Mg/Al-hydrotalcite with intercalated polysulfide ions for selective adsorption of U(VI)

In this study, the polysulfide-intercalated Mg/Al hydrotalcite (Mg/Al-S 2 -LDH) with nanometer scale was prepared by a facile intercalation reaction to remove uranyl (VI) from aqueous solution. The as-synthesized adsorbents were characterized by a variety of techniques such as XRD, SEM, EDS, FTIR, laser particle size analyzer and XPS. Results indicated that the alkali content (governed by the HMT/Al molar ratio parameter f) significantly influenced the particle size, rather than the morphology, of the Mg/Al hydrotalcite. The particle size decreased from 9.37 μm to 0.91 μm with increasing f value. Batch experiment results indicated that Mg/Al-S 2 -LDH adsorbent prepared at f = 3 exhibited the excellent removal performance for uranyl (VI) with the removal rate approaching 100% and a maximum adsorption capacity of 343.64 mg·g −1 . The adsorption process followed the pseudo-second-order model, and the adsorption thermodynamics conformed to Langmuir isotherm adsorption model, indicating that the adsorption process was primarily chemical adsorption and monolayer adsorption. The adsorption mechanism revealed that uranyl (VI) ions were removed by the UO 2 2+ forms inner-sphere complexes with interlayer S 2 2− groups and the formation of an amorphous UO 2 S 2 -like phase on the surface. In addition, results from competitive adsorption suggested that Mg/Al-S 2 -LDH adsorbent processed excellent affinity to uranyl (VI) in the co-exist ions of Na + , K + , Ca 2+ , Mg 2+ , which revealed a potential application prospect in the treatment of U(VI)-contaminated wastewater.