THE GM-IX PROCESS - A PILOT-STUDY FOR RECOVERING ZINC CYANIDES

The GM-IX process is a novel process that combines ion exchange (IX) a nd gas-permeable membrane (GM) technologies for the separation and rec overy 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 com plete service and regeneration cycles. The study demonstrated that a s trongly basic anion-exchange resin reduced free and complexed cyanides to acceptable levels in spite of wide variations in influent concentr ations. No early breakthrough of free cyanide was observed, and the io n exchanger removed > 98% of the total influent cyanide as well as > 8 7% of the zinc. As the resin was regenerated with acid, HCN was contin uously stripped from the acid regenerant by a caustic solution that wa s circulated through a commercial gas-permeable membrane contactor. Th e resulting regenerant solution was essentially cyanide-free and zinc sulfate-rich, while the caustic solution was rich in sodium cyanide. T he annualized costs for the GM-IX process are 8% less than published v alues for the cost of alkaline chlorination, and the chemical costs ar e 17% less.