Conversion of lead chloride into lead carbonate in ammonium bicarbonate solution

This study aimed to characterize the kinetics and mechanism of the phase transformation from lead chloride to lead carbonate in ammonium bicarbonate solution. The dechlorination rate of PbCl2 was consistently high: it increased with increasing concentrations of NH4HCO3 and decreased only moderately with the increasing total concentration of Cl in the solution. The rate also increased systematically with increasing temperatures, and the apparent activation energy was 14.363 kJ/mol. The reaction obeyed the shrinking-core model, which involved diffusion through the thickening product layer formed on the PbCl2 particles. The pH of the leaching solution strongly influenced the conversion results. A reduction in the pH led to a decrease in the dechlorination rate owing to the conversion of the carbonate ions into slowly reacting bicarbonate species. In contrast, an increase in the pH from 11.0 to 12.0 by the use of ammonium hydroxide led to a significant increase in the conversion rate of PbCl2; the main conversion products were Pb-3(CO3)(2)(OH)(2) and PbCO3, with a high conversion rate of around 99%.