Metal decontamination of soil, sediment, and sewage sludge by means of transition metal chelant [S,S]-EDDS

The biodegradable strong transition metal chelant [S,S] stereoisomer of eth ylenediamine disuccinate was investigated for its applicability for the was hing extraction of heavy metals from soil, sewage sludge, and harbor sedime nt. Heavy metals Pb, Zn, Cu, and Cd were extracted from authentically pollu ted samples by means of an ex situ washing procedure at the laboratory scal e. The exposure time necessary to achieve maximum metal extraction from the authentically polluted solids used in this study was longer than that repo rted elsewhere with solids polluted artificially in the laboratory. Require d exposure time was I day for the extraction of Pb, 3 days for Zn, and 6 da ys for Cu, irrespective of solid type. Speed and extent of metal extraction were increased by facilitating mass transfer from the solids to the liquid (e.g., by lowering calcium concentration, increasing temperature, adding f atty acid soap, and most of all, by using intermittent but intense agitatio n). Slightly alkaline pH was necessary to eliminate the interference by iro n. This pH effect as well as observed metal selectivity was explained with a speciation model. It was feasible to achieve 70-90% extraction of Zn, Pb, and Cu from all three solids tested, These extraction efficiencies were eq ual or superior to those obtained with the benchmark chelants, ethylenediam ine tetraacetic acid and nitrilotriacetate, provided extraction time was su fficient.