Cesium leaching

Kryukova, A. I., Artemyeva, G. Yu., Demarin, V. T., Alferov, V. A. 1991. Cs-containing complex phosphates. Constitution. Cesium Leaching. Radiochemistry, 33, 186-191 (in Russian). 

Cesium will be separated from the supemate and loaded onto zeolite. The cesium-zeolite product could then be mixed with a solid matrix, such as cement or glass, to further reduce the cesium leach rate. A possible alternative is to mineralize the cesium by methods developed by Robert Barrer in England (2) and by Atlantic Richfield Co. at Hanford... 

Decomposition with Bases. Alkaline decomposition of poUucite can be carried out by roasting poUucite with either a calcium carbonate—calcium chloride mix at 800—900°C or a sodium carbonate—sodium chloride mix at 600—800°C foUowed by a water leach of the roasted mass, to give an impure cesium chloride solution that is separated from the gangue by filtration (22). The solution can then be converted to cesium alum [7784-17-OJ, CS2SO4 Al2(S0 2 24H20. Extraction of cesium from the poUucite is almost complete. Solvent extraction of cesium carbonate from the cesium chloride solution using a phenol in kerosene has also been developed (23). 

Hydrochloric acid digestion takes place at elevated temperatures and produces a solution of the mixed chlorides of cesium, aluminum, and other alkah metals separated from the sUiceous residue by filtration. The impure cesium chloride can be purified as cesium chloride double salts such as cesium antimony chloride [14590-08-0] 4CsCl SbCl, cesium iodine chloride [15605 2-2], CS2CI2I, or cesium hexachlorocerate [19153 4-7] Cs2[CeClg] (26). Such salts are recrystaUized and the purified double salts decomposed to cesium chloride by hydrolysis, or precipitated with hydrogen sulfide. Alternatively, solvent extraction of cesium chloride direct from the hydrochloric acid leach Hquor can be used. 

The residue is leached to give cesium sulfate solution, which can be converted to cesium chloride by ion exchange on Dowex 50 resin and elution with 10% HCl, treatment using ammonia or lime, to precipitate the alurninum, or by solvent extraction, followed by purification at neutral pH using hydrogen peroxide or ammonia. 

Rubidium is recovered from its ore lepidolite or pollucite. Mineral lepidolite is a lithium mica having a composition KRbLi(OH,F)Al2Si30io. The ore is opened by fusion with gypsum (potassium sulfate) or with a mixture of barium sulfate and barium carbonate. The fused mass is extracted with hot water to leach out water-soluble alums of cesium, rubidium, and potassium. The solution is filtered to remove insoluble residues. Alums of alkali metals are separated from solution by fractional crystallization. Solubility of rubidium alum or rubidium aluminum sulfate dodecahydrate, RbAl(S04)2 I2H2O falls between potassium and cesium alum. 

Rubidium acid salts are usually prepared from rubidium carbonate or hydroxide and the appropriate acid in aqueous solution, followed by precipitation of the crystals or evaporation to dryness. Rubidium sulfate is also prepared by the addition of a hot solution of barium hydroxide to a boiling solution of rubidium alum until all the aluminum is precipitated. The pH of the solution is 7.6 when the reaction is complete. Aluminum hydroxide and barium sulfate are removed by filtration, and rubidium sulfate is obtained by concentration and crystallization from the filtrate. Rubidium aluminum sulfate dodecahydrate [7488-54-2] (alum), RbA SO 12H20, is formed by sulfuric acid leaching of lepidolite ore. Rubidium alum is more soluble than cesium alum and less soluble than the other alkali alums. Fractional crystallization of Rb alum removes K, Na, and Li values, but concentrates the cesium value. Rubidium hydroxide, RbOH, is prepared by the reaction of rubidium sulfate and barium hydroxide in solution. The insoluble barium sulfate is removed by filtration. The solution of rubidium hydroxide can be evaporated partially in pure nickel or silver containers. Rubidium hydroxide is usually supplied as a 50% aqueous solution. Rubidium carbonate, Rb2C03, is readily formed by bubbling carbon dioxide through a solution of rubidium hydroxide, followed by evaporation to dryness in a fluorocarbon container. Other rubidium compounds can be formed in the laboratory by means of anion-exchange techniques. Table 4 lists some properties of common rubidium compounds. 

