DE1047185B - Process for the extraction of anhydrous uranium and thorium fluorides - Google Patents

Description

GERMAN

The invention relates to a method for the recovery of anhydrous uranium and thorium fluorides the corresponding fluoride hydrates.

There are already processes for the production of beryllium and aluminum fluoride from the corresponding Oxydhydrates have become known, but apart from the fact that between the production of the anhydrous fluoride from the oxide hydrate on the one hand and the fluoride containing water of crystallization on the other hand there is a considerable difference in the relationship between aluminum, beryllium and Thorium-uranium so low that the transfer of technical measures is not an obvious choice.

In the production of anhydrous fluorides, which are mainly used for the reduction to the corresponding metals are required, it is advantageous to use a precursor containing water of crystallization by wet chemical means To precipitate fluoride. It becomes, for example, thorium after the removal of the rare earths by a a suitable separation method is usually obtained in the form of a nitrate solution, and it is proposed Thorium fluoride hydrate in a very pure form from such a solution with aqueous hydrofluoric acid to be separated quantitatively. If you try to dehydrate such fluoride hydrates by heating, so hydrolysis occurs with the formation of undesired oxyfluorides.

It has now become a continuous process for the recovery of anhydrous fluorides from uranium and Thoriums, whose fluoride hydrates tend to hydrolyze at higher temperatures, found that through the treatment of fluoride hydrates with hydrogen fluoride or gases containing hydrogen fluoride at temperatures marked above the dew point of the gases containing hydrogen fluoride and water vapor is. Fluoride hydrates and gases containing hydrogen fluoride must be carried in countercurrent will; At the same time, the supplied hydrogen fluoride-containing gases should also be preheated above the dew point be.

In the technical implementation of the method of the invention, certain difficulties arise, which mainly consist in the aggressiveness of the gases containing hydrogen fluoride at higher temperatures and in the difficulty of choosing suitable materials that are not only chemical but also at the same time withstand the thermal stress and avoid undesirable contamination of fluoride lead.

It has now been shown that the dewatering apparatus can consist in all parts of predominantly magnesium or aluminum-containing alloys' or aluminum-magnesium alloys, which are known for the above-identified Bean process for extraction
anhydrous uranium and thorium fluorides

Applicant:
German gold and silver separator

formerly Roessler,
Frankfurt / M., Weißfrauenstr. 9

Dipl.-Chem. Dr. Günter Wirths

and Friedrich Krall, Hanau / M.,

have been named as inventors

can be used at temperatures up to approx. 450 ° C are, while pure magnesium or aluminum is corrosion-resistant up to 550 ° C. It is also possible to use only the parts that come into contact with gases containing hydrogen fluoride to line these metals. Because of the sensitivity of the metals mentioned, one uses Particular care must be taken with aluminum and its alloys against moist hydrogen fluoride ensure that the work is carried out at temperatures which are certainly above the dew point of the resulting Mixtures of water and hydrogen fluoride lie.

It is also possible to use suitable temperature-resistant materials, also known per se, such as certain Special steels, to be lined with graphite .. Such a measure is particularly suitable for a rotary kiln or a vibrating chute suitable. Another possibility is the use of calcium fluoride as lining material for reaction tubes or channels. However, graphite or calcium fluoride should also be used Lined devices maintain temperatures above the dew point of the reaction gases will.

It is particularly advantageous in the practical implementation, not one along the reaction vessel Maintain uniform reaction temperature, but in the direction of movement of the solid to set a gradient according to increasing temperatures. On the inlet side of the crystal water containing Fluoride and in the adjacent part of the reaction vessel are accordingly temperatures

809 700/398

adhered to, although above the dew point of the mixture formed from hydrogen fluoride and Water lie, however, the limit temperature only exceed a little, above which the fluorides containing water of hydration no longer exist in any appreciable amount can exist. In contrast, in the part of the reaction vessel adjacent to the discharge for the anhydrous fluoride, temperatures are used, in which a complete dehydration of the hydrated fluoride takes place. For the first part temperatures above the dew point, preferably between 150 and 250 ° C., have proven to be the case for the reaction proved advantageous, while according to the invention those above for the other end of the reaction vessel 300 ° C, preferably between 350 and 550 ° C, * 5 to get voted.

The process of the invention can be carried out in the customary manner in rotary kilns, with a reliable fluorine-resistant sealing of the moving parts must be ensured. With regard to on the difficult handling of hydrogen fluoride, however, it has proven to be beneficial to carry out the process in a stationary reaction vessel, in which there are no moving ones Parts are to be sealed and the conveyance of the material through the reaction zone by periodically acting To make impulses. You can use the well-known vibration promotion, through the reaction vessel or a support located in it for the solid periodic vibrations that can be generated mechanically, magnetically or electrically. Unless in the rotary kiln, but according to the preferred embodiment described last, it is further advantageous to use those with a rectangular cross-section instead of tubular reaction vessels, the width of which significantly exceeds its height. One achieves that the material in a thin layer the reaction mass passes through and the oxide or the fluoride to be dehydrated in intimate contact with reaches the gaseous medium. It is advisable to further ensure that the gas pressure in the reaction vessel is above atmospheric pressure to e.g. B. to prevent ingress of atmospheric oxygen.

