Extraction of metals from a contaminated sandy soil using citric acid

Twenty-four-hour washing of a contaminated soil with 0.5 M citric acid reduced the levels of Cd, Cu, Zn, and Pb from 0.01, 0.04, 0.42, and 41.52 mg g-1 to 0, 0.02, 0.18 and 5.21 mg g-1, respectively. Extending the washing period beyond 24 hours did not influence the results significantly. Metal ions present in higher amounts were removed more easily. A column study was also conducted to compare metal leaching with surface and subsurface application of 0.3 M citric acid to 60 cm long soil columns packed with metal-contaminated soil. Results indicated that the uniform distribution of citric acid, applied through the subirrigation system, resulted in a more efficient extraction of metal ions. The extraction of Zn and Pb from the columns with subsurface application of citric acid was, respectively, 38 and 27 times higher than from the columns with surface application of citric acid. After washing the contaminated soil with various citric acid concentrations, the metal-rich wash solution was treated effectively using chitosan flakes.