Copper Deoxidation Kinetics Utilizing Carbon
Monoxide
R. J. ANDREINI, J. S. F O S T E R , AND R. B. P H I L L I P S
G a s e o u s deoxidation of liquid copper with c a r b o n monoxide as the r e d u c i n g gas has b e e n
e x a m i n e d . The r e d u c i n g gas was i n t r o d u c e d at a s u b m e r g e d o r i f i c e so that well c h a r a c t e r i z e d , s i n g l e b u b b l e s w e r e f o r m e d . The d e o x i d a t i o n k i n e t i c s a r e d e t e r m i n e d p r i m a r i l y
by the m a s s t r a n s p o r t of oxygen in liquid copper. No effect of s u l f u r o v e r the r a n g e of 10
to 200 ppm was o b s e r v e d . I n c r e a s i n g the t e m p e r a t u r e f r o m 1113 to 1173~ s l i g h t l y
i n h i b i t the k i n e t i c s of oxygen r e m o v a l .
ALTHOUGH
the k i n e t i c s of r e a c t i o n s b e t w e e n m o l t e n
m e t a l s and gas b u b b l e s a r e i m p o r t a n t in s e v e r a l
m e t a l l u r g i c a l p r o c e s s e s , v e r y little e x p e r i m e n t a l
work has b e e n done in this a r e a . T h i s is l a r g e l y due
to a lack of i n f o r m a t i o n on the c h a r a c t e r i s t i c s of b u b b l e s in liquid m e t a l s , such as s i z e and r e s i d e n c e t i m e .
In a c o m p a n i o n i n v e s t i g a t i o n1 the b e h a v i o r of s i n g l e
b u b b l e s in liquid m e t a l s was s t u d i e d u s i n g an a c o u s t i c
t e c h n i q u e , and a c c u r a t e c h a r a c t e r i z a t i o n of bubble s i z e ,
f r e q u e n c y of f o r m a t i o n , and v e l o c i t y was a c h i e v e d u n d e r
a v a r i e t y of conditions in liquid lead, tin and copper.
With this i n f o r m a t i o n a v a i l a b l e a k i n e t i c study of the
r e a c t i o n of d i s s o l v e d oxygen in copper with c a r b o n
monoxide was u n d e r t a k e n .
A v a r i e t y of o r i f i c e c o n d i t i o n s w e r e e x a m i n e d and
e x p e r i m e n t s w e r e conducted at both 1113~ and 1173~
to i n v e s t i g a t e the effect of t e m p e r a t u r e on the s y s t e m
k i n e t i c s . V a r i a t i o n s in the i n i t i a l oxygen and s u l f u r
c o n t e n t s of the m e l t w e r e made to e x a m i n e the i m p o r t a n c e of t h e s e i m p u r i t i e s in the r e f i n i n g o p e r a t i o n .
T h e t y p i c a l content of a m e l t at the i n i t i a t i o n of the
deoxidation o p e r a t i o n ( b l i s t e r copper) is 0.60 to 0.80
pct oxygen and 0.02 pct s u l f u r by weight. In this r e gard, i n i t i a l oxygen c o n c e n t r a t i o n s w e r e v a r i e d f r o m
0.10 to 0.50 wt pct, and the s u l f u r c o m p o s i t i o n was
v a r i e d i n the r a n g e of 0.001 to 0.02 wt pct. T h e r e s u l t s of this study m a y u l t i m a t e l y be u s e f u l to copper
p r o d u c e r s as they a t t e m p t to a c h i e v e g r e a t e r c o n t r o l
and e f f i c i e n c y in the deoxidation step of copper p r o cessing.
REVIEW OF PREVIOUS WORK
The f i r s t s i g n i f i c a n t k i n e t i c study i n v o l v i n g a gas
b u b b l e - m o l t e n m e t a l s y s t e m was done by P e h l k e and
B e m e n t . z They studied the h y d r o g e n d e g a s s i n g of
a l u m i n u m at 700~ u s i n g a r g o n . At c o n s t a n t f l o w r a t e
they found that the r a t e of r e m o v a l of h y d r o g e n i n R. J. ANDREINI and R. B. PHILLIPS, formerly Graduate Students,
Michigan Technological University, Houghton, MI 49931, are now
Research Metallurgist, Paul D. Merica Research Laboratory, International Nickel Inc., Sterling Forest, NY 10901, and Research Engineer,
Phelps Dodge Corporation, Morenci, AZ 85540, respectively. J, S.
FOSTER is Professor, Department of MetallurgicalEngineering,
Michigan Technological University, Houghton, MI 49931. This paper
is based on a portion of the dissertation submitted by R. J. Andreini
in partial fulfillment of the requirements for the degree of Doctor of
Philosophy at MichiganTechnological University.
Manuscript submitted April 9, 1976.
METALLURGICALTRANSACTIONSB
c r e a s e d as the b u b b l e s i z e d e c r e a s e d . I n c r e a s i n g
the flow r a t e of f l u s h i n g gas was a l s o o b s e r v e d to i n c r e a s e the r a t e . T h e y showed that the r e m o v a l of hyd r o g e n f r o m liquid a l u m i n u m by a f l u s h i n g gas t e c h nique is a n o n e q u i l i b r i u m p r o c e s s and p o s t u l a t e d that
the r a t e of r e m o v a l could be d e s c r i b e d in t e r m s of
liquid p h a s e m a s s t r a n s p o r t c o n t r o l . T h e m a s s t r a n s f e r c o e f f i c i e n t for the r e m o v a l of h y d r o g e n f r o m
liquid a l u m i n u m at 700~ was found to be e q u a l to 3.9
x 10 -2 c m s -1. T h e i r work, h o w e v e r , u s e d a r b i t r a r y
b u b b l e s i z e s (bubble r a d i u s a s s u m e d to be twice that
of the i n l e t tube r a d i u s ) to e s t i m a t e the bubble v e l o c i t i e s and r i s e t i m e s i n the m e l t .
