JPH11278849A - Method for producing ferric polysulfate solution and apparatus for performing the method - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To enable a nitrogen component removed in the production of a ferric polysulfate solution to be used again as an oxidizing agent for the production of polyiron sulfate without leaking out of the system. A ferric polysulfate solution with a controlled nitrogen content is produced. SOLUTION: Ferrous iron in a ferrous sulfate solution containing a predetermined amount of iron salt and having a molar ratio of iron to sulfuric acid of the iron salt adjusted to a predetermined range is converted into trivalent iron by nitrogen oxide and oxygen / air. A first step of producing a ferric polysulfate solution by oxidizing the ferric polysulfate solution, and adding a divalent iron salt or metallic iron to the nitrogen content contained in the obtained ferric polysulfate solution. A second step of removing nitrogen, and a reaction of oxidizing the iron sulfate solution prepared in the same manner as described above with nitrogen oxides and oxygen / air together with oxygen / air with the nitrogen removed in the second step. Feeding the phase to produce a ferric polysulfate solution to produce a ferric polysulfate solution.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a ferric polysulfate solution used as a flocculant for sewage, human waste, or various industrial wastewaters, and an apparatus therefor. The present invention relates to a method for producing another ferric polysulfate solution using nitrogen oxides removed during production as an oxidizing agent, and an apparatus for performing the method.

[0002]

2. Description of the Related Art A ferric polysulfate solution is different from a ferric chloride solution conventionally used generally as an iron-based flocculant.
It has the advantages of low corrosivity and little pH drop, and has been widely used as a flocculant for sewage, human waste, and various industrial wastewaters. Japanese Patent Publication No. 51-17516 (Japanese Patent No. 842085) discloses a method for producing the same.
The sulfuric acid in the ferrous sulfate solution, as described in
It is adjusted so as to be less than 0.5 mol per 1 mol of ferrous sulfate, and is oxidized by an oxidizing agent such as oxygen, nitrogen oxide or manganese dioxide. Usually, inexpensive nitrogen oxides such as sodium nitrite are used as catalysts, and they are often produced by a closed-type reactor in order to improve the oxidation reaction rate and prevent the leakage of nitrogen oxide gas. In this case, the nitrogen oxide used in the reaction system of the closed system was produced polysulfuric acid secondarily.
Almost 100% remains in iron solution. In this case, the nitrogen oxide functions as a “catalyst”, but also functions as an oxidizing agent as an “indispensable auxiliary material” in producing iron polysulfate.

[0003]

In the case of producing a ferric polysulfate solution using an inexpensive nitrogen oxide as a catalyst, the produced ferric polysulfate solution contains nitrogen oxide as an oxidizing agent. The nitrogen content to be contained is several hundred to several thousand mg / liter, and when the place of use falls in a closed water area, eutrophication in the water area becomes a problem, and the reduction of nitrogen content is strongly desired. is there. Therefore, it is important to use a ferric polysulfate solution having a different nitrogen content depending on the application. In view of this, the present applicants previously disclosed in Japanese Patent Application No. 8-95662 a low-nitrogen polysulfuric acid sulfate produced by oxidizing nitrogen oxide as a primary oxidizing agent and using an oxidizing agent containing no nitrogen as a secondary oxidizing agent. A method for producing an iron solution was proposed, and as an improvement, Japanese Patent Application No. 9-192767 proposed that the secondary oxidizing agent be added little by little. Further, the oxidation reaction rate of this reaction can be improved by increasing the molar ratio of nitrogen oxide to ferrous ion. However, increasing the use amount of nitrogen oxides causes an increase in the amount of nitrogen contained in the ferric polysulfate solution, which is not preferable for the above reason. Further, when sodium nitrite is used as the nitrogen oxide, the produced polysulfuric acid
The amount of sodium contained in the iron solution also increases, and precipitates are generated as sodium gyrosite, which causes clogging of the pump and the like, which is not preferable.

[0004] As a result of further study on such a proposal, the present invention has made it possible to use the removed nitrogen component as an oxidizing agent for the production of polyiron sulfate without leaking out of the system. It is possible to produce a ferric polysulfate solution with a controlled amount, to improve the reaction rate, and to reduce the sodium content,
Another object of the present invention is to open the possibility of constructing a closed system in the production of a ferric polysulfate solution.

