JPS60115174A - Method of preparing solution for redox-flow battery - Google Patents

Abstract

PURPOSE:To enable an active material solution which can be favorably used for a redox-flow battery to be easily prepared by dissolving a raw material containing chromium and iron, such as a chromium ore or chromite, in hydrochloric acid before removing mainly heavy metals contained in the solution by depositing them on the electrode of a cathodic chamber through electrodeposition or adsorption. CONSTITUTION:After a raw material containing chromium and iron is crushed and dissolved into hydrochloric acid, the residue is filtered off from the solution. When a chromium ore or a similar material which does not easily dissolve in hydrochloric acid is used as the raw material, it is preferable that nitric acid be added as necessary in addition to performing heating during the dissolution. The thus prepared hydrochloric acid solution of chromium and iron is then introduced into the cathodic chamber of an electrolyzer so as to remove mainly heavy metals contained in the solution by depositing them on the electrode of the cathodic chamber through electrodeposition or adsorption. Through performing this process, heavy metals and nitrate ions contained in the solution are removed, thereby enabling current efficiency to be greatly increased.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for preparing a solution for a redox flow battery, and more particularly to a method for preparing a solution containing iron and chromium halides as battery active materials.

As a typical example of a storage battery, in a flow type battery, for example, divalent chromium ions (Cr) are present in the charged state, as shown in Figure 1. aqueous solution of and 3
Water 7'8 liquid containing valent iron ions (Fe3'''') is stored in each tank 1 and 4, and this is transferred to a flow-through electrolytic cell l.
When flowing into O, Fe31 receives one electron at the positive electrode 3 and becomes bivalent Fe'+, and at the negative electrode 2, Cr'+ loses one electron and becomes trivalent cr3+. Electrons exchanged between the negative electrode 2 and the positive electrode 3 pass through an external circuit, perform work, and emit power.

The charging and discharging reactions occurring at the negative and positive electrodes in a redox flow battery are expressed by the following equation.

Negative electrode Positive electrode charging reaction Cr (III) → Cr (II) Fe
(Ilow・I”f! (III) Discharge reaction Cr (old-C
r (Ill) Fe (Ill)-・Fc ('II
) What should I prepare when operating this battery? 8 liquid is C
r (II) and Fe(I [
, (II) is difficult to prepare, Cr(II
A liquid in a discharge state containing Fe (II) and Fe (II) has been produced.

The solution for this battery is preferably an aqueous chloride solution with hydrochloric acid, considering factors such as the solubility of iron and chromium, the price of acid, and the characteristics of charge/discharge reactions. There is a demand for preparation from such sources.

Conventionally, the method of obtaining a chromium (III) solution from chromium ore, etc. is to oxidize and dissolve the raw material in an alkaline environment to obtain a chromic acid solution, and then reduce it to chromium (III).
ll)? However, this method has the disadvantage that it is necessary to add a chemical to make it alkaline, and the oxidation and reduction operations are complicated. A method of dissolving chromium ore in hydrochloric acid was also attempted, but this method was difficult because the solubility of chromium ore in hydrochloric acid was low.
Disadvantages include low concentration and impurities in the chromium ore that reduce current efficiency.

Light 1! An object of the present invention is to provide the ability to easily prepare an active material solution suitably used in a redox flow battery from a raw material of iron ore containing chromium ore.

Hassara Natsuyooka The present invention is directed to adhesives such as chromite and chromite.

and raw materials containing iron are dissolved in acid containing hydrogen chloride, the dissolved solution is introduced into the cathode chamber of the electrolytic cell, and mainly heavy metals in the /8/& are removed by electrodeposition on the electrodes of the cathode chamber. It is characterized by

Raw materials containing chromium and iron used in the present invention include chromium ore, chromite, chromium monoxide, iron oxide, iron chloride,
Mention may be made of ferrochrome, metallic iron, metallic chromium, and the like.

To prepare 1k of this battery from these raw materials, first crush the raw materials, dissolve them in hydrochloric acid, and filter the residue. However, when using chromium ore as raw materials, dissolve them in hydrochloric acid. Since it does not dissolve easily, it is advisable to heat it during dissolution and to add nitric acid if necessary. In this way, the total concentration of iron and chromium is δtl~2 mol/7! The above solution can be easily obtained.

In the above-mentioned dissolution step, it is preferable that the raw material is washed with a dilute acid to dissolve it. By washing with this dilute acid, impurities that are more soluble than iron and chromium can be eluted and removed, and in the case of chromium ore, magnesium ore is removed by cage operation. The concentration of the above-mentioned dilute acid is preferably 2N or less in order to suppress the elution of chromium and iron. After washing with this dilute acid and washing with water, impurities other than iron and chromium are removed in advance by melting with the aforementioned acid containing hydrogen chloride, thereby removing iron and chromium from the solution. Solubility can be increased.

