JPH01249188A - Temperature control method for waste acid neutralization treatment plant - Google Patents

Abstract

PURPOSE:To form a high-concn. iron oxyhydroxide slurry by increasing the temp. in a reaction vessel for the contact settling and removing reaction of iron oxyhydroxide with ferrous ions to >=25 deg.C by direct constant-rate supply of powdery quicklime, etc., to said reaction vessel. CONSTITUTION:A device 15 for feeding the powery quicklime at a constant rate is provided to feed the quicklime at the constant rate to the reaction vessel 2. The quicklime in the vessel 2 induces an exothermic reaction and changes to slaked lime. The slaked lime acts as a neutralizing agent. The pH is adjusted by replenishing an alkaline agent 10 with a pH indicator 11 if the slaked line is not sufficient. The temp. in the vessel can be controlled by steam blowing from a valve 13 if the calorific value of the quicklime is not sufficient. The reason for increasing the temp. in the vessel 2 is because >=15% slurry concn. can be stably maintained at >=25 deg.C. However, a large quantity of steam is needed at the temp. exceeding 50 deg.C. The temp. below 50 deg.C is thus adequate.

Description

[Detailed Description of the Invention] The JI Kakudome Civil Engineering invention provides a method for neutralizing iron-based waste acids using a catalytic precipitation iron removal reaction against the first iron ion of iron oxyhydroxide, especially for high-concentration iron-based waste acids. The present invention relates to a temperature control method in the reaction system for stably obtaining iron oxyhydroxide slurry.

Among the waste acid neutralization treatment methods, the so-called DIFEX process, which utilizes the catalytic precipitation iron removal reaction of iron oxyhydroxide, is used to neutralize waste acid containing a large amount of ferrous ions in a slurry of iron oxyhydroxide. This is a method in which a high concentration of iron oxyhydroxide (FeOOII) is produced by adding an acid stock solution to oxidize ferrous ions, and circulating a portion of the resulting sludge as a seed slurry to the reaction tank again. Although the specific details are clear in the specification of Japanese Patent Publication No. 49-21040, an outline of this method is shown in a block diagram in FIG.

That is, the liquid being stirred in the reaction tank 2 is Pe001
It is a slurry containing 1 particle at a predetermined concentration, and contains 1 waste acid stock solution containing ferrous ions, 9 compressed air, and pH!
When the alkaline agent 10 is administered according to the instructions from the II moderator 11, the ferrous ions are instantaneously oxidized to precipitate Fe0OII, and the surplus Fe0OII slurry 3 is led to the precipitation tank 4 where it is supernatant. Liquid 5 and sludge (
This sludge 6, which becomes a high-concentration Fe0OIl slurry) 6, is dehydrated through a slurry pit 8. On the other hand, a part of the sludge 6 is returned to the reaction tank 2 as a seed slurry 7.

This Fe0OH has very good sedimentation and concentration properties, and is usually 2
Because a highly concentrated slurry of 0 to 30% can be obtained and the iron content in the treated water (supernatant liquid after treatment) is extremely low4, it is widely used in cold rolling mill pickling wastewater treatment at steel mills. .

, I]<n" r However, this catalytic precipitation iron removal reaction stabilized Fe0
In order to create 0H, there are several factors such as pH control of the reaction system, slurry circulation ratio, and oxidation temperature. If failure occurs, Fe0OH will not be produced and it will become Fe(Oft)s, with a concentration of 5 to 8%. It has the disadvantage that it is very difficult to process, and the pH of the above reaction system and slurry vaI! Even though 2 m was appropriate, the temperature conditions had been overlooked, so no temperature control device was installed, and seasonal changes were observed in the slurry concentration.

An object of the present invention is to provide a treatment method that can stably obtain a highly concentrated iron oxyhydroxide slurry when the Diffex process is applied to the neutralization treatment of the iron-based waste acid.

1 ° For the purpose of
As a result of research focusing on the oxidation temperature conditions among the conditions for stably producing Fe0OII, it was found that adjusting the reaction temperature in the reaction tank within a certain range is extremely important for stably producing Fe0OII. The temperature range is 25°C or higher, preferably up to 50°C, and steam injection into the reaction tank is preferred because the temperature inside the reaction tank can be easily adjusted and has high accuracy. It was found to be effective.

Furthermore, supplying a fixed quantity of powdered quicklime to the reaction tank and maintaining the temperature of the reaction tank through the exothermic reaction of the quicklime also supplies a neutralizing agent, which is a more effective method. They discovered that scales can be made using blowing in combination, leading to the present invention.

