Efficiency of EDTA-Na2 and Oxalic Acid Mixture in Removing Lead from Calcareous and Gypsum Soils

The soil washing method is an effective approach for treating polluted soils with high heavy metals concentrations.Oxalic acid and EDTA are both chelating agents that can form stable complexes with heavy metals and increase their solubility and mobility in the soil solution.By mixing oxalic acid and EDTA, the synergistic effect of the two agents can be achieved.In a recent study, two types of soils, calcareous and gypsum, were selected from agricultural lands (depth 0-30 cm).The washing solution comprising an equal ratio (1:1) of EDTA-Na2 (0.05 M) and oxalic acid (0.05 M) was used to remove lead (Pb) from the soil samples.Five factors were selected to evaluate their impact on lead removal efficiency, which include pH (2 -4 -6 -8), washing time (15 min -30 min -60 min -90 min), lead concentrations (0 mg.L --300 mg.L --400 mg.L --500 mg.L --600 mg.L -), temperature (20℃ -40℃ -60℃ -80℃), and liquid/solid ratio (L/S) (5/1 ml/g -10/1 ml/g -15/1 ml/g -30/1 ml/g).The results indicated that the pH level significantly influenced the removal of Pb, with higher removal at lower pH levels.Additionally, the removal percentage increased with higher temperature, Pb concentrations, washing time, and L/S ratio.The results of this study can be summarized, that is Pb removal efficiency of 60.19% at pH 2, 94.24% at 30 min of washing time, 78.25% at 0 mg.L -of Pb concentrations, 66.47% at 20℃, and 84.77% at 15/1 ml/g of liquid/solid ratio (L/S).However, the presence of used engine oil (UEO) reduced the removal of Pb.There is no clear difference in the efficiency of removing lead from both types of soil (gypsum and calcareous).