Preparation And Adsorption Properties Of Novel Uranium Composite Adsorbent

With the development of nuclear energy,the uranium containing waste water has caused certain pollution to the environment.In order to develop new uranium resources and ensure the long-term development of nuclear energy,the extraction of uranium from seawater has been paid more attention all over the world.In this paper,Four new composite adsorbents with high efficiency,low cost and excellent performance were prepared,and were used for the adsorption and extraction of uranium in low concentration waste water and simulated seawater.Some important findings and achievements are obtained as follows:?1?Linear?-Cyclodextrin polymer?CDP?functionalized multi-walled carbon nanotubes?MWCNTs-CDP?as a novel composite adsorbent was synthesized by chemical grafting.The structure and morphology of MWCNTs-CDP were characterized by Fourier transform infrared spectroscopy?FT-IR?,powder X-ray diffraction?XRD?,scanning electron microscopy?SEM?and Brunauer-Emmett-Teller surface area?BET?.In addition,Batch experiments was carried out to investigate the adsorption efficiency of U?VI?from aqueous solutions by MWCNTs-CDP as a function of pH,ionic strength,contact time,initial U?VI?concentration and temperature.It was confirmed that the CDP was successfully modified on the MWCNTs,the surface complexes were formed for the binding of U?VI?with the hydroxyl groups on adsorbent by coordination interaction.The optimum pH and temperature were 6.0 and 323.15K,respectively.The adsorption of uranyl ions reached the adsorption equilibrium after 3 h at the initial uranium concerntration for 1.0 mg L^-1.The adsorption kinetic data can be well fitted by the pseudo-second-order model,indicating that chemical adsorption was the control step of adsorption rate.Freundlich and Langmuir were all suitable for describing the adsorption process,which showed that the adsorption behaviors has both physical and chemical adsorption.The thermodynamic analysis proved that the adsorption process was endothermic and spontaneous.The solution of 0.5 mol L^-11 NaHCO₃ was selected as desorbent for the study of reusability,and the desorption rate reached 92.95%,After the adsorption-desorption cycles for three times,the absorption capacity was decreased only 10.1%,indicating that the adsorbent has good renewable performance.In the presence of competitive ions such as K⁺,Ca²⁺,Na⁺,Mg²⁺,Al³⁺,Fe³⁺,Mn²⁺in uranium wastewater,MWCNTs–CDP showed an enhanced selectivity for uranium.However,Mn²⁺can also be effectively adsorbed on MWCNTs-CDP.The adsorption rates of uranium in Weak acid uranium wastewater with uranium concentration of 3.56 mg L^-11 and 3.89 mg L^-11 were98.72%and 99.02%,respectively.?2?A functional plant-organic composite adsorpbent was prepared by modifying cinnamomum camphor leaf powder with tributylphosphate?CCL-TBP?for uranium adsorption.The structure and morphology of CCL-TBP were characterized by FTIR,EDS and SEM.Furthermore.The influence of test conditions on the adsorption of uranium by adsorbent was studied.It was indicated that Uranyl ions were adsorbed on the surface of the adsorbent by coordination with phosphoryl groups in CCL-TBP.The experimental results showed that the adsorption rate of uranium was 92.7%under optimum conditions?pH8.3,0.02 g for adsorbent dosage,10?g L^-11 for initial uranium concentration and 60 min for adsorbing time?.The pseudo-second-order kinetic model can better describe the adsorption process,and showed that chemisorption controlled the adsorption.The Freundlich isotherm model was the most suitable for describing the adsorption behavior of uranium,and the result revealed that the adsorption was mainly multi-layer inhomogeneous adsorption.The Gibbs free energy change??G?,enthalpy change??H?and entropy change??S?showed that the adsorption process was spontaneous,feasible and Exothermic.After adsorption-desorption cyclic for five times,the adsorption efficiency was still above 90%,demonstrating that CCL-TBP maintains excellent repeatability.In the presence of competitive ions such as Cl^-,Na⁺,Mg²⁺,Ca²⁺,K⁺,Zn²⁺,Fe³⁺,Ni⁺,Cu²⁺,Mn²⁺,Co⁺,Pb²⁺in simulated seawater?pH8.3?,CCL-TBP showed a good selectivity for uranium.The adsorption rates of uranium on CCL-TBP was 86.87%in simulated seawater with uranium concentration of 3.2?g L^-1.?3?An inorganic composite adsorbent was prepared for the adsorption of uranium using a method of modifying Sago cycas leaf powder with phosphoric acid?SCL-P?.The adsorbent was characterized by FTIR,EDS and SEM for analyzing the surface morphology,chemical structure and functional groups.In the meantime,the effect of test conditions on the adsorption of uranium by adsorbent was studied by batch experiments.It was demonstrated that the uranyl ion combines with the hydroxyl group of the phosphoric acid group to form a complex adsorbed on the surface of the SCL-P.The results showed that The adsorption equilibrium was reached in 240 min at 25?,the initial uranium concentration of 10?g L^-11 and pH8.7.The adsorption process was better in accordance with Freundlich isothermal model with a maximum adsorption capacity for 43.6?g L^-1.The adsorption kinetics was in good agreement with the pseudo-second order model,indicating that chemisorption controlled the adsorption.The 0.08mol L^-11 HNO₃ solution was used as desorbent for the study of reusability of SCL-P,and the desorption rate reaches 92.3%.The adsorption rates of uranium on SCL-P was 79.60%in simulated seawater with uranium concentration of 3.2?g L^-1.?4?An inorganic-organic composite adsorbent?Ti-MPP-TBP?was prepared with titanium tetrachloride,potassium pyrophosphate and ammonium molybdate?Ti-MPP?as raw materials and tributylphosphate?TBP?as modifier.The adsorbent was characterized by FT-IR,SEM and EDS.In addition,the influence of test conditions on the adsorption of uranium by adsorbent was investigated by batch experiments.It was confirmed that the proton hydrogen on the surface of heteropoly acid in Ti-MPP-TBP was exchange with uranyl ion and the coordination compound was formed due to strong affinity of phosphatidyl group to uranyl ion,which can synergistically adsorb uranium.The results showed that the adsorbent had the highest adsorption efficiency for uranium with initial concentration for 10?g L^-1,pH8.5,adsorbent dosage for 0.02 g and adsorption time for 4 h.The pseudo-second-order kinetic model is more suitable for describing the adsorption process,indicating that chemisorption controlled the adsorption.The adsorption process was dominanted Freundlich isotherm model,indicating that the adsorption behavior was multilayer inhomogeneous adsorption.The thermodynamic parameters indicated that the adsorption process was spontaneous and exothermic.The 0.04 mol L^-11 HNO₃ solution was selected as desorbent for the study of reusability of Ti-MPP-TBP,and the desorption rate reached 95.57%.After three times of adsorption-desorption cycles,the adsorption efficiency of uranium is still over 94%.The adsorption rates of uranium on Ti-MPP-TBP was 79.60%in simulated seawater with initial uranium concentration of 3.2?g L^-1.As a result,the MWCNTs-CDP can be potentially utilized as a cost-effective adsorbent for the disposal of uranium-loading wastewater.CCL-TBP,SCL-P and Ti-MPP-TBP have good adsorption effect on very low concentration uranium in alkaline environment,and have potential application value in the field of uranium extraction from seawater.