JP3696712B2 - Regeneration method to ferric sulfate solution and regeneration apparatus used therefor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for regenerating a non-polluting ferric sulfate solution capable of efficiently regenerating a ferric sulfate solution used for pickling and removing oxide scale formed on the surface of a metal material such as stainless steel. And a reproducing apparatus used therefor.
[0002]
[Prior art]
For example, a stainless steel wire is usually finished into a rod having a diameter of, for example, 6 mm by hot rolling of a billet. In particular, in the case of Cr stainless steel, a relatively thick oxide is formed on the surface because it is heat-treated in the atmosphere. Scale, that is, an oxide film is generated.
[0003]
Conventionally, such an oxide film has been removed by a two-step process including a primary descaling process immersed in an alkali molten salt and a subsequent pickling process using nitric hydrofluoric acid.
[0004]
However, in this method, since nitric acid is used for the treatment solution, it is a cause of environmental destruction such as enrichment due to NOx gas generated and nitrogen contained in the treated wastewater. It has been determined that use is substantially limited, and alternative methods are desired.
[0005]
By the way, Japanese Patent Publication No. 57-1590 proposes treatment with a solution containing 0.5 wt% or more of ferric sulfate for removing smut of Cr-based stainless steel.
[0006]
In this method, it is shown that ferric sulfate is reduced and ferrous sulfate, chromium sulfate, nickel sulfate and the like are accumulated during the reaction between ferric sulfate and iron.
[0007]
On the other hand, in Japanese Examined Patent Publication No. 56-8109, hydrogen peroxide and sulfuric acid are added to ferrous sulfate accumulated internally as an aging product of such a ferric sulfate solution. It is proposed that the ferric sulfate solution is repeatedly used by regenerating and activating it by maintaining the oxidation-reduction potential within a predetermined range.
[0008]
[Problems to be solved by the invention]
However, the former invention uses a ferric sulfate solution for removing smut, and its content is as low as 0.5 wt%, and there is no indication of actively regenerating this solution. .
[0009]
In the latter invention, it is disclosed that hydrogen peroxide and sulfuric acid are added and managed for regeneration. However, mixing hydrogen peroxide and sulfuric acid directly can reduce the labor of equipment, maintenance and management. Nonetheless, the amount of remaining ferrous sulfate varies with temperature, and therefore the amount of ferric sulfate regenerated varies, making it difficult to control the components of the mixed solution and stabilizing the pickling quality. May be lacking.
[0010]
Furthermore, if ferrous sulfate remains excessively, it is uneconomical to increase the total amount of hydrogen peroxide, sulfuric acid, and other additives for regeneration, and to the extent necessary for ferric sulfate. When iron is not regenerated, the concentration of ferric sulfate is low, making descaling difficult.
[0011]
In addition, when ferrous sulfate is removed excessively and residual ferrous sulfate is insufficient, ferric sulfate after regeneration is also reduced, and conversely, excessive residual ferrous sulfate and excessive addition of additives. In the case of a mixed solution having a concentration, it becomes a peracid wash and roughens the product surface.
[0012]
The present invention pays attention to the physical properties of ferrous sulfate, and by cooling it within a predetermined temperature range while taking out the mixed solution, both the removal amount and remaining amount of ferrous sulfate can be controlled. It aims at providing the reproduction | regeneration method to the ferric sulfate solution which can improve reproduction | regeneration and precision, and can improve pickling efficiency and quality, and the reproduction | regeneration apparatus using the same. Further, when the closed system is adopted, a pollution-free reproduction method and apparatus are obtained.
