Kinetics of Alkaline Leaching of Solid Wastes Bearing Zinc and Lead

Abstract

The leaching reaction kinetics of waste bearing zinc and lead are studied. For waste bearing zinc, plot of 1 − (1 − η)1/3 versus leaching time giving linear relationship indicates that the velocity of leaching is controlled by the chemical reaction step; the apparent activation energy is obtained to be 49.22 kJ/mol from an Arrhenius plot. For smithsonite and willemite, during the early stage of leaching reaction, 1 − (2/3)η − (1 − η)2/3 is linear with leaching time, with the apparent activation energy of 19.95 kJ/mol and 19.32 kJ/mol, respectively. In the later stage, 1 − (1 − η)1/3 is linear with leaching time, with the apparent activation energy of 46.54 kJ/mol and 32.64 kJ/mol, respectively. Thus, it indicates that the leaching mechanism of smithsonite changes from inner diffusion control to chemical reaction control and that of willemite changes from inner diffusion control to mixed control, during the leaching process in alkaline solution. The leaching of lead oxide may be controlled by diffusion of NaOH solution passing through the solid-phase layer at lower temperature and less NaOH concentration and by surface chemical reaction at high temperature and high NaOH concentration.