D a v e n p o r t 3 s t u d i e d the a b s o r p t i o n r a t e of oxygen i n
s i l v e r at 1010~ but e x p e r i m e n t a l d i f f i c u l t i e s led to
a n o v e r a l l u n c e r t a i n t y of a p p r o x i m a t e l y +30 to 40 pct
in the m e a s u r e m e n t of m a s s t r a n s f e r c o e f f i c i e n t s .
G u t h r i e and B r a d s h a w 4 s t u d i e d the b e h a v i o r of l a r g e
b u b b l e s r i s i n g in m o l t e n s i l v e r . They b u b b l e d n i t r o g e n
t h r o u g h the m e l t to t e s t the b e h a v i o r and a c c u r a c y of
the e x p e r i m e n t a l s y s t e m and s t u d i e d the k i n e t i c s of
the a b s o r p t i o n of oxygen in liquid s i l v e r at 1020~
S p h e r i c a l cap shaped b u b b l e s w e r e a s s u m e d and r e s i d e n c e t i m e s w e r e d e t e r m i n e d by m o n i t o r i n g p r e s s u r e
f l u c t u a t i o n s above the m e l t in a c l o s e d s y s t e m . No
d i r e c t m e a s u r e m e n t s of bubble s h a p e s w e r e done i n
this study. D u m p i n g - c u p t e c h n i q u e s w e r e u s e d in both
of the s t u d i e s d e s c r i b e d in this p a r a g r a p h .
I n t e r e s t in the k i n e t i c s of the d e o x i d a t i o n of c o p p e r
by g a s e o u s r e d u c t i o n has i n c r e a s e d s i n c e the d e v e l o p m e n t of the P h e l p s Dodge p r o c e s s to deoxidize c o p p e r
u s i n g r e f o r m e d n a t u r a l gas i n j e c t e d into the m e l t f r o m
s u b m e r g e d tuyeres.~ B r a n t l e y and Schack ~ s t u d i e d
p r o p a n e , n a t u r a l gas, r e f o r m e d n a t u r a l gas, c a r b o n
monoxide, and b u t a n e for p o s s i b l e u s e as g a s e s for
the d e o x i d a t i o n of copper in a study done by the U.S.
B u r e a u of M i n e s , and found b u t a n e to be s u p e r i o r to
a l l o t h e r s t e s t e d . H e n y c h e t a l 7 have p e r f o r m e d g a s e ous d e o x i d a t i o n of m o l t e n copper u s i n g a m m o n i a
(patented C z e c h p r o c e s s ) .
T h e m e l i s and S c h m i d t s have s t u d i e d the k i n e t i c s of
the d e o x i d a t i o n of liquid copper at 1170~ u s i n g a jet
of CO gas. The k i n e t i c s of the p r o c e s s w e r e e x a m i n e d
on a l a b o r a t o r y s c a l e by v a r y i n g o r i f i c e d i a m e t e r ,
depth of s u b m e r s i o n in the m e l t , and gas v e l o c i t y . A
gas c h r o m a t o g r a p h was used to a n a l y z e the exit gas.
T h e y found that the r a t e of d e o x i d a t i o n i n c r e a s e d as
the d i a m e t e r of the o r i f i c e i n c r e a s e d , and c o n c l u d e d
that gas p h a s e m a s s t r a n s f e r c o n t r o l l e d the r e a c t i o n
VOLUME 8B, DECEMBER 1977-633
r a t e at oxygen c o n c e n t r a t i o n s g r e a t e r than 0.1 wt pct.
Below this oxygen content they p o s t u l a t e d that liquid
f i l m diffusion was the r a t e c o n t r o l l i n g step. In the
m o s t r e c e n t d e o x i d a t i o n k i n e t i c study a v a i l a b l e , Nanda
and G e i g e r 9 i n v e s t i g a t e d the k i n e t i c s of the d e o x i d a t i o n
of p u r e Cu, C u - 5 0 Ag, and C u - 6 0 Sn a l l o y s u s i n g a
solid state e l e c t r o l y t e technique and CO as the r e d u c ing gas. U s i n g e s t i m a t e d bubble s i z e s and v e l o c i t i e s ,
a m o l t e n m e t a l bath of 2.54 cm depth and an o r i f i c e
s u b m e r s i o n depth of 1.27 cm, they found that the
k i n e t i c s of the p r o c e s s were i n d e p e n d e n t of the i n i t i a l
oxygen c o n c e n t r a t i o n in the m e l t in the r a n g e of 100 to
500 ppm. A k i n e t i c model i d e n t i c a l to that u s e d by
Pehlke and B e m e n t 2 was u t i l i z e d to e x a m i n e the exp e r i m e n t a l data, and m a s s t r a n s f e r coefficient c o r r e l a t i o n s w e r e t e s t e d . It was found that H u g h m a r k ' s
c o r r e l a t i o n 1~ for the m a s s t r a n s f e r coefficient y i e l d e d
the b e s t a g r e e m e n t with t h e i r e x p e r i m e n t a l r e s u l t s .
E s t i m a t i o n s of such c r i t i c a l p a r a m e t e r s as b u b b l e s i z e
and velocity were a g a i n u t i l i z e d in this work.
E X P E R I M E N T A L APPROACH
Materials
P u r e c a r b o n monoxide was blown into a copper m e l t
of a p p r o x i m a t e l y 500 c m 3 at e i t h e r 1113 o r 1173~
A
flow of a r g o n was m a i n t a i n e d o v e r the m e l t at a l l
t i m e s to act as a n exit gas p h a s e d i l u t a n t and p r o h i b i t
u n d e s i r a b l e oxidation of the m e l t d u r i n g t i m e s when
it was n e c e s s a r y to have the s y s t e m open for s a m p l i n g ,
m e l t additions, and so forth. Oxygen was c h a r g e d to
the m e l t in the f o r m of CuO w i r e s , while s u l f u r was
added in the f o r m of p r e s s e d Cu2S powder. Both m a t e r i a l s w e r e of r e a g e n t grade.
