Effects of CaO, Al2O3, and MgO additions on the copper solubility, ferric/ferrous ratio, and minor-element behavior of iron-silicate slags

The effects of CaO, Al2O3, and MgO additions, singly or in combination, on the copper solubility, the Fe3+/Fe2+ ratio in slag, and on the minor-element behavior of silica-saturated iron silicate slags were examined at 1250 degrees C and a p(O2) of 10(-12) to 10(-6) atm. The results indicated that copper solubility in slag was lowered with the addition of CaO, MgO, and Al2O3, in decreasing order. The Fe3+/Fe2+ ratio in the slag decreased with the additions, but this effect was smaller at lower oxygen potentials. The presence of small amounts (about 4 pet) of CaO, Al2O3, and MgO in the slag resulted in increased absorption of Bi and Sb into molten copper, but had a smaller effect at large additions (about 8 to 11 pet). The distribution behavior of Pb was a function of oxygen partial pressure, which indicates the oxidic dissolution of Pb in the slag as PbO, while the behavior of Bi, Sb, and As was found to be independent of oxygen potential, supporting the atomic (neutral) dissolution hypothesis of these elements in the slag. The distribution behavior of Pb and As was not significantly affected by the additions. The activity coefficients of Bi and Sb in the slags were determined to be as follows: (1) for no addition, gamma(Bi) = 40 and gamma(Sb) = 0.4; (2) for small additions (about 4.4 pet), gamma(Bi) = 70 to 85 and gamma(Sb) = 0.8; and (3) for large additions (about 8 to 11 pet), gamma(Bi) = 60 to 75 and gamma(Sb) = 0.5 to 0.7.