JPH1135328A - Production of low-nitrogen polyferric sulfate solution - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the method for producing a polyiron sulfate soln. by oxidation using nitrogen oxides as an inexpensive oxidizing agent by which the nitrogen content in the product is made extremely low. SOLUTION: A polyferric sulfate soln. is produced by an iron sulfate soln. having a specified content of iron salt and with the molar ratio of the iron content in the iron salt to sulfuric acid controlled to 1-1.5 by oxidizing the iron(II) to iron(III) with air or oxygen with the nitrogen oxides such as sodium nitrite as a catalyst. Subsequently, a ferrous salt or metallic iron is added as a reducing agent in small amts. to the nitrogen component contained to remove the nitrogen component as NOx. The addition in small amts. is repeated to produce a low-nitrogen polyferric sulfate soln.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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 particularly to a method for producing nitrogen oxide as an oxidizing agent used in the production. The present invention relates to a method for producing a ferric polysulfate solution having an extremely small amount of residual nitrogen while using the method.

[0002]

2. Description of the Related Art A ferrous polysulfate solution has the advantages of lower corrosivity and less pH drop than ferric chloride solution which has been generally used as an iron-based flocculant, and has advantages such as sewage, night soil, and It has been widely used as a flocculant for various industrial wastewaters. The manufacturing method is as follows:
As described in Japanese Patent Publication No. 1-151616 (Japanese Patent No. 842085), the amount of sulfuric acid in the ferrous sulfate solution is adjusted so as to be less than 0.5 mol per mol of ferrous sulfate. By oxidizing with an oxidizing agent such as nitrogen oxide or manganese dioxide, a polyiron sulfate solution can be obtained.

[0003]

However, when an inexpensive nitrogen oxide is used to produce a ferrous polysulfate solution, the produced polyferrous sulfate solution contains several hundred to several thousand mg / nitrogen.
Liters will be contained. Such content,
In recent years, eutrophication in closed waters is a problem,
I can't overlook it. As a countermeasure, for example,
No. 12 proposes to add a predetermined amount of ferric oxide to a sulfuric acid aqueous solution and stir to produce a polyiron sulfate solution. This production method is based on the fact that, contrary to the conventional common knowledge that triiron tetroxide is hardly soluble in sulfuric acid, it is found that it is well soluble when the sulfuric acid solution is adjusted to a certain concentration. However, when the production method is carried out, the dissolution rate of sulfuric acid is still low, and in order to improve this, it is a fact that oxidizing agents such as sodium chlorate, hydrogen peroxide and sodium perchlorate are used. Was. Sodium chlorate is also used as a raw material for explosives and has other difficulties in handling it.In addition, chlorine will be contained in the polyferrous sulfate solution to be produced, There is a problem in that it is contrary to the conventional feature of low corrosion. On the other hand, other hydrogen peroxide and sodium perchlorate have a problem that the production cost is too high. Furthermore, a step for separating and removing iron sesquioxide remaining without dissolving after the oxidation is required.

As another example, Japanese Patent Application Laid-Open No. Hei 8-48526 discloses a method of greatly increasing the oxidation reaction by adding solid ferrous sulfate to a sulfuric acid solution in which an oxidizing agent such as nitric acid or sodium nitrite is adjusted in advance. A method for producing a ferric polysulfate solution which has realized a considerable shortening has been proposed. According to this proposed method, a ferric polysulfate solution can be efficiently produced in a short time, but the residual nitrogen content is as high as several thousand mg / liter, and the problem of eutrophication has not been solved. In view of this, the present applicants have previously disclosed in Japanese Patent Application No. 8-95662 the production of low-nitrogen polyiron sulfate which is oxidized using a nitrogen oxide as a primary oxidizing agent and an oxidizing agent containing no nitrogen as a secondary oxidizing agent. Although a method has been proposed, room for further improvement remains because the final step requires a nitrogen-free oxidizing agent.

The present invention has been made in view of such a problem. The object of the present invention is to produce an oxidized product using nitrogen oxide which is an inexpensive oxidizing agent. It is an object of the present invention to devise a method for producing an iron polysulfate solution capable of extremely reducing the temperature.

[0006]

The above object is achieved by the following steps. That is, as a first step, a predetermined amount of iron salt is contained, and the molar ratio of iron to sulfuric acid in the iron salt is 1 or more and 1.5 or more.
A ferric polysulfate solution is prepared by oxidizing iron (II) to iron (III) with air or oxygen using a nitrogen oxide such as sodium nitrite as a catalyst with respect to the iron sulfate solution prepared below. The first step of producing the ferric polysulfate solution is a known production method. At this point, the ferrous polysulfate solution contains several hundred to several thousand mg / liter of nitrogen. Next, a divalent iron salt or metallic iron is added little by little as a reducing agent to the nitrogen content contained in the polyiron sulfate solution produced in the first step, and the nitrogen content is removed as NOx. At this time, all the added ferrous iron is oxidized to trivalent iron. When this oxidation reaction is completed, a small amount of ferrous iron is added again.
By repeating this operation, the nitrogen content is removed as NOx, and the nitrogen content in the polysulfate solution can be reduced. The amount of ferrous iron added at a time may be a small amount with respect to the nitrogen content. However, according to experiments, it is effective to remove nitrogen up to about 2 mol per 1 mol of the nitrogen content. there were. Desirably, it is about 0.5 mol to 1 mol per 1 mol of the nitrogen content. It is effective to monitor the oxidation-reduction potential as a means for confirming the generation of NOx gas. That is, when divalent iron is added, the oxidation-reduction potential decreases, but the oxidation-reduction potential increases with NOx generation by the reduction reaction of nitrogen and the oxidation reaction of the added ferric iron, and thus the oxidation-reduction potential starts to increase. The following addition of divalent iron can be performed, and the processing can be sped up. If a large amount of ferrous iron is added at one time, the reaction time becomes very long, or the nitrogen content in the polyferrous sulfate solution is not removed, and ferrous iron remains, so that the ferrous polysulfate solution Nitrogen content cannot be reduced.

