JP7188239B2 - Method for producing electrolytic cell and acid solution - Google Patents

Description

The present invention relates to an electrolytic cell and a method for producing an acid solution. More particularly, it relates to an electrolytic cell and a method for producing an acid solution using this electrolytic cell.

Metals such as nickel or cobalt are valuable metals used as plating or alloying materials. Moreover, in recent years, the demand for battery materials such as positive electrode materials for secondary batteries such as nickel-hydrogen batteries and lithium-ion batteries is increasing. When manufacturing the above battery materials, metals such as nickel and cobalt are often used in solutions in which these metals are dissolved, for example, sulfuric acid solutions of nickel sulfate, cobalt sulfate, and the like.

As an example, when nickel is used as the positive electrode material for the lithium ion battery, a general method for producing the positive electrode material for the lithium ion battery is to neutralize an aqueous solution containing nickel ions mixed in a predetermined ratio to obtain a precursor. There is a method of forming a metal hydroxide called a solid, then mixing this precursor with a lithium compound and sintering to obtain a positive electrode material. Here, the aqueous solution containing nickel ions is specifically an acid solution in which a nickel salt such as nickel sulfate or nickel chloride is dissolved.

For example, the sulfuric acid solution containing the above nickel ions is obtained by leaching nickel ore, nickel sulfide, which is an intermediate product thereof, and other nickel-containing compounds with sulfuric acid, and then removing impurities in a refining process such as precipitation separation or solvent extraction. can be obtained by removing However, when the above raw materials are used, halogens or other impurities are irregularly mixed in the raw materials or in the refining process, and there is a problem that the required quality cannot be stably maintained.

As a method of stably maintaining the required quality, there is a method of dissolving metallic nickel in sulfuric acid to obtain a sulfuric acid solution containing nickel ions. High-quality metal nickel with a nickel purity of 99.99% or more is easily available on the market, for example, as electrolytic nickel, and this electrolytic nickel cut into 2 to 5 cm square sizes is even easier to handle. and can be used as a precursor material without requiring a large-scale purification process as described above.

However, as nickel is used for corrosion-resistant alloys such as stainless steel, it is difficult to dissolve even a cut product simply by immersing nickel metal in an acid such as sulfuric acid. For this reason, there are several methods for promoting the dissolution of metallic nickel and allowing the concentration of nickel ions to reach a predetermined concentration. For example, as a method of dissolving metallic nickel in sulfuric acid to obtain a sulfuric acid solution containing nickel ions, powdery nickel (nickel powder), Alternatively, a method of obtaining a sulfuric acid solution containing nickel ions by using briquettes obtained by sintering nickel powder and dissolving them with sulfuric acid has been proposed (Patent Document 1).

However, the nickel powder or nickel briquette used in Patent Literature 1 is difficult to obtain stably because the production volume is limited. For this reason, there has been a demand for a technique for dissolving plate-like or block-like electrolytic nickel on the market in sulfuric acid in a short period of time.

A solution to this requirement is, for example, the electrolysis method. That is, in this method, a metal to be dissolved is used in the anode, a sulfuric acid solution is used as the electrolyte, and an electric current is passed between the anode and the cathode to dissolve the target metal in sulfuric acid.

Japanese Patent Application Laid-Open No. 2004-067483

In the electrolysis method, metal is dissolved from the anode and an electrodeposition reaction occurs at the cathode. At this time, if the metal dissolved from the anode is deposited on the cathode as it is, the liquid in which the metal is dissolved cannot be efficiently obtained. On the other hand, the inventors of the present application have already filed a separate application for a method of separating the anode side and the cathode side using a diaphragm to prevent metal ions dissolved from the anode from easily moving to the cathode. In this case, in order to effectively suppress the movement of metal ions, the liquid level of the electrolyte on the cathode side is maintained higher than that on the anode side. It is also done so that it cannot be moved easily.

In addition, the configuration of the invention according to the above application is said to be effective in solving the problem of passivation (also referred to as "passivation") at the anode, which has been a major problem. Passivation is a phenomenon in which the electrolytic solution on the surface of the anode becomes supersaturated, making metal elution difficult. Since the elution of metal ions from the anode is proportional to the amount of current applied, the passivation described above generally occurs more easily as the amount of current per unit area (that is, current density) increases.

In the generally known electrolysis method, when a metal such as nickel is dissolved in a sulfuric acid solution, the current density of the anode must be set to about 1000 A/m ² or more in order to rapidly dissolve the nickel metal. It is desired to electrolyze with a higher temperature. However, when electrolysis is carried out at such a high current density, there is a problem that an oxide film is formed on the surface of metallic nickel of the anode, causing passivation and almost no current flow. When electrolysis is carried out at a low current density so as to suppress the occurrence of passivation, dissolution is not promoted and the original purpose of promoting dissolution cannot be achieved.

In particular, for a sulfuric acid solution containing nickel ions required for producing positive electrode materials for batteries, a solution with a high nickel ion concentration of about 100 g/liter is required. When the concentration of nickel ions in the electrolyte solution increases, there is a problem that passivation is more likely to occur, and there is also a problem that nickel is deposited on the cathode side electrode and the dissolution efficiency is lowered.

In order to solve these problems, the invention according to the above application makes it possible to obtain a high-concentration solution by, for example, separating the anode side and the cathode side using a diaphragm and taking out the electrolytic solution from the anode side. ing.

