Centrifugal Contactors for Laboratory-Scale Solvent Extraction Tests

Abstract

A 2-cm contactor (minicontactor) was developed and used at Argonne National Laboratory for laboratory-scale testing of solvent extraction flowsheets. This new contactor requires only 1 L of simulated waste feed, which is significantly less than the 10 L required for the 4-cm unit that had previously been used. In addition, the volume requirements for the other aqueous and organic feeds are reduced correspondingly. This paper (1) discusses the design of the minicontactor, (2) describes results from having applied the minicontactor to testing various solvent extraction flowsheets, and (3) compares the minicontactor with the 4-cm contactor as a device for testing solvent extraction flowsheets on a laboratory scale.

     

Numerical Simulation of Uranium Extraction from Nitric Acid Medium Using Hollow-Fiber Contactor

ABSTRACT

A two-dimensional axisymmetric computational fluid dynamics (CFD) model is presented to simulate uranium extraction from nitric acid medium using tri-n-butyl phosphate in n-dodecane in a hollow-fiber membrane contactor operated in non-dispersive solvent extraction mode. CFD model solves continuity and momentum-transport equations for the feed and shell sides and species transport equations for the feed side, shell side, as well as the membrane. Complex boundary conditions of flux continuity and concentration jump are implemented in the CFD model. The estimates of percentage of uranium extraction obtained from CFD simulations for different parametric conditions are compared with the experimental results, and a good agreement is observed. The validated CFD model is used to gain detailed insights into the hydrodynamics and mass transfer.

Abbreviations CFD: Computational fluid dynamics; NDSX: Non-dispersive solvent extraction; TBP: Tri n-butyl phosphate     

TRUEX Processing of Plutonium Analytical Solutions at Argonne National Laboratory

Abstract

The TRUEX (TRansUranic EXtraction) solvent extraction process was developed at Argonne National Laboratory (ANL) for the Department of Energy. A TRUEX demonstration completed at ANL involved the processing of analytical and experimental waste generated there and at the New Brunswick Laboratory. A 20-stage centrifugal contactor was used to recover plutonium, americium, and uranium from the waste. Approximately 84 g of plutonium, 18 g of uranium, and 0.2 g of americium were recovered from about 118 L of solution during four process runs. Alpha decontamination factors as high as 65,000 were attained, which was especially important because it allowed the disposal of the process raffinate as a lowlevel waste. The recovered plutonium and uranium were converted to oxide; the recovered americium solution was concentrated by evaporation to approximately 100 mL.

The flowsheet and operational procedures were modified to overcome process difficulties. These difficulties included the presence of complexants in the feed, solvent degradation, plutonium precipitation, and inadequate decontamination factors during startup. This paper will discuss details of the experimental effort.

     

Separation of Ionic Liquid Dispersions in Centrifugal Solvent Extraction Contactors

Abstract

Separations of dispersions formed by mixing immiscible organic room‐temperature ionic liquids (IL)/hydrocarbon/and aqueous systems using a centrifugal solvent‐extraction contactor have been successfully demonstrated in proof‐of‐concept testing. This accomplishment is significant in that physical property factors that are typical of ionic liquid systems (e.g., similar densities of the bulk phases, low interfacial tensions, and high viscosities) are typically unfavorable for dispersion separation, particularly in continuous processes. Efficient separation of dispersions containing ionic liquid solvents is essential for utilization of these compounds in liquid‐liquid extraction applications to maximize both solute transfer efficiency and solvent recovery. Efficient solvent recovery is of particular concern in IL applications because of the high cost of most IL solvents.

This paper presents the results of initial experiments with three hydrophobic ionic liquids to determine how their physical properties affect phase mixing and phase disengagement in contact with an aqueous solution using a centrifugal contactor. While the results of the reported work are promising, additional work is needed to optimize existing mathematical models of contactor hydraulics to address special considerations involved in IL‐based processes and to optimize the equipment itself for IL applications.     

Use of the SEPHIS-MOD4 Program for Modeling the Purex and Thorex Solvent Extraction Processes

Abstract

The SEPHIS-MOD4 computer program simulates solvent extraction in the Purex and Thorex processes. The program employs simple mass balance equations to describe the movement of solutes through the idealized mixer-settler stages which are used in the model. These differential mass-balance equations are integrated by an iterative scheme that allows the user to observe transient changes and the resulting steady state profile in the mixer-settler system. Correlations describe the equilibrium concentrations in the aqueous and organic phases. Kinetic rate equations are used to simulate the reduction of plutonium by hydroxylamine nitrate and uranium(IV).

