p r e t owing to the complex c h e m i c a l n a t u r e of the o r e s , the p r e s e n c e of m a n y c o m p o n e n t s , and the i n h e r e n t v a r i a t i o n s in ore c o m p o s i t i o n . T h i s paper d e s c r i b e s an e x p e r i m e n t a l study of the m e c h a n i s m and k i n e t i c s of r e d u c t i o n of s y n t h e t i c i l m e n i t e (chemically pure FeTiO3) u s i n g graphite as a r e d u c i n g agent at t e m p e r a t u r e s up to 1140~ i . e . , b e l o w the m e l t i n g point of FeTiO3 and below the t e m p e r a t u r e at which r e d u c t i o n of