R. Scott Herbst

THE UNIVERSAL SOLVENT EXTRACTION (UNEX) PROCESS. I. DEVELOPMENT OF THE UNEX PROCESS SOLVENT FOR THE SEPARATION OF CESIUM, STRONTIUM, AND THE ACTINIDES FROM ACIDIC RADIOACTIVE WASTE

A synergistic extraction mixture containing chlorinated cobalt dicarbollide (CCD), carbamoylmethyl phosphine oxide (CMPO), and polyethylene glycol (PEG) has been investigated for the simultaneous recovery of cesium, strontium, lanthanides, and actinides from highly acidic media. The extraction properties of this mixture depend on the concentration ratio of the components. For recovery of all major radionuclides, the optimal ratio of [CCD]:[PEG]: [CMPO] = 5:1:1 should be used. The use of diphenyl-N,N-dibutylcarbamoylmethyl phosphine oxide and PEG-400 provides the most efficient recovery of cesium, strontium, lanthanides, and actinides. The possibility of using polyfluorinated ethers, esters, ketones, and sulfones as diluents was examined. Phenyltrifluoromethyl sulfone was the most suitable diluent tested. The use of this diluent allows good extraction properties, chemical and radiation stability, excellent explosion/fire-safety properties, and favorable hydrodynamic characteristics. The extraction of radionuclides from HNO3 media by mixtures of CCD:PEG:CMPO in phenyltrifluoromethyl sulfone and the subsequent stripping behavior were evaluated.

THE UNIVERSAL SOLVENT EXTRACTION (UNEX) PROCESS. II. FLOWSHEET DEVELOPMENT AND DEMONSTRATION OF THE UNEX PROCESS FOR THE SEPARATION OF CESIUM, STRONTIUM, AND ACTINIDES FROM ACTUAL ACIDIC RADIOACTIVE WASTE

A novel solvent extraction process, the Universal Extraction (UNEX) process, has been developed for the simultaneous separation of cesium, strontium, and the actinides from acidic waste solutions. The UNEX process solvent consists of chlorinated cobalt dicarbollide for the extraction of 137Cs, polyethylene glycol for the extraction of 90Sr, and diphenyl-N,N-dibutylcarbamoyl phosphine oxide for the extraction of the actinides and lanthanides. A nonnitroaromatic polar diluent consisting of phenyltrifluoromethyl sulfone has been developed for this process. A UNEX flowsheet consisting of a single solvent extraction cycle has been developed as a part of a collaborative effort between the Khlopin Radium Institute (KRI) and the Idaho National Engineering and Environmental Laboratory (INEEL). This flowsheet has been demonstrated with actual acidic radioactive tank waste at the INEEL using 24 stages of 2-cm diameter centrifugal contactors installed in a shielded cell facility. The activities of 137Cs, 90Sr, and the actinides were reduced to levels at which a grout waste form would meet NRC Class A LLW requirements. The extraction of 99Tc and several nonradioactive metals by the UNEX solvent has also been evaluated.

UNIVERSAL SOLVENT EXTRACTION (UNEX) FLOWSHEET TESTING FOR THE REMOVAL OF CESIUM, STRONTIUM, AND ACTINIDE ELEMENTS FROM RADIOACTIVE, ACIDIC DISSOLVED CALCINE WASTE

