Montmorillonite-supported nanoscale zero-valent iron for removal of arsenic from aqueous solution: Kinetics and mechanism

•Novel adsorbent consisting of montmorillonite-supported nZVI have been synthesized.•Mt-nZVI consists of core shell Fe(0) structure with an outer oxide/hydroxide shell.•Mt-nZVI showed higher affinity for As(III) than As(V).•As(V) was not reduced but As(III) was oxidized to As(V) on reaction with Mt-nZVI.

Montmorillonite-supported nanoscale zero-valent iron (Mt-nZVI) has been synthesized to remove inorganic arsenic (As) from aqueous solutions. BET, SEM, EDX, XRD and XPS were used to characterize the clay-supported material which consists mainly of core shell Fe(0) structure with an outer oxide/hydroxide shell. The dispersion of nZVI onto montmorillonite was found to be increased with decreasing tendency to agglomerate into larger particles. Batch experiments revealed that adsorption kinetics followed pseudo-second order rate equation with high affinity towards both As(III) and As(V) over a wide pH range (4–8) which was decreased at pH > 9. The maximum adsorption capacity calculated from the Langmuir adsorption isotherm was found to be 59.9 and 45.5 mg g−1 for As(III) and As(V) respectively at pH 7.0. Although the presence of competing anions like SO42-, HCO3- and NO3- did not show pronounced effect, PO43- had an inhibitory action on the adsorption. The XPS analyses of As-reacted Mt-nZVI indicated the occurrence of surface catalyzed oxidation of As(III) to As(V). The possible regeneration using 0.1 M NaOH and performance of Mt-nZVI was investigated by repeating adsorption-elution process. This study has great significance for demonstrating Mt-nZVI as potential adsorbent to reduce elevated levels of As in groundwater.

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