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

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 g1 for As(III) and As(V) respectively at pH 7.0. Although the presence of competing anions like SO2, HCO3 and NO3 did not show pronounced effect, PO3 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 0.1M 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.