[0013]
[Means for Solving the Problems]
According to the first aspect of the present invention, as a stock solution, an excess of the ferrous sulfate is previously removed from a mixed solution of ferric sulfate containing ferrous sulfate, and the ferrous sulfate in the mixed solution is converted into sulfuric acid. A regenerating method for ferric sulfate solution regenerated to ferric iron, a cooling unit for cooling to a predetermined temperature below the temperature at which ferrous sulfate in the stock solution taken out from the pickling tank is crystallized. A crystal nucleation step of crystallizing the ferrous sulfate to form a crystal nucleus mixed solution having the crystal nuclei by cooling by the cooling unit, and the crystal nucleus mixed solution is added to the liquid surface of the crystallization tank. The excess ferrous sulfate is separated by allowing the crystal nuclei of the ferrous sulfate to grow while the crystal nucleus mixed solution rises to the liquid level from the inlet provided below. And a separation process for producing a non-surplus mixed solution, and a non-surplus mixing solution flowing out of the crystallization tank. And characterized in that the ferrous sulfate in the mixed solution by adding hydrogen peroxide and sulfuric acid from a continuously circulating supply regeneration step in regeneration solution Toshikatsu pickling bath reproduced ferric sulfate solution To do.
[0014]
A mixed solution of ferric sulfate for pickling, that is, a ferric sulfate solution, excessively contains ferrous sulfate produced as a secondary product during pickling. That is, the surplus mixed solution contains surplus ferrous sulfate exceeding the amount necessary for regeneration to ferric sulfate. Therefore, a crystal nucleus generating step of generating crystal nuclei by cooling the excess to a temperature that can be removed due to supersaturation, for example, the liquid temperature is cooled to a predetermined temperature of about 50 ° C. Apply. Thus, a crystal nucleus mixed solution in which the ferrous sulfate is crystallized is obtained.
[0015]
Further, in the separation step, this crystal nucleus mixed solution is fed into the lower part of the crystallization tank, and crystals grow as the ferrous sulfate crystal nuclei are bonded to each other while the mixed solution rises to the liquid surface. Crystals grown in the crystallization tank in this way are deposited under the tank due to their high specific gravity and are separated. As a result, a non-surplus mixed solution from which excess ferrous sulfate is separated and removed is formed by this separation step. In determining the surplus and non-surplus, the capacity, concentration, etc. of the deposited layer are set and suppressed in advance by calculation or measurement. Further, by setting the cooling temperature to a predetermined temperature, the non-surplus mixed solution in which a desired ratio of ferrous sulfate remains can be obtained as a supernatant solution. The amount remaining as ferrous sulfate is appropriately determined according to, for example, the material to be pickled and the concentration of ferric sulfate required accordingly.
[0016]
Furthermore, a regeneration solution in which ferrous sulfate in the mixed solution is oxidized and regenerated to ferric sulfate can be obtained by an oxidation regeneration step of adding hydrogen peroxide and sulfuric acid to the non-surplus mixed solution after this step. Thus, since the excess ferrous sulfate is separated in advance as crystals, the solution can be efficiently regenerated with less hydrogen peroxide solution and sulfuric acid. Moreover, the ferrous sulfate separated and taken out from the crystallization tank can be used as a recycled resource. In addition, a crystallization tank is a tank body which can remove ferrous sulfate as a crystal | crystallization, and the thing of various forms is employable.
[0017]
In the invention of claim 2, the ratio of the total height H to the total height H between the liquid surface and the bottom of the crystallization tank and the height h between the inlet of the mixed solution and the liquid surface is within a predetermined range. The excess ferrous sulfate can be efficiently settled and separated by making the inlet close to the vicinity of the bottom. Then, by setting the ratio of the cross-sectional area of the body part of the crystallization tank to the cross-sectional area of the pipe line of the inlet to the range of 10 to 40 times, the flow rate of the cooled mixed solution entering from the inlet is alleviated. Separation can be performed more efficiently by preventing the outflow of ferrous sulfate and promoting crystal growth.
[0018]
In addition, like the invention of Claims 3-6 of this invention, the regeneration process in which the said reproduction | regeneration is performed, taking out the mixed solution (raw solution) in a pickling tank sequentially, and the pickling process in a pickling tank are performed. By performing both continuously, a closed cycle in which a predetermined amount of the mixed solution is always circulated can be obtained. Furthermore, it is possible to constantly measure the concentration of the ferrous sulfate in the mixed solution, or to add hydrogen peroxide and sulfuric acid to the regeneration tank according to the amount required by the measurement. It can be suitably used for regenerating a mixed solution for pickling stainless steel.
