Adsorption Of U(Ⅵ) In Wastewater By Environmental Protection Activated Carbon

Along with the development of nuclear technology, more and more uranium-bearing radioactive wastes and effluents are generated by nuclear industry and the corresponding hazard becomes more and more serious. In order to reduce such hazard, these wastes and effluents shall be preprocessed to meet relevant emission standard as required by the country. Therefore, people pay more and more attention to reliable and economic uranium removal methods.In recent years, in order to respond to the national environmental protection policy, many agricultural residues（such as barks, roots and straws） have been well utilized and processed into briquettes fuels（such as sticks, environment-friendly carbons, particles and briquettes）. The activated carbon used in this experiment is the environmental protection activated carbon obtained through processing the agricultural residues. Chemical modification of environmental protection activated carbon can change the surface area, pore density and pore size distribution, it aslo can change the type and amount of oxygen functional groups on the surface active sites, thus to improve the adsorption efficiency and the adsorption capacity. In this study, three different concentrations（0.005mol/L, 0.01mol/L, 0.02mol/L） of the oxidant（KMnO₄, H₂O₂, HNO₃） were used to modify the environmental protection activated carbon, and the best method was selected. Through the adsorption experiment, it is concluded that the 0.01mol/L KMnO₄ modified activated carbon has the best effect on the removal of uranium.We investigated the effects of dosage, initial solution p H, adsorption time, initial concentration, temperature and other factors on uranium removal rate.Removal mechanism is studied by these characterization methods, such as BET, Boehm, SEM, XRD, FITR, etc. Thermodynamic model and kinetic model are used to fit removal process and study the removal characteristics, adsorption mechanism was analyzed by data fitting.The results show that the environmental protection activated carbon can be modified effectively by 0.01mol/L KMnO₄ and when the dosage of absorbent is 0.3g/L, the original U（VI） concentration is 10 mg/L, the wastewater p H value is 6, the absorbing time is 120 minutes, the removal rate of U（VI） could be higher than 97.61%, the adsoption capacity could reach 32.54mg/g. The removal process of U（VI） by using modified environmental protection activated carbon can be well described by pseudo-second-order model and also fits to Langmuir isotherm equation.Thermodynamic analysis showed that the adsorption was spontaneous exothermic reaction. With SEM,XRD and determination of oxygen functional groups on surface to analyzed the environmental protection activated carbon before and after modification, the analysis showed that the chemical adsorption capacity of the adsorbent was enhanced with the increase of the oxygen containing functional groups, and the adsorption capacity of the adsorbent was obviously improved.