Theoretical elucidation of rare earth extraction and separation by diglycolamides from crystal structures and DFT simulations

Diglycolamides(DGAs) show excellent application prospects for the extraction and separation of rare earth metals from highly radioactive liquid wastes and rare earth ores.The extraction ability of DGAs for rare earth ions in nitrate or chloride media increases with increasing atomic number of the rare earth metal.To understand the origin of this phenomenon,three binuclear crystals [Ln(TEDGA)_(3)][Ln(NO_(3))_(6)] of N,N,N’,N’-tetraethyldiglycolamide(TEDGA) with rare earth ions La(Ⅲ),Pr(Ⅲ) and Eu(III) were prepared and characterized crystallographically.The three complexes belong to the triclinic crystal system,P-1 space group.The bond lengths of Ln-O_(amide) are significantly shorter than those of Ln-O_(ether) in the same crystal.The Ln-O_(amide) and Ln-O_(enher) bond lengths gradually decrease with increasing atomic number of the rare earth ion.The dihedral angle formed by TEDGA and metal ions through the tridentate coordination gradually increases with increasing metal ion atomic number,tending toward the formation of sizeable planar coordination structures for the most massive rare earth ions.The structures of the compounds formed by the extractant and metal ion were optimized by means of DFT simulations.We find that the interaction between TEDGA and the rare earth ion is dominated by electrostatic interaction by analyzing binding energy,WBIs,Mulliken charge,natural electron configurations,and molecular orbital interaction.The covalent component of the Ln-O bonds of the complexes increases with increasing metal atomic number.The observed increase in extraction and separation capacity of diglycolamides for rare earth ions with increasing atomic number might be due to the formation of two fivemember rings by one tridentate ligand.The rare earth ions with large atomic numbers tend to form planar structures with large dihedral angles with DGA ligands.

Adsorption of Er(Ⅲ ) and Its Mechanism on Diglycolamidic Acid Resin

The adsorption behavior and mechanism of a novel chelate resin, diglycolamidic acid resin (DAAR) for Er(Ⅲ) were investigated. The optima adsorption condition of DAAR for Er(Ⅲ) is pH 6.20 in HAc NaAc medium. The statically saturated adsorption capacity is 189 mg·g -1 resin at 298 K. The Er (Ⅲ) adsorbed on DAAR can be eluted reaching 100% by 2 mol·L -1 HCl used as eluant. The resin can be regenerated and reused without apparent decreasing of adsorption capacity. The apparent adsorption rate constant is k 298 =1.94×10 -5 s -1 . The apparent activation energy is 24.7 kJ·mol -1 . The adsorption behavior of DAAR for Er(Ⅲ) obeys the Freundlich isotherm. The thermodynamic adsorption parameters, enthalpy change Δ H of DAAR for Er(Ⅲ) is 24.1 kJ·mol -1 . The molar coordination ratio of the functional group of DAAR to Er (Ⅲ) is 3∶1. The adsorption mechanism of DAAR for Er (Ⅲ) was examined by using chemical method and IR spectrometry. The coordination compound is formed between oxygen atoms in the functional group of DAAR and Er(Ⅲ).

ADSORPTION OF SAMARIUM(III) ON DIGLYCOLAMIDIC ACID RESIN

The sorption behavior and mechanism of a novel chelate resin, diglycolamidic acid resin (DAAR), for Sm(III) were investigated. The optimal sorption condition of DAAR for Sm(III) is pH=6.0 in HAc-NaAc medium. The statically saturated sorption capacity is 190mg/g resin at 298K. The Sm(III) adsorbed on DAAR can be eluted reaching 100% by 0.5~2.0mol/L HCl used as eluant. The resin can be regenerated and reused without apparent decrease of sorption capacity. The apparent sorption rate constant is k298= 1.96×10-5s-1. The apparent activation energy is 26kJ/mol. The sorption behavior of DAAR for Sm(III) obeys the Freundlich isotherm. The thermodynamic sorption parameters, enthalpy change 腍 of DAAR for Sm(III) is 16.9kJ/mol. The molar coordination ratio of the functional group of DAAR to Sm (III) is 3. The sorption mechanism of DAAR for Sm(III) was examined by using chemical method and IR spectrometry. The coordination bond was formed between oxygen atoms in the functional group of DAAR and Sm(III).

Extraction and separation of Nd(Ⅲ), Sm(Ⅲ), Dy(Ⅲ), Fe(Ⅲ), Ni(Ⅱ), and Cs(Ⅰ) from concentrated chloride solutions with N,N,N',N'-tetra(2-ethylhexyl) diglycolamide as new extractant

The feasibility of using N,N,N＇,N＇-tetra（2-ethylhexyl）diglycolamide （TEHDGA） in 75 vol.% n-dodecane-25 vol.% n-octanol as agents for the extraction and separation ofNd（III）, Sm（III）, Dy（llI）, Fe（III）, Ni（II）, and Cs（I） from concentrated chlo- ride solution was investigated. Different extraction behaviors were obtained towards rare earth elements （REE） studied and Fe（IIl）, Ni（II） and Cs（I）. Efficient separation of Nd（III）, Sm（III） and Dy（III） from Fe（III）, Ni（II）, and Cs（I） was achieved by TEHDGA, depending on the HCI, HNO3 or H2SO4 concentration. A systematic investigation was carried out on the detailed extraction prop- erties of Nd（III）, Sm（III）, and Dy（III） with TEHDGA from chloride media. The IR spectra of the extracted species were investi- gated.

New’Non-phosphorous’and Efficient Diglycolamide-acid Based Extraction Systems

In this paper,we briefly reviewed the new non-phosphorous extraction systems proposed according to the different applicational ends.These systems were established by choosing the suitably modified chemical group and the corresponding substrate with unique chemical/physical properties.The guiding principle for the foundation of these new systems was to combine the advantages of the substrate and functions of the modified chemical group,majorly the diglycolamide-acid.The induced physical/chemical properties of the substrate and the functions of modified moieties had the potential to import unique traits to the as-founded adsorbent,establishing a task-tailored bi-/multi-functional system.We believe the new systems had the potential to create new adsorption/desorption extraction/bask-extraction paradigms to improve the selectivity and capacity of the extraction/adsorption process,as well as to be more time-efficient and environmentally friendly.