Crown ethers strontium extraction

For the crown ether strontium extractant, speculate how the active agent for separating strontium functions in this analysis. 

Extraction of tetrahedral pertechnetate anion from aqueous solutions using several crown ethers is well known. The coextraction of cesium (or strontium) and technetium from nuclear waste by calix[4]arene-crown-6 has been reported from alkaline media. Although technetium in its common pertechnetate form does not complex directly with crown ethers, pertechnetate extraction may be facilitated by crown ethers as the coanion of sodium (for alkaline nitrate waste). Pertechnetate at trace levels in the waste may be more than a 1000-fold more extractable than the smaller nitrate anion in ion-pair extraction processes.87... 

Dai, S., Ju, Y.H., and Barnes, C.E., Solvent extraction of strontium nitrate by a crown ether using room-temperature ionic liquids, /. Chem. Soc., Dalton Trans., 1201,1999. 

Nonetheless, the United States and other nations have been developing additional chemical separation processes to bring about these goals. Strontium and cesium can be removed from HLW by extraction with crown ethers, such as ditertiarybutyl-dicyclohexanone-18-crown-6, which can also extract 99Tc. In the United States,... 

Dozol, J.F., Dozol, M., Macias, R.M. 2000. Extraction of strontium and cesium by dicarbollides, crown ethers and functionalized calixarenes. J. Incl. Phenom. Macrocycl. Chem. 38 (1-4) 1-22. 

Delmau proposed the combined extraction of cesium and strontium from caustic wastes by adding a crown ether and a carboxylic acid to the CSSX solvent.126 The classical DtBuC18C6 and one carboxylic acid 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 SRS. The promising results of these batch tests showed that the system could reasonably be tested on actual waste. 

Previously, we saw that the extractants used for the extraction of strontium were DC18C6 derivatives or dicarbollide derivatives. Strontium can be effectively extracted with a synergistic mixture of dicarbollide and polyethylene glycols or crown ethers. A drawback of this process is the use of high-polarity diluents, such as nitrobenzene or chlorinated compounds, in order to solubilize the mixture of the extractants.127... 

It has been pointed out that the octamers CA9 (.S Sr/Na = 51.3) and CA13 (SSr/Na = 42) are much more selective than the crown ether DC18C6 (SSr/Na = 16.4) (Table 4.19).132 These results were confirmed for extraction of strontium from acidic medium. For all the calixarenes tested except CA8, the distribution ratios are higher than those obtained with DC18C6.133 The selectivity SSr/Na is very high thanks to a negligible sodium extraction. 

In the early 1990s, there existed several classes of extractants for actinides (CMPO), for cesium and more generally alkali cations, and for strontium and alkaline earth cations (crown ethers and cosan). The combination of these extractants and the grafting of these functions on calixarene platforms have led to new classes of extremely efficient and selective extractants, in particular calixarene-crown, which are presently applied in the United States to treat the huge amounts of waste at the SRS. Calixarenes/ CMPO, crown ethers/cosan, CMPO/cosan, and more recently calixarenes/CMPO/ cosan are promising compounds. It is desirable that these studies, conducted at the international level, continue in particular to obtain a better understanding of the complex mechanisms of extraction of these compounds.127187... 

There are special extractants to extract each class of radionuclides crown ethers for cesium and strontium and phosphine oxides, carbamoylmethylphosphine oxides, and diamides for actinides, etc. It is unrealistic to have a single extractant that can extract all target nuclides with nearly the same effectiveness. So, a promising technical decision is to mix extractants for different radionuclides and extract them simultaneously. 

Simulated solutions of Russian waste and INL (Idaho National Laboratory, USA) waste were used as feed solutions. Extraction of cesium was 98.4%, and of strontium, 98.1%. A problem with low solubility of the crown ethers (<180 mg/L for all type of solutions) was shown in the tests. The authors pointed out the main positive features of the proposed flowsheet a salt-free strip product with very low nitric acid concentration (<0.1 M), possibility to extract both cesium and strontium, and low losses of extractants. A last step in the modification of this solvent was the addition of polyalkylphosphonitrilic acid to the mixture of crown ethers.65 Positive results were obtained for extraction of not only Cs and Sr, but also MAs from simulated HLW. 

Meikrantz, D.H., Todd, T.A., Riddle, C.L., Law, J.D., Peterman, D.R., Mincher, B.J., McGrath, C.A., Baker, J.D. Cesium and strontium extraction using a mixed extractant solvent including crown ether and calixarene extractants. Pat W02006016892 (Publ. 16-02-16-2006). 

The variation of strontium distribution ratios DSr from nitric acid solution was investigated as a function of the irradiation dose. In toluene DCH18C6 solution, DSl was minimally affected by radiolysis, but decreased with the absorbed dose in the other nonaromatic solvents (254). Nevertheless, the distribution ratios measured after radiolysis were higher than expected, given the remaining extractant concentration, indicating some contribution from the degradation products (e.g., after an irradiation of 0.84 MGy, 70% of the crown ether was destroyed in chloroform, while the distribution ratio exhibited a decrease of only 30%) (254). 

Blasius, E., Klein, W., Schon, U. 1985. Separation of strontium from nuclear waste solutions by solvent extraction with crown ethers. J. Radioanal. Nucl. Chem. 89(2) 389-398. 

Horwitz, E. P, Dietz, M. L., and Fisher, D. E., Separation and preconcentration of strontium from biological, environmental, and nuclear waste samples by extraction chromatography using a crown ether, Anal. Chem., 63, 522-525, 1991. 

THE STRONTIUM EXTRACTION BY CROWN ETHERS TO A ROOM -TEMPERATURE IONIC LIQUID. SOLVATION IN DRY VERSUS "HUMID" FORMS OF THE LIQUID, AND PARTITIONING AT THE AQUEOUS INTERFACE... 

Dai, S., Ju, Y. H., Barnes, C. E. (1999), Solvent Extraction of Strontium Nitrate by a Crown Ether using Room-temperature Ionic Liquids, Dalton Trans. 1201-1202. 

Discuss the advantages and disadvantages of this type of column separation (specific crown ether extractant) for strontium. Why not use four times the column size to accommodate a normal amount of carrier (20 mg) ... 

Crown ethers are also used to remove radioactive elements from radioactive waste. For example, radioactive cesium and strontium can be extracted using specialized derivatives of 18-crown-6. 

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