ABSTRACT The presence of long-lived radionuclides presents a challenge to the management of radioactive wastes. Separation of the radionuclides from the waste solutions has the potential of significantly decreasing the costs associated with the immobilization and disposal of the radioactive waste by minimizing waste volumes. Typically, several separate processes are required for the separation of cesium, strontium, and actinides from radioactive wastes. A novel solvent extraction process, the Universal Extraction (UNEX) process, has been developed for the simultaneous separation of cesium, strontium, and the actinides from radioactive acidic waste solutions. The UNEX process solvent consists of chlorinated cobalt dicarbollide for the extraction of 137Cs, polyethylene glycol for the extraction of 90Sr, and diphenyl-N,N-di-n-butylcarbamoylmethyl phosphine oxide for the extraction of the actinides and lanthanides. A non-nitroaromatic polar diluent, phenyltrifluoromethyl sulfone, is used for this process. A UNEX flowsheet consisting of a single solvent extraction cycle has been developed as a part of a collaborative effort between the Khlopin Radium Institute (KRI) and the Idaho National Engineering and Environmental Laboratory (INEEL). This flowsheet has been demonstrated with actual dissolved radioactive calcine waste at the INEEL using 24 stages of 2-cm diameter centrifugal contactors installed in a shielded hot cell facility. For the major radionuclides, 99.99% of the 137Cs, 99.73% of the 90Sr, and >99.9% of the actinides in the initial dissolved calcine feed were extracted and recovered in the high activity fraction. For the stable matrix elements, 12% of the Mo, 0.7% of the Zr, and 2% of the Fe were extracted and recovered in the strip product. The minor components Ba and Pb were quantitatively extracted and recovered in the strip product; 23% of the Mn was also present in this fraction. Very little Al, Ca, Cr, Na, and Ni were extracted into the UNEX solvent.

Fundamental Chemistry of Cesium Extraction from Acidic Media by HCCD in FS‐13

Abstract We previously published a model for cesium extraction from acidic media by the protonated form of the hexachlorinated derivative of the chloro‐protected cobalt bis(dicarbollide), HCCD, dissolved in trifluoromethylphenyl sulfone, FS‐13. The model indicated that Cs extraction proceeds through a series of ion‐paired and/or dissociated extraction equilibria. Additional Cs distribution ratio data has been obtained and the model refined and simplified. It is demonstrated that the equilibrium exclusively involving the exchange of proton for cesium by formation of ion‐paired CsCCD models the Cs distribution data very well, particularly for the concentrations of HCCD greater than ∼0.0005 M (0.5 mM). Finally, activity corrections for the aqueous phase to the Cs distribution data results in good agreement to the theoretical value of −1 for slope (log‐log) analysis of the data over a wide range of HNO3 and HCCD concentrations.

Development of a Cobalt Dicarbollide/Polyethylene Glycol Solvent Extraction Process for Separation of Cesium and Strontium to Support Advanced Aqueous Reprocessing

Abstract A chlorinated cobalt dicarbollide(CCD)/polyethylene glycol (PEG) based solvent extraction process is being developed for the separation of Cs and Sr from leached spent light water reactor (LWR) fuel as part of the Advanced Fuel Cycle Initiative (AFCI). The separation of Cs and Sr would significantly reduce the heat generation of spent nuclear fuel requiring geologic disposal. A solvent composition for this process has been verified, and the distribution coefficient acid dependency for Cs, Sr, Am, and Eu have been measured for the CCD/PEG solvent. Leached spent fuel simulant, traced with 137Cs, 85Sr, 241Am, and 154Eu, was used to perform batch contact flowsheet experiments for the extraction, scrub, and strip sections of the CCD/PEG process. Additionally, the effects of acetohydroxamic acid and its decomposition products, as well as the effects of the uranium extraction (UREX) process solvent, on the extraction of Cs and Sr with the CCD/PEG process were evaluated.

Development Of The Universal Extraction (Unex) Process For The Simultaneous Recovery Of Cs, Sr, And Actinides From Acidic Radioactive Wastes

