title: New treatment method for boron in aqueous solutions using Mg-Al layered double hydroxide: Kinetics and equilibrium studies.
abstract: Mg-Al layered double hydroxides (LDHs) intercalated with NO3(-) (NO3 · Mg - Al LDHs) and with Cl(-) (Cl · Mg - Al LDHs) were found to take up boron from aqueous solutions. Boron was removed by anion exchange of B(OH)4(-) in solution with NO3(-) and Cl(-) intercalated in the interlayer of the LDH. Using three times the stoichiometric quantity of NO3 · Mg-Al LDH, the residual concentration of B decreased from 100 to 1.9 mg L(-1) in 120 min. Using five times the stoichiometric quantity of Cl · Mg - Al LDH, the residual concentration of B decreased from 100 to 5.6 mg L(-1) in 120 min. It must be emphasized that, in both cases, the residual concentration of B was less than the effluent standards in Japan (10 mg L(-1)). The rate-determining step of B removal by the NO3 · Mg - Al and Cl · Mg - Al LDHs was found to be chemical adsorption involving anion exchange of B(OH)4(-) with intercalated NO3(-) and Cl(-). The removal of B was well described by a pseudo second-order kinetic equation. The adsorption of B by NO3 · Mg - Al LDH and Cl · Mg - Al LDH followed a Langmuir-type adsorption. The values of the maximum adsorption and the equilibrium adsorption constant were 3.6 mmol g(-1) and 1.7, respectively, for NO3 · Mg - Al LDH, and 3.8 mmol g(-1) and 0.7, respectively, for Cl · Mg-Al LDH. The B(OH)4(-) in B(OH)4 · Mg - Al LDH produced by removal of B was found to undergo anion exchange with NO3(-) and Cl(-) in solution. The NO3 · Mg - Al and Cl · Mg - Al LDHs obtained after this regeneration treatment were able to remove B from aqueous solutions, indicating the possibility of recycling NO3 · Mg - Al and Cl · Mg - Al LDHs for B removal.
authors.affiliation: 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.forename: Tomohito
authors.initials: T
authors.lastname: Kameda
authors.affiliation: Graduate School of Environmental Studies, Tohoku University, 6-6-07 Aoba, Aramaki, Aoba-ku, Sendai 980-8579, Japan.
authors.forename: Jumpei
authors.initials: J
authors.lastname: Oba
authors.affiliation: Graduate School of Environmental Studies, Tohoku University, 6-6-07 Aoba, Aramaki, Aoba-ku, Sendai 980-8579, Japan.
authors.forename: Toshiaki
authors.initials: T
authors.lastname: Yoshioka
mesh_terms: D000327:Adsorption; D000535:Aluminum / Q000737:chemistry*; D001895:Boron / Q000737:chemistry*; D002712:Chlorides / Q000737:chemistry; D006878:Hydroxides / Q000737:chemistry*; D007474:Ion Exchange; D007700:Kinetics; D008274:Magnesium / Q000737:chemistry*; D009566:Nitrates / Q000737:chemistry; D012996:Solutions; D014865:Waste Disposal, Fluid / Q000379:methods; D014874:Water Pollutants, Chemical / Q000737:chemistry*; D018508:Water Purification / Q000379:methods
chemical_list: D002712:Chlorides; D006878:Hydroxides; D009566:Nitrates; D012996:Solutions; D014874:Water Pollutants, Chemical; D000535:Aluminum; D008274:Magnesium; D001895:Boron
keywords: Boron; Cyclic usage; Equilibrium; Kinetics; Layered double hydroxide; Removal