JPH0124227B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for reducing iron salts, particularly a method for electrolytically reducing trivalent iron salts.

For example, when plating a steel plate with an alloy of zinc and iron, divalent iron exhibits good adhesion to the steel plate, but trivalent iron exhibits good adhesion to the steel plate along with zinc. This decreases significantly, making plating industrially virtually impossible. In general, iron is more stable at higher charges than at lower charges, so there is a strong tendency for iron to dislocate there. Moreover, it is not limited to the above-mentioned plating, and has various uses as a divalent iron salt. Of course, there is a way to prevent the formation of trivalent iron salts by adding antioxidants to such iron salts, but such additives may have an adverse effect on the material to be treated or the reaction system. There are many cases in which it is harmful.

In order to cope with such a case, the present invention was developed as a result of various studies and examinations aimed at easily reducing trivalent iron salts and rearranging lower iron salts without using any additives. It has been found that the above object can be easily achieved by electrolytic reduction using an ion exchange membrane.

Thus, the present invention uses an electrolytic cell having an anode chamber and a cathode chamber separated by an ion exchange membrane,
An object of the present invention is to provide a method for reducing an iron salt, which comprises introducing a mineral acid into the anode chamber and a trivalent iron salt into the cathode chamber, and causing electrolysis.

The mineral acids used in the present invention include hydrochloric acid, sulfuric acid, and phosphoric acid, and these can be used alone or in combination. The concentration of the mineral acid used is generally about 1 to 30%. If the concentration is less than the above range, it will be difficult to flow a current with an industrially appropriate current density, and if it exceeds the above range, water in the cathode chamber may permeate into the anode chamber, or Both are unfavorable because the mineral acid may diffuse into the cathode chamber.

In addition, the trivalent iron salt introduced into the cathode chamber is
Ferric chloride and ferric sulfate are two common, and these may be used alone or in combination.

The concentration of these trivalent iron salts used is generally about 1 to 200 g/appropriate.
If the concentration is less than the above range, the current efficiency will be extremely reduced, and if it exceeds the above range, a large amount of iron will be deposited on the cathode, which is not preferable.

Next, the material and shape of the anode used in the present invention are not particularly limited, and the material may be a base material plated or coated with a noble metal such as platinum or a noble metal oxide, and the shape may be, for example, a flat plate. Appropriate shapes such as a shape, a net shape, an expanded metal shape, etc. can be adopted.

The material of the cathode may be lead, iron, platinum, carbon, titanium, etc., and the shape may be similar to that of the anode.
Further, as for the material, it is particularly preferable to use lead or platinum among the materials mentioned above, since this prevents the electrodeposition of iron.

Next, the ion exchange membrane used in the present invention may be either a cation exchange membrane or an anion exchange membrane.

The cation exchange membrane is made of a polymer containing a mixture of sulfonic acid groups, sulfonic acid groups and cation exchange groups such as carboxyl groups, phosphoric acid groups, and phenolic hydroxyl groups. A copolymer of a vinyl monomer such as fluoroethylene or chlorotrifluoroethylene and a perfluorinated vinyl monomer having an ion exchange group such as a sulfonic acid, carboxylic acid, or phosphoric acid group, or a reactive group that can be converted into an ion exchange group. is preferred.

Further, a film-like polymer of trifluoroethylene into which an ion exchange group such as a sulfonic acid group has been introduced, or a polymer into which a sulfonic acid group has been introduced into styrene divinylbenzene may also be used.

In addition, when using a hydrocarbon-based cation exchange membrane, the ion exchange membrane is composited with a porous membrane of a fluorine-containing resin such as polytetrafluoroethylene or tetrafluoroethylene-hexafluoropropylene copolymer. By using such a fluororesin porous membrane facing the anode surface, the cation exchange membrane can be exposed to high temperatures,
Can be protected from strongly oxidizing and strongly acidic atmospheres. This also applies to hydrocarbon-based anion exchange membranes.

Further, the above-mentioned fluorine-containing resin cation exchange membrane having a sulfonic acid group is particularly preferred since it has high heat resistance and acid resistance and can be used as is in the present invention.

In addition, examples of anion exchange membranes include quaternary ammonium bases, primary, secondary, and tertiary amino groups,
Examples include mixtures of quaternary ammonium bases and primary, secondary, and tertiary amino groups.