In the dissolving process of the present invention, when nitric acid is added to the hydrogen chloride-containing aqueous solution, extremely high solubility can be exhibited for chromite, ferrochrome, etc., and as a result, even higher concentrations of iron and chromium can be dissolved. A hydrochloric acid solution can also be obtained.

It is preferable to contain nitric acid in an amount of 0.05N or more.

In the present invention, chromium obtained as described above,
A hydrochloric acid solution of iron is further introduced into the cathode chamber of the electrolytic cell, and mainly heavy metals in the solution are removed by electrodeposition on the electrodes of the cathode chamber. By performing this step, heavy metals and nitrate ions in the solution can be removed and current efficiency can be significantly increased. However, is it common for redox flow batteries to melt? (The presence of these impurities in l' will appear as a decrease in current efficiency in battery performance. For example, if heavy metals are present in the solution, these will adhere to the battery electrodes during charging and discharging of the battery.) However, the hydrogen overpressure at the negative electrode decreases, and a side reaction called hydrogen gas generation occurs, reducing the cooling efficiency during battery charging and discharging.In addition, nitrate ions react with Cr(II). and convert this into Cr(m
), this also reduces the charge/discharge coulombic efficiency of the battery.

In order to solve these problems, in the present invention, after filtering an electrolyte solution in which a raw material containing iron is dissolved, the solution is introduced into the cathode chamber of an electrolytic cell. By this operation, heavy metals are deposited on the cathode or as insoluble matter, and nitrate ions are electrolyzed and removed using chromium as a catalyst. moreover,
Fe(III) in solution by these electrolytic processes
A solution in the above-mentioned discharge state can be prepared by reducing the ions to Fe (II) ions and making the solution composition an ion aqueous solution of Cr (Ill) and Fe (■).

The self-effective cathode potential in the above electrolytic reduction process is saturated U
Based on the water electrode standard, it is more base than +0, 3V, preferably more base than +0, IV. If nitric acid is added during melting, the voltage will be less than 10.4 V, preferably -0.55 V.
It's more base.

The solution preparation method according to the present invention has the following advantages compared to the conventional method, which involves crushing Zunawara chromium ore, oxidizing and dissolving it to produce chromic acid, and reducing this to chromium oxide. Since inexpensive raw materials such as ore and chromite are used, the solution preparation cost is 1! (2) By using an electrolytic process that removes impurities, the coulombic efficiency of charging and discharging batteries can be improved. (3) Impurities that increase the internal resistance of batteries are removed. (4) The production process becomes easier and the quality control of the solution becomes easier.

Hereinafter, the present invention will be specifically explained with reference to Examples.

Example 1 Chromium ore was dissolved in 12N hydrochloric acid while heating, and the residue was filtered. When the iron concentration of this filtrate was measured by polarographic method, it was 0.5-1 mol/p, and the chromium concentration was 0.87 mol/I! Met. After adding a calculated amount of water so that the concentration of hydrochloric acid in the solution was 4N, this solution was passed through the cathode chamber of an electrolytic cell with a carbon felt cathode, and the current density was 40N.
Electrolytic reduction was performed at mA/cJ. The electrode potential of the cathode at this time was +0.05 V based on the saturated Amagi electrode. The solution after electrolysis was used as a solution for a small liquid flow type car battery with an electrode area of IQcnl. The structure of the electrolytic cell section of this battery consists of a carbon plate bonded with phenol resin as a current collector plate, and l
Carbon cloth was used as the night fIc pass-through electrode, a cation exchange membrane was used as the diaphragm, and the positive and negative electrodes had the same structure.

As a result of a charge/discharge experiment at a temperature of 40°C and a current density of 40 mA/cl, the charge/discharge coulomb efficiency (hereinafter referred to as ηC) was 97% and the charge/discharge voltage efficiency (hereinafter referred to as ηV).
was 82%.

Comparative Example 1 To the solution melted, filtered, and diluted in Example 1, ζascorhinic acid was added as a reducing agent in an amount equivalent to iron (Ill). It has been confirmed that ascorbic acid quickly reduces iron (l[I) to iron (n), and that excess ascorbic acid and its decomposition products do not affect the charging and discharging reactions of the battery. When this liquid was used in the battery system of Example (2) and a charge/discharge experiment was conducted under the same conditions as in Example 1, ηC was 83% and ηV was 79%.

Example 2 In place of the chromium ore in Example 1, 1 chromium was used, and 1 chromium was used to produce 1 chromium in 1 column and 1 strip.

The iron concentration in the solution after dissolution and filtration was 0.98 mol/l,
The chromium concentration was 0.89 mol/l. Hydrochloric acid concentration is 4
When a charging/discharging experiment was conducted using the electrolytically reduced solution in which a calculated amount of water was added to the battery system according to Example 1, ηC was 97% and ηV was 83%.

