Development of Pumice-Nano Zerovalent Iron Composite and its Application in a Continuous Flow System for Arsenic Removal

Large active surface area and high arsenic adsorption capacity make nano-zero valent iron (nZVI) a promising adsorbent for arsenic removal, however, due to high surface energy and the inherent magnetic forces of nZVI, it gets agglomerated and reduces its efficiency for adsorption. The objective of the present study was to develop supported nZVI over the porous material, Pumice, and its subsequent use for As (III) removal in the continuous flow system. Liquid Phase Synthesis was used to impregnate the iron nanoparticle on the surface of the porous material via reduction of iron in the presence of the base material by sodium borohydride. The shape, size, and surface morphology studied by Fe-SEM and shows a uniform distribution of nZVI over the surface of granular (0.5-1 mm) base materials. Batch studies were performed to determine the applicability of prepared composites as an adsorbent for As (III) removal at varying initial As (III) concentration (25 -200 mg/L), adsorbent dose ( 0.5-5 g/L ) and pH (3-12). Batch experiments demonstrated a quick removal of As (III) at initial stages followed by a slower removal rate, making it a two-stage process. The adsorption kinetics data were fitted to pseudo second-order kinetic model with the highest value of correlation coefficient. The freundlich isotherm model was used to describe the adsorption of As(III) on the heterogeneous surface of the composite. The developed composite was applied in a continuous flow column study for 30 days, and it demonstrated 99 % removal of arsenic with an average arsenic loading of 0.95 mg/gm over the adsorbent. The hydraulic conductivity of the adsorbent media was observed to be reduced by 20 % during the experiment, but it was still comparable enough to the average conductivity of the arsenic affected aquifer media. High removal efficiency over wide pH range, low cost and better hydraulic and mechanical properties makes it a promising adsorbent for field application.