JP2020055729A - Method of producing sulfuric acid solution - Google Patents

Abstract

To provide a method of producing a sulfuric acid solution that highly efficiently dissolves a metal at a high anode current density while suppressing passivation and an electrolytic cell used in the production method.SOLUTION: A method of producing a sulfuric acid solution comprises: an initial electrolytic solution supplying step of supplying a sulfuric acid solution containing chloride ions as an initial electrolytic solution to an electrolytic cell 10, the inside of which is partitioned into an anode chamber 21 and a cathode chamber 22 by a cation-exchange membrane, at least to the anode chamber 21; and an electrolytic solution taking-out step of supplying current to an anode 13 and a cathode 14 provided in the electrolytic cell 10 and taking out a metal-dissolving electrolytic solution with a metal constituting the anode 13 dissolved therein from the anode chamber 21. According to the steps, there can be suppressed the movement of the metal dissolved on the anode 13 side to the cathode 14 side, as well as the production of passivity on the anode 13 side, and thus a high-quality sulfuric acid solution with the metal dissolved therein can be efficiently produced.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for producing a sulfuric acid solution. More specifically, the present invention relates to a method for producing a sulfuric acid solution containing metal ions in which a metal such as nickel or cobalt is dissolved in sulfuric acid.

  Metals such as nickel or cobalt are precious metals used as materials for plating or alloys. Recently, however, as applications other than plating or alloys, electrodes such as cathode materials for secondary batteries such as nickel-metal hydride batteries or lithium ion batteries Use as a material is also increasing. At this time, a metal such as nickel or cobalt is often used as a solution in which these are dissolved, for example, a sulfuric acid solution containing nickel ions and containing nickel ions.

  As an example, when nickel is used as the positive electrode material of the above-described lithium ion battery, a general method of manufacturing the positive electrode material of the lithium ion battery is to neutralize an aqueous solution containing nickel ions mixed at a predetermined ratio to obtain a precursor. There is a method in which a metal hydroxide called a body is formed, and then the precursor and a lithium compound are mixed and fired to obtain a positive electrode material. Here, the above-mentioned aqueous solution containing nickel ions is specifically a solution in which a nickel salt such as nickel sulfate or nickel chloride is dissolved. When this solution is used in the above-mentioned production method, it is necessary to suppress the halogen (chlorine) in the solution below the specification for the application.

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

  On the other hand, as a method of stably maintaining required quality, there is a method of dissolving metallic nickel in sulfuric acid to obtain a sulfuric acid solution containing nickel ions. High quality nickel metal having a purity of 99.99% or more can be easily obtained from the market as, for example, electric nickel. The electric nickel cut into a size of 2 to 5 cm square is easier to handle. Thus, the precursor material can be provided without requiring a large-scale purification step as described above.

  However, nickel is hardly dissolved even by cutting metal nickel in an acid such as sulfuric acid, even if it is a cut product, as is used for corrosion-resistant alloys such as stainless steel. For this reason, there are several methods for accelerating the dissolution of metallic nickel and bringing the concentration of nickel ions to a predetermined concentration. For example, as a method of obtaining a sulfuric acid solution containing nickel ions by dissolving metallic nickel in sulfuric acid, powdered nickel (nickel powder) or briquettes obtained by sintering nickel powder are used, and these are dissolved in sulfuric acid to obtain nickel. A method for obtaining a sulfuric acid solution containing ions 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 amount is limited. For this reason, there is a need for a technique for dissolving plate-shaped or massive electric nickel in the market in sulfuric acid in a short time.

  As a solution to this demand, there is an electrolysis method disclosed in Patent Documents 2 and 3, for example. That is, a method in which a metal to be dissolved in an anode (anode) is used, a sulfuric acid solution is used as an electrolytic solution, and a current is applied between the anode and the cathode (cathode) to dissolve the target metal in sulfuric acid.

  In the method disclosed in Patent Document 2, an electrode using metallic cobalt as an anode material and platinum or a metal coated with platinum as a cathode material is immersed in an electrolytic solution having a sulfuric acid concentration of 0.5 to 7.0 mol / l. I do. Then, a direct current is passed between the anode and the cathode to generate a cobalt solution. At this time, supersaturated cobalt sulfate crystals precipitated from the cobalt solution are separated, and the cobalt sulfate crystals are dissolved in water to obtain a cobalt sulfate solution. This is a method for producing a cobalt sulfate solution through these steps.

JP 2004-067483 A JP 2003-096585 A JP-A-1-301526

In a conventionally generally known electrolysis method, when a metal, for example, nickel or cobalt is dissolved in a sulfuric acid solution, the current density of the anode is set to 1000 A / m in order to quickly dissolve the metal nickel or metal cobalt. It is desired to perform electrolysis at about ^two or more. However, when the electrolysis method is performed at such a high current density, an oxide film is formed on the surface of the metallic nickel or metallic cobalt of the anode, and passivation (sometimes referred to as “passivation”) occurs, and almost no current flows. There is a problem that the flow stops. When the electrolysis method is performed at a low current density so as to suppress the occurrence of passivation, dissolution is not promoted, and there is a problem that the original purpose of promoting dissolution cannot be achieved.

  In particular, for a sulfuric acid solution containing nickel ions required for manufacturing a positive electrode material of a battery, a solution having a high nickel ion concentration of about 100 g / liter is required. When the concentration of nickel ions in the electrolytic solution increases, passivation tends to occur more easily, and nickel also precipitates on the cathode-side electrode, resulting in lower dissolution efficiency.

  Similarly, with respect to cobalt, there is a concern that as the cobalt ion concentration of the solution to be obtained is increased, the dissolution efficiency is reduced and passivation is promoted.

