Significance of Fe contents on the surface of the gold ores in gold leaching by thiourea and ethylene thiourea

Environmentally friendly ligands, alternatives to cyanide, are desired to extract gold for the sustainable hydrometallurgy of gold. Leaching characteristics of gold were examined using thiourea (TU) and ethylene thiourea (ETU) as ligands from three types of gold ores with different Fe contents from 2.70 to 14.09 wt% under the acidic condition. The Au recovery by TU leaching reached the extractable maximum with the lowest Fe-bearing gold ore. This type of gold ore is suitable for TU/ETU leaching. The highest Fe-bearing gold ore was the most difficult to extract Au in ETU/TU leaching. There are at least two detrimental factors in TU leaching of Fe-rich gold ores, that is (i) the oxidative decomposition of TU, and (ii) complexation of TU with Fe3+, which both cause to deduce the complexation of TU with Au+. However, adding Na2SO3 improved the Au extraction from such an ore to reduce Fe3+ to Fe2+. ETU facilitated the formation of more stable complexes with Au than TU against the coexisting Fe3+. This finding is useful when considering the cyanide-free leaching of different types of gold ores.