JP3102907B2 - Salt bath treatment method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating a salt bath, and more particularly to a method for treating a salt bath in which a high concentration of a free alkali agent and a neutral salt coexist.

[0002]

2. Description of the Related Art For example, a steel film covered with a very strong oxide film, such as stainless steel, is ruptured and immersed in a high-temperature composite salt bath for the purpose of removing scale components. Has been proposed. As a method of treating the solution generated in this immersion treatment step, a nitrate group causing eutrophication and an oxidizing metal salt of toxic chromium are discharged at a high alkali concentration, and these metal salts are separated. After maintaining the system strongly acidic, a method of adding a chemical having a strong reducing power, making the system alkaline again, and separating a metal component is employed. However, expensive chemicals contained therein have not been recovered, and furthermore, the operation of removing metal components consumes a large amount of cost.

[0003] Among the salt roots contained in the wastewater, there is no problem if there is a method of reacting the salt with an externally added compound to change it into an insoluble form and separating it out of the system. It is very difficult to find a method. Therefore, if the salt root can be easily separated from the discharge system, or if the separation in the form of a solution is easy and the separation accuracy is good, there is a possibility that it is welcomed in a very wide field from the viewpoint of environmental problems. However, no practical technology has been found so far.

[0004] Conventionally, especially in a state where a considerable concentration of soluble metal salt coexists under a high concentration of free alkali, in order to insolubilize and separate the dissolved metal ion, a large amount of neutralizing an alkali component first. Add the acid
Further, after acidification, a strong reducing agent purchased from the outside is added to reduce the ionic valence, thereby performing a process of adjusting pH, which is a general method for insolubilizing metal salts.

[0005] Japanese Patent Application Laid-Open No. 2-145786 discloses that a free acid in a pickling bath is recovered using a diffusion dialysis membrane, while a divalent solution remaining in a metal salt component solution from which generated free components have been removed. It is described that the reducing power of an iron ion component is utilized.

However, there is no description in JP-A-2-145786 about an effective method for removing the soluble metal salt discharged from the salt treatment step and containing a large amount of nitrate.

[0007]

The high-temperature salt bath is one in which a solid material is brought into a dissolved state by increasing the temperature. The surface treatment is performed by immersing the steel material in this salt bath, and the treated product is attached to the steel material and taken out. This product is
By cleaning the steel surface with a large amount of water, it is dissolved and removed in the cleaning water.

The composition ratio of the salt bath is generally superior to the caustic soda side when the equivalent of caustic soda and the equivalent of nitrate are 6 to 7 to 4 to 3. Furthermore, the number of equivalents of caustic soda tends to be larger than the total amount of acid radicals used in the process, and the wastewater from the factory tends to be strongly alkaline. Therefore, it is a general tendency that an acid must be purchased from the outside for its neutralization.

In the overflow water after the washing treatment, not only expensive chemicals are dissolved and flown out, but also chromium and manganese metal ions of the constituent components constituting the treated steel material are oxidized to form a strong alkali. Although it is a region, it is dissolved at a high concentration. In order to remove this component together with the insoluble component, a large amount of coexisting alkali component is first neutralized with an acid purchased from outside, and then a strong reducing agent is further purchased and added from outside while maintaining the acidity. This brings the metal into a reducing atmosphere that reduces the ionic valence of the metal,
By moving the metal ions back to alkaline, the general metal ions are made insoluble and then must be separated from the solution, which requires a costly operation.

When this operation is analyzed well, A) there is a problem that expensive and large amounts of caustic soda are neutralized and converted into a salt having low value and low utility value. An effective collection method should be proposed. B) The nitrate which coexists at the same time, when mixed into the discharge system, is not only difficult to separate alone, but also contains a large amount of nitrogen root which causes eutrophication which is an environmental problem. For this reason, there are restrictions on emissions, not as poisonous substances, but in some areas.
However, even if a great deal of money is spent, an effective removal effect cannot be expected. However, nitrate is an expensive salt, and it is assumed that if the salt can be separated, it can be reused as nitric acid used in the process. If the ion electrolytic dissociation operation is adopted for this operation, it is assumed that the removal of the metal components accumulated in the acid bath and the sodium reacted with the nitrate group can be removed together. C) Furthermore, this solution contains a large amount of toxic chromium and manganese oxidizing salts, and its removal is subject to strict regulations in terms of pollution control values, and its complete removal is necessary. The most expensive operation for performing the insolubilization treatment after the reduction is the cost of an acid purchased from outside for the operation of neutralizing the coexisting alkali. If this cost is reduced, 1)
The removal of the free alkali component described in the section and the simultaneous cost reduction can be achieved.

