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| Study on arsenate adsorption by synthetic iron and aluminum oxides/hydroxides |
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Abstract Batch experiments were used to investigate arsenate adsorption by synthetic iron and aluminum oxides/hydroxides. The effects of adsorption time and pH on the adsorption behavior were also studied. The results showed that, As(V) adsorption by four iron and aluminum oxides/hydroxides increased with initial As(V) concentrations (0.1~100 mg/L), in which ferrihydrite showed a rising adsorption trend in the whole concentration range, with the adsorption amount of 22.56 mg/g at the initial As(V) of 100 mg/L . While the rapid increase in lower initial concentration and slow change in higher initial concentrations for the adsorption capacities of goethite, gibbsite, and hematite were obtained. When the initial As(V) reached 100mg/L, the least adsorption capacity of 4.75mg/g was received for hematite. Furthermore, the Freundlich equation fitted the data better than the Langmuir equation. The adsorption capacity of ferrihydrite is the highest, followed by goethite and gibbsite, and hematite shows lower adsorption capacity. With the increase of adsorption time, As(V) adsorption amount of four synthetic iron and aluminum oxides/hydroxides increased gradually, especially for ferrihydrite, reaching 96.3% of adsorption equilibrium in 10 minutes. The adsorption amount of goethite and gibbsite reached 97.4% and 97.2% of the equilibrium at 48h, respectively, while hematite required 96 hours to reach the equilibrium. Except ferrihydrite, four equations fitted the kinetic data better, especially the two-constant equation. The effect of pH on As(V) adsorption was associated to As(V) initial concentrations. In lower initial concentrations, adsorption of four synthetic iron and aluminum oxides/hydroxides decreased only under extremely alkaline conditions (pH>10), and when the initial concentrations were higher, adsorption amount dropped sharply with pH increasing.
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Received: 13 August 2010
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