However, when attempting to acid-dissolve metals from the anode at the operational level, it is desirable to line up a large number of electrodes closely spaced one after the other in order to reduce the facility area and investment. In this case, since the anode side and the cathode side must be separated by a diaphragm, for example, a box covering the cathode side is provided, and the diaphragm between the anode and the cathode is provided on the side of the box. structure is adopted.

Here, when a plurality of cathodes are provided, a plurality of boxes covering the cathode side are provided. At this time, if the electrolytic solution with a high metal concentration on the anode side enters the plurality of boxes provided with the cathodes, the metal is electrodeposited, and the dissolution efficiency, that is, the productivity is reduced accordingly. Therefore, it is necessary to prevent the liquid on the anode side from entering the cathode side. However, the diaphragm often breaks, deteriorates, or clogs with use, and in an electrolytic cell using multiple electrodes, it is necessary to maintain the anode side liquid level evenly with the individual cathode liquid level. The problem is that it is not easy.

In addition, in an electrolytic cell in which a plurality of anodes and cathodes are respectively provided, a constant current (that is, a method of supplying a constant current with respect to load fluctuations) is used to stably perform electrorefining. However, if passivation occurs in one anode, the current that was flowing in that anode will flow to the other anode, and passivation is likely to occur in other anodes. There is That is, there is a problem that passivation tends to proceed in a chain reaction throughout the electrolytic cell.

Furthermore, as another electrolytic refining, if we take up the electrolytic refining of copper using the principle of dissolving metal from the anode, the anode and cathode with an electrode area of about 1 m × 1 m are separated from each other by a distance of about 25 to 35 mm. It is performed by making them face each other at a narrow interval. When a similar large-sized electrolytic cell is used in the method for producing an acid solution, the water pressure of the electrolytic solution in the depth direction cannot be ignored, and when the liquid is drained from the electrolytic cell or the liquid is filled, the anode There is a problem that the partition may be deformed by the water pressure, or the box may swell and be damaged.

In view of the above circumstances, the present invention provides an electrolytic cell in which a plurality of cathodes is provided, in which the height of the liquid level on the cathode side with respect to the anode side can be easily controlled, and highly efficient and stable operation is possible. An object of the present invention is to provide a method for producing an acid solution using an electrolytic bath.

The electrolytic cell of the first invention is an electrolytic cell for dissolving a metal constituting an anode by supplying an electric current, the electrolytic cell comprising an anode chamber in which the anode is arranged and a plurality of cathodes. a connecting pipe connecting the plurality of cathode chambers, and a liquid level in the cathode chamber; and a liquid level monitor pipe for checking the level of the liquid is provided.
The electrolytic cell of the second invention is characterized in that, in the electrolytic cell of the first invention, the metal constituting the anode contains at least nickel or cobalt.
The electrolytic cell of a third invention is the electrolytic cell of the first invention or the second invention, wherein the diaphragm has a water permeability of 0.01 liter/(m ² s) or more and 0.5 liter/(m ² s) or less. It is characterized by being cloth.
An electrolytic cell according to a fourth invention is characterized in that, in any one of the first to third inventions, an opening of a take-out pipe for taking out the electrolyte in the electrolytic cell is provided below the anode. do.
The electrolytic cell of a fifth invention is the electrolytic cell according to any one of the first to fourth inventions, wherein the upper part of the cathode chamber, which is not immersed in the electrolytic solution, has a sealed structure, and the gas generated from the cathode is conveyed out of the cell. It is characterized by being connected to a conveying pipe.
A method for producing an acid solution according to a sixth aspect of the invention is a method for producing an acid solution using the electrolytic cell according to any one of the first to fifth aspects of the invention, comprising: The liquid level in the anode chamber is made lower than the liquid level in the cathode chamber by controlling the discharge amount of the electrolytic solution.

According to the first aspect of the invention, the electrolytic cell is provided with a connecting pipe that connects a plurality of cathode chambers, whereby the electrolytic solution in the cathode chambers communicates, and the amount of sulfuric acid or the like supplied to the plurality of cathode chambers varies. However, by controlling the total supply amount of the electrolytic solution, it is possible to control the liquid level in the cathode chamber. Also, even if some of the diaphragms are clogged, the liquid level in some of the cathode chambers will not rise due to the clogging. In addition, since the electrolytic cell is equipped with a liquid level monitor pipe for checking the liquid level in the cathode chamber, the user of the electrolytic cell can easily check the liquid level between the anode chamber and the cathode chamber. difference can be grasped. By knowing the height of the liquid surface, it is possible to know that the electrolyte is flowing from the cathode chamber to the anode chamber. These effects make it possible to provide an electrolytic cell capable of highly efficient and stable operation.
According to the second invention, the metal constituting the anode contains at least nickel or cobalt, so that the produced acid solution can be used as the positive electrode of the secondary battery.
According to the 3rd invention, a diaphragm can be obtained at low cost by using a filter cloth as the diaphragm. Further, the water permeability is 0.01 liter/(m ² s) or more and 0.5 liter/(m ² s) or less, so that the metal ion concentration in the electrolyte discharged from the anode chamber is predetermined. In addition, passivation of the anode can be suppressed.
According to the fourth aspect of the invention, the opening of the take-out pipe for taking out the electrolytic solution in the electrolytic cell is provided below the anode, so that even if the electrolytic cell becomes large, the predetermined metal ion concentration can be maintained. Electrolyte can be easily obtained.
According to the fifth aspect of the invention, the cathode chamber has a sealed upper portion which is not immersed in the electrolytic solution, and is connected to a conveying pipe for conveying the gas generated from the cathode to the outside of the chamber. Gases that are difficult to handle can be easily discharged.
According to the sixth invention, the acid solution manufacturing method controls the amount of electrolyte supplied to the cathode chamber and the amount of electrolyte discharged from the anode chamber, thereby adjusting the liquid level in the anode chamber to the cathode. It is possible to lower the liquid level in the chamber and create a flow of electrolyte from the cathode side to the anode side to suppress the metal concentration at the cathode and increase the efficiency of electrolysis.

