The solubility of copper in lime-saturated and calcium ferrite-saturated liquid iron oxide
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I.
INTRODUCTION
THE high-grade mattes processed in modern copper smelting and the consequent high concentrations of copper produced in the slags require that the slag be processed for recovery of the copper before it is discarded, t~l This processing involves the settling out of mechanically entrained matte and the removal of copper from chemical solution in the slag, and the latter requires an understanding of the t h e r m o d y n a m i c s of the s o l u t i o n of copper in slags. Several studies have been made of the solubility of copper in silica-saturated iron silicate melts, t2,3,41 the influence of minor additions of MgO, A1203, and CaO to these melts tS'6j, the solubility of copper in aluminasaturated iron silicate melts, tT] and the solubility of copper in lime-saturated calcium ferrite melts, ts,9,~~ The purpose of the present study was to examine further the thermodynamics of solution of copper in lime-saturated calcium ferrite melts. II.
which varied from virtually zero to 0.065 wt pct, did not show any correlation with the copper contents of the slags. The final slag compositions were in excellent agreement with the limits of saturation determined by Yazawa e t a l . t81 It was noted that with oxygen potentials of 10 -'~ and 10 -9 atm, significant penetration of the crucible wall by the slag occurred as the slag approached saturation with lime, whereas with oxygen potentials of 10 -8 and 10 -7 atm, a thin, impervious film of 2CaO- Fe203 formed on the crucible wall, which prevented any penetration by the slag. Double saturation of the slag with CaO and 2CaO. F e 2 0 3 at 1300 ~ occurs with po2-= 10 -8.6 a t m . 18]
III.
EXPERIMENTAL RESULTS
The experimental results for copper dissolved in limesaturated melts at oxygen pressures of 10 -7 , 10 -8 , 10 -9 , and 10 -~~ atm are listed in Table I.
IV.
EXPERIMENTAL PROCEDURE
DISCUSSION
Buttons of copper-gold alloys and wustite-lime mixtures were melted in slip-cast lime crucibles under CO2-CO atmospheres at 1300 ~ in a horizontal molybdenum resistance tube furnace. In each run, two crucibles, each containing a metal alloy button of mass 0.5 g, were equilibrated with 1.5 g of slag, and it was determined that metal-slag-gas equilibrium was achieved in 10 hours. Measurements were made with oxygen potentials of 10 -7, 10 -8, 10 -9, and 10 -~~ atm, and the copper contents of the alloys varied from 13.5 to 100 pct. After equilibration, the gold, copper, and iron contents of the metal and the slag were determined by atomic absorption spectrometry, and the activities of copper in the equilibrated system were obtained from interpolation of the measurements of activities in the system Cu-Au made by Hager e t a l . lj2j T h e concentrations of gold in the slags,
In a copper-slag-gas system, the copper content of the slag is governed by the equilibrium
J. PALACIOS, formerly Graduate Student, Purdue University, is Assistant Professor of Metallurgical Engineering, Atacama University, Copiapo, Chile. D.R. GASKELL, Professor of Metallurgical Engineering, is with
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