JP3093421B2 - How to generate lithium - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing lithium by electrolyzing a molten salt of lithium.

[0002]

2. Description of the Related Art For example, in the production of an Al-Li alloy,
Metallic Li is extremely active and has a difficulty due to a large difference in density from Al.

As a manufacturing technique for avoiding such difficulties, an electrolytic manufacturing method using molten lithium chloride (LiCl) or molten lithium chloride-potassium chloride (LiCl-KCl) as an electrolytic bath has been proposed. According to such an electrolytic manufacturing method, an Al-Li alloy with few impurities can be manufactured with high efficiency.

[0004]

However, in such a conventional manufacturing method, chlorine gas is generated along with the generation of Li by electrolysis of LiCl itself, which is an electrolytic bath component. When the method is to be carried out on a large scale, a large-scale treatment facility for the chlorine gas is required as a production facility.

[0005] Further, since LiCl itself is electrolyzed to extract Li, LiCl is consumed and replenishment of LiCl is required.
Since is expensive, deliquescent, and tends to contain moisture, it is necessary to handle LiCl carefully, which is a factor in reducing productivity in industrial production.

The present invention has been made based on such a background, and does not generate chlorine gas which requires a large-scale processing facility with electrolysis, and is easy and inexpensive to handle.
It is an object of the present invention to provide a method for producing Li using Li ₂ CO ₃ as a Li source and producing lithium at a low cost, which requires less electric energy for electrolysis.

[0007]

Means for Solving the Problems In order to achieve this object, the invention according to claim 1 is a method for electrolysis using a molten salt electrolytic bath containing a lithium salt, wherein carbon is contained in the anode chamber. An oxidation reaction of lithium carbonate generates carbon dioxide gas and lithium ions, the lithium ions are moved to a cathode chamber, and the lithium ions are reduced and reacted in the cathode chamber.

[0008]

According to the first aspect of the present invention, carbon and lithium carbonate are oxidized in the anode chamber to generate lithium ions, so that most of the generated gas is CO ₂ , and chlorine gas is generated as in the conventional case. Does not occur, so large-scale processing equipment is not required.

[0009] Lithium carbonate used as a lithium source has no deliquescence like conventional lithium chloride and is stable in the air, so that it can be easily handled.

Further, lithium carbonate is a starting material for all lithium compounds, and is inexpensive. In practical use, the cost can be expected to decrease, and the reaction in the anode chamber is performed by electrochemical reaction between carbon and lithium carbonate. Because of the reaction, a significant reduction in the electrolysis voltage can be expected, and a method for producing lithium which requires less electric energy for electrolysis and lowers costs can be provided.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to an embodiment of a method for producing an Al-Li alloy shown in the drawings.

In FIG. 1, reference numeral 1 denotes an apparatus for producing an electrolytic molten salt of an Al--Li alloy (hereinafter, simply referred to as an apparatus), and reference numeral 2 denotes a heating furnace.

The heating furnace 2 has a structure that can be sealed by a lid 3. A large-diameter first crucible 4 is installed in the heating furnace 2, and an electrolytic bath 5 is stored inside the first crucible 4. In this embodiment, the electrolytic bath 5 is in a molten state. Of LiCl is used simply.

Then, the electrolytic bath 5 in the first crucible 4
Inside, the second and third crucibles 6 and 7 each having a small diameter are provided.

The second crucible 6 is a crucible made of porous MgO, and has a cathode chamber 6a formed therein.
Contains 99.99% of molten aluminum 8. The conductor 12 to the cathode chamber 6a is W
(Tungsten) wire, which is protected by a protective tube 13 made of high-purity Al ₂ O ₃ .

The third crucible 7 is a crucible made of porous Al ₂ O ₃ , in which an anode chamber 7 a is formed, and is filled with the same molten LiCl as the electrolytic bath 5. The graphite electrode 1 is contained in the molten LiCl in the third crucible 7.
4 is immersed.

As described above, since both the second crucible 6 and the third crucible 7 are porous, they are electrically connected to each other through the electrolytic bath 5, but the macro flow of the molten salt is minimized. It is suppressed to.

This is because lithium carbonate (Li ₂ CO ₃ ) has a strong oxidizing power to the molten metal and, when it reaches the second crucible 6, oxidizes Li and significantly reduces the current efficiency of deposition. This is for keeping Li ₂ CO ₃ in the third crucible 7.

The above-mentioned LiCl and Li ₂ CO ₃ use transparent large crystals purified by blowing HCl and CO _{2 while} melting.

A guide tube 16 made of quartz and supported by the lid 3 is provided toward the third crucible 7 constituting the anode chamber 7a.

In the apparatus 1 of this embodiment, a reference electrode 17 and a thermocouple 18 are provided in order to grasp various phenomena in the method of the present invention in addition to the above-mentioned manufacturing-related structures.

The production of an Al-Li alloy using such an apparatus 1 is performed as follows.

That is, dry argon (A) is supplied into the heating furnace 2 of the apparatus 1 through the protective tube 13 and the guide tube 16.
r) is supplied, the atmosphere is dried Ar, and the inside of the heating furnace 2 is maintained at a constant temperature (973K) in the state shown in FIG.

In this state, electrolysis is performed. In order to observe a voltage change accompanying the electrolysis, the electrolysis is performed at a constant current.
In the electrolysis, Li ₂ CO ₃ as a Li source is introduced into the anode chamber 7 a in the third crucible 7 through the guide tube 16. This Li ₂ CO ₃ is a predetermined amount that has been weighed in advance.

