Robert V. Fox

Supercritical Fluid Extraction of Plutonium and Americium from Soil using Thenoyltrifluoroacetone and Tributylphosphate Complexation

Samples of clean soil from the source used to backfill pits at the Idaho National Engineering and Environmental Laboratory´s Radioactive Waste Management Complex were spiked with 239Pu and 241Am to evaluate ligand-assisted supercritical fluid extraction as a decontamination method. The actual soil in the pits has been subject to approximately three decades of weathering since it was originally contaminated. No surrogate soil can perfectly simulate the real event, but actual contaminated soil was not available for research purposes. However, fractionation of Am and Pu in the surrogate soil was found to be similar to that previously measured in the real soil using a sequential aqueous extraction procedure. This suggests that Pu and Am behavior are similar in the two soils. The surrogate was subjected to supercritical carbon dioxide extraction, in the presence of the fluorinated beta diketone thenoyltrifluoroacetone (TTA), and tributylphosphate (TBP). As much as 69% of the Pu and 88% of the Am were removed from the soil using 3.2 mol.% TTA and 2.7 mol.% TBP, in a single 45 minute extraction. Extraction conditions employing a 5 mol.% ethanol modifier with 0.33 mol.% TTA and 0.27 mol.% TBP resulted in 66% Pu and 68% Am extracted. To our knowledge, this is the first report of the use of supercritical fluid extraction (SFE) for the removal of actinides from soil.

Neptunium and plutonium sorption to Snake River Plain, Idaho soil

Summary The behavior of Np and Pu on soil collected from the subsurface disposal area at the Idaho National Engineering and Environmental Laboratory was investigated by performing short-duration, sorption experiments to measure sorption isotherms. Neptunium sorption can be described with a Freundlich isotherm; however, Pu sorption can only be described in this fashion as a conservative estimate of minimum sorption. Geochemical modeling predictions suggest that initial sorption of Np is controlled predominantly by surface complexation on clay minerals, while Pu is controlled by a competition between complexation with iron oxyhydroxides and the precipitation of hydrolysis products. Longer-term sorption is governed by the transformation of these species to oxide minerals. Solution ionic strength and carbonate alkalinity did not significantly affect Np or Pu soil sorption.

Strontium and cesium sorption to Snake River Plain, Idaho soil

Summary The behavior of strontium and cesium on soil from the Radioactive Waste Management Complex (RWMC) of the Idaho National Engineering and Environmental Laboratory (INEEL), located on the Snake River Plain of southern Idaho, USA, was investigated using sequential aqueous extractions and batch sorption methods over six orders of magnitude in aqueous ion concentration. Sequential extractions revealed that most Sr is retained in the operationally-defined ion exchangeable and carbonate fractions, while Cs is predominantly found in the residual fraction. Strontium sorption was reversible, while Cs was not, except at the lowest concentrations. Freundlich isotherms can describe sorption of both metals at low aqueous concentrations, but Langmuir isotherms were needed to describe Cs and Sr sorption over the entire range used in this study. Slightly higher sorption was observed for both when experiments were repeated on soil that was treated to remove carbonates.

Free-radical chemistry of disinfection byproducts. 3. Degradation mechanisms of chloronitromethane, bromonitromethane, and dichloronitromethane.

Halonitromethanes (HNMs) are byproducts formed through ozonation and chlorine/ chloramine disinfection processes in drinking waters that contain dissolved organic matter and bromide ions. These species occur at low concentration but have been determined to have high cytotoxicity and mutagenicity and therefore may represent a human health hazard. In this study, we have investigated the chemistry involved in the mineralization of HNMs to nonhazardous inorganic products through the application of advanced oxidation and reduction processes. We have combined measured absolute reaction rate constants for the reactions of chloronitromethane, bromonitromethane, and dichloronitromethane with the hydroxyl radical and the hydrated electron with a kinetic computer model in an attempt to elucidate the reaction pathways of these HNMs. The results are compared to measurements of stable products resulting from steady-state (60)Co gamma-irradiations of the same compounds. The model predicted the decomposition of the parent compounds and ingrowth of chloride and bromide ions with excellent accuracy, but the prediction of the total nitrate ion concentration was slightly in error, reflecting the complexity of nitrogen oxide species reactions in irradiated solution.