A synergistic extraction mixture containing chlorinated cobalt dicarbollide (CCD), polyethylene glycol (PEG), and diphenyl-N,N-dibutylcarbamoyl phosphine oxide (CMPO) in a suitable polar diluent is being developed for the simultaneous recovery of Cs, Sr, and the actinides from highly acidic radioactive wastes. Development of this UNEX process was by a successful collaboration between scientists from the Idaho National Engineering and Environmental Laboratory (INEEL) and the Khlopin Radium Institute (KRI) in St. Petersburg, Russia. Development efforts focused on the treatment of radioactive waste currently stored at the INEEL. The development of the UNEX process has and continues to be an evolutionary process. Numerous countercurrent flowsheet demonstrations have been conducted to date, including two tests with several liters of actual radioactive tank waste, one test with dissolved radioactive calcine, and several tests with surrogate INEEL tank and dissolved calcine wastes. All countercurrent flowsheet tests have been performed in banks of centrifugal contactors. Removal efficiencies of 99.95% for 137Cs, 99.995% for 90Sr, and 99.96% for total α (predominately 241Am, 238Pu, and 239Pu) were observed in countercurrent tests with samples of actual INEEL tank waste. The evolutionary concepts included in the development of the UNEX process are discussed, including development of the current diluent, phenyltrifluoromethyl sulfone, to replace nitroaromatic diluents used in earlier studies. Results from the most recent countercurrent flowsheet testing with 1.2 L of actual dissolved INEEL calcine are also presented, which represents the current state of UNEX development. Finally, future research directions in the development and understanding of the UNEX process are discussed. #The submitted manuscript has been authored by a contractor of the U.S. Government under contract No. DE-AC09-96SR18500. Accordingly, the U.S. Government retains a non-exclusive, royalty-free license to publish or reproduce the published form of this contribution, or allow others to do so, for U.S. Government purposes.

Development of a Regenerable Strip Reagent for Treatment of Acidic, Radioactive Waste with Cobalt Dicarbollide‐based Solvent Extraction Processes

Abstract A regenerable methylamine carbonate (MAC)/diethylenetriamine pentaacetic acid (DTPA) strip solution has been developed, as a collaborative effort between the Khlopin Radium Institute (KRI) and the Idaho National Engineering and Environmental Laboratory (INEEL), for the stripping of actinides, lanthanides, Cs, and Sr from cobalt dicarbollide‐based solvent extraction processes. Methodology and experimental results of developing this strip reagent and a distillation method for regeneration of the resulting strip solution are presented. Additionally, countercurrent flowsheet testing of the Universal Solvent Extraction (UNEX) process, using 26 stages of 3.3 cm diameter centrifugal contactors, has been performed at the INEEL using dissolved pilot plant calcine and this regenerable strip solution. Results of stripping Cs, Sr, actinides, and lanthanides from the UNEX solvent with a MAC + DTPA strip solution that was freshly prepared and that has been regenerated are presented. Overall results of the flowsheet test are also presented.

The Radiolytic and Thermal Stability of Diamides of Dipicolinic Acid

The thermal and radiolytical stabilities of three isomers of N,N′-diethyl-N,N′-ditolyl-dipicolinamide (EtTDPA) were investigated. Radiolysis was performed at doses up to 125 kGy and thermogravimetric analysis was performed at temperatures of up to 450°C. Infrared data showed increasing amounts of aromatic nitration by nitric acid correlating to larger doses. However, gamma ray doses of up to 125 kGy did not cause any significant effects in separation performance with the studied extraction mixtures containing americium or europium within the studied range. The highest separation factor between americium and europium was seen using the meta isomer with an average value of 4.1 across all doses applied in this work.

Fundamental Chemistry of the Universal Extractant (UNEX) for the Simultaneous Separation of Major Radionuclides (Cesium, Strontium, Actinides, and Lanthanides) from Radioactive Wastes

Scientists at the INEEL and KRI collaboratively developed and validated the concept of a Universal Extractant (UNEX) for simultaneously removing the major radionuclides (Cs, Sr, actinides, and lanthanides) from acidic radioactive waste in a single solvent extraction process. The UNEX solvent incorporates three active extractants: chlorinated cobalt dicarbollide, polyethylene glycol, and a carbamoylmethylphosphine oxide derivative, dissolved in a suitable organic diluent to simultaneously extract target radionuclides. The process chemistry is unique, but complicated, since the extractants operate synergistically to extract the radionuclides. Furthermore, interactions with the diluent are quite important as the diluent strongly influences the extraction properties of the solvent system. We are currently studying the fundamental chemical phenomena responsible for the selective extraction of the different species to understand the underlying mechanisms and facilitate enhancements i n process chemistry. Our efforts to date have relied on a combination of classical chemistry techniques, infrared (IR) spectroscopy, and nuclear magnetic resonance (NMR) spectroscopy to identify and explain the structures formed in the organic phase, elucidate the operative chemical mechanisms, and evaluate the diluent effects on extraction properties.