Vaporization of iron and phosphorus from iron-phosphorus melts in oxygen-bearing gas streams
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O N the b a s i s of p r e v i o u s findings, it has b e e n p o s tulated '-z that g a s - d i f f u s i o n - l i m i t e d enhanced v a p o r i zation m a y play an i m p o r t a n t role in p n e u m a t i c m e t a l r e f i n i n g p r o c e s s e s . In the oxygen and l i m e bottom blowing p r o c e s s , t h r e e r e a c t i o n zones m a y be c o n s i d ered. 1) The v a p o r i z a t i o n of e l e m e n t s or t h e i r oxides e n hanced by the oxidation of v a p o r s in the oxidizing a t m o s p h e r e of the t u y e r e zone. 2) The r e a c t i o n of bulk m e t a l o r slag with the p a r t i cles of the p r o d u c t of the g a s - v a p o r phase r e a c t i o n . 3) The s l a g - m e t a l - g a s r e a c t i o n in the e m u l s i f i e d slag l a y e r . The effective phosphorus r e m o v a l in l i m e bottom blowing with oxygen, as in the Q-BOP, was explained in t e r m s of v a p o r i z a t i o n m e c h a n i s m as follows. At high oxygen p o t e n t i a l s in the t u y e r e zone the phosphorus is l i k e l y to be evolved from the m e t a l as PO and PO 2, and the r a t e of the r e a c t i o n will be i n c r e a s e d by a g a s - v a p o r phase r e a c t i o n with l i m e , such as 3 CaO(s) + 2 PO(g) + 3/2 O2(g) ~ Ca3P208(s o r l) [1] It should be noted that a s i m i l a r r e a c t i o n can o c c u r with phosphorus v a p o r i z i n g f r o m the m e t a l as P2 and PO~. An i m p o r t a n t point to be made h e r e is that the proposed r e a c t i o n m e c h a n i s m can b r i n g about e x t e n sive phosphorus r e m o v a l f r o m the m e t a l , b e c a u s e the phosphate f o r m e d has a low phosphorus potential in the oxidizing a t m o s p h e r e of the t u y e r e zone. When the p a r t i c l e s of this r e a c t i o n p r o d u c t m i x with the melt, t h e r e m a y be s o m e phosphorus r e v e r s i o n . In the a b s e n c e of l i m e i n j e c t i o n , the product of the g a s vapor phase r e a c t i o n will be i r o n phosphate, which will be r e d u c e d r e a d i l y when m i x e d with the b a t h ; hence t h e r e is no phosphorus r e m o v a l d u r i n g d e c a r b u r i z a l i o n in B e s s e m e r p r a c t i c e . However, r e v e r s i o n of p h o s phorus to the m e l t f r o m c a l c i u m phosphate will be m o r e sluggish; consequently, this m e c h a n i s m could b r i n g about dephosphorization of the bath to phospho-
G. J. W. KOR is Senior Scientist and E. T. TURKDOGANis Senior Research Consultant, U.S. Steel Research Laboratory, Monroeville, Pa. 15146. Manuscript submitted December 17, 1974 METALLURGICALTRANSACTIONSB
r u s l e v e l s much below those for the s l a g - m e t a l equil i b r i u m , as achieved in the Q-BOP. F u r t h e r m o r e , if the oxygen a c t i v i t y at the g a s - m e t a l i n t e r f a c e in the t u y e r e zone is much above that c o r r e sponding to the c a r b o n c o n t e n t of the m e l t , the c a r b o n in the bath m a y e n h a n c e PO f o r m a t i o n , and hence dep h o s p h
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