  In view of the above circumstances, the present invention relates to an electrolytic method, which is one of the methods for promoting the dissolution of a metal in a sulfuric acid solution. It is an object of the present invention to provide a method for producing the same.

In the method for producing a sulfuric acid solution of the first invention, a chloride ion-containing sulfuric acid solution is supplied as an initial electrolytic solution to at least the anode chamber of an electrolytic cell in which the inside of the cell is divided into an anode chamber and a cathode chamber by a cation exchange membrane. An initial electrolytic solution supply step, and an electrolytic solution removing step of supplying a current to the anode and the cathode provided in the electrolytic cell, and extracting a metal-dissolved electrolytic solution in which the metal constituting the anode is dissolved from the anode chamber; , And is characterized by comprising.
A method for producing a sulfuric acid solution according to a second invention is characterized in that, in the first invention, the metal constituting the anode contains at least either nickel or cobalt.
A method for producing a sulfuric acid solution according to a third invention is characterized in that, in the first invention or the second invention, the chloride ion-containing sulfuric acid solution has a chloride ion concentration of 1 g / L or more and 20 g / L or less.
A method for producing a sulfuric acid solution according to a fourth invention is characterized in that, in the first to third inventions, in the electrolyte removal step, a pulse current that repeats periodic power interruption is supplied to the anode and the cathode. I do.
In the method for producing a sulfuric acid solution according to a fifth aspect of the present invention, in the fourth aspect, in the periodic power interruption, a ratio of an energization time in one cycle of the periodic power interruption is 0.8 or more and less than 1.0. It is characterized by the following.

According to the first invention, in the method for producing a sulfuric acid solution, since the electrolytic cell used is divided into the anode chamber and the cathode chamber by the cation exchange membrane, the cations existing in the anode chamber, that is, hydrogen ions and nickel ions Alternatively, among cobalt ions, hydrogen ions having high mobility can be selectively transferred. Thereby, it is possible to suppress the metal dissolved in the anode chamber from moving to the cathode chamber. Furthermore, when a monovalent selective cation exchange membrane is used, most of the dissolved nickel ions (divalent cations) are maintained in the anode compartment, and hydrogen ions (monovalent cations) can move freely. A high concentration nickel solution can be obtained in the anode compartment. In the case of a monovalent selective cation exchange membrane, a thin layer having a positive charge is formed on the membrane surface, and the difference in electrostatic repulsion between the charged layer and monovalent cations and divalent cations results. Divalent ions are hardly permeated. In addition, by performing an electrolytic solution removing step, that is, supplying a current to the anode and the cathode and performing a step of removing the metal-dissolved electrolytic solution from the anode chamber, a sulfuric acid solution having a high concentration of metal ions is removed from the anode chamber. . For this reason, since the value of the concentration of nickel ions in the anode chamber does not increase, the formation of passivation on the anode side can be suppressed, and a high-quality sulfuric acid solution in which a metal is dissolved can be efficiently produced.
According to the second invention, since the metal constituting the anode contains at least either nickel or cobalt, the produced sulfuric acid solution can be used as a positive electrode of a secondary battery.
According to the third invention, when the concentration of chloride ions in the sulfuric acid solution is 1 g / L or more and 20 g / L or less, the formation of a passive film is appropriately suppressed, and the current density when dissolving the anode can be increased. Therefore, a sulfuric acid solution can be produced more efficiently, and when a cathode material for a lithium ion battery is used, it is preferable that the chloride ion concentration be lower.
According to the fourth aspect, the passivation can be further suppressed by supplying the anode and the cathode with the pulse current that repeats the periodic power interruption in the electrolyte removing step.
According to the fifth aspect, the ratio of the energization time in one cycle of the power interruption is 0.8 or more and less than 1.0, so that the efficiency of the production of the sulfuric acid solution can be maintained while suppressing the passivation.

It is sectional drawing from the side surface direction of the electrolytic cell used in the manufacturing method of the sulfuric acid solution which concerns on this invention. It is explanatory drawing of the pulse current supplied to an electrolytic cell.

  Next, an embodiment of the present invention will be described with reference to the drawings. However, the embodiment described below exemplifies a method for producing a sulfuric acid solution for embodying the technical idea of the present invention, and the present invention does not specify a method for producing a sulfuric acid solution as follows. In addition, the size or the positional relationship of the members shown in each drawing may be exaggerated for clarity of description. Further, in the present specification, the “electrolyte” means a liquid used to supply electricity in the electrolysis tank 10, and an “initial electrolyte” supplied to the electrolysis tank 10 first and an electrolysis are performed. "A metal-dissolved electrolytic solution in which a metal is dissolved". The “electrolyte solution” taken out of the electrolytic cell 10 is a “sulfuric acid solution” manufactured by the manufacturing method of the present invention.

  FIG. 1 is a sectional view from the side of an electrolytic cell 10 used in the method for producing a sulfuric acid solution according to the present invention. In the method for producing a sulfuric acid solution according to the present invention, a chloride ion-containing sulfuric acid solution is initially charged in an electrolytic tank 10 in which a tank is divided into an anode chamber 21 and a cathode chamber 22 by a diaphragm 12 using a cation exchange membrane. And supplying an electric current to the anode 13 and the cathode 14 provided in the electrolytic cell 10, and taking out the metal-dissolved electrolytic solution in which the metal constituting the anode 13 is dissolved from the anode chamber 21. And an electrolyte removal step.

  Further, the metal constituting anode 13 preferably contains at least either nickel or cobalt.

  Further, the concentration of chloride ions in the sulfuric acid solution is preferably 1 g / liter or more and 20 g / liter or less.

  Further, in the electrolyte removal step, it is preferable to supply the anode 13 and the cathode 14 with a pulse current that repeats periodic power interruption.

