ABSTRACT: The leaching kinetics of willemite in ammonia-ammonium chloride solution was investigated. The effects of the ammonia-ammonium
ratio, particle size, temperature, and total ammonia concentration on the leaching rate of willemite were determined. The
results show that the optimum ammonia-ammonium ratio is 1:2 over the studied range. The zinc extraction increases with the
reduction of particle size and with the increase of temperature and the total ammonia concentration. Leaching kinetics indicate
that the grain pore model could be adopted to describe the leaching process, and diffusion is the main rate-controlling step.
The apparent activation energy was determined to be 54.47±6.39kJ/mol and a reaction order with respect to NH3(aq) was 3.16±0.40, both of which are likely a result of the parallel nature of the chemical reaction and diffusion in porous
solids, even if the chemical reaction is not the rate-controlling step.
Metallurgical and Materials Transactions B 04/2012; 42(4):633-641. · 0.90 Impact Factor