JPH0213032B2 - - Google Patents

Description

[Detailed description of the invention]

(Technical Field) The present invention relates to a method for producing high-purity metallic lithium, and in particular, the present invention relates to a method for producing high-purity metallic lithium.
High-purity lithium metal with suppressed concentrations of alkali metals such as calcium and alkaline earth metals,
It relates to a method by which it can be advantageously manufactured. (Prior art and its problems) Traditionally, the manufacturing method of metallic lithium is as follows:
The molten salt electrolysis method is known, and uses lithium chloride as the lithium raw material and potassium chloride to lower the melting point of the bath as an electrolytic bath. In the molten state, a graphite anode and iron By electrolyzing using a cathode, the desired metallic lithium is produced by depositing it on an iron cathode. However, metallic lithium obtained by such electrolytic methods contains a considerable amount of impurities such as sodium and calcium derived from sodium chloride, calcium chloride, etc. contained in the raw material salt, and cannot be called high-purity lithium. It was not something that could be done. Therefore, in order to produce high-purity metallic lithium only by the electrolytic process as described above, it is conceivable to use high-purity lithium chloride as a raw material. Both sodium chloride and calcium chloride have lower decomposition voltages than lithium chloride, so
This is because sodium and calcium are precipitated more preferentially than lithium. However, the use of such high-purity lithium chloride leads to a rise in manufacturing costs, making the obtained metallic lithium extremely expensive. In addition, as another method, when obtaining high-purity lithium from crude lithium containing impurities, a vacuum distillation operation is applied to the crude lithium. This requires considerable high temperature and high vacuum, which necessitates a large investment in equipment, and the yield is also low, which inevitably leads to an unavoidable increase in the cost of the high-purity metallic lithium obtained. . (Solution Means) Here, the present invention has been made against this background, and its gist is that 34 to 64% by weight of lithium chloride and 66% by weight of potassium chloride
A mixed molten salt consisting of ~36% by weight, or by further adding 1~20% by weight of sodium chloride to a mixture of both components, is heated to 0.005~1A using solid aluminum as the cathode. By electrolyzing at a cathode current density of /cm ² , part or all of such cathode is converted into a high-purity aluminum-lithium alloy, and then this obtained aluminum-lithium alloy is loaded into a given distillation apparatus, Lithium vapor is generated by distillation under reduced pressure, and the lithium vapor is condensed and collected to obtain the desired high-purity metallic lithium. (Specific configuration/effect) As described above, the present invention provides a method for using lithium chloride (LiCl).
The first step is the electrolytic manufacturing process of Al-Li alloy, in which the aluminum (Al) cathode is converted into a high-purity Al-Li alloy by molten salt electrolysis, and the Al-Li alloy thus obtained is distilled under reduced pressure. The second step is to obtain high-purity lithium metal by condensing and collecting the lithium vapor that is formed. Patent application 1989-215989
(Japanese Patent Publication No. 61-46557), the method for producing a high-purity Al-Li master alloy is used as is. That is, the first example shows an example of an electrolytic cell for producing Al-Li alloy for carrying out the first step of the present invention.
In the figure, a crucible 2 made of sintered alumina or the like is placed in an electrolytic furnace outer cylinder 1 made of stainless steel or the like that is heated by an external heat source, and a mixture of LiCl and KCl of a predetermined composition is placed in the crucible 2. The electrolytic bath 3 is constituted by storing salt or a mixed salt obtained by adding NaCl to the salt in a molten state. In this electrolytic bath 3,
An anode 4 made of graphite and a cathode 7 made of solid Al are immersed and electricity is applied between these electrodes to carry out a predetermined electrolytic operation. The anode 4 is suspended from above by a lead rod 6 in an exhaust pipe 5 for collecting and discharging chlorine gas generated by electrolysis, and a solid Al cathode 7 Even in this case, it is suspended from above by a lead rod 8. In such an electrolytic cell configuration, LiCl
An electrolytic bath 3 consisting of a mixed molten salt containing
By electrolyzing at a cathode current density of 0.005 to 1 A/cm ² , Li deposited on the cathode 7 can be alloyed with solid Al constituting the cathode 7 to form a high-purity Al-Li alloy. It can be done. In this electrolytic operation, the composition of the electrolytic bath 3 is LiCl: 34 to 64% by weight and KCl: 66 to 36% by weight.
The desired effect can be obtained within such a range of ingredients, but NaCl can also be added in an amount of 1 to 20% by weight of the mixture of both ingredients. The addition of NaCl lowers the melting point of the LiCl-KCl mixed salt and lowers the electrical resistance of the electrolytic bath 3, which is advantageous in reducing power consumption in the electrolytic process. In addition, in the electrolytic operation of such a mixed molten salt, the cathode current density at the solid Al cathode 7 is set to 0.005.
~1A/ ^cm2 is required. Note that when this cathode current density exceeds 1 A/cm ² , the amount of precipitated Li floating on the bath surface near the cathode becomes larger than the amount of precipitated Li that diffuses into the Al of the cathode.
This causes a problem that the alloying yield of Li with respect to Al is low, and on the other hand, the cathode current density is
If it is lower than 0.005 A/cm ² , the amount of Li precipitated will be small, resulting in a small amount of Al-Li alloy produced, causing problems such as reduced productivity. However, it is desirable that such electrolytic operation be continued within a range where molten Li metal, impurities, etc. do not float on the bath surface around the cathode 7. Such molten Li metal is generated as a function of cathode current density and electrolysis time, and if such a substance is generated, it will adhere to the surface of the cathode 7 and alloying will not proceed. This is because further electrolysis lowers the alloying yield and deteriorates the alloy purity. Incidentally, such floating of metal, etc. can be easily detected not only by visual observation but also by a change in cathode potential or bath voltage (furnace voltage). The Li deposited on the cathode 7 by the electrolytic operation as described above is the solid that constitutes the cathode 7.
