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Effective alternatives to nitric acid stripping in the Caustic-Side Solvent Extraction (CSSX) solvent have been demonstrated in this work. The CSSX solvent employs calix[4]arene-bis(tert-octylbenzo-18-crown-6) (BOBCalixC6) as the cesium extractant in a modified alkane diluent for decontamination of alkaline high-level wastes, such as those found at the Savannah River and Hanford sites. Results reported in this paper support the idea that replacement of the nitrate anion by a much more hydrophilic anion like borate can substantially lower cesium distribution ratios on stripping. Without any other change in the CSSX flowsheet, however, the use of a boric acid stripping solution in place of the 1 mM nitric acid solution used in the CSSX process marginally, though perhaps still usefully, improves stripping. The less-than-expected improvement was explained by the carryover of nitrate from scrubbing into stripping. Accordingly, more effective stripping is obtained after a scrub of the solvent with 0.1 M sodium hydroxide. Functional alternatives to boric acid include sodium bicarbonate or cesium hydroxide as strip solutions. Profound stripping improvement is achieved when trioctylamine, one of the components of the CSSX solvent, is replaced with a commercial guanidine reagent (LIX® 79). The more basic guanidine affords greater latitude in the selection of aqueous conditions in that it becomes protonated even at mildly alkaline pH values. Under process-relevant conditions, cesium distribution ratios on stripping are approximately 100-fold lower compared with the current CSSX performance. The tolerance to surfactants is good, and the extraction properties of the solvent remain unchanged over three successive extract-scrub-strip cycles. From the point of view of compatibility with downstream processing, boric acid represents an attractive stripping agent, as it is also a potentially ideal feed for borosilicate vitrification of the separated 137Cs product stream. The possibilities for use of these results toward a dramatically better next-generation CSSX process, possibly one employing the more soluble cesium extractant calix[4]arene-bis(2-ethylhexylbenzo-18-crown-6) (BEHBCalixC6) are discussed. [ABSTRACT FROM AUTHOR]

The combined extraction of cesium and strontium from caustic wastes can be achieved by adding a crown ether and a carboxylic acid to the Caustic-Side Solvent Extraction (CSSX) solvent. The ligand 4,4′(5′)-di(tert-butyl)cyclohexano-18- crown-6 and one of four different carboxylic acids were combined with the components of the CSSX solvent optimized for the extraction of cesium, allowing for the simultaneous extraction of cesium and strontium from alkaline nitrate media simulating alkaline high level wastes present at the U.S. Department of Energy Savannah River Site. Extraction and stripping experiments were conducted independently and exhibited adequate results tot mimicking waste simulant processing through batch contacts. The promising results of these batch tests showed that the system could reasonably be tested on actual waste. [ABSTRACT FROM AUTHOR]

This work emphasizes the crucial role of polar solvating molecules known as phase modifiers in solvent-extraction systems. The focus of these studies was the extraction of cesium by calix[4tarene-bis(tert-octylbenzo-crown-6) in dodecane modified with various lipophilic alcohols. Results of equilibrium modeling are consistent with aggregation of the alcohol molecules with each other and with the calixarene-cesium nitrate complexes. These modeling results are supported by electrospray mass spectrometry experiments, clearly showing the alcohol:anion adducts containing several alcohol molecules. They are also supported by crystallographic evidence showing the existence of a hexameric aggregate in the solid state for a derivative of one of the alcohol modifiers used for solvent extraction, in agreement with the species giving the best modeling results. [ABSTRACT FROM AUTHOR]

