Water Science & Technology: Water Supply—WSTWS Vol 9 No 2 pp 121–126 © IWA Publishing 2009 doi:10.2166/ws.2009.246

Adsorption of arsenic in aqueous solution by RH-Fe-MCM-41

W. Tong-on, S. Sthiannopkao, K. W. Kim and S. Chiarakorn

RH-Fe-MCM-41 adsorption efficiency and capacity were examined with arsenic in lower concentrations in aqueous solution under varying pH values. The adsorption of arsenite (As^3 + ) and arsenate (As^5 + ) by RH-Fe-MCM-41 at the molar ratio of Si/Fe 10 gave removal efficiencies of 47% and 99% for As^3 +  and As^5 + , respectively, in the 100–1,000 mg l^-1 concentration range. For the adsorption test of arsenic the best conditions were found to be an equilibrium time of 12 h at pH 7 for As^3 +  and 2 h at pH 4 for As^5 + . The adsorption capacity by the Langmuir constants (Q_m) for As^3 +  and As^5 +  were 416.67 mg g^-1 and 277.78 mg g^-1, respectively, while the Freundlich constants (K_F) were 0.583 mg g^-1 for As^3 +  and 112.87 mg g^-1 for As^5 + . The fit for As^5 +  was good with both the Langmuir and Freundlich isotherms by considering the R² values, which were quite similar (0.916 and 0.912); As^3 +  fit well only with the Langmuir isotherm. The impregnation of iron (Fe^3 + ) into the RH-Fe-MCM-41 structure increases the adsorption capacity of As^3 +  and As^5 +  both by oxidizing As^3 +  to As^5 +  and by co-precipitation with As^5 + .

Keywords: adsorption; arsenate; arsenite; RH-Fe-MCM-41

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