Stability of bentonite colloid carried with kaolin-supported nanoscale zero-valent iron together as composite remediation materials and its adsorption property onto multi-heavy metals

In order to improve the defects of fast sedimentation rate and poor mobility of kaolin-supported nano-zero-valent iron (K-nZVI), bentonite colloid with strong suspension and adsorption was selected as the carrier in this study, and the stability and adsorption of bentonite colloid carried with K-nZVI (B-K-nZVI) were studied. The sedimentation tests as well as viscosity tests were prepared to determine the best solid mass ratio of the stable suspension fluid. The adsorption tests combined with adsorption kinetics and isotherm models were conducted to reveal the adsorption and reduction properties of B-K-nZVI to remove chromium, zinc and lead ions. The results showed that B-K-nZVI greatly presented superior stability and determined 5% of bentonite and 0.2% of K-nZVI as the best solid mass ratio. The removal rate of Pb and Zn exceeded 90% within 30minutes; meanwhile, the removal efficiency was Pb(II) > Zn(II) > Cr(total), indicating that the effect of B-K-nZVI on cations was significantly better than that on anions. In addition, the adsorption capacity of Pb(II), Zn(II) and Cr(total) by B-K-nZVI were 19.11mg·g-1, 17.33mg·g-1 and 1.03mg·g-1 after 30minutes of reaction, respectively. Compared to K-nZVI, the new composite remediation material has achieved significant improvements in stability and adsorption performance. This study has great significance for demonstrating B-K-nZVI as potential remediation materials to reduce the levels of some heavy metals in groundwater and providing reliable theoretical basis for remediation material design.