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

Abstract

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.