| A large amount of cesium-containing radioactive wastewater has been produced in the nuclear industry,which poses a serious potential threat to the ecological environment and human health.Finding efficient adsorbents is the key in the adsorption treatment of cesium-containing radioactive wastewater.A new method of grafting β-cyclodextrin and graphene oxide onto bentonite to modify bentonite was proposed in this study.Two kinds of polymer-grafted bentonites were prepared,and the mechanisms of Cs+ adsorption onto polymer-grafted bentonites was discussed.The main research results are as follows:The composite adsorbent β-CD/BNC was prepared by grafting β-cyclodextrin with Ca-bentonite,using ammonium persulfate and sodium bisulfite as initiator and epichlorohydrin as crosslinking agent.The morphology and properties of β-CD/BNC were characterized by means of modern analysis such as surface area analyzer,SEM-EDS,SEM,EDS,FTIR and TG-DSC.The influencing factors and mechanisms of Cs+ adsorption onto β-CD/BNC were discussed.The experimental results showed that Cs+ adsorption onto β-CD/BNC basically reached the adsorption equilibrium in 30 min.The adsorption capacity and efficiency of β-CD/BNC for Cs+ increased with the increase of p H value.The adsorption efficiency of Cs+onto β-CD/BNC was positively correlated with β-CD/BNC dosage,and the adsorption capacity decreased with the increase of β-CD/BNC dosage.Adsorption kinetic of Cs+ by β-CD/BNC was fitted with pseudo-second-order.The equilibrium data fit Freundlich isotherm satisfactorily.When p H value was 7 and temperature was 303 K,the theoretical maximum adsorption capacity of β-CD/BNC for Cs+was 48.83 mg·g-1,which is higher than that of Ca-bentonite at 32.37 mg·g-1.After 5 times of adsorption and desorption,the adsorption efficiency of β-CD/BNC for Cs+ was 93.04%.The results of SEM-EDS,FTIR and XPS showed that the adsorption mechanism of β-CD/BNC was mainly ion exchange reaction,followed by surface coordination reaction.The effects of coexisting cations(K+,Na+,Ca2+,and Mg2+)on Cs+ adsorption by β-CD/BNC were investigated.A single cation had an inhibitory effect on the Cs+ adsorption by β-CD/BNC,respectively,and the effects of Ca2+and Mg2+ on the Cs+ adsorption were greater than K+ and Na+.The two binary cations had an inhibitory effect on Cs+ adsorption by β-CD/BNC.The combination of Na+ and K+ had a relatively small impact.Three and four combination cations had a greater inhibitory effect on the adsorption process.Single coexisting anions(Cl-,F-,CO32-,SO42-)had little effect on the adsorption of Cs+ by β-CD/BNC.The two to four combination of coexisting anions had an inhibitory effect on Cs+ adsorption.The experimental results of the effect of CO32-,Cl-,Na+ and Mg2+ on the Cs+ adsorption by β-CD/BNC showed that the adsorption process was in accordance with the pseudo-second-order kinetic model and the Freundlich isothermal adsorption model when co-existing ions existed.When there were no co-existing ions,the theoretical maximum adsorption capacity of β-CD/BNC for Cs was 48.83mg·g-1.The theoretical maximum adsorption capacities for Cs+ by β-CD/BNC in presence of CO32-,Cl-,Na+ and Mg2+ were 48.90 mg·g-1(Cs++CO32-),46.19 mg·g-1(Cs++Cl-),47.30 mg·g-1(Cs++Na+)and 42.52(Cs++Mg2+)mg·g-1,respectively.Effect of Mg2+ on Cs+ adsorption by β-CD/BNC was relatively larger.EDS and FTIR results showed the effect of Mg2+ on the Cs+ adsorption mainly inhibited ion exchange adsorption between Cs+ and β-CD/BNC rather than compete with Cs+ for the functional groups of β-CD/BNC.Thermodynamic parameters indicated the negative ΔG and positive ΔH at different temperatures,which confirmed that the adsorption processes of Cs+ onto β-CD/BNC were spontaneous and endothermic nature.The composite adsorbent GO/BNC was prepared by grafting graphene oxide with Na-bentonite.The influencing factors and mechanisms of Cs+ adsorption onto GO/BNC were studied.The adsorption efficiency of Cs+ by GO/BNC increased with the increase of GO/BNC dosage,and adsorption capacity decreased with the increase of GO/BNC dosage.The adsorption capacity and efficiency of Cs by GO/BNC increased with the increase of p H value.The adsorption of Cs+ by GO/BNC was fitted with the pseudo-second-order kinetic and the Langmiur isothermal adsorption model.When p H value was 7 and temperature was 303 K,the theoretical maximum adsorption capacity of GO/BNC for Cs+was 73.31mg·g-1.After 5 times of adsorption and desorption,the adsorption efficiency of GO/BNC was 90.13%.Microanalysis showed that hydroxyl group and carbonyl group were the main adsorption functional groups in the adsorption process of Cs+ by GO/BNC.Aluminum participated in adsorption as the lost electron side in the process of adsorption of Cs+,while silicon atom basically did not participate in the coordination. |
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