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Membrane contactors for cyanide treatment and recovery: implementation and evaluation at gold processing facilities in Arequipa, Peru
Hammer, Vincent
Hammer, Vincent
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2024
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Abstract
Cyanide is widely used in the gold extraction industry but poses environmental and human health hazards due to its acute toxicity. The first objective of this thesis was to characterize gold processing facilities in the Arequipa region of Peru and evaluate current cyanide usage and management approaches. Through the analysis of six different gold processing facilities, volatilization of free cyanide during processing and accumulation of metals, cyanide and metal-cyanide complexes, through zero effluent discharge policies were identified as key issues. Analysis of tailings revealed higher levels of cyanide and metals than previously reported in literature, indicating cyanide retention in tailings storage facilities, even after months of inactivity. Findings from this study highlighted the need for cyanide treatment and/or recovery and reuse at these facilities.
The core component of this thesis was to develop and apply a novel membrane contactor system to evaluate the feasibility of recovering cyanide at gold extraction facilities. A lab-scale membrane contactor system was constructed that allowed evaluation of different membranes (polypropylene (PP) and polytetrafluoroethylene (PTFE)) for recovering cyanide from synthetic effluent solution and an effluent from a US-based gold processing plant. The effects of variables including distillate pH, temperature, and feed cyanide concentration on cyanide recovery efficiency were examined. The results showed that PTFE and PP membranes could be used to effectively recover cyanide, and that membrane contactors are cost competitive with current recovery methods.
Based off the lab-scale research, a pilot-scale membrane contactor was built and tested with effluents from gold processing plants in the US and Arequipa. Although treatment of US effluents was similar to results generated from lab-scale experiments, Arequipan effluents presented more challenges as mineral
precipitation affected system performance. A stepwise pH adjustment of the feed solution improved cyanide recovery for one Arequipan facility. Despite these additional challenges, economic analysis suggested that cyanide recovery via membrane contactors is more cost-effective than purchasing new cyanide. Results from this thesis underscore the potential of membrane contactors as a sustainable and scalable solution for cyanide recovery in gold processing and are expected to contribute to the further development and implementation of this technology.
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