Synthesis,characterization And Extractive Performance For U(?)and Th(?)of Dialkyl Imides

TBP has been widely applied in the spent fuel reprocessing technology as well as some rare earth element hydrometallurgy process,and achieved good extraction effect.TBP as a kind of excellent extraction agent,but this kind of extraction agent still has many problems.Amides extraction agent,for its synthesis is simple,irradiation resistance,not easy to hydrolysis,degradation products shall not affect the extraction process,complete combustion and the advantages of solid product residue may provides a possible to replace TBP and it has aroused people's great interest.Based on the fatty acids as raw materials reacted with acyl chlorination reagent sulfoxide chloride,a series of intermediates-acyl chloride were prepared.At low temperature,ammonia was acylated by acyl chloride to be another intermediate-fat amide.A series of dialkyl imide extractants with symmetrical structure were preparated from these two kinds of intermediates which have same carbon chain length by N-acylation.Those fat amides and dialkyl imides were characterized by elemental analysis,FT-IR,UV,¹H NMR and HPLC-MS.We studied the extractive behavior for U???and Th???in nitric acid medium of dialkyl imide extractants and mainly studied the oscillation time,temperature,extractant concentration,nitric acid concentration,kinds of dilute solvents and carbon chain length of extracting agent on the influence of extraction,and then confirmed the optimum extraction conditions.The mechanism of dialkyl imide extracting U???and Th???from nitric acid was explored preliminary by slope method.In addition,we investigated the reextraction behavior of these two kinds of metal ions.The study found that:?1?The extraction capacity of dialkyl imides in different diluents follows the sequence:carbon tetrachloride>chloroform>toluene>kerosene.Considering the disadvantages of the carbon tetrachloride,chloroform is a better dilution solvent.In addition,the distribution ratio wasn't impacted for U???with the change of carbon chain length of these extractants,the maximum ration could reach to 7.However,the long carbon chain is unfavorable to the extraction for Th???,the maximum ration could reach to 0.6.?2?With the increasing of nitric acid concentration,the extraction for U???and Th???were presented increases at first and then decreases,it could be due to the cooperation between the salting-out effect and extractive competition of nitric acid.But at the extremely low acidity,the extraction for UO₂²⁺showed abnormal phenomenon.It may be because quite a number of uranyl ions were hydrolyzed to be precipitation that leading to the calculation of distribution ratio increases.At the low acidity,the reextraction rate for U???and Th???can reach more than 50%,but at the same acidity,the reextraction rate for Th⁴⁺is higher than UO₂²⁺.?3?The extraction of dialkyl imides for U???and Th???are exothermic reaction.Low temperature is beneficial to the extraction of metal ions.The various thermodynamic functions of extraction for U???were?H_U???=-29.2 KJ·mol^-1,and?H_Th???=-16.49KJ·mol^-1.?4?Slope method experiment preliminary showed that the dialkyl imide associated with UO₂²⁺mainly at 1 to 1 ratio and formed a bidentate ligand.But the complex-ratio of Th⁴⁺was 1.7:1,the coordination was relatively complex.It is not explicit and needs further research that the specific way of coordination between Th⁴⁺and dialkyl imide.