It is a cross-sectional view from the side direction of the electrolytic cell according to the first embodiment of the present invention.

Next, embodiments of the present invention will be described with reference to the drawings. However, the embodiment shown below exemplifies the manufacturing method of the electrolytic cell 10 and the acid solution for embodying the technical idea of the present invention, and the present invention is the manufacturing method of the electrolytic cell 10 and the acid solution. are not specified as: Note that the sizes, positional relationships, etc. of members shown in the drawings may be exaggerated for clarity of explanation. Further, the term "electrolyte" used herein means a liquid used to conduct electricity in the electrolytic cell 10, and the "initial electrolytic solution" initially supplied to the electrolytic cell 10 and the The description includes "metal-dissolving electrolyte" in which metal is dissolved by Moreover, the "electrolyte" taken out from the electrolytic cell 10 is the "acid solution" produced by the production method of the present invention.

<Electrolytic cell 10 according to the first embodiment>
The electrolytic cell 10 according to the present invention is an electrolytic cell 10 for dissolving a metal constituting an anode 13 by supplying an electric current, and the electrolytic cell 10 includes an anode chamber 21 in which the anode 13 is arranged. , a plurality of cathode chambers 22 in which a plurality of cathodes 14 are respectively arranged, and a diaphragm 12 separating the anode chamber 21 and the cathode chamber 22 from each other. The electrolytic cell 10 is provided with a connecting pipe 26 connecting the plurality of cathode chambers 22 and a liquid level monitor pipe 27 for checking the liquid level in the cathode chamber 22 .

Hereinafter, after explaining the electrolytic cell 10 according to the present invention based on the drawings, a method for producing an acid solution using the electrolytic cell 10 will be explained. The electrolytic cell 10 according to the present invention can be used for a reaction in which metals such as nickel, cobalt, and copper are eluted by electrolysis using a mineral acid such as sulfuric acid or hydrochloric acid. A method for producing nickel sulfate, which is one of them, will be described as an example.

(Electrolyzer body 11)
The electrolytic cell main body 11 has a structure capable of holding an acid solution inside. Materials constituting the electrolytic cell main body 11 are known materials. The electrolytic cell main body 11 includes an anode chamber 21 in which the anode 13 is arranged and a plurality of cathode chambers 22 in which a plurality of cathodes 14 are respectively arranged. In this embodiment, the inside of the electrolytic cell main body 11 is the anode chamber 21 , and a plurality of cathode chambers 22 are arranged in the anode chamber 21 . However, the forms of the anode chamber 21 and the cathode chamber 22 are not limited to this.

The cathode chamber 22 preferably has a so-called box shape, in which the cathode 14 is preferably arranged. The electrolytic cell 10 is further positioned between the anode 13 and the cathode 14 and is provided with a diaphragm 12 for restricting movement of the electrolyte therebetween. In this embodiment, the diaphragm 12 that separates the anode chamber 21 and the cathode chamber 22 is provided at an opening on the side of the box-shaped cathode chamber 22 and positioned between the anode 13 and the cathode 14. . In this embodiment, this configuration divides the electrolytic cell 10 into an anode chamber 21 and a cathode chamber 22 by the diaphragm 12 .

A DC power source 17 connected to a plurality of anodes 13 and a plurality of cathodes 14 is provided outside the electrolytic cell body 11 . In FIG. 1, the line connecting the DC power source 17 to the anode 13 or the cathode 14 represents an electric wire, and the black arrow along this line indicates the direction of the current.

Since the electrolytic cell 10 used is divided into the anode chamber 21 and the cathode chamber 22 by the diaphragm 12, the metal dissolved on the anode 13 side can be suppressed from moving to the cathode 14 side.

(Cathode chamber 22)
As shown in FIG. 1 , the cathode chamber 22 in this embodiment has a so-called box shape and is positioned between two anodes 13 . As mentioned above, the material constituting the cathode chamber 22 is a known material, preferably vinyl chloride. A diaphragm 12 is provided at an opening on the side of the cathode chamber 22 . This diaphragm 12 is preferably located between the anode 13 and the cathode 14 . Moreover, when a predetermined amount of electrolyte is supplied to the electrolytic cell main body 11 , it is preferable that the liquid surface of the electrolyte is above the uppermost end of the diaphragm 12 . The cathode chamber 22 preferably has a sealed upper portion when a predetermined amount of electrolytic solution is supplied to the electrolytic cell main body 11 . At this time, the upper part of the cathode chamber 22 is preferably connected to a carrier pipe 24 for carrying the gas generated from the cathode 14 out of the tank. In the method for producing an acid solution using the electrolytic cell 10 of the present embodiment, the generated gas is hydrogen. 1 indicates that the generated gas is transported out of the tank.