The remaining problem is to simplify the operation of reducing metal ions that have been changed to maintain a dissolved state even in an alkaline atmosphere. In this reduction operation, when divalent iron coexists in an acidic atmosphere, when the iron ion is oxidized and changes to trivalent, an atmosphere that takes away electrons from the other side is searched for and injected under that state. To reduce the ionic valency of the soluble salt.

The atmosphere that satisfies these conditions is set by the conditions in a pickling bath installed next to the same steel processing and manufacturing line, which is equivalent to 0.7 to 1.0 N of free acid radicals, which is always strong. The acidity is maintained, the temperature of the solution is 40 to 60 ° C., which is the temperature required for the reaction, and a large amount of divalent iron ions required as a reducing agent is present. The preferred composition of the stainless pickling bath is
Appropriate ferrous and trivalent iron ions are effective to enhance the pickling effect of the treated steel, and if such an environment can be used successfully, purchase expensive reducing agents from the outside as before. And there is no need to increase sludge for the reduction treatment.

In addition, since the operation of reducing hexavalent chromium to trivalent chromium with divalent iron is performed in the same bath as that for removing the scale of the stainless steel material, the surface of the stainless steel material is removed. It was found that the chromium was reduced and adhered to the activated metal surface at the same time as the scale remaining on the activated metal was removed, thereby changing the scientific properties of the metal surface. As described above, the present invention is applied to, for example, the treatment of a liquid taken out of a metal rinsing bath, in which a steel material is immersed in a high-temperature alkaline bath to change the state of the steel material surface, and a chemical is recovered with high purity. In addition, by changing the composition ratio of coexisting salts, the characteristics of coexisting substances in other treatment tanks, which had not been able to be exhibited in the past, can be effectively used, and remarkable resource saving compared with the conventional method is possible In addition, it is an object of the present invention to propose a processing step to which a special processing effect is added in which the antiseptic property can be much improved in the surface treatment state of the treated steel material as compared with the conventional technology.

[0014]

The following points are required to enable the above-mentioned examination items to be solved. a) Find a method that can efficiently remove the amount of free caustic soda from the overflow liquid from the washing bath of the salt bath treated steel, and make sure that the neutralization of excess alkali components is not performed by supplying acid from outside. And find a way to reuse the separated caustic soda. b) It is possible to remove the sodium component, which is the cation component of nitrate, contained in the liquid after removing the caustic soda. c) Find an atmosphere that reduces the metal salts contained in the solution from which the free caustic soda has been removed, and remove the cation component, which is the metal ion component accumulated in the system.

Therefore, according to the present invention, the washing tank is divided into a plurality of tanks, and the liquid in each of the divided tanks is filtered by a filter using a filter medium resistant to high temperature and concentrated alkali. The suspended matter to be accumulated is removed, and the liquid after removing the suspended matter is jetted from the first nozzle for washing the steel material, and fresh washing water and pressurized air from outside the washing tank are removed. In the washing tank, the mixed fluid is ejected from the second nozzle toward the steel material, and the second nozzle is vibrated in the lateral direction, so that the steel material heated in the salt bath is brought into the washing tank from The overflow water that has been washed in the washing tank is allowed to flow out, and the fresh washing water is supplied from the carry-out side of the steel material to wash the steel material in a countercurrent multi-stage system, and the heat storage of the carried steel material. Depending on the volume, the cleaning solution sprayed on this steel material In order to make up for the concentrated and reduced liquid volume by the emission, the liquid obtained by removing the caustic soda attained when recovering the salt component contained in the overflow water discharged to the outside of the cleaning tank is again washed with the cleaning tank. And reused as washing water.

Further, the present invention forcibly dissociates ions of a dissolved salt, makes effective use of the charge characteristics of the dissociated ions, and selectively allows only cations to pass through iontophoresis under a DC electric field. By using an ion electrolysis separation tank that uses an ion exchange membrane as a membrane, it is possible to separate the anion component and the cation component, and the components that reversely charge and separate in the solutions in the separation chambers are removed from each other. And the removal of unnecessary components.

