Thermodynamic behavior of bismuth in copper pyrometallurgy: Molten matte, white metal and blister copper phases
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BISMUTHoccurs in the minerals found in many copper ore bodies. The removal of bismuth from copper is a problem that has long plagued pyrometallurgists. Since there is little detailed thermodynamic data in the literature, the objective of this study was to determine the thermodynamic behavior of bismuth in molten copper, white metal, slag, and matte under conditions similar to those in copper smelters. The experimental data were then used to calculate the distribution coefficient of bismuth between copper-white metal, copper-matte, and matte-slag phases. Part I of this study deals with the experimental procedure and results in metal and matte phases; Part II (to be published) reports results for the slag and presents distribution coefficients. E X P E R I M E N T A L SYSTEM A dynamic system, using the transportation method, was chosen to establish a known bismuth vapor pressure over melts of the various phases. The transportation method is a general method of fixing a vapor pressure. A steady, measured stream of inert gas (argon) is passed over the substance under investigation, bismuth, which is maintained at a constant temperature, T 1. The gas removes the bismuth vapor at a constant rate, which is dependent upon their relative pressures and upon the rate of gas flow. The activity of bismuth, relative to pure liquid bismuth, is fixed above the melt at T z by the ratio: PBi,T ,
-
aBi
0 PBi,T2 where P~i,r2 is the sum of the bismuth vapor pressure
[1]
established in the gas stream passing over the pure bismuth at T~. Two kinds of bismuth vapor species exist at the experimental temperatures, 1200 and 1250 ~ Therefore, these two species, Bi~ and Bi 2 must be taken into account in vapor pressure calculations. Assuming there is an equilibrium between monatomic and diatomic bismuth species, the equilibrium constant, K, can be calculated from the published thermodynamic data for the following equilibria: 2Bi(g) = BiE(g) and the equilibrium constant is: K-
SABRI ARAC, formerly ResearchAssistant at Universityof Arizona, is Research Metallurgist, Kennecott Minerals Company, Process Technology,Salt Lake City, UT 84147. GORDON H. GEIGER, formerlyhead of the Department of Metallurgical Engineering at the Universityof Arizona, is Senior ProcessConsultant, Inland Steel Company, East Chicago, IN. Manuscript submitted August 1, 1980. METALLURGICALTRANSACTIONSB
9
eBi2
pEh.
[31
If some of the monatomic vapor forms diatomic Bi2(g), the actual pressure, P~i, will be less than the theoretical that would exist if it were all present as Bi~, Phi: P~i = PBi, + 2PBiz
[4]
where PB~, and PBi2are the equilibrium partial pressures of monatomic and diatomic gas species. P~i, the apparent vapor pressure for a purely monatomic bismuth gas, is: WBi 22.414 - MBi eli = PT Wm 22.414 ~ + Vg
[5]
Combining Eq. [3], [4] and [5] yields the following relations, and they are used to calculate Pai, and PB{,:
species that would exist above pure bismuth at T v and
P~i,r, is the sum of the bismuth vapor pressure species
[21
- 1 +_ V/1 + 8K[n]Pr
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