title: Sorption of H₃BO₃/B(OH)₄⁻ on calcined LDHs including different divalent metals.
abstract: LDHs with different divalent metals (Zn-LDH, Mg-LDH and Ca-LDH) have been synthesized and produced calcined LDHs (Zn-CLDH, Mg-CLDH and Ca-CLDH) for borate removal. Based on XRD, SEM, BET, (27)Al NMR, CO2-TPD, and (11)B NMR, detailed characterization of different CLDHs before and after reaction with the boron species was systematically performed. The surface area, basicity and the particle charge of the different CLDHs, which are related to the hydration and regeneration, were markably influenced by the nature of the divalent metals. Transformation of crystal phases and the types of boron species adsorbed by the different CLDHs varied as time changed. The regeneration of Ca-CLDH required the shortest time. However, Ca-LDH decomposed to release Ca(2+) ions, forming ettringite with borate. Zn-CLDH also rapidly transformed into Zn-LDH. During this reconstruction, B(OH)4(-) was intercalated into the interlayer of Zn-LDHs, which is the predominant mechanism of borate removal by Zn-CLDH. Increase in the initial pH caused a competition between borate and OH(-) so that the removal efficiency of borate by Zn-CLDH decreased. For Mg-CLDH, surface complexation and electrostatic attraction were included in the first stage, immobilizing boric acid into Mg(OH)2 and attracting borate as interlayer anionic species into the new forming Mg-LDHs in the second stage.
authors.affiliation: Department of Earth Resources Engineering, Kyushu University, Fukuoka 819-0395, Japan. Electronic address: qxinhong@gmail.com.
authors.forename: Xinhong
authors.initials: X
authors.lastname: Qiu
authors.affiliation: Department of Earth Resources Engineering, Kyushu University, Fukuoka 819-0395, Japan.
authors.forename: Keiko
authors.initials: K
authors.lastname: Sasaki
authors.affiliation: Department of Materials Science and Engineering and Department of Energy and Mineral Engineering, Penn State University, University Park, PA 16802, USA.
authors.forename: Kwadwo
authors.initials: K
authors.lastname: Osseo-Asare
authors.affiliation: Department of Earth Resources Engineering, Kyushu University, Fukuoka 819-0395, Japan.
authors.forename: Tsuyoshi
authors.initials: T
authors.lastname: Hirajima
authors.affiliation: Institute for Materials Chemistry and Engineering, Kyushu University, Kasuga 816-8180, Japan.
authors.forename: Keiko
authors.initials: K
authors.lastname: Ideta
authors.affiliation: Institute for Materials Chemistry and Engineering, Kyushu University, Kasuga 816-8180, Japan.
authors.forename: Jin
authors.initials: J
authors.lastname: Miyawaki
keywords: Anion exchange; Boron; Complex; Intercalation; LDH; Mechanism