New Cesium-Selective Hydrophilic Ligands:  UV Measures of Their Interactions toward Cs and Cs/Na Separation by Nanofiltration Complexation

Abstract

Separating traces of cesium from aqueous medium containing large sodium amounts is a difficult problem because cesium and sodium ions have a similar behavior in aqueous medium. We selected a highly cesiumselective ligand in aqueous medium, and we determined the best conditions for using this ligand in a nanofiltration-complexation process in order to achieve Cs + /Na + separation. We also tried to find a relation between the ligand structure and its activity toward cesium complexation. Tetrahydroxylated bis-crown-6 calix[4]arene was found to be very cesium selective (S ) (Cs + )/ (Na + ) ) 6600). Combined with a nanofiltration process, this ligand helped reaching 90% cesium retention in a highly concentrated aqueous medium ([NaNO 3 ] ) 3 mol/L). IntroductionAmong the different available separative methods (liquidliquid and solid-liquid extractions, ion-exchange resins), nanofiltration (NF) is a new pressure-driven membrane process which produces very few additional wastes. Located between ultrafiltration and reverse osmosis, nanofiltration membranes " cutoffs " are in the range of 300-1000 g/mol molecular weight. 1-3 Moreover, to increase ionic separation, nanofiltration can be combined with a selective complexation step: retention of the target element is improved because the complex with the ligand, of larger size and mass than the target ion, prevents this ion from passing through the membrane. 4 For such a purpose, water-soluble ligands with molecular weight of about 500 g/mol can be used in the case of the nanofiltrationcomplexation association, whereas micro-or ultrafiltrationcomplexation systems need larger ligands and induce some specific problems of increasing viscosity and precipitation. 5 Our laboratory has been developping the nanofiltrationcomplexation technique since 1993. [6][7][8][9] We showed that using EDTA with a Desal 5 DK or a Nanomax 50 membrane allowed a 100% retention (rejection) of Sr 2+ and other polyvalent ions, and only a 10% retention of Na + and Cs + ions. Then, with the use of a cesium-selective ligand such as resorcinarene, Cs + / Na + separation was also improved but not satisfactorily. In fact, to remove radioactive traces of cesium in highly salted aqueous medium, a minimum of 99% Cs + retention with a maximum of 10% Na + retention is required for industrial applications.So the aim of the present study was to select a highly cesiumselective ligand in aqueous medium, and then to determine the

Rejection of Gd(III) by nanofiltration assisted by complexation on charged organic membrane: Influences of pH, pressure, flux, ionic strength and temperature

“…The -potential value is then determined by extrapolating the regressed line P/ ϕ s = f(1/2h) at infinitely large channel heights according to Eq. (7). A value of about −3.3 mV is found forpotential of the Desal G10 membrane at pH 4.0.…”

“…The experimental signal ( ϕ s ) is found to be dependent on the channel height in agreement with Eq. (7). As the channel height is much greater than the Debye length in all experiments (2h ≥ 300 m), the surface conductance phenomenon within the channel should be negligible and cannot explain the channel height dependence of the streaming potential [23].…”

“…Thus the resulting complexes could be rejected by the membrane, whereas the non-complexed ions pass through it. It is this principle of nanofiltration assisted by complexation [4][5][6][7][8][9][10] which was applied throughout this study. This study deals with the rejection of Gd(III) by nanofiltration assisted by complexation on organic charged membranes using DTPA (diethylentriaminepentaacetic acid).…”

Polyaminocarboxylic acids rejection by charged nanofiltration membrane

“…Rejection and transport mechanisms of inorganic ions through nanofiltration membranes have been described in several publications [1][2][3][4]. It can be applied for drinking water softening [5,6], selective concentration of uranium traces from sea water [7] or separation of metal by nanofiltration assisted by complexation [8,9].…”

Cs+/Na+ Separation by Nanofiltration-Complexation with Resorcinarene

“…The NF-organic membranes are ideally suited for rejecting organics with molecular weights.200 Da and multivalent ions. [8,9] However multistep synthesis of calixarenes [6] and their solubility at pH .12 limit their used with NForganic membranes. These properties allow the separation of different ion valences, but this selectivity is not generally ensured for the separation of ions with the same valences.…”