JP3532095B2 - Method for producing ferric polysulfate solution and apparatus for performing the method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a ferric polysulfate solution used as a coagulant for sewage, night soil, or various industrial wastewater, and an apparatus therefor, and particularly to a low nitrogen polyferric sulfate solution. The present invention relates to a method for producing another ferric polysulfate solution by utilizing nitrogen oxides removed during production as an oxidant, and an apparatus for carrying out the method.

[0002]

2. Description of the Related Art A ferric polysulfate solution is compared with a ferric chloride solution which has been conventionally generally used as an iron-based flocculant.
It has the advantages of low corrosivity and low pH drop, and has been widely used as a coagulant for sewage, night soil, and various industrial wastewater. As its manufacturing method, Japanese Patent Publication No. 51-17516 (Patent No. 842085)
Sulfuric acid in ferrous sulfate solution as described in
It is adjusted to be less than 0.5 mol with respect to 1 mol of ferrous sulfate, and is oxidized with an oxidizing agent such as oxygen, nitrogen oxide, manganese dioxide or the like. Usually, inexpensive nitrogen oxide such as sodium nitrite is used as a catalyst, and it is often produced by a closed reactor in order to improve the oxidation reaction rate and prevent leakage of nitrogen oxide gas. In addition, the nitrogen oxide used at this time is the same as the produced polysulfuric acid secondary compound in the closed reactor.
Almost 100% remains in the iron solution. The nitrogen oxide in this case also functions as a "catalyst", but also functions as an "indispensable auxiliary material" oxidizing agent in the production of polyiron sulfate.

[0003]

When a ferric polysulfate solution is produced by using an inexpensive nitrogen oxide as a catalyst, the polyferric sulfate solution produced is derived from nitrogen oxide which is an oxidant. When the amount of nitrogen content to be contained is several hundred to several thousand mg / liter and the destination of use is a closed water area, eutrophication in the water area becomes a problem, and 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. Therefore, the present applicants previously described in Japanese Patent Application No. 8-95662, a low-nitrogen polysulfate No. 2 in which a nitrogen oxide is used as a primary oxidizing agent and a nitrogen-free oxidizing agent is used as a secondary oxidizing agent. A method for producing an iron solution was proposed, and as an improvement plan thereof, in Japanese Patent Application No. 9-192767, it was proposed to add the secondary oxidizing agent little by little. Further, the oxidation reaction rate of this reaction can be improved by increasing the molar ratio of nitrogen oxide and ferrous ion. However, increasing the amount of nitrogen oxide used causes an increase in the nitrogen content contained in the ferric polysulfate solution, which is not preferable for the above reason. Furthermore, when sodium nitrite is used as nitrogen oxide, the produced polysulfate second
The amount of sodium contained in the iron solution also increases, and a precipitate is produced as sodium gyrosite, which causes blockage of the pump and the like, which is not preferable.

As a result of further studies on such a proposal, the present invention makes it possible to use again the removed nitrogen component as an oxidizing agent for the production of polyferric sulfate without leaking out of the system. It is possible to produce a ferric sulfate polysulfate solution with a controlled amount, improve the reaction rate, and reduce the content of sodium.
Furthermore, it aims at opening the possibility of constructing a closed system in the production of ferric polysulfate solution.

[0005]

