Pilot-Scale Assessment of a Mobile Off-Grid Membrane Contactor System for the Recovery of Cyanide from Gold Processing Wastewater

• Published in: ACS ES&T water 2024-12, Vol.4 (12), p.5811-5820
• Main Authors: Hammer, Vincent, Vuono, David C., Alejo-Zapata, Francisco D., Zea, Julia, Bolaños-Sosa, Héctor G., Zevallos-Rojas, Carlos A., Figueroa, Linda A., Bellona, Christopher, Vanneste, Johan
• Format: Article
• Language: English
• ISSN: 2690-0637; 2690-0637
• DOI: 10.1021/acsestwater.4c00797

A pilot-scale membrane contactor was constructed to determine the effectiveness of cyanide recovery from real gold processing effluents from the United States and the Arequipa region of Peru. The system was designed to operate off-grid using a mobile solar array to enable implementation independently of power-grid availability. Although a 98% recovery of free cyanide was obtained during experiments with the U.S. process effluents, effluents from the Arequipa region posed a larger challenge. Free cyanide recovery from the first Arequipan facility’s effluent (Aq1) yielded only a 45% cyanide recovery, while the effluent of the second Arequipan facility (Aq2) showed a free cyanide recovery of 81%. Precipitation of minerals was observed throughout experimentation with both effluents and likely contributed to the overall lower recovery. Maintaining a feed solution pH of >7 limited precipitations, albeit at a lower mass transfer rate. However, a subsequent pH drop in the feed solution to 5 yielded an improved cyanide recovery rate of 95% for the Aq2 effluent. Economic analysis revealed that operational and CAPEX costs for cyanide recovery in each case were lower than those for the purchase of new cyanide. However, pretreatment and staged pH adjustment may be required for the efficient recovery of cyanide by using membrane contactors.