Apparatus
The a p p a r a t u s used in this p h a s e of the r e s e a r c h
was v e r y s i m i l a r to that i l l u s t r a t e d in F i g . 1 of Ref. 1.
The gas t r a i n was capable of d e l i v e r i n g e i t h e r c a r b o n
monoxide o r a r g o n to the melt. The g a s e s w e r e
p a s s e d through f l o w m e t e r s p r e c e d e d by a c o n s t a n t
t e m p e r a t u r e bath. The CO and A r w e r e c l e a n s e d by
s t a n d a r d p r o c e d u r e s . The o r i f i c e tubes c o n s i s t e d of
100 cm lengths of fused q u a r t z tubing, 15 m m ID by
17 m m OD, with a 1.27 cm length p r e c i s i o n b o r e
c a p i l l a r y tip s e r v i n g as the a c t u a l o r i f i c e . The c h a r a c t e r i s t i c s of the flow s y s t e m w e r e such that c o n s t a n t
p r e s s u r e conditions w e r e m a i n t a i n e d throughout all
e x p e r i m e n t s . 11 The g a s e s e x i t i n g f r o m the f u r n a c e
were p a s s e d through a s a m p l i n g tube w h e r e s a m p l e s
could be t a k e n for a n a l y s i s by gas c h r o m a t o g r a p h y .
The f u r n a c e p r o p e r c o n s i s t e d of a 7.5 cm 113, 5 kW,
N i c h r o m e would v e r t i c a l tube f u r n a c e r a t e d at 1200~
A 4 kg m e l t s i z e was u t i l i z e d throughout and was cont a i n e d in a 6.35 c m ID m u l l i t e c r u c i b l e and s u p p o r t e d
f r o m the bottom by an a l u m i n a tube. The m e l t t e m p e r a t u r e was d e t e r m i n e d p e r i o d i c a l l y u t i l i z i n g a
c h r o m e l - a l u m e l t h e r m o c o u p l e to i n s u r e that the f u r nace had not d r i f t e d f r o m its d e s i r e d setting, and it
was found that the m e l t was c o n t r o l l e d to +2~
A
b r a s s s e a l was used to close the top of the c r u c i b l e
a s s e m b l y . A q u a r t z view p o r t was a l s o i n s t a l l e d so
that o b s e r v a t i o n s of the m e l t d u r i n g o p e r a t i o n could
readil~r be made. A s m a l l , c o n d e n s e r type m i c r o p h o n e
was placed over the melt to m o n i t o r the s y s t e m n o i s e .
634-VOLUME 8B, DECEMBER 1977
U t i l i z i n g i d e n t i c a l e l e c t r i c a l c i r c u i t r y and t e c h n i q u e s
as that d e v e l o p e d by the a u t h o r s to c h a r a c t e r i z e gas
b u b b l e b e h a v i o r in liquid m e t a l s , gas b u b b l e f o r m a t i o n
f r e q u e n c i e s w e r e obtained so that b u b b l e s i z e s w e r e
k n o w n ) Gas bubble v e l o c i t y r e l a t i o n s h i p s o b t a i n e d
f r o m Ref. 1 w e r e a l s o u t i l i z e d in this work. T h e o r i fice depth (under quiet conditions) was m a i n t a i n e d at
15.00 ~ 0.05 c m .
T h e k i n e t i c d a t a w e r e g e n e r a t e d p r i m a r i l y by a n a l y s i s of the exit gas f r o m the f u r n a c e s y s t e m u s i n g gas
chromatography. The partial pressure ratio
was d e t e r m i n e d and used t o g e t h e r with the gas
flow r a t e to c a l c u l a t e the t o t a l m a s s flux of oxygen
f r o m the m e l t at v a r i o u s t i m e s . T h e oxygen c o n t e n t s
of the m e l t p r i o r to and upon c o m p l e t i o n of b l o w - d o w n
w e r e d e t e r m i n e d u s i n g Leco a n a l y s i s . I n t e g r a t i o n
of the total m a s s flux of oxygen o v e r t i m e u s i n g the
a m o u n t s known to be in the m e l t at the b e g i n n i n g and
end of a r u n p r o v i d e d the m e a n s to d e t e r m i n e the oxygen c o n t e n t of the m e l t with t i m e . T h e t o t a l c h a n g e s
in oxygen c o n t e n t d e t e r m i n e d by the two i n d e p e n d e n t
a p p r o a c h e s a l w a y s a g r e e d within e2 pct. Melt s a m p l e s
for Leco a n a l y s i s of both oxygen and s u l f u r w e r e obt a i n e d u s i n g 6 m m ID q u a r t z tubes with a p i p e t t e b u l b
on one end which p r o v i d e d s u c t i o n .
(Pc02/
Pco)
RESULTS AND DISCUSSION
G e n e r a l T h e r m o d y n a m i c and K i n e t i c C o n s i d e r a t i o n s
The o v e r a l l r e a c t i o n which o c c u r s when oxygen is
r e m o v e d f r o m m o l t e n copper by r e a c t i o n with c a r b o n
monoxide is
CO(g) + o ~ co~(g)
[1]
w h e r e O r e p r e s e n t s the oxygen d i s s o l v e d in the m o l t e n
m e t a l . At 1113~ the e q u i l i b r i u m c o n s t a n t , a s s u m i n g
a 1 wt pct s t a n d a r d s t a t e for oxygen, is 12
gco
PCO 2
= ( P c o ) f o [wt pct O] = 6"58(10)3'
[2]
T h u s , at oxygen c o n c e n t r a t i o n s of a p p r o x i m a t e l y
100 ppm o r g r e a t e r , any CO p r e s e n t will tend to c o m p l e t e l y r e a c t to f o r m CO2. As the oxygen c o n c e n t r a tion in the m e l t d e c r e a s e s , the e q u i l i b r i u m gas p r e s s u r e r a t i o d e c r e a s e s also. T h e s e r a t i o s , h o w e v e r ,
r e m a i n r e l a t i v e l y high even at e x t r e m e l y low oxygen
l e v e l s . F o r e x a m p l e , at 10 ppm oxygen, the e q u i l i b r i u m
p r e s s u r e r a t i o of
is 6.6.
