Continuous Liquid Membrane Research Articles

Parametric studies on an innovative waste vegetable oil-based continuous liquid membrane (WVCLM) for Cu(II) ion separation from aqueous solutions

Abstract Separation of Cu(II) ions from aqueous solutions using an innovative waste vegetable oil-based continuous liquid membrane (WVCLM) was studied with waste vegetable oil as diluent, di-2-ethylhexylphosphoric acid (D2EHPA) as carrier and sulphuric acid (H 2 SO 4 ) as stripping phase. For an initial Cu(II) ion concentration of 500 mg/L, the maximum percentages of extraction (96%) and stripping (80%) were achieved in 8 h and 24 h, respectively, with feed phase buffered at pH 4.5, 250 mM of inert salt, 88 mM of D2EHPA, 1.5 M of H 2 SO 4 , 2.5 L/h of membrane phase, 4.0 L/h of feed phase and 0 L/h of stripping phase.

Simulation of nonequilibrium extraction of rare-earth elements with liquid membranes: I. Generalized mathematical model

A mathematical model adequately describing extraction separation of chemically similar elements under nonequilibrium conditions was developed. Both single-extractor systems and systems of two extractors connected via an organic phase (continuous liquid membrane) were studied. The closed and flow modes of oscillatory extraction were considered. A general study of the properties of the model was performed. The model is capable to reproduce the majority of oscillatory modes described in the literature for chemical oscillators based on the Belousov-Zhabotinskii reaction. The correlations between the characteristic features of the oscillations and some parameters of the system were determined. Regular trends in the effect of the rate constants of the Field-Koros-Noyes mechanism simplified in accordance with the irrevesrsible Oregonator scheme and of the intensity of Ce(IV) interphase exchange on the behavior of the system were revealed. Algorithms were suggested for efficient simulation of some common experimental oscillatory modes.

Kinetics of REE separation by nonequilibrium extraction at oscillating temperature

The effect of periodic oscillations of temperature on the extraction and backwashing in the extraction systems 6 M NaNO3-Nd(NO3)3-Pr(NO3)3-TBP-kerosene and [Nd(NO3)3 · 3TBP]-[Pr(NO3)3 · 3TBP]-kerosene-0.1 M HNO3 was studied. Application of periodic temperature oscillations to the extraction system NaNO3-Nd(NO3)3-Pr(NO3)3-TBP-kerosene-0.1 M HNO3 increased the REE separation factor in a unit consiting of a continuous liquid membrane between two extractors. A mathematical model of nonstationary membrane extraction supplemented by the block of the temperature dependences of the extraction rate constants was developed. The activation energies of the forward and reverse reactions of the extraction and backwashing of Pr and Nd were calculated. For the extraction process of REE separation with a liquid membrane under the effect of periodic temperature oscillations, the following parameters were optimized: frequency and amplitude of temperature oscillations, distribution of the total volume of the organic phase between the extractors, and flow rate of the liquid membrane.

Oscillatory Extraction System with a Liquid Membrane for Separating REEs

A nonstationary oscillating system consisting of two extractors separated by a continuous liquid membrane is examined, including the effects of the pumping rate of the organic phase of the membrane and of the acid concentration. The time dependences of the enrichment factors of the aqueous and organic phases (Pr/Nd) are studied. The enrichment factor depends on the low-frequency oscillations of the redox potential (high-frequency oscillations were low-frequency-modulated). The HNO3 concentration optimal for Nd - Pr separation is determined. The enrichment factor of the aqueous phase (Pr/Nd) increases with increasing rate of pumping of the liquid membrane between the extractors. The 142Ce/140Ce ratios in the aqueous phase of both extractors are measured.

Analysis of semi-volatile organics in aqueous process streams using solid-phase microextraction and gas chromatography

Analysis of aqueous streams contaminated with complex organic mixtures commonly used in industrial processes can be problematic. In this study, we describe the development of the solid-phase microextraction (SPME) headspace extraction technique in combination with gas chromatography (GC) to measure the leakage of n-decanol and Exxsol® D-110 (commercial solvent containing primarily napthenes and paraffins) into aqueous streams. These streams were derived from a continuous liquid membrane separator for the removal and recovery of Cr(VI) from industrial effluents. In one stream that was dilute in Cr(VI) at pH 2–3, a method giving good results for n-decanol analysis involved the addition of n-octanol as an internal standard to GC calibration standards and test samples prior to SPME extraction with the appropriate adjustment of pH. The addition of 20 w/w% NaCl as an additional solute to all standards and test samples with pH adjustment was found to be successful for quantitative determination of Exxsol® D-110. In a second stream that was strongly alkaline and more concentrated in Cr(VI), GC calibration using standards containing NaOH and 300–500 ppm Cr(VI) gave satisfactory results for quantitative determination of both species.