Vacuum Distillation-Assisted Hydrometallurgical Route for Industrial Production of 99.999% Pure Gold from Au–Ag Alloys Feedstocks

In response to the growing industrial demand for ultra-high-purity gold, a vacuum distillation-assisted hydrometallurgical process is developed in this study for the industrial-scale production of 99.999% pure (5N) gold from crude Au–Ag alloy feedstocks. This integrated approach combines vacuum distillation, aqua regia dissolution, solvent extraction, and in situ reduction. An alloy containing approximately 56.47 wt% Au and 43.06 wt% Ag was first vacuum distilled, yielding a pre-enriched alloy with 94.76 wt% Au and less than 5.17 wt% Ag. The enriched Au alloy was subjected to aqua regia dissolution, solvent extraction, and Na2SO3-assisted reduction. The influence of the liquid-to-solid ratio, settling time, phase ratio, extraction time, and centrifugation speed on gold purity and recovery was systematically investigated. Under optimized conditions, the process achieved 99.999% purity and over 99.5% overall recovery, meeting the GB/T 25933-2010 standard. The use of Na2SO3 as a combined reducing and stripping agent simplified the operation, lowered reagent consumption, and improved environmental compatibility. This method provides a scalable, cost-effective, and environmentally friendly alternative to conventional refining techniques and is suitable for advanced manufacturing applications.