Thermodynamic analysis of the bottom-blown direct reduction of lead sulfate with carbon

Abstract

The thermodynamic analysis of bottom-blown direct reduction of lead sulfate with carbon was studied in this investigation, and the industrial verification test was carried out. The thermodynamic analysis results indicated that lead sulfate was easily decomposed into lead sulfide at $$P_{{{\text{SO}}_{2} }}$$ values above 10−3 atm and $$P_{{{\text{O}}_{2} }}$$ values below 10−12 atm. The lead sulfide could be converted into lead oxide or metallic lead in the decomposition of lead sulfate by the addition of Fe, FeS and CaO. The phase diagrams for the C–CaO–PbSO4 and C–Fe–PbSO4 systems were constructed at 1273–1573 K, indicating that the addition of coal, limestone and scrap iron during reduction could cause the slag chemical composition variation, which consequently changed the Pb-liq + CaS and Pb-liq + FeS zones area. The industrial verification test demonstrated that the average addition of limestone, scrap iron and coal in the direct reduction of lead paste was approximately 2.8%, 5.4% and 11.5%, respectively. The direct recovery rate of lead bullion was about 61%, and the total recovery rate of lead could reach 99%. The average content of lead, zinc and sulfur in the reduced slag was 2.42%, 1.55% and 0.51%, respectively.