JP2654928B2 - Method for producing ferric sulfate or basic ferric sulfate solution - 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 sulfate or basic ferric sulfate solution using sodium nitrite as a catalyst. The present invention relates to a method for efficiently producing a basic ferric sulfate solution.

[0002]

2. Description of the Related Art A ferric sulfate or basic ferric sulfate solution is less corrosive to an apparatus and has excellent coagulation performance as compared with other ferric coagulants such as ferric chloride solution. For,
In recent years, it is frequently used for various wastewater treatments.

[0003] As a method for obtaining such a ferric sulfate or basic ferric sulfate solution, for example, sulfuric acid in a ferrous sulfate solution containing 50 g / l or more of total iron is added per mole of ferrous sulfate.
A method of oxidizing with an oxidizing agent such as hydrogen peroxide, manganese dioxide or the like so as to be less than 0.5 mol, or with air using nitrogen oxide as a catalyst (Japanese Patent Publication No. 51-17516), a specific ratio of iron oxide and sulfuric acid Prepare and mix to be 75 ° C
Dissolving at the above temperature, a method of oxidizing divalent iron in the obtained iron sulfate (Japanese Patent Application Laid-Open No. 61-286228), dissolving an adjusted mixture of iron oxide, metallic iron and sulfuric acid at 50 ° C or more, A method for oxidizing ferrous sulfate in the obtained ferrous sulfate solution (JP-A-61-286229)
No.) are known. However, these methods, that is, the method of oxidizing using an oxidizing agent such as hydrogen peroxide, manganese dioxide, ozone, sodium chlorate, etc., require a large amount of the oxidizing agent and thus increase the cost of the oxidizing agent. In addition, the method of air oxidation in the presence of a catalyst such as sodium nitrite,
Since it takes a long time to oxidize ferrous iron to ferric iron, and the oxidation efficiency is poor and not economical, a newly developed method is to mix a ferric sulfate solution with hydrous diiron trioxide to form sulfuric acid. This is a method for producing basic ferric sulfate by partially neutralizing ferric iron (JP-A-6-47205). However, this method is very costly because of the use of diiron trioxide to produce the ferric sulfate solution.

[0004]

On the other hand, in recent years, as a part of various industrial waste treatments, methods for effectively utilizing ferrous sulfate contained in waste acid have been studied. Under such circumstances, the present inventors have conducted intensive studies on a method for producing ferric sulfate or a basic ferric sulfate solution using ferrous sulfate as a raw material. The method using an oxidizing agent such as hydrogen peroxide, manganese dioxide or sodium chlorate as an oxidizing method requires a high cost of raw materials, and is simple, using air or oxygen gas, and is efficient, that is, in a short time. The method of oxidizing was studied. As a result, in an absorption tower reactor filled with Raschig rings or a method of generating fine bubbles of air or oxygen gas using an atomizer and oxidizing it, which is generally used, oxidation takes a long time and is not efficient. Was obtained. Therefore, a method for efficiently oxidizing ferrous sulfate with a new oxidizing device was studied.

[0005]

As a result, a reaction tube filled with a static mixer element in relation to a sodium nitrite catalyst is used in such an apparatus for oxidizing ferrous sulfate. By circulating and introducing a solution or slurry of an oxygen-containing gas and ferrous sulfate from the lower part of the ferrous sulfate and oxidizing ferrous sulfate, ferric sulfate or basic ferric sulfate can be obtained with a very simple apparatus at a high oxidation efficiency. It has been found that a solution can be obtained, and the present invention has been completed based on such findings.

That is, the present invention relates to a method for producing a ferric sulfate or basic ferric sulfate solution using sodium nitrite as a catalyst, wherein a solution or slurry of an oxygen-containing gas and ferrous sulfate is mixed with a static mixer. The solution or slurry of NOx and oxygen-containing gas and ferrous sulfate generated is introduced into the lower part of the reaction tube filled with the element, and the solution or slurry is introduced from the upper part of the reaction tube into the storage tank, and the storage tank solution is repeatedly circulated into the reaction cylinder. Accordingly, the present invention relates to a method for producing ferric sulfate or a basic ferric sulfate solution, which comprises oxidizing ferrous sulfate.