Therefore, the present invention provides a temperature control method for iron-based waste acid neutralization treatment equipment using a catalytic precipitation iron removal reaction against ferrous ions of iron oxyhydroxide, which stabilizes highly concentrated iron oxyhydroxide slurry. In order to obtain the above reaction, the temperature inside the reaction tank is raised to 25°C or higher by directly quantitatively supplying powdered quicklime, by blowing steam, or by using a combination of supplying quicklime and blowing steam. It is characterized by maintaining control.

The method of the present invention for improving the disadvantages of the Diffex process is shown in FIG.
1 A thermometer 14 is attached to the reaction tank 2 to which a FIya valve 13 is attached, and the flow rate regulating valve 13 is operated according to the temperature of the slurry to maintain the temperature of the slurry at a predetermined temperature.

It has also been found that it is more effective to use powdered quicklime and slaked lime slurry as a neutralizing agent for the reaction +ff2, and to utilize the heat generated by quicklime for temperature adjustment.

That is, a powder quicklime quantitative cutting device f15 is installed,
Extract quantitative amount to reaction tank 2.0 In the reaction tank, quicklime undergoes an exothermic reaction and turns into slaked lime (Ca (Oll) *), but Ca (011) x acts as a neutralizing agent, and if insufficient, pl + instruction In total 11, alkaline agent 10 is replenished and pH adjustment is performed.

Furthermore, if the calorific value of the quicklime is not sufficient, the temperature inside the tank can be controlled by blowing steam through the valve 13.

The reason why the temperature inside the reaction tank 2 is set to 25°C or higher is as follows.
This is because a slurry concentration of 15% or more can be stably maintained at temperatures above 50°C.On the other hand, raising the temperature inside the tank above 50°C requires, for example, a large amount of steam, making it economically difficult. It is preferable to set the temperature to 50'C from above.

The present invention will be further explained below with reference to Examples.

1 cliff ■ Using the equipment shown in Figure 1, circulate the slurry by approximately 1
00 ffi, and a waste acid neutralization treatment was performed by injecting the pickling waste liquid into the reaction tank and circulating it. At that time, the temperature inside the reaction tank was variously changed from about 18° C. to 33° C. by steam injection, and the relationship with the concentration of the iron oxyhydroxide slurry obtained in the precipitation tank at each temperature was tested. The test results are shown in Figure 3.

As can be seen from this figure, the slurry concentration is low at about 5% below 20°C, but as the set temperature rises, the slurry concentration increases. In order to obtain a stable high slurry and lee concentration higher than the 15% slurry concentration control line shown by the horizontal dotted line in this figure, it is essential that the temperature inside the tank be at least 25°C.

By setting the reaction temperature at 25 to 50°C when launching the plate, a stable high-concentration Fe0O1L slurry can be obtained, which improves processing capacity and dewatering efficiency compared to slurry with a concentration of 7 to 8%. It was done.

Furthermore, when quicklime is used, the quicklime itself acts as a neutralizing agent, which is effective in reducing the cost of the neutralizing agent and the use of steam for heating.

[Brief explanation of the drawing]

FIG. 1 is a block diagram illustrating the method of the present invention in the Diffex process. FIG. 2 is a block diagram of the differential process. FIG. 3 is a graph showing the relationship between reaction tank temperature and iron oxyhydroxide slurry concentration. The numbers in FIGS. 1 and 2 above indicate the following. l Waste acid stock solution 2 Reaction tank 3 Fe0011 slurry 4 Sedimentation tank 5 Supernatant liquid
6 Highly concentrated Fe00) 1 slurry 7 Seed slurry 8 Slurry pit 9 Compressed air 10
Alkaline agent 11 Pi adjuster 12 Steam piping 13 Flow rate adjustment valve 14 Thermometer 15
Powdered quicklime quantitative cutting device Patent applicant: Sumitomo Metal Industries, Ltd.

Claims (1)

[Claims] A temperature control method for iron-based waste acid neutralization treatment equipment using a catalytic precipitation iron removal reaction against ferrous ions of iron oxyhydroxide, which stabilizes a highly concentrated iron oxyhydroxide slurry. In order to obtain the above reaction, the temperature inside the reaction tank can be raised to 25°C or higher by directly quantitatively supplying powdered quicklime or by blowing steam into the reaction tank where the above reaction is carried out, or by using a combination of supplying quicklime and blowing steam. 1. A temperature control method for waste acid neutralization treatment equipment, characterized in that the above neutralization treatment is carried out while maintaining the temperature at a temperature controlled at .