The value of the SEPHIS-MOD4 program lies primarily in its application to the design and testing of solvent extraction flowsheets. Given a set of operating conditions, the program can predict the solute concentration profile at steady state and during the approach to steady state. Changes in the operating conditions can be used to determine the influence of important system variables or to simulate the effects of a process upset.     

The Centrifugal Contactor as A Concentrator in Solvent Extraction Processes

Abstract

The possibility was explored of using solvent extraction in centrifugal contactors to concentrate metal ions from a waste stream when their distribution ratio values are favorable. The theoretical basis for such a concentrator was developed and is presented here, along with experimental results which show that a centrifugal contactor is capable of acting as such a concentrator.     

Separation of Strontium-90 from Hanford High-Level Radioactive Waste

Abstract

Current guidelines for disposing of high-level radioactive wastes stored in underground tanks at the U.S. Department of Energy's Hanford Site call for vitrifying high-level waste (HLW) in borosilicate glass and burying the glass canisters in a deep geologic repository. Disposition of the low-level waste (LLW) is yet to be determined, but it will likely be immobilized in a glass matrix and disposed of on site. To lower the radiological risk associated with the LLW form, methods are being developed to separate ⁹⁰Sr from the bulk waste material so this isotope can be routed to the HLW stream. A solvent extraction method is being investigated to separate ⁹⁰Sr from acid-dissolved Hanford tank wastes. Results of experiments with actual tank waste indicate that this method can be used to achieve separation of ⁹⁰Sr from the bulk waste components. Greater than 99% of the ⁹⁰Sr was removed from an acidic dissolved sludge solution by extraction with di-t-butylcyclohexano-18-crown-6 in 1-octanol (the SREX process). The major sludge components were not extracted.     

DEVELOPING AND TESTING AN ALKALINE-SIDE SOLVENT EXTRACTION PROCESS FOR TECHNETIUM SEPARATION FROM TANK WASTE

ABSTRACT

Engineering development and testing of the SRTALK solvent extraction process are discussed in this paper. This process provides a way to carry out alkaline-side removal and recovery of technetium in the form of pertechnetate anion from nuclear waste tanks within the DOE complex. The SRTALK extractant consists of a crown ether, bis-4,4′(5′)[(tert-butyl)cyclohexano]-18-crown-6, in a modifier, tributyl phosphate, and a diluent, Isopar®L. The SRTALK flowsheet given here separates technetium from the waste and concentrates it by a factor of ten to minimize the load on the downstream evaporator for the technetium effluent. In this work; we initially generated and correlated the technetium extraction data, measured the dispersion number for various processing conditions, and determined hydraulic performance in a single-stage 2-cm centrifugal contactor. Then we used extraction-factor analysis, single-stage contactor tests, and stage-to-stage process calculations to develop a SRTALK flowsheet. Key features of the flowsheet are (1) a low organic-to-aqueous (O/A) flow ratio in the extraction section and a high O/A flow ratio in the strip section to concentrate the technetium and (2) the use of a scrub section to reduce the salt load in the concentrated technetium effluent. Finally, the SRTALK process was evaluated in a multistage test using a synthetic tank waste. This test was very successful. Initial batch tests with actual waste from the Hanford nuclear waste tanks show the same technetium extractability as determined with the synthetic waste feed. Therefore, technetium removal from actual tank wastes should also work well using the SRTALK process.

     

Reactive Extraction of Levulinic Acid Using TPA in Toluene Solution: LSER Modeling,Kinetic and Equilibrium Studies

Abstract

Levulinic acid, a carboxylic acid containing ketone structure, is a clear to brownish semi‐solid melting at 37°C; soluble in alcohol, ether, and chloroform, levulinic acid can be used as an acidulant in foods and beverages. Organic solutions of amines are being used increasingly to separate organic acids from aqueous mixture solutions by reactive extraction. The design of an amine extraction process requires kinetic data for the acid–amine+solvent system used. Kinetic studies for the extraction of levulinic acid from aqueous solution with tripropylamine (TPA) diluted in toluene were carried out using a stirred cell for kinetic studies. Equilibria for levulinic acid extraction by TPA in toluene as a diluent have been determined. All measurements were carried out at 298.15 K. The equilibrium data were also interpreted by a proposed mechanism of complexation by which (1∶1) and (2∶1) acid‐amine complexes are formed. Kinetics of extraction of levulinic acid by TPA in toluene has also been determined. The results of the liquid‐liquid equilibrium measurements were correlated by a linear solvation energy relationship (LSER).     

