Sorption properties of boron on Mg–Al bimetallic oxides calcined at different temperatures

• The basicity per unit surface area of bimetallic oxides was smaller than single-phase MgO.
• The bimetallic oxides predominantly adsorbed tetrahedralborate ([4]B).
• [4]B gradually intercalated in the interlayers of LDH with times.
• The Mg–Al873 and Mg–Al1073 samples were more effective than single-phase MgO.
• Regeneration of hydrotalcite-like compounds is the key to increasing the B sorption.

Mg–Al bimetallic oxides produced via the calcination of hydrotalcite-like compounds ([(Mg0.75Al0.25(OH)2](An−)0.75/n·mH2O, where A is an anionic species) exhibited high potential for the removal of boron from aqueous solutions. X-ray diffraction patterns for the produced bimetallic oxides revealed that MgO was the primary phase within the range of investigated calcination temperatures. In addition, 11B NMR spectral analyses indicated that the Mg–Al bimetallic oxides captured trigonal B ([3]B) and tetrahedral B ([4]B) after the sorption of boron, regenerating hydrotalcite-like compounds. As the initial concentration of boron increased, the percentage of tetrahedral [4]B in solid residues after the sorption of boron increased. The [4]B/[3]B ratios in the solid residues increased with time along with the regeneration of hydrotalcite-like compounds. Furthermore, the Mg–Al bimetallic oxides produced from hydrotalcite-like compounds were more favorable than other bimetallic oxides and effective than single-phase MgO produced from MgCO3 at the same temperature, indicating that Mg–Al bimetallic oxides are stable materials with the potential for use in the remediation of contaminated sites and water.

Figure optionsDownload as PowerPoint slide