[0017] This process can be applied to continuous supply of a strip-shaped steel material, batch immersion of a rolled rod-shaped wire, or treatment of a small object to be treated in a basket. It can be adapted as well.

[0018]

Therefore, according to the present invention, it is possible to combine the operation method of the ion electrolytic separation tank according to the required operation and to exert the effect according to the purpose. That is, the present invention separates the free alkali agent remaining in the solution independently from the coexisting salt solution at a higher separation rate.
At the same time, the coexisting and remaining salts are again sub-decomposed into the free acid of the anion root and the alkali of the cation in a later step. It insolubilizes the metal salt.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS 1) In a salt bath 1 shown in FIG. 1, a steel material such as a stainless steel strip is continuously immersed. Next, the steel material is supplied to the salt cleaning tank 2, and the salt attached to the steel material is dissolved and removed by the cleaning liquid supplied from the outside by the multi-stage cleaning mechanism of the salt cleaning tank 2. Thereafter, the steel material is supplied to the pickling bath 3 to finish the processing operation.

2) The composition of the high-temperature salt bath is a mixture of solid caustic soda and solid nitrate in a weight ratio of 65:35, and heat is applied from the outside to maintain the temperature at 400-600 ° C. The inside of the tank is brought into a molten state and used for the intended treatment. With the elapse of the use time, the amount reduced by being attached to the steel material and taken out of the tank is replenished by the solid salt mixed in the above composition ratio.

3) FIG. 2 shows a multi-stage cleaning mechanism of the cleaning tank 2. As a steel material, for example, a strip steel having a width of 600 mm and a thickness of 1 mm is carried and immersed in each of the treatment tanks 1, 2, and 3 at a speed of 6 m / min.
Processing is performed. In the cleaning tank 2, as shown in FIG. 2, a multi-stage countercurrent cleaning operation is performed in which the entry side of the steel strip coincides with the discharge side of the rich overflow water that has been cleaned. Inside of cleaning tank 2 is 3
The tank is partitioned and fresh washing water is supplied to the discharge side of the steel strip. That is, a nozzle 4 having a diameter of 0.6 mm is provided at the outlet of the steel strip, and the nozzle 4 is provided with a pipeline of 3 kg / cm ² of water pumped from a pump and air compressed to 3 kg / cm ^2. The mixture is supplied by the mixer 5. By spraying the water and air in a mixed state at a ratio of 1: 0.2 to 0.4, it is possible to spray the steel surface with a high water pressure with a small amount of water, thereby improving the cleaning effect.

Six nozzles 4 are attached to the pipe in parallel at intervals of 10 cm in the horizontal direction, and the end of the pipe is reciprocated in the horizontal direction by an external drive eccentric cam. . By using the external vibration mechanism 9 having the eccentric cam to reciprocate the pipe in the horizontal direction at a stroke of 15 times or more at a cycle of 80 times / min or more, the water flow from the nozzle is sprayed on the steel material to thereby obtain the conventional fixed nozzle. In this case, the cleaning effect can be improved as compared with the case where the supply water amount is tripled. And when the nozzle is fixed,
After spraying on the cleaning surface, the cleaning may be uneven and the cleaning may be uneven. However, this point can be solved.

Such a moving nozzle group is arranged on the back side and the front side with respect to the steel strip. In addition to the nozzles on the back side and the front side, the nozzle can be further removed from the steel strip at a position closer to the carry-out port, and the cleaning effect can be further improved.

It is more effective to install these nozzle groups downward at a position where the steel strip moves upward.

4) Inside the high-temperature salt bath 1, the carbon component obtained by carbonizing the oil component adheres to the steel material. The carbon component and the salt in the salt bath 1 adhere to the steel material in the liquid stored in the intermediate tank of the separated cleaning tank 2 or the tank near the portion where the steel material is carried in. As they are brought in, they accumulate as buoyant solids.
For this reason, when the stored liquid in the tank is sucked by the pump 6 attached to each tank and sprayed through the washing nozzle 7 on the surface of the steel material to wash the attached salt, the washing nozzle 7 is clogged and the washing effect is obtained. May be reduced. Therefore, a filter 8 is provided downstream of the pump 6, and the liquid is supplied through the filter 8, whereby the washing nozzle 7 is provided.
Can be operated continuously without clogging.

