This work includes study of separation of Ag(I), Co(II), Ni(II), Zn(II) and Cr(III) ions for the transport through liquid membranes based on triethanolamine in cyclohexanone supported in microporous hydrophobic polypropylene films. V(V) transport study has been conducted through tri-n-octylamine-cyclohexane based similar membranes. The purpose of this study has been (i) to optimize the conditions for moving the given metal ions against their concentration gradient from feed to stripping phase, (ii) characterize the membranes by determining flux, permeability, diffusion coefficient and mobility of the complexed metal ions for their use later on in practical hydrometallurgical plants design to recover these ions. Their mutual separation and recovery from industrial effluents is another practical purpose of this study. Speciation of the metal ions in the membrane organic carrier (extractant) phase has also been carried out using theoretically derived equations to elucidate the stoichiometry and mechanism of transport of these metal ions across the supported liquid membranes (SLMs).
Optimum conditions of transport (OCT) for these metal ions have been found to be; for Ag(I) ions, 1.0 mol/dm3 HNO3 in the feed, 2.25 mol/dm3 TEA in the membrane and 1.5 mol/dm3 KCN in the stripping phase; for Co (II) ions, 1.0 mol/dm3 HCl in the feed, 3.75 mol/dm3 TEA in the membrane and 1 mol/dm3 NaOH in the stripping phase; for Ni(II) ions 2.0 mol/dm3 HCl in the feed, 3.00 mol/dm3 TEA in the membrane and 2.0 mol/dm3 NaOH in th stripping phase; for Zn(II) ions, 2.0 mol/dm3 HCI in the feed, 3.75 mol/dm3 TEA in the membrane and 2.0 mol/dm3 Na2SO4 in the stripping phase; for Cr(III) ions, 1.5 mol/dm3 Na SO4 in the feed, 5.26 mol/dm3 TEA in the membrane and 1.5 mol/dm3 H2SO4 in the stripping phase and for V(V) ions OCT are 2.0 mol/dm3 HCI in the feed, 0.665 mol/dm3 TOA in the membrane.
Co (II) and Ni(II) separation is possible due to their more than 100 times mutual difference in flux. Cr(III) ions direct transport without its oxidation in feed membrane or stripping phase is helpful to treat tannery effluent aqueous waste. Nickel and zinc ions can be extracted from their plating wastes.
The species extracted into organic phase for Ag(I) ions are (LH)3.Ag(NO3)4; for Co(II) ions are mixed LH.CoCl3 and (LH)2.CoCI4, for Ni(II) ions, LH.NiCl3, for Zn(II), LH.ZnCl3, for Cr(III), LH.O.CrSO4 (L = TEA) and for V(V) ions, LH.VO2 (I)- TOA. The complex of Ni(II) ions with TEA in the presence of EDT A has also been studied, which forms complex as LH.MB where MBH is represented as
Nickel was removed from Ni-plating actual waste up to 93%. In case of tannery waste, Cr(III) ions were removed from industrial effluent actual sample up to 99% and Ag(I) ions from plating waste up to 99%. If the membrane area is increased the ions can be removed and recovered completely at a very fast rate, indicating the practical utility of the SLM coupled transport systems, which holds its superiority over classical solvent extraction system due to simultaneous extraction and back extraction steps and highly reduced carrier (solvent) inventory. Mechanisms of transport of the metal ions studied are also elucidated.