KR20040069388A - An apparatus and a process for withdrawing lithium from a mixture of molten salts including lithium precursor using nonconducting porous ceramic container - Google Patents

Abstract

PURPOSE: An apparatus and a method for recovering lithium from molten salt containing lithium precursor using non-conductive porous ceramic container are provided to effectively recover lithium by effectively blocking reaction between byproducts and lithium, easily separate molten salt and lithium and semi-continuously manufacture lithium in electrolytic cell relatively inexpensively. CONSTITUTION: The lithium recovery apparatus comprises an electrolytic cell comprising oxidation electrodes(2), a reduction electrode(1), a non-conductive porous ceramic container(7) surrounded on the reduction electrode, cooling water supply pipe(3) and cooling water discharge pipe(9), inert gas supply pipe(4) and inert gas discharge pipe(8), and a molten salt supply pipe(5); a vacuum absorption pipe(10); and a lithium storage tank(11), wherein the non-conductive porous ceramic container is formed of magnesium oxide, and wherein the non-conductive porous ceramic container has an average pore diameter of 2 to 100 μm. The lithium recovery method comprises a process of collecting lithium in the non-conductive porous ceramic container after electrolyzing the molten salt(6) by supplying molten salt comprising lithium precursor into a reduction electrode mounted electrolytic cell surrounded by a non-conductive porous ceramic container; a process of separating lithium from the molten salt by ascending the container; and a process of transferring the separated lithium into a lithium storage tank using a vacuum absorption pipe, wherein the lithium precursor is one or more of precursors selected from the group consisting of lithium oxide, lithium carbonate and lithium chloride.

Description

An apparatus and method for recovering lithium from a molten salt containing a lithium precursor using a non-conductive porous ceramic container

The present invention relates to a lithium recovery apparatus and method in a molten salt comprising a lithium precursor using a non-conductive porous ceramic container, more specifically, 1) an anode; A cathode; A nonconductive porous ceramic container surrounding the cathode; Cooling water supply pipe and discharge pipe; Inert gas supply and discharge lines; And a lithium precursor in an electrolytic cell including a molten salt supply tube, 2) a vacuum recovery tube, and 3) a lithium recovery device including a lithium storage tank, and 1) an electrolytic cell surrounded by a non-conductive porous ceramic container. Supplying a salt to electrolyze, and then collecting lithium into a non-conductive porous ceramic container; 2) lifting the vessel to separate lithium from the molten salt; And 3) transferring the separated lithium to a lithium storage tank using a vacuum absorption tube.

Lithium is the lightest metal while having high conductivity. Lithium is used in the manufacture of lithium-cured bearings and organolithium compounds. Recently, lithium is widely used as a constituent of lithium batteries and as a metal reducing agent in other high temperature molten salt metal reduction processes. In addition, lithium-ion secondary batteries using lithium are currently used as batteries of PCS mobile phones, notebook PCs and cam cords, and are expected to be actively utilized in electric vehicles in the future. However, there has been a need to recover such lithium since lithium is disposed of after use and has a great impact on the environment.

As a method of recovering lithium, a method of reducing lithium ions by an electrochemical method, a method of reducing lithium oxide with magnesium or aluminum metal, and the like have been known.

US Pat. No. 4,617,098 and US Pat. No. 4,724,055 disclose a method for recovering lithium by successive electrolysis of molten salt composites comprising lithium chloride. In these patents, lithium is recovered in a mixed state with an unreacted molten salt, and chlorine gas is recovered by separately recovering a product obtained by electrolysis, 1) a mixture of metal lithium and molten salt, and 2) a chlorine gas generated from an anode. Suppresses the recombination of and lithium. Lithium is separated and recovered from the mixture of metallic lithium and molten salt obtained by electrolysis in a separation tank, and the molten salt is transferred to the electrolytic cell again to complete a continuous process for lithium recovery. However, the forced convection of molten salts suggested in these patents effectively prevents the carbon generated by the elution of the graphite anode from reacting with lithium produced at the cathode and the side reactions in which carbon dioxide and chlorine gas generated from the anode are combined with lithium. There is a disadvantage that cannot be suppressed. In addition, the separation and transfer process of the molten salt is required for the continuous process, which has the disadvantage that the entire process is complicated.

In addition, U. S. Patent No. 4,988, 417 discloses a method for recovering lithium by direct electrolysis of lithium carbonate. Lithium chloride commercially used for the recovery of lithium is made from lithium carbonate. Since the manufacture of lithium chloride from lithium carbonate required a high cost, the patent seeks to reduce lithium recovery costs by directly electrolyzing lithium carbonate. In order to prevent the reaction of the lithium carbonate present in the anode part to recombine with the lithium of the cathode part to generate lithium oxide and carbon, a porous magnesium oxide film was separated between the anode part and the cathode part. However, due to the structure of the electrolytic cell, the continuous process is not possible and it is not easy to separate the reduced lithium from the reduction electrode part, and thus there is a disadvantage in that economic efficiency cannot be increased in terms of process operation.