The new cesium-selective macrocycle calix[4]arene-bis[4-(2-ethylhexyl) benzo-crown-6] (“BEHBCalixC6”) has been found to have improved solubility in a modified alkane diluent over calix[4]arene-bis(4-tert-octylbenzo-crown-6) (“BOBCalixC6”). The synthesis of this new calixcrown extractant, together with its solubility and extraction properties, is described in this report. The solubility, cesium extraction, and potassium loading behavior are compared with those of BOBCalixC6, the macrocycle currently employed in the caustic-side solvent extraction (CSSX) process for extracting cesium from alkaline nitrate solutions such as high-level nuclear waste. Replacement of the tert-octyl alkyl chains on the benzo-crown portion of the calixcrown by 2-ethylhexyl chains improves the equilibrium solubility of the free calixcrown in aliphatic diluents while not affecting the cesium extraction strength. Equilibrium concentrations of BEHBCalixC6 in Isopar L diluent modified with 0.5 M 1-(2,2,3,3-tetrafluoropropoxy)-3-(4-sec-butylphenoxy)-2-propanol (Cs-7SB) over the course of 41 weeks of gentle agitation at 25°C maintained the initial concentration of 57 ± 2 mM, with no evidence of precipitation or third-phase formation. In contrast, 57 ± 2 mM solutions of BOBCalixC6 prepared using sonication were not stable, with precipitation occurring to afford an equilibrium concentration of only 6.7 ± 0.2 mM after 41 weeks. Third-phase tests showed that BEHBCalixC6 resists third-phase formation as well as, or better than, BOBCalixC6. With increasing potassium loading from an alkaline sodium nitrate solution, both calixcrowns at 20 mM in modified Isopar L exhibited comparable onset of third-phase formation, gauging by the decreasing mass balance in cesium extraction from the same solutions. However, the BEHBCalixC6 solvent exhibited no visible indications of third-phase formation until the aqueous potassium concentration reached 0.75 M, whereas the BOBCalixC6 suffered visible third-phase formation when the aqueous potassium nitrate concentration reached 0.25 M. Calixcrowns with higher solubility in alkane diluents may find application in cesium extraction from waste matrices containing moderate (≥0.2 M) quantities of potassium, such as that stored at the US Department of Energy's Hanford Site, where higher concentrations of the calixcrown extractant may be required to obtain practical cesium distribution coefficients for process flowsheets. [ABSTRACT FROM AUTHOR]

Results obtained in this work show that four calix[4]arene mono and bis(benzo-crown-6) ethers functionalized with primary amine groups feature markedly enhanced cesium stripping under acidic conditions compared with nonfunctionalized analogs. The four amine-derivatized calixarenes were surveyed in nitrobenzene diluent at 25°C, demonstrating the effect under controlled conditions, where it was seen that the amino functionalization entailed at most a mild sacrifice of cesium extraction strength or selectivity. Limited solubility of the protonated forms of the extractants appears to be a potential issue for future development, however. In the best case, calix[4]arene bis[4-(2-ethylhexyl)benzo-crown-6], possessing an aminomethyl group on the upper rim, (AMBEHB) exhibited a cesium extraction strength comparable to that of a control system containing calix[4]arene bis(tert-octylbenzo-crown-6) (BOB) under alkaline conditions, whereas stripping of the cesium from AMBEHB was 56-fold more effective than BOB. A proof-of-principle extraction, scrubbing, and stripping (ESS) cycle using AMBEHB in Isopar L modified with 0.75 M 1-(2,2,3,3-tetrafluoropropoxy)-3-(4-sec-butylphenoxy)-2-propanol (Cs-7SB) showed that a greater than three-fold more efficient stripping may be obtained with AMBEHB vs. its nonfunctionalized control BEHB. A slope analysis of systematic extraction data under caustic and acidic conditions confirmed that the extraction of cesium nitrate by AMBEHB in dodecane modified by 0.5 M Cs-7SB involves the formation of a 1:1:1 metal:ligand:nitrate organic species. [ABSTRACT FROM AUTHOR]

Investigates the effectiveness of alkylphenoxy fluorinated alcohols as modifiers in solvents for the extraction of cesium from alkaline nitrate media. Experimental details; Influence of the fluorinated portion of the modifier on chemical stability; Impact of the structure of the alkyl substituent of the alkylphenoxy moiety on the phase behavior of the solvent.