[0019]
Furthermore, the regenerator according to claim 7 comprises a cooling part, a crystallization tank, and a regenerating means, and can be directly used for convenience for carrying out the regenerating method to the ferric sulfate solution.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram showing an embodiment of a pickling line in which a regenerator 1 that can be used in the method for regenerating ferric sulfate solution of the present invention is connected to a pickling process. The pickling line is connected to a pickling section A that uses a pickling tank 10 that is hung by a hanger, for example, and pickles a material 2 that is a coil of a stainless steel wire, for example. The pickling section A sequentially takes out the deteriorated mixed solution (stock solution) in the pickling tank 10 and regenerates it with the regenerator 1.
[0021]
Moreover, the regenerated solution that has been regenerated is returned to the pickling tank 10 and subjected to a pickling process, thereby forming a closed cycle that continuously circulates through the regenerating process and the pickling process. ing.
[0022]
The material 2 to be treated is, for example, various metal materials including other various alloys such as iron, chromium, nickel, etc. in addition to the stainless steel, and various oxide materials (oxide scales) that can be removed with a ferric sulfate solution. Metal materials are included.
[0023]
The pickling tank 10 may be of various types such as a strand or batch type, and a shape and structure depending on the purpose is selected.
[0024]
In addition to ferric sulfate, hydrofluoric acid or nitric acid is added to the solution used for this pickling treatment, and ferrous sulfate necessary for crystallizing ferrous sulfate at a predetermined temperature is added. It may be a solution that has been added and has a balanced composition, and varies depending on the object to be treated. Stainless steel is known, for example, from Japanese Patent Publication No. 4-20996.
[0025]
Thus, the concentration of ferric sulfate in the pickling solution and the building bath should be in a predetermined ratio range according to the material of the material 2 to be treated, the nature of the oxide film, the state, the finished quality of the product, the accuracy, etc. Set. A solution having a low concentration of ferric sulfate is generally inferior in processing efficiency. On the other hand, an overconcentrated solution causes peracid washing to roughen the product surface. In order to control the concentration of the mixed solution in the pickling treatment, necessary components such as ferric sulfate and hydrofluoric acid are usually measured separately and adjusted by adding a predetermined amount and mixing.
[0026]
Usually, pickling is performed for a predetermined time, for example, with stirring in a temperature range of about 40 ° C. to 80 ° C. for promotion. Along with the pickling treatment, the pickling solution is converted into ferrous sulfate by accumulating due to the reaction with the iron content in the oxide film of the material to be treated. It becomes an excess mixed solution containing iron and reduced in the ferric sulfate, thereby reducing the pickling treatment ability.
[0027]
The mixed solution is taken out from the pickling tank 10 by a predetermined amount, regenerated by the regenerating apparatus 1 and returned to the oxidizing tank 10 as a regenerated solution. The “excess mixed solution” means that the ferrous sulfate is excessive and the pickling ability is inferior, but also has a certain pickling ability as in the case of this example in which a closed cycle is performed. From the reference range to be set, a mixed solution containing excess ferrous sulfate is also included, and is also referred to as a stock solution.
[0028]
The regenerator 1 cools the surplus mixed solution taken out from the pickling tank 10, that is, a stock solution, to a temperature below the temperature at which ferrous sulfate is crystallized to produce a crystal nucleus mixed solution in which crystal nuclei are produced. The cooling unit 20 for performing the above and the crystal nucleus mixed solution are introduced from an inlet 30A provided below the liquid surface, and crystal nuclei are grown while rising to separate and remove the excess ferrous sulfate, thereby removing the non-surplus A crystallization tank 30 for performing a separation step for obtaining a mixed solution, and a regeneration for performing an oxidative regeneration means for obtaining a regenerated solution by adding hydrogen peroxide and sulfuric acid to the non-surplus mixed solution flowing out from the outlet 30B of the crystallization tank 30. Means 50.
