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 redu ced 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 per iod beyond 24 hours did not influence the results significantly. Metal ions present in higher amounts were removed more easily. A column study was als o conducted to compare metal leaching with surface and subsurface applicati on of 0.3 M citric acid to 60 cm long soil columns packed with metal-contam inated soil. Results indicated that the uniform distribution of citric acid , applied through the subirrigation system, resulted in a more efficient ex traction of metal ions. The extraction of Zn and Pb from the columns with s ubsurface application of citric acid was, respectively, 38 and 27 times hig her than from the columns with surface application of citric acid. After wa shing the contaminated soil with various citric acid concentrations, the me tal-rich wash solution was treated effectively using chitosan flakes.