Chemistry of inorganic compounds – Treating mixture to obtain metal containing compound – Alkali metal
Patent
1996-09-18
1999-05-04
Bos, Steven
Chemistry of inorganic compounds
Treating mixture to obtain metal containing compound
Alkali metal
423203, 423165, 423179, C01D 300, C01D 1700, C22B 2600
Patent
active
059002212
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to a process of preparing a solution which contains cesium and rubidium salts and has a density between 1.6 and 3.3 g/cm.sup.3. This process includes hydrothermal digestion of uncalcined pollucite and/or calcined lepidolite with an aqueous solution of Ca(OH).sub.2 at a digestion temperature of 200 to 280.degree. C. and under a pressure from 15 to 65 bars and at a suspension density between 8 and 18% by weight for 0.5 to 3 hours, separation from the insoluble solids, optional removal of calcium ions and lithium ions by an aeration with carbon dioxide and removal of the precipitated carbonates from the digestion filtrate and formation of the salts of cesium and rubidium by an addition of an acid or an acid anhydride to adjust the pH to at least 6. The density of the solution of cesium and rubidium salts is increased by an evaporation performed after the digestion, after the removal of the precipitated carbonates and/or after the addition of the acid or the acid anhydride.
The periodical "Tsvetnye metally--The Soviet Journal of Non-Ferrous Metals", Volume II, No. 5, pages 57 to 59 (1961) discloses a method of preparing cesium carbonate by a hydrothermal digestion of a pollucite-spodumene concentrate. The calcined minerals are subjected to a hydrothermal digestion with an aqueous solution of Ca(OH).sub.2 at 220.degree. C. and under a pressure of 20 atm for four hours. Optimum digestion conditions are achieved with 3 moles Ca(OH).sub.2 per mole SiO.sub.2. 88.3 percent by weight of the cesium contained in the mineral can be recovered and the alumo-cesium-alum can be recrystallized to prepare a cesium salt having a purity >99%. The Chemical Abstracts Reference 79/4949v (1973) discloses the conversion of Cs.sub.2 CO.sub.3 to CsHCO.sub.2 in a process in which the carbonate is reacted with formic acid in water.
Besides, the unpublished German Patent Application P 42 37 954.7 describes a process of preparing solutions which contain cesium salts and rubidium salts and have a density from 1.6 to 3.3 g/cm.sup.3 by a hydrothermal digestion of minerals which contain cesium and rubidium. That process has the process features mentioned first hereinbefore.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a process for preparing a solution of cesium and rubidium salts of the above-described type, which has a high yield in comparison to prior art processes and a suspension density above 8% by weight, permits a decrease of the fineness to which the starting materials must be ground and utilizes calcium oxide in a slight excess over silica.
That object is accomplished in accordance with the invention in a method of the above-described type in which uncalcined pollucite and/or calcined lepidolite having an average particle size up to 0.5 mm is digested in a rotary tubular autoclave and the mole ratio of SiO.sub.2 to CaO is in the range between 1:2.5 and 1:1.25.
The suspension density is defined by the concentration of the pollucite and/or lepidolite and of the undissolved CaO and/or Ca(OH).sub.2 in water.
It is surprising that it is possible under the stated process conditions to recover more than 90% by weight of the cesium and rubidium contained in the mineral by the hydrothermal digestion in a rotary tubular autoclave and to recover cesium and rubidium at low cost as a solution which contains cesium salts and rubidium salts and has a density between 1.6 and 3.3 g/cm.sup.3. In that process the grinding expenditure is relatively low because the minerals are used with an average particle size up to 0.5 mm and the surplus of CaO over the SiO.sub.2 contained in the mineral is also comparatively low.
In a preferred embodiment of the invention the first filtrate obtained after the separation of the carbonates and/or the post-filtration washing liquid is used as a mashing liquid for the next digestion. With that feature of the process in accordance with the invention it is possible to prepare solutions which contain cesium salts and rubidium salts and have a
REFERENCES:
patent: 3207571 (1965-09-01), Berthold
patent: 3489509 (1970-01-01), Johnson
patent: 5593650 (1997-01-01), Prinz et al.
Chem. Abstract: 100: 160074p, 1984, no month.
Chem. Abstract: 79: 4949v, 1973, no month.
Chem. Abstract: 73: 79009y, 1970, no month.
Tsnetnye Metallurgy, The Soviet J. Non-Ferrous Met., Bd. 2, Nr. 5, 1961, no month, pp. 57-59.
Hofmann Hartmut
Kobele Klaus
Prinz Horst
Schade Klaus
Bos Steven
Metallgesellschaft Aktiengesellschaft
Striker Michael J.
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