The leach rates seen here can be compared to those from a similar test on simulated waste glass of the same composition. The leach rates for cesium and strontium from the fully radioactive Rlass were the same as the leach rates of the simulated glass. Although both tests were done on bulk glass samples, they differed in configuration. The fully radioactive samples were disks cm (height) x 3.5 cm (diameter)], and the... 

The release rate was determined for 10 radioisotopes from fully radioactive waste glasses in deionized water for a period of 1.75 years. For cesium and strontium, good agreement exists between the leach rates for simulated and fully radioactive glass of the same composition. 

The agreement between these two tests indicated no significant change in leach rate with time on this short time scale, for the particular elements studied ( i.e.j barium, strontium, cerium, and rare earths). It was not possible to determine the cesium content in these granules because, for economy reasons, cesium was not included in the calcine production. The results of these measurements are given in Table III. Significant differences in the leach rates of the alkaline earths (barium, strontium) the RE (europium), and cerium are observable. 

To verify that carriers were not leaching from the membrane, cesium fluxes were measured for 24 h with diisopropoxy calix[4]arene crown-6 and di-NPOE calix[4] arene crown-6 (for this calixarene, the alkoxy group is replaced by a NPOE moiety) as carriers, after which both the source phase and the receiving phase were replaced. The cesium flux remained constant even after three replacements thus it, was concluded that the carriers are not leaching from the membrane (Table 4.13).79... 

Our program to determine leach rates is just beginning. The data needed are leach rates of plutonium, strontium, and cesium at ambient temperature. The simplest fastest method to calculate leach rates is... 

The cancrinite product has a low leach rate. Values obtained by leaching with distilled water are in the range of lO to 10" g of sample/ cm -day based on BET surface areas of powdered samples. Diffusion of cesium ion from the product into the leachant is slower than for the sodium ion. 

In this respect, the recently discovered family of materials synthetized by silicate condensation around surfactant micelles (Micelle-Templated Silica, MTS) provides unique inorganic support [11,12] due to their regular arrays of uniformly sized channels in the mesopore range of 20-100 A. This solid was recently impregnated with cesium oxides with the aim to obtain superbase catalysts [13]. Nevertheless, the leaching of the basic particles cannot be excluded. In view to avoid such possible phenomena, we have studied the covalent attachment of basic functions such as amino groups on the MTS surface... 

Concrete is a cheap fire and corrosion resistant material. However, active species, especially easily soluble ions such as cesium, can be leached from it by water. Addition of plastic binders to the concrete in order to improve its properties have been suggested. In the continuous bitumen extruder process for semi-liquid wastes all water is directly eliminated, considerably reducing the waste volume. The bitumen mixture is placed in steel drums of standard size (150-2001). When additional shielding is desired, the filled drums are placed into disposable or reusable sleeves of concrete, iron, or lead. Such a sleeve of 12 cm lead weighs 7 t, and reduces the surface dose rate by a factor of —10. A typical unshielded bitum i drum may have a surface dose rate of 1 Sv h necessitating remote handling. 

Quantitatively cesium does not appear to be particularly abundant in the earth s crust. It is generally found as a constituent of complex minerals, not in a pure halide form as are potassium and sodium. The two best known minerals are pollucite and rhodizite, though cesium can be found dispersed in rocks, soils, and clays [3]. High-purity cesium is produced from Canadian pollucite ore by a cyclic sulfuric acid leach followed by fractional crystallization to give a rubidium-ftee cesium alum, which is subsequently converted to cesium chloride by thermal decomposition and ion exchange [4j. 

With regard to the fission product isotopes of Zr, Nb, Ru, Ce, Pr, La it can be assumed that they are not liberated directly from the fuel of a failed rod but that they are released by leaching of the fuel pellets and that the amount transported to the coolant is equivalent to the amount of fuel released from the defective rod. On the other hand, a direct release is assumed for strontium and barium, with the investigations suggesting a release rate lower by a factor of 10 than that of cesium (Beslu et al., 1984). 

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