Separation and Recovery of Scandium from Sulfate Media by Solvent Extraction and Polymer Inclusion Membranes with Amic Acid Extractants

[Image: see text] We report on the separation and recovery of scandium(III) from sulfate solutions using solvent extraction and a membrane transport system utilizing newly synthesized amic acid extractants. Scandium(III) was quantitatively extracted with 50 mmol dm(–3)N-[N,N-di(2-ethylhexyl)aminocarbonylmethyl]glycine (D2EHAG) or N-[N,N-di(2-ethylhexyl)aminocarbonylmethyl]phenylalanine (D2EHAF) in n-dodecane at pH 2 and easily stripped using a 0.5 mol dm(–3) sulfuric acid solution. The extraction mechanisms of scandium(III) extraction with D2EHAG and D2EHAF were examined, and it was established that scandium(III) formed a 1:3 complex with both extractants (HR), that is, Sc(SO(4))(2)(–)(aq) + 1.5(HR)(2org) ⇄ Sc(SO(4))R(HR)(2org) + H(+)(aq) + SO(4)(2–)(aq). The equilibrium constants of extraction were evaluated to be 4.87 and 9.99 (mol dm(–3))(0.5) for D2EHAG and D2EHAF, respectively. D2EHAG and D2EHAF preferentially extracted scandium(III) with a high selectivity compared to common transition metal ions under high acidic conditions (0 < pH ≤ 3). In addition, scandium(III) was quantitatively transported from a feed solution into a 0.5 mol dm(–3) sulfuric acid receiving solution through a polymer inclusion membrane (PIM) containing D2EHAF as a carrier. Scandium(III) was completely separated thermodynamically from nickel(II), aluminum(III), cobalt(II), manganese(II), chromium(III), calcium(II), and magnesium(II), and partially separated from iron(III) kinetically using a PIM containing D2EHAF as a carrier. The initial flux value for scandium(III) (J(0,Sc) = 1.9 × 10(–7) mol m(–2) s(–1)) was two times higher than that of iron(III) (J(0,Fe) = 9.3 × 10(–8) mol m(–2) s(–1)).