Abstract
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.
Highlights
Ternary zinc-nickel-aluminum hydrotalcites (ZnNiAl-layered double hydroxides (LDHs)) were prepared by hydrothermal synthesis
The R 2 value of the pseudo-secondorder kinetic model is higher than those of the pseudo-first-order kinetic model and Elovich model, the theoretical equilibrium adsorption capacity (303.95 mg/g) of ZnNiAl-LDHs calculated by the pseudo-secondorder kinetic model is closer to the real experimental result (278.26 mg/g), implying that the pseudo-secondorder kinetic model can better describe the kinetic process of adsorption of uranium ions by ZnNiAl-LDHs, indicating the adsorption process of the adsorbent is dominated by chemisorption on a homogeneous surface[33,34]
ZnNiAl-LDHs with microspherical structure were prepared by a simple hydrothermal synthesis method, and the microspheres had uniform particle size and good dispersibility
Summary
Ternary zinc-nickel-aluminum hydrotalcites (ZnNiAl-LDHs) were prepared by hydrothermal synthesis. The R 2 value of the pseudo-secondorder kinetic model is higher than those of the pseudo-first-order kinetic model and Elovich model, the theoretical equilibrium adsorption capacity (303.95 mg/g) of ZnNiAl-LDHs calculated by the pseudo-secondorder kinetic model is closer to the real experimental result (278.26 mg/g), implying that the pseudo-secondorder kinetic model can better describe the kinetic process of adsorption of uranium ions by ZnNiAl-LDHs, indicating the adsorption process of the adsorbent is dominated by chemisorption on a homogeneous surface[33,34].
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