JP2014070011A - Production method of polyferric sulfate solution - Google Patents

Abstract

The present invention provides a novel method for producing a ferric sulfate solution that can produce a ferric sulfate solution with high yield and low cost.
SOLUTION: A gas that volatilizes from a solution containing nitric acid is blown into a solution containing ferrous sulfate and a gas that volatilizes from a solution containing ferrous sulfate is blown into a solution containing nitric acid. Ferrous sulfate is converted to polyferric sulfate by circulating gas between solutions containing iron. Alternatively, nitric acid is directly added to a solution containing ferrous sulfate and stirred to convert the ferrous sulfate to polyferric sulfate.
[Selection] Figure 1

Description

  The present invention relates to a method for producing a polyferric sulfate solution.

  As a method for producing a polyiron sulfate solution, it is disclosed that a ferric sulfate solution is produced by oxidizing divalent iron in a ferrous sulfate solution to trivalent iron with oxygen or air using a nitrogen oxide as a catalyst. (For example, refer to Patent Document 1). However, when this method was further tested, it was found that 30% ferrous sulfate remained.

  Moreover, it is disclosed that a high-concentration hydrogen peroxide is added to a sulfuric acid solution containing ferrous sulfate to perform iron oxidation reaction to produce a polyferric sulfate ferric solution (for example, Patent Document 3). See). However, in this method, the chemical cost of high-concentration hydrogen peroxide is expensive, and since the polyferric sulfate solution is diluted by the addition of hydrogen peroxide, further concentration must be performed. There was a problem that it was expensive.

JP 11-278849 A JP 2000-16816 A

  Then, an object of this invention is to provide the manufacturing method of the novel polyferric sulfate solution which can manufacture a polyferric sulfate solution with a high yield and low cost.

First method of manufacturing a poly iron sulfate solution of the present invention, the molar ratio of the pre-iron gas evaporated from a solution containing nitric acid (T-Fe) and sulfuric acid (T-SO ₄₎ is 1.0 <(T- SO _{4 /} T-Fe) <1.5, and blowing into a solution containing ferrous sulfate, and blowing a gas that volatilizes from the solution containing ferrous sulfate into the solution containing nitric acid. The ferrous sulfate in the solution containing the ferrous sulfate is converted to polyferric sulfate by circulating a gas between the solution containing the ferrous sulfate and the solution containing the ferrous sulfate. .

  The solution containing nitric acid is a nitric acid solution or an acidic solution of nitrate.

  The solution containing ferrous sulfate is characterized in that nitric acid or nitrate is added in advance.

  Moreover, a part of gas which volatilizes from the solution containing the said ferrous sulfate is removed, It is characterized by the above-mentioned.

  In addition, gas circulation between the solution containing nitric acid and the solution containing ferrous sulfate is performed in a closed system, and the ferrous sulfate is included when the inside of the closed system exceeds a predetermined pressure. A part of the gas that volatilizes from the solution is discharged out of the closed system and removed.

  The conversion reaction to polyferric sulfate is controlled by monitoring the pH and oxidation-reduction potential of the solution containing nitric acid and the solution containing ferrous sulfate.

  Also, at the end of the conversion reaction to polysulfuric acid ferric sulfate, the circulation of gas to and from the solution containing nitric acid is stopped, and purge nitrogen is blown into the polysulfuric acid ferric sulfate solution to remove residual nitrate nitrogen. It is characterized by that.

The manufacturing method of the second poly-iron sulphate solution of the present invention, pre-iron (T-Fe) and the molar ratio of sulfuric acid (T-SO ₄₎ is _{1.0 <(T-SO 4 /} T-Fe) While stirring a solution containing ferrous sulfate adjusted to <1.5, the molar ratio of iron (T-Fe) to nitric acid (T-NO ₃ ) is (1 / 2.9) <(T-NO ₃ / T-Fe) <(1 / 2.2.7), and nitric acid is added to the solution containing ferrous sulfate so that the iron (T-Fe) concentration is 210 g / l to 230 g / l. Then, by continuing stirring, the ferrous sulfate in the solution containing ferrous sulfate is converted to polyferric sulfate.

  In addition, the conversion reaction from the solution containing ferrous sulfate after addition of nitric acid to polyferric sulfate is performed in an open system, and the gas volatilized from the solution containing ferrous sulfate is discharged to the outside as it is. It is characterized by removing.

  In addition, a conversion reaction from the solution containing ferrous sulfate after addition of nitric acid to polyferric sulfate is performed in a closed system, and when the inside of the closed system exceeds a predetermined pressure, A part of the gas which volatilizes from the solution containing 1 iron is discharged to the outside of the closed system and removed.

  In addition, the conversion reaction to ferric sulfate is controlled by monitoring the pH and redox potential of the solution containing ferrous sulfate.

  Further, at the end point of the conversion reaction to ferric sulfate, ferric sulfate is blown into the ferric sulfate solution to remove remaining nitrate nitrogen.

  Further, the removed gas is recovered as nitric acid.

  Further, the recovered nitric acid is reused as a solution containing nitric acid or nitric acid.

  According to the method for producing a ferric sulfate solution of the present invention, it is possible to produce a ferric sulfate solution with high yield and low cost by using an apparatus having a simple configuration. The removed gas can be recovered and reused as nitric acid.

It is the schematic which shows an example of the apparatus used for the manufacturing method of the polyferric ferric sulfate solution of this invention. It is the graph which showed pH, oxidation-reduction potential, and temperature in the acid solution containing the ferrous salt in Example 1 of the manufacturing method of the polyferric sulfate ferric solution of this invention.

  Hereinafter, the manufacturing method of the polyferric sulfate ferric solution of this invention is demonstrated.

Manufacturing method of the first poly ferric sulfate solution of the present invention, the molar ratio of the pre-iron gas evaporated from a solution containing nitric acid (T-Fe) and sulfuric acid (T-SO ₄₎ is 1.0 <( Blowing into a solution containing ferrous sulfate adjusted to T-SO ₄ /T-Fe)<1.5, and blowing a gas that volatilizes from the solution containing ferrous sulfate into the solution containing nitric acid, By circulating a gas between the solution containing nitric acid and the solution containing ferrous sulfate, ferrous sulfate in the solution containing ferrous sulfate is converted to polyferric sulfate. .

  That is, when a gas that volatilizes from a solution containing nitric acid is blown into a solution containing ferrous sulfate, the following reaction for oxidizing ferrous sulfate starts in the solution containing ferrous sulfate. In addition, the gas which volatilizes from the solution containing nitric acid is nitric acid, and this works as a reaction initiator. And the reduced form nitrogen oxide volatilizes from the solution containing ferrous sulfate.

