JPS5985880A - Method and apparatus for continuously manufacturing lithium by electrolyzing lithium chloride in fused salt mixture - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a process for the continuous production of lithium by electrolyzing lithium chloride in a mixture of molten salts and to the apparatus used to carry out the process.

For example, U.S. Pat.
Within the scope of the method for producing silanes of specification No. 63.590,
A method for producing lithium by electrolyzing alkali chloride contained in a mixture of molten salts mainly consisting of lithium chloride and one or more alkali metal chlorides and/or alkaline earth metal chlorides is already known. A feature of this known method is that it utilizes at least one of the following properties.

- operation is semi-continuous; That is, an electrolytic mixture is charged into an electrolytic cell, a desired amount of lithium chloride is electrolyzed using this mixture, and lithium chloride is newly charged into the remaining mixture.

- the use of complex equipment, on the one hand, to separate the molten salt mixture and the resulting lithium in the electrolyzer itself, and on the other hand, to prevent the recombination of the chlorine gas products and the lithium; For example, try to control the atmosphere in the bath above the lithium layer very carefully and use a diaphragm in the bath between the anode and cathode.

The present invention aims to provide a simplified method for realizing this electrolysis. This method has the following characteristics.

Continuously carried out.

The electrolytic operation is considerably simplified because the product lithium is not separated from the molten salt mixture in an electrolyzer, and a mixture consisting of metallic lithium and molten salt mixture is therefore removed from the electrolyzer.

Electrolysis is carried out without using a diaphragm between the anode and cathode, by creating a lump of electrolytic medium in the gap between the anode and cathode to achieve rapid natural circulation.

Although it is possible for the anode to be attacked by lithium floating on the surface of the electrolytic medium and for the lithium to be reoxidized directly on the anode, the anode can be protected by lining the anode with an insulating heat-resistant material below the surface of the electrolytic medium. protected.

-Furthermore, since chlorine produced by electrolysis is continuously extracted without being diluted with inert gas, it can be used directly industrially.

If it is desired to recover pure lithium from the mixture withdrawn from the electrolyzer, it is of course advantageous to use known techniques for separating this metal from the molten salt mixture.

The electrolytic medium is lithium chloride and about 320-360
at least one forming a eutectic mixture that melts at a temperature of °C.
It consists of a mixture of molten salts based on other alkali metal chlorides and/or alkaline earth metal chlorides. An example of a binary mixture that can be used is a mixture of lithium chloride and potassium chloride. Examples of ternary mixtures that can be used include mixtures containing, in addition to lithium chloride and potassium chloride, sodium chloride, rubidium chloride, strontium chloride, magnesium chloride, calcium chloride and barium chloride.

In any case, the operation is carried out in a liquid medium, the electrolysis must be carried out at a temperature of about 400-500 °C, preferably about 450 °C, and the composition of the molten salt mixture fed to the electrolyzer is such that Advantageously, the mixture used approximates a eutectic composition of the lithium chloride which is subjected to excess electrolysis. In this way, for example when using a mixture of lithium chloride and potassium chloride as electrolytic medium, approximately 45
It is believed that at 0°C the amount of lithium chloride in this mixture can vary from about 69 mole percent of the molten salt mixture entering the electrolyzer to about 56 mole percent of the mixture leaving the electrolyzer. In this case, lithium chloride can be used in excess and may be present up to 10 mol % based on the eutectic composition of the molten salt mixture of lithium chloride-potassium chloride.

The first feature of the method of the invention is that it is operated continuously. That is, a fluid consisting of a mixture of molten salts containing lithium chloride as the electrolyzable material is continuously fed into the electrolytic cell, and from the AM device the electrolysis products, namely chlorine on the one hand and metallic lithium and molten salts on the other hand, are fed into the electrolytic cell. Take out the mixture.

Another feature is that lithium is not separated from the molten salt mixture. This feature, in combination with the natural circulation described below, protects against the possible recombination of lithium floating on the surface of the molten salt mixture with chlorine forming a -F atmosphere at the surface of the electrolytic medium. The result is that it fulfills its role. Therefore, no special precautions need to be taken to isolate the electrolytic medium from the chlorine atmosphere.

Thanks to the rapid natural circulation of the electrolytic medium, large amounts of electrolysis can be carried out without the use of diaphragms. This circulation is called ``natural'' because it can be achieved simply by introducing chlorine bubbles generated at the anode into the electrolytic medium. Therefore, although it is not necessary to use circulation means independent of this natural circulation means, it is not impossible.