The cleaning nozzle 7 in the latter stage has a diameter of 0.
It is effective to use one with a diameter of 8 mm or more. In the washing tank in the latter stage, when the salt attached to the surface of the steel material to be carried in is washed and removed, the washing water sprayed by the heat storage of the steel material is heated and evaporated, and the amount of water stored in the washing tank gradually increases. There is a tendency to decrease.

In response to such a decrease in the amount of washing water, the reduced salt solution generated by the operation of recovering the salt contained in the overflow water from the washing tank 2 is supplied again into the tank, thereby reducing the amount of the washed water. By compensating the amount, a stable amount of water can be secured, and the amount of liquid required for the washing operation can be maintained.

5) As described in 4), caustic soda and nitrate are dissolved in the overflow water in which the salt adhering to the steel material is concentrated in the same manner as the salt bath composition. Regarding its concentration,
In relation to the cleaning effect corresponding to the amount of salt remaining on the surface of the steel material, the more the final stage cleaning effect is improved, the higher the emission concentration can be.

6) In one actual measurement example of the concentration of the soluble salt contained in the overflow water discharged from the washing tank 2, caustic soda 1.2N (4
8N), Nitrate 0.3N (25.5gr / L), Cr ⁶⁺ 5500mg /
1, 1800 mg / l of Mn, 1 mg / l of Fe, and 4 mg / l of Ni. As shown in FIG. 3, this liquid is continuously injected into the circulation tank 13 of the anode electrode chamber 12 of the ion electrolytic separation tank 11. Then
Cathode electrode compartment 15 partitioned by cation exchange membrane 14 as diaphragm
The free caustic soda is electrophoretically separated in the cathode electrode compartment liquid, and this concentrates over time. The concentration of the concentrated solution is related to the state of maintaining the concentration of the anode compartment solution. If the concentration of the anode compartment is high and the concentration is stable, it is possible to maintain the concentration higher than the concentration of the cathode compartment solution.

7) The liquid supplied to the circulating tank 13 of the anode chamber liquid described in 6) is circulated to the ion electrolytic separation tank 11 so that Na ⁺ cations are electrophoretically separated in the cathode electrode chamber 15. This lowers its concentration. The processing solution having the reduced concentration returns to the final nozzle 7 of the cleaning tank 2 again, and is used again for cleaning the steel material. By combining the increase in concentration due to the removal of attached salt and the concentration by evaporation,
It is possible to return to the anode electrode chamber 12. In the actual measurement example, 4 hours after the start of circulation, the concentration described in 6) is
Caustic soda 1.2N (48gr / l), nitrate soda 1.5N (127.5gr / l)
, Cr ⁶⁺ 27500 mg / l and Mn 9000 mg / l, and maintaining this state was confirmed to be a stable operation in the ion electrolytic separation tank.

8) The pH of the circulating fluid of the anode compartment liquid described in 7)
Is always alkaline, but if the salt concentration decreases due to a trouble in the operation system or a trouble in the washing operation, the migration of the Na ⁺ cation to the cathode electrode chamber 15 proceeds too much, and the anode electrode chamber 12 It is sufficient to acidify. In such a state, the characteristics of the ion exchange membrane may be impaired due to a difference in the ion dissociation rate in the cation exchange membrane due to a trouble such as expansion of water in the ion exchange membrane. Therefore, it is necessary to install and monitor a pH meter, and maintaining the salt concentration of the anode compartment liquid as well as maintaining the salt concentration of the anode compartment liquid is an important matter from the viewpoint of the management of the ion exchange membrane 14. .

