Polishing in jewellery manufacturing produced polishing dust containing gold particle that need to be recovered. Two methods are available, hydrometallurgical method (aqua regia) and pyrometallurgical method (direct melting). The two methods are compared from recovery, process time, economic, and safety aspects. Recovery of direct melting show higher result of 99.97 compared to 97.08% recovery of aqua regia from fire assay sample. Direct melting is shorter in process time compared to aqua regia due to simpler steps involved, thus reducing production time, minimizing labour requirement, and human error. Inert slag waste produced by direct melting also safer and cheaper for handling compared to acidic waste produced by aqua regia. From safety aspect, direct melting with appropriate Air Pollution Control System (APCS) has manageable thermal risk compared to toxic gas and corrosive risk of aqua regia. From these aspects, jewellery industry can be recommended to transition to direct melting compared to aqua regia method for gold recovery from polishing dust.
Chiong et al. (Mon,) studied this question.