[0005]

According to the present invention, there is provided an iron sulfate containing a predetermined amount of iron salt, wherein the molar ratio of iron to sulfuric acid in the iron salt is adjusted to 1 or more and 1.5 or less. A first step of producing a ferric polysulfate solution by oxidizing ferrous iron in the solution to trivalent iron with oxygen or nitrogen using a nitrogen oxide as a catalyst, and containing the ferric polysulfate solution obtained A second step of adding a divalent iron salt or metallic iron as a reducing agent to the nitrogen content to remove the nitrogen content as nitric oxide gas, and converting the nitrogen content removed in the second process to oxygen or Along with nitrogen, an iron sulfate solution prepared in the same manner as described above is supplied to a reaction phase oxidized by oxygen or air using nitrogen oxides as a catalyst, and the ferrous iron is oxidized to ferric iron to form polysulfate. Producing a ferric polysulfate solution by the third step of producing an iron solution. To. Here, the nitrogen oxide gas generated and removed in the second step is converted into an oxygen-containing fluid immediately after the generation as the third gas.
It is important and necessary to be supplied to the process. That is, if the nitric oxide gas generated in the second step is kept in the reaction tank as it is, it is absorbed again in the ferric polysulfate solution there, and the operation for removing nitrogen does not work. The nitrogen oxide gas generated and removed in the step is replaced as an oxygen-containing fluid as the oxygen gas consumed in the third step. When oxygen is oxidized from ferrous iron using nitrogen oxides as a catalyst, the general formula [Fe2 (OH) n (SO4) 3-n / 2] m (where
It is known that ferric polysulfate represented by n <2, m> 10) is produced. Therefore, the amount of nitrogen oxide used varies depending on the oxidation rate and the difference in efficiency depending on the apparatus. However, when the amount of iron sulfate to be oxidized with respect to the amount of nitrogen oxide used in the first step is equivalent, The nitrogen component removed in step 3 is used in the third step to produce a ferric polysulfate solution containing low nitrogen in the first reactor and a normal amount of nitrogen in the second reactor. When the two reaction tanks are considered in total, they react with iron sulfate in an equivalent amount of about half, so that ferric polysulfate can be efficiently produced. Further, the amount of nitrogen oxide has a close relationship with the oxidation reaction rate, and the presence of a predetermined amount of nitrogen in the reaction step contributes to the acceleration of the reaction rate. In other words, when sodium nitrite in the first reaction tank is supplied in a larger amount than the predetermined amount,
The ferric polysulfate solution can be produced even more efficiently in the reaction tank using the nitrogen oxide gas derived from the first tank.

[0006]

Embedded image

In order to carry out the above method, the apparatus for producing a ferric polysulfate solution according to the present invention comprises a first reaction tank and a second reaction tank each provided with a stirring means and a circulation pump, respectively.
These first and second reaction vessels are connected via a valve,
The first and second reaction tanks are configured to be piped so that an iron sulfate solution, sulfuric acid, an oxygen-containing fluid, and nitrogen oxide can be respectively supplied. It is preferable that an oxidation-reduction potentiometer is attached to each of the reaction tanks, since the residual amount of nitrogen and the oxidation state can be grasped.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described based on the following examples. Of course, the following examples illustrate the present invention and do not limit the technical scope of the present invention.

FIG. 1 shows an outline of a batch-type facility for implementing a method according to the present invention to realize a closed system for producing a ferric polysulfate solution. Therefore,
In order to continuously carry out the method according to the present invention, it is necessary to provide a piping system capable of arbitrarily supplying an iron sulfate solution, sulfuric acid, an oxygen-containing fluid, and nitrogen oxide. The first reaction tank 1 is a reactor for producing a conventional ferric polysulfate solution. The first reaction tank 1 is provided with a stirrer 2 and a circulation pump 3. Further, an oxidation-reduction potentiometer 4, a pressure gauge 5, and a thermometer 6 are additionally provided. A pipe is provided so as to supply oxygen to the first reaction tank 1, and a ferrous sulfate liquid tank 7 is also connected so as to supply ferrous sulfate.

The second reaction tank 11 is a reactor for carrying out the method according to the present invention. As in the first reaction tank 1, a stirrer 12 and a circulating pump 113 are attached, and an oxidation-reduction potentiometer 14, A pressure gauge 15 and a thermometer 16 are provided. The first reaction tank 1 and the second reaction tank 11
It is openably and closably connected via a valve 20. Further, the first reaction tank 1 and the second reaction tank 11 are connected to the sodium nitrite liquid tank 25 via the second valve 21 and the third valve 22, respectively.
And openably and closably connected to supply sodium nitrite.

