Study On The Extraction Of Lanthanides With Diamide Extractants

Lanthanides are important non-ferrous metals. They have an important value in the new material explotation and the preparation of ultrapure materials. Solvent extraction has been the primary means to separate and purify rare-earth due to the fast reaction rate and the good separation effect. One of the aim of nuclear fuel reprocessing is to change the long-lived actinides into short-lived isotope by neutronirradiation. However, the lanthanides can capture neutrons. So we should separate trivalent actinides from lanthanides in the liquid wastes by solvent extraction.The development of novel extractants and the design of extraction process are important. Therefore, exploring novel extractants and suitable extraction condition have important significance on extraction chemistry. Diamide extractants have high affinity toward actinides and lanthanides. However, the corresponding extraction chemistry and the separation behavior are not considered comprehensively. In this paper, five kinds of diamide extractants have been synthesized, and the extraction capacity has been studied in detail. The main results are concluded as follows:(1) Five kinds of diamide extractants have been synthesized: N,N,N',N'-tetrabutylmalonamide (TBMA) , N,N,N',N'-Tetrabutyl-3-oxa-diglycolamide (TBDGA), N,N,N',N'-tetraethyl-3-oxa-diglycolamide(TEDGA) , N,N'-dimethyl-N,N'- diphenyl-3-oxa-diglycolamide (DMDPhDGA), N,N'-dimethyl-N,N'-didecyl-3-oxa- diglycolamide (DMDDDGA), and characterized by infrared spectrum, elemental analysis and nuclear magnetic resonance.(2) The extraction of nitric acid shows that it primarily forms 1:1 adduct between extractant and nitric acid molecules at lower acid concentration.(3) The extraction performance and mechanism of lanthanides with TBDGA, DMDPhDGA, DMDDDGA from nitric acid solution have been studied. The influence of the concentration of nitric acid, extractant and the temperature on the extraction distribution ratio have been investigated. The extraction mechanisms are established as: one lanthanide ion coordinates with three extractant molecules, however, for Dy(III) ion there are four extractant molecules, in chloroform diluents. The structures of complexes Ln(NO3)3·3TBDGA were studied by means of IR and conductivity firstly, which proved that the complexes are ionic compounds.(4) The distribution ratio of Ln(III) ions increases with the increase in the concentration of nitric acid, extractants and atomic number in lower nitric acid. The distribution ratio decreases with the increase in the temperature and the extraction reactions are exothermic. The equilibrium constant and thermal physical constant have been calculated. The IR spectra results of the extracted species indicate that the carbonyl oxygen of extractants are coordinated with Ln(III) ions.(5) The extraction performance and mechanism of Ln(III) with TBDGA and DMDDDGA in different diluents from nitric acid solution were studied. The order of extraction ability of Gd(III) ions with TBDGA in various diluents is as follows: Xylene>CCl4>Toluene>CHCl3. The stoichiometry of the extraction species is Gd(NO3)3·TBDGA. The extraction efficiency of Gd(III), Dy(III) with DMDDDGA decrease in the order: CCl4>Toluene>Benzene>CHCl3. The stoichiometry of the extraction species are Gd(NO3)3·3DMDDDGA and Dy(NO3)3·4DMDDDGA. The extraction efficiency and extraction mechanism are affected by diluents.(6) Synergistic extraction of Yb(III) in different extraction conditions using mixture of TBMA and CA-12, TBMA and P204, TBMA and TOPO was studied. The results indicated that there are no synergistic effect.(7) The crystal structures of La2(NO3)6·3TEDGA,Pr2(NO3)6·3TEDGA have been determined by X–ray diffraction. They are all triclinic and P1 space group. In each molecule three tridentate TEDGA coordinate with one lanthanide and six bidentate nitrate ions coordinate with the other lanthanide.