T h e a c t u a l r e a c t i o n is g e n e r a l l y thought to o c c u r a t
the g a s / l i q u i d i n t e r f a c e , and the o v e r a l l p r o c e s s m a y
be s u b d i v i d e d into s e v e r a l s u c c e s s i v e s t e p s . T h e s e
s t e p s i n c l u d e the t r a n s p o r t of r e a c t a n t s and p r o d u c t s
to and f r o m the i n t e r f a c e , a d s o r p t i o n and d e s o r p t i o n
of v a r i o u s s p e c i e s , as well as the c h e m i c a l r e a c t i o n .
O f t e n t i m e s one step o c c u r s at a s i g n i f i c a n t l y l o w e r
r a t e than the o t h e r s and b e c o m e s r a t e l i m i t i n g . Two
o r m o r e s t e p s may, h o w e v e r , p r o c e e d at a p p r o x i m a t e l y e q u i v a l e n t r a t e s c a u s i n g mixed c o n t r o l , and
such b e h a v i o r was found in this i n v e s t i g a t i o n .
(Pco2/Pco)
Sulfur and Oxygen L o s s e s f r o m Melt U n d e r I n e r t
Gas B u b b l i n g C o n d i t i o n s
At 1113~ a s s u m i n g a 1 wt pct s t a n d a r d s t a t e for
both d i s s o l v e d oxygen and s u l f u r , the e q u i l i b r i u m conMETALLURGICAL TRANSACTIONS B
sta nt fo r the r e a c t i o n z2'~3
s + 2o
so ,g,
[31
is 1.55 x 102. B e c a u s e SO2 f o r m a t i o n is f a v o r e d in this
r e a c t i o n , e x p e r i m e n t s w e r e c o n d u c t e d in which a r g o n
was bubbled t h r o u gh the m e l t to d e t e r m i n e the s i g n i f i c a n c e of this m e c h a n i s m with r e s p e c t to o x y g e n r e m o v a l f r o m the m e l t .
Both 0.050 and 0.100 c m o r i f i c e s w e r e u s e d in t h e s e
t e s t s , and al l w e r e conducted u n d e r the h i g h e s t o r i f i c e
R e y n o l d s n u m b e r u t i l i z e d in the k i n e t i c p h a s e of the
w o r k (to m a x i m i z e g a s / m e l t t u r b u l e n c e and h e n c e p r e sumably m a s s transfer). Initial oxygen levels were
a p p r o x i m a t e l y 0.10 and 0.50 wt pct o x y g e n and the s u l fur was v a r i e d f r o m about 0.001 and 0.02 wt pct. T h e
t o t a l bubbling t i m e in t h e s e e x p e r i m e n t s w a s 3 h.
No s i g n i f i c a n t oxygen o r s u l f u r m e l t l o s s e s w e r e
r e c o r d e d u n d e r any c o n d i ti o n s , and no t r a c e of SO2
was d e t e c t e d in the s y s t e m exit gas e v e n when 0.50
wt pct oxygen and 0.02 wt pct s u l f u r ( e q u i l i b r i u m PSO2
= 52.5 kPa) w e r e p r e s e n t t o g e t h e r in the m e l t . It m u s t
t h e r e f o r e be concluded that although the c o m b i n a t i o n
of d i s s o l v e d oxygen and s u l f u r is f a v o r a b l e f r o m t h e r m o d y n a m i c c o n s i d e r a t i o n s , in a c t u a l i t y it d o e s not o cc ur to any s i g n i f i c a n t d e g r e e . T h e r e s u l t s of t h e s e
e x p e r i m e n t s a l s o i n d i c a t e that o x y g e n t r a n s f e r a c r o s s
the s t i r r e d m e l t s u r f a c e a l s o d o e s not p r o c e e d to any
s i g n i f i c a n t d e g r e e . T h e e f f e c t of t h e s e m e c h a n i s m s
with r e s p e c t to oxygen r e m o v a l f r o m the m e l t is thus
negligible.
run, the i n i t i a l s e g m e n t of the p l o t is c u r v e d and c o r r e s p o n d s to 100 pct c o n v e r s i o n of r e a c t a n t to gas p r o duct. U n d e r t h e s e c o n d i t i o n s , the b u b b l e s c o m p l e t e l y
s a t u r a t e a s they r i s e t h r o u g h the m e l t (e.g., s t a r v a tion k i n e t i c s ) . T h e s e c o n d p o r t i o n is l i n e a r and the
r a t e d e c r e a s e s in p r o p o r t i o n to the o x y g e n content, r e m a i n i n g in the m e l t . T h i s p o r t i o n of the plot is d e f i n e d
by the a r r o w s i n c l u d e d in the f i g u r e s . T h e n u m b e r s app e a r i n g on the p l o t s a r e the o x y g e n c o n c e n t r a t i o n at the
end of the i n i t i a l l i n e a r p o r t i o n and the f i n a l c o n c e n t r a t i o n (in p p m ) . At m e l t oxygen c o n c e n t r a t i o n s of a pp r o x i m a t e l y 50 p p m o r l e s s , a d i s t i n c t b r e a k o v e r in
the l i n e a r p o r t i o n is o b s e r v e d . T h i s t h i r d s e g m e n t
( f r o m the b r e a k o v e r to the end of blow) is a l s o r e l a t i v e l y l i n e a r , and the r a t e is ag ai n p r o p o r t i o n a l to the
o x y g e n c o n t e n t of the m e l t . Th e o v e r a l l r a t e in t h i s
s e g m e n t of the plot is m u c h l o w e r than that o b s e r v e d
in the i n i t i a l l i n e a r s e g m e n t .