[0007]

The present invention will be described below in more detail with reference to the apparatus flow sheet shown in FIG. In the flow sheet of FIG. 1, 1 is a reaction tube filled with a static mixer element (hereinafter, abbreviated as a reaction tube), 2 is an oxygen cylinder,
Reference numeral 3 denotes a storage tank for a ferrous sulfate solution or slurry, and reference numeral 4 denotes a sodium nitrite solution storage tank.

In the present invention, first, ferrous sulfate, sulfuric acid necessary for a desired basicity of product, and water necessary for a desired product concentration are charged into the storage tank 3. When using waste ferrous sulfate solution as the ferrous sulfate solution, since typically Fe ₂ O ₃ concentration is about 5 to 10 wt%, when it is necessary to further increase the Fe ₂ O ₃ concentration, sulfate Ferrous heptahydrate is added to the desired concentration. When ferrous sulfate heptahydrate is used as a raw material,
If this does not completely dissolve at room temperature, the slurry is circulated in the reaction system to carry out the oxidation reaction. As the oxidation reaction proceeds, ferrous sulfate heptahydrate dissolves and complete ferric sulfate or basic It becomes a ferric sulfate solution. However, when the slurry is circulated through the reaction system, clogging, pressure loss, abrasion, etc. occur in the reaction tube. Therefore, it is preferable to increase the solubility of ferrous sulfate by heating the slurry.

The ferrous sulfate solution or slurry in the storage tank 3 is introduced into the lower part of the reaction tube 1. Next, a sodium nitrite solution is further introduced from a sodium nitrite solution storage tank 4 while introducing oxygen gas into the lower portion of the reaction tube from the oxygen cylinder 2. The ferrous sulfate solution or slurry that has passed through the reaction tube 1 is introduced into the storage tank 3 together with NOx and oxygen-containing gas generated during the reaction. Further, the solution in the storage tank 3 is repeatedly circulated into the lower portion of the reaction tube.

In the present invention, based on such a flow,
Ferrous sulfate or a basic ferric sulfate solution is produced by oxidizing ferrous sulfate. Ferrous sulfate is oxidized based on the following chemical formula (Formula 1), ferric or basic ferric sulphate _{(Fe 2 (OH) n (} SO 4) 3-n / 2) is generated.

[0011]

Embedded image

The introduced sodium nitrite solution is:
The reaction with ferrous sulfate generates NOx gas, which is recycled as a catalyst. The reaction tube used in the present invention will be described in more detail. In the reaction tube, an element 5 used for a static mixer type mixer is filled in a reaction tube, and an example thereof is described in JP-A-6-254369. The reaction tube used in the present invention is commercially available, for example, from Noritake Co., Ltd. under the trade name SM Pack.
Its internal structure is shown in FIG. A plurality of static mixer elements 5 are disposed inside the cylinder, and the oxygen-containing gas introduced from the conduit A and the solution or slurry of ferrous sulfate introduced from the conduit B pass through the static mixer element 5. And efficient contact.

The static mixer element 5 will be described in further detail. As shown in FIG. 3, one sheet having a right twisted portion R (twist angle 180 °) and a left twisted portion L (twist angle 180 °) around the axis. It consists of a twisted plate. Such an element has a shape in which the end faces in the respective axial directions of the right-hand twisted plate and the left-handed twisted plate are continuous, and these axial directions are arranged in parallel in the same direction to constitute a filler unit. Such units are arranged in series in the axial direction of the element to constitute a reaction tube. The shape of the reaction tube is not particularly limited, but the height of the reaction tube is preferably about 1 to 10 times the filling height of the static mixer element, and about 1 to 50 times the diameter of the reaction tube.

A mixer using a static mixer element generally has a gas flow rate (G) and a liquid flow rate (L).
It is considered that the reaction efficiency is best when the ratio is used in the range of 2.5 to 20. However, the present inventors have conducted various studies, and as a result, surprisingly completely different results, that is, the volume of the circulating introduction amount of the oxygen-containing gas (G) and the solution or slurry (L) of ferrous sulfate into the reaction cylinder (L) It was most preferable to use the G / L ratio in the range of 0.2 to 2.0. This phenomenon occurs because the oxidation reaction of the present invention is not caused by mere gas-liquid contact, but is caused by Nitrite caused by sodium nitrite.
It is presumed that this is due to the fact that O and NO ₂ gases are proceeding by producing complex addition compounds with ferrous sulfate. If the G / L ratio deviates from this range, the oxidation efficiency of ferrous sulfate decreases, which is not preferable.

