Stable and efficient immobilization of lead and cadmium in contaminated soil by mercapto iron functionalized nanosilica

Abstract

Mercapto as an effective functional group for immobilizing heavy metal ions is usually grafted into various materials. However, mercapto is easily oxidized, which limits its practical application to a great extent. Therefore, mercapto iron complex functionalized nanosilica (RNS-SF) was prepared to improve the stability of amendments and the immobilization efficiencies in Pb/Cd-contaminated soil. RNS-SF was characterized with SEM, TEM, FTIR. The long-term stability and immobilization governing factors of RNS-SF were investigated. The results showed that the immobilization efficiencies of Pb and Cd in contaminated soil via RNS-SF were 98.7% and 97.9% with the dosage of 3% (w/w), respectively. Moreover, its immobilization efficiencies remains unchanged from −20 °C to 50 °C. And after 360 days storage at room temperature, the immobilization efficiencies of Pb and Cd were all about 90%. RNS-SF had the best passivation effect on Pb and Cd when the soil moisture maintained at 60% after 6 days aging. Sequential extraction experiments demonstrated that the fractions of EXC species and Carb species of Pb and Cd in the contaminated soil before and after RNS-SF immobilization declined from 22.62% and 43.12% to 0.321% and 0.94%, resulting in substantially reduced environmental risk of Pb and Cd.