Dissolution kinetics of enargite in dilute Cl2/Cl− media

A study was made of the dissolution kinetics of enargite, Cu3AsS4, with chlorine generated in solution by the reaction between sodium hypochlorite and hydrochloric acid. The effects of stirring speed, initial chlorine concentration, particle size, and temperature were investigated. The kinetics of the dissolution were characterized by two sequential stages: relatively fast reaction initially, while later the reaction became very slow. In the first stage, the fraction of copper extracted varied linearly with time according to α=k1t, whereas in the second stage, the dissolution was well represented by the shrinking core model controlled by diffusion through a porous product layer with kinetic equation: 1−3(1−α)2/3+2(1−α)=k2t. The S0 product layer acts as a diffusion barrier. The calculated activation energies were 15.0 kJ mol−1 (3.5 kcal/mol) for the first stage and 21.0 kJ mol−1 (5.0 kcal/mol) for the second. e first stage, an apparent reaction order of 1.0 was found with respect to the chlorine concentration; for the second stage, an apparent reaction order of 1.8 was obtained.