Effect of SiO2 Nanoparticles and Cement on the Performance of Stabilized Ni-Contaminated Clayey Soils

This study investigates the capability of cement-SiO2 nanoparticles (CNS) mixture to the promotion of stabilization/solidification (S/S) process of heavy metal (HM) contaminated soils. For this purpose, artificially contaminated soil samples were first prepared by mixing kaolinite with nickel (Ni) and then a set of tests were performed to assess the effectiveness of the CNS treatment. The results indicate that the addition of cement markedly increases the HM retention of soil; however, the TCLP tests show that leaching of cement treated samples leads to return a part of pollutants to soil pore fluid. The cement and Ni interaction has a destructive impact on particles solidification which adversely affects the strength development and compressibility of the cement-stabilized specimens. At same condition, the CNS blend is more efficient in immobilizing Ni and modifying the soil engineering properties as compared to sole cement. Based on the physicochemical, XRD and SEM tests, the better performance of CNS agent is mainly associated with the more and faster growth of cement compounds, reducing the adverse effect of heavy metal precipitation on the hydration reactions and increasing the particle density. The study concluded that with the consideration of EPA criteria, an optimum cement content of 0.5 wt% per one cmol/kg.soil of HM within 28 days of curing can successfully remediate the Ni contaminated soils. The incorporation of SiO2 nanoparticles into the binder system improves the microstructure and geomechanical performance of stabilized materials and causes a significant reduction in the cement consumption (up to 35%) and time of curing (up to 3 times)