Effect of Na chloride on the bioleaching

Oxidative dissolution of chalcopyrite at ambient temperatures is generally slow and subject to passivation, posing a major challenge for developing bioleaching applications for this recalcitrant mineral. Chloride is known to enhance the chemical leaching of chalcopyrite, but much of this effect has been demonstrated at elevated temperatures. This study was undertaken to test whether 100–200 mM Na-chloride enhances the chemical and bacterial leaching of chalcopyrite in shake flasks and stirred tank bioreactor conditions at mesophilic temperatures. Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans and abiotic controls were employed for the leaching experiments. Addition of Na-chloride to the bioleaching suspension inhibited the formation of secondary phases from chalcopyrite and decreased the Fe(III) precipitation. Scanning electron micrographs and energy-dispersive analysis of X-rays revealed the presence of precipitates that were identified as brucite and jarosite in solid residues. Electrochemical analysis of solid residues was inconclusive on the differential effects between chemical controls, chalcocite and bacteria. Impedance spectroscopy was used to characterize interfacial changes on chalcopyrite surface caused by different bioleaching conditions.