The efficiency of five different single leaching reagents (tartaric acid (TA), citric acid (CA), CaCl2, FeCl3, EDTA) and two different composite leaching reagents (CA + FeCl3, CA + EDTA) on removing Cu, Pb, Zn, and Cd from contaminated paddy soil in Hunan Province (in China) was studied. The results indicated that the efficiencies of CA, FeCl3, and EDTA on extracting Cu, Pb, Cd, and Zn from soil were greater than that of TA and CaCl2, and their extraction efficiencies were EDTA ≥ FeCl3 > CA. The efficiencies of CA + FeCl3 on extracting Cu, Pb, Cd, and Zn were higher than that of single CA or FeCl3. The 25 mmol L-1 CA + 20 mmol L-1 FeCl3 was a promising composite leaching reagent for paddy soil, and it could remove Cu (57.6 %), Pb (59.3 %), Cd (84.8 %), and Zn (28.0 %), respectively. With the same amount of leaching reagent, the efficiency of continuous leaching by several times was higher than that by once. In addition, the easily reducible and oxidizable fractions of heavy metals showed significant decrease during the process of leaching.
Keywords: Chemical speciation; Composite leaching; Heavy metal; Paddy soil; Remediation.