Comparison of Selenite and Selenate Adsorption with Iron-Coated GAC

N. Zhang, D. Gang, and L.-S. Lin (USA)

Keywords

Selenite, selenate, ironcoated GAC, adsorption,competitive, AMD

Abstract

Iron-coated granular activated carbon (Fe-GAC) was developed in this study for adsorptive removal of selenite and selenate from aqueous phase. Five different types of GACs were coated by ferrous chloride. Brunauer Emmett-Teller (BET) specific surface area, pore size, and pore volume of the treated GACs all decreased according to nitrogen adsorption-desorption analyses. The Darco 12x20 GAC coated with 0.1 M ferrous chloride was found most effective for selenite removal. Scanning electron microscopic analysis showed that pore sizes decreased with increase of ferrous chloride concentration. Similar pH effects were observed for selenite and selenate adsorption, which showed that the Fe-GAC adsorbent was more effective selenite and selenate removal at low pHs than in alkaline range. Adsorption kinetics indicated that selenite and selenate adsorption equilibrium could both be reached after 48 hours, but lower removal efficiency was observed for selenate (80%) than selenite (97%). Pseudo second-order kinetic model characterized adsorption kinetics well (i.e., R2 ≥ 0.99). The Freundlich model was used to characterize selenite (R2 ≥ 0.99) and selenate adsorption isotherms (R2 ≥ 0.97). Competitive adsorption between selenite and selenate revealed that total adsorption capacity for both anions in the binary adsorbate system was slightly lower than the sum of the single adsorbate systems.

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