Gold extraction from paleochannel ores using an aerated alkaline glycine lixiviant for consideration in heap and in-situ leaching applications

The decreasing grades of some gold deposits combined with the increasing depths, difficult surface topography, socioeconomic and geopolitical pressures often make the processing of such deposits infeasible by conventional mining, comminution and leaching technologies. To overcome these problems, the application of in-place, in situ, and heap leaching often represent an optimal solution that minimises the capital and operating costs associated with mining and processing operations. Non-toxic, low cost lixiviants that are stable over an extended range of pH and Eh are required to provide any practical solution to in-situ leaching (ISL). Since ISL has the inherent benefit of increased natural rock temperature and pressure, glycine-based systems can be considered to extract valuable metals. Based on earlier studies on glycine leaching of pure gold foil, this research shows that Western Australian paleochannel ores are amenable to glycine-based ISL, at elevated alkalinity. The effects of pH, temperature, free glycine, ferric ions, sodium chloride and solids percentages on the kinetics of gold extraction were assessed. More than 85% of the gold can be extracted from ore with solutions containing 15 g/L glycine at pH 12.5 in 336 h. The presence of ferric ions did not improve the gold extraction, and most of the ferric has been precipitated from the leach solutions, implying that the chosen ferric complex was not sufficiently stable at the operating pH. The impurities dissolution during glycine leach was very low and highly selective leaching of gold over gangue was observed.