Immobilization of Ni (Ⅱ) at three levels of contaminated soil by rhamnolipids modified nano zero valent iron (RL@nZVI): Effects and mechanisms.

A kind of biosurfactant rhamnolipid modified zero-valent iron nanoparticles have been synthesized and applied to evaluate the immobilization efficiency of Ni (Ⅱ) contaminated soil at three concentration levels (200Ni, 600Ni and 1800Ni). The results of SEM and XRD were clearly indicative of the well-attached phenomenon of rhamnolipid on the nZVI, featuring better stability and dispersity, and FTIR analysis proposed the interactions between rhamnolipid and nZVI through monodentate chelating between carboxylate groups and nZVI or hydrogen bonding with Fe-O groups on the surface. Sequential extraction procedures (SEP) analysis illustrated that the majority of labile fractions had been transformed into less accessible fractions (Fe-Mn oxide-bound fractions and residual fractions) after 28 days of incubation. And for low-concentrations polluted soil, soil self-remediation played a dominant role, while RL@nZVI exhibited a more significant stabilizing effect for medium and high-concentrations pollution. Furthermore, XPS and XRD analyses of Ni-adsorbed RL@nZVI identified the formation of NiO, Ni(OH) and revealed the possible interaction mechanisms including reduction, adsorption and precipitation/co-precipitation. These results confirmed that RL@nZVI presented a promising prospect for the immobilization of Ni polluted soil.