TIME EFFECT ON CHEMICAL FRACTIONS OF CADMIUM AND LEAD WITH EDTA EXTRACTION IN A CONTAMINATED SOIL

extraction, soil remediation Chemical extraction is an essential process for the abatement of heavy metal contaminated soils to minimize environmental and health risks. In this work, the chemical distribution of Cd and Pb with a sequential extraction procedure in a contaminated soil was determined before and after treating the soil by an ethylenediaminetetraacetatic acid (EDTA) solution for 0.5-24 h. The largest amount of Cd in the original soil was acid extractable fraction (16 mg kg-1) and the lowest was residual fraction (0.66 mg kg-1); lead was present mainly in the reducible fraction (619 mg kg-1), with much lower amount in the acid extractable fraction (24 mg kg-1). After the EDTA extractions with different time, more than 80 % of total Cd and Pb could be removed from the contaminated soil. The efficiencies in removing Cd from the soil by EDTA significantly (p < 0.05) increased with the extraction time with the highest amounts of removed Cd from acid extractable form. However, the largest amounts of Pb recovered by the EDTA treatment were in the reducible fractions whereas the removed Pb increased with extracting time. Considering the overall metal removal, the best extraction time of EDTA was around 6 h. The solution pH was not affected by mixing time, remaining constant at the values of 7.0-7.3 which was close to the native soil pH value. It is obvious that pH, although being very important for promoting metal solubilization, does not influence the degree of metal extraction with time, since it remains almost constant for the entire period of mixing