Experimental Verification of Caustic‐Side Solvent Extraction for Removal of Cesium from Tank Waste

Abstract

A caustic‐side solvent extraction (CSSX) process was developed to remove Cs from Savannah River Site (SRS) high‐level waste. The CSSX process was verified in a series of flowsheet tests at Argonne National Laboratory (ANL) in a minicontactor (2‐cm centrifugal contactor) using simulant. The CSSX solvent, which was developed at Oak Ridge National Laboratory (ORNL), consists of a calixarene‐crown ether as the extractant, an alkyl aryl polyether as the modifier, trioctylamine as the suppressant, and Isopar®L as the diluent. For Cs removal from the SRS tank waste, the key process goals are that: (1) Cs is removed from the waste with a decontamination factor greater than 40,000 and (2) the recovered Cs is concentrated by a factor of 15 in dilute nitric acid. In the flowsheet verification tests, the objectives were to: (1) prove that these process goals could be met; (2) demonstrate that they could be maintained over a period of several days as the CSSX solvent is recycled; and (3) verify that the process goals could still be met after the solvent composition was adjusted. The change in composition eliminated the possibility that the calixarene‐crown ether could precipitate from the solvent. The process goals were met for each of the verification tests. The results of these tests, which are summarized here, show that the CSSX process is a very effective way to remove Cs from caustic‐side waste.     

Application of Annular Centrifugal Contactor on Separating Indium from Iron

Abstract

It is hard to separate indium from iron in sulfuric acid leachate without reducing Fe³⁺ to Fe²⁺ with di(2-ethylhexyl) phosphoric acid (HDEHP) by the equilibrium extraction process. A nonequilibrium extraction process with annular centrifugal contactors is studied through the extraction kinetics difference between In and Fe. The mass transfer velocities of In and Fe were determined. Laboratory- and industry-scale extraction tests with miniature and industry scale annular centrifugal contactors, respectively, were conducted. The results indicate the mass transfer velocity of In is much faster than that of Fe, the contact time between the two phases is very short in the contactor, and the In can be well separated from Fe in the nonequilibrium extraction process with annular centrifugal contactors.     

Development and Performance of a Glass Fiber Reinforced Plastic Centrifugal Contactor

Abstract

Centrifugal contactors are efficient extraction equipments and have been successfully used in some industrial fields. But many of the extraction systems contain H₂SO₄ or HCl, therefore, centrifugal contactors that their main material is the stainless steel or titanium can be corroded by these acids not to be used in these systems. In order to solve the problem, a centrifugal contactor with 70 mm of the rotor diameter that the main material is the glass fiber reinforced plastic (GFRP) has been developed at Institute of Nuclear and New Energy Technology, Tsinghua University, China (INET). The mechanical performance of GFRP satisfies the operating requirements of the centrifugal contactor. The maximum total flow of the single stage contactor can reach 200 L/h at suitable operating conditions for H₂O‐kerosene system. The extraction stage efficiency is greater than 95% at suitable operating conditions for both extracting Co²⁺ with 35% N₂₃₅ (tertiary amine)‐20% iso‐octyl alcohol‐45% kerosene from CoCl₂ solution and stripping Co²⁺ with 0.1 mol/L HCl solution from the organic phase (35% N₂₃₅‐20% iso‐octyl alcohol‐45% kerosene) containing Co²⁺.     

Application of Single-Ion Activity Coefficients to Determine the Solvent Extraction Mechanism for Components of High-Level Nuclear Waste

Abstract

The TRUEX solvent extraction process is being developed to remove and concentrate transuranic (TRU) elements from high-level and TRU radioactive wastes that are currently stored at U.S. Department of Energy sites. Phosphoric acid is one of the chemical species of concern in the application of solvent extraction processes for removal of actinides, for instance at the Hanford site, where bismuth phosphate was used to recover plutonium.

The mechanism of phosphoric acid extraction with TRUEX-NPH solvent at 25°C was determined from phosphoric acid distribution ratios, which were measured by using a phosphoric acid radiotracer and a variety of aqueous phases containing different concentrations of nitric acid and nitrate. A model was developed for predicting phosphoric acid distribution ratios as a function of the thermodynamic activities of nitrate ion, and hydrogen ion. The Generic TRUEX Model (GTM) was used to calculate these activities based on the Bromley method. The derived model supports extraction by CMIO and TBP in TRUEX-NPH solvent of a phosphoric acid-nitric acid complex and a CMPO-phosphoric acid complex.     