As the oxygen-containing gas introduced into the lower portion of the reaction tube, air, a gas having an oxygen concentration of about 90%, which is concentrated from air by an oxygen concentrator, or an oxygen gas utilizing an oxygen cylinder or the like can be used. . The most preferred embodiment of the present invention is to use oxygen gas as the oxygen-containing gas and oxidize ferrous sulfate in a closed system. In this case, the internal pressure of the reaction system hardly rises, the oxidation rate increases remarkably, and the oxygen utilization efficiency becomes 100%.

The ratio of the raw materials used varies depending on the use of industrial water, tap water, sewage and the like, but the ferrous sulfate solution or slurry is used in the range of about 5 to 20% by weight as Fe ₂ O ₃ . Also, the amount of sulfuric acid used is Fe ₂ O _{3 of} ferrous sulfate.
The amount is 1 mol or less per 1 mol of the amount. Although it is possible to use sulfuric acid in excess of 1 mol, it is not preferable because the acid strength becomes strong and corrosion of the apparatus occurs, neutralization of the target water is required, or coagulation performance is reduced. Incidentally, in terms of basicity when obtaining a basic ferric sulfate solution,
The basicity (%) can be calculated by the formula (1-x) / 3 × 1 assuming that the amount of sulfuric acid used per mole of Fe ₂ O ₃ of ferrous sulfate is x mole.
It is represented by 00. Therefore, the basicity of the basic ferric sulfate solution obtained in the present invention is 33% or less. Further, the amount of sodium nitrite was 0.1 to 1 mol of Fe ₂ O _{3 of} ferrous sulfate.
The range is from 01 to 0.2 mole. In addition, as for the method of adding the sodium nitrite solution, the sodium nitrite solution may be added in its entirety before the introduction of the oxygen-containing gas, or may be appropriately added during the reaction.

With respect to the temperature during the oxidation reaction, it is not limited by the raw materials used and the desired product concentration, but it is 10 to 80.
C. is preferred. More specifically, at the start of the reaction, it is desirable to heat to dissolve the raw materials. The heating operation may be performed by a method of appropriately heating the storage tank 1 with steam or the like.

By performing the above operations, ferrous sulfate is converted into ferric sulfate or a basic ferric sulfate solution by oxidation. Further, such a reaction requires a long reaction time according to the use of a conventionally known general oxidizer, but according to the method of the present invention, it is generally 1/1 of the conventional one.
The reaction is completed in about 10 hours, and a ferric sulfate or basic ferric sulfate solution can be obtained with high reaction efficiency.

[0019]

EXAMPLES Examples of the present invention will be described below for further explanation. In the examples, all percentages are by weight unless otherwise specified.

Example 1 A reaction apparatus was assembled based on the flow sheet of the apparatus used in the method for producing a ferric sulfate or basic ferric sulfate solution of the present invention shown in FIG. The specifications of each device are as follows.

<Reaction tube> Tube inner diameter: 100 mm, tube height: 2000 mm
, 13 static mixer elements having a width of 20 mm and a length of 65 mm in the torsion direction were bundled in parallel in a cylindrical shape, and a total of 9 stages were arranged in series in the vertical direction. In addition, a perforated plate having 30 pores having a diameter of 2 mm between each stage was provided as a support for the element. In addition, an oxygen introduction pipe was provided below the reaction tube. <Reservoir> This is a 100L storage tank equipped with a stirrer,
The upper part of the storage tank was sealed, and an opening valve was provided so that the internal pressure could be adjusted if necessary.