The upper part of the cathode chamber 22, which is not immersed in the electrolytic solution, has a sealed structure, and is connected to a conveying pipe 24 for conveying the gas generated from the cathode 14 to the outside of the chamber. can be easily discharged. If such a configuration is not used, a hood and a suction device for recovering gas from the entire electrolytic cell 10 will be required, and the configuration of the entire electrolytic cell 10 will be complicated. When configured like the electrolytic cell 10 according to the present embodiment, the electrolytic cell 10 has a simple configuration.

(Anode 13)
Anodes 13 used in electrolytic cell 10 may take a number of forms. For example, when an acid solution of nickel is to be obtained, the first form of the anode 13 corresponds to plate-shaped metallic nickel (electrolytic nickel) industrially electrorefined or electrowinning. The second form corresponds to a basket made of a material such as titanium that is insoluble in acid and filled with nickel metal cut into small pieces. In the case of the second form, it is necessary to replace the metal before it is completely melted, and cutting the metal is costly and time-consuming, but the metal can be efficiently melted without waste. In the case of the first form, it is necessary to replace it after it has finished dissolving. Exchanges are made when a predetermined size is reached. Metallic nickel that has fallen below a predetermined size can also be filled and melted into a second form of basket. In this embodiment, the electrolytic cell 10 includes a plurality of cathodes 14 and cathode chambers 22 in which the respective cathodes 14 are arranged, and the anode 13 is sandwiched between these cathode chambers 22. Therefore, the number of anodes 13 is one or more.

(Cathode 14)
Plate-shaped metals such as titanium, stainless steel, nickel, cobalt, and platinum are preferably used for the cathode 14 . In this embodiment, the electrolytic cell 10 includes a plurality of cathodes 14 and cathode chambers 22 in which the cathodes 14 are respectively arranged.

(Diaphragm 12)
The diaphragm 12 divides the interior of the electrolytic cell main body 11 into an anode chamber 21 and a cathode chamber 22 . Diaphragm 12 restricts the passage of liquids or ions. Specifically, the diaphragm 12 is preferably a filter cloth. However, it is not limited to this, and in addition to the filter cloth, a neutral membrane, an anion exchange membrane, a cation exchange membrane, or the like may be used.

Specifically, as the filter cloth, product model numbers P89C, TA72, P91C, P26-2, etc. manufactured by Shikishima Canvas Co., Ltd. are preferably used. The water permeability (liter/(m ² ·s)) of these products is 0.05, 0.1, 0.3 and 1, respectively. Filter cloth is preferred in that it is relatively easy to handle.

Filter fabrics with low values for water permeability are preferred. For example, when a pressure of 200 mmH ₂ O is applied at 25° C., the water permeability per unit area and unit time (s: seconds) must be 0.5 liter/(m ² s) or less. . Moreover, it is preferable that it is 0.3 liter/(m< ² >*s) or less. This is because if the permeability per unit area per unit time is greater than 0.5 liter/(m ² ·s), the liquid diffuses easily and the function of the diaphragm 12 becomes insufficient.

When the diaphragm 12 is a filter cloth having a water permeability of 0.5 liter/(m ² s) or less, it is possible to suppress the movement of metal ions from the anode chamber 21 to the cathode chamber 22, and to prevent metal ions from being wasted in the anode chamber 21. Since it can be taken out from, the sulfuric acid solution can be produced more efficiently.

When a filter cloth is used, the lower limit of water permeability is set so that the liquid does not overflow from the cathode chamber 22 . Specifically, it is preferably 0.01 liter/(m ² ·s) or more. Since the lower limit of the filter cloth is 0.01 liter/(m ² s), the same amount of liquid as the replenished sulfuric acid moves from the cathode chamber 22 to the anode chamber 21 through the filter cloth, and the liquid is mixed by diffusion. is reduced.

Since the diaphragm 12 is a filter cloth, the diaphragm 12 can be obtained at a low cost. In addition, since the water permeability is 0.01 liter/(m ² s) or more and 0.5 liter/(m ² s) or less, the metal ion concentration in the electrolyte discharged from the anode chamber 21 can be adjusted in advance. A certain range can be obtained, and passivation of the anode 13 can be suppressed.

(Connecting pipe 26)
The electrolytic cell 10 of the present embodiment is provided with connecting pipes 26 for communicating the electrolytic solution between the plurality of cathode chambers 22 . By providing such connecting pipes 26, the liquid level in each cathode chamber 22 becomes constant. The opening of the connecting pipe 26 in the cathode chamber 22 must be below the liquid level in the cathode chamber 22 and preferably below the liquid level in the anode chamber 21 . Specifically, as shown in FIG. 1, a configuration in which an opening of the connecting pipe 26 is provided below the cathode 14 is preferable. This is because if it is installed above the liquid surface of the cathode chamber 22, the function of making the liquid surface uniform does not work. Also, the connecting pipe 26 is installed at a place where it does not interfere with other structures in the electrolytic cell 10 . It should be noted that the material of the connecting pipe 26 is preferably metal. However, it is not limited to this, and a nonmetallic hose or the like is also preferably used. In this case, the hose or the like needs to be strong enough not to be crushed by the water pressure of the electrolyte.