It is alloyed with Al to produce a high-purity Al-Li alloy. In the present invention, the high-purity Al-Li alloy obtained in this way (part or all of the cathode 7) is used. From this, they were able to advantageously obtain high-purity metal Li. That is,
The alloy obtained by such electrolysis is a high-purity Al- containing about 18 to 25% by weight of Li, generally about 20% by weight.
However, in the present invention, by separating the alloyed portion of the cathode 7 or using the entire cathode 7 as it is, loading it into a predetermined distillation apparatus and distilling it under reduced pressure, By generating Li vapor, condensing and collecting the Li vapor, the desired high-purity metallic Li is obtained. Figure 2 shows an apparatus for distilling such an Al-Li alloy.
There, 9 is an electric furnace as a heating furnace, and this electric furnace 9 includes a crucible 1 made of alumina or the like.
A distiller outer cylinder 10 made of stainless steel or the like and having a cylindrical shape with a sealable bottom and housing the distiller 1 is set,
It can be heated to a predetermined temperature. In the crucible 11, a high-purity Al--Li alloy 12 obtained by alloying by the electrolytic operation described above is accommodated. In addition, the Li
The iron rod 13 for steam condensation hangs down to the middle of the outer cylinder 10, and a container for collecting condensed Li (made of stainless steel, etc.) is suspended from the lower end of the iron rod 13. A cooling pipe 15 is attached to the exposed portion so that the iron rod 13 can be cooled. Furthermore, the inside of the sealed space of the distiller outer cylinder 10 is maintained at a predetermined degree of reduced pressure by being sucked by a vacuum pump 17 through a suction path 16. Note that a trap 18 is provided on the suction path 16 to capture the escaping Li vapor.
Further, a pressure gauge 19 for detecting the degree of reduced pressure and a thermocouple 20 for detecting the temperature of the molten Al--Li alloy 12 are provided. Therefore, in such a distillation apparatus, the alloy obtained by the electrolytic operation is maintained in the sealed space of the distiller outer cylinder 10 under a predetermined reduced pressure by suction by the vacuum pump 17. The high-purity Al-Li alloy 12 is melted in the crucible 11 by heating in the electric furnace 9, and when further heated, Li, which has a higher vapor pressure than Al, is evaporated first. Therefore, by separating and collecting such evaporated Li vapor, Li can be advantageously separated from Al. Note that such high purity Al-Li alloy 12 is heated,
Since the melting point of the Al-20wt% Li alloy is 718°C, it is necessary to melt it at a temperature higher than that, but if the distillation temperature becomes too high, Al vapor will also be generated. , generally because it causes Al contamination of the metal Li to be separated,
As the distillation temperature, a temperature within the range of 720°C to 900°C will be suitably employed. In addition, the high-purity Al-Li alloy 1 in the crucible 11
2. The Li vapor generated from the molten metal comes into contact with the Li vapor condensing iron rod 13, which is cooled by the cooling pipe 15 and is located above the distiller outer cylinder 10. It condenses on the surface, flows down the surface of the iron rod 13, and drips into the Li collection container 14, and is collected as pure Li in the container 14, thereby forming a crucible. Al− in 11
It can be easily separated from the Li alloy 12. As described above, in the distillation operation according to the present invention, since the high-purity Al-Li alloy 12 is targeted, the vacuum distillation mainly involves separation and purification of Al and Li. Therefore, distillation purification is possible at a relatively low degree of vacuum.
For example, even if the degree of reduced pressure (degree of vacuum) is several hundred mmHg,
Distillation operation is possible, but usually 100mmHg~
Vacuum distillation is carried out at a low vacuum level of about 10 ⁻² mmHg, and the desired high-purity metallic Li can be advantageously extracted. However, conventional distillation purification of crude lithium (removal of Na, K, Ca, etc.) generally requires a degree of vacuum of 10 ^-2 mmHg or more, but as in the present invention, high purity Al-Li This is because when an alloy is used, it is sufficient to simply separate and purify Al and Li since it contains almost no Na, K, Ca, etc. In this way, the pure Li molten material dropped and stored in the Li collection container 14 is cooled and taken out from the distillation apparatus together with the container 14, thereby producing pure Li metal. It will be collected and used for the intended purpose. Note that the distillation residue in the crucible 11 can be reused as an Al cathode or an Al-several % Li alloy. (Examples) Examples of the present invention will be shown below to clarify the present invention more specifically, but the present invention is not limited in any way by the description of such examples. It goes without saying that it is nothing. In addition to the following examples and the above-mentioned specific description, the present invention includes various changes, modifications, and changes based on the knowledge of those skilled in the art, as long as they do not depart from the spirit of the present invention. It should be understood that improvements and the like may be made. First, using the electrolytic bath for manufacturing Al-Li alloy shown in Fig. 1, the composition of the electrolytic bath 3 was changed to 50% by weight LiCl.
The solid Al cathode 7 is alloyed to form a high-purity Al-Li alloy by electrolyzing it at 450°C under the conditions shown in the table below. Manufactured. Next, using this obtained Al-Li alloy, it was loaded into the distillation apparatus shown in Figure 2 and distilled under reduced pressure under the conditions shown in the table below to remove impurities as shown in the table below. We obtained extremely high-purity metallic Li with significantly less amount of metal.