  On the other hand, when a gas that volatilizes from a solution containing ferrous sulfate is blown into a solution containing nitric acid, the following reaction for oxidizing nitrogen oxides proceeds in the solution containing nitric acid. The oxidized form of nitrogen oxides volatilizes from the solution containing nitric acid.

  Then, when the gas which volatilizes from the solution containing nitric acid is blown into the solution containing ferrous sulfate, the following reaction for oxidizing ferrous sulfate proceeds constantly in the solution containing ferrous sulfate. The reduced form of nitrogen oxides volatilizes from the ferrous sulfate solution.

  The overall reaction formula in the circulation loop when the gas is circulated between the solution containing nitric acid and the solution containing ferrous sulfate is as follows.

  By the above reaction, ferrous sulfate in the solution containing ferrous sulfate is converted to polyferric sulfate.

In the present invention, as the solution containing ferrous sulfate, for example, the copper sulfate waste liquid used in copper plating and the copper sulfate waste liquid used in the etching of metal copper is added with metallic iron to replace the iron with copper. A solution obtained by adding a predetermined amount of sulfuric acid chemical solution or waste sulfuric acid to the obtained ferrous sulfate solution may be used, and after crystallizing and separating ferrous sulfate heptahydrate from the obtained ferrous sulfate solution. , You may use a predetermined amount of water and a predetermined amount of sulfuric acid chemical solution, waste sulfuric acid or sulfuric acid washing waste liquid of metallic iron, or use a solution of metallic iron sulfuric acid washing waste liquid with a predetermined amount of sulfuric acid chemical solution or waste sulfuric acid. The molar ratio of iron (T—Fe) and sulfuric acid (T—SO ₄ ) is 1.0 <(T—SO ₄ /T—Fe)<1.5. By adjusting the molar ratio in this way, it is possible to convert all of the ferrous sulfate to polyferric sulfate.

  The solution containing ferrous sulfate needs to be acidic with a predetermined concentration of sulfuric acid. On the other hand, even if it contains ferric sulfate in addition to ferrous sulfate, it can be converted into polyferric sulfate. There is no hindrance. Moreover, the impurity may be included in the range which does not interfere with the use of the polyferric sulfate manufactured.

  In the present invention, the solution containing nitric acid may be a solution in which nitric acid gas is volatilized, and a nitric acid solution or an acidic solution of nitrate can be used. As a raw material of a solution containing nitric acid, a waste containing nitric acid or nitrate in addition to a nitric acid chemical solution can be used regardless of liquid or solid. For example, nitric acid stripping of metal, nitric acid passive waste liquid, nitrate waste, and the like can be used. When using nitrate waste, nitrate waste may be dissolved in a sulfuric acid solution at a predetermined acid concentration. Moreover, what added acids, such as a sulfuric acid which does not volatilize at normal temperature, may be used. Nitric acid can be liberated from the nitrate by adding an acid suitable for a salt such as nitrate contained in the solution containing nitric acid, and the acid in the solution containing nitric acid as the nitrogen oxides volatilize by adding an excess of acid. Even if the concentration is decreased, the chemical reaction rate of the chemical formulas 1 to 4 can be prevented from decreasing, and as a result, all of the ferrous sulfate can be converted to polyferric sulfate, and the conversion rate is also improved. Can be improved. However, it is not preferable to volatilize gases other than nitric acid and nitrogen oxides under acidic conditions because the purity of the resulting ferric sulfate is lowered. Note that even a volatile substance such as hydrogen halide such as hydrochloric acid is acceptable as an impurity if the content is extremely small.

  In the present invention, the solution containing ferrous sulfate may be previously added with nitric acid or nitrate. Although the reaction starts without adding nitric acid or nitrate to the solution containing ferrous sulfate, the lag time at the start of the reaction is reduced by adding nitric acid or nitrate in advance. That is, the lag time until nitric acid as a reaction initiating substance is absorbed into a solution containing ferrous sulfate, reacts with ferrous sulfate, and volatilizes as a reduced form of nitrogen oxide is shortened.

  In the present invention, a part of the gas that volatilizes from the solution containing ferrous sulfate may be removed. When the reduced form of nitrogen oxides is blown into a solution containing nitric acid, the reduced form of nitrogen oxides is oxidized, and at the same time, nitrogen oxides in which nitric acid is reduced and decomposed are generated. For this reason, the quantity of the gas circulated between the solution containing nitric acid and the solution containing ferrous sulfate increases as the reaction proceeds. By removing a part of the increased gas, the reaction of converting the ferrous sulfate solution into the polyferric sulfate solution can be further promoted.

  Gas circulation between a solution containing nitric acid and a solution containing ferrous sulfate is performed in a closed system, and volatilizes from the solution containing ferrous sulfate when the inside of the closed system exceeds a predetermined pressure. A part of the gas may be discharged outside the closed system and removed. Alternatively, a part of the gas may be removed based on pH, redox potential, reaction elapsed time, etc., and part of the gas is removed by automatic control from the start of gas circulation to the end of the reaction. You may do it.

  In the present invention, the conversion reaction to polyferric sulfate may be controlled by monitoring the pH and oxidation-reduction potential of a solution containing nitric acid and a solution containing ferrous sulfate. In addition, by monitoring the pH and oxidation-reduction potential, it is possible to monitor the progress of the conversion reaction, determine the abnormality of the production process, determine the end point of the conversion reaction, and the like.

  Also, in the present invention, at the end of the conversion reaction to polysulfuric acid ferric sulfate, the circulation of gas to and from the solution containing nitric acid is stopped, and purge gas is blown into the polyferric sulfate ferric sulfate solution to remain nitrate nitrogen. May be removed. Thereby, the quality of the polyferric sulfate ferric solution can be improved.

Second method for manufacturing a poly ferric sulfate solution of the present invention, pre-iron (T-Fe) and the molar ratio of sulfuric acid (T-SO ₄₎ is _{1.0 <(T-SO 4 /} T-Fe) While stirring a solution containing ferrous sulfate adjusted to <1.5, the molar ratio of iron (T-Fe) to nitric acid (T-NO ₃ ) is (1 / 2.9) <(T-NO ₃ / T-Fe) <(1 / 2.2.7), and nitric acid is added to the solution containing ferrous sulfate so that the iron (T-Fe) concentration is 210 g / l to 230 g / l. Then, by continuing stirring, the ferrous sulfate in the solution containing the ferrous sulfate is converted to polyferric sulfate.

