Experimental Study On Extraction Of Uranium From Biological Matrix Using Supercritical CO₂ Fluid

The treatment of the radioactive wastewater produced during the mining and milling process of uranium and the surface water and groundwater contaminated by radioactive elements is an important environmental issue.Phytoremediation technology,which is a new type of environmental management technology,has been widely used for the treatment of radioactive pollution.However,after the plants uptake uranium from the uranium contaminated wastewater or soil,these uranium-rich plants are badly needed to be treated.In this study,we used some powerful uranium-tolerant plants to repair the uranium contaminated wastewater,and then extracted uranium from these uranium-containing plants matrix using supercritical carbon dioxide.This study can provide technical basis for the subsequent processing of the plants which are used for decontamination of uranium from wastewater.The main results are as follows:?1?Three kinds of aquatic plants?Du Dou Ping,Huai ye Ping,Man Jiang hong?were cultivated eighteen days with uranium-containing hoggland's nutrient solution to screen out the most effective uranium-rich plants.Then the uranium content of these three plants was determined,it shows that the uranium enrichment capacity of Manjianghong is higher than the other two plants.Therefore,we use the Man Jiang Hong to absorb uranium from the uranium-containing wastewater,and cultivate uranium-rich Man Jiang Hong by batch experiments.The average uranium content of the cultivated Man Jiang Hong is 0.035%.?2?Five kinds of complexing agents?eg.,HNO₃-TBP,DC18C6,TOPO,MEOH,EDTA?were respectively used to carry out the extraction experiment with supercritical carbon dioxide fluid.It indicates that the extraction rate of uranium using HNO3-TBP is the highest under condition of the same temperature and pressure,.?3?The effects of HNO₃/TBP ratio,pressure,temperature and reaction time on the extraction rate of uranium were studied using HNO₃-TBP as complexing agent.The experimental results show that the extraction rate of uranium is 89.54%when the ratio of HNO₃/TBP is 1.2,the pressure is15MPa,the temperature is 50?and the reaction time is 40min.?4?The thermodynamic parameters,such as the free energy,enthalpy change and entropy change of the extraction reaction,were calculated.The results show that the free energy decreases slowly with the increase of temperature and is always less than zero,which means that the reaction is spontaneous and feasible and the increase of temperature can promote the progress of the reaction.The kinetic analysis of the experimental data shows that the extraction reaction is mainly controlled by the diffusion effect.In addition,the kinetic equation of the extraction reaction is established.