The separation of lanthanides and actinides in supercritical fluid carbon dioxide

Supercritical fluid carbon dioxide presents an attractive alternative to conventional solvents for recovery of the actinides and lanthanides. Carbon dioxide is a good solvent for fluorine and phosphate-containing ligands, including the traditional tributylphosphate ligand used in process-scale uranium separations. Actinide and lanthanide oxides may even be directly dissolved in carbon dioxide containing the complexes formed between these ligands and mineral acids, obviating the need for large volumes of acids for leaching and dissolution, and the corresponding organic liquid–liquid solvent extraction solutions. Examples of the application of this novel technology for actinide and lanthanide separations are presented.

Extraction behavior of selected rare earth metals from acidic chloride media using tetrabutyl diglycolamide

ABSTRACT Rare earth elements (REEs) are vital to modern, high-tech devices. Recycling REEs from post-consumer electronics can potentially diminish supply chain risks. Toward that end, liquid–liquid solvent extraction of various REEs was investigated with tetrabutyl diglycolamide (TBDGA) in 1-octanol from hydrochloric acid media. Metal partitioning to the organic phase was shown to increase as [Cl−] increased. In contrast, increasing [H+] did not improve extraction. The use of the polar diluent 1-octanol provided high extraction efficiency, especially for the partition of heavy lanthanides from solutions of high chloride concentration. Although the polar diluent also extracted molar amounts of water and acid, it was concluded that a neutral metal/TBDGA complex as mainly the di-solvate was extracted, and that complexation was observed to be exothermic. These results indicate that REE extraction from aqueous chloride solutions can be efficient without the use of high acid concentrations.

Transition of Iodine Analysis to Accelerator Mass Spectrometry

This NA 22 funded research project investigated the transition of iodine isotopic analyses from thermal ionization mass spectrometry (TIMS) to an accelerator mass spectrometry (AMS) system. Previous work (Fiscal Year 2010) had demonstrated comparable data from TIMS and AMS. With AMS providing comparable data with improved background levels and vastly superior sample throughput, improvement in the sample extraction from environmental sample matrices was needed to bring sample preparation throughput closer to the operation level of the instrument. Previous research used an extraction chemistry that was not optimized for yield or refined for reduced labor to prove the principle. This research was done to find an extraction with better yield using less labor per sample to produce a sample ready for the AMS instrument. An extraction method using tetramethyl ammonium hydroxide (TMAH) was developed for removal of iodine species from high volume air filters. The TMAH with gentle heating was superior to the following three extraction methods: ammonium hydroxide aided by sonication, acidic and basic extraction aided by microwave, and ethanol mixed with sodium hydroxide. Taking the iodine from the extraction solvent to being ready for AMS analysis was accomplished by a direct precipitation, as well as, using silver wool tomorexa0» harvest the iodine from the TMAH. Portions of the same filters processed in FY 2010 were processed again with the improved extraction scheme followed by successful analysis by AMS at the Swiss Federal Institute of Technology. The data favorably matched the data obtained in 2010. The time required for analysis has been reduced over the aqueous extraction/AMS approach developed in FY 2010. For a hypothetical batch of 30 samples, the AMS methodology is about 10 times faster than the traditional gas phase chemistry and TIMS analysis. As an additional benefit, background levels for the AMS method are about 1000 times lower than TIMS. This results from the fundamental mechanisms of ionization in the AMS system and which produces a beneficial cleanup of molecular interferences. Continued clean operation of the extraction process was demonstrated through blank analysis included with all sample sets analyzed. INL work showed improvement on the first year’s demonstration of AMS vs. TIMS. An improved extraction of high volume air filters followed by isotopic analysis by AMS, can be used successfully to make iodine measurements with results comparable to those obtained by filter combustion and TIMS analysis. More progress on the conversion from an extract solution to an AMS sample ready for analysis is still needed. Although the preparation scheme through AMS is already at a higher performing thoughput than TIMS, the chemical preparation cannot match the instrument capability for number of samples per day without further development.«xa0less

Electrochemical Synthesis of 2,2-dinitropropanol

Bench-scale electrochemical synthesis of 2,2-dinitropropanol (DNPOH) was performed to evaluate scale-up potential. The synthesis scheme employs a reversible chemical mediator Fe(CN)6-3/-4 couple to perform oxidative nitration of nitroethane using the anode of the electrochemical cell as the oxidant source. The flow-cell based system operated in a continuous fashion with the intermediate product (1,1-dinitroethanate K-salt) precipitated and removed from reaction, and starting materials (nitroethane and potassium nitrate) added as consumed in the reaction. The intermediate product was condensed with formaldehyde to produce DNPOH. A discussion of the waste reduction over the chemical route is presented.