[0029]
In this example, the oxidation regeneration means 50 is provided with a regeneration tank 60 for mixing hydrogen peroxide and sulfuric acid in the non-surplus mixed solution. Sulfuric acid can also be injected into the pickling tank 10, and at that time, the pickling tank 10 is considered to form part of the regeneration means 50. Moreover, you may make it flow in directly into the conduit | pipe 15 of FIG. 1, without providing a regeneration tank in particular.
[0030]
The outlet 10A at the bottom of the pickling tank 10 communicates with the cooling unit 20 through the first conduit 11 having the first pump P1 and the second conduit 12 having the second pump P2. In the present example, a receiving portion 37 of the crystallization tank 30 is interposed between the first conduit 11 and the second conduit 12. In this example, the stock solution solution in the pickling tank 10 is directly fed to the cooling unit 20 by selectively conducting the first conduit 11 and the second conduit 12 at the receiving unit 37. In addition, the supernatant mixed solution of the crystallization tank 30 in the receiving portion 37 can be fed again to the cooling portion 20 from the second conduit 12.
[0031]
The cooling unit 20 includes a coil 21 through which a refrigerant having a variable temperature and a regulated temperature passes, and a weir-shaped partition plate 22 in the box body 23, while the stock solution from the second conduit 12 overflows. Further, the coil 21 is cooled to a temperature at which a desired crystal ratio is 50 ° C. or lower, preferably 0 to 30 ° C. A temperature of 0 ° C. or lower is usually not preferable economically. As a result, the stock solution becomes a crystal nucleus mixed solution in which crystal nuclei of ferrous sulfate are generated, and flows out into the third conduit 13 extending from the bottom of the box body 23. The crystal nucleus mixed solution in the conduit 13 is guided to the intake 30C at the upper end of the crystallization tank 30. Some of the ferrous sulfate crystals remain attached to the cooling unit 20, the conduit 13, etc., but most of them are introduced into the inlet 30 </ b> C of the crystallization tank 30.
[0032]
Thus, in the crystal nucleus generation step, the crystal nucleus mixture in which the ferrous sulfate crystal nuclei are generated in the stock solution by cooling the surplus mixed solution to a temperature below the temperature at which ferrous sulfate crystallizes. A solution is formed, and in the next separation step using the crystallization tank 30, this crystal nucleus grows and settles, and the excess can be removed.
[0033]
In this example, the crystallization tank 30 has a main part 34 provided with a small-diameter take-out part 33 below the cylindrical body part 31 and an outer peripheral surface of the body part 31 below the upper end of the main part 34. A base 40 composed of a receiving portion 37 having a peripheral wall 36 formed around the bottom portion 35 projecting from the bottom, and a long tubular inflow tube that hangs down from above the receiving portion 37 and passes through the inside of the main portion 34 to the vicinity of the bottom portion. 42 is provided.
[0034]
Thus, the lower end of the inflow tube 42, that is, the inflow port 30 </ b> A is located at the bottom of the crystallization tank 30 and below the liquid level E.
[0035]
In this way, by positioning the inlet 30A at the lower end of the inflow cylinder 42 below the liquid level E of the discharged solution, the crystal nucleus mixed solution from the third conduit 13 is gently moved from the inlet 30A to the main portion 34. Flows in. Furthermore, it rises to the liquid level E by static flow, and during that time, the crystal nuclei of ferrous sulfate aggregate and grow. The grown crystal nuclei settle due to the difference in specific gravity to form a deposited layer 44 deposited below the main portion 34. The inlet 30A is located below the upper surface 44A of the deposited layer 44. The take-out part 33 causes ferrous sulfate to flow down into the crystal receiving tank 49 by opening the valve 47 as appropriate.
[0036]
The crystallization tank 30 has a height h between the inlet 30A and the liquid level E, for example, to make the settling of ferrous sulfate in the main portion 34 smooth. 80% to 98% of H (up to liquid level E), and the total height H is 800 mm or more. In order to further reduce the rising flow velocity, the cross-sectional area of the body portion 31 is preferably 10 to 40 times (preferably 20 to 30 times) the opening area of the inflow port 30A.