B e c a u s e of the f i r s t o r d e r k i n e t i c s s t r o n g l y i m p l i e d
by the l i n e a r i t y of the In (C/C o) vs t i m e p l o t s , a f i r s t
0.0 Il~e;N~."
i
ONRe o
m ~
-I.0
-i\ .i
-2.0
9
(D
v
\
-~.0
" e O .--.._.
An a c c u r a t e d e t e r m i n a t i o n of the s u l f u r content of
the m e l t at high s u l f u r c o n c e n t r a t i o n s (i.e., 100 and
200 ppm) was found to be d i f f i c u l t to a c h i e v e due to an
a p p a r e n t p r o b l e m with s e g r e g a t i o n d u r i n g s a m p l e s o l i d i f i c a t i o n . H o w e v e r , it was d e t e r m i n e d that r e l i a b l e
s u l f u r a n a l y s e s could be o b t a i n e d if the t o t a l s a m p l e
p u l l e d f r o m the m e l t was a n a l y z e d f o r s u l f u r . Ob t ai n ing this s a m p l e p r o v e d s o m e w h a t d i f f i c u l t b e c a u s e of
the s m a l l s a m p l e s i z e r e q u i r e d (0.25 g at 200 ppm s u l fur). S a t i s f a c t o r y s a m p l e s w e r e , h o w e v e r , obtained in
s e v e r a l e x p e r i m e n t s and the r e s u l t s i n d i c a t e d that
e s s e n t i a l l y no s u l f u r was l o s t f r o m the m e l t u n d er any
of the e x p e r i m e n t a l c o n d i ti o n s .
Deoxidation Results
T h e e f f e c t of gas f l o w r a t e on the k i n e t i c s of oxygen
r e m o v a l is i l l u s t r a t e d in F i g . 1. I n c r e a s i n g the f l o w r a t e i n c r e a s e s the r a t e of d e o x i d a t i o n of the m e l t ,
as is to be e x p e c t e d . I n c r e a s i n g the o r i f i c e d i a m e t e r
(at c o n s t a n t o r i f i c e R e y n o l d s n u m b e r ) a l s o s i g n i f i c a n t l y
i n c r e a s e s the r a t e of oxygen r e m o v a l , as is shown in
F i g . 2. F i g u r e 3 r e v e a l s that the k i n e t i c s of d e o x i d a tion o v e r the r a n g e of 10 to 200 ppm s u l f u r a r e e s s e n t i a l l y i n d ep en d en t of the s u l f u r content. T h e e f f e c t of
t e m p e r a t u r e o v e r the r a n g e of 1113 to 1173~ is i l l u s t r a t e d in F i g . 4 and the e f f e c t of i n i t i a l o x y g e n c o n c e n t r a t i o n is p r e s e n t e d in F i g . 5. P l o t s of In (C/C o) vs
t i m e a r e p r e s e n t e d in a l l c a s e s b e c a u s e the i n i t i a l
oxygen content v a r i e d s l i g h t l y f r o m t e s t to t e s t with
r e s p e c t to that d e s i r e d .
A l l of the p l o t s g e n e r a t e d c o n s i s t of t h r e e r e l a t i v e l y
d i s t i n c t s e g m e n t s . C o m m e n c i n g at the i n i t i a t i o n of a
METALLURGICAL TRANSACTIONS B
60
InlttQI Oxygen= lO00ppm
Initial Sulfur w I0 ppm
c
Sulfur B e h a v i o r in M e l t
9 NRao = 180
&NR6o : 1:90
9 "~30
~
9
-4.0
\A
-15
~A
~A_~
0
S
I
i
i
l
l
20
40
60
80
I00
-5.O
TIME (rain)
Fig. 1--Effect of orifice Reynolds number (gas flowrate) on the
kinetics of oxygen removal by carbon monoxide. Segments of
curves are divided by arrows.
oe NRe~ =
o.o
~
" --
'~o
\~--~
-1,0
~e\
Z~
oZ~Orlfice OJometer
~/k
= O.050cm.
eAOrifice Diom,ter = 0 . 1 0 0 Cm
~
O~
L~
lnitiol O.yg.n -" l O 0 0 ppm
~/X
Initlot Sulfur = IOppm
\
\ \
21-- ~A__14
-4.0
-5,0
0
A
I0
20
A~24
~LX~
30
40
ZX
50
TIME (rain)
Fig. 2--Effect of orifice diameter on the kinetics of oxygen r e moval by carbon monoxide. Segments of curves are divided by
arrows.
VOLUME 8B, DECEMBER 1977 -635
9 Initial :Sulfur = I O p p m
0.0 ""4b......&,..~9 ~.,=..& ~'&
\
-2.0
Sulfur
[
- 1)1/2
E(e
1
1)',q
• (DLVb/db) '/2
[5]
was used a s the b a s i s of c o m p a r i s o n . In this e q u a t i o n
E is the b u b b l e e c c e n t r i c i t y ( w i d t h / h e i g h t r a t i o ) and
(1 + K) ~176is the d i m e n s i o n l e s s e q u a t o r i a l v e l o c i t y .
B u b b l e e c c e n t r i c i t i e s w e r e d e t e r m i n e d f r o m the data
p r e s e n t e d by C a l d e r b a n k and L o c h i e l ~5 for e q u i v a l e n t
b u b b l e d i a m e t e r s . Although liquid p h a s e m a s s t r a n s f e r c o e f f i c i e n t p r e d i c t i o n s a r e a v a i l a b l e for a l l b u b b l e
s h a p e s , it was felt that the coefficient p r e d i c t e d by
Eq. [5] was a p p r o p r i a t e due to the n a t u r e of the c h a r a c t e r i z a t i o n data a v a i l a b l e on the i n j e c t e d gas b u b b l e s .
\
\
\\
-3.O
-4.0
~ 3 6
-5.0
D i s c u s s i o n of P o s s i b l e Rate
Controlling Mechanisms
oA
-6,0
"\
-7.0
n
30
O\o
,
60
~5
!
