Experiments were carried out on equilibrium between calcium ferrite slag and metallic copper under a controlled partial pressure of oxygen by using a mixture of CO₂ and CO. Lime, magnesia or iron crucibles were used in the temperature range from 1423 to 1623 K. The results were summarized as follows:
(1) The solubility of copper in the slags is affected by the oxygen potential and temperature, and the solubility amounts to 70% of that in the case of iron silicate slags.
(2) The value of (Fe⁺⁺⁺/Fe⁺⁺) in slags fits the equation previously obtained in the plain FeO–FeO_1.5–CaO ternary system, and this ratio in the basic calcium ferrite slags is ten times as large as that in acidic iron silicate slags.
(3) The iron contents in metallic copper are related to the oxygen potential, temperature and iron content in the slag.