Silver solubility in sodium silicate slags

During copper electrorefining silver reports to the anode slimes, which are then smelted to recover the silver. Smelting involves the use of a slag, s uch as sodium silicate, to hold the oxidized copper, but some silver is als o inevitably oxidized to the slag. Some work has been published on the effe ct of oxygen partial pressure on the solubility of silver in slags, but the re is disagreement on the actual silver content and the identity of the dis solving species. The solubility of silver in sodium silicate slags at 1100 degrees C and 115 0 degrees C has now been determined over a very wide range of oxygen partia l pressures. Silver was shown to be present in the slags as both neutral si lver atoms, Ag degrees, and AgO0.5. The values of the activity coefficients of both Ag degrees and AgO0.5(s) in the slag, defined as SiO2-NaO0.5, were determined. That for Ag degrees was found to be a very strong function of both slag composition and temperature, whereas that for AgO0.5(s) was much less affected by slag composition and was almost independent of temperature over the limited range examined. The results reveal that dissolved silver in sodium silicate smelting slags cannot be fully recovered by reduction of the slag with very reducing gases.