Heavy metal ions extraction using new supported liquid membranes containing ionic liquid as carrier

This article reports the extraction of Hg(II), Cd(II) and Cr(III) ions from acidic media using new supported liquid membranes (SLM). The novelty of this work is the use of an ionic liquid (IL) (isooctylmethylimidazolium bis-2-ethylhexylphosphate) as carrier for the SLM. The ionic liquid was synthesized under microwave and characterized (volumetric mass density, viscosity and thermal stability). The influences of the membrane support hydrophobicity and of the operating conditions (carrier concentration, metallic ions nature and concentration, acidity of the aqueous phases and temperature) were studied. Fluxes, permeability, diffusion coefficients and association constants were determined by kinetic studies. The SLM appeared more suitable for the extraction of Cd(II) ions at pH = 3 (higher permeability coefficient: 40.3 × 10−7 cm2 s−1, extraction ratio: 35% after 4 h run; selectivity coefficients: αCd(II)/Hg(II) = 1.8 and αCd(II)/(Cr(III) = 1.5). Thermodynamic data were gathered by studying the influence of temperature. In view of future applications to the purification of real wastewaters, the effect of the competition in multimetallic mixtures and the stability of the membrane were also studied. The extraction ratio order was Cd(II) > Hg(II) > Cr(III) and an increase of the Cd(II) extraction ratio was observed with the number of reuses. The transport performances were correlated to the absolute hardness of ions and the structure of the carrier. All data highlighted that the transport mechanism should be of mobile-site jump type.