An environmentally friendly strategy for reducing the environmental risks of heavy metals adsorbed by kaolinite

Plenty of heavy metals (HMs) that are adsorbed on clay minerals (such as kaolinite), in addition to low molecular-weight organic acids (such as oxalic acid (OA)) with high activities, are widespread in the natural environment. In the present study, the effects of OA on the environmental behaviors of Pb²⁺/Cd²⁺ adsorbed by kaolinite have been investigated. The effectiveness and mechanisms of calcium silicate (CS) and magnesium silicate (MS) in reducing the environmental risks of the HMs have also been studied. The results showed that the releases of Pb²⁺/Cd²⁺ increased with an increasing concentration of OA. When different dosages of CS/MS were added to the aging system, a redistribution of HMs took place and the free form of Pb²⁺/Cd²⁺ decreased to very low levels. Also, the unextractable Pb²⁺/Cd²⁺ increased to high levels. Furthermore, a series of characterizations showed that the released HMs were re-captured by the CS/MS. In addition, the CS immobilized the OA in the solution during the aging process, which also facilitated an immobilization of the carbon element in the environment. In general, the present study has contributed to a further understanding of the transport behaviors of the HMs in natural environments, and of the interactions between CS (or MS), the environmental media, and the heavy metal contaminants. In addition, this study has also provided an eco-friendly strategy for an effective remediation of heavy metal pollution.