Using the above apparatus, the production of ferric sulfate or basic ferric sulfate solution was carried out as follows. First, 55.67 kg of ferrous sulfate (heptahydrate), 10.66 kg of 70% sulfuric acid and 30.69 kg of water were put into a storage tank, and heated until the liquid temperature reached 65 ° C. with stirring to obtain a uniform solution. Then, while introducing this solution at a liquid flow rate (L) of 37 L / min from the lower part of the reaction tube, at the same time, 100% pure oxygen gas was supplied from the oxygen cylinder at a gas flow rate (G) of 1
8.5NL / min, 40% sodium nitrite aqueous solution
1.38 kg was introduced from the lower part of the reaction tube at a rate of 0.14 kg / min. In this case, the introduction ratio (G / L ratio) of the oxygen gas (G) and the ferrous sulfate solution (L) is 0.5. The mixed solution of the gas and the solution was introduced into the storage tank provided with a degassing valve from the upper portion of the reaction tube, and was repeatedly circulated from the storage tank to the lower portion of the reaction tube to oxidize ferrous sulfate. The reaction system in this case was performed in a closed state.

While the circulation is being introduced into the reaction tube, the circulating liquid is collected every 5 minutes in the vicinity of the time when the progress of the reaction is completed, and the Fe ²⁺ concentration becomes 0.07% or less. The time was defined as the reaction time. Hereinafter, all the reaction times in the examples were determined by this method. The reaction time in this case was 65 minutes. The solution obtained after the reaction was analyzed, and as a result, the reaction solution was Fe ₂ O ₃ 16.1%, SO ₄ 26.7%,
The solution was a basic ferric sulfate solution having a basicity of 8%.

Comparative Example 1 A basic ferric sulfate solution was produced in the same manner as in Example 1 except that a reaction cylinder filled with Raschig rings as described below was used instead of the reaction cylinder used in Example 1. . <Rashig ring filled reaction tube> 100 mm inside diameter, 2000 mm height
Was filled with a 3/4 inch Raschig ring to a filling height of 600 mm. In addition, an oxygen inlet tube is provided at the bottom of the reaction tube, a sodium nitrite inlet tube and a ferrous sulfate solution inlet tube are provided at the upper portion, and the solution passing through the reaction tube is vented from the lower portion of the reaction tube. It was circulated and introduced into the storage tank to which the valve was attached.

Incidentally, as a result of using such a reaction tube, the reaction efficiency was poor and the internal pressure in the reaction system increased. Therefore, the reaction was carried out with the gas vent valve at the top of the storage tank opened.
Otherwise, the reaction was carried out under the same conditions as in Example 1, and as a result, the reaction time was 600 minutes.

(Comparative Example 2) A basic ferric sulfate solution was produced in the same manner as in Example 1 except that a reaction vessel equipped with the following atomizer was used instead of the reaction tube used in Example 1. did. <Reactor equipped with an atomizer> A cylindrical cup (with an internal capacity of 98L) with an inner lid of 500mm in height and 500mm in height with an upper lid fitted with a degassing valve, and a downward cup-shaped rotation of 50mm in inner diameter of wing and 60mm in height Atomizer device with wings (rotation speed 1
300 rpm). An oxygen introduction tube is arranged under the blade of this atomizer, ferrous sulfate solution is put into the reaction tank, and then stirred with an atomizer while introducing oxygen gas, and sodium nitrite solution is added from the top of the reaction tube. The reaction was performed in the following manner.

Since the reaction efficiency was poor and the internal pressure in the reaction system increased as a result of using such a reaction tank, the reaction was carried out with the gas vent valve at the top of the reaction tank opened.
Otherwise, the reaction was carried out under the same conditions as in Example 1, and as a result, the reaction time was 900 minutes.

(Example 2) A basic ferric sulfate solution was produced by using the reactor used in Example 1 and introducing a gas flow rate of oxygen gas at a rate shown in Table 1. The reaction was carried out under the same conditions as in Example 1 except that the gas vent valve at the top of the storage tank was opened and the inside of the reaction system was opened. The reaction time under each G / L ratio condition is shown in Table 1.

[0029]

[Table 1]

Example 3 Using the reactor used in Example 1, an oxygen gas having a purity of 90% was used in place of the oxygen gas having a purity of 100% in Example 1, An iron solution was prepared. The reaction was carried out under the same conditions as in Example 1 except that the gas vent valve at the top of the storage tank was opened and the inside of the reaction system was opened, and the reaction time was 420 minutes.

(Example 4) A basic ferric sulfate solution was similarly produced in a slurry solution state by using the reactor used in Example 1 and setting the solution temperature in the storage tank to 30 ° C. .
The reaction was carried out under the same conditions as in Example 1 except that the gas vent valve at the top of the storage tank was opened and the inside of the reaction system was opened, and the reaction time was 150 minutes.

