Existent state and removal rate of silver in lead-silver slag during the melt-vaporization process

Abstract

In this paper, Ag containing in lead-silver slag was recovered during the melt-vaporization process, the existent state of Ag in soot was analyzed, the influence of reaction temperature, the carbon ratio, and reaction time on the removal rate of silver was explored, and process conditions were optimized by using the response surface methodology. Silver chloride, silver metal, silver sulfide, silver oxide, and silver sulfate are the main silver phases in the lead-silver slag, among which silver chloride and silver sulfide are major phases. The silver oxide (Ag2O) and silver chloride (AgCl) in the lead-silver slag volatilize into soot, the silver sulfide (Ag2S) is oxidized by oxygen to form silver sulfate (Ag2SO4), and elemental silver volatilizes with Pb and Zn to form alloys. The silver in the final exists as Ag, AgCl, Ag2O and Ag2SO4 in the soot. The removal rate of silver increases gradually with increasing reaction temperature and tends to remain stable at 1300?C. With a gradual increase in the carbon ratio, the removal rate of silver first increases and then decreases, and the highest value is 80.12 wt% when the carbon ratio is 16.30 wt%. With increasing holding time, the removal rate of silver increases gradually and then stabilizes about 79.97 wt% even at the holding time of 150 min. The optimum process conditions for silver removal are a reaction temperature of 1340?C, a carbon ratio of 16.10 wt%, and a holding time of 165 min, and the average removal rate of silver under these conditions is 80.42 wt%. The research in this paper lays a theoretical foundation for the removal and utilization of silver from lead and silver residue.