Pilot-scale washing of Pb, Zn and Cd contaminated soil using EDTA and process water recycling

Abstract

Pb, Zn and Cd contaminated garden soil (5249, 3348 and 20.6mgkg−1, respectively) rich with fines and organic matter was washed with a solution of 120mmol EDTA kg−1 of soil in a pilot-scale remediation plant operating in a batch (60kg of soil) mode. After soil washing, the solid phase and used washing solution were separated in a chamber filter press. A base/acid pair Ca(OH)2/H2SO4 was used to impose a pH gradient for EDTA recycling from used washing solution and, coupled with an electrochemical advanced oxidation process using a graphite anode, for cleansing and recycling the process water, which was used for rinsing the soil solid phase in the press. On average (5 batches), 75%, 26% and 66% of Pb, Zn and Cd, respectively, was removed from the soil, 71% of EDTA was recycled and no waste water was generated. The variable costs of the novel remediation process (materials, energy but not labour) amounted to 66€t−1 of remediated soil. The results of the pilot-scale testing indicate that scaling-up the process to a commercial level is technically and economically feasible.