9) The anion component liquid removed from the caustic soda and accumulated in the anode electrode chamber 12 described in 7) is injected into the pickling tank 3 which is the next processing tank. . Then, Cr ⁶⁺ is reduced to Cr ³⁺ and Mn ⁵⁺ is reduced to Mn ²⁺ by the reducing power of the iron ions accumulated in the pickling tank 3, and the movement of cations in the acidic solution. To be changed. As a specific example, the composition of the bath in the acid bath is adjusted to a free nitric acid concentration of 0.
5N, free hydrofluoric acid 0.6N, divalent iron ion 0.6N, and trivalent iron ion 0.25N. The rate of increase in ferrous iron was set to 100 N / hr at a bath temperature of 50 to 55 ° C. and a bath volume of 10 m ³ .
Then, into this bath, the above-mentioned solution of 27.5 g / l (3.2 N) with Cr ⁶⁺ was injected at 10 l / hr, and the Cr in the acid bath after 5 hours was injected.
The concentration of ⁶⁺ was measured. As a result, Cr ⁶⁺ was not detected, and Cr ³⁺ was 2.81 g / l, confirming that the chromium ion was completely reduced by the ferrous ion in the acid bath. In addition, JIS standard 300 series stainless steel was immersed in the acid bath to remove scale components adhering to the steel, followed by pickling. Observation of the surface of the steel material after the pickling revealed that scale components remaining on the surface were removed and the steel was in an acceptable finished state. Thereafter, a comparison between the steel material subjected to this treatment and the steel material pickled with a calcium chloride solution revealed that the former was significantly improved in terms of antiseptic properties.

10) brought into the pickling bath described in 9),
The metal ions subjected to the reduction treatment must be removed together with other metal ions accumulated in the pickling tank 3. This processing method is, for example, as shown in FIG.
No. 234582, the cations accumulated in the acidic bath are electrophoresed into a cathode electrode chamber 17 maintained alkaline in an ion electrolytic separation tank 16 using a cation exchange membrane as a membrane, and this is converted into an insoluble metal salt. By changing it to a precipitate, it becomes possible to separate it from the system. In FIG. 4, reference numeral 17 denotes a cathode chamber liquid separation tank.

[0034]

As described above, according to the present invention,
When a steel material such as stainless steel is treated in a high-temperature salt bath containing an oxidizing salt, salt contained in a liquid discharged from a washing tank as a subsequent treatment device can be recovered again as a single free salt. In addition, the metal salts contained in this solution, which are highly toxic and cannot be separated by sedimentation without undergoing reduction treatment, utilize the iron salts accumulated in the pickling bath in the same line to perform reduction treatment. And by using an ionic electrolytic tank installed to remove the metal salts accumulated in the pickling bath, the consumption of chemicals can be significantly reduced compared to conventional methods. In addition, since the emission of nitrate which cannot be insolubilized to the outside can be suppressed, the effect is great.

[Brief description of the drawings]

FIG. 1 is a view showing an arrangement state of processing tanks in one embodiment of the present invention.

FIG. 2 is a detailed view of a cleaning mechanism in the salt cleaning tank of FIG.

FIG. 3 is a diagram for explaining an operation of recovering dissolved free alkali components from overflow water discharged from the salt washing tank of FIG. 2;

FIG. 4 is a view for explaining an ion electrolytic separation operation of a metal salt accumulated in the acid bath of FIG. 1;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Salt bath 2 Salt washing tank 3 Pickling bath 8 Filtration device 9 External vibration mechanism 11 Ion electrolytic separation tank 16 Ion electrolytic separation tank

────────────────────────────────────────────────── (5) References JP-A-2-245213 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C23G 1 / 08,1 / 32 C23G 1 / 36,3 / 02

Claims (4)

