Thermal decomposition of CuS to Cu 1.8 S
- PDF / 196,945 Bytes
- 2 Pages / 612 x 792 pts (letter) Page_size
- 97 Downloads / 182 Views
Communications
dw _ ~A
Thermal Decomposition of CuS to CuLsS
[3]
dt
I. D. SHAH A N D S. E . K H A L A F A L L A T H I S n o t e d e s c r i b e s a p a r t of t h e w o r k d o n e by t h e U. S. B u r e a u of M i n e s on t h e f u n d a m e n t a l s of r o a s t i n g of c o p p e r s u l f i d e s . T h e c o n v e r s i o n of c o v e l l i t e (CuS) to d i g e n i t e (Cul.sS) r e p r e s e n t s t h e f i r s t s t e p in t h e o x i d a t i v e r o a s t i n g of CuS. P a v l y u c h e n k o and S a m a l 1 r e p o r t e d that the t h e r m a l d e c o m p o s i t i o n of p o w d e r e d CuS to Cul.sS in v a c u u m and N2 in t h e t e m p e r a t u r e r a n g e 310 ~ to 338~ f o l l o w e d t h e k i n e t i c e q u a t i o n of an u n r e a c t e d core model
w h e r e k is t h e r e a c t i o n r a t e c o n s t a n t e x p r e s s e d in g -2 cm s e c -1. If A r e m a i n s c o n s t a n t d u r i n g t h e r e a c t i o n progress, a linear relationship between the weight loss p e r unit a r e a and t i m e w i l l b e e x p e c t e d . In t h e c a s e of t h e u n r e a c t e d c o r e m o d e l , w h e r e r e a c t i o n b e g i n s at t h e s u r f a c e of t h e p a r t i c l e and p r o c e e d s i n w a r d s t o w a r d s t h e c e n t e r , E q . [3] r e d u c e s to R(ot) = f o d o f = /3t
[4]
w h e r e ro is a n y c o n v e n i e n t m e a s u r i n g d i s t a n c e in t h e p a r t i c l e , do i s t h e o r i g i n a l d e n s i t y , and f i s f r a c t i o n a l 60
I
I
I
I
I
Initial wt. of Pellet = 357.0 mg
i - (I
oz)'/3 = /31:
[1] 50
w h e r e ot is the fractional decomposition and ~3 is a constant. They found that the activation energy for the reaction ranged from 27.6 to 59.8 kcal depending upon the thermal history of CuS. In the present work, the conversion of CuS pellets to Cu~.sS at 340 ~ to 400~ w a s studied in flowing N2 (i00 cu c m per rain) at i atm. The reaction rate w a s extremely slow below 340~ Reagent-grade (99.8 pct) CuS powder, w h o s e chemical analysis w a s reported in a previous publication, 2 w a s used in this work. Cylindrical pellets of 0.14 and 0.28 c m radii having 94 pct of true density w e r e m a d e from the C u S powder. The details of the equipment have been described elsewhere. 3 Essentially it consisted of an automatic thermogravimetric electro-balance. The sample, contained in a platinum basket, w a s heated by a resistance furnace in a 19 m m ID V y c o r reaction chamber. The temperature w a s m e a s u r e d by m e a n s of a Pt-vs-Pt-10 pct R h thermocouple. The rate of the reaction
40
oO
i 30 a 20
l0
'
0
:0
20
[2]
d e c r e a s e d c o n t i n u o u s l y w h e n the flow of N2 w a s i n c r e a s e d b e y o n d 100 cu c m p e r rain. T h i s w a s found to be due to s u r f a c e c o o l i n g of t h e p e l l e t at the h i g h flow r a t e s and s u g g e s t s that t h e c r i t i c a l flow r a t e w a s f a i r l y w e l l b y p a s s e d , and t h a t t h e r e a c t i o n w a s out of t h e g a s diffu
Data Loading...
