Competition of mixed divalent ions through supported liquid membranes: Co-ion and concentration effects on permeability

Zn²⁺, Cu²⁺ and Ni²⁺ permeabilities through supported liquid membranes (SLMs) were determined experimentally from single, binary, and ternary ionic mixtures. Microporous polypropylene membrane was used as the frame to retain isopar-L solvent and di (2-ethylhexyl) phosphoric acid (D2EHPA) carrier. Sulfuric acid solution was used as a strip (receiving) solution. The ion permeability values were in the 10⁻⁷-10⁻⁶ cm² s⁻¹ range and increased with the concentrations of D2EHPA in isopar-L and the stripping sulfuric acid. The ion ideal selectivity ranged from 1.05 (Zn/Cu) to 8.40 (Zn/Ni), depending on the feed concentration. The single ion permeability was significantly higher than the binary mixtures, probably due to ion competition with D2EHPA carrier molecules. High selectivity was achieved using ternary mixtures: Zn²⁺ was the fast-permeating species due to preferential sorption with D2EHPA. Separating Zn²⁺ from Cu²⁺ and/or Ni²⁺ mixtures was most efficient with high D2EHPA concentration, concentrated H₂SO₄ strip solution, concentrated feed solution, and from multiple ionic mixes.