the chemical fractionation of zn, pb and cd in contaminated soils before and after batch extraction by edta

soil washing by mobilizing is one of in-situ techniques for soil decontamination. applying this technique to the contaminated soils could be followed by many environmental problems. therefore, it is important to study the effective factors on removal of heavy metals from different forms. in the present research, the forms of zn, pb, and cd in three contaminated soils from the zinc-lead smelting plant area in zanjan before and after batch extractions by 0.1 mole of edta per one kilogram of soil were determined using two methods of sposito et al. and tessier et al. the results indicated the higher effectiveness of hot nitric acid in extraction of cd and in turn the higher effectiveness of aqua regia in extraction of zn and pb. the sposito’s method introduced carbonate and residual forms as dominant form for all three metals in all three soils. these forms, particularly carbonate form, showed major removal after washing. the sum of different forms of a given heavy metal obtained from sposito’s method was greater than that of modified tessier’s method. unlike the sposito’s method, in which the dominant removal of pb by edta was from the carbonate form, this removal was from the oxide form in the modified tessier’s method. the highest and lowest removal efficiencies were observed for cd (using sposito’s method) and pb (using tessier’s method), respectively. the mobility factor of zn after batch extraction by edta intensely decreased. additionally, the mobility factor of pb after extraction significantly increased.