Kinetics of Pressure Dissolution of Enargite in Sulfate-Oxygen Media

Enargite (Cu₃AsS₄) is an increasingly common impurity in Chilean copper concentrates and its presence complicates the conventional treatment of the concentrates by smelting-converting because of the environmental risk of arsenic emissions to the atmosphere. Therefore, the recovery of copper from concentrates with high arsenic content must be carried out by nonconventional technologies. Sulfuric acid leaching processes are viable alternatives to treat copper concentrates with high content of enargite. Hence, in this article, the pressure leaching of enargite in the sulfuric acid-oxygen system is discussed. The leaching was studied at 160 °C to 220 °C and partial pressures of oxygen of 303 to 1013 kPa. The enargite dissolution was determined to occur as predicted by thermodynamics according to \( {\text{Cu}}_{3} {\text{AsS}}_{4}+{\text{8.75O}}_{2}+2{\text{.5H}}_{2} {\text{O}}+{\text{2H}}^{+} =3{\text{Cu}}^{2+}+{\text{H}}_{3} {\text{AsO}}_{4} +{\text{4HSO}}^{-}_{4}.\) The leaching rate increased substantially with increasing temperature. Complete dissolution of enargite with particle size 64 μm was obtained at 220 °C and 689 kPa of oxygen partial pressure in 120 minutes. The dissolution kinetics was analyzed by using the shrinking core model for spherical particles with surface chemical control. The rate of reaction was found to be 1/3 order with respect to the oxygen partial pressure and zero order with respect to sulfuric acid concentration. Activation energy of 69 kJ/mol was estimated for the dissolution reaction, which is a typical value for a chemically controlled process.