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

Abstract

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 (As3+) and arsenate (As5+) by RH-Fe-MCM-41 at the molar ratio of Si/Fe 10 gave removal efficiencies of 47% and 99% for As3+ and As5+, respectively, in the 100-1,000 μgl-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 As5+. The adsorption capacity by the Langmuir constants (Qm) for As3+ and As5+ were 416.67 μgg-1 and 277.78 μgg-1, respectively, while the Freundlich constants (KF) were 0.583 μgg-1 for As3+ and 112.87 μgg-1 for As5+. The fit for As5+ was good with both the Langmuir and Freundlich isotherms by considering the R2 values, which were quite similar (0.916 and 0.912); As3+ fit well only with the Langmuir isotherm. The impregnation of iron (Fe3+) into the RH-Fe-MCM-41 structure increases the adsorption capacity of As3+ and As5+ both by oxidizing As3+ to As5+ and by co-precipitation with As5+. © IWA Publishing 2009.