Kinetics of simultaneous leaching of Ag and Pb from hydrometallurgical zinc residues by chloride

Abstract

The leaching kinetics of silver and lead simultaneously from zinc residue by chloride was investigated. The effects of stirring speed, temperature, sodium chloride concentration, particle size and liquid/solid ratio on Ag and Pb dissolution in sodium chloride were studied. It was determined that the dissolution rates increased with increasing sodium chloride concentration, temperature and decreasing particle size. The dissolution kinetics followed a shrinking core model, with inter-diffusion through gangue layer as the rate determining step. This finding is in accordance with the apparent activation energy (E a) of 26.8 kJ·mol−1 (Ag) and 26.5 kJ·mol−1 (Pb), and a linear relationship between the rate constant and the reciprocal of squared particle size. The orders of reaction with respect to sodium chloride concentration, temperature and particle size were also achieved. The rate of reaction based on diffusion-controlled process can be expressed by semi-empirical equations.