Treatment of metal-loaded soil leachates by electrocoagulation

Abstract

This study evaluates the effectiveness of electrocoagulation process for treating acidic soil leachates (SL) having different metal and chloride contents. Electrocoagulation process was evaluated via an electrolytic cell using mild steel electrodes operated at current intensity of 3.0 A through 90 min of treatment. In the presence of relatively low concentration of Pb (30–120 mg/l) and Zn (18–40 mg/l), the effectiveness of electrocoagulation was quite similar while treating SL with low (SL 1) and high (SL 2) Cl − concentrations. For SL enriched with toxic metals (Cd, Cr, Cu, Ni, Pb and Zn), concentration of the selected metal being initially adjusted to 100 mg/l, with the exception of Cd and Ni, the residual metal concentrations at the end were below the acceptable level recommended for effluent discharge in the sewage urban works (more than 99% of each metal was removed) either while treating SL having a low or high Cl − concentrations. Electrocoagulation treatment was more effective in removing Cd from SL 1 than from SL 2, whereas Ni was more easily removed from SL 2 than from SL 1. On the other hand, electrocoagulation was also found to be very efficient in removing Pb from very contaminated solutions (200–1950 mg Pb/l). At least 94% of Pb was removed regardless of the initial Pb concentration in these leachates. However, with the overall reaction being first-order, the rate coefficient ( k) indicated that Pb was more easily removed from SL 1 leachate (0.104–0.091 min −1) than from SL 2 leachate (0.02–0.073 min −1).