When a cation exchange membrane is used as the ion exchange membrane, hydrogen moves from the anode chamber through the membrane to the cathode chamber due to electrolysis, which literally has a reducing effect.Also, when electrolysis is performed using an anion exchange membrane, A part of the anions constituting the iron salt in the cathode chamber moves to the anode chamber, resulting in a state apparently similar to that in which reduction occurs in the cathode chamber, and such a state is defined as reduction in the present invention. It also includes.

Furthermore, in the present invention, a liquid and gas permeable anode is directly attached to these ion exchange membranes, or a porous thin layer of liquid and gas permeable material, such as a metal oxide, which has no electrode function is applied. By using the anode and the cation exchange membrane in close contact with each other, the electrolysis voltage can be reduced and the purpose of energy saving may be achieved.

Thus, when carrying out the method of the present invention, the liquid temperature is
It is appropriate to adopt a temperature of about 10 to 70°C. If the liquid temperature is lower than the above range, the voltage will become high, making economical operation difficult; if it is higher, on the other hand, the amount of gas generated will increase and the operation will become unstable, both of which are unfavorable. Also, the current density is 0.1~30A/
It is appropriate to adopt ^dm2 .

When the current density is less than the above range, the required membrane area becomes large and is not economical when considering industrial equipment. On the other hand, if it exceeds the above range, the efficiency decreases and iron precipitation tends to occur, which is not preferable. Further, it is appropriate to adopt an electrolytic voltage of 2 to 6V. If the electrolytic voltage is less than the above range, the reduction rate will be extremely reduced, while if it exceeds the above range, the temperature will increase and iron precipitation will occur more easily, which are both unfavorable.

Next, the present invention will be explained by examples.

Example 1 Between a platinum anode with an effective electrode area of 6 dm ² and a lead cathode with the same area, an average pore diameter of 0.1 μ and a porosity of 10 to 40
%, a 100μ thick polytetrafluoroethylene membrane is composited with a cation exchange membrane (Celemion CMV manufactured by Asahi Glass Co., Ltd.) in which sulfonic acid groups are introduced into styrene divinylbenzene, and the polytetrafluoroethylene membrane is placed opposite to the anode. A battery case was constructed by arranging the membranes with a negative and anode spacing of 35 mm. Hydrochloric acid with a concentration of 15% is introduced at a rate of 0.66/hour into the anode chamber of such a container, while 20 g/hour of ferric chloride is introduced into the cathode chamber.
A hydrochloric acid solution with a pH of ^1.2 containing It was. Analysis of the product revealed that it contained 19.63 g/ferrous chloride, and the conversion rate was 45%.

Example 2 An electrolytic cell was assembled using the same anode and cathode as in Example 1, with a gap of 35 mm between the anode and cathode, and a fluorine-containing resin membrane containing a sulfonic acid group as a cation exchange group. Sulfuric acid with a concentration of 10% was introduced into the cathode chamber at a rate of 0.66/hr, and a PH1.2 sulfuric acid solution containing 10 g/hr of ferrous sulfate was introduced into the cathode chamber at a rate of 110/hr, and the current density was 20 A/dm ^{2 .} When electrolysis was carried out at a cell voltage of 6 V, the product was taken out from the cathode chamber at a rate of 110/hour. Analysis of this product revealed that it contained 9.32 g of ironous sulfate, with a conversion rate of 30%.
It was hot.

Claims (1)

[Claims] 1. An electrolytic cell having an anode chamber and a cathode chamber separated by an ion exchange membrane is used, and a mineral acid is introduced into the anode chamber, and a trivalent iron salt aqueous solution is introduced into the cathode chamber. , a method for reducing iron salts characterized by electrolysis. 2. The method according to claim 1, wherein the ion exchange membrane is a cation exchange membrane or an anion exchange membrane. 3. The method according to claim 2, wherein the cation exchange membrane is a hydrocarbon-based cation exchange membrane, a composite membrane of a hydrocarbon-based cation exchange membrane and a fluorine-containing porous membrane, or a fluorine-containing cation exchange membrane. 4. The method according to claim 2, wherein the anion exchange membrane is a hydrocarbon anion exchange membrane or a composite membrane of a hydrocarbon anion exchange membrane and a fluorine-containing porous membrane. 5. The method according to claim 1, wherein the mineral acid is hydrochloric acid, sulfuric acid, or phosphoric acid. 6. Claim 1, wherein the concentration of mineral acid is 1 to 30%.
the method of. 7. The method according to claim 1, wherein the trivalent iron salt aqueous solution is ferric chloride or ferric sulfate. 8 The concentration of the trivalent iron salt aqueous solution is 1 to 200 g/
The method according to claim 1 or 7.