Paul G. Rickert

Lifetime of supported liquid membranes: the influence of interfacial properties, chemical composition and water transport on the long-term stability of the membranes

Abstract The permeability coefficients of some metal species through selected supported liquid membranes (SLM) have been measured over extended periods of time, in the presence and absence of osmotic pressure gradients. The composition of the SLMs was varied in such a way to obtain membranes with variable interfacial properties. The interfacial tensions, viscosities, contact angles and water solubilities in the organic phases of the various liquid membranes were measured. The ability of these SLMs to transport water under the influence of osmotic pressure gradients of different magnitude was also measured. In this way correlations were established among the following factors: the lifetime of the SLMs, their interfacial and water extraction properties, the concentrations of the feed and strip solutions adjacent to the SLM and the ability of the SLM to transport water. The results of long-term operation of several types of SLMs indicate that they are relatively stable when the osmotic pressures of the feed and strip solutions are approximately equal, but become increasingly unstable as the difference between the osmotic pressures of the feed and strip solutions increases. In addition, the rate at which water is transported through the SLMs under the influence of a given osmotic pressure difference is inversely related to membrane lifetime. The following mechanism of water transport through SLMs was proposed: (i) in presence of an osmotic pressure gradient water tends to flow through the organic-filled pores of the SLM, providing the organic phase can appreciably solubilize water; this initial water flow can be imagined as the diffusion of water molecules through a stationary organic diluent; (ii) when the amount of flowing water becomes massive and the SLM is easily wetted by the aqueous phases, the organic phase is eventually displaced from the support pores and replaced by water; at this point the membrane behaves as a semipermeable diaphragm containing water-filled micropores and its ability to perform carrier-mediated coupled transport of metal species is completely lost.

Transport of Eu3+ through a Bis(2-ethylhexyl)-phosphoric Acid, n-Dodecane Solid Supported Liquid Membrane

Abstract The coupled transport of Eu3+ and H+ ions through a solid supported liquid membrane consisting of a porous polypropylene film immobilizing an HDEHP solution in n-dodecane has been studied as a function of the membrane area, stirring speed of the aqueous solutions, membrane composition, and acidity of the feed solution. The experimental results are in agreement with predictions derived from a theoretical permeability coefficient equation which assumes that membrane diffusion and aqueous film diffusion are the only rate-controlling factors.

SEPARATION OF ACTINIDES AND LANTHANIDES FROM ACIDIC NUCLEAR WASTES BY SUPPORTED LIQUID MEMBRANES

ABSTRACT Supported liquid membranes, SLM, consisting of a solution of 0.25 M octyl(phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide (CMPO) and 0.75 μ tributylphosphate (TBP) in decalin absorbed on thin micropocous polypropylene supports, have been studied for their ability to perform selective separations and concentrations of actinide and lanthanide ions from synthetic acidic nuclear wastes. The permeability coefficients of selected actinides (Am, Pu, U, Np) and of some of the other major components of the wastes have been measured using SLMs in flat-sheet and hollow- fiber configurations. The results have shown that with the thin (25 μm) flat-sheet SLMs, using Celgard® 2500 as support, the membrane permeation process is mainly controlled by the rate of diffusion through the aqueous boundary layers. With the thicker (430 μmpar; hollow-fiber SLMs, using Accurel® hollow-fibers as support, the membrane permeation process Is controlled by the rate of diffusion through both the SLM and the aqueous boundar...

Fluorous ionic liquids as solvents for the liquid-liquid extraction of metal ions by macrocyclic polyethers.

The predominant mode of strontium ion transfer from aqueous nitrate media into a series of 1-fluoroalkyl-3-methylimidazolium bis[(trifluoromethylsulfonyl)]imides containing dicyclohexano-18-crown-6 (DCH18C6) is shown to shift from cation exchange to strontium nitrato-crown ether complex partitioning as the length of the fluoroalkyl substituent is increased. Fluoroalkyl substituents are shown to be only slightly more effective than their non-fluorous analogs at inducing this shift. At the same time, the fluorinated ionic liquids (ILs) yield strontium distribution ratios as much as an order of magnitude lower than the corresponding 1-alkyl-3-methylimidazolium (C(n)mim(+)) salts. Fluorous ILs thus appear to offer no compelling advantages over C(n)mim(+) ionic liquids as extraction solvents.

Hydrolytic and Radiolytic Degradation of Oφd(iB)Cmpo: Continuing Studies

Abstract The hydrolytic and radiolytic degradation of octyl(phenyl)-N, N-diisobutylcarbamoyl-methylphosphine oxide (CMPO) in tetrachloro-ethylene (TCE) and in tributylphosphate-TCE mixtures (TRUEX process solvent) in contact with HNO3 has been investigated. Gas chroma-tographic analysis of the degraded solutions has allowed identification and quantitation of a variety of organophosphorus degradation compounds derived from CMPO. The effect of degradation of the extractant solutions on the extraction and stripping of americium has been addressed, as has the effectiveness of Na2CO3 scrub procedures for restoring extractant performance. Extrapolation of these results to normal process application conditions indicates that neither hydrolysis nor radiolysis should compromise the americium extraction performance of TRUEX-TCE.

