The solubility of silver in MO–B₂O₃ (MO = CaO, BaO and Na₂O) slags at high temperatures was measured in order to understand the dissolution mechanism of silver in the slags, and the effects of CaO, BaO, and Na₂O on the solubility of silver. The solubility of silver in the Na₂O_satd–B₂O₃ system exhibits a minimum value as a function of oxygen partial pressure at about p_O2=8.49×10⁻⁹ Pa. Therefore, the dissolution reaction of silver in basic slags at higher oxygen potential can be estimated by the following equation:
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The solubility of silver in B₂O₃–bearing slags also exhibits a minimum value as a function of slag composition. The minimum composition shifts to the acidic region following the order of CaO–, BaO–, and Na₂O–B₂O₃ slag. Based on these minimum compositions, i.e., 65 (mol%) CaO, 45 (mol%) BaO, and 35 (mol%) Na₂O, the value of the CaO-equivalence of BaO and that of Na₂O are suggested as 1.44 (=mol% CaO/mol% BaO) and 1.86 (=mol% CaO/mol% Na₂O), respectively.