Removal of Lead from Calcareous Contaminated Soils by Organic Acids

The comparative performance of two organic acids (EDTA, citric acid) for the removal of Pb from two texturally different soils (loamy sand, sandy clay loam soil) was evaluated. The extraction of Pb increased with increasing organic acid concentration and removal from sandy clay soil was lower than from loamy sand soil. Maximum Pb removal (330.6 mg kg-1) was achieved in loamy sand soil where highest concentration (32 mmol kg-1) of EDTA was applied. However, in sandy clay loam soil, same rate of EDTA application had 1.4 times less Pb extraction (240.0 mg kg-1) than that of loamy sand soil. In the case of citric acid relatively poor performance was observed at all the rates of application except at 32 mmol kg-1. Calcium extraction efficiency for each soil was different and it was a function of the concentration of organic acids. At lower rates, comparing EDTA performance in different soils, lower application rates (0-16 mmol kg-1) resulted in higher extraction of Ca in loamy sand soil as compared to sandy clay loam soil. However at the highest rate (32 mmol kg-1), EDTA application resulted in more Ca extraction in sandy clay loam soil. In the case of CA treatments, both the soil responded differently and Ca extraction from soils varied with the concentration of organic acid i.e., increasing CA concentration from 2 to 32 mmol kg-1 resulted in increased removal of Ca from both the soils. Increasing concentration of CA from 2 to 32 mmol kg-1 increased Ca extraction from 206.6 to 731.0 mg kg-1 in loamy sand soils where as for sandy clay loam soil Ca extraction was increased from 92.6 to 747.0 mg kg-1.