[0037]
When this area ratio is smaller than 10 times, the flow rate of the solution is large, and when it flows in from the inlet 30A and rises, crystal growth and separation cannot be performed sufficiently, and it overflows and tends to flow out to the next stage. If it is larger, more space is required than the processing capacity.
[0038]
Thus, the dimensions of each part of the main part 34 are set so that the growth and separation of crystal nuclei can be controlled. In this example, the main part 34 is a vertical cylindrical tank (outer diameter 300 mm, height 1000 mm). In addition, an inlet 30A having a diameter of 50 mm is provided near the bottom, and the height H between the inlet 30A and the liquid level E is 850 mm.
[0039]
Further, the main portion 34 may be formed in a hemispherical shape in which the inlet 30A is substantially extended to the vicinity of the bottom as shown in FIG. 2, for example, and the small tubular extraction portion 33 in FIG. 1 may be omitted. At the same time, the inflow tube 42 of FIG. 1 may be directly connected to the cooling bath 20 as a conduit.
[0040]
The deposited layer 44 grows by gradually combining the crystal nuclei. At this time, the deposited layer 44 captures the crystal nuclei as a filter for the inflowing solution and relaxes the ascending flow rate to statically. Brings the effect of flowing.
[0041]
Thus, in the separation step, the crystal nucleus mixed solution is caused to flow from the inlet 30A provided below the liquid surface E of the crystallization tank 30, and the crystal nucleus mixed solution rises to the liquid surface E to become a supernatant solution. Thus, a surplus mixed solution is obtained by separating the surplus of the crystal nuclei of the ferrous sulfate. As the crystallization tank 30, various types can be adopted as long as the crystal nucleus of ferrous sulfate is grown, coarsened and separated.
[0042]
Next, the non-surplus mixed solution from which a predetermined excess of ferrous sulfate has been separated overflows into the receiving portion 37 from the upper end of the main portion 34, and enters the regeneration tank 60 of the regeneration means 50 into the regeneration conduit 60. Inflow through. Further, the regeneration tank 60 communicates with the pickling tank 10 through the fifth conduit 15. Note that, as described above, the second conduit 12 can be sent to the cooling unit 20 again and processed again.
[0043]
The regeneration tank 60 is preferably provided with a stirring device 60A, and in this example, the spouts from the chemical injection pumps 61 and 62 of hydrogen peroxide and sulfuric acid are opened. The sulfuric acid chemical injection pump 62 can be opened in the oxidation tank 10, and at this time, the pickling tank 10 constitutes a part of the regeneration means 50 as described above.
[0044]
By adding hydrogen peroxide and sulfuric acid to the non-surplus mixed solution in the regeneration tank 60, a regenerated solution obtained by oxidizing and regenerating ferrous sulfate in the mixed solution to ferric sulfate is obtained.
[0045]
The regenerated solution is recycled to the pickling tank 10 and is subjected to a pickling process, and the reclaimed process is performed by sequentially removing the stock solution in the pickling tank and performing the regeneration. In a closed cycle so that the pickling treatment in step 2 is continued.
[0046]
In order to perform these cycles, the pickling tank 10 is provided with a concentration measuring means 70 for measuring the composition distribution of the mixed solution in the pickling process, for example, the concentration of ferrous sulfate. Concentration etc. are constantly measured. Similarly, the concentration measuring means 70 is provided in the oxidation tank 60 in the regeneration means 40. It is preferable to measure both, but either one may be used. In addition to ferrous sulfate, ferric sulfate, sulfuric acid, and hydrofluoric acid concentrations can also be measured. As these concentration measuring means 70, an automatic analyzer using a titanium trichloride titration method can be adopted for ferric sulfate, and an automatic analyzer using a potassium permanganate titration method can be adopted for measuring ferrous sulfate. Furthermore, known appropriate means can be used for sulfuric acid and the like.
[0047]
In addition to the concentration measuring means 70, various factors such as the temperature of each part, the liquid volume, the flow rate, the height of the deposited layer 44, and the crystal grain size are measured, and those measured values are given to a control device (not shown). In addition, the control device is provided with information such as the properties, finish accuracy, quality, quantity, time, etc. of the oxide film of the object to be processed in advance, so that the control device gives necessary control signals to each part and also measures the measured values. In response, control is performed based on various control theories such as feedback, and the operation of the regenerator 1 is automated according to given conditions, and the concentration is kept within a predetermined range.
