Selective leaching of arsenic from enargite in NaHS–NaOH media

The dissolution kinetics of arsenic from enargite (Cu3AsS4) was investigated in sodium hydrosulfide (NaHS) solution of concentration range 0.68 M–1.35 M S2− and 1.25 M OH− (NaOH) in the temperature range from 298 K to 363 K. The kinetic equation from evaluation of experimental data using several heterogeneous and pseudo-homogeneous reaction models was found to be 1−3(1−α)2/3+ 2(1−α) = kt and from the Arrhenius plot, using k values determined experimentally, an activation energy of 70.26 ± 4.74 kJ/mol was obtained. This result indicates that the rate-determining process for the reaction between Cu3AsS4 and NaHS is controlled by product layer diffusion process. Characterization of solid samples by XRD and chemical analysis by ICP showed that Cu3AsS4 was transformed to Cu2S and complete removal of arsenic into solution can be achieved within 60 to 120 min.