  Further, in the periodic power interruption, it is preferable that a ratio of an energization time in one cycle of the periodic power interruption is 0.8 or more and less than 1.0.

  Hereinafter, the electrolytic cell 10 used in the method for producing a sulfuric acid solution according to the present invention will be described with reference to the drawings, and then a method for producing a sulfuric acid solution using the electrolytic cell 10 will be described.

<Configuration of electrolytic cell 10>
(Electrolyzer main body 11)
The electrolytic cell main body 11 has a configuration capable of holding an electrolytic solution inside. The material constituting the electrolytic cell main body 11 is a known material. The electrolytic cell main body 11 includes an anode chamber 21 in which an anode 13 is located inside by a diaphragm 12 using a cation exchange membrane, and a cathode chamber 22 in which a cathode 14 is located. A DC power supply 17 connected to the anode 13 and the cathode 14 is provided outside the electrolytic cell main body 11. In FIG. 1, a line connected from the DC power supply 17 to the anode 13 or the cathode 14 represents an electric wire, and an arrow along this line indicates the direction of current.

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

(Anode 13)
The anode 13 used in the electrolytic cell 10 has a plurality of forms. For example, in the case of obtaining an acidic solution of nickel, the first form of the anode 13 corresponds to plate-shaped metallic nickel (electric nickel) which is industrially electrolytically purified or electrolytically collected. In the second embodiment, a basket made of a material insoluble in an acid such as titanium is filled with small-sized metal nickel. In the case of the second embodiment, it is necessary to replace the metal before it is completely melted, or the cost and labor for cutting the metal are required, but the metal can be melted efficiently without waste. In the case of the first mode, it is necessary to replace the entire anode 13 after the dissolution is completed. The exchange is performed when a predetermined size is reached. A two-stage melting method in which the metallic nickel having a size smaller than the predetermined size is filled and melted in the basket of the second form can also be used.

(Cathode 14)
For the cathode 14, a plate-like metal such as titanium, stainless steel, nickel, cobalt, and platinum is preferably used. Further, a structure in which the surface of aluminum, iron, or the like is plated with nickel, cobalt, or the like can also be used.

(Diaphragm 12)
The diaphragm 12 divides the inside of the electrolytic cell main body 11 into an anode chamber 21 and a cathode chamber 22. The diaphragm 12 suppresses passage of liquid or ions. Specifically, as the diaphragm 12, a cation exchange membrane is used in the present invention.

  The cation exchange membrane has a property that, since the negative charge exchange group is fixed, anions are repelled and cannot pass, but only cations pass. A highly concentrated nickel solution can be obtained in the anode chamber 21 by using the difference in mobility between hydrogen ions and nickel ions. This is because hydrogen ions do not move alone, but can move by transferring hydrogen ions and surrounding oxonium ions, and thus have a higher mobility than other ions.

  Cation exchange membranes (cation exchange membranes) have high current density, low membrane resistance, small voltage drop, high transport number, no scale deposition inside the membrane, high mechanical strength, thermal and chemical It is required to have characteristics such as stable stability.

  When a current density sufficiently higher than the current density at which the metal of the anode 13 is dissolved cannot be obtained, the productivity depends on the current density of the cation exchange membrane. As the membrane resistance increases, the voltage drop increases, and the cell voltage increases, resulting in an increase in power cost. If scale is deposited inside the membrane, or if the mechanical strength or the thermal or chemical stability is insufficient, the durability is poor and the cation exchange membrane is frequently replaced. Specifically, the cation exchange membrane corresponds to Nafion N324 (trade name of DuPont). The monovalent selective cation exchange membrane corresponds to Selemion HSF manufactured by Asahi Glass Co., Ltd.

  Since the electrolytic cell 10 is divided into the anode chamber 21 and the cathode chamber 22 by the cation exchange membrane, cations existing in the anode chamber 21, that is, hydrogen ions and hydrogen of high mobility among nickel ions or cobalt ions Ions can be selectively moved. Thereby, the movement of the metal melted in the anode chamber 21 to the cathode chamber 22 can be suppressed. Furthermore, by using a monovalent selective cation exchange membrane, most of the dissolved nickel ions (divalent cations) are maintained in the anode chamber 21 and hydrogen ions (monovalent cations) are more selectively formed. Can be moved.

(Removal pipe 15 etc.)
When the configuration is such that the metal-dissolved electrolytic solution can be continuously obtained from the anode chamber 21, the extraction chamber 15 for extracting the sulfuric acid solution from the anode chamber 21 in the direction indicated by the arrow is provided in the anode chamber 21 of the electrolytic cell main body 11. Is provided. Further, an extraction pump 20 for extracting the sulfuric acid solution from the anode chamber 21 is connected to the extraction pipe 15. In addition, a second supply pipe 31 for supplying sulfuric acid is provided in the anode chamber 21, and a predetermined amount of sulfuric acid is supplied to the anode chamber 21 by the second supply pump 32 as shown by an arrow.

  Since the specific gravity of nickel ions and cobalt ions is higher than that of water, the concentration of nickel and the like in the deeper part of the anode chamber 21 becomes higher with energization. Therefore, by recovering the sulfuric acid solution from a deeper portion of the anode chamber 21, that is, by providing the opening 15 a of the extraction pipe 15 below the anode 13 in the anode chamber 21, the sulfuric acid solution having a high concentration of nickel or the like is provided. Can be recovered.

  If the opening 15a of the extraction pipe 15 is provided below the anode 13, even if the nickel concentration near the surface of the anode 13 is lower than 100 g / liter, the sulfuric acid solution is recovered from the deep part of the anode chamber 21 to reduce the nickel concentration. Can recover a 100 g / liter sulfuric acid solution. Thereby, passivation of nickel on the surface of the anode 13 is suppressed.

