Kinetics of the sulfidation of chalcopyrite with gaseous sulfur

The sulfidation of chalcopyrite with gaseous sulfur in the temperature range of 325 degreesC to 400 degreesC occurs with the formation of covellite and pyrite as the final products. The rate of sulfidation depends strongly on the temperature, with nearly complete conversion in less than 30 minutes at 400 degreesC. Microscopic analysis of partially and completely reacted particles showed that the sulfidation proceeded topochemically, with a shrinking core of unreacted chalcopyrite surrounded by successive layers of FeS(2) and CuS. The experimental data exhibited an induction period at the beginning of the reaction. An electrochemical mechanism is proposed for the sulfidation reaction, which involves simultaneous diffusion of Cu(+) and electrons through the product layers. The rate data showed that the fraction reacted is well represented by a shrinking-core model controlled by the reaction occurring at the chalcopyrite-pyrite interface, resulting in the conversion-vs-time relationship 1 - (1 - X)(1/3) k(t - t(ind)). An activation energy of 98.4 kJ/mol was determined for the temperature range of 325 degreesC to 400 degreesC.