Study On The Extraction And Separation Of Rare Earth Ions With New Unsymmetrical Diglycolamides

The rare earth elements have an important position in the exploration and preparation ofnew functional materials due to their electronic configuration and changeable radius of atomand ion. Therefore, the pure and simple rare earth compounds are necessary. Solventextraction has been the main means in partition and purification of rare earth elements due toits fast reaction rate and good separation effects.Although tetrabutyl phosphate （TBP） has been used widely,3-oxy-diglycolamides wereselected as promising extractants in this research project because they are widely used innuclear fuel reprocessing. The products of radiolytic and hydrolytic degradation of amides areless detrimental to the extraction and separation processes than those of organic phosphorusextractants. The amide ligands are completely incinerable, which implies that the secondarywastes generated in nuclear waste treatment could be significantly reduced. Besides,3-oxy-diglycolamides show higher extractability than amides due to the soft ether oxygenatom. In this paper，three new unsymmetrical diglycolamides have been synthesized, and theextraction behaviors have been studied in detail, which were concluded as follows:（1） Three new unsymmetrical diglycolamides were synthesized:N,N’-dibutyl-N,N’-dioctyl-3-oxa-diglycolamide（DBDODGA）, N,N’-dibutyl-N,N’-di（1-methylheptyl）-3-oxa-diglycolamide（DBD1MHDGA）, N,N’-dibutyl-N,N’-di （2-ethylhexyl）-3-oxa-diglycolamide（DBD2EHDGA）, and characterized by High PerformanceLiquid Chromatography（HPLC）, infrared spectrum, nuclear magnetic resonance（NMR）, et al.（2） The extraction behaviors and mechanism of rare earth elements withN,N’-dibutyl-N,N’-dioctyl-3-oxa-diglycolamide （DBDODGA） from hydrochloride acid andnitric acid system using kerosene-octanol（V:V=7:3） as diluent were studied, respectively. Andthe distribution ratio have been studied as a function of aqueous HCl （HNO3） concentration,DBDODGA concentration and temperature. The extracted species were characterized byinfrared spectrum and confirmed to be MCl₃·2DBDODGA （M=Nd,Sm,Gd,Er）、MCl₃·3DBDODGA （M=Dy,Yb） in hydrochloric acid solutions andM（NO₃）₃·3DBDODGA（M=Nd,Sm,Gd,Dy,Er,Yb） in nitric acid. The extraction mechanismscan be established as: three diglycolamide molecules were coordinated to one rare earth ion in nitric acid system.（3） The results of extraction experiments with DBD1MHDGA suggest that: thedistribution ratio of RE（III） ions increase with the increase in HCl （HNO3） concentration,DBD1MHDGA concentration and atomic number in lower hydrochloric acid （nitric acid）.The distribution ratios decrease with the increase in the temperature，which demonstrates theextraction reactions are exothermic. Low reaction temperature is in favor of the extractionprocess.（4） The extraction performance of RE（III） with DBD2EHDGA from HCl （HNO3） havebeen investigatied. The extracted species were confirmed to be MCl₃·2DBD2EHDGA（M=Nd,Sm,Gd,Dy,Er,Yb） in HCl system and Nd（NO3）3·2DBD2EHDGA,M（NO₃）₃·3DBD2EHDGA （M=Sm，Gd，Dy，Er，Yb） in HNO3solution. The infrared spectrumcharacterizations of extracted species indicate that the carbonyl oxygen and ether oxygen ofextractants are all coordinated with rare earth ion; in other words, DBD2EHDGA is tridentateligand.（5） The extraction ability of Sm（III） with DBDODGA in different diluents fromhydrochloric acid were studied. The order of extraction ability of Sm（III） in different diluentsis: kerosene-octanol（V:V=7:3）﹥CHCl₃～Toluene. The low extraction ability in CHCl₃andtoluene indicates that both are not suitable as diluents for DBDODGA to extract rare earthions from hydrochloric acid.（6） The selection of the substituents on the nitrogen atoms in diglycolamides is veryimportant for facilitating metal-ion coordination. And the structure-extractability relationshipwas studied in this paper. The extraction ability increase in the order: N,N’-dibutyl-N,N’-di（2-ethylhexyl）-3-oxa-diglycolamide﹤N,N’-dibutyl-N,N’-dioctyl-3-oxa-diglycolamide﹤N,N’-dibutyl-N,N’-di（1-methylheptyl）-3-oxa-diglycolamide（DBD1MHDGA）.