George F. Vandegrift

Mass Transfer Rate through Liquid Membranes: Interfacial Chemical Reactions and Diffusion as Simultaneous Permeability Controlling Factors

Abstract Equations describing the permeability of a liquid membrane to metal cations have been derived taking into account aqueous diffusion, membrane diffusion, and interfacial chemical reactions as simultaneous permeability controlling factors. Diffusion and chemical reactions have been coupled by a simple model analogous to the one previously described by us to represent liquid-liquid extraction kinetics. The derived equations, which make use of experimentally determined interfacial reaction mechanisms, qualitatively fit unexplained literature data regarding Cu2+ transfer through liquid membranes. Their use to predict and optimize membrane permeability in practical separation processes by setting the appropriate concentration of the membrane carrier [LIX 64 (General Mills), a commercial β-hydroxy-oxime] and the pH of the aqueous copper feed solution is briefly discussed.

Review: Solvent Systems Combining Neutral and Acidic Extractants for Separating Trivalent Lanthanides from the Transuranic Elements

Abstract This paper is a review of recent publications that have focused on combined extractant systems for separating trivalent actinides from the lanthanides. These mixed solvent systems combine an acidic extractant with a neutral extractant to achieve the actinide/lanthanide separation. Depending on the neutral extractant used, three categorizations of systems can be considered, including combinations of acidic extractants with 1) diamides, 2) carbamoylmethylphosphine oxides, and 3) polydentate nitrogen-donor ligands. This review of relevant publications indicates that, although there is significant potential for practical exploitation of mixed neutral/acidic extractant systems to achieve a single-step separation of trivalent actinides from acidic high-level waste solutions, the fundamental chemistry underlying these combined systems is not yet well understood. For example, although there is strong evidence suggesting that adducts form between the neutral and acidic extractants, the nature of these adducts generally is not known. Likewise, the structures of the mixed complexes formed between the metal ions and the two different extractants are not fully understood. Research into these basic phenomena likely will provide clues about how to design practical mixed-extractant systems that can be used to efficiently separate the transuranic elements from the lanthanides and other components of irradiated fuel.

Waste remediation using in situ magnetically assisted chemical separation

Abstract The magnetically assisted chemical separation process (MACS) combines the selective and efficient separation afforded by chemical sorption with the magnetic recovery of ferromagnetic particles. This process is being developed for treating the underground storage tanks at Hanford. These waste streams contain cesium, strontium, and transuranics (TRU) that must be removed before this waste can be disposed of as grout. The separation process uses magnetic particles coated with either 1) a selective ion exchange material or an organic extractant-containing solvent (for cesium and strontium removal) or 2) solvents for selective separation of TRU elements (e.g., TRUEX process). These coatings, by their chemical nature, selectively separate the contaminants onto the particles, which can then be recovered from the tank using a magnet. Once the particles are removed, the contaminants can either be left on the loaded particles and added to the glass feed slurry or stripped into a small volume of solution so...

DEVELOPMENT OF A SOLVENT EXTRACTION PROCESS FOR CESIUM REMOVAL FROM SRS TANK WASTE

An alkaline-side solvent extraction process was developed for cesium removal from Savannah River Site (SRS) tank waste. The process was invented at Oak Ridge National Laboratory and developed and tested at Argonne National Laboratory using singlestage and multistage tests in a laboratory-scale centrifugal contactor. The dispersion number, hydraulic performance, stage efficiency, and general operability of the process flowsheet were determined. Based on these tests, further solvent development work was done. The final solvent formulation appears to be an excellent candidate for removing cesium from SRS tank waste.

A Thermodynamic Model of Nitric Acid Extraction by Tri- n -Butyl Phosphate

A thermodynamic model is presented for nitric acid extraction by tri-n-butyl phosphate (TBP). This model is based on the formation of the organic phase species: TBP.HNO/sub 3/ and (TBP)/sub 2/.HNO/sub 3/. The model works successfully at TBP concentrations of 5 to 100 vol% and was found to be effective at predicting the extraction of HNO/sub 3/ from HNO/sub 3//NaNO/sub 3/ and HNO/sub 3//LiNO/sub 3/ solutions. Within the TBP concentration range of 5 to 30%, a single set of extraction constants was sufficient to fit extraction data. Stoichiometric activity coefficients of nitric acid in HNO/sub 3//NaNO/sub 3/ and HNO/sub 3//LiNO/sub 3/ mixtures were calculated using a model developed by Bromley.