  It is preferable that a predetermined space is provided below the anode 13. However, if the space is too large, the volume of the electrolytic cell 10 increases, and the equipment cost increases. Therefore, it is preferable that the standard of the depth from the lower end of the anode 13 to the bottom of the anode chamber 21 of the electrolytic cell main body 11 is 10% or more of the liquid level height of the anode chamber 21.

  The cathode chamber 22 is provided with a cathode chamber electrolyte extraction pipe 38 and a third supply pipe 34 for circulating the electrolyte in the cathode chamber 22. The electrolyte in the cathode chamber 22 is circulated.

  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 having a relatively large specific gravity is efficiently taken out.

(DC power supply 17)
The DC power supply 17 has not only a function of continuously supplying a constant value of DC current but also a function of supplying a pulse current. “Supplying a pulse current” means performing intermittent energization in which power-on (ON) and power-off (OFF) times are set and power-on and power-off are repeated periodically (pulse energization or pulse electrolysis is sometimes used). is there).

  FIG. 2 shows an example of a pulse current supplied to the electrolytic cell 10. The vertical axis represents the current value A, and the horizontal axis represents the time T. As shown in FIG. 2, after the current A1 is supplied for a certain period of time, the supply of the pulse current is stopped and the pulse current is repeated. That is, the pulse current is supplied in a rectangular shape.

  If the metal ion concentration in the vicinity of the anode 13 is too high, passivation tends to occur. To suppress this, a pulse current is supplied. That is, when the current is periodically turned off, the elution of metal ions from the anode 13 temporarily stops, and during that time, the metal ions eluted using the liquid flow in the tank are moved away from the vicinity of the anode 13. As a result, an increase in the metal ion concentration in the vicinity of the anode 13 can be suppressed.

The ratio of the ON time to the cycle is defined as a duty ratio. In addition, the current density in the case of using the pulse current is described as an average current density including ON time and OFF time. For example, when the current density at the time of ON is 1250 A / m ² and the duty ratio is 0.8 (that is, current is supplied for 80% of the time), the average current density is 1250 × 0.8 = 1000 A / m ² . Note that the term “stop” of the “power interruption” described in the claims includes not only completely reducing the current to 0 A, but also considerably lowering the current value than when the switch is ON. In the case of the duty ratio 1, it means a simple one-way energization in which the energization time ratio is 100%.

<Method for producing sulfuric acid solution>
(Initial electrolyte supply step)
In the method for producing a sulfuric acid solution according to the present invention, first, a sulfuric acid solution containing chloride ions is supplied to the electrolytic cell 10 of FIG. 1 as an initial electrolytic solution (initial electrolytic solution supply step). The initial electrolyte may be supplied to both the anode compartment 21 and the cathode compartment 22, but at least the anode compartment 21 is supplied with a sulfuric acid solution containing chloride ions. Preferably, the initial electrolyte has a chloride ion concentration and a sulfuric acid concentration as described below.

(Chloride ion concentration)
When the nickel metal is dissolved in the sulfuric acid solution without taking any measures, an oxide film, that is, a passivation film is easily formed on the surface of the anode 13, and a passivation state where almost no current flows is obtained. It is said that the formation of the passivation film is suppressed by the presence of halogen ions, a decrease in hydrogen ion concentration (pH), an increase in temperature, and the like. The present inventor studied the dissolution of metallic nickel in the anode, and found that the addition of chloride ions to the electrolytic solution was particularly effective. The chloride ion concentration refers to the concentration of chloride ions in the electrolyte after a predetermined chloride has been added to the electrolyte.

The chloride ion concentration in the electrolyte is desirably from 1 g / liter to 20 g / liter. This is because the formation of the passivation film is appropriately suppressed, and the lower chloride ion concentration is more preferable when used for manufacturing a positive electrode material of a lithium ion battery. When the amount is less than 1 g / liter, the effect of suppressing the formation of a passive film becomes insufficient. In particular, when the anode 13 is separated from the cathode 14 using an ion-exchange membrane as in the present invention, if chloride ions are not contained in the electrolyte on the anode 13 side, the anode 13 is easily passivated and the anode 13 It is not preferable because the elution of nickel from methane is suppressed and only oxygen or chlorine is generated. In this case, it is difficult to make the current density at the time of performing metal electrolysis 1000 A / m ² or more. Further, the chloride concentration is more preferably 4 g / liter or more. In dissolving the metallic nickel in the anode, the concentration can be increased to a level at which the solubility of the metallic nickel can be ensured.

  However, when a sulfuric acid solution containing metal ions is used for producing a positive electrode material for a lithium ion battery, the chloride ion concentration in the resulting sulfuric acid solution is preferably low. In this case, the chloride ion concentration is preferably 20 g / liter or less.

  The chloride ions can be supplied in the form of sodium chloride or lithium chloride. However, since it is preferable to reduce impurities in the sulfuric acid solution as much as possible, it is preferable to add nickel chloride or the like in the form of chloride salt or hydrochloric acid of the same ion as the metal ion contained in the sulfuric acid solution.

  When the concentration of chloride ions in the sulfuric acid solution is 1 g / L or more and 20 g / L or less, the current density when dissolving the anode 13 can be increased, so that the sulfuric acid solution can be produced more efficiently.

  The chloride ion concentration is preferably in the range of 1 g / liter to 20 g / liter in the case where nickel metal is dissolved in the anode, but the same applies to the case of metal cobalt. However, in the case of metallic cobalt, dissolution may proceed even if the chloride ion concentration is 0 g / liter.

