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 1.9mgL-1 in 120min. Using five times the stoichiometric quantity of Cl·Mg-Al LDH, the residual concentration of B decreased from 100 to 5.6mgL-1 in 120min. It must be emphasized that, in both cases, the residual concentration of B was less than the effluent standards in Japan (10mgL-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 3.6mmolg-1 and 1.7, respectively, for NO3·Mg-Al LDH, and 3.8mmolg-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.
- Cyclic usage
- Layered double hydroxide
ASJC Scopus subject areas
- Environmental Engineering
- Environmental Chemistry
- Waste Management and Disposal
- Health, Toxicology and Mutagenesis