Highly efficient arsenic sorbent based on residual from water deironing - Sorption mechanisms and column studies

The hybrid polymer obtained by entrapment of Fe-Mn waste oxides from water deironing into a chitosan matrix was evaluated as an As(III) and As(V) sorbent. Its maximum adsorption capacity determined from a Langmuir isotherm model was 44.17 mg As(III)/g or 26.80 mg As(V)/g and 50.73 mg As(III)/g or 82.99 mg As(V)/g under neutral and acidic conditions, respectively. The pH markedly influenced the efficiency and the rate of As(V) adsorption, whereas its impact on As(III) removal was slight. The sorbent was simply regenerated using NaOH solution, and no drop in adsorption capacity was observed after 6 cycles. The physical form and the durability of the sorbent enabled continuous work in a fixed-bed system without clogging of the bed. Arsenic concentration in the effluent exceeded 0.01 mg As/L only after passing about 2700 bed volumes. Arsenates formed surface complexes with iron oxides and were bounded by the imine groups of cross-linked chitosan. Arsenites were oxidized by MnO₂ before adsorption but, because of the low Mn:Fe ratio, a fraction of them were also directly bound to the iron oxides, especially at neutral pH. The conducted studies confirmed the usability of the examined material as a highly efficient sorbent for arsenic removal from water.