Example 5 Using the reactor used in Example 1, a reaction was carried out using waste sulfuric acid containing ferrous iron as a ferrous sulfate raw material. Waste sulfuric acid (Fe ²⁺ 5.92%, S
45.81 kg (containing 14.18% of O ₄ ), 42.1 kg of ferrous sulfate (heptahydrate), 70
11.35 kg of 0.6% sulfuric acid and 0.66 kg of water were added, and the mixture was heated with stirring until the liquid temperature reached 65 ° C. to form a uniform solution. Less than,
The reaction was carried out in the same manner as in Example 1 to produce a normal salt solution of ferric sulfate. As a result, the reaction time was 65 minutes.

Example 6 A reaction was carried out using waste sulfuric acid in the same manner as in Example 5 using the reactor used in Example 1. Waste sulfuric acid in the storage tank (containing 5.92% of Fe ^{2+ and} 14.18% of SO ₄ ) 5
6.59 kg, ferrous sulfate (7-hydrate) 39.0 kg and 70% sulfuric acid 4.42 kg
Was added thereto, and the mixture was heated until the liquid temperature reached 65 ° C. while stirring to obtain a uniform solution. Thereafter, the reaction was carried out in the same manner as in Example 1 to produce a basic ferric sulfate solution having a basicity of 15%. As a result, the reaction time was 65 minutes.

(Example 7) In the reactor used in Example 1, the number of vertical stages of the static mixer element disposed in the reaction tube was changed to 6 in place of 9 in Example 1, and Manufactured a basic ferric sulfate solution in a reactor under the same conditions. The liquid flow rate (L) of the ferrous sulfate solution in Example 1 was 11 L / min, and the oxygen gas flow rate (G) of 100% purity was 22 NL / min (G / L ratio 0.5). The reaction was carried out under the same conditions as in Example 1 except for the above. As a result, the reaction time was 105 minutes.

[0035]

The method for producing a ferric sulfate or basic ferric sulfate solution of the present invention uses ferrous sulfate as a raw material,
This is a method for producing a ferric sulfate or basic ferric sulfate solution efficiently with high oxidation efficiency. In the method of producing ferric sulfate or basic ferric sulfate solution by oxidation with air or oxygen gas using ferrous sulfate as a raw material, the oxidation efficiency is extremely low. However, according to the present invention, a ferric sulfate or basic ferric sulfate solution can be efficiently produced with a simple apparatus and in a short time, and the production efficiency is poor. It is possible to effectively utilize the ferrous sulfate contained in the waste acid which has not been used.

[Brief description of the drawings]

FIG. 1 is an apparatus flow sheet used in the method for producing a ferric sulfate or basic ferric sulfate solution of the present invention.

FIG. 2 is a diagram showing an internal structure of a reaction tube filled with a static mixer element used in the present invention.

FIG. 3 is a diagram showing a static mixer element inside a reaction tube used in the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Reaction tube filled with static mixer element 2 Oxygen cylinder 3 Reservoir of ferrous sulfate solution or slurry 4 Reservoir of sodium nitrite solution 5 Static mixer element A Pipe of oxygen-containing gas B Solution or slurry of ferrous sulfate Of pipe R Right twist of element L Left twist of element

Claims (3)

(57) [Claims] In a method for producing a ferric sulfate or basic ferric sulfate solution using sodium nitrite as a catalyst, a static mixer element is filled with a solution or slurry of an oxygen-containing gas and ferrous sulfate. By introducing the solution or slurry of NOx and oxygen-containing gas and ferrous sulfate generated from the upper part of the reaction cylinder into the storage tank, and repeatedly circulating the storage tank solution into the reaction cylinder, A method for producing ferric sulfate or basic ferric sulfate solution, comprising oxidizing ferrous sulfate. 2. The volume ratio of the oxygen-containing gas (G) and the solution or slurry (L) of ferrous sulfate circulated into the reaction cylinder is G / G.
2. The method according to claim 1, wherein the L ratio is in the range of 0.2 to 2.0. 3. Use of oxygen gas as an oxygen-containing gas,
3. The method according to claim 1, wherein ferrous sulfate is oxidized in a closed system.