Process simulation based life cycle assessment of cyanide-free refractory gold concentrate processing - Case study: Cupric chloride leaching

The development of cyanide-free gold leaching methods is becoming increasingly important due to the treatment of complex ores, where treatment by cyanidation is not economically viable. Cupric chloride leaching provides an alternative leaching process to replace cyanidation. A detailed simulation of refractory gold concentrate processing by cupric chloride leaching is presented in this study. The simulation with mass and energy balances was built to be used as life cycle inventory data to evaluate the environmental impacts of the development stage cupric chloride process. Three cases, the Base Case (125 g/L Cl-), Mild Case (50 g/L Cl-), and Extremely Mild Case (20 g/L Cl-), were investigated in two flowsheet options. Loss of gold to wash waters was observed in the Flowsheet 1 cases, and therefore Flowsheet 2, with the recirculation of wash water to solvent extraction, was developed and investigated in order to achieve higher gold recovery. The gold extraction improved from around 85% to 99%. Chemical consumption (NaCl, NaBr, CuCl2) was greatly affected by the leaching conditions, higher concentrations consuming more initial chemicals. In milder conditions, efficient recycling of chlorides could be obtained in the process, and no addition of NaCl was required. In the Extremely Mild Case, the chloride concentration was close to sea water conditions (20 g/L), where sea water could be used to provide chlorides for the process, and the effluent waters could be disposed of in the sea after purification. The global warming potential was estimated to be 12.5 t CO2-e/kg Au in chloride leaching and was further decreased to 10.6 t CO2-e/kg Au in the mildest conditions (20 g/L Cl-). The milder chloride leaching conditions (20 g/L Cl - and 50 g/L Cl-) were shown to decrease the acidification potential, eutrophication potential, and water depletion.