Extraction Behavior Of Several Lanthanides From Nitric Acid With DMDODGA In [C₄mim][NTf₂] Ionic Liquid

the high-level liquid waste（HLLW）issuing from reprocessing contains residual U,Pu,minor actinides and long-life fission products.The separation and transmutation technology can reduce the large volume of HLLW,and can also reduce the geological disposal burden and long-term risk of high-level waste liquid.Separation is the key technology,and the amides pod-ether compounds is one of the representative extractants proposed internationally for the separation of lanthanides in HLLW.The asymmetric amide pod-ether developed on this basis compensates for the steric hindrance caused by the long carbon chain in the symmetric pod ether,and also reduces the water solubility caused by the short carbon chain,and has better extraction performance.In recent years,room temperature ionic liquid（IL）has been widely studied as an alternative to aliphatic hydrocarbon diluent,which has the characteristics of non-toxic,stable physical and chemical properties,and can greatly improve the distribution ratio of extraction.In this research,an asymmetric amide pod-ether N,N’-dimethyl-N,N’-dioctyl-3-oxadiglycolamide（DMDODGA）was used as the extractant,and the ionic liquid 1-butyl-3-methylimidazolium bistrifluoromethysulfonyl imide（[C4min][NTf2]）was as a diluent.The extraction performance and extraction mechanism of HNO3 and five lanthanides:La（III）,Nd（III）,Sm（III）,Gd（III）and Yb（III）from HNO3 medium was studied.The effects of temperature;H⁺concentration,NO3^-concentration,nitric acid concentration in aqueous phase,as well as extractant concentration on the extraction performance were analyzed.The structural changes before and after extraction of the organic phase were analyzed at the same time.The results show:For the five lanthanides studied,the distribution ratio decreased with the H⁺concentration,NO3^-concentration and nitric acid concentration increased in aqueous phase.In addition,as the concentration of the extractant increases,the distribution ratio increases linearly.Under the same experimental conditions,the extraction performance is inversely proportional to the ionic radius of the lanthanide.This solvent system exhibits better extraction properties for the heavy lanthanide（Yb）than the light lanthanide（La）.On the other hand,compared with the traditional alkane diluent solvent system,the ionic liquid solvent system exhibits superior extraction performance,and the former system belongs to the neutral complex extraction mechanism,well the latter system belongs to the cation exchange extraction mechanism.The expression of the complex was calculated by slope method as9)（1）₂)₃·（）_（34）.The IR spectra of the organic phase before and after extraction were compared.It can be seen that Ln³⁺was coordinated with two C=O bonds in DMDODGA.For all metal ions studied,the extraction ratio of the extraction reaction always decreases with an increase in temperature,the reaction can be judged to be an exothermic reaction.In the aqueous phase with a nitric acid concentration of 3M,the extraction experiment of neodymium was calculated,and the enthalphy was-868.082J/mol,and the entropy was 17.085 J/（mol·K）.