The Application Of Biochar In The Sorption Of Radionuclides

With the development of civil nuclear industry,"radioactive contamination" has aroused public attention increasingly.The study on the interface can reveal more about the migration regularity of radionuclides in the environment,so that people can deal with them effectively.As an emerging carbon materials,biochar has shown great potential in the fields of pollution control due to its multiple advantages,such as the wide availability,the low cost and the large sorption capacity.However,its application in environmental radiochemistry is quite limited.In this study,batch experiments were conducted to investigate the sorption behavior of typical radionuclides?such as U-238,Ni-63 and Cu-64?on biochar?montmorillonite@carbon and carbon nanofibers?.Surface complexation models?SCM?were used to reveal the mechanism of surface reactions and advanced spectrum technologies were employed to bring to light the structure of surface species.The main results and conclusions are as follows.1.Sorption of uranium?VI?on montmorillonite@carbon.The sorption of U?VI?on montmorillonite@carbon?MMT@C?,which was made from montmorillonite and glucose,was studied as a function of contact time,ionic strength,pH,initial concentration and temperature.It was found that the sorption reactions are endothermic and the kinetic process can be described by pseudo-second-order equation.PH had significant effect on sorption with a critical value of 6,i.e.sorption increased first and then decreased with the pH increase.The sorption isotherms can be better fitted by Langmuir equation,from which the saturated sorption capacity was calculated to be 66.22 mg·g-1 at room temperature.It was also found that U?VI?existed in the form of inner-sphere complex at the surface,sorption edges and isotherms were independent of ionic strength.XPS results indicated that Si-O-UO₂⁺,Al-O-UO₂⁺ and CO-O-UO₂⁺ might be the main surface species.Besides,MMT@C had considerable cycle stability in the application of uranium-containing waste water.2.Sorption of uranium?VI?on carbon nanofibers.Carbon nanofibers?CNFs?were prepared through "one-pot" method using Te nanowires as templates and glucose as carbon source.It was found that CNFs could well inherit the one-dimensional morphology and three-dimensional network structure of the templates,and the surface was covered with large amount of oxygen-containing functional group which can capture U???from aqueous solution efficiently.DLM results revealed that U?VI?formed inner-sphere complex at the surface of CNFs with ?SOUO₂⁺ and ?XOUO₂⁺ being the main species at low pH value.When it became higher,=XOUO₂OH was the dominate complex while?SOUO₂OH,?SOUO₂?OH?₂^-and ?SOUO₂?OH?₃^2-could appear at even higher pH values.XPS results indicated that electrically neutral complex?i.e.?XOUO₂OH and=SOUO₂OH?and cationic complex(i.e.=SOUO₂⁺ and =XOUO₂⁺were the main species under near neutral condition.XANES and EXAFS results confirmed that the adsorbed uranium is U???which was inner-sphere complex at pH 4.5 and precipitation under near neutral condition.It was also found that CNFs had considerable cycle stability and could accelerate the desorption of U???from montmorillonite.3.Sorption of copper???and nickel???on carbon nano fibers.CNFs had great sorption capacity towards Cu???and Ni???,the sorption isotherms of which can be described by Langmuir equation.When co-existed in the aqueous solution,Cu???and Ni???would be adsorbed simultaneously,while Cu???was more competitive.CCM results revealed that Cu???and Ni???formed inner-sphere complex at the surface of CNFs.Under low pH condition,?SOM+ was the main surface species,which could be confirmed by FT-IR and XPS,while?SOMOH was dominate at higher pH values.At even higher pH values,?SOCu₃?OH?₄⁺ would surpass all the other species of Cu.EXAFS results confirmed that Ni???existed as inner-sphere complex under near neutral condition while formed surface precipitation at higher pH values.To be conclude,we have prepared novel biochar materials in the above three experiments,the law of the interaction between radionuclides and biochar materials was explored,the microstructure of surface complex were studied and the influence of environmental conditions on sorption were obtained.This is the preliminary systematical investigation of biochar as potential effective sorbents in the field of environmental radiochemistry and also is the development of SCM.The results obtained can provide important references for the correlational studies.