Abstract:To study the removal effects of different eluents on heavy metals contaminated soil with different leaching conditions, a batch experiment was conducted to compare the effects of four eluents (citric acid (CA), tartaric acid (TA), ethylene diaminetetra acetic acid disodium salt (EDTA), and triacetintrisodium salt (NTA)) on removing heavy metals (Pb, Cd, Cu and Zn) from a paddy soil at different concentrations, leaching time, pH values and solid-liquid ratios. Changes in fractions of heavy metals in soil before and after leaching with eluents were analyzed at single factor optimal leaching conditions. The results showed that the optimum leaching concentrations were 0.3 mol/L CA and TA, and were 0.05 mol/L for EDTA and NTA; the optimal leaching time was 480 min for CA and NTA, and was 720 min for EDTA and TA; the optimum leaching pH value was 3 for all 4 eluents; and the optimum solid-liquid ratio was 1:20 for all 4 eluents. At the single factor optimal leaching conditions, EDTA had the best effects removing heavy metals from paddy soil, and the removal rates were 67.4%, 61.0%, 13.8% and 76.0% for Pb, Cd, Zn and Cu, respectively, followed by NTA, and the removal rates were 41.6%, 42.4%, 9.9% and 54.3%, respectively. The removal rates of heavy metals increased with the decreasing eluention pH values, with the increasing solid-liquid ratios, and with the increasing CA and TA concentrations. The desorption kinetics curves of the eluents removing heavy metals from paddy accorded with the pseudo second-order kinetic model. The desorption process was mainly a chemical desorption, and the desorption rates were controlled by heavy metal contents in soil and eluent concentrations. The desorption rates of heavy metals from soil followed the sequence of Cd>Pb≈Zn≈Cu. EDTA and NTA leaching significantly reduced the contents of iron/manganese oxidation and organic binding fractions of Pb, Cd, Zn and Cu, and CA and TA leaching significantly decreased the contents of iron/manganese oxidation fraction of these four heavy metals. The efficiency of the eluents removing heavy metals was EDTA > NTA > CA > TA.