Effective removal of selenate from aqueous solutions by the Friedel phase

This research has demonstrated that the Friedel phase, e.g. a chloride-containing hydrocalumite (Ca2Al(OH)6Cl(H2O)2·mH2O), can rapidly adsorb large amounts of SeO42− (up to 1.37 mmol/g). SeO42− is removed via anionic exchange, as evidenced by the expansion of the d-spacing from 0.78 nm of Cl-hydrocalumite to 0.97-0.98 nm of SeO4-hydrocalumite. The newly formed SeO4-adsorbed hydrocalumite is stable in water at pH 4-13, indicating the strong fixation of selenate within the phase. In contrast, intercalated selenate in the Freidel phase can be recovered by desorbing in the NaCl solution, which can also regenerate and recycle the used adsorbent. The findings in this research strongly suggest that the Friedel phase is a new, environmentally friendly and cost-effective adsorbent to adsorb selenate from wastewater streams and dilute solutions.