[0025] This describes the desired electrolysis while introducing Li ₂ CO ₃ to the third crucible 7 through guide tube 16, lithium ions are Li ₂ CO ₃ in the anode chamber 7a reacts with the carbon of the graphite electrodes 14 The generated lithium ions move to the cathode chamber 6a, and Li is generated in the molten aluminum 8 in the second crucible 6. The precipitation of Li in the molten aluminum 8 in this way directly produces an Al-Li alloy.

The reaction accompanying the formation of this Al-Li alloy is as follows.

That is, FIG. 2 shows a change in potential with the progress of electrolysis. The potential of the electrode is measured by a current interruption method with reference to a reference electrode 17 composed of an Ag / AgCl electrode.

The potential of the second crucible 6 as a cathode is
This is a precipitation reaction of Li represented by the formula (1) into Al,
This is accompanied by the formation of an l-Li alloy.

Li ⁺ + e = Li (in Al) (1) The potential of the second crucible 6 shifts in a lower direction as the electrolysis proceeds. This is because the activity of Li precipitated in the equation (1) increases.

However, the potential in the composition range where Li is about 0 to 5 mass% is 0.2 to 0.2% lower than the potential of pure metal Li precipitation indicated by the broken line.
It shows a noble potential of about 0.3 V and shows that electrolysis is facilitated by alloying.

On the other hand, the potential on the side of the third crucible 7 as the anode shows a large change due to the addition of Li ₂ CO ₃ as is apparent from FIG.

That is, the potential of the third crucible 7 is always constant because Li ₂ CO ₃ does not exist at the initial stage and only the oxidation reaction of Cl ⁻ shown in the equation (2) is performed.

2Cl ⁻ = Cl ₂ + 2e (2) When Li ₂ CO ₃ is added to this, the potential is largely shifted in the base direction. This reaction involves the reaction of the electrode with graphite as in equations (3) and (4), and the potential change is extremely large at 1 V or more because the reducing power of carbon is used.

CO ₃ ^2- + 0.5C = 1.5CO ₂ + 2e (3) CO ₃ ^2- + 2C = 3CO + 2e (4) At 973K, the reaction of these two compounds is thermodynamically at 973K. The generation reaction should be dominant, but the reaction rate is different, so the CO ₂ generation reaction of equation (3) is actually dominant. This was confirmed by the fact that the amount of carbon consumed in both reactions was different by a factor of four from the weight reduction of the graphite electrode.

This indicates that the generated gas is safe CO ₂ instead of chlorine gas as in the prior art, and the consumption of the graphite electrode 14 is small (theoretical value is about 0.43 g / 1 g Li). ing.

The upper broken line in the figure is the potential when the activity of CO ₃ ^2- in the third crucible 7 is 1 (corresponding to pure Li ₂ CO ₃ ).

In the method of the present invention, in order to keep CO ₃ ^2- in the third crucible 7, it is preferable that the introduced Li ₂ CO ₃ be consumed quickly, and the concentration of CO ₃ ^2- is increased. That is not a good idea. Further, the potential can be sufficiently reduced as shown in the figure without increasing the potential.

As described above, according to the method of the present invention, LiCl itself is electrolyzed to obtain metal Li, which requires only about 60% of the decomposition voltage in the conventional case, and is very advantageous in terms of electric energy.

Further, as described above, in the method of the present invention, despite the final Li concentration of the alloy being 5 mass% or more, which is considerably higher than the practical composition, the electrolysis is performed favorably and the current efficiency is also improved.
_The value was as high as 90% or more, which was the same as when ₂ CO ₃ was not used.

[0040]

As described above, according to the first aspect of the present invention, since the lithium ion is generated by electrochemically oxidizing carbon and lithium carbonate in the anode chamber, almost no gas is generated. Is carbon dioxide gas and does not generate chlorine gas as in the prior art, so that large-scale processing equipment is not required.

Then, lithium carbonate is used as a lithium source, which has no deliquescence like conventional lithium chloride and is stable in the air, so that its handling is easy.

In addition, lithium carbonate is a starting material for all lithium compounds and is inexpensive.
A reduction in cost can be expected, and since the reaction in the anode chamber is a reaction between carbon and lithium carbonate, a drastic reduction in electrolysis voltage can be expected. Can be provided.

Therefore, according to the method of the present invention, industrially
This is advantageous in terms of processing equipment, handling of raw materials, and cost, which are important when manufacturing an Al-Li alloy, and facilitates industrial production of an Al-Li alloy having excellent characteristics.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of an apparatus for producing a molten salt electrolytic Al-Li alloy.

FIG. 2 is a graph showing a change in potential of an electrode as electrolysis proceeds.

[Explanation of symbols]

 Reference Signs List 5 electrolytic bath 6 second crucible 6a cathode chamber 7 third crucible 7a anode chamber 14 graphite electrode

Claims (2)

(57) [Claims] 1. A method for electrolysis using a molten salt electrolytic bath containing a lithium salt, wherein carbon dioxide and lithium carbonate are oxidized in an anode chamber to generate carbon dioxide gas and lithium ions, and the lithium ion In the cathode chamber, and the lithium ions are reduced in the cathode chamber. 2. The method for producing lithium according to claim 1, wherein the electrolytic bath contains lithium chloride, and a cathode chamber in which the molten aluminum is stored in the electrolytic bath so as to be able to conduct electricity in the electrolytic bath. An anode chamber having an electrode formed of a substance, surrounding the lower end of the electrode and internally storing a molten material of the same quality as the electrolytic bath so as to be able to conduct with the external electrolytic bath; By inputting
A method for producing an Al-Li alloy, wherein lithium is generated in aluminum in the cathode chamber.