  That is, in the second method, the gas is circulated between the solution containing nitric acid and the solution containing ferrous sulfate, and the gas circulated into the solution containing nitric acid and the solution containing ferrous sulfate is blown. Instead of adding ferric sulfate directly to a solution containing ferrous sulfate, oxidation of ferrous sulfate in the solution containing ferrous sulfate is oxidized. The reaction starts. And the reduced form nitrogen oxide volatilizes from the solution containing ferrous sulfate. If stirring is continued as it is, the reaction proceeds according to the reaction formula of Chemical Formula 1, the reduced form of nitrogen oxides volatilizes, and ferrous sulfate in the solution containing ferrous sulfate is converted to polyferric sulfate. .

  In the second production method of the present invention, the solution containing ferrous sulfate can be the same as the solution containing ferrous sulfate described above, and ferrous sulfate after adding nitric acid. It is preferable to use one that has been adjusted so that the concentration of iron (T-Fe) in the solution containing is 210 g / l to 230 g / l. If the iron (T-Fe) concentration is lower than 210 g / l, not only does the reaction rate of ferrous sulfate in a solution containing ferrous sulfate convert to polyferric sulfate, but also all Cannot be converted to ferric sulfate. Moreover, when an iron (T-Fe) density | concentration is higher than 230 g / l, it can convert to poly ferric sulfate, but precipitates in the solution after completion | finish of reaction. For this reason, the operation which isolate | separates and removes the deposit which precipitated in the obtained polyferric-sulfuric acid solution or dissolves the deposited precipitate is needed, and a process increases and is complicated and is not economical.

  In the second production method of the present invention, nitric acid chemical solution or the like can be used as nitric acid. However, nitric acid containing impurities is not preferable because the purity of polyferric sulfate obtained is lowered. In addition, if the content of impurities is extremely small, it is allowed as impurities.

  In the second production method of the present invention, the conversion reaction from the solution containing ferrous sulfate after addition of nitric acid to polyferric sulfate can be performed in an open system or a closed system. The gas which volatilizes from the solution containing ferrous sulfate after the addition of nitric acid is discharged and removed as it is in the open system, and the nitric acid is added when the internal pressure exceeds a predetermined pressure in the closed system. What is necessary is just to discharge | emit and remove a part of gas which volatilizes from the solution containing ferrous sulfate after that to the exterior of the said closed system.

  Further, in the second production method of the present invention, by monitoring the pH and redox potential of the solution containing ferrous sulfate after the addition of nitric acid, monitoring of the progress of the conversion reaction and determination of abnormality in the production process The end point of the conversion reaction can also be determined.

  Further, in the second production method of the present invention, purge gas is blown into the polyferric sulfate ferric sulfate solution at the end point of the conversion reaction from the solution containing ferrous sulfate to the polyferric sulfate ferric after adding the nitric acid. The remaining nitrate nitrogen may be removed. Thereby, the quality of the polyferric sulfate ferric solution can be improved.

  Further, in both the first and second production methods of the present invention, the nitrogen oxide contained in the removed gas may be recovered as a nitric acid solution in contact with water and oxygen and reused. When the removed gas is not recovered as a nitric acid solution, it may be processed by a general NOX gas exclusion facility.

  Hereinafter, the present invention will be described in more detail with reference to specific examples, but the present invention is not limited to these examples.

  FIG. 1 is a schematic view showing an example of an apparatus used in the method for producing a ferric sulfate sulfate solution of the present invention. In addition, the structure of the apparatus used for the manufacturing method of the polyferric sulfate ferric solution of this invention is not limited to this embodiment, A various change is possible.

  In FIG. 1, 1 includes a stirrer 2, an instrument 3 including a pH meter, a redox potential meter, and a thermometer, and a pipe 25 provided with a pressure gauge 11 and a valve 24 for introducing a chemical solution. A PVC reaction vessel (approximate inner diameter 150 mm, height 140 mm) containing a solution containing ferrous sulfate. 4 includes a stirrer 5, an instrument 6 including a pH meter, a redox potential meter, and a thermometer, and a pressure gauge 12, and a PVC cylindrical reaction tank (approximate) containing a solution containing nitric acid. The inner diameter is 150 mm and the height is 140 mm. 16 is a nitric acid recovery device for recovering nitrate nitrogen gas as nitric acid. The reaction tank 1 and the reaction tank 4 have a sealed structure. Between the reaction tank 1 and the reaction tank 4, a pipe 7 for introducing the gas in the head space of the reaction tank 4 into the solution contained in the reaction tank 1, and the gas in the head space of the reaction tank 1 A pipe 9 and a pipe 10 are provided via an air pump 8 for introduction into the solution contained in 4. A gas diffuser (not shown) for efficiently making contact between the solution accommodated in the reaction tank 1 and the reaction tank 4 and the gas introduced into circulation at the gas outlet side ends of the pipe 7 and the pipe 10, respectively. Is provided. The reaction tank 1 is provided with pipes 13 and 15 through a valve 14 for introducing the gas in the head space of the reaction tank 1 into the nitric acid recovery device 16. A valve 17 is provided on the gas inlet side of the pipe 9, and a pipe 22 provided with a valve 20 for taking in air is provided in the pipe 9 between the valve 17 and the pump 8. A valve 18 is provided on the gas outlet side of the pipe 10, and a valve 19 is provided on the gas inlet side of the pipe 7, and a path for bypassing the reaction tank 4 is formed between the pipe 10 and the pipe 7. A pipe 23 provided with a valve 21 is provided. When the valve 18 and the valve 19 are closed after the completion of the reaction, the structure is such that the nitrate nitrogen gas remaining in the pipe 9, the air pump 8, the pipe 10, the pipe 7 and the reaction tank 1 can be purged.

  When a polyferric sulfate solution is produced by the first method of the present invention using the above apparatus, a solution containing ferrous sulfate is sealed in the reaction tank 1, and nitric acid is contained in the reaction tank 4. The solution to be contained is hermetically sealed, the valves 14, 20, 21, 24 are closed, the valves 17, 18, 19 are opened, the instrumentation 3, 6, the pressure gauges 11, 12, the stirrers 2, 5, and the air pump 8 are installed. Operate. In the closed system composed of the reaction tank 1 and the reaction tank 4, the gas volatilized from the solution containing nitric acid accommodated in the reaction tank 4 is a solution containing ferrous sulfate accommodated in the reaction tank 1 via the pipe 7. At the same time, the gas volatilized from the solution containing ferrous sulfate contained in the reaction tank 1 is blown into the solution containing nitric acid contained in the reaction tank 4, and the nitric acid contained in the reaction tank 4 is Gas circulates between the solution containing and the solution containing ferrous sulfate contained in the reaction vessel 1.

