Recovery of metallic lead of cupel wastes from gold analysis by alkaline fusion in the presence of sulfur.

Abstract

High precision and accuracy make Pb-Fire assay the method of choice for gold analysis in mineralogical samples. The second stage of this method, called cupellation, leaves the used container (cupel) highly contaminated with PbO. Since tons of cupel waste are generated annually from gold analysis worldwide, the disposal of such material constitutes a serious risk to the environment. In the present paper the recovery of the lead from cupel waste by means of an alkaline fusion in the presence of sulfur was evaluated considering the efects of the following variables: amount of NaOH and sulfur, time, and temperature. Gravimetric analyses indicated 81.3% (w/w) recovery of lead in the form of metallic lead from 5.00 g of cupel waste using 3.00 g of NaOH, 0.5 g of S8, after 15 min at 650 °C. During the process, sulfur promoted the reduction of lead oxide. After the process, both the cupel wastes and the resulting secondary wastes presented lead concentrations below the maximum limits determined by both Brazilian legislation and that followed by US Environmental Protection Agency, and can be considered safe for disposal. Furthermore, the proposed method allows cupel wastes to be converted from an environmental liability to a raw material for the production of metallic Pb.