Quantitative study of the carboxylic acids in Green River oil shale bitumen

Abstract Bitumen fractions were extracted by a benzene/methanol reflux of Green River oil shale (GROS) before and after treatment with HCl, HF, and HCl/HF. Acid leaching released 80% more bitumen than could be extracted without acid treatment. This additional bitumen had greater concentrations of carboxylic acids and their salts than the untreated oil shale bitumen. The carboxylic acids were separated from all bitumen fractions (untreated, post HCI, post HF, and post HF/HCl) and individual acids were identified and quantified by gas chromatography—mass spectrometry and high resolution mass spectrometry. The same types of acids were present in all four bitumen fractions but showed significant differences in their relative abundances. These carboxylic acids and salts were present in the original GROS and were not formed during the treatment. The post-HCl bitumen fraction contained Mg and Fe salts of long-chain aliphatic carboxylic acids with carbon numbers in the range of 21–38. Significantly, even though calcium is the major cation in the carbonate minerals of GROS, no Ca was present in the ash of these carboxylic acid salts. These results indicate that there is a strong interaction between carboxylic acids present in GROS and its mineral matrix (especially carbonate minerals). These carboxylic acids are possible coupling agents that ‘glue’ mineral and organic material together. The treatment of the oil shale also resulted in the formation of highly purified kerogen, low in ash yield (2 wt %) which had undergone only very mild acid treatment.

Actinide Separation of High-Level Waste Using Solvent Extractants on Magnetic Microparticles

Abstract Polymeric-coated ferromagnetic particles with an absorbed layer of octyl(phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide diluted by tributyl phosphate are being evaluated for application in the separation and the recovery of low concentrations of americium and plutonium from nuclear waste solutions. Due to their chemical nature, these extractants selectively complex americium and plutonium contaminants onto the particles, which can be recovered from the waste solution using a magnet. The effectiveness of the extractant-absorbed particles at removing transuranics (TRU) from simulated solutions and various nitric acid solutions was measured by gamma and liquid scintillation counting of plutonium and americium. The HNO3 concentration range was 0.01 to 6 M. The partition coefficients (K d) for various actinides at 2 M HNO3 were determined to be between 3000 and 30,000. These values are larger than those projected for TRU recovery by traditional liquid/liquid extraction. Results from transmission...

The TRUSPEAK Concept: Combining CMPO and HDEHP for Separating Trivalent Lanthanides from the Transuranic Elements

Combining octyl(phenyl)-N,N-diisobutyl-carbamoylmethyl-phosphine oxide (CMPO) and bis-(2-ethylhexyl) phosphoric acid (HDEHP) into a single process solvent for separating transuranic elements from liquid high-level waste is explored. Co-extraction of americium and the lanthanide elements from nitric acid solution is possible with a solvent mixture consisting of 0.1 M CMPO plus 1 M HDEHP in n-dodecane. Switching the aqueous-phase chemistry to a citrate-buffered solution of diethylene triamine pentaacetic acid (DTPA) allows for selective stripping of americium, separating it from the lanthanide elements. Potential strategies have been developed for managing molybdenum and zirconium (both of which co-extract with americium and the lanthanides). The work presented here demonstrates the feasibility of combining CMPO and HDEHP into a single extraction solvent for recovering americium from high-level waste and its separation from the lanthanides.

Optimizing the coating process of organic actinide extractants on magnetically assisted chemical separation particles

Abstract The coatings of ferromagnetic-charcoal-polymer microparticles (1–25 gm) with organic extractants specific for actinides were optimized for use in the magnetically assisted chemical separation (MACS) process. The organic extractants, octyl (phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide (CMPO) dissolved in tributyl phosphate (TBP), coated the particles when a carrier organic solvent was evaporated. Coated particles were heated in an oven overnight to drive off any remaining carrier solvent and fix the extractants on the particles. Partitioning coefficients for americium obtained with the coated particles routinely reached 3000–4000 ml g−1, approximately 10 times the separation efficiency observed with the conventional solvent extraction system using CMPO and TBP.

Radiochemical and isotope separations by high-efficiency liquid-liquid chromatography

Abstract A very-high-efficiency liquid-liquid chromatographic (LLC) system based on 5- and 20-μm diameter porous silica microspheres was used to effect radiochemical separations of metal ions that required very large decontamination factors and/or high speeds. The stationary phase was 25–30% (w/w) of di(2-ethylhexyl) orthophosphoric acid (HDEHP) in dodecane. Nitric acid was used as the mobile phase. The mass transfer coefficient term, C , was determined from height equivalent to a theoretical plate vs. interstitial linear velocity data for the elution of Ca 2+ and compared with values calculated from the interfacial mass transfer coefficients measured in the corresponding liquid-liquid extraction system. The HDEHP high-efficiency LLC system was also investigated for possible usein enriching the naturally occurring isotopes of calcium. Isotopic exchange constants for 40 Ca or 42 Ca and 48 Ca were measured chromatographically as a function of temperature. The enrichment of calcium isotopes was attempted on coupled columns at low flow velocities.