Effects of halide stripping with ferric ions and hydrogen peroxide oxidants for 18K gold alloys

A stripping solution with ferric ions and hydrogen peroxide oxidants, and sodium chloride complex agent is suggested for use with 18 K yellow and red gold alloys. After stripping for 5 min, stripping properties such as passivation layer elimination, weight loss, microstructure, Lab colour index, and elemental content change were analysed. The stripping process led to the usual passivation layer of metal sulphides being eliminated. Weight loss occurred in the alloy during the initial 1 min of stripping, and after this the weight loss slowed down. Stripping rate was similar to the traditional cyanide process. Microstructure examination showed the passivation layer’s uneven surface was removed and the alloy’s lustre was enhanced after 3 min stripping. However, the lustre was decreased after 5 min stripping due to excessive surface etching. For red colour, the colour became yellowish as stripping time increased by formation of a 0.6 μm-thick Au-rich zone. The results suggest that the proposed halide stripping could replace the conventional cyanide process.