This reaction is presumed as follows. As shown in the following formula, nitric acid ions are removed as NOx by a reduction reaction by ferrous iron.

[0008]

(Equation 1)

However, a reaction intermediate product of ferrous iron and nitrate ions is a so-called clock reaction in which this reaction acts as a catalyst, and ferrous iron is considered to be an inhibitor in this reaction.

Further, the process of removing nitrogen as NOx gas can be easily recognized by measuring the oxidation-reduction potential, and it is possible to control the addition of excess divalent iron. In addition, the reaction speed is higher as the temperature is higher, but it is preferable to perform the reaction at 60 to 70 ° C. from the viewpoint of product stability. The oxidation reaction in the first step is an exothermic reaction,
Usually, the temperature is 60 to 70 ° C. at the end of the reaction, so that the second step can be carried out immediately without heating, which is preferable. The ferrous iron mentioned here may be anything as long as it can be dissolved as divalent iron ions in the polyiron sulfate solution obtained in the first step, but it must be free from impurities and easily soluble. Therefore, iron, desirably ferrous sulfate is preferred.

[0011] By the above steps, the oxidative production is carried out using nitrogen oxide which is an inexpensive oxidizing agent, but a polyiron sulfate solution having an extremely low nitrogen content is produced.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described based on one example and a comparative example. Of course, the following example:
It is intended to exemplify the present invention and does not limit the technical scope of the present invention.

(Example 1) As a first step, ferrous sulfate 7
Oxygen is oxidized with oxygen while intermittently adding 50 cc of a 20% sodium nitrite solution to an iron sulfate solution consisting of 794 g of hydrate, 62 cc of 96% sulfuric acid and 300 g of water. A ferric solution was obtained.
At this time, the liquid temperature was 68 ° C., and the oxidation-reduction potential was 810 mV. Analysis of this liquid, Fe3 + 160g / l, Fe2 + <0.1g / l, SO ₄ 2-380g /
Liter, total nitrogen 767 mg / liter.

Next, as a second step, 1 liter of the obtained ferric polysulfate solution is measured while measuring the oxidation-reduction potential with an oxidation-reduction potentiometer having silver / silver chloride electrodes as shown in FIG. The mixture was stirred at 120 rpm using a stirrer, and 5 g of ferrous sulfate heptahydrate was added. As a result, the oxidation-reduction potential became 680 mV. After about 10 minutes, the oxidation-reduction potential started to increase, NOx gas was generated, the pressure became 720 mV, and 5 g of ferrous sulfate heptahydrate was added again. Perform this operation in total 6
Repeated twice, 30 g of ferrous sulfate heptahydrate was added. Next, a total of 12 g was added in a single addition amount of 3 g, and finally a total of 3 g was added in 1 g portions, and a total amount of 45 g was added. The time required for the entire reaction was about 1 hour. As a result, Fe3 +
167 g / l, Fe2 + <0.1 g / l, S
A ferric polysulfate solution of O ₄ 2-394 g / l and total nitrogen 94 mg / l was obtained.

(Comparative Example) One liter of the ferric polysulfate solution obtained in the first step shown in Example 1 was stirred at 120 rpm using a stirrer while measuring the oxidation-reduction potential.
45 g of ferrous sulfate heptahydrate was added at a time, and the stirring was maintained for about 6 hours. As a result, Fe @ 3 + 158 g / l, was the Fe @ 2 + 9.2 g / l, SO ₄ 2-393g / l, NO ₃ 1-3300mg / l, poly ferric sulfate solution Total nitrogen 745 mg / liter.

[0016]

According to the present invention, when a polyiron sulfate solution is produced by oxidizing with nitrogen or oxygen, which is an inexpensive oxidizing agent, with oxygen or air, almost all the nitrogen content of the nitrogen oxide sodium nitrite used is polyiron sulfate. It is contained in the solution and its value is several hundred to several thousand mg / liter as nitrogen. By the method according to the present invention, the nitrogen content in the polyiron sulfate solution is reduced to 100 mg / liter.
It can be reduced to liters or less, and for example, the use of the solution as a flocculant does not cause the problem of eutrophication. In addition, the iron polysulfate solution produced by the method according to the present invention has no inferiority in the aggregation effect and the like as compared with the polyiron sulfate solution produced by the conventional method.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram illustrating a state in which a divalent iron salt or the like is added as a second step.

 ──────────────────────────────────────────────────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 (2)

[Claims] An iron sulfate solution containing a predetermined amount of iron salt and having a molar ratio between iron and sulfuric acid of the iron salt adjusted to 1 or more and 1.5 or less, using air as a catalyst with nitrogen oxide as air or A first step of producing a ferric polysulfate solution for oxidizing ferric iron to trivalent iron with oxygen, and divalent iron as a reducing agent for a nitrogen content contained in the obtained ferric polysulfate solution A second step of removing the nitrogen content by adding a salt or metallic iron little by little. 2. The process according to claim 1, wherein when the ferrous salt or metallic iron is added little by little in the second step, the redox potential is measured to control excessive addition. Method.