Ammonium-Carbonate Leaching of Metal Values from Water-Treatment Sludges.

摘要

This project was undertaken to explore and develop processes based on ammoniacal leaching to recover metal values from metal-finishing wastewater treatment sludges. The objective was to eliminate or to reduce sufficiently the heavy metal content of the sludge so that it would no longer constitute a potential ecological hazard,thus greatly reducing the cost of sludge disposal. Preferred leaching conditions were defined. With two-stage leaching at 50C in concentrated ammonium carbonate,the copper-plus-nickel content can be reduced to a level of less than 1percent from an original content on the order of 10percent. By roasting the depleted sludge with soda ash,at least 80percent of the chromium can be recovered in water-soluble form. Controlled-potential electrodeposition was shown to be capable of separately winning copper and nickel values from the pregnant ammoniacal leaching liquor. A process flow sheet is presented,and process economics are reviewed. The process studied would be an alternative only if costs for disposal of sludge rose to the highest part of the current range.