Preparation Of Chitosan-based Composites And Their U(?) Adsorption Properties

The radioactive pollution brought about by the rapid development of the nuclear industry has great harm to the environment and human body.Efficient separation of uranium from radioactive liquid waste can both effectively recover uranium resources and reduce environmental pollution.Utilizing adsorption technology to separate and enrich uranium has the advantages of simplicity,high efficiency,and easy industrialization.Chitosan is the second largest natural polymer and has biodegradability and environmental friendliness.Its molecular structure contains a large number of amino and hydroxyl adsorption sites,and can form a stable complex structure with uranyl ions.Therefore,it is a uranium separation.Good adsorbent.However,there are still some defects in the adsorption of uranium on chitosan-based adsorbents,which limits their practical application.One is that chitosan is easy to dissolve in acidic medium,and its mechanical strength and chemical stability are poor.Second,chitosan has low porosity,which is not conducive to the rapid adsorption of adsorbent into the adsorbent;the third is the adsorption capacity of uranium by chitosan itself.Low adsorption selectivity.Based on this,the chemical stability,mechanical strength and uranium separation performance of the chitosan-based adsorbent were improved by using chitosan cross-linking,compounding,and modification methods.We have specifically done the following three aspects of research work:Firstly,the carboxymethyl chitosan nanoparticles were modified by amination and carboxymethylation,and amino and carboxyl functional groups with good affinity for uranyl ions were introduced to increase the uranium adsorption capacity and adsorption selectivity.Due to the small particle size of the magnetic nanoparticles,the internal diffusion resistance is reduced,thereby accelerating the adsorption rate,and is easily separated by using an external magnetic field.Adsorption U?VI?experimental results show that EDA-MCCS can quickly adsorb U?VI?,the adsorption equilibrium time is 40min,and the adsorption kinetics conforms to the pseudo-second model.The adsorption isotherm conformed to the Langmuir equation and the maximum adsorption capacity was 175.4 mg/g.The adsorption of U?VI?by EDA-MCCS is a self-distribution thermal process,and 0.20 M EDTA-0.10 M HNO₃ can effectively regenerate EDA-MCCS.Secondly,the use of chitosan and carbon nanotubes composites to prepare magnetic chitosan/carbon nanotube composite beads,one is to improve the dispersion of carbon nanotubes,the second is to improve the mechanical strength and performance of chitosan-based adsorbent,while Use magnetic to facilitate the separation of the adsorbent.The separation performance of U?VI?on magnetic chitosan/carbon nanotubes was investigated.The results showed that the magnetic chitosan/carbon nanotubes had good separation effect on U?VI?.The adsorption kinetics was in line with the pseudo-two-level model,indicating that the chemical adsorption was the main and the adsorption isotherm was in line with the Langmiur model,indicating that monolayer adsorption was the main mechanism.Adsorption efficiency was best when the chitosan content was 3%.The maximum adsorption capacity was 109.47 mg/g at pH 5.5 and 298 K.Calculation of thermodynamic parameters showed that the adsorption was an endothermic spontaneous process.Finally,the chitosan/Ni?OH?₂ composite adsorbent?CSNi?was prepared by the composite of chitosan and in-situ nano-sized Ni?OH?₂,and the adsorption mechanism was initially explained.Adsorption experiment results show that the adsorption performance of CSNi on U?VI?is closely related to its composition.The adsorption effect of CSNi30?Ni?OH?₂ content 30%?is the best,the adsorption capacity is up to 164.2 mg/g,and the inner layer complexation is the main factor.mechanism.U?VI?adsorption is a spontaneous endothermic process with chemo-adsorption as the rate-control step.The above results show that the adsorption rate of magnetic carboxymethyl chitosan nanoparticles is the fastest among the three different types of chitosan-based adsorbents.The adsorption capacity of U?VI?for the three are 175.4 mg/g,109.47 mg/g and 164.2 mg/g respectively.The overall difference is not large,but they all can effectively adsorb uranium from the water,which is expected to be used for the treatment of waste water containing uranium.