DE1098932B - Method and device for the separation of isotopes of lithium by electrolysis of a lithium salt melt - Google Patents

Description

ÜKUTSGHES

The invention relates to a method for separating the isotopes of lithium by electrolysis of a Lithium salt dimelze, in which a countercurrent required for the separation of the isotopes · in the electrolyte by introducing substances into the cathode space, which is what is deposited on the cathode Convert lithium into the salt that forms the electrolyte.

The mode of action of such a separation process is based on the difference in migration speeds of the isotopic anions or cations as they migrate to the corresponding electrodes. The separating effect can be increased by moving the electrolyte in one direction to the movement allows the ions to be separated to flow in the opposite direction. This countercurrent can also be found in generate molten salts. It keeps the slowest isotope away from the target electrode and makes it possible hence an accumulation of the fastest isotope in the area of the relevant electrode. Should. Ka, -tions are separated from each other, so · one can counterflow z. B. produce that brings the cation deposited on the cathode back together with an anion of the type of which it has just been separated by adding such aiiions e.g. B. introduces into the area of the cathode.

It is already known to separate lithium isotopes from molten Li NO _{3 by electrolysis, NO 2} and O _{2 being} continuously fed to the cathode compartment for the purpose of converting the lithium deposited on the cathode into lithium nitrate. A mixture of two different gases has to be introduced into the cathode compartment, and it is generally very difficult to establish an intimate contact between the lithium which is deposited and these gases, even when using a screen cathode, which requires a complete conversion of the lithium into the corresponding one Would result in salt. This disadvantage is particularly troublesome when used on an industrial scale.

The invention is based on the object of a method and to provide a device which avoids this disadvantage.

The solution to this problem is to keep the lithium salt melt in the cathode compartment steady or to add discontinuously one or more salts which are easily thermally decomposable into gases, the anion of which is the is the same as that of the electrolyte.

Carrying out the separation process according to this feature has the advantage that the Zugal> e one or more thermally decomposable salts in the cathode compartment a very complete and without Recombination of the metal process released at the cathode, achievable with special technical effort and a device for separating isotopes of lithium by electrolysis of a lithium salt melt

Applicant: Commissariat a l'Energie Atomique, Paris

Representative: Dipl.-Ing. R. Beetz, patent attorney, Munich 22, Steinsdorfstr. 10

Claimed priority: France of December 5, 1957

Eiichi Saito, Chateau du VaI Fleuri,

Gif sur Yvette, Seine-et-Oise (France),

has been named as the inventor

Lischen lithium is possible, since the amount of salt added is relative within the liquid electrolyte quickly diffuse into the area of the cathode and consequently the lithium in statu nascendi convert back into the salt that forms the electrolyte. The chemical units necessary to neutralize the positive lithium ions at the cathode are to a certain extent formed in situ, and the quantities required in each case can be supplied with regulate quite simple means.

According to a further feature of the invention, any excess of the added salt by additional heating of the electrolyte at one between the anode and cathode compartment decompose the lying point, so that the electrolytic separation process of the isotopes in is not disturbed in any way. This is also a flawless and against inaccuracies in the Dosing largely insensitive implementation of the process possible.

In a preferred embodiment of this electrolysis process according to the invention, the salt immediately subjected to electrolysis is lithium nitrate. Lithium nitrate is preferred to lithium chloride, although its mass effect μ is 0.050 smaller than the mass effect of chloride, which is μ = 0.147 {μ is defined as the ratio of

109 509/398

relative differences in mobility ν and masses m, so

Δ ν

μ =

m m

This disadvantage is offset by the much lower temperature at which the lithium nitrate can be electrolyzed in the melt flow (the melting point of LiNO ₃ is 255 ° C.), which also reduces the risk of corrosion by the lithium.

The countercurrent is generated by adding ammonium nitrate in the area of the cathode. The NOg ions, which are _{supplied by the NH 4} NO ₃ , combine at the cathode with the Li ions, which in turn arise during electrolysis.

The ions ⁶ Li have a migration speed which is greater than that of the ions ⁷ Li; After a certain period of electrolysis, the ions ⁶ Li are in a significantly higher concentration at the cathode than at the anode.

About dragging the additional salt into the diaphragm and thus the possible development of gases within this. To prevent part of the device, you can add the additional salt to a suitable thermally decompose at another point.