METAL EXTRACTION BY ALKYL SUBSTITUTED DIPHOSPHONIC ACIDS. PART 4 P,P′-DI(2-ETHYLHEXYL) BUTANEDIPHOSPHONIC ACID

ABSTRACT As part of an ongoing investigation of the properties of dialkyl substituted diphosphonic acids as solvent extraction reagents for metal cations, we have studied the extraction of alkaline earth cations, Fe(III) and representative actinides (Am(III), U(VI) and Th(IV)) at tracer-level concentration by o-xylene solutions of P,P′-di(2-ethylhexyl) butanediphosphonic acid, H2DEH[BuDP]. The extractant and acid dependencies of these metal ions exhibited significant differences from those of the previously investigated analogous extractants in which the two phosphonate groups are separated by a methylene or an ethylene bridge. The aggregation of H2DEH[BuDP] was investigated in toluene at 25° C by vapor pressure osmometry. H2DEH[BuDP] was found to exist predominantly as a trimeric species in the 0.1-0.005 molal concentration range. Osmometric measurements and infrared spectra indicate that Ca(II) is extracted into H2DEH[BuDP] solutions with little disruption of the structure of the extractant. Iron(III) c...

Application of supported liquid membranes for removal of uranium from groundwater

Abstract The separation of uranium from Hanford site groundwater was studied by hollow-fiber supported liquid membranes, SLM. The carrier bis(2,4,4-trimethylpentyl)phosphinic acid, H[DTMPeP], contained in the commercial extractant CyanexTM 272 was used as membrane carrier, because of its selectivity for U over calcium and magnesium. The water soluble complexing agent, 1-hydroxyethane-1,1-diphosphonic acid, HEDPA, was used as stripping agent. Polyproylene hollow-fibers and n-dodecane were used as polymeric support and diluent, respectively. Laboratory scale hollow-fiber modules were employed in a recycling mode, using as feed synthetic groundwater at pH 2, to confirm the capability of the proposed SLM system to separate and concentrate U(VI) in the strip solution. Information was obtained on the U(VI) concentration factor and on the long-term performance of the SLMs. Encouraging results were obtained both with a conventional module and with a module containing a carrier solution reservoir. Industrial scale...

FUNDAMENTAL INVESTIGATIONS OF SEPARATIONS SCIENCE FOR RADIOACTIVE MATERIALS

ABSTRACT Fundamental investigations of solvent extraction and ion exchange separations of radioactive materials have been conducted within the National Laboratory system of the U. S. Department of Energy (and its predecessor agencies) for the past 50 years. Basic research conducted at Oak Ridge and Argonne National Laboratories has produced both high quality new science and important applications in nuclear technology. The present contribution is an attempt to summarize the most important scientific results arising from this research during the past 10 years, a time of great change in the nuclear separations field, and to suggest possible directions for the next stage of research and development in this field.

DEGRADATION OF TRUEX-DODECANE PROCESS SOLVENT

ABSTRACT The hydrolysis and radiolysis of TRUEX-dodecane process solvent (0.2 M octyl(phenyl)N,N-diisobutycarbamoylmethylphosphine oxide (CMPO)-1.2 M tributylphosphate (TBP) in n-dodecane) has been Investigated in a series of experiments conducted in a biphasic mode involving contact with aqueous nitric acid solutions. The stability of the principle extractant (CMPO) is observed to be considerably greater than that reported previously for similar studies in chlorinated diluents. The concentration profiles for the degradation products determined by capillary gas chromatography have been successfully fit assuming pseudo-first order kinetics and mechanistic information derived from these fits.

An iron-dependent and transferrin-mediated cellular uptake pathway for plutonium

Plutonium is a toxic synthetic element with no natural biological function, but it is strongly retained by humans when ingested. Using small-angle X-ray scattering, receptor binding assays and synchrotron X-ray fluorescence microscopy, we find that rat adrenal gland (PC12) cells can acquire plutonium in vitro through the major iron acquisition pathway--receptor-mediated endocytosis of the iron transport protein serum transferrin; however, only one form of the plutonium-transferrin complex is active. Low-resolution solution models of plutonium-loaded transferrins derived from small-angle scattering show that only transferrin with plutonium bound in the proteins C-terminal lobe (C-lobe) and iron bound in the N-terminal lobe (N-lobe) (Pu(C)Fe(N)Tf) adopts the proper conformation for recognition by the transferrin receptor protein. Although the metal-binding site in each lobe contains the same donors in the same configuration and both lobes are similar, the differences between transferrins two lobes act to restrict, but not eliminate, cellular Pu uptake.