Remediation of chromium and mercury polluted calcareous soils using nanoparticles: Sorption -desorption kinetics, speciation and fractionation.

Stabilization is an emerging technology for the cost-effective remediation of heavy metals polluted soils. To evaluate the potential of water treatment residual nanoparticles (nWTR) in reducing Hg and Cr mobility in contaminated calcareous soil, sorption-desorption kinetics; speciation and fractionation experiments were performed. Application of nWTR strongly enhanced Cr and Hg sorbed in the calcareous soil, whereas the released amount of both metals through 6 successive desorption steps dramatically decreased. The power function model best described the desorption kinetic data of Cr and Hg from nWTR amended and non-amended calcareous soil. Fractionation experiment data demonstrated that nWTR amendment significantly increased metals concentration in the residual fraction (RS) and simultaneously decreased the more accessible forms of Hg and Cr. Addition of nWTR at a rate of 0.3% to the contaminated calcareous soil significantly increased Hg and Cr in the RS fraction from 69.27% and52.62% to 93.89% and 90.05% respectively. Additionally, the formation of stable Hg and Cr species such as Hg(OH) amor, CrSO. xHO and Cr(OH)) were increased as a result of nWTR application. These findings jointly indicate the enhancement of Hg and Cr immobilization in the nWTR amended calcareous soil. FTIR spectroscopy analysis indicated the contribution of OH group and Al-O-Si of nWTR in Hg and Cr sorption process and suggests chemo-sorption reaction between both metals and the nWTR surface functional groups. Overall, the final results confirm the strong capability of nWTR application in reducing Hg and Cr risks in highly contaminated sites of the calcareous soil.