Impermeability Effect of Heavy Metal Cr⁶⁺ in Bauxite Leachates by Polymer-modified Bentonite Composite Geosynthetic Clay liners

Abstract Bauxite leachate, a byproduct of the alumina extraction process, is characterized by its high alkalinity (pH > 12) and elevated concentrations of heavy metal ions, such as Cr 6+ . It poses a serious threat to the surrounding environment and human health once leaked. In this study, polymer-modified bentonite geosynthetic clay liner (BPC GCL) was used as the impermeability material of bauxite leachate. The results showed that the combination of bentonite and polymer hydrogel could significantly reduce the permeability coefficient of bentonite. Additionally, the transport model of Cr 6+ in BPC GCL found that the color of the transport map of Cr 6+ at each interface of BPC GCL changed from dark to light within 10 years, indicating that the concentration of Cr 6+ showed a attenuation trend and played a impermeability role. Further comparison of different polymer contents of BPC GCL shows that the concentration of Cr 6+ at the same interface of BPC GCL CP6.5, CP7.5 and CP10.8 exhibits a decrease from high to low, indicating that the concentration of Cr 6+ gradually decreases with the increase of polymer and the impermeability is progressively increased.