Sustainable Mining and Metallurgy

The phase evolution of silver in lead-silver slag during melting-fuming process was studied. The thermodynamic mechanism of silver phase volatilization in lead-silver slag was analyzed by thermodynamic calculation and analysis. Based on the thermodynamic theory calculation, the influence of single factor (reaction temperature, carbon proportion and holding time ) on silver recovery rate was studied, and the optimum process parameters were obtained. Then, by observing the microstructure morphology, combined with theoretical calculation and experimental results, the evolution law of silver phase in lead-silver slag during melting-fuming process was clarified. The thermodynamic analysis results show that Ag₂O in the lead-silver slag is preferentially volatilized into the soot. AgCl in the slag does not undergo oxidation reaction, reduction reaction and decomposition reaction, and will volatilize into the dust. Ag₂S in lead-silver slag does not volatilize or undergo reduction reaction, and will be oxidized to Ag₂SO₄. At low temperature, Ag₂SO₄ will be reduced to elemental silver, and elemental silver will form an alloy with lead and zinc, which will be carried into the soot. At high temperatures, the vapor pressure of Ag₂SO₄ increases sharply and Ag₂SO₄ volatilizes into the dust. The experimental results of silver slag show that the phases in the dust are Ag₂O, AgCl, Ag₂SO₄ and elemental silver, which is consistent with the results of thermodynamic analysis. The single factor experiment showed that the optimum process parameters for silver recovery from lead-silver slag were reaction temperature of 1300℃, carbon proportion of 16.30%, holding time of 150min. Under these conditions, the silver recovery rate was 80.26%.