The device for carrying out the method comprises a heatable electrolysis cell, its anode compartment from the cathode compartment through a diaphragm - preferably in the form of a tube with a Filling of finely divided inert substances - is separated, being between the cathode compartment and the diaphragm an additional space that is open to the outside and must be kept at a higher temperature than the cathode space is provided.

The additional space is preferably provided with a special heating device.

The anode compartment of the cell can also be provided with an additional heating device.

With reference to the drawing, an embodiment of the method according to the invention will now be shown and a device used to carry out the method are described. This example shows the utilization of the present invention for the separation of the isotopes of lithium by Melt-flow electrolysis of the salts.

The devices for carrying out the method, as they are exemplary together with this Application described form part of the present invention.

In the drawing, essentially only one electrolysis cell manufactured in accordance with the laboratory is shown. According to the invention, this cell contains between the anode compartment t and the cathode compartment 2 an additional open space or chamber 3. The anode space 1 is with the additional chamber 3 Connected via a U-shaped bent pipe section 4, in which the diaphragm necessary for the electrolysis 5 is arranged. This very fine diaphragm can consist of silica or glass powder.

The cathode space 2 and the additional chamber 3 are in turn also via a U-shaped connecting tube 6 connected to each other. The upper leg ends of the U-shaped tube 4 and parts the anode space 1 and the chamber 3 are according to the invention provided with an additional electrical heater 7.

The ammonium nitrate is fed into the filling funnel 8 which opens into the cathode space 2 in a regular sequence supplied via a conveyor belt 9. It can be supplied either as a powder or in the form of compressed tablets which then follow each other at a greater distance on the conveyor belt.

This cell is placed in a heating furnace (not shown), the temperature of which is between 280 and 300 ° C is maintained.

At the beginning of the electrolysis, the cell only contains pure lithium nitrate. As well as the electrolysis used the ammonium nitrate is added to the cathode compartment 2 or the cathode-side chamber of the cell regularly and continuously or in a discontinuous sequence, partly when the lithium is recombined is decomposed and continues to generate the desired countercurrent in the cell. That in excess existing ammonium nitrate is then in the intermediate chamber 3 by additional heating thermally completely decomposed with the formation of volatile gases. In this way one avoids disturbances that could trigger such a decomposition if it took place within the diaphragm 5. Also prevented the additional heating of the upper one Part of the anode space or container 1 there the formation of a salt crust, parts of which of vapor bubbles nitroeer vapors could be thrown upwards.

Merely as an example, it should be stated that in such a device with a current of 0.1 A / dm ² at 80 V after 3 days of electrolysis, a change in concentration of 3% in the melt flow within the anode compartment on the one hand and the cathode compartment on the other, was observed, which corresponds to an enrichment of the different lithium ions of 1.5% compared to the original concentration.

Claims (6)

Patent claims: 1. Process for separating the isotopes of lithium by electrolysis of a lithium salt melt, in which a counterflow in the electrolyte required for the separation of the isotopes by introducing substances into the cathode space, which is what is deposited on the cathode Convert lithium into the salt forming the electrolyte, characterized in that the im Cathode chamber located lithium salt melt steady or discontinuous one or more thermally Adds salts which are easily decomposable into gases and whose anion is the same as that of the electrolyte. 2. The method according to claim 1, characterized in that it is carried out such that a Excess of the added salt by additional heating of the electrolyte at an intermediate Anode and cathode compartment is decomposed. 3. The method according to claim 1, characterized in that it is with lithium nitrate and ammonium nitrate is carried out. 4. Device for performing the method according to one of claims 1 to 3, consisting from a heatable electrolysis cell, the anode compartment of which is separated from the cathode compartment by a Diaphragm - preferably in the form of a tube with a filling of finely divided inert substances - is separated, characterized by a space between the cathode compartment and the diaphragm, to the outside open, to be kept at a higher temperature than the cathode space additional space. S. Device according to claim 4, characterized 6. Apparatus according to claim 4 or 5, characterized in that the anode compartment of the Cell is provided with an additional heating device. Considered publications: ~ - ~ "■ -" ^ ™ ^ "~" ~ ~ - —— ^^ ■ - - - ~ '^ - j ~ - ~ - ι - ~ —'— ^ j - g —ι ~ - ~ a— ^ ^ ^ - - - ~ - ^ ^ '--- ^ indicates that the additional room is equipped with a magazine for nature research, vol. lla, p. 75 special heating device is provided. to 79. 1 sheet of drawings © 109 509/398 1.61