The electrolytic medium is introduced vertically by the upward movement of the chlorine bubbles in the gap between the anode and the cathode, so that this medium can newly enter the gap between the anode and the cathode through a suitably provided opening. Preferably, the recirculation of the medium in the electrolytic cell is organized in such a way that it descends again into the cavity located beyond the cathode. If Vo is the rate of passage of the electrolytic medium through the gap between the anode and cathode in the absence of natural recirculation, the rate ■ actually achieved by this recirculation is about 100 of Vo.
(This value is the average value of various tests carried out at 05-5α/sec), so the circulation rate of the electrolytic medium is high.

To allow this natural circulation of the electrolytic medium, the top of the cathode is sunken, preferably funnel-shaped.

The rise of the electrolytic medium and the fact that the cathode is preferably funnel shaped forces the lithium against the cell walls, thereby overflowing while minimizing recombination with chlorine.
This facilitates the natural removal of lithium.

Finally, the anode must be protected from possible attack by floating lithium by a rim of insulating, refractory material immersed in the electrolytic bath. Refractory material refers to a material that is inert to the products it comes into contact with at electrolysis temperatures, essentially a mixture of molten salts, chlorine and lithium. This material must be electrically insulating. Therefore, the anode rim uses materials such as alumina, quartz, silica, thorium oxide, zircon or beryllium oxide.

According to another embodiment of the process of the invention, lithium-calcium alloys containing at least 50 mol % lithium can be produced in a similar manner. In this case, electrolysis of the lithium chloride-calcium chloride mixture is ensured under similar conditions in the same molten salt mixture as described above.

The method according to the invention leads to the realization of an electrolytic cell having the technical characteristics described below. - the electrolytic cell comprises an anode surrounded by a cathode, the upper part of which is immersed in the bath is preferably funnel-shaped, and the bottom of the cathode is provided with a plurality of openings; thing.

Feeding the electrolytic cell is preferably accomplished by introducing the molten salt mixture at its bottom.

Finally, the electrolytic cell is equipped with a withdrawal device for discharging the mixture of molten salts and metallic lithium on the one hand and the gaseous chlorine on the other hand.

These devices consist of overflow means and means for evacuation of the gas phase floating above the electrolytic medium.

Hereinafter, an embodiment of the present invention will be described for an electrolytic cell having a single anode-cathode pair, but the present invention is not limited to this embodiment. A schematic cross section of this electrolytic cell is shown in FIG.

In FIG. 1, the main body of the electrolytic cell 1 is made of stainless steel.

The cathode 2 is likewise made of stainless steel and has a cylindrical shape.

This cathode is welded to the bottom of the electrolyzer and has an opening 3 in the lower part that allows circulation of the electrolytic medium within the electrolyzer. The upper part 4 of the cathode is arranged so as to be below the surface of the electrolytic medium (when the cell is functioning) and is funnel-shaped.

The positive jfM6 is made of graphite and has a cylindrical shape, and is located inside the cathode 2. This anode is bordered by alumina 10 above the electrolytic medium and up to a certain distance below the surface of the medium (when functioning as an electrolytic cell).

The supply of the molten salt mixture takes place at the bottom of the electrolytic cell by means of a supply pipe 5 which leads directly below the anode-cathode gap.

Gas (chlorine) is taken out at a point 9 in the upper part of the electrolytic cell. The mixture obtained by electrolysis is removed via conduit 7. The level 8 of this conduit 7 determines the level of the electrolytic medium in the electrolytic cell.

An explanation of the magnitude of the dimensions of this type of electrolytic cell is that the distance between the anode and cathode is of the order of 1-50 rIL;
The height of the electrolytic medium (approximately the depth to which the anode is immersed) is 2-1.
It is about 0cIIL.

As is clear from the above description, the chlorine generated during electrolysis is discharged from the electrolyzer without being diluted with, for example, an inert gas. This feature is important to the extent that chlorine can be used industrially as it is.

The electrolyzer is used for electrolyzing lithium chloride in a mixture of molten salts or, according to another embodiment of the invention, for simultaneously electrolyzing lithium chloride and calcium chloride when calcium chloride is present in the mixture. Do (Li
-Ca alloys).