I 9
,
o
120
150
0
90
180
TIME (rain)
F i g . 3 - - E f f e c t of s u l f u r c o n c e n t r a t i o n f r o m 10 to 200 p p m on
t h e k i n e t i c s of o x y g e n r e m o v a l by c a r b o n m o n o x i d e w i t h an
i n i t i a l o x y g e n c o n t e n t of 5000 p p m . S e g m e n t s of c u r v e s a r e
d i v i d e d by a r r o w s .
0`0
9 1113e C
O&'~,l .~4b
-I.0
g
2'26E~
k,. = [2(1 + K)/3]
NRe ~ = 180
tNIIQI O~y~n ~- 5 0 0 0 p p m
\&
- 1.0
i.e.,
liquid p h a s e m a s s t r a n s f e r c o e f f i c i e n t ,
-" 200pprn
Orifice Olameter =O.050cm
Z~lnltlal
9
9
NReo= 180
~'~e~e ~
Initial Oxygen = 1 0 0 0 p p m
Initial Sulfur = 2 0 0 ppm
2.,.\L
-2.0
OrifiCe
Diameter = 0.050 cm
Gas p h a s e c o n t r o l of the o v e r a l l r a t e in high t e m p e r a t u r e m e t a l l u r g i c a l r e a c t i o n s y s t e m s of the type
i n v e s t i g a t e d h e r e s e e m s e x t r e m e l y doubtful. D a v i d s o n
and H a r r i s o n ~6 have shown that the r a t i o of m a s s t r a n s f e r c o e f f i c i e n t s of the gas and liquid p h a s e s is r e l a t e d
to the s q u a r e r o o t of the r e l a t i v e d i f f u s i v i t i e s . At
1113~ the d i f f u s i v i t y of oxygen is about 6.5(10) -~
c m 2 / s (Refs. 17-20) while the diffusion c o e f f i c i e n t of
CO in CO2 is p e r h a p s five o r d e r s of m a g n i t u d e
l a r g e r . 2~'~2 T h u s , kg/le L m u s t be v e r y l a r g e , p a r t i c u l a r l y when c o n v e c t i o n in the gas is c o n s i d e r e d .
T h e r e l a t i v e p r o p o r t i o n s of the liquid p h a s e d i f f u s i o n
and r e a c t i o n p r o c e s s e s with r e s p e c t to the o v e r a l l
t r a n s p o r t r e s i s t a n c e m a y be e x a m i n e d by a n a l y s i s of
the n a t u r e of the r e a c t i o n s y s t e m . F o r s e r i e s type
t r a n s f e r of the type c o n s i d e r e d h e r e , the e x p e r i m e n t a l ,
O.O
c)
9 I~iflO] Oxygen = ~000 ppm
c
9 Initial Oxygen ~ 3000ppm
-3.0
9 Initial
-I.O
"'X
\
\
\l
Oxygen :~ 5000pprn
Initial
Sulfur
-~ 1 0 p p m
Oiomefer : 0 . 0 5 0 cm
Orifice
NRe ~ = i 8 0
-4.0
Xalk 9
~
9
9 ~14
\
-2.0
-5,0
0
'
I0
'
'
20
30
TIME (min)
,
40
49~ 9
~
r
9
'o
-3`0
b
~o
o"
\
"9
4 ~
[4]
(Note: P l e a s e r e f e r to D e f i n i t i o n of S y m b o l s list for
e x p l a n a t i o n of the s y m b o l s used in the text.) T h i s experimentally determined first order rate constant
may be c o m p a r e d to t h e o r e t i c a l r a t e c o n s t a n t p r e d i c tions in an a t t e m p t to e l u c i d a t e the m e c h a n i s m ( s )
which c o n t r o l s the o v e r a l l r a t e of the p r o c e s s .
The bubble c h a r a c t e r i z a t i o n w o r k d e m o n s t r a t e d that
the gas b u b b l e s f o r m e d d u r i n g the d e o x i d a t i o n s t u d i e s
w e r e all s p h e r o i d a l in shape (based on b u b b l e R e y n o l d s
and W e b e r n u m b e r s , s e e Ref. 1). T h u s L o c h i e l and
C a l d e r b a n k ' s ~4 e x p r e s s i o n for the p r e d i c t i o n of the
6 3 6 - V O L U M E 8B, DECEMBER 1977
-~30
c -4.0
o r d e r r a t e c o n s t a n t was d e r i v e d f r o m the r e l a t i o n
(C/Co)/dt ] VOlM F-* t~.~d~~.
'\
\
,
50
F i g . 4 - - E f f e c t of t e m p e r a t u r e in t h e r a n g e of 1113 to 1173~
on t h e k i n e t i c s of o x y g e n r e m o v a l by c a r b o n m o n o x i d e . S e g m e n t s of c u r v e s a r e d i v i d e d b y a r r o w s ,
kexp = - [d In
lll3aC
~3o
\
\
-5.0
32~n
\
\
-e~o
\
-7.o
0
I
I
I
I
30
60
90
120
TIME
~\.:5
150
I
180
(rain)
F i g . 5 - - E f f e c t of i n i t i a l o x y g e n c o n c e n t r a t i o n on t h e k i n e t i c s of
o x y g e n r e m o v a l by c a r b o n m o n o x i d e . S e g m e n t s o f c u r v e s a r e
d i v i d e d by a r r o w s .
M E T A L L U R G I C A L TRANSACTIONS B
diffusion, and reaction rate constants are related by
the expression
k L " kR
kexp = k L + ~ .
[6]
The first order chemical rate constant, kR, may be
r e a d i l y d e t e r m i n e d f r o m E q . [6] t o g e t h e r w i t h the e x p e r i m e n t a l l y d e t e r m i n e d v a l u e of kexp a n d t h e p r e d i c t e d v a l u e o f k L f r o m E q . [5] f o r e a c h s e t of e x p e r i m e n t a l c o n d i t i o n s . T h e n t h e p e r c e n t a g e of r e s i s t a n c e
which is associated with the process or reaction at
the i n t e r f a c e b e t w e e n the g a s a n d t h e m e t a l c a n b e
found by using the expression
pct reaction resistance
= 100 k L / ( k L + k R ) .