[Table] In contrast, by using an iron cathode as the cathode 7 according to a conventional Li metal production method such as molten salt electrolysis, Li metal can be directly produced under the same electrolytic conditions of impure molten salt as described above. When I tried to manufacture it,
The obtained metal Li contains Na: 9000ppm, Ca:
400 ppm, K: 70 ppm, and the impurity concentration was extremely high. (Effects of the Invention) As is clear from the above explanation, the present invention provides the following advantages:
First, a high-purity Al-Li alloy is produced (first step), and then the resulting Al-Li alloy is distilled under reduced pressure (second step), mainly to
By separating and purifying Al and Li,
Since it is designed to produce the target high-purity metallic Li, NaCl and
Regardless of the amount of impurities such as CaCl ₂ , in other words, even if it is impure LiCl, extremely high purity Li metal can be obtained. Therefore, by adopting the method of the present invention, it is possible to use inexpensive, low-grade LiCl, that is, LiCl with many impurities, as a raw material, which makes it possible to effectively reduce the manufacturing cost of metallic Li, and also to reduce the vacuum distillation operation. Since the main purpose is simply the separation and purification of Al and Li, the distillation pressure can be relatively low vacuum, and therefore the distillation equipment configuration can be simplified. This also makes it possible to reduce the manufacturing cost of Li metal.

[Brief explanation of drawings]

FIG. 1 and FIG. 2 are schematic diagrams respectively showing an example of an electrolytic cell and a distillation apparatus for producing an Al-Li alloy used in the present invention. 1: Electrolytic furnace outer cylinder, 2: Crucible, 3: Electrolytic bath,
4: graphite anode, 5: exhaust pipe, 6, 8: lead rod,
7: solid Al cathode, 9: electric furnace, 10: distiller outer cylinder, 11: crucible, 12: Al-Li alloy, 13:
Iron rod for Li steam condensation, 14: Condensed Li collection container, 1
5: Cooling pipe, 16: Suction path, 17: Vacuum pump,
18: Trap, 19: Pressure gauge, 20: Thermocouple.

Claims (1)

[Claims] 1. 34 to 64% by weight of lithium chloride and 66% by weight of potassium chloride
A mixed molten salt consisting of ~36% by weight, or by further adding 1~20% by weight of sodium chloride to a mixture of both components, is heated to 0.005~1A using solid aluminum as the cathode. By electrolyzing at a cathode current density of / ^cm2 , such a cathode is converted into a high-purity aluminum-lithium alloy, and then this obtained aluminum-lithium alloy is loaded into a distillation apparatus and distilled under reduced pressure.
A method for producing high-purity metallic lithium, which is characterized by generating lithium vapor, and condensing and collecting the lithium vapor. 2. The method for producing high-purity metallic lithium according to claim 1, wherein the vacuum distillation is carried out at a temperature within the range of 720°C to 900°C. 3. The method for producing high purity metallic lithium according to claim 1 or 2, wherein the vacuum distillation is carried out under a pressure within the range of 100 mmHg to 10 ^-2 mmHg.