According to the present invention, lithium chloride is electrolyzed in a mixture whose main components are lithium chloride-potassium chloride and which has a composition close to that of a eutectic composition. Current intensity 45A, cathode active surface area 80crIL2, cathode active surface area 4o, 2. A Faraday yield of 85-90X was obtained at a voltage of 6V for a distance t6ari between the poles.

It can therefore be seen that lithium can be obtained with this relatively simple device at very satisfactory energy costs (27 kwh/kg I, i).

In another embodiment, a mixture containing lithium chloride-potassium chloride, calcium chloride as main components and having a composition close to a eutectic composition is electrolyzed. Faraday yield is 85N for current intensity 40A, cathode active surface area t5dm2, anode active area α47am2 (distance between both poles 2am)
The interfacial voltage of the electrolytic cell was 6.6μ, and the obtained Li
-Ca alloy is T, +76 mol% and Ca24 mol%
Contains.

The industrial application of the electrolyzer described above is achieved, for example, by using a plurality of anode-cathode pairs, as shown in FIGS. 2 and 2-2.

In FIGS. 2 and 2-2, 11 indicates the partition of the electrolyzer, and 12 is the cathode arranged inside the electrolyzer, these cathodes having a perforation 16 in their bottom. 14 indicates an anode edged with alumina at a predetermined height. 15 indicates a supply means for supplying the mixture to the electrolyzer. 16 indicates a means for discharging the electrolyzed mixture.

The total diameter of such an electrolytic cell is approximately 120 cIrL;
The diameter of the graphite anode (4) is approximately 14 cIIL, and the cathode placed around the anode is made of steel and has an inner diameter of approximately 2
It is 0crIL. The high part of the anode is lined with alumina.

The electrolytic cell was fed with a lithium chloride-potassium chloride mixture containing approximately 10% excess of lithium chloride relative to the eutectic composition, the electrolysis temperature was 450°C, and the electrolysis temperature was 12 kA (or 4
x3 kA) (anode current density 85,2, A/am2
and cathodic current densities of 5 B, 7 A/dm2) and 7 ■. At the appropriate flow rate, 2.8 kg of lithium was produced dispersed in the molten salt mixture. This corresponds to a Faraday yield of 90%.

[Brief explanation of the drawing]

FIG. 1 shows a schematic cross-sectional view of an electrolytic cell according to one embodiment of the invention having a single anode-cathode pair. 2 and 2-2 respectively show a schematic cross-sectional view and a schematic cross-sectional view of an electrolytic cell according to an industrial scale embodiment having a plurality of anode-cathode pairs. 1 : Electrolytic cell 2 : Cathode 3 : Opening 4 : Cathode top 5 : Supply pipe 6 : Anode 7 : Conduit 8 : Level 9 : Chlorine extraction point 10 : Alumina 11 : Partition wall 12 : Cathode 13 : Perforation 14 : Anode 15 : Supply Means 16: Discharge means

Claims (1)

[Claims] 1) Lithium in a mixture of molten salts obtained by continuous electrolysis without using a diaphragm between the anode and cathode so that an electrolytic medium naturally circulates between the two electrodes, and without any separation operation. A method for continuously producing lithium by electrolyzing lithium chloride in a mixture of molten chloride, characterized by continuously recovering gaseous chlorine. 2) A mixture of molten salts consisting of a mixture of lithium chloride and potassium chloride, containing up to 10 mol% of lithium chloride in excess of the eutectic composition.
2. Process according to claim 1, characterized in that the heating is carried out at a temperature of 0'lC1, preferably 450°C. 3) The electrolytic cell comprises an anode surrounded by a cathode, the bottom part of which is provided with a plurality of openings, and the upper part of the cathode immersed in the bath is preferably funnel-shaped. ,
The electrolytic cell is supplied by introducing lithium chloride into the molten salt mixture at its bottom, and the electrolytic cell is provided with a device for removing the resulting mixture, said device being equipped with an overflow means and an electrolysis device. means for evacuation of the gas phase floating above the medium, and characterized in that the anode is lined with an insulating heat-resistant material at the part where it comes into contact with the atmosphere floating above the electrolytic medium and is submerged in the medium. An electrolytic cell that can be used to carry out the method according to claim 1 or 2. 4) The electrolytic cell according to claim 3, comprising a plurality of anode-cathode pairs.