According to the present invention, the above object is to provide iron sulfate containing a predetermined amount of iron salt and having a molar ratio of iron of the iron salt to sulfuric acid adjusted to 1 or more and 1.5 or less. The first step of producing a ferric polysulfate solution by oxidizing divalent iron in the solution to trivalent iron with oxygen or nitrogen using nitrogen oxides as a catalyst, and the resulting ferric polysulfate solution. A divalent iron salt or metallic iron as a reducing agent to the nitrogen content to remove the nitrogen content as nitrogen oxide gas, and the nitrogen content removed in the second step to oxygen or Along with nitrogen, an iron sulfate solution prepared in the same manner as described above is supplied to the reaction phase which is being oxidized by oxygen or air using nitrogen oxide as a catalyst, and the divalent iron is oxidized to trivalent iron to produce polysulfate second. The ferric polysulfate solution is produced by the third step of producing the iron solution. To. Here, the nitric oxide gas generated and removed in the second step is used as the oxygen-containing fluid in the third
It is important and necessary to be supplied to the process. That is, if the nitric oxide gas generated in the second step is allowed to stay in the reaction tank as it is, it is absorbed again in the ferric polysulfate solution and the removal of the nitrogen component will not be successful. The nitric oxide gas generated and removed in the process is used as an oxygen-containing fluid and is replaced as the oxygen gas consumed in the third process. When divalent iron is oxygen-oxidized using nitrogen oxides as a catalyst, the general formula [Fe2 (OH) n (SO4) 3-n / 2] m (however,
It is known that ferric polysulfate represented by n <2, m> 10) is produced. Therefore, although the amount of nitrogen oxide used varies depending on the difference in the oxidation rate and the efficiency of the apparatus, when the amount of iron sulfate to be oxidized is equivalent to the amount of nitrogen oxide used in the first step, the above second step is used. The nitrogen content removed in step 3 is used in the third step to produce a ferric polysulfate solution containing low nitrogen in the first reaction vessel and a normal amount of nitrogen in the second reaction vessel. Therefore, when the two reaction tanks are viewed in total, they react with iron sulfate in an equivalent amount of about half, and it is possible to efficiently produce ferric polysulfate. Further, the amount of nitrogen oxides has a close relationship with the oxidation reaction rate, and the presence of a predetermined amount of nitrogen component in the reaction step contributes to promotion of the reaction rate. In other words, if the sodium nitrite in the first reaction tank is supplied in an amount larger than the predetermined amount, the second
In the reaction tank, the ferric polysulfate solution is more efficiently produced by the nitric oxide gas derived from the first tank.

[0006]

[Chemical 1]

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 equipped with a stirring means and a circulation pump,
These first and second reaction tanks are connected via a valve,
The first and second reaction tanks are arranged so that iron sulfate solution, sulfuric acid, oxygen-containing fluid, and nitrogen oxide can be supplied respectively. It is preferable that each of the above reaction tanks is provided with an oxidation-reduction potentiometer, because the residual amount of nitrogen and the oxidation state can be grasped.

[0008]

DETAILED DESCRIPTION OF THE INVENTION The details of the present invention will be described based on the following examples. Naturally, the following examples illustrate the present invention and do not limit the technical scope of the present invention.

FIG. 1 shows a schematic of a batch-type facility for carrying out the method according to the invention to enable a closed system for the production of ferric sulphate solutions. Therefore,
In order to continuously carry out the method according to the present invention, it is necessary to provide a pipe facility for supplying the iron sulfate solution, the sulfuric acid, the oxygen-containing fluid, and the nitrogen oxides arbitrarily. The first reaction tank 1 is a reactor for producing a conventional ferric polysulfate solution. An agitator 2 and a circulation pump 3 are attached to the first reaction tank 1. Further, an oxidation-reduction potentiometer 4, a pressure gauge 5, and a thermometer 6 are attached. A pipe is provided so that oxygen can be supplied to the first reaction tank 1, and a ferrous sulfate liquid tank 7 is also connected so that ferrous sulfate can be supplied.

The second reaction tank 11 is a reactor for carrying out the method according to the present invention, and like the first reaction tank 1, the stirrer 12 and the circulation pump 113 are attached, and the redox potential meter 14, A pressure gauge 15 and a thermometer 16 are attached. The first reaction tank 1 and the second reaction tank 11 are the first
It is connected via a valve 20 so as to be openable and closable. In addition, the first reaction tank 1 and the second reaction tank 11 are connected via the second valve 21 and the third valve 22, respectively, to the sodium nitrite liquid tank 25.
It is connected so that it can be opened and closed freely and is supplied with sodium nitrite.

In the equipment having the above-mentioned structure, 135 kg of ferrous sulfate, 58 kg of water, 17.3 kg of 75% sulfuric acid
Was weighed and put in the first reaction tank 1. With the first valve 20 closed, operate the stirrer 2 and the circulation pump 3,
While the second valve 21 is opened, a total of 6.5 kg of 10% sodium nitrite solution is intermittently supplied from the sodium nitrite solution tank 25 while oxygen is supplied so as to keep the internal pressure at 0.2 kgf / cm 2. Since the first ferric polysulfate solution was obtained in 4 hours by oxidizing 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 / liter in total iron concentration, 0.05 g / liter or less in divalent iron concentration, 381 g / liter in SO4 concentration, 3.9 g / liter in NO3 concentration, and Na concentration. It is 1.4 g / liter and the liquid temperature is 6
The temperature was 2 ° C., the redox potential was 775 mV, and the liquid volume was 150 liters.

