Removing Hexavalent Chromium by Nano Zero-Valent Iron Loaded on Attapulgite

In the present study, attapulgite (ATP)-maintained nanoscale zero-valent iron (nZVI) at different Fe/ATP mass ratios (1:3 and 1:5) was synthesized by liquid phase reduction for its use to remove chromium Cr(VI) in aqueous solution. The morphology, crystalline structure, chemical composition, and valent states of these nZVI/ATP composites were evaluated before and after the reaction. Obtained characterization data indicated an effective dispersion of nZVI on ATP surface, preventing the agglomeration of nZVI particles. Results showed that the introduction of ATP has higher Cr(VI) removal efficacy as compared to the bare nZVI or ATP. At Cr(VI) initial level of 40 mg L⁻¹, the remediation efficacy of Cr(VI) in nZVI/ATP(1:3) reached 91.63%, which was substantially higher than that of bare nZVI (48.68%) and ATP (2.52%). Co-precipitation and reduction of Cr-containing metal deposited onto nZVI/ATP were found as the major reaction mechanisms. At lower initial level of Cr(VI) (20 mg L⁻¹), the reduction was the dominant process where Fe(II) was the major form of iron in the reaction product. However, adsorption was the major mechanism at higher initial level of Cr(VI) (100 mg L⁻¹) whereas the reaction product mainly comprised the ferric form of iron (Fe(III). The main reaction product was the FeCr₂O₄ under low or high Cr(VI) concentrations which can reduce the risk of secondary pollution because of its high stability.