(Liquid level monitor pipe 27)
As shown in FIG. 1, the electrolytic cell 10 of this embodiment is provided with a liquid level monitor pipe 27 for checking the level of the liquid level in the cathode chamber 22 . Preferably, the liquid level monitor pipe 27 is provided inside the anode chamber 21 of the electrolytic cell main body 11 and is communicated with the connecting pipe 26 . The liquid level monitor pipe 27 is a pipe having an axial center in the vertical direction, and the vertical height of the opening thereof is the liquid level height of the cathode chamber 22 when a predetermined electrolytic solution is supplied to the cathode chamber 22. higher than The material of the liquid level monitor pipe 27 is preferably metal. However, it is not limited to this, and a nonmetallic hose or the like is also preferably used. In this case, the hose or the like must be strong enough not to be crushed by the water pressure of the electrolyte. If the upper part of the liquid level monitor pipe 27 is transparent or a level display is provided outside, the user of the electrolytic cell 10 can easily check the liquid level in the anode chamber 21 and the liquid level in the cathode chamber 22. You can compare heights.

(liquid level gauge, etc.)
As shown in FIG. 1, the electrolytic cell 10 of the present embodiment includes a first liquid level gauge 29 for measuring the liquid level in the anode chamber 21 and a liquid level monitor pipe 27 for measuring the liquid level. A second liquid level gauge 25 for measuring is provided. Since the liquid level monitor pipe 27 communicates with the cathode chamber 22 , the liquid level in the cathode chamber 22 can be measured by measuring the liquid level in the liquid level monitor pipe 27 . As the first liquid level gauge 29 and the second liquid level gauge 25, for example, a laser type liquid level gauge can be used. However, it is not limited to this, and it is also possible to use other types of liquid level gauges such as liquid level gauges using floating. It is also possible to control the liquid levels in the anode chamber 21 and the cathode chamber 22 using numerical values from these liquid level gauges.

(Extraction pipe 15, supply pipe 16)
The anode chamber 21 of the electrolytic cell main body 11 is provided with a take-out pipe 15 for taking out the electrolytic solution from the anode chamber 21 . The cathode chamber 22 of the electrolytic cell main body 11 is provided with a supply pipe 16 for supplying new sulfuric acid or a sulfuric acid solution to the cathode chamber 22 . The white arrow on the left side of the take-out tube 15 in FIG. indicates that it is supplied.

Since nickel ions and cobalt ions have higher specific gravities than water, the concentration of nickel and the like becomes higher in the deeper part of the anode chamber 21 as the current flows. Therefore, by extracting the electrolytic solution from a deeper portion of the anode chamber 21, that is, by providing the opening 15a of the extraction pipe 15 below the anode 13 in the anode chamber 21, an electrolytic solution having a high concentration of nickel or the like can be extracted. can be taken out.

If the opening 15a of the take-out pipe 15 is provided below the anode 13, even if the nickel concentration near the surface of the anode 13 is less than 100 g/liter, the nickel concentration can be reduced by taking out the electrolyte from the deep part of the anode chamber 21. 100 g/liter of electrolyte can be recovered. This suppresses passivation of nickel on the surface of the anode 13 .

A supply pipe 16 for replenishing the cathode chamber 22 with new sulfuric acid or the like is provided, and a withdrawal pipe 15 capable of recovering the same amount of electrolytic solution as the replenishment from the anode chamber 21 is provided. Liquid volume balance in the 10 tanks is maintained.

The cathode chamber 22 is replenished with fresh sulfuric acid or the like, and the presence of the diaphragm 12 allows the liquid level in the cathode chamber 22 side to be maintained at a position higher than the liquid level in the anode chamber 21 . The position of the liquid surface depends on the water permeability and area of the filter cloth, which is the diaphragm 12 . The water permeability of the diaphragm 12 must be set within a range in which the liquid does not overflow from the cathode chamber 22 .

Since the opening 15a of the take-out pipe 15 for taking out the metal-dissolved electrolyte is provided below the anode 13, the metal-dissolved electrolyte with a relatively large specific gravity is efficiently taken out.

Since the electrolytic cell 10 is provided with the connecting pipes 26 that connect the plurality of cathode chambers 22, the electrolytic solution in the cathode chambers 22 is communicated, and the amount of sulfuric acid or the like supplied to the plurality of cathode chambers 22 is uniform. Even if there is, it is possible to control the liquid level in the cathode chamber 22 by controlling the overall supply amount of the electrolytic solution. Moreover, even if some of the diaphragms 12 are clogged, the liquid level in some of the cathode chambers 22 will not rise. In addition, since the electrolytic cell 10 is provided with a liquid level monitor pipe 27 for checking the liquid level in the cathode chamber 22, the user of the electrolytic cell 10 can easily identify the anode chamber 21 and the cathode chamber 22. It is possible to grasp the difference in the height of the liquid surface. Since the height of the liquid surface can be grasped, it can be grasped that the electrolytic solution is flowing from the cathode chamber 22 to the anode chamber 21 . These effects make it possible to provide the electrolytic cell 10 capable of highly efficient and stable operation.

Regarding the take-out pipe 15 for taking out the electrolytic solution from the lower part of the electrolytic cell main body 11, it extends vertically outside the electrolytic cell main body 11, rises up to a point exceeding the liquid surface of the anode chamber 21, and overflows from there. It is also possible to have it discharged. In this case, the user of the electrolytic cell 10 can easily finely adjust the liquid level in the anode chamber 21 . In the case of a metal-dissolved electrolyte having a large specific gravity depending on the type of liquid or the concentration of metal ions, the liquid is pumped up from the take-out pipe 15 which is raised vertically by a pump or the like.

