Removal of Iron Cyanide from Gold Mill Effluents by Ion Exchange

Using a strongly basic anion exchanger (Rohm & Haas Amberlite IRA-958) laboratory ion exchange tests were conducted on the removal of iron cyanide from synthetic and actual gold mill effluents. Variables examined included the effects of pH, concentration and hydraulic loading of the feed on the resin exchange capacity and resin column utilization. The results showed ion exchange to be an effective method of removing iron cyanide to concentrations of less than 3 mg/L. Tests with synthetic gold mill effluents gave resin exchange capacities ranging from 13 to 34 mg CNFe/mL resin depending on the concentration of iron, copper and zinc cyanides in these solutions. When raw barren bleed was tested, an exchange capacity for the ferro/ferricyanides was determined to be ~6 to 8 mg CNFe/mL resin. For chlorinated barren bleed, a resin exchange capacity of 14 mg CNFe/mL resin was observed. A capacity of 19 mg CNFe/mL resin was achieved for tailings pond decant. Regeneration with 15% NaCl provided mixed results with recoveries ranging from 40 to 100% of the iron cyanide exchanged by the resin. Upon multiple exchange-regeneration cycles, the resin lost 25% of the exchange capacity for total cyanide during the first cycle. Subsequently, the loss in exchange capacity was approximately 1% per cycle. Pilot scale tests were considered essential prior to full scale system design.