Soil samples contaminated with heavy metals such as lead (Pb), copper (Cu) and zinc (Zn) were leached with citric acid solution. A five step-sequential extraction method involving “exchangeable”, “bound to carbonate”, “bound to Fe–Mn oxide”, “bound to organic matter” and “residue” fractions was also carried out to investigate the leaching behavior of Pb, Cu and Zn with citric acid.
The leaching efficiencies of Pb, Cu and Zn increased with increasing citric acid concentration. About 86.5, 88.9 and 83.3% leaching efficiencies were obtained for Cu, Zn and Pb, respectively, under the following leaching condition: 2 kmol·m−3 in citric acid concentration, 120 min in leaching time, 10% in pulp density, 50°C in temperature, and 80 rpm in shaking speed. In the sequential extraction test, the heavy metal contaminants were extracted more in “bound to carbonate” and “bound to Fe–Mn oxide” fractions than in “bound to organic matter” and “residue” fractions. When the leaching efficiencies of Pb, Cu and Zn with 2 kmol·m−3 citric acid solution were compared with the results of the sequential extraction, a good agreement with the summation of amount leached in “exchangeable”, “bound to carbonate” and “bound to Fe–Mn oxide” fractions was noted.