Abstract
In this paper, a gold extraction process from an acidic biooxidative residue was studied. Pretreatment by washing the biooxidation residues with a pH = 2 sulphuric acid solution was needed to eliminate the excessive thiourea consumption by iron (III). By adding Na 2SO 3 powder into the acidic thiourea medium, the consumption of thiourea decreased significantly from 12 g/kg to 3 g/kg of ores and the gold extraction time was shortened remarkably from 6 hours to 1 hour. The optimum conditions for efficient gold extraction were: a lixiviant of 3 g/kg of thiourea and 4.5 g/L of sodium sulphite in a pulp density of 33% (w/v) in a pH = 2 medium with stirring for 1 hour at room temperature. A gold extraction of more than 95% was achieved with a non pre-concentrated low-grade ore obtained after biological oxidation. The direct gold extraction technique in the low pH Na 2SO 3 — thiourea system is of great advantage over the traditional cyanide process as it eliminates the costly neutralization process and greatly reduce the risks of environmental pollution.
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