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, • NO 3 , and • NO 2 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.

The Reactivity of the Nitrate Radical (• NO3 ) in Aqueous and Organic Solutions

“…As there are only two C─H bonds in this modifier group, we correct our calculated value of (4.8 ± 0.8) × 10 9 M −1 s −1 by multiplying by 0.67, to give an overall predicted nitrate radical rate constant with Cs7SB of (3.2 ± 0.6) × 10 9 M −1 s −1 . While it is recognized that no consideration of inductive or steric effects has been made in this simple analysis, the predicted value is in very good agreement with the measured value of this rate constant of 2.7 × 10 9 M −1 s −1 .…”

“…For example, the compound 1‐(2,2,3,3,‐tetrafluoropropoxy)‐3‐(4‐sec‐butyl‐phenoxy)‐2‐propanol, also called Cs‐7SB (Fig. ), is used as a solvent modifier in formulations containing calixarene and crown ether ligands for cesium and/or strontium extraction from nuclear waste solutions . It is not expected that the reaction of the nitrate radical is with the Cs‐7SB aromatic ring (≤10 6 M −1 s −1 for benzene in Table ).…”

Recent trends in metals extraction

“…Originally, the organic phase has been constituted by three organic compounds, with a specific work to do, dissolved in Isopar L (aliphatic diluent): the extractant, actually calix [4]arene-bis-(tert-octylbenzo-crown-6) (BOBCalixC6), a modifier 1-(2,2,3,3-tetrafluoropropoxy)-3-(4-sec-butylphenoxy)-2-propanol (Cs-7SB) and finally a small amount of trioctylamine (TOA). While the modifier is needed to improve the extractant dissolution in the diluent, the presence of the amine overcomes related stripping problems of the process [53][54][55][56] .…”

Radiation chemistry in solvent extraction: FY2010 Research

“…Kinetic data for the free radical reactions of Cs-7SB were combined with liquid chromatography mass spectrometry results to postulate mechanisms for the oxidative nitration of Cs-7SB in irradiated nitric acid. This information was collected and used to prepare a manuscript (Swancutt et al 2010) and the discussion below is adapted from that paper.…”

“…These species are probably also formed by nitrosonium ion nitration. A detailed discussion of these and other products of Cs-7SB irradiation is found in Swancutt et al (2010). Table 3.…”