Use of Mg-Al oxide for boron removal from an aqueous solution in rotation: Kinetics and equilibrium studies

Mg-Al oxide prepared through the thermal treatment of CO32- intercalated Mg-Al layered double hydroxides (CO3 center dot Mg-Al LDH) was found to remove boron (B) from an aqueous solution. B was removed by the rehydration of Mg-Al oxide accompanied by combination with B(OH)(4)(-). When using twice the stoichiometric quantity of Mg-Al oxide for Mg/Al = 4, the residual concentration of B dropped from 100 to 2.8 mg/L in 480 min, and for Mg/Al = 2, it decreased from 100 to 2.5 mg/L in 240 min. In both cases, the residual concentration of B was highlighted to be lower than the current Japanese effluent standards (10 mg/L). The removal of B can be explained by way of pseudo-first-order reaction kinetics. The apparent activation energy of 63.5 kJ mol(-1), calculated from the Arrhenius plot indicating that a chemical reaction dominates the removal of B by Mg-Al oxide (Mg/Al = 2). The adsorption of B acts upon a Langmuir-type phenomena. The maximum adsorption (q(m)) and equilibrium adsorption constants (Kt) were 7.4 mmol g(-1) and 1.9 x 10(3), respectively, for Mg-Al oxide (Mg/Al = 2)center dot B(OH)(4)(-) in B(OH)(4)(-)center dot Mg-Al LDH produced by the removal of B was observed to undergo anion exchange with CO32- in solution. Following regeneration, the Mg-Al oxide maintained the ability to remove B from an aqueous solution. This study has clarified the possibility of recycling Mg-Al oxide for B removal. (C) 2015 Elsevier Ltd. All rights reserved.