| With the rapid development of the printing industry and the nuclear industry,a large number of wastewater containing dyes and radioactive elements have been brought.These wastewater need to be treated reasonably before it can be discharged into the ecological environment.Layered double hydroxide is a common anionic clay or hydrotalcite-like compound,which has received extensive attention due to its adjustable layer structure and nanometer size.In this paper,the Eu???,a trivalent lanthanide and a lanthanide analog substitute,and U?VI?and methyl orange,which is a common anion azo dye as the target pollutants.Ni/Al hydrotalcite-like compounds?noted as G-LDH?modified by glycerol with Ni:Al mole ratio of 3:1,which are prepared by traditional hydrothermal synthesis method as an adsorbent.The effects of solid-to-liquid ratio,pH value,ionic strength,humic acid,contact time and temperature on the adsorption of Eu???,U?VI?and methyl orange on G-LDH were investigated by static adsorption method and batch treatment method.The crystal structure,morphology and functional groups and other characteristics of the modified hydrotalcite adsorbent materials were analyzed by SEM,FT-IR,XRD,XPS and Zeta-potential microscopic characterization methods.Adsorption kinetics model,adsorption isotherm model and particle diffusion model were used to analyze the adsorption process and explore the adsorption mechanism.Concluded as follow:?1?The microscopic characterization results show that the glycerol-modified Ni/Al hydrotalcite-like compound material is successfully synthesized.The morphology of the synthetic material G-LDH is cluster-spherical,and its spherical structure is composed of multi-layer structure.After adsorption,the surface of the material was agglomerated and its structure became massive.It can be seen from the XRD pattern analysis before and after adsorption that the synthetic material has a relatively stable structure.XPS analysis showed that G-LDH successfully adsorbed the adsorbate in the solution onto the material.Most of the functional groups on the surface of the material are retained after adsorption.?2?The static adsorption experiments show that the G-LDH exhibits good adsorption effect on Eu???,U?VI?and methyl orange in aqueous solution.At room temperature,when the Eu???initial concentration is 4.546×10-5 mol/L,the solid-to-liquid ratio is 0.016g/L,and the pH=8.0,the removal rate of Eu???in the solution by G-LDH can reach99.01%and the adsorption capacity is 427.59 mg/g.At room temperature,initial concentration is 10 mg/L,solid-to-liquid ratio is 0.03 g/L and pH=6.5,the adsorption rate of U?VI?by G-LDH reached 84.64%and the maximum adsorption capacity reached282.13 mg/g.Meanwhile,initial concentration is 10 mg/L,solid-to-liquid ratio is 0.02 g/L and pH=4.0,the adsorption rate of G-LDH on anionic methyl orange in solution can reach96.17%and the adsorption capacity is 480.85 mg/g at room temperature.?3?The adsorption kinetics analysis indicated that the three reactions of G-LDH adsorption of Eu???,U?VI?and methyl orange were in accordance with the pseudo-second-order kinetics model,and the adsorption reaction is mainly controlled by chemical adsorption.The particle diffusion model fitting shows that the three adsorption reactions are controlled by internal diffusion,and there are also affected by external diffusion such as liquid membrane diffusion or exchange external substances.The thermodynamic analysis showed that the adsorption process of Eu???by G-LDH accorded with the Langmuir isotherm model,and the fitting coefficient of the Freundlich isotherm model was also high,indicating that the surface monolayer adsorption was dominant,and the irregular multilayer adsorption was auxiliary.The adsorption of U?VI?and methyl orange by G-LDH conforms to the Langmuir isotherm model,which is mainly surface monolayer adsorption.The adsorption of Eu???and U?VI?by G-LDH is a spontaneous and endothermic chemical reaction process,while the adsorption of methyl orange by G-LDH is a spontaneous and exothermic chemical reaction process.?4?In this paper,the adsorption of Eu???,U?VI?and methyl orange by G-LDH under different environmental conditions is discussed and analyzed.Compared with other adsorbent materials,the G-LDH exhibits a higher adsorption capacity for Eu???,U?VI?and methyl orange in solution,indicating that synthetic material has a great application prospect in the efficient purification and remediation of wastewater containing this kind of contaminant. |
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