The GM‐IX process: A pilot study for recovering zinc cyanides

Abstract

The GM‐IX process is a novel process that combines ion exchange (IX) and gas‐permeable membrane (GM) technologies for the separation and recovery of metals and cyanides from electroplating rinsewaters. A pilot plant capable of treating 3.5–7.5 L/min of rinsewater was installed on a commercial zinc cyanide plating line and operated through three complete service and regeneration cycles. The study demonstrated that a strongly basic anion‐exchange resin reduced free and complexed cyanides to acceptable levels in spite of wide variations in influent concentrations. No early breakthrough of free cyanide was observed, and the ion exchanger removed > 98% of the total influent cyanide as well as > 87% of the zinc. As the resin was regenerated with acid, HCN was continuously stripped from the acid re‐generant by a caustic solution that was circulated through a commercial gas‐permeable membrane contactor. The resulting regenerant solution was essentially cyanide‐free and zinc sulfate‐rich, while the caustic solution was rich in sodium cyanide. The annualized costs for the GM‐IX process are 8% less than published values for the cost of alkaline chlorination, and the chemical costs are 17% less.