Surface mechanism of the boron adsorption on alumina in aqueous solutions

ABSTRACT

The adsorption of boron (boric acid) from aqueous solutions on alumina has been investigated at pH 8.0, I = 0.1 M NaClO₄, T = 22 ± 3°C, and under normal atmospheric conditions. The characterization of the adsorbed species was performed by Raman spectroscopy and the spectroscopic speciation was assisted by theoretical DFT calculations. Evaluation of the spectroscopic data points to the formation of inner-sphere surface complexes and indicates the formation of two different types of adsorbed boron species. The theoretical calculations corroborate the spectroscopic data and indicate that at low boron concentration the monodentate surface species dominates, whereas increased boron concentration favors the formation of a bidentate surface species. Assuming low coverage, the conditional formation constant for the monodentate surface species has been evaluated to be log  β ^∗ = 4.1 ± 0.1.

Keywords:

• Boric acid
• Alumina
• Raman spectroscopy
• DFT calculations
• Surface complexes
• Formation constant