Process of Preparing Cesium Salts From Cesium Aluminum Alum

This invention relates to a process of preparing cesium salts from cesium-aluminum-alum.

U.S. Pat. No. 3,489,509 discloses a process of preparing cesium compounds having a high purity. Cesium-alu-minum-alum is treated with barium hydroxide and is subsequently reacted with carbon dioxide. Thereafter barium halide is added in a stoichiometric amount so that pure cesium halide is formed. For the formation of cesium halide from cesium-aluminum-alum it is undesirable that the use of barium hydroxide and barium halides involves substantial costs and that a neutralization must be effected by a reaction with carbon dioxide.

It is an object of the invention to provide a process by which the disadvantages described hereinbefore can be avoided.

That object is accomplished in accordance with the invention in that cesium-aluminum-alum is reacted in a single vessel in the presence of water with calcium hydroxide in an amount which is equimolar to the amount of aluminum and with a readily water-soluble calcium salt in an amount which is equimolar to the amount of cesium and the precipitated aluminum hydroxide and the precipitated calcium sulfate are separated by filtration or centrifugation. In the process in accordance with the invention the use of barium compounds, which are more expensive than calcium compounds, and the neutralization with carbon dioxide are omitted and the further advantage is provided that the direct reaction results in cesium salt solutions in the concentration range of >10%. This considerably reduces the work required to remove water in the preparation of concentrated cesium salt solutions and of solid salts.

Whereas it would be obvious to directly react cesium-aluminum-alum with the stoichiometric amount of calcium hydroxide according to the equation

that reaction will not give satisfactory yields of cesium hydroxide, probably because the resulting precipitate of aluminum hydroxide and gypsum masks the surface of suspended calcium hydroxide so that it is not available for the reaction. On the other hand it is not possible to compensate the amount of masked calcium hydroxide by the use of calcium hydroxide in a surplus which can be so exactly controlled that a contamination of the desired product cesium hydroxide with calcium hydroxide, which can be removed only with difficulty, can be avoided. For this reason it is common in the art to use barium hydroxide, which is more readily soluble but is much more expensive.

By the process in accordance with the invention the pure cesium salts can surprisingly be prepared by a reaction in a single vessel. The formate, acetate, citrate, chloride or bromide of calcium, can desirably be used as a readily water-soluble calcium salt.

The cesium salts are preferably prepared from cesium-aluminum-alum in that the reaction is carried out at temperatures in the range from 80.degree. to 120.degree. C. and at a suspension density which at the beginning of the reaction amounts to 100 to 500 g insoluble solids per liter water. The insoluble solids consist of those partial amounts of Ca(OH).sub.2, of the cesium salt, and of the cesium-aluminum-alum which are insoluble at the beginning of the reaction.

The invention will be explained more in detail in the following examples.

A heatable and stirrable vessel having a capacity of 500 liters was charged with 290 liters water, 17 kg calcium oxide, and 13 kg calcium formate. The suspension was heated to the boiling point with stirring and then 111 kg cesium-aluminum-alum were added. The reaction mixture was stirred at its boiling point for two hours and was subsequently allowed to cool and was then filtered. The filtrate contained about 11% cesium formate, 0.1% calcium ions, 0.05% aluminum ions, and 1% sulfate ions. The filtration residue was re-washed with water. About 95% of the cesium that had been supplied were converted to cesium formate and were detected in the combined filtrates.

An apparatus which was similar to that used in Example 1 but had a capacity of 1000 liters was charged with 375 liters water, 43.8 kg calcium oxide, and 45.8 kg calcium acetate. The suspension was heated to its boiling point; then 296 kg cesium-aluminum-alum were added. Thereafter the suspension was stirred at its boiling point for 2 hours and was allowed to coot and was then filtered. The resulting solution contained about 20% cesium acetate and contained 58% of the cesium that had been supplied. The filtration residue was re-washed to recover additional 37% of the supplied cesium as an aqueous solution of cesium acetate.