  Then, for example, when the pressure value by the pressure gauge 11 exceeds a predetermined pressure, the valve 14 is opened, and the gas volatilized from the solution containing ferrous sulfate is taken out via the pipes 13 and 15. Thereafter, nitrogen oxides contained in the taken-out gas are introduced into the nitric acid recovery device 16 and converted into nitric acid by a known method for producing nitric acid from the nitrogen oxides and recovered.

  When the polyferric sulfate solution is produced by the second method of the present invention using the above apparatus, a solution containing ferrous sulfate is accommodated in the reaction tank 1, and the valves 14, 17, 18, 19 are stored. , 20, 21 are closed, and the instrument 3, pressure gauge 11, and stirrer 2 are operated. The reaction tank 1 is maintained in this state, the valve 24 is opened, and a predetermined amount of nitric acid is added from the pipe 25.

  Then, for example, at the stage where the addition of a predetermined amount of nitric acid to the reaction tank 1 is completed, the valve 14 may be opened immediately, and the gas volatilized from the solution in the reaction tank 1 may be taken out via the pipes 13 and 15. Alternatively, for example, when the pressure value by the pressure gauge 11 exceeds a predetermined pressure, the valve 14 may be opened, and the gas volatilized from the solution in the reaction tank 1 may be taken out via the pipes 13 and 15. Thereafter, nitrogen oxides contained in the taken-out gas are introduced into the nitric acid recovery device 16 and converted into nitric acid by a known method for producing nitric acid from the nitrogen oxides and recovered.

Example 1
In the reaction tank 1 configured as described above, sulfuric acid containing ferrous sulfate composed of 900 mL of water, 1260 g of ferrous sulfate heptahydrate (reagent manufactured by Wako Pure Chemical Industries) and 120 mL of 95% sulfuric acid (reagent manufactured by Junsei Kagaku). 1690 mL of the solution was accommodated as a solution containing ferrous sulfate, and about 600 mL of an aqueous nitric acid solution composed of 300 mL of water and 300 mL of 60% nitric acid aqueous solution (a reagent manufactured by Wako Pure Chemical Industries) was accommodated in the reaction tank 4 as a solution containing nitric acid. . Then, the valves 14, 20, 21, and 24 are closed, the valves 17, 18, and 19 are opened, the stirrer 2, the stirrer 5, and the air pump 8 are operated, and the gas in the sealed system is discharged at a gas discharge rate of about 50 L / min. The reaction was started by circulating. In addition, since the ferrous sulfate heptahydrate contained in the reaction tank 1 hardly dissolves at room temperature because of solubility, the reaction tank 1 was stirred in a slurry state at the start of the reaction.

  The progress of the reaction in the reaction tank 1 and the reaction tank 4 and the presence or absence of abnormality are measured by the instrumentation 3 and 6 attached to the reaction tank 1 and the reaction tank 4, and the pressure gauges 11 and 12, and the reaction tank 1 and the reaction tank 4 The amount of gas circulating between the pressure gauges 11 and 12 was monitored.

When the gauge pressure value by the pressure gauge 11 showed 0.15 kg / cm ² , the air pump 8 was stopped, the valve 14 was opened, and the gas in the sealed reaction system was taken out from the pipes 13 and 15. When the gauge pressure value of the pressure gauge 11 showed 0.00 kg / cm ² , the valve 14 was closed and the air pump 8 (gas discharge amount of about 50 L / min) was operated to restart the reaction.

The operation of taking out the gas and restarting the reaction in this series of sealed reaction systems were repeated. When the reaction was judged to have reached the end point from the change in the pH of the reaction tank 1, the change in redox potential, and the change in temperature, the gas was removed from the sealed reaction system, and 1 minute had passed after the reaction was restarted. However, after confirming that the gauge pressure value of the pressure gauge 11 did not increase while showing 0.00 kg / cm ² , the valves 20 and 21 were opened, the valves 17, 18 and 19 were closed, and purged with air for 1 hour. The purged gas was taken out via the pipes 13 and 15.

  Table 1 shows the reaction time from the start to the end of Example 1, the concentration and amount of ferrous salt in the solution containing ferrous sulfate accommodated in the reaction tank 1 and the ferric salt produced by the reaction. , Changes in the concentration and amount of nitrate nitrogen in the solution containing nitric acid accommodated in the reaction tank 4, and the amount and recovery rate of the recovered nitrate nitrogen. The total iron concentration in the solution is the ICP emission method (SPS-3100 manufactured by SII), the ferrous ion in the solution is the o-phenanthroline spectrophotometry, and the nitrate nitrogen concentration in the solution is the catalytic combustion chemiluminescence method ( It was measured by Shimadzu TNM-1).

  The reaction end point was reached in about 190 minutes from the start of the reaction, and all of the ferrous iron in the solution containing ferrous sulfate contained in the reaction tank 1 was oxidized to ferric iron to produce a polyferric sulfate ferric solution. Was confirmed. In addition, at the reaction end point, all of the ferrous sulfate heptahydrate that was not dissolved at the start of the reaction was dissolved. The nitrate nitrogen concentration in the manufactured polyferric sulfate solution was also less than 0.1%. Further, from the solution containing nitric acid accommodated in the reaction tank 4, nitrate nitrogen gas was extracted in accordance with the chemical reaction of the chemical reaction shown in chemical formula 4.

  FIG. 2 shows the pH, redox potential, and temperature in the solution containing ferrous sulfate contained in the reaction tank 1 from the start to the end of Example 1. Here, the horizontal axis represents the reaction time from the start to the end point, and the vertical axis represents pH (unit:-), oxidation-reduction potential (unit: mV), and temperature (unit: ° C).

  In FIG. 2, the oxidation-reduction potential rapidly increases near the end point of the reaction in which the ferrous salt in the solution containing ferrous sulfate contained in the reaction tank 1 is converted to the ferric salt, and the ferrous salt is It was confirmed that there exist inflection points that disappear. Further, the pH was increased in the vicinity of the end point of the reaction as the acid was consumed at the start of the reaction as shown in the chemical reaction formula shown in Chemical formula 4. In FIG. 2, the pH from 0 minute to 50 minutes is a negative value. Therefore, it was confirmed that the progress of the reaction can be monitored and the end point of the reaction can be determined by monitoring the pH and the oxidation-reduction potential.

