Leaching kinetics of natural cobalt triarsenide in chlorine solutions

The influence of stirring speed, particle size, chlorine and hydrochloric acid concentrations, and temperature on the kinetics of chlorine leaching of skutterudite particles in a stirred vessel has been investigated. The reaction rate is limited by transport in the aqueous phase with significant resistance of the chemical reaction at temperatures below 20 °C. This is supported by (a) the rate constant increases with decrease in particle size, (b) the first-order dependence of the leaching rate with the total chlorine concentration and the insignificant effect of the hydrochloric acid concentration, (c) an apparent activation energy of 18 kJ/mole for transport control and an approximate value of 85 kJ/mole for the chemical reaction, and (d) the agreement of the experimental transport constants with the expected values for mass transfer coefficients. The reaction kinetics were analyzed by a shrinking core model in which (Sh) _p − 2] (D/d) was considered virtually independent of particle size, which is consistent with the experimental data.