Leaching Behavior of Lead and Silver from Lead Sulfate Hazardous Residues in NaCl-CaCl2-NaClO3 Media

Abstract

The leaching behavior of lead and silver from lead sulfate residues in NaCl-CaCl2-NaClO3 media was studied systematically. The results indicate that Cl− concentration, NaClO3 concentration, leaching time and temperature had significant effects on lead and silver leaching, whilst agitation speed and the liquid–solid ratio had a secondary effect on silver leaching but little effect on lead leaching. The Ca2+ concentration had an important effect on $$ {\text{SO}}_{4}^{2 - } $$ removal but little effect on lead and silver leaching. The optimum parameters for lead and silver leaching were: initial Cl− concentration: 207.5 g/L; NaClO3 concentration: 12 g/L; Ca2+ concentration: 1.3 times of stoichiometric quantity; temperature: 90 ± 2 °C; time: 1 h; liquid–solid ratio: 8:1–10:1; and agitation speed: 450 rpm. The lead and silver leaching were > 98% and 95%, respectively. The removal ratio of $$ {\text{SO}}_{4}^{2 - } $$ was > 98%. The leaching kinetics of lead follow the shrinking core model of mixed control, and the apparent activation energy was 13.4 kJ/mol.