Stabilization of nanoscale zero-valent iron with mordenite for remediation of hexavalent chromium from groundwater in dynamic columns

In this study, mordenite-supported nanoscale zero-valent iron (nZVI@MOR) composites were prepared for the in-situ remediation of Cr(VI) from groundwater. Batch experiments and dynamic column tests were conducted to investigate the adsorption mechanism and long-term removal performance. The batch results revealed that the optimum pH for Cr(VI) adsorption was ∼3 with a capacity of 101.52 mg/g, following an endothermic adsorption process. The dynamic column test results showed that higher seepage velocities resulted in rapid remediation failure, but an increase in adsorption capacity which increased from 9.61 to 15.53 mg/g with the increase of seepage velocity from 3.9 to 15.6 mL/h at Cr(VI) initial concentration of 20 mg/L, which due to the establishment of dominant seepage channels at elevated velocities, facilitating flow circumvention of the nZVI@MOR composites. The experimental breakthrough curve was best fitted by the Thomas model, with the agreement of fit positively correlated with effective remediation time. The mechanism underlying Cr(VI) removal involves the electrostatic attraction of Cr(VI) to the surface of nZVI@MOR, subsequent reduction to Cr(III) by nZVI as an electron donor to form a complex precipitation for remediation. This result suggests that nZVI@MOR can effectively achieve long-term remediation of Cr(VI)-contaminated groundwater by appropriately controlling the flow rate and material filling methods.