<Method for producing an acid solution using the electrolytic cell 10 according to the first embodiment>
(Initial electrolyte supply step)
As described above, the method for producing the acid solution according to the present embodiment will be described by taking the method for producing nickel sulfate, which is one of the acid solutions, as an example.

In the method for producing an acid solution according to the present invention, first, a sulfuric acid solution is supplied as an initial electrolyte to the electrolytic cell 10 according to the first embodiment (initial electrolyte supply step). An initial electrolyte is supplied to both the anode chamber 21 and the cathode chamber 22 . The initial electrolyte preferably has a chloride ion concentration and a sulfuric acid concentration as described below. The position of the liquid level when the initial electrolyte is supplied is such that the liquid level in the cathode chamber 22 is higher than the liquid level in the anode chamber 21 .

(chloride ion concentration)
If metallic nickel is anodically dissolved in a sulfuric acid solution without taking any measures, an oxide film, that is, a passive film, is easily formed on the surface of the anode 13, resulting in a passivated state in which almost no current flows. The configuration of the electrolytic cell 10 according to the first embodiment is one method of suppressing this passivation. Furthermore, as another method, the formation of a passive film is said to be suppressed by the presence of halogen ions, a decrease in the hydrogen ion concentration (pH), and an increase in temperature. It is also possible to The chloride ion concentration refers to the concentration of chloride ions in the electrolytic solution after a predetermined chloride has been added to the electrolytic solution.

(sulfuric acid concentration)
It is preferable that the concentration value of sulfuric acid (also referred to as “free sulfuric acid” or “free sulfuric acid”) supplied as the initial electrolytic solution be as small as possible. This is because when the concentration of sulfuric acid is small, the cost of chemicals for neutralizing the sulfuric acid solution containing metal ions taken out of the electrolytic cell 10 can be reduced.

However, when the concentration value of the sulfuric acid supplied as the initial electrolyte decreases, the electrical conductivity of the electrolyte (simply referred to as "conductivity" or "conductivity") decreases, resulting in an increase in the liquid resistance and the cathode. As the diffusion limit current value of hydrogen ions at 14 decreases, a problem such as an increase in voltage occurs. Considering the cost of electricity and the cost of neutralizing chemicals, it is desirable to set the most economical conditions. For this reason, a pH meter or an electrical conductivity meter (simply called a "conductivity meter" or "conductivity meter") is used to adjust the current amount or the sulfuric acid solution supplied to the cathode 14 side so that the free concentration is optimal. It is preferable to adjust the supply amount of

(Electrolyte extraction process)
Next, a current is supplied to the anode 13 and the cathode 14 provided in the electrolytic cell 10 according to the first embodiment, and a metal-dissolved electrolyte in which the metal constituting the anode 13 is dissolved is taken out from the anode chamber 21 ( electrolyte removal step). This metal-dissolved electrolyte becomes an acid solution when taken out from the electrolytic bath 10 . The metal-dissolved electrolyte preferably has a metal ion concentration and an electrolyte temperature as described below. The electrolyte removal step includes a case where the metal-dissolved electrolyte is taken out at the same time that the current is supplied to the anode 13 and the like, and a case where the metal-dissolved electrolyte is taken out after the current supply is finished.

The cathode chamber 22 is replenished with sulfuric acid from the supply pipe 16 . The liquid level on the cathode chamber 22 side is made higher than the liquid level on the anode chamber 21 side. The position of the liquid surface depends on the water permeability and area of the filter cloth, which is the diaphragm 12 . The water permeability of the diaphragm 12 must be set within a range in which the liquid does not overflow from the cathode chamber 22 . In this way, the user of the electrolytic cell 10 considers the amount of sulfuric acid supplied from the supply pipe 16, the amount of electrolyte taken out from the take-out pipe 15, and the water flow rate of the filter cloth, A balance point between the liquid level and the height of the liquid level in the cathode chamber 22 is confirmed in advance, and these are controlled. If the liquid level fluctuates due to evaporation from the electrolytic solution or the like, water is added to the anode chamber 21 or the supply flow rate of the initial electrolytic solution is adjusted in order to control the liquid levels of the anode chamber 21 and the cathode chamber 22 . It is also possible to

In addition, in the electrolytic cell 10 of the present embodiment, the cathode chamber 22 is communicated with the connecting pipe 26, so if, for example, one of the filter cloths is damaged, the liquid level difference decreases, and the user of the electrolytic cell 10 can also detect this as an anomaly in the production process.

(metal ion concentration)
The metal ion concentration of the acid solution produced by the method for producing an acid solution according to this embodiment is determined according to the use of the acid solution. For example, when a sulfuric acid solution is used as a nickel raw material for a positive electrode material of a secondary battery, a sulfuric acid solution containing nickel ions at a high concentration of about 90 to 100 g/liter is required. .

The metal ion concentration in the sulfuric acid solution is determined by the following parameters. That is, when the anode 13 is metallic nickel, the amount of dissolution is determined by the value of the current supplied to the anode 13 if all reactions at the anode 13 are dissolution of nickel. Sulfuric acid is replenished in the cathode chamber 22 so that the dissolved amount reaches the desired nickel ion concentration, and the same amount of metal-dissolved electrolyte is taken out from the anode chamber 21 as a sulfuric acid solution.