(Sulfuric acid concentration)
The concentration of sulfuric acid (also referred to as "free sulfuric acid" or "free sulfuric acid") supplied as the initial electrolyte is preferably as small as possible. This is because if the value of the concentration of sulfuric acid is small, the cost of chemicals for neutralizing the sulfuric acid solution containing metal ions extracted from the electrolytic cell 10 can be reduced.

  However, when the value of the concentration of sulfuric acid supplied as the initial electrolytic solution decreases, the electric conductivity of the electrolytic solution (also simply referred to as “conductivity” or “conductivity”) decreases and the liquid resistance increases, As the diffusion limit current value of the hydrogen ions at 14 decreases, the voltage increases. It is desirable to set the most economical conditions in consideration of the electricity bill and the cost of the chemical for neutralization. Therefore, the amount of current and the sulfuric acid solution supplied to the cathode 14 side are adjusted so as to obtain an optimum free concentration by using a pH meter or an electric conductivity meter (also simply referred to as “conductivity meter” or “conductivity meter”). Is preferably adjusted.

(Electrolyte removal process)
Next, in the method for producing a sulfuric acid solution according to the present invention, a current is supplied to the anode 13 and the cathode 14 provided in the electrolytic cell 10 of FIG. The dissolved metal dissolved electrolyte is taken out (electrolyte taking out step). This metal-dissolved electrolytic solution becomes a sulfuric acid solution when taken out of the electrolytic cell 10. The metal-dissolved electrolyte preferably has a metal ion concentration and an electrolyte temperature as described below. Note that the electrolytic solution removing step includes a case where the metal-dissolved electrolytic solution is taken out while supplying the current to the anode 13 and the like, and a case where the metal-dissolved electrolytic solution is taken out after the current supply is completed.

  In the electrolytic cell 10 of FIG. 1, when the metal-dissolved electrolyte is taken out from the anode chamber 21, sulfuric acid corresponding to the amount of the metal-dissolved electrolyte taken out is supplied from the second supply pipe 31 to the anode chamber 21. . Further, hydrogen ions in the cathode chamber 22 are reduced to hydrogen gas by electrolysis, but hydrogen ions are supplied from the anode chamber 21 through the cation exchange membrane. Therefore, it is sufficient to circulate the electrolyte in the cathode chamber 22.

  Since the method for producing a sulfuric acid solution includes an electrolyte extracting step, that is, a step of supplying a current to the anode 13 and the cathode 14 and extracting the metal-dissolved electrolyte from the anode chamber 21, A sulfuric acid solution having a high concentration of metal ions is taken out, the formation of passivation on the anode 13 side can be suppressed, and a high-quality sulfuric acid solution in which the metal is dissolved can be efficiently produced.

(Metal ion concentration)
The metal ion concentration of the sulfuric acid solution produced by the method for producing a sulfuric acid solution according to the present invention is determined depending on the use of the sulfuric 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 a high concentration of nickel ions of about 90 to 100 g / liter in a sulfuric acid solution is required. . The same is true for cobalt.

  The metal ion concentration in the sulfuric acid solution is determined by the following parameters. That is, when the anode 13 is metallic nickel and the reaction at the anode 13 is all nickel dissolution, the amount of dissolution is determined by the current value supplied to the anode 13. In the case of the continuous electrolytic cell 10 shown in FIG. 1, the anode chamber 21 is replenished with sulfuric acid containing chloride ions so that the dissolved amount becomes a desired nickel ion concentration. It is removed from 21 as a sulfuric acid solution. In the case of the batch type, the integrated current amount (also referred to as the amount of current) to be supplied to the anode 13 is determined so as to obtain a desired nickel ion concentration.

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

  When the continuous electrolytic cell 10 is used, 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 start of the removal, a sulfuric acid solution having a predetermined nickel ion concentration can be obtained from the beginning. When the sulfuric acid solution supplied to the anode chamber 21 as an initial electrolytic solution has a concentration lower than a predetermined nickel ion concentration, the sulfuric acid solution which has not reached the predetermined nickel ion concentration at the beginning of the dissolution starts from the anode chamber 21. There is no problem even if it repeats to the side. Further, there is no problem even if the electrolytic solution in the anode chamber 21 is stirred by a pump or the like in order to make the nickel ion concentration in the electrolytic solution uniform.

(Electrolyte temperature)
It is preferable that the temperature of the electrolytic solution in the electrolytic cell 10 is high. When the electrolyte temperature is high, passivation of nickel that dissolves in the anode can be suppressed. In particular, in order to suppress the generation of passivation, the temperature of the electrolytic solution held in the electrolytic cell 10 is preferably higher than 30 ° C., and more preferably 40 ° C. or higher. However, the ion exchange membrane is easily deteriorated when the temperature exceeds 60 ° C., and it is necessary to set the temperature to 60 ° C. or less in practical use. Furthermore, the higher the temperature of the electrolytic solution, the higher the heat resistance of equipment materials such as the electrolytic cell 10 and the cost required for heating. Therefore, it is desirable to set the most economical conditions in consideration of productivity and cost. Considering the heat resistance of vinyl chloride, which is an industrially common material, the temperature of the electrolyte is preferably 65 ° C. or lower, more preferably, about 50 to 60 ° C. That is, the temperature of the electrolytic solution in the electrolytic cell 10 is preferably 40 ° C. or higher from the viewpoint of suppressing passivation of nickel, and is preferably 65 ° C. or lower from the viewpoint of deterioration of the ion exchange membrane and the like.