(Example 2)
The same operation as in Example 1 was performed except that about 600 mL of nitric acid aqueous solution composed of 400 mL of water and 200 mL of 60% nitric acid aqueous solution (a reagent manufactured by Wako Pure Chemical Industries) was accommodated in the reaction tank 4 as a solution containing nitric acid. The gas was taken out via 13 and 15.

  Table 2 shows the reaction time from the start to the end of Example 2, the concentration and amount of ferrous salt in the solution containing ferrous sulfate accommodated in the reaction tank 1 and the ferric salt produced by the reaction. , Changes in the concentration and amount of nitrate nitrogen in the solution containing nitric acid contained in the reaction tank 4, and the amount and recovery rate of the recovered nitrate nitrogen.

  As a result of producing a polyferric sulfate ferric sulfate solution with a nitric acid concentration of 2/3 with the amount of the nitric acid-containing solution of Example 1 as it is, the time to reach the reaction end point was 630 minutes and Example 1 The ferrous sulfate in the solution containing ferrous sulfate contained in the reaction vessel 1 is all oxidized to ferric iron, and the nitrate nitrogen concentration is less than 0.1%. The ferric sulfate solution was prepared, and from the solution containing nitric acid accommodated in the reaction tank 4, nitrate nitrogen gas was extracted in accordance with the chemical formula of the chemical reaction shown in Chemical formula 4.

(Example 3)
All operations were performed in the same manner as in Example 1 except that 600 mL of a 60% nitric acid aqueous solution (a reagent manufactured by Wako Pure Chemical Industries, Ltd.) was contained in the reaction tank 4 as a solution containing nitric acid, and the gas was taken out via the pipes 13 and 15.

  Table 3 shows the reaction time from the start to the end point of Example 3, the concentration and amount of ferrous salt in the solution containing ferrous sulfate accommodated in the reaction tank 1 and the ferric salt produced by the reaction. , Changes in the concentration and amount of nitrate nitrogen in the solution containing nitric acid contained in the reaction tank 4, and the amount and recovery rate of the recovered nitrate nitrogen.

  As a result of producing the polyferric sulfate solution with the nitric acid concentration doubled while keeping the amount of the nitric acid solution of Example 1 as it was, the time until reaching the reaction end point was 16 minutes. Compared to about 1/12 of the time, the ferrous sulfate in the solution containing ferrous sulfate contained in the reaction vessel 1 is all oxidized to ferric iron, and the polysulfuric acid containing 0.17% nitrate nitrogen. A ferric iron solution was manufactured, and from the solution containing nitric acid contained in the reaction vessel 4, nitrate nitrogen gas of 86% of the chemical reaction formula amount shown in Chemical formula 4 was extracted.

Example 4
All operations were performed in the same manner as in Example 1 except that 300 mL of a 60% nitric acid aqueous solution (a reagent manufactured by Wako Pure Chemical Industries, Ltd.) was contained in the reaction tank 4 as a solution containing nitric acid, and gas was taken out via the pipes 13 and 15.

  Table 4 shows the reaction time from the start to the end of Comparative Example 2, the concentration and amount of ferrous salt in the solution containing ferrous sulfate accommodated in the reaction tank 1 and the ferric salt produced by the reaction. , Changes in the concentration and amount of nitrate nitrogen in the solution containing nitric acid accommodated in the reaction tank 4, and the amount and recovery rate of the recovered nitrate nitrogen.

  As a result of producing the polyferric sulfate solution in the amount of 1/2 without changing the concentration of the solution containing nitric acid in Example 4, the time required to reach the reaction end point was 47 minutes as compared with Example 3. The ferric sulfate solution containing 0.18% nitrate nitrogen is obtained by oxidizing all the ferrous iron in the solution containing ferrous sulfate contained in the reaction tank 1 into ferric iron. From the solution containing nitric acid produced and contained in the reaction tank 4, nitrate nitrogen gas of 86% of the chemical reaction formula amount shown in Chemical formula 4 was extracted.

(Example 5)
The same operation as in Example 1 was carried out except that about 300 mL of the nitric acid aqueous solution remaining in the reaction tank 4 after the production of the ferric sulfate ferric sulfate solution of Example 4 was directly stored in the reaction tank 4 as a solution containing nitric acid. The gas was taken out via the pipes 13 and 15.

  Table 5 shows the reaction time from the start to the end point of Example 5, the concentration and amount of ferrous salt in the solution containing ferrous sulfate accommodated in the reaction tank 1 and the ferric salt produced by the reaction. , Changes in the concentration and amount of nitrate nitrogen in the solution containing nitric acid contained in the reaction tank 4, and the amount and recovery rate of the recovered nitrate nitrogen.

  In Example 4, the aqueous solution of nitric acid having a reduced nitric acid concentration remaining in the reaction tank 4 was used as a solution containing nitric acid, and as a result, the time until reaching the reaction end point was 140 minutes. 4 times longer than 4 but the ferrous iron contained in the reaction vessel 1 containing ferrous sulfate was all oxidized to ferric iron and nitrate nitrogen was less than 0.1%. A ferric sulfate solution was manufactured, and from the solution containing nitric acid accommodated in the reaction tank 4, nitrate nitrogen gas was taken out in accordance with the chemical formula of the chemical reaction shown in Chemical formula 4.

(Example 6)
The same as in Example 1, except that 600 mL of a sodium nitrate aqueous solution composed of 335 g of sodium nitrate (reagent manufactured by Wako Pure Chemical Industries) and 110 mL of 95% sulfuric acid (reagent manufactured by Junsei Kagaku) was accommodated in the reaction tank 4 as a solution containing nitric acid. The gas was taken out via the pipes 13 and 15.

  Table 6 shows the reaction time from the start to the end of Example 6, the concentration and amount of ferrous salt in the solution containing ferrous sulfate accommodated in the reaction tank 1 and the ferric salt produced by the reaction. , Changes in the concentration and amount of nitrate nitrogen in the solution containing nitric acid contained in the reaction tank 4, and the amount and recovery rate of the recovered nitrate nitrogen.

  A solution of polyferric sulfate as a solution containing nitric acid by adding nitrate and sulfuric acid to water so that the amount of liquid stored in the reaction tank 4, the concentration of nitrate nitrogen and the concentration of acid are almost the same as in Example 1. As a result of the production, the time required to reach the reaction end point was 750 minutes, which was about 3.9 times longer than that in Example 1. However, the first solution in the solution containing ferrous sulfate contained in the reaction vessel 1 was used. A ferric sulfate polysulfate solution in which all iron is oxidized to ferric iron and nitrate nitrogen is also less than 0.1% is manufactured. From the solution containing nitric acid contained in the reaction vessel 4, the chemical reaction is represented by the following chemical formula. Nitrate nitrogen gas was taken out as much as possible, and almost the same result as in Example 1 was obtained.