Selective Actinide Extraction with a Tri‐Synergistic Mixture Using a Centrifugal Contactor Battery

Abstract

The reprocessing of spent nuclear fuels produces a quantity of high‐level liquid waste (HLLW), which is subsequentely vitrified. The most important contributors to the long‐term radiotoxicity of the vitrified HLLW are the so‐called minor actinides (MAs), which are neptunium, americium, and curium. This paper presents the results obtained during some extraction tests of americium(III) in a synthetic liquid waste representative of that coming from the PUREX and DIAMEX processes, obtained by dissolving the respective nitrate salts of the lanthanides(III) in a diluted solution of nitric acid and spiked with ²⁴¹Am and ¹⁵²Eu. The extraction process employed a tri‐synergistic organic extractant mixture and a centrifugal contactor battery of eight stages.     

Effect of α-Radioiysis on TRUEX-NPH Solvent

Abstract

An unexpectedly high degradation of the TRUEX (TRansUranic Extraction) solvent occurred during the treatment of waste solutions from the New Brunswick Laboratory. The waste solutions treated contained approximately 1 g/L of Pu-239 and 20 mg/L of Am-241. Earlier studies of α-radiolysis using carbon tetrachloride rather than normal paraffinic hydrocarbons (NPH) as a diluent indicated greater resistance to radiation damage than observed. For this study, the TRUEX-NPH solvent was loaded with Am-241 in nitric acid, irradiated with doses up to 3.5 Mrad, and monitored for decline in extraction capability as a function of absorbed dose. Results of this study are being used to improve the Generic TRUEX Model, a thermodynamic model that permits flow-sheet design for solvent extraction processing.     

Pilot-Scale Multi-Stage Countercurrent Extraction of Scutellarein from Erigeron breviscapus (Vant.) Hand-Mazz

Abstract

A low-temperature, timesaving, lower solvent consumption, and energy cost and multi-stage countercurrent extraction (MCCE) technique was developed for pilot-scale production of scutellarein from Erigeron breviscapus (Vant.) Hand-Mazz. The optimum conditions of MCCE process were obtained using the orthogonal array design method, i.e., 70% (v/v) of ethanol water solution, 16 L/kg of solvent to herbal sample ratio, 45°C of extraction temperature and 30 min of extraction time. A comparison between the MCCE technique and single pot extraction (SPE) under respective optimized operation conditions was made and time courses of scutellarein of MCCE and SPE processes were plotted, indicating that the MCCE technique can lower the extraction temperature and decrease five-sixth of the extraction time and two-thirds of the solvent consumption at the equivalent extraction yield of scutellarein.     

Extracting Acetic Acid from Acidic Solutions

Abstract

In the UREX + process, acetic acid must be removed from the raffinate stream to avoid interference with the recovery and recycle of nitric acid solutions. Solvent extraction was selected to be the most promising approach to accomplish this cleanup. Acetic acid partitioning into pure diluents used in the UREX + process were found to be too low for an effective separation. Of the solvents tested, the most promising solvents for the extraction of acetic acid were found to be TBP in dodecane and TBP in FS-13.     

DEVELOPMENT OF COMPACT MINIATURE ANNULAR CENTRIFUGAL CONTACTOR FOR HOT CELL PLACEMENT

The development of a compact 1 cm rotor diameter annular centrifugal contactor suited for experimental testing of nuclear fuel reprocessing processes in a hot cell environment is described. Twelve-stage and 50-stage batteries of the 1 cm contactor are used to implement the extraction hot test processes for the cleanup of nuclear waste liquids in hot cells in Germany and China, respectively. The advances are: (1) a simple way of assembly and disassembly between the rotor and housing of the contactor, making manipulator operation easy; (2) compact multistage housing system; (3) easy inter-stage link; (4) compact miniature size of the contactor, taking up less space in the hot cell; (5) automatic sampling from housing of contactor in the hot cell; and (6) rotor speed control.     

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 that the extracting particles can be reused. The status of the chemistry and separation process is discussed in this paper.     

Single-stage microscale solvent extraction in parallel microbore tubes using a monoblock distributor with integrated microfluidic junctions

This study is focused on the scale-up of solvent extraction in microbore tubes. A monoblock distributor with integrated microfluidic junctions (MDIMJ) is used for generating liquid–liquid dispersion and feeding the parallel microbore tubes. Experiments involve solvent extraction of U(VI) from simulated lean streams using 30% (v/v) tributyl phosphate (TBP) in dodecane. Polytetrafluoroethylene (PTFE) microbore tubes are used as a microscale contactor. The effects of inlet flow rate and O/A ratio on stage efficiency and percentage extraction (PE) are studied. Maximum capacity tested is 1.33 × 10^–6 m³/s (4.8 LPH). With O/A = 2/1, more than 90% extraction is achieved in a contact time of less than 3 s.