Example 3 After pulverizing chromium ore, it was dissolved in normal sulfuric acid (151;

The iron concentration in this liquid was 0.67 mol/l, and the iron concentration was 1.05 mol/l. After dilution and electrolysis according to the method of Example 1, a charge/discharge experiment was conducted using the same battery system, and ηC was 96% and ηV was 86%.

Example 4 Pulverized chromium ore was washed with 1N sulfuric acid and water in the same manner as in Example 3, and then heated and dissolved in an acid having a volume ratio of concentrated hydrochloric acid to concentrated nitric acid of 20:1. The iron concentration in the solution after separation of the residue 9F was 1.11 mol/β, and the 1:1 molar ratio was 1.52 mol/e. After diluting this solution to 4LJJ constant hydrochloric acid concentration,
Electrolytic reduction was carried out under the same conditions as in Example 1, except that the cathode potential was less saturated than -0°6 at a permanent electrode base of 1 1, and then a charging/discharging t/h test was conducted using the same battery system.
ηC was 98% and ηV was 90%.

[Brief explanation of the drawing]

FIG. 1 is a conceptual diagram showing the configuration of a Redo Nox flow type battery system used in the present invention. 1.4...Tank, 2...Negative electrode, 3...Positive electrode, 5
．． 6... Pump, 10... Flow type defrosting tank. Agent: Takenaga Kawakita Diagram 1 Procedural Amendments March 31, 1980 Commissioner of the Patent Office Kazuo Wakasugi 1, Description of the case 1981 Patent Application No. 221738 2, Name of the invention: Redox. Flow battery solution preparation method 3, person making the amendment 4, agent 103 Address 11-8-6, Kayaba-cho, Nihonbashi, Chuo-ku, Tokyo
, 1ili Positive Object Claims section of the specification and Detailed Description of the Invention section of the specification. (1) The scope of claims in the specification shall be amended as shown in the attached sheet. (2) “Battery storage” on page 2, line 4 of the specification is changed to “power storage 1.” (3) “Flow type battery” on page 2, line 5 of the specification is changed to “flow type secondary battery.” (4) "Flow type battery" on page 2, line 4 of the specification is changed to "r flow type secondary battery." (5) "Solubility of chromium" on page 3, line 7 of the specification has been changed to "solubility of chromium in acid." (6) From page 3, line 18 to page 4, line 2 of the specification, ``There are drawbacks such as dissolving chromium ore in hydrochloric acid'' has been amended as follows. ``Although it is preferable to directly dissolve chromium ore in hydrochloric acid and filter out the residue, there are two problems with this method.Firstly, chromium ore does not dissolve easily in hydrochloric acid, and some auxiliary measures must be taken. The second problem is that impurities eluted from chromium ore reduce current efficiency. Changed to "Next battery". (9) "Removal of electrodeposition" on page 4, line 12 of the specification has been changed to "removal by electrodeposition or adsorption." (lO) Specification page 6, line 1, 1. Even higher concentration of iron.”
Sharpen. (11) "Obtain an acid solution" on page 6, line 2 of the specification is changed to "Obtain an acid solution relatively quickly." (12) "Heavy metals" on page 6, line 6 of the specification will be changed to "heavy metals." (13) On page 6, line 7 of the specification, ``electrodeposit'' should be changed to ``electrodeposit or adsorption''. (14) "Heavy metals" on page 6, line 8 of the specification has been changed to "1 heavy metals." (15) "Flow type battery" on page 6, line 10 of the specification is replaced with "
Changed to flow type secondary battery J. (16) "Electrode" on page 6, line 14 of the specification has been changed to "battery." (17) On page 7, line 3 of the specification, 1. “Heavy metals” will be changed to “heavy metals, etc.” (18) "Electrodeposition" on page 7, line 3 of the specification is changed to "electrodeposition, adsorption J." (19) "Ion wo" on page 7, line 6 of the specification is changed to "ion wa." Claims (1) Raw materials containing chromium and iron such as chromite and chromite are dissolved in an acid containing hydrogen chloride, and the dissolved solution is introduced into the cathode chamber of an electrolytic cell, 1. A method for preparing a solution for a redox flow battery, which method comprises removing heavy metals by removing electrodeposition from the electrodes of the cathode chamber. (2. A method for preparing a solution for a redox flow battery according to claim 1, characterized in that the dissolution is carried out under heating and addition of JJ nitric acid.

Claims (1)

[Claims] (1) Raw materials containing chromium and iron such as chromite and chromite are dissolved in an acid containing hydrogen chloride, and the dissolved solution is introduced into the cathode chamber of an electrolytic cell to remove mainly heavy metals from the solution. A redox method characterized by removing electrodeposition from the electrodes in the cathode chamber.
Solution preparation method for flow type batteries. (2. A method for preparing a solution for a redox flow battery, characterized in that the melting of the acid is performed by heating and adding nitric acid according to claim 1).