Absorption of the selenite anion from aqueous solutions by thermally activated layered double hydroxide

Abstract

The presence of selenite or selenate in potable water is a health hazard especially when consumed over a long period of time. Its removal from potable water is of importance. This paper reports technology for the removal of selenite from water through the use of thermally activated layered double hydroxides.
Mg/Al hydrotalcites with selenite in the interlayer were prepared at different times from 0.5 to 20 hours through ion exchange. X-ray diffraction of the MgAlSeO3 hydrotalcites indicates that the selenite anion entered the interlayer spacing of Mg/Al hydrotalcite and MgAlSeO3 hydrotalcite was formed. Raman spectra proved the presence of selenite anion in the hydrotalcite interlayer as the counter anion. The band intensity and width of MgAlSeO3 hydrotalcite in the region of 3800 to 3000 cm-1 increases with the adsorption of selenite by the Mg/Al hydrotalcite. The characteristic bands of free selenite anions in the MgAlSeO3 hydrotalcites are located between the region between 850 and 800 cm-1. The Raman spectra of the lower wavenumber region of 550 to 500 cm-1 show a shift toward higher wavenumbers with adsorption of the selenite. Thermally activated LDHs provide a mechanism for removing selenite anions from aqueous solutions.