Therefore, the lithium recovery method known to date is not only able to effectively separate the lithium from the by-products resulting from the molten salt and the anode, but also solve the problem because the device is complicated and the continuous process is impossible to increase the economic efficiency. In order to effectively block the reaction between the by-products and the lithium resulting from the molten salt and the anode, the separation of the molten salt and lithium is easy, and the development of a lithium recovery method that can be produced relatively inexpensively has been urgently required. .

An object of the present invention is to provide a lithium recovery apparatus and method in a molten salt comprising a lithium precursor using a non-conductive porous ceramic container.

1 is a schematic diagram of an apparatus for recovering lithium from a molten salt comprising a lithium precursor using a non-conductive porous ceramic vessel,

1) cathode 2) anode

3) Cooling water supply pipe 4) Inert gas (argon) supply pipe

5) molten salt supply pipe 6) molten salt

7) Non-conductive porous ceramic container 8) Inert gas (argon) discharge pipe

9) Cooling water discharge pipe 10) Vacuum absorption pipe (syphon)

11) Lithium Storage Tank

FIG. 2 relates to a porosimetry graph of mercury with respect to the pore size distribution of the non-conductive porous magnesium oxide container used in the examples.

In order to achieve the above object, the present invention is 1) an anode; A cathode; A nonconductive porous ceramic container surrounding the cathode; Cooling water supply pipe and discharge pipe; Inert gas supply and discharge lines; And an electrolytic cell including a molten salt supply pipe, 2) a vacuum absorption tube, and 3) a lithium storage tank.

In particular, the container used in the lithium recovery apparatus of the present invention should be a non-conductive porous ceramic container to prevent the precipitation of lithium outside the container, and the surface area of the container is small in order to suppress the reaction with the reactants, It is required that the distribution be uniform. In addition, in the case of using a consumable anode such as graphite, a non-conductive porous ceramic container composed of pores of a certain size or less should be used to prevent carbon, etc., caused by its elution from reacting with lithium produced in the cathode. do.

The non-conductive porous ceramic container is made of magnesium oxide, the non-conductive porous magnesium oxide container is characterized in that the pore average diameter is in the range of 2 ㎛ to 100 ㎛.

In addition, the present invention is 1) supplying a molten salt containing a lithium precursor to the electrolytic cell equipped with a reduction electrode surrounded by a non-conductive porous ceramic container, and then electrolyzed, to collect lithium in the non-conductive porous ceramic container; 2) lifting the vessel to separate lithium from the molten salt; And 3) transferring the separated lithium to a lithium storage tank using a vacuum absorption tube.

That is, the present invention is equipped with a non-conductive porous ceramic container having a constant pore distribution to the cathode, and after the electrolytic reaction of the lithium precursor, the ceramic container containing lithium is raised above the molten salt level to be in the lithium and ionic state The present invention relates to a lithium recovery method capable of performing separation of molten salt and transferring lithium collected in a ceramic container with a vacuum absorber to a separate storage tank.

In the electrolytic process of lithium, a molten salt containing a lithium precursor is supplied to an electrolytic cell of a reaction system as shown in FIG. 1 at room temperature, and then the temperature is raised above the melting point of the molten salt to electrolytically reduce the lithium precursor.

The interior of the electrolyzer used in the electrolytic reaction flows an inert gas, in particular argon gas, to maintain a non-oxidizing atmosphere, thereby preventing the reoxidation of recovered lithium.

In addition, the lithium precursor used in the electrolytic reaction is at least one selected from the group consisting of lithium oxide, lithium carbonate and lithium chloride, lithium oxide, lithium carbonate or chloride as long as the precursor of lithium in the selected molten salt has a certain solubility The lithium is not particularly limited.

In addition, the molten salt which is an electrolyte used in the electrolytic reaction is not particularly limited, such as lithium chloride, lithium chloride-potassium chloride, sodium chloride-potassium chloride, but the melting point of the molten salt should be considered. For example, when a lithium chloride molten salt is used as an electrolyte, the melting point of lithium chloride is 613 ° C., and thus the temperature of the electrolytic cell should be 613 ° C. or higher.

In addition, the anode used in the electrolytic reaction is preferably a noble metal electrode such as graphite, platinum, or a ceramic electrode such as magnetite, but is not particularly limited as long as it has corrosion resistance in the molten salt. The molten salt is not particularly limited as long as it has corrosion resistance.

