Arsenic sequestration by iron oxide coated geopolymer microspheres

Abstract

A green, low-cost adsorbent based on geopolymer “microspheres” is reported for the first time for arsenic adsorption. A simple two-step process involves synthesizing geopolymer microspheres by inverse suspension polymerization and impregnating them with iron oxide. The low hydraulic conductivity of fine iron oxide powders demands the use of suitable support materials. Iron oxide modified geopolymer microparticles synthesized here, are small, spherical, porous, mechanically, and chemically stable, have high surface area of 270 m 2 /g and can be easily separated from water after adsorption is complete. A comprehensive adsorption study was conducted by employing environmentally critical arsenic species, viz. As(III), As(V), monomethyl arsenate and dimethyl arsenate. The role of contact time, initial arsenic concentration, temperature, adsorbent dosage, pH and competing ions was evaluated. Highest arsenic adsorption was observed at an iron content of 20 wt%. High percent removal of ∼86%, 100%, 95% and 96% for As(III), As(V), DMA and MMA respectively, were observed at initial arsenic concentration of 0.5 mg/L, an adsorbent dosage of 10 g/L and in just 60 min. Low pH favored adsorption of As(V), monomethyl arsenate and dimethyl arsenate while high pH favored adsorption of As(III). The applicability of the novel adsorbent in column mode, its high regeneration capacity and, facile, green, and cheap production are few of its advantages. Moreover, unmodified geopolymer microspheres, introduced here, can be employed as adsorbents for other toxic heavy metals such as Pb, Cd and Hg. • Inverse suspension polymerization was used to synthesize geopolymer microspheres. • Geopolymer microspheres were infused with iron oxide for arsenic adsorption. • Highest amounts of arsenic was removed by geopolymer containing 20 wt% iron. • Removal of As(III), As(V), monomethyl arsenate and dimethyl arsenate was evaluated. • New adsorbent showed excellent regeneration, hence making it economically viable.