Release of Zn, Pb and Cd from Some Contaminated Soils by EDTA Using Batch Method

Consequences of heavy metals accumulation in soils are of concern. One way of decontaminating heavy metals from soils is the use of chelating agents، particularly EDTA. In this research، three soils contaminated by Zn، Pb and Cd with total amounts (of these metals) of 10. 5، 55. 8 and 80. 6 mmol kg-1 were collected from the surface layer (0-20 cm) of the lands surrounding a zinc-lead smelting plant in Zanjan province. The release of Zn، Pb and Cd by Na2H2EDTA using a one-step batch method for 180 minutes as well as the effects of EDTA concentration، solution/soil ratio، kinetics of release of metals، changes in pH and concentration of Ca and Fe in extracts were investigated. Results showed that increasing concentration of EDTA raised Zn and Pb release much greater than that of Cd. Furthermore، the orders of the release percentages for the three metals were quite different in the three soils. During the release process، pH of the extracts exceeded 7. 2 and then fixed at about 8. 1. Meanwhile، the average concentration of Ca in extracts became more than 1000 times greater than that of Fe. On average، 96 percent of the extracted Cd was released at less than 30 minutes. This figure was 76 percent for Zn and Pb and the release time were sometimes greater than 30 minutes. Compared to other kinetic models، the kinetic data was best described by simplified Elovich، power function and parabolic diffusion equations. According to the results، release of Cd and Pb from the soils was enhanced by low (5:1) and high (50:1) solution/soil ratios، respectively.