Loading capacity and emulsification phenomena of HREE extraction by dialkylphosphinic acids with different β,γ,δ-substituents

The relationship between dialkylphosphinic acid structure and their loading capacity for HREEs and emulsification phenomena has rarely been studied. In this paper, we took Lu extraction as an example to study the effect of β , γ , δ -substituents of dialkylphosphinic acids on their loading capacity and anti-emulsification performance for HREEs. To discuss conveniently, the dialkylphosphinic acids were classified into two groups: β -substituent group (P208, INET-1, P218, USTB-1 and P227) and γ , δ -substituent group (P218, P2132 and Cyanex 272). For β -substituent group extractants, their loading capacities are in the order P208 (299.7 mg/L) ≈ INET-1 (299.5 mg/L) > P218 (270.8 mg/L) >> USTB-1 (163.1 mg/L) > P227 (151.4 mg/L), while their anti-emulsification/gelation performances are just in the opposite order P227 > USTB-1 > P218 > P208 ≈ INET-1 under the studied conditions. For γ , δ -substituent group extractants, their loading capacities are in the order P218 (270.8 mg/L) > P2132 (192.3 mg/L) > Cyanex 272 (131.7 mg/L), while the anti-emulsification performance of P218 is better than those of P2132 and Cyanex 272. The loading capacity data given in the parentheses are obtained through repeatedly extracting Lu from ∼4 × 10 −4  mol/L of Lu aqueous feed solution with initial pH of 2.40 by 0.01 mol/L extractant at phase ratio A/O of 1:1.