Process simulation and environmental footprint of gold chlorination and cyanidation processes

Chlorination was applied widely in gold processing throughout the 1800s as vat and barrel leaching, with chlorine gas acting as an oxidant. In the early 1900s, hydrometallurgical gold process technology changed from chlorination to cyanidation, which replaced chlorination as the predominant gold leaching process due to technical and financial advantages. The challenges in the chlorination process were related to the highly corrosive leaching chemicals and associated high reagent consumption. In the past, new gold extraction technologies have not been evaluated by their environmental footprint, but rather by the financial, technological and operational advantages. In order to determine the associated ecological impact and sustainability, new transformative technologies need to be evaluated from the environmental footprint point of view prior commercialization. In this study, the environmental indicator category chosen for evaluation was global warming potential (GWP) and the other impact categories, such as human toxicity potential and acidification were left out of the scope. The global warming potentials (GWP) were determined both for the historical chlorination process and for a state-of-art cyanidation process by modelling with HSC Chemistry 8.0 HSC-Sim module combined with life cycle analysis by GaBi 6.0. This analysis provides a baseline scenario for comparison, which can be used to support the future life cycle assessment research for development stage gold processes. The combination of HSC-Sim and GaBi was shown to be an efficient way for the investigation of the environmental footprint of the historical and current gold processes. The GWP of the cyanidation process was 455 kg CO2 equivalent and the GWP of chlorination process was 10500 kg CO2 equivalent. The main emission source in cyanidation was found to be electricity, whereas in chlorination the main emissions originated from the chlorine gas, although, it is worth noting that environmental impacts are not defined for all chemical products in the GaBi database. Additionally, some compromises had to be made when the LCA Equivalents were applied to the process streams modelled in HSC-Sim. The corresponding or most appropriate LCA Equivalents were defined from the HSC/GaBi database and the LCA group was defined for all the inputs and outputs within the scope of the process.