(Example 7)
The same operations as in Example 1 were performed except that 50 g of sodium nitrate (Wako Pure Chemicals Reagent) was contained in 1690 mL of the solution containing ferrous sulfate contained in the reaction tank 1 of Example 1, and pipes 13 and 15 were connected. The gas was taken out via.

  Table 7 shows the reaction time from the start to the end of Example 7, the concentration and amount of ferrous salt in the solution containing ferrous sulfate accommodated in the reaction tank 1 and the ferric salt produced by the reaction. , Changes in the concentration and amount of nitrate nitrogen contained in the reaction tank 1 and the reaction tank 4, and the amount and recovery rate of the recovered nitrate nitrogen.

  As a result of producing a ferric sulfate sulfate solution under the same conditions as in Example 1 except that sodium nitrate was added to the reaction vessel 1 as a reaction initiator, the time until reaching the reaction end point was 130 minutes. Compared with the result, the effect of adding a reaction initiator to the reaction tank 1 was recognized. Further, ferrous sulfate contained in the reaction vessel 1 containing ferrous sulfate is all oxidized to ferric iron to produce a polyferric sulfate solution containing 0.12% nitrate nitrogen, and the reaction vessel From the solution containing the aqueous nitric acid solution stored in 1 and the nitric acid stored in the reaction vessel 4, nitrate nitrogen gas of 91% of the chemical reaction formula amount shown in Chemical Formula 4 was extracted.

(Comparative Example 1)
Except that the reaction tank 1 contained 1130 mL of a solution containing ferrous sulfate composed of 300 mL of water, 1260 g of ferrous sulfate heptahydrate (a reagent manufactured by Wako Pure Chemical Industries), and 120 mL of 95% sulfuric acid (a reagent manufactured by Junsei Kagaku). All the same operations as in Example 3 were performed, and the gas was taken out via the pipes 13 and 15.

  Table 8 shows the reaction time from the start to the end of Comparative Example 1, the concentration and amount of ferrous salt in the solution containing ferrous sulfate accommodated in the reaction tank 1 and the ferric salt produced by the reaction. , Changes in the concentration and amount of nitrate nitrogen in the solution containing nitric acid contained in the reaction tank 4, and the amount and recovery rate of the recovered nitrate nitrogen.

  As a result of reducing the amount of water in the solution containing ferrous sulfate contained in the reaction tank 1 of Example 3 to 1/3 and producing a polyferric sulfate solution, the reaction end point was reached in 180 minutes from the start of the reaction. The ferrous sulfate in the solution containing ferrous sulfate contained in the reaction vessel 1 was all oxidized to ferric iron to produce a polyferric ferric sulfate solution. Nitrate nitrogen remained 1.1%. Moreover, the gas volatilized from the solution containing nitric acid accommodated in the reaction tank 4 remains in the reaction tank 1 and is taken into the produced polyferric sulfate ferric solution, and 40% of the chemical reaction formula amount shown in Chemical formula 4 Only nitrate nitrogen gas was extracted.

(Comparative Example 2)
In Example 1, Example 2, and Example 3, all operations were the same as in Example 1 except that the air pump 8 was further operated for 10 minutes after it was determined and confirmed that each reaction had reached the end point. The gas was taken out via the pipes 13 and 15 to produce a polyferric sulfate solution.

Table 9 shows the concentration of nitrogen remaining in the liquid in the reaction tank 1 when the polyferric sulfate ferric solution was produced in Comparative Example 2.
Compared with Example 1, Example 2, and Example 3, when the circulation pump was operated excessively even after completion of the reaction, nitrate nitrogen remained twice or more in the produced polyferric sulfate solution.

(Example 8)
In the reaction tank 1, 1080 mL of a sulfuric acid solution containing ferrous sulfate composed of 340 mL of water, 1260 g of ferrous sulfate heptahydrate (a reagent manufactured by Wako Pure Chemical Industries) and 100 mL of 95% sulfuric acid (a reagent manufactured by Junsei Kagaku) Housed as a solution containing iron. Then, the valves 17, 18, 19, 20 and 21 were closed, the valves 14 and 24 were opened, the stirrer 2 was operated, and 125 mL of 60% nitric acid was added little by little from the pipe 25. When the nitric acid was added and introduced, the valve 24 was closed and the valve 14 was left open, and stirring was continued as it was.

At this time, the amount of liquid in the reaction tank 1 was 1200 mL. Moreover, the iron (T-Fe) concentration in the liquid in the reaction tank 1 is 210 g / l, and the molar ratio of iron (T-Fe) and nitric acid (T-NO ₃ ) in the reaction tank 1 is 1/2. 76. The gas volatilized from the solution in the reaction tank 1 was taken out via the pipes 13 and 15.

  The progress of the reaction in the reaction tank 1 was monitored and the presence or absence of abnormality was monitored by an instrument 3 attached to the reaction tank 1. The reaction reached the end point in 15 minutes with a stirring time from the change in pH of the reaction tank 1, the change in redox potential, and the change in temperature. Thereafter, the valves 20 and 21 were opened while the stirrer 2 was operated, and the pipe 22 was purged with air for 30 minutes, and the purged gas was taken out via the pipes 13 and 15.

  Table 10 shows the reaction time from the start to the end of Example 8, the concentration and amount of ferrous salt in the solution containing ferrous sulfate accommodated in the reaction tank 1 and the ferric salt produced by the reaction. , Changes in the concentration and amount of nitrate nitrogen added and introduced into the reaction tank 1, and the amount and recovery rate of the recovered nitrate nitrogen.

  The reaction end point was reached in 15 minutes from the start of the reaction, and all of the ferrous iron in the solution containing ferrous sulfate contained in the reaction tank 1 was oxidized to ferric iron to produce a polyferric sulfate solution. It was confirmed. In addition, at the reaction end point, all of the ferrous sulfate heptahydrate that was not dissolved at the start of the reaction was dissolved. Moreover, the nitrate nitrogen in the manufactured polyferric sulfate solution was also less than 0.1%. Further, from the nitric acid added and introduced into the reaction tank 1, nitrate nitrogen gas was taken out almost according to the chemical formula of the chemical reaction shown in Chemical Formula 4.