Since the metal constituting the anode 13 contains at least either nickel or cobalt, the produced sulfuric acid solution is used as the positive electrode of the secondary battery.

The sulfuric acid solution supplied to the anode chamber 21 as the initial electrolytic solution is preferably a sulfuric acid solution having a predetermined nickel ion concentration or higher. In this case, since the metal-dissolved electrolyte has a predetermined nickel ion concentration immediately after the extraction starts, a sulfuric acid solution having a predetermined nickel ion concentration can be obtained from the beginning. Further, when the sulfuric acid solution supplied to the anode chamber 21 as the initial electrolytic solution has a nickel ion concentration lower than the predetermined nickel ion concentration, the sulfuric acid solution having a nickel ion concentration not reaching the predetermined nickel ion concentration at the beginning of dissolution is There is no problem if you try to repeat on the side. Further, in order to make the nickel ion concentration in the electrolyte uniform, there is no problem even if the electrolyte in the anode chamber 21 is agitated by a pump or the like.

(Electrolyte temperature)
The higher the temperature of the electrolytic solution in the electrolytic bath 10 is, the better. If the temperature of the electrolytic solution is high, it is possible to suppress passivation of the nickel that is anodically dissolved. However, the higher the temperature of the electrolytic solution, the higher the heat resistance of equipment materials such as the electrolytic cell 10 and the higher the cost required for heating. Considering the heat resistance of vinyl chloride, which is an industrially common material, the electrolyte temperature is preferably 65°C or less, preferably about 50 to 60°C.

(Evaluation of current efficiency)
When a sulfuric acid solution is produced by the method for producing an acid solution according to the present embodiment, a sulfuric acid solution containing metal ions can be efficiently obtained in a short period of time. The extent to which the current applied at this time contributed to dissolution of the metal was calculated as current efficiency. The current efficiency was calculated as a percentage obtained by subtracting the weight increase of the cathode 14 from the weight decrease of the anode 13 and dividing it by the theoretical dissolution amount obtained from the amount of current applied, as shown in Equation 1 below. Then, it was determined that electrolysis was efficiently performed when the current efficiency was 90% or more.

Current efficiency (%) = (decreased weight of anode - increased weight of cathode)/theoretical dissolution amount x 100 (Equation 1)

(others)
In the electrolytic cell 10 according to the present invention, the electrical conductivity or pH of the solution on the anode 13 side can be measured using a known measuring instrument, and used for operation management such as adjustment of the supply amount of sulfuric acid and the current to be energized. be.

(Example 1)
In the electrolytic cell 10 of Example 1, three anodes 13 as anode electrodes and two cathodes 14 as cathode electrodes were alternately provided in the electrolytic cell 10 . The anode electrode was configured by filling a titanium basket with pieces of cut nickel. A cathode electrode was provided in a box-shaped cathode chamber 22 . Of the side surfaces of the cathode chamber 22, the side surface positioned between the anode 13 and the cathode 14 was provided with an opening. A filter cloth having a water permeability of 0.1 liter/(m ² ·s) was installed as a diaphragm in this opening. Each cathode chamber 22 was connected by a connecting pipe 26 , and a liquid level monitor pipe 27 was connected to the connecting pipe 26 . A display for confirming the liquid level was attached to the outside of the electrolytic cell main body 11 . This display shows the measured value from the first liquid level gauge 29 that measures the liquid level in the anode chamber 21 and the measured value from the second liquid level gauge 25 that measures the liquid level in the cathode chamber 22 . The effective area of one side of the cathode electrode was 75 cm ² . Regarding the anode 13 side, although the exact effective area was not obtained, the area of the mesh portion of the titanium basket was set to be approximately the same size as the cathode 14 .

The following sulfuric acid solution was supplied to the anode chamber 21 as an initial electrolyte. This initial electrolytic solution was prepared by dissolving nickel sulfate crystals in water and adjusting the acid concentration or chloride concentration with sulfuric acid and hydrochloric acid to obtain a nickel ion concentration of 100 g/liter, a sulfuric acid concentration of 26 g/liter, and a chloride ion concentration of 100 g/liter. It has a concentration of 5 g/liter.

The following sulfuric acid solution was supplied to each cathode chamber 22 as an initial electrolytic solution so that the liquid level of the cathode chamber 22 was higher than that of the anode chamber 21 . This initial electrolytic solution is obtained by supplying hydrochloric acid to sulfuric acid having a concentration of 193 g/liter so that the chloride ion concentration in the cathode chamber 22 is 5 g/liter. Table 1 shows the conditions before metal melting in Example 1.

A current was supplied to the anode 13 and the cathode 14 provided in the electrolytic cell 10 so as to have a current density of 2000 A/m ² . At this time, the temperature of the electrolytic solution was controlled to 60°C. At the same time that the electric current was supplied, a total of 0.011 liter/min of sulfuric acid and hydrochloric acid having a concentration of 193 g/liter were supplied to the electrolytic cell 10 through the supply pipe 16 to each cathode chamber 22 . The amount of hydrochloric acid at this time is adjusted so that the chloride ion concentration in the cathode chamber 22 is 5 g/liter. The amounts of sulfuric acid and hydrochloric acid supplied to each cathode chamber 22 are not individually controlled. In addition, from the opening 15a of the extraction tube 15 located 5 mm above the bottom of the anode chamber 21, the same amount of metal-dissolving electrolyte as the total amount of sulfuric acid and hydrochloric acid supplied was taken out.

