Cesium-containing liquid waste

Tetraphenylborate (TPB) was used at Savannah River to recover cesium from alkaline solutions, but attempts to treat HLW tanks with TPB resulted in the production of benzene (a TPB decomposition product) at levels that did not permit the safe operation of the process.8 Crown ethers and dicarbollides were proposed as extractants to remove cesium from acidic HAW, but these compounds are not selective enough to allow cesium to be removed from solutions containing large amounts of nitric acid or sodium nitrate.9 Dicarbollides were used in Russia at industrial scale to recover cesium from HAW, but the removal of cesium was only possible after partial denitration of the liquid waste.10... 

From a practical point of view, these calixarenes could be used to remove cesium from very alkaline liquid waste containing significant amounts of potassium, the selectivity for cesium over potassium being the most important for a synthetic ligand. 

To summarize, l,3-calix[4]-6/5-crowns containing six oxygen atoms appeared to be a promising family of carriers for the selective removal of cesium from high salinity media, such as medium-level radioactive liquid wastes, with SLMs. By choosing a highly hydrophobic organic diluent, 2-NPOE, and a very lipophilic cafix[4]- /5-crown in the 1,3-altemate conformation suitable for cesium complexation over sodium, very selective and stable SLMs can be obtained (over a period of 50 days). 

Z. Asfari, C. Bressot, J. Vicens, C. Hill, J.-F. Dozol, H. Rouquette, S. Eymard, V. Lamare and B. Tournois, Cesium Removal from Nuclear Waste Water by Supported Liquid Membranes Containing Calix-bis-brown Compounds, in ACS Symposium Series 642 (Anaheim CA, April 2-6, 1995), eds. R. A. Bartsch and J. D. Way, American Chemical Society, Washington, DC, Editon edn., 1996, pp. 376-390. 

Kandwal, R, Ansari, S.A., and Mohapatra, P.K. 2011. Transport of cesium using hollow fiber supported liquid membrane containing calix[4]arene-bis(2,3-naphtho)crown-6 as the carrier extractant Part II. Recovery from simulated high level waste and mass transfer modeling. J. Membr. Sci. 384 37 3. 

Cesium Removal from Nuclear Waste Water by Supported Liquid Membranes Containing Calix-bis-crown Compounds... 

Calix[4]-W5-crowns 1-7 are used as selective cesium-carriers in supported liquid membranes (SLMs). Application of the D esi diffusional model allows the transport isotherms of trace level Cs through SLMs (containing calix[4]-6/5-crowns) to be determined as a function of the ionic concentration of the aqueous feed solutions. Compound 5 appears to be much more efficient than mixtures of crown ethers and acidic exchangers, especially in very acidic media. Decontamination factors greater than 20 are obtained in the treatment of synthetic acidic radioactive wastes. Permeability coefficient measurements are conducted for repetitive transport experiments in order to determine the SMLs stability with time. Very good results (over 50 days of stability) and high decontamination yields are observed with l,3-calfac[4]-Aw-crowns 5 and 6. 

As an example, most of the radioactivity from plutonium production is found in the liquid high-level waste from the first cycle of the Purex process. This liquid is neutralized with sodium hydroxide and stored in earth-shielded tanks. There a sludge settles out that contains most of the radioactivity. The residual liquor is partially evaporated to decrease the volume of the waste, and sodium nitrite crystallizes on top of the sludge. In a process to be used at the Savannah River plant, the sodium liquor fraction, containing most of the cesium fission product, is pumped from the tank and precipitated with tetra-phenyl borate. The precipitate will be calcined and packaged for disposal in a high-level repository, and the sodium nitrate crystallized from the residual liquor and sent to a low-level waste repository. 

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