Preparation Of Pomelo-modified Biochar And Study On Its Adsorption Behavior Of Strontium

With the rapid development of society,the contradiction between the needs of human production and life and energy demand has become increasingly prominent,and nuclear energy occupies an important strategic position in the energy structure.While the rapid development of nuclear energy brings significant benefits,it will inevitably generate a large amount of radioactive waste,which will pose a serious threat to human survival if it spreads or leaks into the ecological environment.Radioactive strontium ⁹⁰Sr is a beta emitter（E=0.546 e V）that is radioactive and osteophilic,easily soluble in water and coexisting with other ions,and migrates with groundwater and seawater and one of the most concerned fission products in spent fuel reprocessing.From the perspective of environmental protection and human health,efficient and rapid removal of ⁹⁰Sr from nuclear effluent is critical for the healthy,orderly and long-term development of nuclear energy.Meanwhile,biochar as a cost-effective and environmentally friendly adsorbent has attracted high attention in the field of environmental remediation and wastewater treatment,and the conversion of biochar into value-added adsorbent products provides a clean,sustainable and effective way to treat radioactive wastewater.In this study,three carbon-based adsorbents PMBN3,PMP,and PMP6 were prepared from pomelo peels using alkali impregnation,acid oxidation combined with modification and different phosphorus-based modifications for more economical,environmentally friendly,and efficient removal of ⁹⁰Sr from low radioactive waters.The adsorption behavior and interaction mechanism of the three materials on Sr（Ⅱ）were investigated to clarify the effect of interfering elements in the actual adsorption process and to provide technical support for the removal of Sr（Ⅱ）from water by biochar adsorbents.The main conclusions are as follows:（1）PMBN3,PMP,and PMP6 biochar adsorbents were prepared.The surface morphology and elemental composition of the adsorbents were analyzed using SEM-EDS,EA,BET and other characterization methods.All three adsorbents have large specific surface area,excellent mesoporous structure and abundant oxygen-containing functional groups.（2）The effects of pH,temperature,time,competing ions,and initial ion concentration on the adsorption behavior of PMBN3,PMP,and PMP6 were investigated,and the experimental data was fit and analyzed using the typical kinetics,isotherms and thermodynamic models.The results show that p H has a significant impact on PMBN3.When p H<3,its maximum adsorption capacity for Sr（Ⅱ）decreases significantly,while PMP and PMP6 can achieve Sr（Ⅱ）adsorption throughtout the p H range（1-9）.PMBN3 reached adsorption equilibrium at 60 minutes with a maximum adsorption capacity of 21.42 mg/g,and the adsorption behavior was consistent with the pseudo-second-order kinetic model and Freundlich isotherm model,indicating that the adsorption involved multilayer chemisorption.The adsorption reaction of PMP6 on Sr（Ⅱ）reached the adsorption equilibrium in 5 min.The adsorption equilibrium times of PMP and PMBN3 were the same,and their adsorption behaviors were consistent with the pseudo-second-order kinetic model and the Langmuir isotherm model,indicating that the adsorption process was monolayer chemisorption with saturated adsorption capacities of 39.09 mg/g and 60.83 mg/g,respectively.The desorption behavior of PMBN3 was investigated,and it was discovered that 0.1 mol/L HNO₃could effectively desorb Sr（Ⅱ）with a desorption rate of 99%.The adsorption selectivity study showed that Ca（Ⅱ）and Mg（Ⅱ）would significantly interfere with the adsorption of Sr（Ⅱ）by the adsorbent.（3）The interaction mechanism between PMBN3,PMP and PMP6 and Sr（Ⅱ）was explored by XPS and FTIR.It was found that during the adsorption process,the deprotonated oxygen-containing functional groups on the surface of PMBN3exchanged ions with Sr（Ⅱ）,and this reaction mechanism was the main influence in the entire adsorption process,and the weak electrostatic interaction between PMBN3 and Sr（Ⅱ）also had an effect on the adsorption effect.During the reaction of PMP and PMP6 with Sr（Ⅱ）,ion exchange occurs between Sr（Ⅱ）and the hydroxyl,carboxyl and phosphate groups adjacent to the adsorbent surface releasing H⁺into the solution,and there is a weak electrostatic attraction between the negative charge on the adsorbent surface and Sr（Ⅱ）,while the C=O or P=O functional groups provide active sites for the surface complexation of Sr（Ⅱ）.