Washing of metal contaminated soil with EDTA and process water recycling

We demonstrate here, in a laboratory scale experiment, the feasibility of using the base/acid pair Ca(OH)(2)/H2SO4 to impose a pH gradient for EDTA recycling and, coupled with an electrochemical advanced oxidation process using a graphite anode, of recycling process water as part of a novel remediation technology for multi-metal contaminated soils. In the first batch, 60 mmol EDTA kg(-1) of soil removed 72, 27, and 71% of Pb, Zn, and Cd, respectively, from soil contaminated with 5329 +/- 685, 3401 +/- 193, and 35 +/- 6 mg kg(-1) of Pb, Zn, and Cd, respectively. In the subsequent four batches, we demonstrated that up to 88% of EDTA was recycled from each batch, with the potential to extract up to 98, 94, and 109% of Pb, Zn, and Cd, respectively, that the fresh EDTA extracted. Accumulation of salts in the process water through multiple remediation batches/recycles was prevented by CaSO4 precipitation. Recycled process water toxicity testing indicated no significant effect on plant seed germination but some inhibition of root elongation. (C) 2012 Elsevier B.V. All rights reserved.