Lithium obtained by the electrolytic process is collected in a non-conductive porous ceramic container by surface tension. That is, lithium is collected in the container when the pressure required to remove lithium in the non-conductive porous ceramic container is greater than the pressure generated by the lithium in the container.

Specifically, the pressure required to remove lithium in the non-conductive porous ceramic container is represented by the following Equation 1,

… (Equation 1)

here, Is the surface tension of lithium and D is the pore diameter of the non-conductive porous ceramic container. In addition, the pressure generated by lithium in the non-conductive porous ceramic container is equal to the following Equation 2,

… (Equation 2)

here, Is the density of lithium, Is the acceleration of gravity, Is the liquid level of lithium in the container. In this case, when the pressure required to remove lithium in the non-conductive porous ceramic container obtained by Equation 1 is greater than the pressure generated by lithium in the non-conductive porous ceramic container obtained by Equation 2, Lithium is collected. For example, when the pore diameter of the porous ceramic container is 100 μm, the generated lithium is present inside the container up to a liquid height of 2.64 m of lithium in the container.

The separation process of lithium raises the non-conductive porous ceramic vessel above the level of the molten salt to separate lithium from the molten salt. That is, the molten salt in the ionic state freely enters and exits through the non-conductive porous ceramic vessel, and the electrolytic reaction proceeds. When the vessel rises above the molten salt level, the lithium and the ionic molten salt are separated.

In the transfer process of lithium, lithium collected in the raised non-conductive porous ceramic container is transferred to a separate storage tank by using a vacuum absorber to recover lithium. After the transfer process, the molten salt containing the precursor of lithium is re-supplied to the electrolytic cell through the molten salt supply device, the non-conductive porous ceramic vessel and the reduction electrode is lowered below the molten salt level again, and the next reaction may proceed. Through this, a semi-continuous lithium recovery process is possible.

Hereinafter, the present invention will be described in more detail with reference to the following examples. However, this embodiment is not intended to limit the present invention and is merely illustrative, and the present invention is not limited by this embodiment.

<Example>

4.82 g of lithium oxide was dissolved in 200 g of lithium chloride so that the lithium oxide in lithium chloride was 2.35 wt%. The molten salt was supplied to the electrolytic cell at room temperature, and then heated at a temperature of 650 ° C. for about 3 hours to melt the lithium precursor. Salts were prepared. The electrolyzer maintained argon atmosphere by flowing argon gas during the reaction. The electrolytic reaction was carried out under the condition of supplying a constant current of 1.0 A at a temperature of 650 ℃. In this case, a stainless steel cathode equipped with a platinum anode and a porous magnesium oxide container was used as the electrode. The pore distribution of the magnesium oxide container used is shown in FIG. 2.

When the lithium oxide in the molten salt of the electrolyzer was 0.23 wt%, the porous magnesium oxide container was raised above the molten salt level and lithium was recovered. Since 0.23 wt% of lithium oxide corresponds to 0.461 g of lithium oxide, the amount of trapped lithium oxide is 4.36 g, or 0.146 mol, and 2 mol of lithium is produced by decomposition of 1 mol of lithium oxide, so 0.292 mol, Ie 2.02 g of lithium has to be recovered. Since 2.0 g of lithium was recovered by the present example, it was confirmed that the recovery rate from lithium oxide to lithium was 90% or more.

The lithium recovery apparatus and method of the present invention effectively block the reaction between by-products and lithium originating from the anode by means of a non-conductive porous ceramic container, facilitate the separation of molten salt and lithium, and relatively inexpensive lithium in a simple electrolyzer. Because it can be manufactured semi-continuously, it can be usefully used for the recovery of lithium.

Claims (5)

1) an anode; A cathode; A nonconductive porous ceramic container surrounding the cathode; Cooling water supply pipe and discharge pipe; Inert gas supply and discharge lines; And an electrolytic cell comprising a molten salt supply pipe, 2) a vacuum absorption tube, and 3) a lithium storage tank. The apparatus of claim 1, wherein the nonconductive porous ceramic container is made of magnesium oxide. The device of claim 2, wherein the non-conductive porous magnesium oxide container has a pore average diameter in the range of 2 μm to 100 μm. 1) supplying a molten salt including a lithium precursor to an electrolytic cell equipped with a reduction electrode surrounded by a nonconductive porous ceramic container for electrolysis, and then collecting lithium into the nonconductive porous ceramic container; 2) lifting the vessel to separate lithium from the molten salt; And 3) A lithium recovery method comprising the step of transferring the separated lithium to a lithium storage tank using a vacuum absorption tube. 5. The method of claim 4, wherein the lithium precursor is at least one selected from the group consisting of lithium oxide, lithium carbonate and lithium chloride.