Catherine L. Riddle

Fission Product Extraction (FPEX): Development of a Novel Solvent for the Simultaneous Separation of Strontium and Cesium from Acidic Solutions

Abstract A synergistic extraction solvent for the simultaneous removal of cesium and strontium from acidic solutions has been investigated. The extraction solvent consists of, 4,4′,(5′)‐di‐(t‐butyldicyclo‐hexano)‐18‐crown‐6 (DtBuCH18C6), calix[4]arene‐bis‐(tert‐octylbenzo‐crown‐6) (BOBCalixC6), and 1‐(2,2,3,3‐tetrafluoropropoxy)‐3‐(4‐sec‐butylphenoxy)‐2‐propanol (Cs‐7SB modifier) in a branched aliphatic kerosene (Isopar® L). Extraction synergy for strontium was observed when DtBuCH18C6 was combined with the BOBCalixC6 cesium extractant solvent and Cs‐7SB modifier or if the Cs‐7SB modifier was substituted into the SREX (Strontium Extraction) solvent in place of TBP. The novel process extracted both cesium and strontium simultaneously from 1 M nitric acid solutions with distribution ratios of 8.8 and 7.7 for strontium and cesium, respectively, at ambient temperature. Distribution coefficients for cesium and strontium as a function of nitric acid concentration and temperature were also obtained with 0.5 M<[HNO3]<2.5 M giving favorable distribution ratios. This new process utilizing the combined solvent has been named the Fission Product Extraction Process (FPEX).

FPEX γ‐Radiolysis in the Presence of Nitric Acid

Abstract The solvent formulation known as FPEX (Fission Product Extraction) contains calix[4]arene‐bis‐(tert‐octylbenzo‐crown‐6) (BOBCalixC6) for Cs extraction; 4,4′,(5′)‐di‐(t‐butyldicyclohexano)‐18‐crown‐6 (DtBuCH18C6) for Sr extraction; 1‐(2,2,3,3,‐tetrafluoropropoxy)‐3‐(4‐sec‐butylphenoxy)‐2‐propanol (Cs‐7SB) modifier and trioctylamine (TOA) to aid in Cs stripping, all in an Isopar L diluent. This formulation has favorable extraction efficiency for Cs and Sr from acidic solution, and was investigated here for γ‐radiation stability. When FPEX was irradiated in contact with aqueous nitric acid, the extraction efficiency decreased only slightly when irradiated to absorbed doses as high as 200 kGy. The color of the organic phase changed to a deep yellow‐orange, and several new peaks related to radiolysis of the Cs‐7SB modifier were detected by GC‐ECD analysis. This had little effect on the solvent extraction distribution ratios. Possible reasons for this unexpected robustness under conditions of high radiation and acidity are discussed.

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.

Complete Recovery of Actinides from UREX-like Raffinates using a Combination of Hard and Soft Donor Ligands

Studies have shown a much enhanced differentiation between trivalent actinides and trivalent lanthanides when substituted alkyl dithiophosphinic acids are utilized as the active phase transfer reagents. We present a study evaluating the use of a synergistic combination of bis(o-trifluoromethylphenyl)dithiophosphinic acid and trioctylphosphine oxide for the complete actinide recovery from UREX-like raffinates. A complete single-step separation of uranium, neptunium, plutonium, and americium from aqueous mixtures containing 0.5 M nitric acid and a total fission product content of 5.5 g/L (45 mM) has been demonstrated.

The Radiation Chemistry of the Cs-7SB Modifier used in Cs and Sr Solvent Extraction

Abstract The compound 1-(2,2,3,3,-tetrafluoropropoxy)-3-(4-sec-butylphenoxy)-2-propanol, also called Cs-7SB, is used as a solvent modifier in formulations containing calixarenes and crown ethers for cesium and strontium extraction from nuclear waste solutions. The compound solvates complexes of both metals and decreases in its concentration result in lowered extraction efficiency for both. The use of Cs-7SB in nuclear-solvent extraction ensures that it will be exposed to high-radiation doses, and thus its radiation-chemical robustness is a matter of interest in the design of extraction systems employing it. The behavior of the compound in irradiated solution, both in the presence and absence of a nitric acid aqueous phase was investigated here using steady state- and pulsed-radiolysis techniques. The rate constants for the aqueous reactions of Cs-7SB with •H, •OH, •NO3, and •NO2 radicals are reported. UPLC-UV-MS results were used to identify major products of the radiolysis of Cs-7SB in contact with nitric acid, and revealed the production of hydroxylated nitro-derivatives. Reaction mechanisms are proposed and it was concluded that the aryl-ether configuration of this molecule makes it especially susceptible to nitration in the presence of radiolytically-produced nitrous acid. Fluoride yields are also given under various conditions.

Characterization of pentavalent and hexavalent americium complexes in nitric acid using X-ray absorption fine structure spectroscopy and first-principles modeling

The speciation of pentavalent and hexavalent americium (Am) complexes in nitric acid have been studied by X-ray absorption fine structure spectroscopy, UV–visible spectroscopy, and density functional theory. Calculated bond distances for the Am(VI) complex are in reasonable agreement with EXAFS data and suggest the presence of a mixture of AmO2+ and AmO22+ as well as a slightly higher kinetic stability for Am(VI) compared to Am(V).