In the equipment having the above configuration, 135 kg of ferrous sulfate, 58 kg of water, and 17.3 kg of 75% sulfuric acid are used.
Was weighed and placed in the first reaction tank 1. With the first valve 20 closed, the stirrer 2 and the circulation pump 3 are operated,
While opening the second valve 21 and intermittently supplying 6.5 kg of 10% sodium nitrite solution from the sodium nitrite solution tank 25 in total, oxygen is supplied so as to maintain the internal pressure at 0.2 kgf / cm 2. Since the first ferric polysulfate solution was obtained in 4 hours by oxidizing the trivalent iron into trivalent iron, the circulation pump 3 was stopped. At this time, the concentration of the first ferric polysulfate solution was 171 g / L of total iron concentration, 0.05 g / L or less of divalent iron, 381 g / L of SO4 concentration, 3.9 g / L of NO3 concentration, and Na concentration. 1.4 g / liter and the liquid temperature was 6
At 2 ° C., the oxidation-reduction potential was 775 mV, and the liquid volume was 150 liters.

Next, the first valve 20 is opened, and sulfuric acid
The stirrer 12 and the circulation pump 13 in the second reaction tank 11 containing 135 kg of iron, 58 kg of water and 17.3 kg of 75% sulfuric acid are operated, and the third valve 22 is opened to add 10% sodium nitrite solution to 0.1%. 5 kg is supplied to the second reaction tank 11, and the internal pressure of the first reaction tank 1 and the second reaction tank 11 is set to 0.2 kgf /
Oxygen was supplied again to the first reaction tank so as to maintain the pressure in cm 2. Simultaneously, a ferrous sulfate solution adjusted to about 40 ° C. with an iron concentration of about 120 g / liter was supplied from the liquid tank 7 to the first reaction tank 1,
It was added until the oxidation-reduction potential reached 690 mV. About 10
One minute later, the pressure rose to 700 mV, so that a ferrous sulfate solution was added again from the liquid tank 7 to the first reaction tank 1 until the oxidation-reduction potential reached 690 mV. This operation is repeated until the oxidation-reduction potential no longer increases, and the nitrogen content is low, the total iron concentration is 164 g / liter, and the divalent iron concentration is 0.05 g.
/ Liter or less, SO4 concentration 372g / liter, NO3
A second ferric polysulfate (low-nitrogen polysulfate) solution having a concentration of 0.7 g / liter and a sodium concentration of 1.2 g / liter was obtained. At this time, the liquid temperature was 57 ° C., and the oxidation-reduction potential was 698 m
V, the liquid volume was 175 liters. This operation took about 2 hours, and the amount of the used iron sulfate solution was about 25 liters. After an additional hour, the supply rate of oxygen decreased, so 0.4 kg of a 10% sodium nitrite solution was supplied to the second reaction tank. After 30 minutes, the total iron concentration is 174 g / l, the divalent iron concentration is 0.05 g / l or less, the SO4 concentration is 376 g / l, the NO3 concentration is 3.7 g / l,
A third ferric polysulfate solution having a Na concentration of 0.2 g / liter was obtained. At this time, the liquid temperature was 63 ° C., the oxidation-reduction potential was 765 mV, and the liquid volume was 145 liters.

Table 1 summarizes the amount charged to each reaction tank in the above example, and Table 2 shows the analysis results. Note that the nitrogen content in the polyiron sulfate produced in the second reaction tank is converted into NO3 by the supply amount of NOx generated from the first reaction tank to the second reaction tank and the amount of sodium nitrite replenished slightly. It becomes 3.7 g / liter. Also, by repeatedly applying this operation to the iron polysulfate obtained in the second reaction tank, the nitrogen oxide can be used very efficiently. Further, depending on the value of the oxidation-reduction potential to be monitored, a ferric polysulfate solution containing an arbitrary nitrogen content is obtained. When the oxidation-reduction potential in the first reaction tank was set to 720 mV, the contained NO3 concentration was 1.5 g / liter.