Reaction rate constants determined in the manner
described above in the initial linear region (marked by
arrows on plots), and the corresponding percentage
of o v e r a l l r e s i s t a n c e a t t a c h e d t o t h e r e a c t i o n m e c h a n i s m , a r e s h o w n i n T a b l e I. O n l y a v e r a g e v a l u e s of
reason for this behavior must remain a mystery at this
time.
T o w a r d t h e c o m p l e t i o n of t h e b l o w - d o w n i n a l l e x p e r i m e n t s , a t o x y g e n c o n c e n t r a t i o n s i n t h e m e l t of a p p r o x i m a t e l y 50 p p m o r l e s s , t h e i n i t i a l l i n e a r p o r t i o n
of t h e p l o t s t r o n g l y d e v i a t e s f r o m i t s p a t h a n d t h e irate
of o x y g e n r e m o v a l i s s u b s t a n t i a l l y r e d u c e d . T h i s
b r e a k - o v e r a n d s u b s e q u e n t d e c r e a s e i n the rate c a n n o t
be explained by equilibrium restrictions, as the equilibrium pressure ratio is far larger than the observed
v a l u e of t h e r a t i o . U t i l i z i n g c a l c u l a t i o n s of t h e t y p e
a p p l i e d p r e v i o u s l y , i t w a s d e t e r m i n e d t h a t o v e r 90 p c t
of t h e o b s e r v e d r e s i s t a n c e i s d u e t o r e a c t i o n c o n t r o l a t
the s u r f a c e d u r i n g t h i s i n t e r v a l of d e o x i d a t i o n . U n f o r t u n a t e l y , a n a l y s i s of t h e k i n e t i c s i n t h e s e s e g m e n t s
of t h e c u r v e s i s i n h i b i t e d b y a n a l y t i c a l l i m i t a t i o n s , a n d
no t r e n d c o u l d b e d e t e r m i n e d f r o m t h e d a t a w i t h r e spect to bubble or melt conditions.
SUMMARY
the c o e f f i c i e n t s are reported.
A n a l y s i s of T a b l e I s h o w s t h a t t h e e x p e r i m e n t a l l y d e t e r m i n e d r a t e c o n s t a n t s f o r CO d e o x i d a t i o n a r e in
generally good agreement with those predicted from
theory if diffusion in the liquid phase is rate controll i n g . No e f f e c t o f s u l f u r w a s o b s e r v e d f o r a g i v e n o r i fice (and hence gas/metal) condition. Data from Table
I a l s o i n d i c a t e s t h a t a s the t e m p e r a t u r e i s i n c r e a s e d
f r o m 1113 to 1173~
a s l i g h t d e c r e a s e of the e x p e r i mentally determined rate constant is observed. This
i n d i c a t e s t h a t a g r e a t e r f r a c t i o n of t h e o v e r a l l r e s i s t ance to mass transfer occurs at the interface (or in
the c h e m i c a l s t e p ) . T h i s p h e n o m e n a m a y b e d u e to the
t e m p e r a t u r e e f f e c t o n t h e r e l a t i v e p a r t i t i o n i n g of o x y gen and sulfur to the interface.
A definite decrease in the experimental rate constant was also observed as the initial oxygen content
of t h e m e l t w a s i n c r e a s e d . T h e r e i s n o o b v i o u s r e a s o n
why this phenomena should occur. No experimental
observations have been made over the same oxygen
r a n g e s b y o t h e r i n v e s t i g a t o r s a n d t h e r e f o r e no c o m p a r i s o n s w i t h s i m i l a r w o r k a r e p o s s i b l e . T h u s , the
T h i s i n v e s t i g a t i o n i n v o l v e d t h e d e o x i d a t i o n of l i q u i d
copper using carbon monoxide bubbles formed at a
submerged orifice. The bubbles were characterized
with respect to size and velocity using an acoustic
technique. The range of melt compositions covered
p a r a l l e l e d t h o s e f o u n d i n i n d u s t r y w i t h r e s p e c t to b o t h
o x y g e n a n d s u l f u r . T h e r e s u l t s d e m o n s t r a t e t h a t the
k i n e t i c s of g a s e o u s d e o x i d a t i o n of l i q u i d c o p p e r u s i n g
c a r b o n m o n o x i d e a r e l a r g e l y c o n t r o l l e d b y d i f f u s i o n in
the l i q u i d p h a s e o v e r t h e r a n g e of o x y g e n c o n t e n t a b o v e
a p p r o x i m a t e l y 50 p p m to a t l e a s t 1000 p p m .
C o m p a r i s o n s of t h e o r y a n d e x p e r i m e n t f o r a s y s t e m
of t h i s t y p e a r e c o m p l i c a t e d b e c a u s e of t h e l a c k of i n f o r m a t i o n a b o u t t h e s i m u l t a n e o u s c o v e r a g e of t h e g a s /
c o p p e r i n t e r f a c e b y s u l f u r a n d o x y g e n . It s e e m s p r o b a b l e t h a t a d y n a m i c i n t e r c h a n g e of o x y g e n a n d s u l f u r a t
the g a s / m e t a l i n t e r f a c e c o n t i n u a l l y o c c u r s a n d t h a t
t h e r e l a t i v e p a r t i t i o n i n g of t h e s e s o t u t e s d e p e n d s u p o n
the m e l t c o m p o s i t i o n . P e r h a p s t h e c o n t r o l l i n g f a c t o r
i s s i m p l y t h e o x y g e n c o n t e n t of t h e m e l t . A t h i g h l e v e l s
s u f f i c i e n t q u a n t i t i e s of o x y g e n m a y r e a c t b y s o m e
Table I. Kinetic Data for the Deoxidation of Liquid Copper by Carbon Monoxide. (All k values are X 10 2 cm/s. Except as noted all experiments conducted at
do, cm
Nge o
~[O] i, ppm
~[S] i, ppm
kexp
kL
0.10
0.10
0.05
0.05
0.05
0.05
0.05
0.05
0.05
0.05
0.05
0.05
0.05
0.05
0.05*
0.05*
180
120
t80
120
60
180
120
60
180
60
180
180
180
120
180
120
1000
1000
I000
1000
1000
1000
1000
1000
1000
1000
5000
5000
3000
2500
1000
1000
lO
10
I0
10
10
100
100
100
200
200
10
200
10
200
200
200
4.53
5.24
3.72
4.44
4.20
4.11
4.86
4.71
4.05
4.21
1.57
1.53
2.98
2.33
3.10
3.51
4.67
4.82
5.16
5.41
5.70
5.16
5.41
5.70
5.16
5.70
5.16
5.16
5.16
5.41
5.44
5.59
kg
151
13.3
24,8
16.1
20.2
47.8
27.1
18.8
16.1
2.26
2.17
7.05
4.09
7.21
9.43
1113~
Pct Reaction
Resistance
[O] Ranger, ppm
3
0
28
18
26
20
10
17
22
26
70
70
42
57
43
37
226-21
281-14
204-49
209-24
109-33
143-10
252-9
153-11
273-21
107-32
888-32
861-36
282-42
485-57
339-72
25246
*Experimental temperature was 1173~
tValues correspond to arrows on Figs. 1-5.
