Complex formation of light and heavy lanthanides with DGA and DOODA, and its application to mutual separation in DGA–DOODA extraction system

Abstract

We studied the stepwise formation constants (β) of water-soluble diglycolamide (DGA) and dioxaoctanediamide (DOODA) for the mutual separation of Ln in a solvent extraction system. TODGA (N,N,N',N'-tetraoctyl-diglycolamide) and DOODA(C8) (N,N,N',N'tetraoctyl-dioxaoctanediamide) exhibit opposite behaviors in extracting both light and heavy Ln through Ln-patterns. Metal complexes of two-and three-folding with watersoluble DOODA and DGA, respectively, were found, and each β value was calculated using distribution ratios. Taking β, their distribution ratio, D, and separation factor, SF, values into consideration, the suitable separation conditions (aqueous phase: 30 mM DOODA(C2) in 1 M HNO3; organic phase: 0.1 M TODGA in n-dodecane

Size Selective Ligand Tug of War Strategy to Separate Rare Earth Elements

“…This system offers a potential strategy to separate radioactive Pm from Sm and Nd. The combination of 2 and 1 outperforms the TODGA–DOODA(C2) 26 and TDdDGA–DOODA(C2) 27 systems and results in 20 and nearly 2 times higher selectivity for Gd over La, respectively ( Table 1 ). Increased concentration of 1 (25 mM) results in minimal change separating Lns ( Table 1 ), suggesting that the system is at its limit and 1 no longer can or has the ability to outcompete DGA in complexing heavier Lns.…”

“…The tandem use of hydrophilic and lipophilic ligands to separate REEs has been rarely investigated, − despite being a common strategy employed to study separation of 4f and 5f elements. − Such hydrophilic ligands, also known as holdback agents or aqueous complexants, include polyaminocarboxylates, − α-hydroxy acids, diglycolamides (DGAs), , and pyridine-based substrates, − among others. In general, ligands with donor groups connected to freely rotating single bonds that can achieve high complementarity with metal ions (e.g., DGAs) exhibit high affinities for lanthanides that are more Lewis acidic. − A combination of lipophilic DGA with hydrophilic dioxaoctanediamide results in improved selectivity for Gd over La (SF Gd/La = 100 or 1130 based on the size of N-alkyl substituents on DGAs). , This improvement is driven by dioxaoctanediamide exhibiting opposite selectivity to that of DGA, but is limited due to dioxaoctanediamide being a weaker extractant than DGA . Other ligands that show opposite selectivity across the trivalent lanthanide (Ln) series include substrates that incorporate conformational rigidity. ,− For example, lipophilic bis-lactam-1,10-phenanthrolines (BLPhen) , and macrocycles (macropa, , macrophosphi, and py-macrodipa) show high affinity for trivalent lanthanides having larger ionic radius.…”

“…The tandem use of hydrophilic and lipophilic ligands to separate REEs has been rarely investigated, 26 − 31 despite being a common strategy employed to study separation of 4f and 5f elements. 32 − 43 Such hydrophilic ligands, also known as holdback agents or aqueous complexants, include polyaminocarboxylates, 28 − 30 α-hydroxy acids, 31 diglycolamides (DGAs), 26 , 27 and pyridine-based substrates, 37 − 41 among others.…”

“…The tandem use of hydrophilic and lipophilic ligands to separate REEs has been rarely investigated, 26 − 31 despite being a common strategy employed to study separation of 4f and 5f elements. 32 − 43 Such hydrophilic ligands, also known as holdback agents or aqueous complexants, include polyaminocarboxylates, 28 − 30 α-hydroxy acids, 31 diglycolamides (DGAs), 26 , 27 and pyridine-based substrates, 37 − 41 among others. In general, ligands with donor groups connected to freely rotating single bonds that can achieve high complementarity with metal ions (e.g., DGAs) exhibit high affinities for lanthanides that are more Lewis acidic.…”

“… 42 − 49 A combination of lipophilic DGA with hydrophilic dioxaoctanediamide results in improved selectivity for Gd over La (SF Gd/La = 100 or 1130 based on the size of N-alkyl substituents on DGAs). 26 , 27 This improvement is driven by dioxaoctanediamide exhibiting opposite selectivity to that of DGA, but is limited due to dioxaoctanediamide being a weaker extractant than DGA. 50 Other ligands that show opposite selectivity across the trivalent lanthanide (Ln) series include substrates that incorporate conformational rigidity.…”