Study On Electrosorption Behavior Of U(Ⅵ) On Carbon-Based Composite Electrodes

The development of nuclear energy has greatly satisfied people’s demand for energy,but the uranium-containing wastewater produced in the process of nuclear fuel preparation poses a huge threat to the environment and human body.At the same time,the shortage of terrestrial uranium resources makes us turn our attention to the ocean,but the concentration of uranium in seawater is low,it is difficult to separate and utilize it.All these situations require us to develop technologies for the efficient separation of uranium from water.Electrosorption,as a technology based on electric double layer charge and discharge,has been widely studied because of its high efficiency,low cost,easy regeneration,and no secondary pollution.At present,there are few studies on the treatment of uranium by electrosorption,and there is a lack of in-depth research on the mechanism of uranium-related electrosorption.Therefore,this paper takes the separation of uranium in water by electrosorption as the core,and conducts in-depth research on three aspects:high-efficiency electrode preparation,electrosorption mechanism research,and process parameter exploration.The following results are obtained:Using graphite fiber as the electrode matrix,nitrile groups were introduced on the electrode surface by homogeneous coating method,and then amidoxime group-modified graphite fiber（GF@AO）was prepared by heterogeneous reaction.The results of material analysis showed that all the nitrile groups on the fiber surface were converted into amidoxime groups.The specific capacitance of the electrode was 46.5 F·g^-1.The results of electrosorption experiments showed that the electrosorption capacity of uranium was 164.75 mg·g^-1（E=-0.9V,p H=5）.Using sodium bicarbonate as the eluent,under the action of reverse voltage,the single elution efficiency was 95%.After 5 adsorption-elution cycles,the adsorption capacity loss of GF@AO was less than 10%.Polyaniline was directly modified on the surface of graphite fibers by in-situ electropolymerization to obtain polyaniline-modified graphite fibers（GF@PANI）.Scanning electron microscopy results showed that the electropolymerized aniline had a 3D structure,and the specific surface area of the modified graphite fibers increased from 24.23 m²·g^-1 to42.17 m²·g^-1.When p H=4,E=-0.9 V,the maximum electrosorption capacity of the electrode was 187.8 mg·g-1.Using 0.1 mol·L^-1 hydrochloric acid as the eluent,the single resolution efficiency was 95%.After five adsorption-regeneration cycles,the adsorption capacity loss of GF@PANI was less than 20%,indicating that the cyclic regeneration performance of GF@PANI was excellent.Using sucrose as carbon source and urea as nitrogen source,composite nitrogen-doped carbon（GO@NC）was prepared by one-step carbonization with the addition of graphene oxide at different temperatures.The results showed that the doping nitrogen mainly existed in the form of pyridine（N-6）,pyrrolic（N-5）and quaternary-N（N-Q）.The addition of nitrogen atoms and graphene oxide effectively improved the electrochemical performance of the material,with a specific capacitance of 289.8 F·g^-1.Among them,the maximum electrosorption capacity of GO@NC-700 was 879.2 mg·g^-1,which was 4 times that of simple adsorption(202.3 mg·g^-1).After 5 cycles,the adsorption performance of the material can still reach 80%of the initial value.Through the polymerization modification of acrylamide,more nitrogen-containing groups were introduced on the surface of nitrogen-doped carbon,which further improved its adsorption capacity for uranium.PAM/NC-2 had the best electroadsorption performance.The maximum electrosorption capacity of PAM/NC-2 can reach 619.5 mg·g^-1,which was lower than GO@NC-700,but the selectivity to uranium was improved.The adsorbed uranium mainly existed in the form of U（VI）,and a small amount was reduced to U（V）.Efficient desorption was achieved using 0.1 mol·L^-1 HNO₃ as the eluent.After 5 cycles,the adsorption performance of the material can still reach 80%of the initial value.Using a self-made electro-adsorption device,the effects of process parameters on the electrosorption of uranium were explored.In the absence of competing ions,the electrosorption properties of the four electrodes were ranked as follows:GO@NC-700>PAM/NC-2>GF@PANI>GF@AO.Under the influence of competing ions,GF@AO had the smallest loss,PAM/NC-2 was comparable to GF@PANI,and GO@NC-700 had the largest performance loss.Under static adsorption,the flow rate of the solution only affected the adsorption rate and had no significant effect on the removal efficiency.The flow rate had a significant effect on the dynamic experimental results.When the flow rate was 1.0 m L·min^-1,the initial uranium concentration in the effluent was less than 1.0 mg·g^-1 and could be maintained for 20 min.