The results of Example 1 are shown in Table 2. The nickel ion concentration of the removed metal-dissolved electrolyte was 101 g/liter, which was sufficient nickel ion concentration for use in the manufacture of battery positive electrodes. Moreover, the current density was sufficiently high, and a sulfuric acid solution was efficiently obtained. In addition, it was found that the current efficiency was 98% when energization of 480 Ah was carried out, indicating that the electrolysis was being carried out efficiently. Furthermore, when the respective nickel ion concentrations in the cathode chamber 22 were measured, they were 5 g/liter and 4 g/liter, respectively, and it was found that the movement of nickel ions to the cathode chamber 22 was suppressed.

(Example 2)
In Example 2, the diaphragm 12 is a filter cloth having a water permeability of 0.3 liter/(m ² ·s). Other parameters are the same as in the first embodiment. Table 1 shows the conditions before metal melting in Example 2.

The results of Example 2 are shown in Table 2. The nickel ion concentration of the removed metal-dissolved electrolyte was 100 g/liter, which was sufficient nickel ion concentration for use in the production of positive electrodes for batteries. Moreover, the current density was sufficiently high, and a sulfuric acid solution was efficiently obtained. In addition, when 480 Ah of current was applied, the current efficiency was confirmed to be 96%, indicating that electrolysis was being performed efficiently. Furthermore, when the respective nickel ion concentrations in the cathode chamber 22 were measured, they were 7 g/liter and 8 g/liter, respectively, and it was found that the movement of nickel ions to the cathode chamber 22 was suppressed.

(Comparative example 1)
Comparative Example 1 has the same parameters as those of Example 1 except that the connecting pipe 26 is not used. Table 1 shows the conditions before metal melting in Comparative Example 1.

Table 2 shows the results of Comparative Example 1. The nickel ion concentration of the removed metal-dissolved electrolyte was 86 g/liter, an insufficient nickel ion concentration for use in the production of positive electrodes for lithium ion batteries. In addition, when the current efficiency was confirmed with respect to the implementation of energization of 480 Ah, it was found to be 88%, and it was found that the current supply could not sufficiently contribute to the melting of the metal. Since the nickel ion concentrations in the two cathode chambers 22 were 5 g/liter and 36 g/liter, in Comparative Example 1, the liquid level in one of the cathode chambers 22 could not be maintained high. The electrolyte may move to the cathode chamber 22, and it is said that the nickel ion concentration of the metal dissolution electrolyte decreased due to insufficient suppression of the movement of nickel ions to the cathode chamber 22. Conceivable.

(Comparative example 2)
In Comparative Example 2, the diaphragm 12 is a filter cloth having a water permeability of 1 liter/(m ² ·s). Other parameters are the same as in the first embodiment. Table 1 shows the conditions before metal melting in Comparative Example 2.

Table 2 shows the results of Comparative Example 2. The nickel ion concentration of the removed metal-dissolved electrolyte was 74 g/liter, which was an insufficient nickel ion concentration for use in the production of positive electrodes for lithium ion batteries. In addition, when the current efficiency was confirmed with respect to the implementation of energization of 480 Ah, it was found to be 75%, and it was found that the current supply could not sufficiently contribute to the dissolution of the metal. Furthermore, the respective nickel ion concentrations in the cathode chamber 22 were measured to be 41 g/liter and 40 g/liter. In Comparative Example 2, the water permeability was too high, and the electrolytic solution flowed not in one direction but in both directions between the anode chamber 21 and the cathode chamber 22, and the movement of nickel ions to the cathode chamber 22 was suppressed. It is thought that the cause was insufficient.

REFERENCE SIGNS LIST 10 electrolytic cell 12 diaphragm 13 anode 14 cathode 15 extraction pipe 15a opening 21 anode chamber 22 cathode chamber 24 transfer pipe 26 connecting pipe 27 liquid level monitor pipe

Claims (6)

An electrolytic cell for dissolving the metals that make up the anode by supplying an electric current,
The electrolytic cell is
an anode chamber in which the anode is located;
a plurality of cathode chambers, each having a plurality of cathodes disposed therein;
a diaphragm separating the anode chamber and the cathode chamber,
a connecting pipe connecting the plurality of cathode chambers;
a liquid level monitor pipe for checking the liquid level in the cathode chamber;
is provided with
An electrolytic cell characterized by: The metal constituting the anode contains at least either nickel or cobalt,
The electrolytic cell according to claim 1, characterized in that: The diaphragm is a filter cloth having a water permeability of 0.01 liter/(m ² s) or more and 0.5 liter/(m ² s) or less.
3. The electrolytic cell according to claim 1 or 2, characterized in that: An opening of a take-out pipe for taking out the electrolyte in the electrolytic cell is provided below the anode,
4. The electrolytic cell according to any one of claims 1 to 3, characterized in that: The cathode chamber has a sealed upper portion that is not immersed in the electrolytic solution,
Connected to a carrier pipe for carrying the gas generated from the cathode out of the tank,
5. The electrolytic cell according to any one of claims 1 to 4, characterized in that: A method for producing an acid solution using the electrolytic cell according to any one of claims 1 to 5,
By controlling the amount of electrolyte supplied to the cathode chamber and the amount of electrolyte discharged from the anode chamber,
making the liquid level in the anode chamber lower than the liquid level in the cathode chamber;
A method for producing an acid solution characterized by:

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