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

[Equation 1]
Current efficiency (%) = (weight reduced by anode 13−weight increased by cathode 14) / theoretical dissolved amount × 100 (1)

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

  In the embodiment of the present invention described below, energization by electrolysis is performed by a general method of energizing the nickel plate or the cobalt plate of the anode 13 continuously without changing the polarity of the anode 13 and the cathode 14, that is, one method. Direct current energization and intermittent energization (also referred to as “pulse energization”) in which energization is performed while repeating a short-time power outage in a fixed cycle are employed. An energization method called energization may be employed. Since these energization methods have the effect of suppressing the occurrence of passivation of the anode 13, the current density is increased by that amount to improve the production efficiency, or the concentration of chloride to be added is reduced, so that the sulfuric acid solution is reduced. Further purification can be achieved.

(Example 1)
In Example 1, the electrolytic cell 10 shown in FIG. 1 capable of continuously obtaining a metal-dissolved electrolytic solution was used. In the electrolytic cell 10, an anode chamber 21 and a cathode chamber 22 are separated by using a cation exchange membrane as a diaphragm 12. The transport number of this cation exchange membrane is 0.92 or more. In the electrolytic cell 10, a metal nickel plate was installed as the anode 13 and the cathode 14 with a distance between the electrodes of 45 mm. Each effective area was 16 cm ² .

  The following sulfuric acid solution was supplied to the anode chamber 21 as an initial electrolyte so that the liquid level in the anode chamber 21 was 120 mm. The initial electrolyte solution was prepared by dissolving nickel sulfate crystals in water and adjusting the acid concentration and the chloride concentration with sulfuric acid and hydrochloric acid so that the nickel ion concentration was 100 g / l, the sulfuric acid concentration was 29 g / l, and the chloride ion was The concentration is 3 g / liter.

  The following electrolytes were supplied to the cathode chamber 22 as initial electrolytes. The initial electrolyte is sulfuric acid at a concentration of 200 g / l. That is, no chloride ion exists in the cathode chamber 22. Table 1 shows the conditions before melting of the metal 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 electrolyte was controlled to be 60 ° C. The metal-dissolved electrolyte was taken out by the take-out pump 20 from the opening 15 a of the take-out tube 15 located 5 mm above the bottom of the anode chamber 21. The amount of the extracted metal-dissolved electrolytic solution is the same as the total amount of sulfuric acid and hydrochloric acid supplied, ignoring the amount of evaporation.

  Table 2 shows the results of Example 1. The nickel ion concentration of the extracted metal-dissolved electrolytic solution was 100 g / liter, which was a nickel ion concentration sufficient for use in manufacturing a battery positive electrode. In addition, the current density was sufficiently high, and a sulfuric acid solution was efficiently obtained. That is, while the current was supplied at 24 Ah, the re-deposition of nickel on the cathode 14 was slight, and the current efficiency was confirmed to be 94%, indicating that the electrolysis was performed efficiently.

(Example 2)
Example 2 is the same as Example 1 except that the following sulfuric acid solution was supplied to the anode chamber 21 and the cathode chamber 22 as the initial electrolyte. The initial electrolyte in the anode chamber 21 of Example 2 was prepared by dissolving nickel sulfate in water and adjusting with sulfuric acid and hydrochloric acid, so that the nickel ion concentration was 100 g / l, the sulfuric acid concentration was 26 g / l, and the chloride ion concentration was It is 5 g / liter. The initial electrolyte in the cathode chamber 22 is sulfuric acid having a concentration of 200 g / liter. That is, no chloride ion exists in the cathode chamber 22. Table 1 shows the conditions before melting the metal in Example 2.

  Table 2 shows the results of Example 2. The nickel ion concentration of the extracted metal-dissolved electrolytic solution was 101 g / liter, which was a nickel ion concentration sufficient for use in manufacturing a battery positive electrode. In addition, the current density was sufficiently high, and a sulfuric acid solution was efficiently obtained. In other words, when the current was supplied for 24 Ah, the re-deposition of nickel on the cathode 14 was slight, and the current efficiency was confirmed to be 96%, indicating that the electrolysis was performed efficiently.

(Example 3)
The third embodiment is different from the first embodiment in that a monovalent selective cation exchange membrane is used as the diaphragm 12, the following sulfuric acid solution is supplied to the anode chamber 21 and the cathode chamber 22 as an initial electrolyte, The parameters are the same as in Example 1 except that the temperature of the solution is 45 ° C., the current density is 1000 A / m ^2, and the effective area of each of the anode 13 and the cathode 14 is 32 cm ² . The initial electrolyte solution in the anode chamber 21 of Example 3 was prepared by dissolving nickel sulfate in water and adjusting with sulfuric acid and hydrochloric acid, so that the nickel ion concentration was 100 g / l, the sulfuric acid concentration was 25 g / l, and the chloride ion concentration was It is 6 g / liter. The initial electrolyte in the cathode chamber 22 is sulfuric acid having a concentration of 200 g / liter. That is, no chloride ion exists in the cathode chamber 22. Table 1 shows the conditions before melting the metal of Example 3.

  Table 2 shows the results of Example 3. The nickel ion concentration of the extracted metal-dissolved electrolyte was 103 g / liter, which was a nickel ion concentration sufficient for use in manufacturing a positive electrode of a battery. In addition, the current density was sufficiently high, and a sulfuric acid solution was efficiently obtained. That is, when the current was supplied at 24 Ah, there was almost no re-deposition of nickel on the cathode 14, and the current efficiency was confirmed to be 99%, indicating that the electrolysis was performed efficiently. Further, the nickel ion concentration in the cathode chamber 22 was 1 g / liter, and the movement of nickel ions in the anode chamber 21 to the cathode chamber 22 was suppressed.