[0014]

[Table 1]

[0015]

[Table 2]

From the above results, it was found that N generated in the first reaction tank
When the removal rate of Ox is calculated in terms of N, the first polysulfuric acid second
The nitrogen content in the iron solution was 150 (liter) × 3.
9 (g / liter) × (14/62) = 132 g, and the nitrogen content in the ferric polysulfate solution is 17
5 (liter) x 0.7 (g / liter) x (14/6
2) = 27 g, thus (132-27) ÷
132 × 100 = 80% reduction.

Further, when the NOx absorption efficiency in the second reaction tank is calculated, the amount of NOx gas generated in the first reaction tank is 132-27 = 105 g in terms of N, and the third ferric polysulfate is The nitrogen content in the solution was 145 (liter) × 3.7 (g / liter) × (14/62) = 12
1 g, and the nitrogen content derived from sodium nitrite in the ferric tertiary polysulfate solution is 0.9 kg × 0.1 × (1
4/69) = 18 g, the absorbed nitrogen content not derived from sodium nitrite is 121-18 = 103 g, and the generated N
The nitrogen absorption efficiency of the ferric tertiary polysulfate solution with respect to Ox gas was 103/105 × 100 = 98%.

Further, as can be understood from the sodium concentration in the analysis results in Table 2, the amount of sodium in the third ferric polysulfate solution was compared with the amount of sodium in the first ferric polysulfate solution of 1.4 g. The amount of sodium in it is 0.2 g,
/ 7, and the amount of SS generated in the product was reduced.

[0019]

According to the present invention, the NOx gas removed in the denitration step of the ferric polysulfate solution can be used for producing another ferric polysulfate solution, and the NOx gas is released to the atmosphere. This eliminates the need for a catalyst and requires less raw material for the catalyst, and can promote the reaction rate. Further, by using the NOx gas as a catalyst, the amount of SS generated in the generated ferric polysulfate solution is reduced, and the problem associated with the generation of SS can be reduced.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram illustrating a process of newly producing a ferric polysulfate solution using NOx gas generated when producing a low-nitrogen polyferric sulfate solution.

[Explanation of symbols]

 1,11 Reaction tank 2,12 Stirrer 3,13 Circulation pump

 ──────────────────────────────────────────────────の Continuing from the front page (72) Keita Yamada 47, Maseguchi, Kanaya, Tamura-cho, Koriyama-shi, Fukushima Prefecture Inside of Asaka Riken Kogyo Co., Ltd. Address: Asaka Riken Kogyo Co., Ltd. (72) Inventor: Yukio Sakuma 47, Maseguchi, Kanaya, Tamuracho, Koriyama

Claims (6)

[Claims] 1. An iron sulfate solution containing a predetermined amount of iron salt and having a molar ratio of iron to sulfuric acid of from 1 to 1.5 adjusted to iron (II) in a nitrogen oxide catalyst. A first step of producing a ferric polysulfate solution by oxidizing to iron (III) with oxygen or air, and divalent iron as a reducing agent for nitrogen contained in the obtained ferric polysulfate solution A second step of removing the nitrogen content by adding a salt or metallic iron;
The nitrogen component removed in the second step is supplied together with oxygen or air, and the iron sulfate solution adjusted in the same manner as above is supplied to a reaction phase oxidized with oxygen or air using nitrogen oxides as a catalyst. A step of producing a ferric polysulfate solution by the third step of producing a ferric polysulfate solution by oxidizing ferrous iron to ferric iron. 2. The method according to claim 1, wherein the ferric polysulfate solution is produced with an amount of nitrogen oxides corresponding to half equivalent. 3. The method according to claim 1, wherein the second step and the third step are repeatedly performed on the ferric polysulfate solution obtained in the third step. 4. The method according to claim 1, wherein the nitrogen content is controlled within a predetermined range by monitoring the oxidation-reduction potential.
The method according to any one of claims 1 to 3. 5. A first reaction tank (1) and a second reaction tank (11) each provided with a stirring means (2, 12) and a circulation pump (3, 13), and the first and second reaction tanks are provided. (1, 11) is connected via a valve, and piping is provided to these first and second reaction tanks (1, 11) so that an iron sulfate solution, sulfuric acid, an oxygen-containing fluid, and nitrogen oxide can be respectively supplied. An apparatus for producing a ferric polysulfate solution. 6. The production apparatus according to claim 5, wherein an oxidation-reduction potentiometer is attached to each of the reaction tanks (1, 11).