Equilibria between liquid Mn-Si alloys and MnO-SiO 2 -CaO-MgO slags
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L O W o r m e d i u m c a r b o n f e r r o m a n g a n e s e is produced by r e d u c i n g m a n g a n e s e oxide, u s u a l l y in the f o r m of high grade m a n g a n e s e ore, with the s i l i c o n contained in s i l i c o m a n g a n e s e ; this is the s o - c a l l e d s i l i c o t h e r m i c p r o c e s s . The p r i n c i p a l c h e m i c a l r e a c t i o n i s : 2MnO x + xSi (in SIMn) = 2Mn + xSiO,~.
[1 ]
L i m e is p r e s e n t in the slag to lower the a c t i v i t y of SiO2 and i n c r e a s e that of MnO. B e c a u s e s i l i c o m a n g a n e s e is e x p e n s i v e , it is a d v a n t a geous to use MnO (x = 1) as a r e a c t a n t . F o r this case the e q u i l i b r i u m constant for Eq. [1] is:
b e t w e e n M n - S i m e l t s and s l a g s c o n t a i n i n g MnO, SiOz, and CaO, with or without MgO. T u s e t e l a l e have s t u d ied e q u i l i b r i a b e t w e e n M n - S i m e l t s and MnO-SiOz-CaO s l a g s at 1530~ However, as a c o n s e q u e n c e of the e x p e r i m e n t a l technique used, T u s e t e t a l were able to study only s l a g s s a t u r a t e d with r e s p e c t to SiO2 or CaO-MnO solid s o l u t i o n s , and not c o n t a i n i n g MgO. M o r e o v e r , they r e s t r i c t e d t h e m s e l v e s to one t e m p e r a t u r e . The p r e s e n t work was u n d e r t a k e n to study s l a g s c o n t a i n i n g MgO, m o r e r e p r e s e n t a t i v e for those e n c o u n t e r e d in p r a c t i c e , and to include the effect of t e m p e r a t u r e on the e q u i l i b r i u m conditions.
2
gl
aMn "asio2 -
2
[2 J
EXPERIMENTAL
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aMnO asi Knowledge of the a c t i v i t i e s of MnO and SiO2 in the s l a g phase and of the a c t i v i t i e s of s i l i c o n and m a n g a n e s e in the m e t a l phase is n e c e s s a r y to p r e d i c t the c o m p o s i tions of s l a g and m e t a l in e q u i l i b r i u m with each o t h e r . In p r a c t i c e , the s i l i c o t h e r m i c r e d u c t i o n is done e i t h e r in a t i l t i n g d i r e c t - a c t s t e e l m e l t i n g f u r n a c e or by a modified f o r m of the s o - c a l l e d P e r r i n p r o c e s s in which s l a g and m e t a l phase a r e e m u l s i f i e d by a s u i t able t e c h n i q u e . 1 In e i t h e r case, the d u r a t i o n of the r e f i n i n g p e r i o d is d e t e r m i n e d by the t i m e r e q u i r e d to reach equilibrium. S i l i c o m a n g a n e s e is p r o d u c e d by e l e c t r i c s m e l t i n g of the p r o p e r a m o u n t s of m a n g a n e s e ore, s i l i c a , and coke in an e l e c t r i c f u r n a c e . L i m e is u s u a l l y p r e s e n t in the s l a g s e n c o u n t e r e d in the p r o d u c t i o n of s i l i c o m a n g a n e s e . Hence, as in the s i l i c o t h e r m i c p r o c e s s , knowledge of the a c t i v i t i e s of MnO and SiO2 in the s l a g as well as the a c t i v i t i e s of s i l i c o n and m a n g a n e s e in the m e t a l is n e c e s s a r y to p r e d i c t the c o m p o s i t i o
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