Preparation of phosphoric-modified aloe vera/chitosan aerogels and their efficient adsorption of U(VI).

The efficient adsorption of radioactive elements from nuclear wastewater is an important research topic in the environmental field. The unique three-dimensional porous structure of aerogels has great potential in the field of adsorption. Phosphoric-modified aloe vera/chitosan aerogel (CS/AL-AP) was prepared from chitosan, phosphoric acid, and aloe powder by vacuum freeze-drying self-assembly. The maximum adsorption of uranyl ions by CS/AL-AP was found to be 322.34 mg/g at pH 6, adsorption time of 120 min, solid-to-liquid ratio of 0.125 g/L, reaction temperature of 303 K, and initial uranyl ion concentration of 50 mg/L. The adsorption process is consistent with the Langmuir isotherm model and the quasi-secondary kinetic model, indicating that the adsorption process is monolayer adsorption. The type of adsorption is mainly chemisorption. FTIR and XPS analyses indicate that the adsorption of U(VI) by CS/AL-AP results from the combined action of coordination or chelation of amino, hydroxyl, and carboxyl groups. In addition, CS/AL-AP shows excellent adsorption capacity in the presence of complex co-existing ions. After five adsorption-desorption experiments, the adsorption capacity of CS/AL-AP for uranyl ions remained at a high level. It indicates that CS/AL-AP has good stability and recoverability. The results indicate that CS/AL-AP has excellent potential in the field of uranium removal.

Preparation of ZnNiAl-LDHs microspheres and their adsorption behavior and mechanism on U(VI).

Ternary zinc-nickel-aluminum hydrotalcites (ZnNiAl-LDHs) were prepared by hydrothermal synthesis. The structure and morphology of the materials were characterized using X-ray diffraction (XRD), fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), nitrogen adsorption-desorption (BET) and other test techniques. ZnNiAl-LDHs was applied in the treatment of uranium-containing wastewater, the effects of initial pH of the solution, adsorption temperature and contact time on its adsorption performance were systematically investigated, and the adsorption performance of ZnNiAl-LDHs and ZnAl-LDHs on uranyl ions were compared. The result showed that ZnNiAl-LDHs were 3D microspheres self-assembled from flakes, with a specific surface area of 102.02 m2/g, which was much larger than that of flake ZnAl-LDHs (18.49 m2/g), and the saturation adsorption capacity of ZnNiAl-LDHs for uranyl ions (278.26 mg/g) was much higher than that of ZnAl-LDHs for uranyl ions (189.16 mg/g), so the ternary ZnNiAl-LDHs had a more excellent adsorption capacity. In addition, kinetic and thermodynamic studies showed that the adsorption process of ZnNiAl-LDHs on uranyl ions conformed to the pseudo-second-order kinetic model and Langmuir isotherm model. The positive value of ΔH and the negative value of ΔG indicated that the adsorption process was endothermic and spontaneous. The adsorption mechanism was analyzed by X-ray energy spectroscopy (EDS), fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). The results showed that the adsorption of uranyl ions by ZnNiAl-LDHs mainly consisted of complexation and ion substitution. The research results prove that ZnNiAl-LDHs is an adsorbent with low cost and excellent performance, and it has a good application prospect in the field of uranium-containing wastewater treatment.