Transport of Mo(VI) Ions through Tri-n-octylamine-Xylene Based Supported Liquid Membranes

Abstract

The study of Mo(VI) ions transport through tri-n-octylamine (TOA)-xylene liquid membranes supported in polypropylene hydrophobic microporous film has been performed with varying concentrations of HC1, TOA, and NaOH in the feed membrane, strip solution, and temperature. Maximum flux of the order of 1.62 × 10⁻⁴ mol · m⁻² · s⁻¹ and permeability of 2.51 × 10⁻¹⁰ m²/s at 1.35 mol/dm³ TOA and 0.1 mol/dm³ NaOH at 35 ± 2°C have been observed. The flux of metal ions increases with an increase in temperature. Decomposition of [Mo₇O₂₄]^6- ions into lower species appears to occur, and a pH decrease in the feed with the passage of time during transport of these metal ions is an indication of this effect. Mixed polymetal anions appear to be responsible for complexing with TOA molecules and the transport through the membrane. The transport mechanism of this metal ion through the membrane is based on the association of metal anions with protonated tri-n-octylamine (TOA) molecules on the feed-side interface, diffusion through the membrane, decomposition of the complex on the strip/solution-side membrane interface in alkaline conditions, and backdiffusion of TOA molecules. Transport with the membrane is dependent on the concentration gradient but in the surrounding solutions it is inversely related to the concentration gradient.