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

• Mg–Al oxide was found to remove boron from an aqueous solution.
• B was removed by the rehydration of Mg–Al oxide by combination with −B(OH)4B(OH)4− .
• B removal can be represented by pseudo-first-order reaction kinetics.
• The adsorption of B follows a Langmuir-type adsorption.
• This study has clarified the possibility of recycling Mg–Al oxide for B removal.

Mg–Al oxide prepared through the thermal treatment of CO32−CO32− intercalated Mg–Al layered double hydroxides (CO3·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)4B(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 (qm) and equilibrium adsorption constants (KL) were 7.4 mmol g−1 and 1.9 × 103, respectively, for Mg–Al oxide (Mg/Al = 2). −B(OH)4B(OH)4− in B(OH)4·Mg–Al LDH produced by the removal of B was observed to undergo anion exchange with CO32−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.

Figure optionsDownload as PowerPoint slide