(Example 4)
In Example 4, the point that a metal cobalt plate was used for the anode 13 and the cathode 14, the point that the following sulfuric acid solution was supplied to the anode chamber 21 and the cathode chamber 22 as initial electrolytes, and that the liquid temperature was 40 ° C. Are the same as those in the third embodiment except for the point that is controlled. The initial electrolyte solution in the anode chamber 21 of Example 4 was prepared by dissolving cobalt sulfate in water and adjusting with sulfuric acid and hydrochloric acid, so that the cobalt ion concentration was 100 g / l, the sulfuric acid concentration was 26 g / l, and the chloride ion concentration was It is 5 g / liter. The initial electrolyte in the cathode chamber 22 is sulfuric acid having a concentration of 200 g / liter. That is, no chloride ion exists in the cathode chamber 22. Table 1 shows the conditions of Example 4 before melting the metal.

  Table 2 shows the results of Example 4. The removed metal-dissolved electrolyte had a cobalt ion concentration of 102 g / liter, which was a sufficient cobalt ion concentration for use in producing a battery positive electrode. In addition, the current density was sufficiently high, and a sulfuric acid solution was efficiently obtained. In addition, although the re-deposition of nickel on the cathode 14 was slight when the current of 24 Ah was applied, the current efficiency was 98% when the current efficiency was confirmed, indicating that the electrolysis was performed efficiently. . Further, when the cobalt ion concentration in the cathode chamber 22 was measured, it was 1 g / liter, and it was found that the movement of the cobalt ions to the cathode chamber 22 could be suppressed.

(Example 5)
Example 5 is the same as Example 4 except that the transport number of the monovalent selective cation exchange membrane is 0.96 or more. That is, the initial electrolytic solution in the anode chamber 21 of Example 5 was prepared by dissolving cobalt sulfate in water and adjusting the concentration with sulfuric acid and hydrochloric acid to obtain a cobalt ion concentration of 100 g / liter, a sulfuric acid concentration of 200 g / liter, and a chloride ion. The concentration is 5 g / liter. The initial electrolyte in the cathode chamber 22 is sulfuric acid having a concentration of 200 g / liter. That is, no chloride ion exists in the cathode chamber 22. Table 1 shows the conditions of Example 5 before melting the metal.

  Table 2 shows the results of Example 5. The removed metal-dissolved electrolyte had a cobalt ion concentration of 102 g / liter, which was a sufficient cobalt ion concentration for use in producing a battery positive electrode. In addition, the current density was sufficiently high, and a sulfuric acid solution was efficiently obtained. In addition, when the current was supplied at 24 Ah, nickel was re-deposited on the cathode 14 slightly. However, when the current efficiency was confirmed, the current efficiency was 99%, indicating that the electrolysis was performed efficiently. . Further, when the cobalt ion concentration in the cathode chamber 22 was measured, it was 1 g / liter, and it was found that the movement of the cobalt ions to the cathode chamber 22 could be suppressed.

(Comparative Example 1)
In Comparative Example 1, the following initial electrolyte was supplied to the anode chamber 21 and the cathode chamber 22 as the initial electrolyte. The initial electrolyte in the anode chamber 21 has a nickel ion concentration of 100 g / liter and a sulfuric acid concentration of 33 g / liter. The initial electrolyte in the cathode chamber 22 is sulfuric acid having a concentration of 200 g / liter. That is, chloride ions do not exist in the anode chamber 21 and the cathode chamber 22. Other parameters are the same as in the first embodiment. Table 1 shows the conditions of Comparative Example 1 before melting the metal.

  Table 2 shows the results of Comparative Example 1. In Comparative Example 1, the dissolution was stopped because the voltage rapidly increased and oxygen was generated from the anode 13 immediately after the current started to flow. That is, under the conditions of Comparative Example 1, the current density could not be increased, and a sulfuric acid solution could not be obtained efficiently.

(Comparative Example 2)
In Comparative Example 2, the following sulfuric acid solution was supplied to the anode chamber 21 and the cathode chamber 22 as the initial electrolyte, the temperature of the electrolyte was 30 ° C. when the current was supplied, and the current density was 1000 A / The parameters are the same as those of the first embodiment except that m ² and the effective area of each of the anode 13 and the cathode 14 are 32 cm ² . The initial electrolyte solution in the anode chamber 21 is prepared by dissolving nickel sulfate in water and adjusting the concentration with sulfuric acid and hydrochloric acid to obtain a nickel ion concentration of 100 g / l, a sulfuric acid concentration of 25 g / l, and a chloride ion concentration of 6 g / l. Is what it is. The initial electrolyte in the cathode chamber 22 is sulfuric acid having a concentration of 200 g / liter. That is, no chloride ion exists in the cathode chamber 22. Table 1 shows the conditions of Comparative Example 2 before melting the metal.

  Table 2 shows the results of Comparative Example 2. In Comparative Example 1, the dissolution was stopped because the voltage suddenly increased and oxygen was generated from the anode 13 some time after the current was started to flow. That is, under the conditions of Comparative Example 1, the current density could not be increased, and a sulfuric acid solution could not be obtained efficiently.

(Comparative Example 3)
In Comparative Example 3, the electrolytic cell 10 of FIG. 1 was used, but at this time, the diaphragm 12 was removed. The following initial electrolyte was supplied. This initial electrolytic solution is adjusted to have sulfuric acid concentration of 29 g / l and chloride ion concentration of 3 g / l by adjusting with sulfuric acid and hydrochloric acid. The parameters other than the absence of the diaphragm 12 and the point of the initial electrolyte are the same as those of the fourth embodiment. Table 1 shows the conditions of Comparative Example 3 before melting the metal.

  Table 2 shows the results of Comparative Example 3. Some time after energization, the anode 13 and the cathode 14 were short-circuited. When the cathode 14 was taken out and confirmed, cobalt was deposited in a dendrite shape. That is, it was found that it was difficult to efficiently obtain a sulfuric acid solution.

