Metals Removal and Recovery from Municipal Sludge

Primary, digested primary, waste activated, and digested waste activated sludges were treated with sulfuric acid or ethylenedinitrilo-tetraacetic acid to effect metal solubilization for metal removal. On the average, one-half metric ton of acid per dry metric ton sludge solids (24 hr) was required to solubilize Cu (5%), Pb (32%), and Cd (66%), these being the most difficult metals to release from the sludge solids. Ethylenedinitrilo-tetraacetic acid showed higher removals than acid for Cu, Pb, and Cd, but an average of one metric ton ethylenedinitrilo-tetraacetic acid per metric ton dry sludge solids was required. Treatment of pregnant metal liquors with lime was effective in precipitating > 93% of the metals of interest; however, the quantities of metals recovered were inconsequential from an economic standpoint.