Removal of Cd, Pb, Zn, Cu in smelter soil by citric acid leaching.

Soil washing has been verified as a feasible technology for source reduction for contaminated soil with heavy metals. We conducted batch and column leaching experiments to investigate the removal of Cd, Pb, Cu and Zn from smelter soil by citric acid. The removal efficiency of heavy metals by batch leaching reached a maximum (89.1% Cd, 26.8% Pb, 41.7% Zn, 14.2% Cu) at a concentration of 0.1 M and a pH of 5. Citric acid also removed 91.3%, 11.1%, 39.2% and 11.1% of Cd, Pb, Zn, and Cu respectively after column leaching. Citric acid mainly removed exchangeable, carbonate bound and oxide bound Cd, Pb, Cu and Zn fractions. Vertical distributions of Cd, Cu and Zn similarly increased with increasing soil depth. Chestnut shells were applied to the recovery of citric acid from the waste eluent, which removed 84.4%, 97.5%, 74.6%, 70.3% of Cd, Pb, Zn, and Cu, respectively, due to chestnut shell chelation. Fresh and regenerated citric acid was used in batch leaching of heavy metal-contaminated soil, and they showed similar ability to extract heavy metals.