Experiments and mechanisms for leaching remediation of lead-contaminated soil by enhancing permeability

In this study, two types of soil columns were constructed to investigate the effect of the Enhanced permeability layers (EPL) on permeability and efficiency. A series of pre-tests of experimental conditons also were performaned to obtain the optimal Pb removal conditions, preventing the influence of the conditions on permeability. The results showed that disodium Ethylenediaminetetraacetic acid (EDTA) had optimal removal ability, followed by Oxalic acid (OA), citric acid, Diethylenetriaminepentaacetic acid (DTPA), and acetic acid (HAc). After the 45 days of column leaching (experimental conditions: 0.20 mol/L of EDTA, pH = 4 +/- 0.02, at environmental temperature), the respective removal ratios of column 2#, 15(cm) and 35(cm) were 80.60% and 88.40%, while those of column 1#, 15(cm) and 35(cm) were 69.46% and 74.67%. BET analyzed that the surface area of column 1# soil was 7.07 m2/g, smaller than the 12.87 m2/g in column 2#, verifying a change in soil pores and specific surface area. SEM and EDS analysis of soil particles showed that the leaching altered the sub-micron structures of soil, and the particle size distribution showed that the particles became smaller after leaching. The permeability coefficient (K) fit analysis result showed that the K of column 2# soil was about 9.78 x 10-3 mm/min, twice that in column 1#, which was 4.27 x 10-3 mm/min. These results demonstrated that the EPL increases permeability of soil heap stackand the leaching mass transfer.