Removal of Complex Copper-Ammonia Ions from Aqueous Wastes with Fly Ash

Compounds of strong copper-ammonia complexes exist in boiler-tube chemical cleaning wastes at many power plants. The conventional wastewater treatment methods were found either unreliable of uneconomical to treat the copper-ammonia wastes to meet effluent limitations of 1 mg/l Cu. An economic process to treat the complex wastes in alkaline ash ponds was evaluated, based on theoretical descriptions and bench-scale testing. The strength of chelated copper-ammonia bonds can be reduced by dilution with ash sluice water to allow about 94 to 99 percent (excluding the dilution factor) copper precipitation at pH above 8.5 In addition, adsorption of copper on fly ash occurs, and the adsorption capacity averaged 4.7 μg Cu per gram of fly ash. The process design criteria are the dilution ratio, pH value, ash concentration during sluicing, and ash pond retention time.