[0048]
【Example】
Using a pickling solution prepared by mixing ferric sulfate, hydrofluoric acid, and water at a ratio of 3:16 in the pickling tank 10, the descaling treatment of the SUS430 Cr-based stainless steel wire 5.0 mmφ wire was performed at a liquid temperature of 65 ° C. went.
[0049]
In addition, this pickling tank is equipped with an automatic analyzer to measure the concentration change of the treatment solution accompanying the treatment for each treatment amount, and examine the change in the concentration of ferric sulfate and ferrous iron in the liquid. It was.
[0050]
FIG. 3 summarizes the results, and 15.0 wt% of ferric sulfate in the new bath decreases rapidly as the treatment amount increases, and the concentration is 2 when the pickling is performed 10 times. It can be seen that the increase in ferrous sulfate is conspicuous.
[0051]
In order to compensate for this decrease in concentration and to regenerate by a regenerator as an experimental plant to promote pickling treatment, a stock solution of 1 liter / min was taken out from the oxidation tank 10. The regenerator was set to cool the stock solution to 15 ° C., remove 30 g / liter of ferrous sulfate and leave 170 g / liter. After crystallization treatment under these conditions, the liquid was regenerated by adding 10 kg of hydrogen peroxide and 9 kg of sulfuric acid to the resulting non-excess mixed solution. About these addition amounts, it is the amount calculated | required from the density | concentration beforehand, and the reproduction | regeneration solution obtained has a ferric sulfate solution density | concentration of 14.9%, and it is almost a new solution, Therefore, the mixed solution in the pickling tank 10 As indicated by the alternate long and short dash line A in FIG. 3, the concentration was maintained without being greatly reduced even by the badge regeneration process, and the processing capability continued even after being reproduced several times. In addition, although the dashed-dotted line B is based on a closed system, even if ferric sulfate was 10.0 wt% previously, it was able to be maintained almost stably. It should be noted that this process can be easily selected by those skilled in the art.
[0052]
As described above, even if the regenerating process was repeated 20 times while performing the pickling process, the workability was not affected and good results could be obtained.
[0053]
In the present experimental example, as a method for detecting and controlling the excess of ferrous sulfate, the height of the ferrous sulfate deposition layer 44 in the crystallization tank 20 can also be adjusted. Note that the regeneration process may be stopped when the height calculated from the concentration range obtained in advance is reached.
[0054]
As another application example of the present invention, for example, a cooling means is also provided on the outer periphery of the crystallization tank 30 to further promote the crystallization process, or a filter member made of an insoluble material is disposed inside the tank to separate the ferrous iron. It is also preferable to increase the efficiency, and it is possible to automate such that an analysis device is provided in the middle of any of the piping circuits and the concentration is regenerated to an appropriate level while analyzing.
[0055]
【The invention's effect】
Thus, in the method for regenerating a ferric nitrate solution of the present invention, the supersaturated ferrous sulfate in the solution is crystallized as crystals and separated and removed by cooling the aged stock solution to a predetermined temperature or lower. This is a method of regenerating by adding hydrogen peroxide and sulfuric acid as additives. Efficient regeneration is possible with a small amount of addition, which also helps improve pickling quality and efficiency.
[0056]
Also, the separated ferrous iron can be taken out and used as a new resource, contributing to resource saving and facilitating maintenance control of the regeneration concentration, and applying this method to pickling treatment By doing so, a closed system can be established in which the pickling process and the regeneration process are circulated, and a stable continuous work can be performed without the need to interrupt the work for renewing the liquid as in the prior art.
[0057]
Also, the reproducing apparatus according to the present invention can be adopted at a low cost with a simple structure, and the technique according to the present invention is also effective from the aspect of pollution-free and greatly contributes to the industry.
[Brief description of the drawings]
FIG. 1 is a flowchart showing processing steps of a method of the present invention.
