Optimization of parameters for the extraction of Pb from lateritic soil using EDTA

In this study, we optimized the factors influencing the remediation of Pb-contaminated laterite soil by Ethylenediamenetetraacetic acid (EDTA) washing technology. Soil was artificially contaminated with Pb and laboratory extractions were carried out by varying (1) pH of EDTA, (2) EDTA-Pb molar ratio, (3) Solution-soil ratio and (4) the number of steps in the sequential extraction process. The batch extraction experiments were designed using central composite design (CCD)-based response surface methodology by varying these four factors at five different levels. The range adopted for these factors were; pH (4-8), EDTA-Pb molar ratio (0-4), Solution-soil ratio (3-21) and number of steps of extraction (1-5). The significance and adequacy of the model given by CCD were tested using analysis of variance (ANOVA). Numerical optimization results showed that the maximum extraction efficiency of 90.82% is obtained at a desirability of 0.97 when pH of EDTA was 4, EDTA-Pb molar ratio was 3, solution-soil ratio was 16.5 and the number of steps was 4. Laboratory extraction carried out adopting the numerically optimized factors gave an extraction efficiency of 89.6%. The optimized parameters can be adopted when ex situ remediation of Pb-contaminated laterite soil is carried out using EDTA washing technique.