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

Abstract

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 45.5mgg-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 0.1M 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