Extractant Class: Phosphates

Controlling Extraction of Rare Earth Elements Using Functionalized Aryl-vinyl Phosphonic Acid Esters

“…The aqueous phases were composed of 0.01–0.1 M solutions of nitric acid, while the styryl phosphonic acid mono 2-ethylhexyl esters were dissolved in CHCl 3 . At the ligand concentrations studied, the phosphonic acids are expected to exist as H-bonded dimers in the CHCl 3 solutions. , The extraction of Eu from the nitric acid solutions was studied as a function of the extractant concentration at constant aqueous acidity (Figure ) and as a function of the aqueous acidity at a constant extractant concentration (Figure ). The three styryl phosphonic acid monoesters are all much stronger extractants than HEHEHP, as indicated by the 1–2 order of magnitude decrease in extractant concentration required to achieve the same degree of Eu extraction ( D Eu ) at constant acidity for HEHSP, HEHDFSP, and HEHTFSP compared to HEHEHP (Figure ).…”

“…This term represents chemical reactions intrinsic to the ligand alone. Both of the equilibrium constants in this term are expected to be strongly dependent on the polarity of the O–H bond in the ligand, and it is generally observed for acidic organophosphorus extractants that the magnitude of K 2 increases as K a increases. , The polarity of the O–H bond will be strongly influenced by the adjacent phosphorus atom and the properties of its aryl-vinyl substituents, which are related to the dipole moment along the P–C bond. Given the substantial differences in the p K a values between HEHEHP and the styryl-bearing ligands, this term is particularly important in understanding the much lower value of K ex observed for HEHEHP.…”

Centrifugal Partition Chromatographic Separations of Platinum Group Metals by Complexation and Ion Pair Formation

“…It is reasonable to assume that the values for K L and K DC are about the same, which yields the only unknown quantity, k 2 , in eq 14. The k 2 values are 3.75 × 10 6 and 5.04 × 10 6 M -1 s -1 for PdCl 2 (TOPO) 2 and PtCl 2 (TOPO) 2 , respectively, using the K ex values (see equilibrium studies) and K L = 10 5 in the heptane−H 2 O phase pair, and using the K - 4 values for PdCl 4 2- (0.0025) and PtCl 4 2- (0.018) in H 2 O from literature . These values are in excellent agreement with the values determined by stopped-flow formation kinetic experiments (MCl 4 2- + TOPO) in Brij 35 micelles: (3.11 ± 0.23) × 10 6 M -1 s -1 for PdCl 4 2- and (5.93 ± 0.36) × 10 6 M -1 s -1 .…”

Kinetic Studies of Extraction for a Mixture of Some Europium Phosphonate Complexes and 2-Benzoyl or 2-Anilinopyridine inn-Hexane

“…Organophosphorous compounds are widely used for the separation of lanthanide and actinide elements (1)(2)(3)(4). Friehmelts et al reported that the rate-controlling step in the extraction of lanthanides and actinides from aqueous systems by organophosphorous reagents may involve diffusion in either phase, complex formation, or the elimination of water from ionic solvation layers (5).…”