A study of the separation of Mo(VI) ions by transport through a tris (2-ethylhexyl) phosphate (TEHP)-sorbitan monooleate (Span-80)-toluene liquid membrane was performed with varying concentrations of HCI, TEHP, Span-80, and NaOH containing Na2CO3 in the feed, membrane, and strip solutions, respectively. Maximum transport was observed with 3.5 to 5.5 mol dm(-3) HCI, 50 to 70% (v/v) TEHP in toluene, 7 to 8% (v/v) Span-80, 0.005 to 0.015 mol dm(-3) NaOH, and 1.4 to 2.0 mol dm(-3) Na2CO3. Mo(VI) was completely separated from binary mixtures containing Fe(II), Co(II), Ni(II), Mn(II), Cr(VI), Al(III), W(VI), Ti(IV), V(V), Sn(IV), U(VI), and Th(IV) ions with this system. Preconcentration of Mo(VI) from dilute aqueous: solution is presented and transport mechanism is discussed. The method was employed for the separation and recovery of Mo(VI) from solutions of samples such as spent catalyst, low-grade molybdenite concentrate, and ferrous scrap.