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Kinetics of Arsenate Sorption–Desorption from Metal Oxides

Effect of Residence Time

Dipartimento di Scienze del Suolo, della Pianta e dell'Ambiente, Univ. di Napoli Federico II, Via Università 100, 80055 Portici (Napoli), Italy; G.S.R. Krishnamurti, present address: 313-855 West 16th St., North Vancouver, BC V7P 1R2, Canada

View larger version (16K): [in a new window]   Fig. 1. X-ray diffraction patterns of (A) goethite and ferrihydrite, and (B) gibbsite and noncrystalline Al hydroxide [Al(OH)x].

View larger version (15K): [in a new window]   Fig. 2. Fourier-transform infrared transmittance spectra of (A) goethite and ferrihydrite, and (B) gibbsite and noncrystalline Al hydroxide [Al(OH)x].

View larger version (14K): [in a new window]   Fig. 3. Arsenate sorption isotherms on gibbsite, noncrystalline Al hydroxide [Al(OH)x], goethite, and ferrihydrite at pH 6.0 and 20°C. The ionic strength was 0.05 mol L–1 KCl and the solid/solution ratio was 5 g L–1.

View larger version (21K): [in a new window]   Fig. 4. Arsenate sorbed at pH 6.0 after 1 h of reaction on ferrihydrite, goethite, noncrystalline Al hydroxide [Al(OH)x], and gibbsite. Final As(V) surface coverage was about 50 or 100% for all sorbents.

View larger version (15K): [in a new window]   Fig. 5. Kinetics of sorption of As(V), at pH 6.0 and 100% surface coverage, on (A) gibbsite and noncrystalline Al hydroxide [Al(OH)x], and (B) goethite and ferrihydrite. The amount of As(V) added was 200 mmol kg–1 for gibbsite, 300 mmol kg–1 for Al(OH)x, 200 mmol kg–1 for goethite, and 600 mmol kg–1 for ferrihydrite.

View larger version (16K): [in a new window]   Fig. 6. Kinetics of sorption of As(V), at pH 6.0 and 100% surface coverage, on gibbsite, noncrystalline Al hydroxide [Al(OH)x], goethite, and ferrihydrite, using the Elovich model. The amount of As(V) added was 200 mmol kg–1 for gibbsite, 300 mmol kg–1 for Al(OH)x, 200 mmol kg–1 for goethite, and 600 mmol kg–1 for ferrihydrite.

View larger version (11K): [in a new window]   Fig. 7. Arsenate desorbed by PO4 at pH 6.0 from gibbsite, noncrystalline Al hydroxide [Al(OH)x], ferrihydrite, and goethite. Phosphate was added at an initial PO4/As(V) molar ratio of 4.