METALLURGICAL TRANSACTIONS B
VOLUME 8B, DECEMBER 1977-637
m e c h a n i s m to m a i n t a i n a r e l a t i v e l y " c l e a n " i n t e r f a c e .
A s t h e o x y g e n c o n t e n t d e c r e a s e s t h e r a t e of o x y g e n a r r i v a l at the i n t e r f a c e d i m i n i s h e s , and the s u l f u r m a y
b e c o m e m o r e s t a b l e at the i n t e r f a c e . T h i s m a y b e the
c a u s e of t h e s u b s t a n t i a l d e c l i n e i n o x y g e n r e m o v a l r a t e
o b s e r v e d a t 50 p p m o x y g e n o r l e s s .
ACKNOWLEDGMENTS
T h e a u t h o r s a r e i n d e b t e d to t h e W h i t e P i n e C o p p e r
C o m p a n y f o r the L e c o a n a l y s e s u t i l i z e d in the w o r k ,
a n d to t h e N a t i o n a l S c i e n c e F o u n d a t i o n f o r t h e f i n a n c i a l
support of this investigation (Grant No. GH-41156).
REFERENCES
DEFINITION OF SYMBOLS LIST
i n t e r r a c i a l a r e a o f a s i n g l e b u b b l e , c m 2,
t o t a l i n t e r f a c i a l a r e a a v a i l a b l e f o r r e a c t i o n , c m 2,
i n i t i a l o x y g e n c o n c e n t r a t i o n i n m e l t , gc/cm ~,
o x y g e n c o n c e n t r a t i o n in m e l t a t a n y t i m e , t,
g//cm ,
db
gas bubble diameter, cm,
do
orifice diameter, cm,
DL
d i f f u s i v i t y of o x y g e n in m e l t , c m 2 / s ,
Dg
gas diffusivity, cm2/s,
E
bubble eccentricity (width/height ratio),
F
b u b b l e f o r m a t i o n f r e q u e n c y , s -~,
kexp experimentally determined first order rate constant, cm/s,
/eL
theoretical liquid phase (diffusion) mass transfer
coefficient, cm/s,
kR f i r s t o r d e r c h e m i c a l r a t e c o n s t a n t , c m / s /
gas phase mass transfer coefficient, cm/s,
NRe o o r i f i c e R e y n o l d s n u m b e r , dovo[~,g] -~,
t
time, s,
r e s i d e n c e t i m e of g a s b u b b l e in m e l t , s ,
tr
g a s b u b b l e v e l o c i t y in m e l t , c m / s ,
Vb
gas velocity at orifice, cm/s,
1)0
V o l M m e l t v o l u m e , c m 3,
~g k i n e m a t i c v i s c o s i t y of g a s , c m Z / s .
A b
As
Co
C
ke
638-VOLUME 8B, DECEMBER 1977
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p. 625.
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3. W. G. Davenport: Ph.D. Thesis, Royal School of Mines,London, 1964.
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2285.
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1962.
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9. C. R. Nanda and G. H. Geiger:Met. Trans., 1971, vol. 2, p. 1101.
10. G. A. Hughmark: L & E. C. Process Design and Development, 1967, vol. 6, p.
218.
11. R. R. Hughes,A. E. Handlos, H. D. Evans,and R. L. Maycock: Chem. Eng.
Prog,, 1955,vol. 51, p. 557.
12. A. D. Kulkarni: Met. Trans., 1973, vol. 4, p. 1713,
13. K. Sano and H. Sakao: J. ,lap. Inst. Metals, 1955,vol. 19, p. 655.
14. A. C. Lochieland P. H. Calderbank: Chem. Eng. Sci., 1964, vol. 19, p. 471.
15. P. H. Calderbank and A. C. Lochiel: Chem. Eng. Sci., 1964, vol. 19, p. 485.
16. J. F. Davidsonand D. Harrison: Flttidized Particles, p. 137, Cambridge University Press, i963.
17. J. Gerlach, F. Heisterkamp,H. G. Kleist,and K. Mager: Metallurgy, 1966,
vol. 20, p. 1272.
18. A. Richert and A. A. El Miligy:Z. Metallk., 1968, vol. 59, p. 635.
19. J. Osterwald and G. Schwarzlose:Z. Phys. Chem., 1968, vol. 62, p. 119.
20. K. E. Oberg,L. M. Friedman,W. M. Boorstein,and R. A. Rapp: Met. Trans.,
1973, vol. 4, p. 61.
21. J. Szekely and N. J. Themelis:Rate Phenomena in Process Metallurgy, p. 368,
John Wileyand Sons, New York, 1971.
22. E. R. Gilliland: lnd. Eng. Chem., 1934, vol. 26, p. 681.
METALLURGICAL TRANSACTIONS B