Next, the first valve 20 is opened and the sulfuric acid first
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 were operated, the third valve 22 was opened, and the 10% sodium nitrite solution was adjusted to 0. 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 0.2 kgf /
Oxygen was supplied again to the first reactor so as to keep it at cm 2. At the same time, the ferrous sulfate solution adjusted to an iron concentration of about 120 g / liter and about 40 ° C. was transferred from the liquid tank 7 to the first reaction tank 1.
It was added until the redox potential reached 690 mV. About 10
After 700 minutes, the voltage increased to 700 mV, and therefore ferrous sulfate solution was added from the liquid tank 7 to the first reaction tank 1 again until the redox potential reached 690 mV. This operation is repeated until the oxidation-reduction potential does not rise, and the total iron concentration is 164 g / liter and the divalent iron concentration is 0.05 g with a low nitrogen content.
/ Liter or less, SO4 concentration 372g / liter, NO3
A second ferric polysulfate (low nitrogen polyiron sulfate) solution having a concentration of 0.7 g / liter and a Na concentration of 1.2 g / liter was obtained. At this time, the liquid temperature is 57 ° C and the redox potential is 698 m.
V, the liquid volume was 175 liters. Further, this operation required about 2 hours, and the iron sulfate solution used was about 25 liters. After a further 1 hour, the supply rate of oxygen decreased, so 0.4 kg of 10% sodium nitrite solution was supplied to the second reaction tank. After 30 minutes, total iron concentration 174 g / liter, divalent iron concentration 0.05 g / liter or less, SO4 concentration 376 g / liter, NO3 concentration 3.7 g / liter,
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 redox potential was 765 mV, and the liquid volume was 145 liters.

The amount charged into each reaction tank in the above example is summarized in Table 1, and the analysis results are shown in Table 2. The nitrogen content in the polyferric sulfate produced in the second reaction tank is converted into NO3 by the amount of NOx supplied from the first reaction tank to the second reaction tank and the amount of sodium nitrite supplemented to some extent. It becomes 3.7 g / liter. Further, by repeatedly applying this operation to the polyiron sulfate obtained in the second reaction tank, nitrogen oxides can be used extremely efficiently. Further, depending on the value of the redox potential monitored, a ferric polysulfate solution containing an arbitrary nitrogen content can be prepared. When the oxidation-reduction potential in the first reaction tank was 720 mV, the NO3 concentration contained was 1.5 g / liter.

[0014]

[Table 1]

[0015]

[Table 2]

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

Further, when the NOx absorption efficiency in the second reaction tank is calculated, the NOx gas amount generated in the first reaction tank is 132-27 = 105 g in terms of N from the above, and the third ferric polysulfate The nitrogen content contained in the solution was 145 (liters) × 3.7 (g / liter) × (14/62) = 12.
1 g, and the nitrogen content derived from sodium nitrite in the third ferric polysulfate solution was 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 third ferric polysulfate solution with respect to Ox gas was 103 ÷ 105 × 100 = 98%.

Further, as can be understood from the sodium concentration in the analysis result of Table 2, the amount of sodium in the first ferric sulfate sulfate solution is 1.4 g, and the third ferric sulfate sulfate solution is compared with the sodium content. The amount of sodium in it is 0.2g, and 1
The amount of SS generated in the product was reduced to / 7.

[0019]

According to the present invention, the NOx gas removed by the denitration step of the ferric polysulfate solution can be used for the production of another ferric polysulfate solution, and the NOx gas is released to the atmosphere. Since it does not need a catalyst raw material, the reaction rate can be accelerated. Furthermore, by using NOx gas as a catalyst, the amount of SS generated in the generated ferric polysulfate solution is reduced, and the problems associated with the generation of SS can be reduced.

[Brief description of drawings]

FIG. 1 is a conceptual diagram illustrating a step of newly producing a ferric polysulfate solution using NOx gas generated during the production of a low nitrogen polyferric sulfate solution.

[Explanation of symbols]

1,11 Reactor 2,12 stirrer 3,13 Circulation pump

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Keita Yamada Keita Yamada, Kanayama, Koriyama, Fukushima 47 Maseguchi, Asaka RIKEN CORPORATION (72) Mitsuhiko Kudo 47, Maseguchi, Kanaya, Kumayama, Koriyama, Fukushima Prefecture Address Asaka Riken Kogyo Co., Ltd. (72) Inventor Yukio Sakuma 47, Kanaya, Tamura-cho, Koriyama City, Fukushima Prefecture Akaka Riken Kogyo Co., Ltd. (56) Reference JP-A-9-278447 (JP, A) Flat 8-225326 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C01G 49/14 B01D 21/01 102

Claims (6)

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