FIG. 2 is a front view showing an example of a crystallization tank.
FIG. 3 is a graph showing a change in concentration accompanying pickling treatment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Pickling tank 20 Cooling part 30A Inlet 30B Outlet 30C Inlet 31 Trunk part 40 Crystallizing tank 50 Regeneration means 60 Regeneration tank 70 Measuring means E Liquid level

Claims (7)

As a stock solution, sulfuric acid that removes the excess of ferrous sulfate in advance from a mixed solution of ferric sulfate containing ferrous sulfate and regenerates the ferrous sulfate in the mixed solution to ferric sulfate A regeneration method to ferric solution,
A cooling unit is provided for cooling to a predetermined temperature below the temperature at which ferrous sulfate in the stock solution sequentially taken out from the pickling tank is crystallized, and the ferrous sulfate is crystallized by cooling by the cooling unit. A crystal nucleus generating step for forming a crystal nucleus mixed solution having the crystal nucleus;
The crystal nucleus mixed solution is allowed to flow into the crystallization tank through an inlet provided below the liquid level of the crystallization tank, and the ferrous sulfate crystal nuclei are removed while the crystal nucleus mixed solution rises to the liquid level. A separation step of separating a surplus of ferrous sulfate by growing it into a non-surplus mixed solution;
By adding hydrogen peroxide and sulfuric acid to the non-surplus mixed solution flowing out from the crystallization tank, ferrous sulfate in the mixed solution is regenerated into ferric sulfate and continuously supplied to the pickling tank. A regeneration process,
A method for regenerating a ferric sulfate solution.   In the crystallization tank, the total height H between the liquid surface and the bottom is 800 mm or more, and the height h between the inlet and the liquid surface is 80 to 98% of the total height H. The method for regenerating ferric sulfate solution according to claim 1, wherein the cross-sectional area of the body of the crystallization tank is 10 to 40 times the cross-sectional area of the inlet.   The regeneration solution is supplied to a pickling tank and is subjected to a pickling process, and the stock solution in the pickling tank is sequentially taken out to perform regeneration including the crystal nucleation process, separation process, and regeneration process. 3. The ferric sulfate according to claim 1, wherein the regeneration treatment and the pickling treatment are performed in a closed cycle by continuously performing the pickling treatment in the pickling tank. Regeneration method to solution.   The method for regenerating a ferric sulfate solution according to claim 3, wherein the concentration of the ferrous sulfate in the stock solution is steadily measured in the pickling process or the regeneration process.   5. The ferric sulfate solution according to claim 4, wherein the regeneration step includes a regeneration tank, and at least one of hydrogen peroxide and sulfuric acid in an amount required by the measurement is added to the regeneration tank. Playback method.   6. The ferric sulfate according to claim 1, wherein the pickled product to be pickled is stainless steel, and the stock solution is a mixed solution for pickling stainless steel. Regeneration method to solution. As a stock solution, sulfuric acid that removes the excess of ferrous sulfate in advance from a mixed solution of ferric sulfate containing ferrous sulfate and regenerates the ferrous sulfate in the mixed solution to ferric sulfate A regeneration device for ferric solution,
A cooling unit that crystallizes the stock solution sequentially taken out from the pickling tank by cooling the ferrous sulfate in the mixed solution to form a crystal nucleus mixed solution having the crystal nucleus;
The crystal nucleus mixed solution is introduced from the inlet, and the ferrous sulfate crystal nuclei are grown while the crystal nucleus mixed solution rises to the liquid surface, thereby separating the excess ferrous sulfate and removing In order to obtain a surplus mixed solution, a crystallizing tank in which the inlet of the crystal nucleus mixed solution is provided below the liquid surface from which the non-surplus mixed solution is discharged;
By adding hydrogen peroxide and sulfuric acid to the non-surplus mixed solution flowing out from the crystallization tank, ferrous sulfate in the mixed solution is regenerated to ferric sulfate, and the regenerated solution is continuously added to the pickling tank. A regenerating apparatus for ferric sulfate solution, comprising regenerating means for circulating and supplying to the apparatus.

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