Slag chemistry, element distribution behaviors, and metallurgical balance of e-waste smelting process

Abstract

The co-smelting of electronic waste (e-waste) in copper/lead pyrometallurgical processes is widely recognized as the preferred solution for sustainable development. However, aluminum and halogen elements in e-waste causes new challenges. To address this, the slag chemistry of high Al₂O₃-containing slag was studied, and the distribution behaviors of Au, Ag, Sn, and other elements in the copper alloy/slag/gas system were investigated in the presence of halogen elements (F/Cl/Br) using the equilibration method. The industrial practice of electronic waste smelting was modeled using METSIM, and the material and energy balances of one industrial process were obtained. Under the conditions of electronic waste smelting, the solubility of Al₂O₃ in the FexO–SiO₂–Al₂O₃–CaO slag system decreased with increasing CaO content. When the CaO content was 20 wt%, and the Fe/SiO₂ mass ratio was 0.62–0.95, the solubility of Al₂O₃ in the slag reached 20 wt%. When 1%–10% CaF₂ was added, 93% of Au entered the metal phase. When the same amount of CaCl₂ or CaBr₂ was added, up to 32% Au entered the gas phase. When CaF₂ was added to the system, 22%–49% of Ag entered the gas phase. However, when CaCl₂ or CaBr₂ was added, 3%–34% of Ag entered the gas phase. The proportion of tin in the gas and slag phases increased with increasing temperature or the addition of halides. The METSIM simulation results showed that under optimized conditions, the crude copper contained more than 90 wt% copper, the discharged slag contained approximately 0.5 wt% copper, and the recovery rates of copper, gold, and silver were ≥98%. The heat generated from raw materials and fuel accounted for the largest part of the heat income, representing 65.32% of the total.