To avoid the risk of temporary condensation and to improve the heat economy of the To improve the process, you can use the fluoride hydrate according to a further advantageous embodiment Introduce preheated into the reaction vessel, the preheating temperature being at least the dew point temperature should correspond to the gaseous or vaporous reaction products. Similarly, can it may also be expedient to bring the gas containing hydrogen fluoride preheated to use, with preheating can also be carried out in vessels made of or with magnesium this metal are lined.

The process of the invention can be carried out using pure hydrogen fluoride will. However, it is sometimes advisable to use inert gases such as hydrogen, nitrogen, Helium, neon, argon and the like.

It is economically advantageous to use the moist, hydrogen-containing substances withdrawn from the reaction vessel To cool gases in a special device so far that the contained, aqueous hydrofluoric acid condensed. This acid can advantageously be used again for the production of fluoride hydrates containing water of crystallization be used. As equipment building material for the condensation device are recommended corrosion-resistant alloys. However, plastics such as polyvinyl chloride or especially are also suitable higher fluorine-containing polymers. Finally, carbon sealed with plastics can also do this be used.

example

Uranium tetrafluoride precipitated from aqueous solution by dilute, aqueous hydrofluoric acid is converted into granules with a grain size of 1 to 3 mm after filtering and washing out (in a manner known per se). After previous drying at 100 to 120 ° C., these granules are introduced in an amount of 25 kg per hour through a rotary valve 11 (see schematic drawing) via a conveyor chute 12 into the reaction tube 13 of a rotary kiln inclined by about 3 ° from the horizontal . The reaction tube 13 made of magnesium and having an inner diameter of 150 mm and a length of 4500 mm is fitted fairly tightly into a supporting steel tube. In the interior of the reaction tube 13 there are some baffles 15 for stowing the granulate. 14 and thus also 13 are heated by a furnace 16 such that a reasonably uniform temperature gradient is produced, starting with 150 ⁰ C at the entry end 17 and endigend 550 ° C about 750 mm from the discharge end 18 of the reaction tube. At this discharge end 18, gaseous, anhydrous hydrogen fluoride, preheated to about 300 ° C., is introduced in an amount of about 1 kg per hour through a pipe 19. The dehydrated granulate leaves the discharge end of the rotary tube and passes through a rotary valve 20 into a collecting container. It is expedient to flush with nitrogen in an amount of 300 to 400 liters per hour. The gases leaving the reaction tube leave the inlet end 17 via the tube 21 and are then condensed to form aqueous hydrofluoric acid.

Claims (7)

Patent claims: 1. Process for the production of anhydrous uranium and thorium fluorides, in particular of Uranium tetrafluoride, characterized in that the fluoride hydrates at temperatures above the dew point of the resulting gas mixtures containing hydrogen fluoride and water vapor in countercurrent guided, appropriately preheated hydrogen fluoride are treated. 2. The method according to claim 1, characterized in that the feed side for the Fluoride hydrate adjacent part of the reaction vessel to temperatures above the dew point the resulting mixture of hydrogen fluoride and water, preferably between 150 and 250 ° C, while in that on the discharge side of the anhydrous fluoride lying part of the reaction space temperatures above 300 ° C, advantageously between 350 and 550 ° C. 3. The method according to any one of the preceding claims, characterized in that the Promotion of the solids through the reaction space by periodically acting pulses, in particular by vibration. 4. The method according to any one of claims 1 to 3, characterized in that the hydrogen fluoride in a mixture with opposite to the fluoride and the Apparatus construction material inert gases is used. 5. The method according to any one of claims 1 to 4, characterized in that the reaction vessel, preferably by an entry device for the fluoride hydrate, such an amount of one inert gas is supplied so that the gas pressure in the reaction vessel is above atmospheric pressure. 6. The method according to any one of claims 1 to 5, characterized in that the apparatus construction material Aluminum or magnesium or an aluminum-magnesium alloy, which optionally may also contain small additions of other metals is used. 7. The method according to any one of claims 1 to 6, characterized in that in the moist Exhaust gases containing hydrogen fluoride is condensed to hydrofluoric acid, which in turn is used for production of fluoride hydrates is used. Considered publications:
Swiss patents 176 917, 198 405. 1 sheet of drawings © 809 700/398 12.58