Effect Of Amide Extractant Structure On Extraction And Separation Performance Of Rare Earth Ions

Rare earth metals are very important strategic resources and have significant application value in various fields.The efficient separation of rare earth is a technical challenge of our times.At present,solvent extraction is commonly used to extract and separate rare earth.The key of solvent extraction is the choice of extraction agent.The design and synthesis of high efficiency and high selectivity extractant is the promise and guarantee of rare earth metallurgy.Compared with phosphoric acid extractant,amide extractant is more environmentally friendly.Moreover,3-oxa-diglycolamide?DGA?extractants are ideal for separation of adjacent lanthanide compounds.DGA type of extractant is a neutral complexation extractant,which does not require acid-base neutralization process during extraction,and basically produces no waste water.Therefore,it is of great ecological significance for rare earth extraction.The structure of the alkyl chain on the N atom has an important effect on the extraction and separation ability of amide extractant.In this paper,the extractants with four different structures,TODGA?N,N,N',N'-tetraoctyl-3-oxa-diglycolamide?,T2EHDGA?N,N,N',N'-tetraisooctyl-3-oxa-diglycolamide?,DPDODGA?N,N'-dipropyl-N,N'-dioctyl-3-oxa-diglycolamide?and DIPDODGA?N,N'-diisopropyl-N,N'-dioctyl-3-oxa-diglycol-amide?were designed and synthesized.The effects of asymmetric alkyl substituents and branch positions on the extraction performance of the extractant were studied.Taking lanthanide ions other than Pm as the research target,the relationship between the structure and properties of the extracted rare earth extracted from nitric acid and hydrochloric acid solution was studied.Firstly,the effects of diluent,temperature,time,acidity,extractant concentration,initial rare earth ion concentration and other factors on the extraction performance of DGA extractant for Nd extraction were studied in the hydrochloric acid system.It can be noted that the extraction process is exothermic,and the enthalpy change decreases with the increase and branching of the alkyl chain on the N atom.After the extraction of Nd rare earth ions by four extractants,the obtained extracted species structure was mononuclear with six coordination,Nd?DGA?2Cl3.In the meantime,extraction properties of four extractants for heavy rare earth were studied in hydrochloric acid medium to understand the relationship between the chemical structure of the extractant and the extraction properties of rare earth metal ions.The extraction order of rare earth in n-octane:n-octanol=9:1 diluent was as follows:DIPDODGA>DPDODGA>TODGA>T2EHDGA.In the extraction of heavy rare earth,the extracts of TODGA,DPDODGA and DIPDODGA were mononuclear extracts,Ln?DGA?3Cl3,and extracts of T2EHDGA were binuclear extracted species,[Ln?DGA?3]?LnCl6?.All the four extraction agents have priority to extract heavy rare earth ions,and the change of the alkyl chain on the N atom has little influence on the separation performance.The separation coefficient shows that these extraction systems can realize the separation of light and light rare earth.Then,in the nitric acid system,the extraction capacity of mixed rare earth was examined by using the above four extractants to understand the relationship between the chemical structure of the extractant and the extraction and separation of rare earth ions.The effects of nitric acid acidity,rare earth metal ion concentration and extractant concentration on the distribution ratio and the extraction rate were also investigated.With the increase and branching of alkyl chains on N atoms,their extraction capacity decreased.The reason why DIPDODGA was abnormal was that,when it was involved in coordination,methyl groups on its branched chain were located on the side far away from the coordination site,so that its branching had no effect on the steric hindrance of the coordination site.All the four extractants show preferential extraction of heavy rare earth ions.Although substituents have a certain impact on the extraction performance of rare earth,they have little influence on the separation performance.Therefore,only the separation of heavy and light rare earth can be made.With the increase of the atomic number,the extraction rate of TODGA,DPDODGA and DIPDODGA increases.In the extraction of Yb by T2EHDGA,the extracted species is the tetra-ligand of monocyte,Yb?DGA?4?NO3?3,and the extraction of monocyte triplicate formed by the other three extractants,Yb?DGA?₃?NO₃?₃.In the extraction of Nd with four extractants,the extracted species was mononuclear with two ligands to train Nd?DGA?₂?NO₃?₃.