The Study Of Extraction And Separation Of UO₂²⁺ And Th⁴⁺ By N,N-di（2-Ethylhexyl）-2,2,3,3,4,4,4-Heptafluorobutanamide

The solvent extraction method is one of the important techniques in concentrating and purifying uranium（VI）.The research and processing of new extractant are two important aspects of solvent extraction technology.In this paper,N,N-di（2-ethylhexyl）-2,2,3,3,4,4,4-heptafluorobutan-amide（DEHFBA）was prepared and evaluated by the extraction and separation of U（VI）and Th（IV）.The results indicated that DEHFBA exhibited high extraction efficiency and distribution ratios of U（VI）and Th（IV）in nitric acid media.And the extraction of U（VI）and Th（IV）by using natural plant tea residue as an adsorbent was also investigated.The main contents are as follows:1)In this work,N,N-di（2-ethylhexyl）-2,2,3,3,4,4,4-heptafluorobutanamide（DEHFBA）was synthesized and identified by ¹H NMR,¹⁹F NMR and IR spectroscopy2)The effects of diluents,extractants,metal ions and nitric acid acidity on the extraction distribution ratios of uranium extraction and extraction rate have been explored.DEHFBA shows much better irradiation stability and extraction performance for UO₂²⁺from nitric acid media at low acidity than N,N-di（2-ethylhexyl）butanamide（DEHBA）and tributylphosphate（TBP）.DEHFBA can extract U（VI）in some extent,but has a poor extraction ability for Th（IV）.3)The extraction mechanism of DEHFBA extraction performance for U（VI）and Th（IV）is discussed.The extractant compounds might consist of UO₂（NO₃）₂·DEHFBA for U（VI）and Th（NO₃）₄·DEHFBA for Th（IV）.4)The irradiation stability of two uranium extractants,DEHBA and DEHFBA,and the effect of irradiation on the extraction efficiency of both extractants were studied.The extraction behavior of uranium（VI）by DEHBA and DEHFBA in nitric acid medium with benzene as solvent before and after irradiation was studied.The effects of extraction concentration,metal ion concentration,metal ion solution acidity and extraction temperature on the distribution ratio of uranium（VI）were also studied.The results show that DEHFBA showed better irradiation stability than DEHBA and was less sensitive to the change of extraction conditions.5)The separation of U（VI）and Th（IV）from DEHFBA in nitric acid medium was studied by using the principle of cascade experiments.It is concluded that when the trace Th in a large amount of UO₂²⁺is reached and the ratio is 19:1,it can be well separated.When a trace of UO₂²⁺is found in a large number of Th（IV）and the ratio is 9:1,a good separation can be achieved.6)The adsorption stability of two kinds of uranium adsorbents,black tea residue and green tea residue,was studied.The effects of adsorbent concentration,adsorption time,uranium ion concentration,uranium ion solution acidity and adsorption temperature on the adsorption behavior of U（VI）by red and green tea residue in nitric acid medium were studied.The adsorption models of U（VI）on red and green tea were analyzed.The Freundlich isothermal adsorption model can better describe the adsorption behavior of U（VI）on black tea residue and green tea residue.