| Heavy metal contaminated soils are a common problem encountered at many hazardous waste sites. Chelating extraction has been proposed as a remediation method for heavy metal contaminated soils. This research develops an approach involving chemical equilibrium modelling for the evaluation of 190 selected chelators as complexation and mobilization agents toward six target metals cadmium, copper, lead, mercury, nickel, and zinc, respectively and, in addition, assesses the recovery potential for each chelator from complexes formed with these metals.; Three promising chelators S-carboxymethylcysteine (SCMC), N-(2-acetamido)iminodiacetic acid (ADA), and pyridine-2,6-dicarboxylic acid (PDA) were selected to test the hypothesis that heavy metals can be selectively removed from soil by chelating extraction and, further, can be separated from their respective ligand-metal complexes by moderate increase of the solution pH. Batch equilibration experiments conducted over 12- or 24-hour periods were performed to assess the respective extraction and recovery capabilities of SCMC, ADA, and PDA toward copper, zinc, and cadmium in spiked soils. All three chelators showed good extraction and reuse potential toward their respective target metals; additionally, all of the target metals were recovered as precipitates following pH elevation of the complex solution.; Finally, SCMC and ADA were tested with an authentic polluted soil containing lead and copper. The two chelators effectively extracted both lead and copper under a wide variety of operating conditions, with ADA being particularly effective at lead removal. Following extraction, each chelator was successfully recovered and reused throughout several consecutive runs with no loss in performance. |
