In this doctoral dissertation simulation based life cycle assessment was adapted in evaluation of process performance and environmental impacts of cyanide-free gold leaching. This methodology enables the evaluation of industrial scale process operation combined with early stage estimation of environmental impacts of the processes. The simulations are based on hydrometallurgical expertise, and can be adjusted according to experimental data. Adapting such a methodology in to evaluation of hydrometallurgical gold processes, is relevant for two reasons. Firstly, the challenges in up-scaling the metallurgical processes from laboratory to industrial scale require that the new technologies are assessed already in development stage, for both process performance and environmental impacts. Secondly, this is extremely timely in gold production, where cyanidation is the dominant processing method and faces several challenges as the gold ore grades diminish and mineralogy of the ores become increasingly complicated, in addition to health and safety risks related to cyanide. Gold production should utilize the best available technology, due to which the research has started to focus on more environmentally friendly alternatives in order to replace cyanidation. In the current study the simulations have been constructed using HSC-Sim, linked to GaBi software. HSC-Sim enables flowsheet simulation of hydrometallurgical processes to create accurate life cycle inventory data that can be used in life cycle assessment. This study presents simulation of six gold extraction processes, including pressure oxidation, cyanidation, chlorination, halogen leaching and cupric chloride leaching. The main challenges for cyanide-free chloride based processes are water balance, in situ method for recovery of gold, and improved gold recovery. However, the faster leaching kinetics, and the simultaneous oxidation of sulfide mineral and gold extraction could offer competitive edge for chloride processes. The estimated environmental impact categories in this work include global warming, acidification and eutrophication potential as well as water resource depletion. Cyanidation shows lowest indicator values in all categories, however by optimization of the chloride processes and improved recovery the indicator values can be brought to same level. The simulation based life cycle assessment was found to be a suitable methodology for evaluation of critical points in development stage processes and estimation of their early stage environmental indicator values. This work does not only contribute to research of cyanide-free processing of gold, but also critically evaluates the existing data and provides more accurate inventory data for other life cycle assessment researchers. Finally, the methodology utilized can provide the supportive information necessary to introduce more sustainable processing methods, not only for gold industry but to any metallurgical processing.
|Translated title of the contribution||Hydrometallurgisten syanidivapaiden kultaprosessien arvioiminen simulaatioon perustuvalla elinkaarianalyysillä|
|Publication status||Published - 2020|
|MoE publication type||G5 Doctoral dissertation (article)|
- cyanide-free gold leaching
- process simulation