Example 9
In reaction tank 1, 980 mL of a sulfuric acid solution containing ferrous sulfate composed of 250 mL of water, 1260 g of ferrous sulfate heptahydrate (reagent manufactured by Wako Pure Chemical Industries) and 100 mL of 95% sulfuric acid (reagent manufactured by Pure Chemical) was added to sulfuric acid first. Except for containing as a solution containing iron, the same operation as in Example 8 was performed, and the gas was taken out via the pipes 13 and 15.

At this time, the amount of liquid in the reaction vessel 1 was 1100 mL. Moreover, the iron (T-Fe) concentration in the liquid in the reaction tank 1 is 230 g / l, and the molar ratio of iron (T-Fe) and nitric acid (T-NO ₃ ) in the reaction tank 1 is 1/2. 76.

  Table 11 shows the reaction time from the start to the end of Example 9, the concentration and amount of ferrous salt in the solution containing ferrous sulfate accommodated in the reaction tank 1 and the ferric salt produced by the reaction. , Changes in the concentration and amount of nitrate nitrogen added and introduced into the reaction tank 1, and the amount and recovery rate of the recovered nitrate nitrogen.

  As a result of changing the iron (T-Fe) concentration in the liquid in the reaction tank 1 of Example 8 from 210 g / l to 230 g / l and producing a polyferric sulfate solution, 15 minutes from the start of the reaction. It reached the end point of the reaction, and it was confirmed that all the ferrous iron in the solution containing ferrous sulfate contained in the reaction vessel 1 was oxidized to ferric iron to produce a polyferric sulfate solution. In addition, at the reaction end point, all of the ferrous sulfate heptahydrate that was not dissolved at the start of the reaction was dissolved. Moreover, the nitrate nitrogen in the manufactured polyferric sulfate solution was also less than 0.1%. Further, from the nitric acid added and introduced into the reaction tank 1, nitrate nitrogen gas was taken out almost according to the chemical formula of the chemical reaction shown in Chemical Formula 4.

(Comparative Example 3)
In the reaction tank 1, 900 mL of a sulfuric acid solution containing ferrous sulfate composed of 170 mL of water, 1260 g of ferrous sulfate heptahydrate (a reagent manufactured by Wako Pure Chemical Industries) and 100 mL of 95% sulfuric acid (a reagent manufactured by Junsei Kagaku) Except for containing as a solution containing iron, the same operation as in Example 8 was performed, and the gas was taken out via the pipes 13 and 15.

At this time, the amount of liquid in the reaction vessel 1 was 1020 mL. The molar ratio of iron in the liquid in the reaction tank 1 at (T-Fe) concentration of 250 g / l, iron in the reaction tank 1 (T-Fe) and nitrate (T-NO ₃₎ 1/2. 76.

  Table 12 shows the reaction time from the start to the end of Comparative Example 3, the concentration and amount of ferrous salt in the solution containing ferrous sulfate accommodated in the reaction tank 1 and the ferric salt produced by the reaction. , Changes in the concentration and amount of nitrate nitrogen added and introduced into the reaction tank 1, and the amount and recovery rate of the recovered nitrate nitrogen.

  As a result of changing the iron (T-Fe) concentration in the liquid in the reaction tank 1 of Example 9 from 230 g / l to 250 g / l and producing a polyferric sulfate solution, it took 15 minutes from the start of the reaction. Although the reaction end point has been reached, it has been confirmed that the ferrous sulfate solution contained in the reaction vessel 1 containing ferrous sulfate was oxidized to ferric iron to produce a polyferric sulfate solution. Part of the ferric salt produced when a yellow precipitate is deposited in the polyferric sulfate ferric solution in the reaction tank 1 and the iron (T-Fe) concentration in the reaction tank 1 is higher than 230 g / l. Was found to precipitate. Moreover, 0.23% of nitrate nitrogen remained in the manufactured polyferric sulfate solution.

(Comparative Example 4)
In the reaction tank 1, 1170 mL of a sulfuric acid solution containing ferrous sulfate composed of 450 mL of water, 1260 g of ferrous sulfate heptahydrate (a reagent manufactured by Wako Pure Chemical Industries) and 100 mL of 95% sulfuric acid (a reagent manufactured by Junsei Kagaku) Except for containing as a solution containing iron, the same operation as in Example 8 was performed, and the gas was taken out via the pipes 13 and 15.

At this time, the amount of liquid in the reaction vessel 1 was 1300 mL. Moreover, the iron (T-Fe) concentration in the liquid in the reaction tank 1 is 200 g / l, and the molar ratio of iron (T-Fe) and nitric acid (T-NO ₃ ) in the reaction tank 1 is 1/2. 76.

  Table 13 shows the time from the start of Comparative Example 4 to the end of the reaction operation, the concentration of the ferrous salt in the solution containing ferrous sulfate contained in the reaction tank 1 and the ferric salt produced by the reaction. Changes in the amount, changes in the concentration and amount of nitrate nitrogen added and introduced into the reaction tank 1, and the amount and recovery rate of the recovered nitrate nitrogen are shown.

  As a result of changing the iron (T-Fe) concentration in the liquid in the reaction tank 1 of Example 8 from 210 g / l to 200 g / l and producing a polyferric sulfate solution, it took 15 minutes from the start of the reaction. Even if the reaction is almost completed and stirring is continued for 24 hours thereafter, the ferrous iron in the solution containing ferrous sulfate contained in the reaction vessel 1 is not oxidized to ferric iron even after the reaction operation is completed. If ferrous iron (Fe (II)) remains in the liquid in the reaction tank 1 at 7.5 g / l and the iron (T-Fe) concentration in the reaction tank 1 is less than 210 g / l, It was confirmed that the oxidation to ferric iron was insufficient.

(Comparative Example 5)
The same operation as in Example 8 was performed except that 118 mL of 60% nitric acid was added to the reaction tank 1 little by little, and the gas was taken out via the pipes 13 and 15.

At this time, the amount of liquid in the reaction vessel 1 was 1190 mL. Moreover, the iron (T-Fe) concentration in the liquid in the reaction tank 1 is 210 g / l, and the molar ratio of iron (T-Fe) and nitric acid (T-NO ₃ ) in the reaction tank 1 is 1/2. 93.

  Table 14 shows the time from the start of Comparative Example 5 to the end of the reaction operation, the concentration of ferrous salt in the solution containing ferrous sulfate accommodated in the reaction tank 1 and the ferric salt produced by the reaction. Changes in the amount, changes in the concentration and amount of nitrate nitrogen added and introduced into the reaction tank 1, and the amount and recovery rate of the recovered nitrate nitrogen are shown.

