title: Kinetics and equilibrium studies on Mg-Al oxide for removal of fluoride in aqueous solution and its use in recycling.
abstract: Mg-Al oxide obtained by the thermal decomposition of Mg-Al layered double hydroxide (LDH) intercalated with CO3(2-) (CO3·Mg-Al LDH) was found to take up fluoride from aqueous solution. Fluoride was removed by rehydration of Mg-Al oxide accompanied by combination with F(-). Using five times the stoichiometric quantity of Mg-Al oxide, the residual concentration of F was decreased from 100 to 6.3 mg/L in 480 min, which was below the effluent standard in Japan (8 mg/L). Removal of F(-) can be represented by pseudo-second-order reaction kinetics. The apparent rate constants at 10 °C, 30 °C, and 60 °C were 2.3 × 10(-3), 2.2 × 10(-2), and 2.5 × 10(-1) g mmol(-1) min(-1), respectively. The apparent activation energy was 73.3 kJ mol(-1). The rate-determining step for F removal by Mg-Al oxide was consistent with chemical adsorption involving intercalation of F(-) into the reconstructed Mg-Al LDH due to electrostatic attraction. The adsorption of F by Mg-Al oxide follows a Langmuir-type adsorption. The values of the maximum adsorption and the equilibrium adsorption constant were 3.0 mmol g(-1) and 1.1 × 10(3), respectively, for Mg-Al oxide. The F(-) in the F·Mg-Al LDH thus produced was found to be anion-exchanged with CO3(2-) in solution. The Mg-Al oxide after regeneration treatment had excellent properties for removal of F in aqueous solution. In conclusion, the results of this study indicated that Mg-Al oxide has potential for use in recycling to remove F in aqueous solution.
authors: Graduate School of Environmental Studies, Tohoku University, 6-6-07 Aoba, Aramaki, Aoba-ku, Sendai 980-8579, Japan. Electronic address: kameda@env.che.tohoku.ac.jp.
authors: Tomohito
authors: T
authors: Kameda
authors: Graduate School of Environmental Studies, Tohoku University, 6-6-07 Aoba, Aramaki, Aoba-ku, Sendai 980-8579, Japan.
authors: Jumpei
authors: J
authors: Oba
authors: Graduate School of Environmental Studies, Tohoku University, 6-6-07 Aoba, Aramaki, Aoba-ku, Sendai 980-8579, Japan.
authors: Toshiaki
authors: T
authors: Yoshioka
mesh_terms: D017607:Aluminum Compounds / Q000737:chemistry*; D005459:Fluorides / Q000737:chemistry*; D006878:Hydroxides; D007220:Industrial Waste / Q000517:prevention & control*; D007564:Japan; D007700:Kinetics; D017616:Magnesium Compounds / Q000737:chemistry*; D059027:Recycling / Q000379:methods*; D012996:Solutions / Q000737:chemistry; D014874:Water Pollutants, Chemical / Q000737:chemistry*; D018508:Water Purification / Q000379:methods*
chemical_list: D017607:Aluminum Compounds; D006878:Hydroxides; D007220:Industrial Waste; D017616:Magnesium Compounds; D012996:Solutions; D014874:Water Pollutants, Chemical; C110424:aluminum magnesium oxide; C031356:hydroxide ion; D005459:Fluorides
keywords: Equilibrium; Fluoride; Kinetics; Mg–Al oxide; Recycling; Removal