Efficacy and risk assessment of methyl glycinatediacetic acid combined hydroxylamine hydrochloride for washing heavy metal contaminated soil

Heavy metal contaminated soils have attracted worldwide attention, and there is a growing interest in the use of detergents to remediate heavy metal contaminated soils. In this study, the response surface methodology was used to determine the optimal drenching parameters by combining the interaction between the factors and the pollution safety index. The elution of heavy metals by the two-step elution method and the mixed elution method was investigated under optimal conditions (77.66 mmol.L^-1 MGDA, 145.01 mmol.L^-1 HH, pH 3.29, 90 min, S/L = 1:10, 25 °C). The results showed that the mixed solution was more effective in the elution of heavy metals, and the removal of lead, copper and nickel was 8.11%, 16.27% and 1.36%, respectively. The different forms of heavy metals were extracted by the modified Tessier method after water washing, and the results showed that the iron-manganese oxide-bound and carbonate-bound fractions of Pb, Cu and Ni were significantly reduced after water washing. Among them, the carbonate-bound state of Pb, Cu and Ni decreased by 90.30, 256.85 and 4.00 mg.kg^-1, respectively; the ferromanganese-oxidised state of Pb, Cu and Ni decreased by 531.00, 1493.33 and 48.74 mg.kg^-1, respectively; before and after drenching MCSI decreased by 10.85% compared with that before drenching. FTIR analysis of heavy metals after water washing showed that the mixture had no significant effect on soil properties after water washing. The above results indicated that the mixture of HH and MGDA can be used as a washing solution for heavy metal contaminated soil.