Solubility of Silver in FeO_x–CaO–SiO₂ Slag Coexisting with Silver and Silver Bromide at 1473 K

Abstract

Silver, Ag, in secondary raw materials such as printed circuit boards is recovered by nonferrous metal thermochemical processes. Because printed circuit boards contain bromine, Br, which is highly reactive with Ag, as a flame retardant, there is concern that Br may affect the recovery of Ag. In this study, the FeO_x–CaO–SiO₂ slags were equilibrated with liquid AgBr and Ag in a MgO crucible at 1473 K, and the effects of concentration of Br in the slags, oxygen partial pressure, p_O2, and slag composition on the dissolution of Ag were experimentally investigated. The results showed that the concentration of Ag in the slag coexisting with Ag and AgBr was higher than that coexisting with only Ag. Moreover, the concentration of Ag in the slag increased with increasing concentration of Br in the slag coexisting with Ag and AgBr. At p_O2 = 10⁻⁹, the concentrations of Ag and Br in the slag in equilibrium with AgBr were minimum at neutral slag basicity Q = 0.45, defined as Q = (mass%CaO + mass%MgO)/(mass%CaO + mass%MgO + mass%SiO₂). The slag loss of Ag can be reduced using neutral basicity slag and by reducing the bromine partial pressure in the system to reduce the concentration of Br dissolved in the slag.

Fig. 7 Relationship between the solubilities of Ag and Br in the FeO_x–CaO–SiO₂ slag at 1473 K.