(Example 6)
A point where a pulse current that repeats a periodic power interruption is supplied to the anode 13 and the cathode 14 provided in the electrolytic cell 10, a point that the electrode effective areas of the anode 13 and the cathode 14 are different, and the anode chamber 21 and the The parameters other than the point that the following sulfuric acid solution was supplied to the cathode chamber 22 are the same as those in the first embodiment. In Example 6, the effective area of the anode 13 and the cathode 14 provided in the electrolytic cell 10 was 32 cm ² . Further, a pulse current was supplied such that the ON time was 0.85 seconds, the duty ratio was 0.85, and the average current density was 1000 A / m ² at a cycle of 1 second. Further, the initial electrolyte solution in the anode chamber 21 of Example 6 was prepared by dissolving nickel sulfate in water and adjusting with sulfuric acid and hydrochloric acid to obtain a nickel ion concentration of 100 g / liter, a free sulfuric acid concentration of 32 g / liter, and a chloride. The ion concentration is 1 g / liter. The initial electrolyte in the cathode chamber 22 is sulfuric acid having a concentration of 200 g / liter. That is, no chloride ion exists in the cathode chamber 22. Table 3 shows the conditions before melting of the metal in Example 6.

  Table 4 shows the results of Example 6. The nickel ion concentration of the extracted metal-dissolved electrolytic solution was 102 g / liter, which was a nickel ion concentration sufficient for use in manufacturing a battery positive electrode. In addition, the current density was sufficiently high, and a sulfuric acid solution was efficiently obtained. In addition, the current efficiency was confirmed to be 96% with respect to the conduction of 24 Ah, indicating that the electrolysis was performed efficiently. Further, when the nickel ion concentration in the cathode chamber 22 was measured, it was 25 g / liter, and it was found that the movement of nickel ions to the cathode chamber 22 could be suppressed.

(Example 7)
A point where a pulse current that repeats a periodic power interruption is supplied to the anode 13 and the cathode 14 provided in the electrolytic cell 10, a point that the electrode effective areas of the anode 13 and the cathode 14 are different, and that the anode chamber 21 and the The parameters other than the point that the following sulfuric acid solution was supplied to the cathode chamber 22 are the same as those in the sixth embodiment. In Example 7, the effective area of the anode 13 and the cathode 14 provided in the electrolytic cell 10 was 20 cm ² . In addition, a pulse current was supplied at a cycle of 2 seconds, an ON time of 1.9 seconds, a duty ratio of 0.95, and an average current density of 1600 A / m ² . In addition, the initial electrolyte solution in the anode chamber 21 of Example 7 was prepared by dissolving nickel sulfate in water and adjusting the concentration with sulfuric acid and hydrochloric acid, so that the nickel ion concentration was 100 g / l, the free sulfuric acid concentration was 30 g / l, The substance ion concentration is 2 g / liter. The initial electrolyte in the cathode chamber 22 is sulfuric acid having a concentration of 200 g / liter. That is, no chloride ion exists in the cathode chamber 22. Table 3 shows the conditions before melting of the metal in Example 7.

  Table 4 shows the results of Example 7. The nickel ion concentration of the extracted metal-dissolved electrolyte was 103 g / liter, which was a nickel ion concentration sufficient for use in manufacturing a positive electrode of a battery. In addition, the current density was sufficiently high, and a sulfuric acid solution was efficiently obtained. In addition, the current efficiency was confirmed to be 95% with respect to the conduction of 24 Ah, indicating that the electrolysis was performed efficiently. Further, when the nickel ion concentration in the cathode chamber 22 was measured, it was 25 g / liter, and it was found that the movement of nickel ions to the cathode chamber 22 could be suppressed.

(Comparative Example 4)
The parameters are the same as those of the sixth embodiment except that a pulse current different from that of the sixth embodiment is supplied to the anode 13 and the cathode 14 provided in the electrolytic cell 10. In Comparative Example 4, the pulse current was supplied such that the period was 1 second, the ON time was 0.5 seconds, and the duty ratio was 0.5. Table 3 shows the conditions of Comparative Example 4 before melting the metal.

  Table 4 shows the results of Comparative Example 4. Some time after the energization, the voltage rapidly increased and oxygen was generated from the anode 13, so that the dissolution was stopped. That is, it was found that it was difficult to efficiently obtain a sulfuric acid solution.

DESCRIPTION OF SYMBOLS 10 Electrolyzer 12 Diaphragm 13 Anode 14 Cathode 17 DC power supply 21 Anode room 22 Cathode room

Claims (5)

An initial electrolytic solution supply step of supplying a chloride ion-containing sulfuric acid solution as an initial electrolytic solution to at least the anode chamber of the electrolytic tank in which the inside of the tank is divided into an anode chamber and a cathode chamber by a cation exchange membrane,
Supplying an electric current to the anode and the cathode provided in the electrolytic cell, and from the anode chamber, an electrolytic solution extracting step of extracting a metal-dissolved electrolytic solution in which the metal constituting the anode is dissolved;
Is configured to include
A method for producing a sulfuric acid solution, comprising: The metal constituting the anode contains at least either nickel or cobalt,
The method for producing a sulfuric acid solution according to claim 1, wherein: The chloride ion-containing sulfuric acid solution has a chloride ion concentration of 1 g / L or more and 20 g / L or less;
The method for producing a sulfuric acid solution according to claim 1 or 2, wherein: In the electrolyte removal step,
To the anode and the cathode, supply a pulse current that repeats a periodic power interruption,
The method for producing a sulfuric acid solution according to any one of claims 1 to 3, characterized in that: In the periodic power interruption,
A ratio of energization time in one cycle of the periodic power interruption is 0.8 or more and less than 1.0;
The method for producing a sulfuric acid solution according to claim 4, wherein:

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