Adsorption of boron on calcined AlMg layered double hydroxide from aqueous solutions. Mechanism and effect of operating conditions

• Boron can be removed from water by adsorption on layered double hydroxide (LDH).
• Both boric acid and borate species are adsorbed on the LDH.
• Adsorption of borate is due to anion exchange and electrostatic interactions.
• Adsorption of boric acid is attributed to acid–base reaction.
• Solution pH plays a key role on the adsorption of the boron species onto LDH.

The adsorption of boron from an aqueous solution on layered double hydroxide (LDH) was investigated in detail in this work. The LDH was synthesized by a co-precipitation method using carbonate as an exchangeable anion; the LDH was calcined at 550 °C and denoted as LDH-550. Experimental adsorption equilibrium data were obtained in a batch adsorber and were interpreted reasonably well using the Langmuir isotherm. The solution pH considerably affected the adsorption capacity of LDH-550 toward boron due to electrostatic interactions between the surface of LDH-550 and the boron species in solution. The adsorption capacity of LDH-550 was independent of temperature when the temperature was increased from 15 to 25 °C but decreased when the temperature was increased from 25 to 35 °C. The reversibility of the adsorption was shown to be dependent on the desorption pH. Boron can be adsorbed on LDH-550 as boric acid and borate. The adsorption of borate on LDH-550 was due to anion exchange and electrostatic attraction, whereas boric acid was adsorbed by an acid–base reaction. The mechanisms were elucidated by evaluating and interpreting the surface charge of LDH-550 before and after boron adsorption, FTIR analysis and the equivalents of anions exchanged during the adsorption of boron.