(57) [Claims] 1. A salt bath having a composition containing caustic soda maintained at a high temperature and also containing an oxidizing salt represented by nitrate, and immersing steel in the salt bath to oxidize the surface thereof. Then, a metal oxidizing salt which is alkaline but water-soluble is generated, and the high-temperature steel material taken out from the salt bath is washed with a salt attached to the steel material in a washing tank prepared next to the salt bath. A method for removing a composition and a metal oxide salt changed on a steel material surface and recovering a soluble bath composition from overflow water from a washing tank in which the salt composition and the metal oxide salt are dissolved. Then, the washing tank is divided into a plurality of tanks, and the liquid in each of the divided tanks is filtered by a filter using a filter medium that can withstand high temperature and concentrated alkali, and is floated to be accumulated in the washing tank. The liquid after removing the suspended matter is In order to wash the steel, the first nozzle is jetted from the first nozzle, and a mixed fluid of fresh washing water and pressurized air from the outside of the washing tank is jetted from the second nozzle toward the steel in the washing tank. The second nozzle is vibrated in the lateral direction, and the overflowed water that has been washed in the washing tank is caused to flow out from the side where the steel material heated in the salt bath is carried into the washing tank. The steel material is supplied from the unloading side and is washed in a countercurrent multi-stage system.The amount of heat stored in the steel material brought in is concentrated and reduced by the evaporation of the cleaning liquid sprayed on the steel material. In order to make up for this, the liquid obtained by removing the caustic soda that is generated when recovering the salt component contained in the overflow water discharged to the outside of the washing tank is returned to the washing tank and reused as washing water. Salt bath treatment method characterized by the following: 2. When performing an operation of separating and recovering a free alkali component of a salt contained in overflow water discharged from a washing tank, an insoluble dispersion contained in the overflow water is removed, and the dispersion is removed. The overflow water from which the water has been removed is treated with a cationic exchange resin membrane that has chemical oxidation resistance and high temperature resistance and exhibits cation separation and selection characteristics. The solution is supplied to the anode electrode chamber of the ion electrolytic separation tank divided into two chambers.In the cathode electrode chamber of the ion electrolytic separation tank, the amount of free caustic soda that has been selectively electrophoresed from the anode electrode chamber is separated and concentrated. By discharging the outlet liquid from which the free caustic soda that migrated to the cathode electrode chamber from the composition component decreased and the electrical resistance tended to increase from the outlet side of the anode chamber, and returning this outlet liquid to the washing tank again, Concentration by evaporation and adhesion to steel 2. The method according to claim 1, wherein the concentration of the overflow water changed by the increase in salt content is adjusted.
The method for treating a salt bath described in the above. 3. A forced circulation system installed outside the anode electrode chamber and a pH value and a neutral salt concentration of the circulating liquid are provided in an anode electrode chamber constituting an ion electrolytic separation tank for separating free caustic soda. With the equipment to monitor, monitor that the circulating fluid always maintains the alkalinity by the information of the pH value, monitor the state of the maintenance of the electrophoretic efficiency characteristics of the ion exchange membrane and the presence or absence of breakage, In case of emergency, by supplying and controlling concentrated caustic soda, the current efficiency of separation and electrophoresis operation is maintained in a stable and high state, and when the neutral salt component gradually accumulating in the circulating fluid exceeds a certain concentration, Out of the system,
Decomposition and recovery of the remaining neutral salt, control of the amount of the oxidizable metal salt to be reduced and insolubilized, and maintenance of the salt concentration of the anode compartment liquid within a predetermined range, and By maintaining the moisture content that can be maintained at a high level, the electrolytic operation is performed under stable conditions while maintaining the high concentration of caustic soda in the cathode chamber, and the leakage of the anode chamber liquid to the cathode chamber due to breakage of the separation membrane is avoided. The cathode electrode chamber is additionally provided with a forced circulation device and an alkali concentration monitoring device installed outside the cathode electrode chamber, and the alkali concentration monitoring device allows the circulating liquid to pass through the separation membrane. Monitors the accumulated concentration of diffused free alkali, indirectly controls the alkali concentration to maintain the salt osmotic pressure balanced with the osmotic pressure of the anode compartment liquid, and controls the salt concentration of the anode compartment liquid whose operation is controlled Find more Claim 2, characterized in that the balance control of the osmotic pressure indicated by the salt concentration of the osmotic pressure and the cathode chamber side
The method for treating a salt bath described in the above. 4. A solution circulating between the washing tank and the ion electrolytic separation tank and supplying a solution containing a soluble metal oxide salt to the ion electrolytic separation tank and remaining in the anode chamber liquid of the separation tank. The free caustic soda is diffused and electrophoresed into the cathode chamber, thereby reducing the concentration of the processing solution so that the amount of acid required to change the solution to an acidic atmosphere is reduced. The soluble metal salt that is injected into the bath of the acid bath with a controlled free acid concentration in the processing equipment line and the soluble metal salt remaining in the input liquid is dissolved in the acid bath bath is converted into trivalent iron ions. The reducing power that is exhibited when oxidized to a value,
The cation dissociated metal salt, which is converted into a reduced metal salt having a lower ionic value and accumulates in the acid bath, is migrated to the cathode chamber of the ion electrolytic separation tank, and this is insoluble. 3. The salt according to claim 2, wherein the metal hydroxide is converted into a metal hydroxide and discharged out of the system, and at the same time, the anion of the nitrate and the sodium cation reacted with the nitrate are recovered as their free salts. Bath liquid treatment method.