Speciation analysis and speciation transformation of heavy metal ions in passivation process with thiol-functionalized nano-silica

Different speciation of heavy metal ions has different toxicity level. The different speciation contents can be used as an important basis to evaluate the passivation efficiency of passivator. In this study, Ni2+, Cu2+ and Zn2+ in soil was passivated with thiol-functionalized nano-silica by solidification/stabilization technology, and the behavior of heavy metal ions in soil were explored. The result shows that, passivation time, soil moisture and passivator dosage can influence the toxicity of heavy metal ions via changing the speciation of metal ions. Passivation time and passivator dosage will promote passivation efficiency, while too low or too high soil moisture are not conducive to the passivation. The change of soil moisture will affect the surface charge distribution of soil and passivator, thus influence the migration of metal ions. According to speciation analysis, four kinds of speciation could be transferred reciprocally and the transformation will cause impact on the toxicity of heavy metal ions in soil. We explained the behavior of different metal ions based on the percentage of various speciation of heavy metal ions and inferred the transformation process of such metal ions in the passivation process. At the same time, based on Webber-Morris equation, the kinetic process during passivation process was discussed.