The molar ratio of iron (T-Fe) and nitric acid (T-NO ₃ ) in the reaction tank 1 of Example 8 was changed from 1 / 2.76 to 1 / 2.93 to produce a polyferric sulfate ferric solution. As a result, the reaction was almost finished in 15 minutes from the start of the reaction, and even after stirring was continued for 24 hours, the ferrous iron in the solution containing ferrous sulfate contained in the reaction tank 1 was finished. After that, all was not oxidized to ferric iron, and 4.9 g / l of ferrous iron (Fe (II)) remained in the liquid in the reaction tank 1, and iron (T-Fe) and nitric acid in the reaction tank 1 remained. It was confirmed that when the molar ratio of (T-NO ₃ ) is smaller than 1 / 2.9, oxidation from ferrous iron to ferric iron becomes insufficient.

(Comparative Example 6)
The same operation as in Example 8 was performed except that 130 mL of 60% nitric acid was added to the reaction tank 1 little by little, and the gas was taken out via the pipes 13 and 15.

At this time, the amount of liquid in the reaction vessel 1 was 1205 mL. Moreover, the iron (T-Fe) concentration in the liquid in the reaction tank 1 is 210 g / l, and the molar ratio of iron (T-Fe) and nitric acid (T-NO ₃ ) in the reaction tank 1 is 1/2. 65.

  Table 15 shows the time from the start of Comparative Example 6 to the end of the reaction operation, the concentration of ferrous salt in the solution containing ferrous sulfate accommodated in the reaction tank 1 and the ferric salt produced by the reaction. Changes in the amount, changes in the concentration and amount of nitrate nitrogen added and introduced into the reaction tank 1, and the amount and recovery rate of the recovered nitrate nitrogen are shown.

The molar ratio of iron (T-Fe) and nitric acid (T-NO ₃ ) in the reaction tank 1 of Example 8 was changed from 1 / 2.76 to 1 / 2.65, and the production of the polyferric sulfate ferric sulfate solution was performed. As a result, the reaction end point was reached in 15 minutes from the start of the reaction, and all of the ferrous iron in the solution containing ferrous sulfate contained in the reaction tank 1 was oxidized to ferric iron, and the polyferric sulfate solution However, when the molar ratio of iron (T-Fe) and nitric acid (T-NO ₃ ) in the reaction vessel 1 is larger than 1 / 2.7, the amount of nitric acid added and introduced increases. Not only economical, but also 0.18% nitrate nitrogen remained in the manufactured ferric sulfate solution.

Claims (14)

The molar ratio of the pre-iron gas evaporated from a solution containing nitric acid (T-Fe) and sulfuric acid (T-SO ₄₎ is adjusted to _1.0 <(T-SO 4 /T-Fe)<1.5 Blowing into a solution containing ferrous sulfate, and blowing a gas that volatilizes from the solution containing ferrous sulfate into the solution containing nitric acid, between the solution containing nitric acid and the solution containing ferrous sulfate. A method for producing a ferric sulfate sulfate solution, wherein the ferrous sulfate in the solution containing ferrous sulfate is converted to ferric sulfate by circulating gas. The method for producing a ferric sulfate polyferric acid solution according to claim 1, wherein the solution containing nitric acid is a nitric acid solution or an acidic solution of nitrate. The method for producing a ferric sulfate polysulfate solution according to claim 1 or 2, wherein the solution containing ferrous sulfate is added with nitric acid or nitrate in advance. The method for producing a polyferric sulfate solution according to any one of claims 1 to 3, wherein a part of the gas that volatilizes is removed from the solution containing ferrous sulfate. Gas circulation between the solution containing nitric acid and the solution containing ferrous sulfate is performed in a closed system, and when the inside of the closed system exceeds a predetermined pressure, from the solution containing ferrous sulfate The method for producing a ferric sulfate polysulfate solution according to claim 4, wherein a part of the volatilizing gas is discharged to the outside of the closed system and removed. The conversion reaction to polyferric sulfate is controlled by monitoring the pH and oxidation-reduction potential of the solution containing nitric acid and the solution containing ferrous sulfate. A process for producing a ferric sulfate ferric sulfate solution according to claim 1. At the end point of the conversion reaction to polysulfuric acid ferric sulfate, the circulation of gas between the nitric acid-containing solution is stopped, and purge gas is blown into the polysulfuric acid ferric sulfate solution to remove residual nitrate nitrogen. The method for producing a polyferric sulfate ferric sulfate solution according to any one of claims 1 to 6. Previously iron (T-Fe) and stirred solution molar ratios including _1.0 <(T-SO 4 ferrous sulfate adjusted to /T-Fe)<1.5 sulfate (T-SO ₄₎ However, the molar ratio of iron (T-Fe) to nitric acid (T-NO ₃ ) is (1 / 2.9) <(T-NO ₃ /T-Fe)<(1/2.2.7), and By adding nitric acid to the solution containing ferrous sulfate so that the iron (T-Fe) concentration becomes 210 g / l to 230 g / l, and then continuing stirring, the ferrous sulfate is reduced. A method for producing a ferric sulfate polysulfate solution, comprising converting ferrous sulfate in a solution containing the solution into polyferric sulfate ferric sulfate. A conversion reaction from the solution containing ferrous sulfate after addition of nitric acid to polyferric sulfate is performed in an open system, and the gas that volatilizes from the solution containing ferrous sulfate is discharged to the outside and removed. The method for producing a polyferric sulfate solution according to claim 8. The conversion reaction from the solution containing ferrous sulfate after addition of nitric acid to polyferric sulfate is performed in a closed system, and when the inside of the closed system exceeds a predetermined pressure, the ferrous sulfate The method for producing a ferric sulfate polysulfate solution according to claim 8, wherein a part of the gas that volatilizes from the solution containing slag is discharged out of the closed system and removed. 11. The poly according to claim 8, wherein the conversion reaction to polyferric sulfate is controlled by monitoring the pH and redox potential of the solution containing ferrous sulfate. A method for producing a ferric sulfate solution. The polynitric acid according to any one of claims 8 to 11, wherein at the end of the conversion reaction to polyferric sulfate, the remaining nitrate nitrogen is removed by blowing a purge gas into the ferric sulfate solution. A method for producing a ferric sulfate solution. The method for producing a polyferric sulfate solution according to any one of claims 4, 5, 7, 9, 10, and 12, wherein the removed gas is recovered as nitric acid. 14. The method for producing a polyferric sulfate ferric sulfate solution according to claim 13, wherein the collected nitric acid is reused as a solution containing nitric acid or nitric acid.

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