Oxidative leaching of refractory sulphid

The effect of temperature in the range of 20-65 °C on gold extraction from refractory gold tailings containing pyrite in 20% (v/v) of 1-butyl-3-methylimidazolium hydrogen sulphate [Bmim⁺HSO₄⁻]-water solution with thiourea as complexing agent and iron(III) sulphate oxidant, at pH of 1 was examined for 12 h leaching time intervals. The experimental results revealed that the extraction of gold improved by increasing the temperature. The effect of time showed that a substantial amount of gold extraction took place during the first day of extraction and thereafter very little gold extraction occurred. The ionic liquid [Bmim⁺HSO₄⁻] is water soluble and in aquatic solution can act like a Brönsted acid by releasing H⁺ ions. The apparent activation energy (Ea) was calculated based on the Arrhenius theory and it suggests that the kinetic process of gold leaching with this acidic ionic liquid follows shrinking core model with mixed and diffusion controlled reaction regions having Ea of 17.97 kJ/mol and 27.17 kJ/mol, respectively. In the SEM image of the solid residue of the leached sample some pores appeared on the reactive pyrite particles, whereas the pyrite particles in the unleached sample looked smooth. Additionally, Raman spectra detected sulphur shifts in the recorded spectra of the solid residue after leaching which can be an indication of the formation of a product surface layer of elemental sulphur, which supports the diffusion through a product layer in the kinetic model.