JPH07178394A - Treatment of spent acid - Google Patents

Abstract

PURPOSE:To inexpensively treat a spent acid by effectively utilizing the characteristic of steel slag. CONSTITUTION:A spent acid is neutralized with steel slag. The grain size of the slag is controlled <=1mm to enhance the treating efficiency. Further, the slag is previously reduced and then added to the spent acid.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating waste acid, and in particular, as a part of effective use of steel slag generated from a refining process of a steel mill, the steel slag is immersed in waste acid,
The present invention relates to a waste acid treatment method that is inexpensive and saves resources by performing a neutralization reaction.

[0002]

2. Description of the Related Art Waste acid is generated from various industrial fields and contains various metal components, so that it is difficult to discard or reuse it as it is. It is divided into sediment and industrial wastewater, and the sediment is discarded. As the neutralizing agent, Ca source or Na source alkali, ammonia water, or the like is used, and a commercially available product is usually purchased. In addition, since the cost of waste acid treatment is generally as high as tens of thousands of yen per ton of waste acid or more, a person who needs waste acid treatment desires the appearance of a neutralizing agent that is as inexpensive as possible.

On the other hand, the reuse of iron and steel slag represented by blast furnace slag and steelmaking slag is also an important problem for the steelmaking industry, and many trials have been conducted since ancient times for the purpose of recycling industrial waste. . Among them, blast furnace slag is overwhelmingly applied to cement raw materials, its chemical composition is close to that of Portland cement, and because of its excellent hydraulic properties, its reuse rate is currently 100. %
Is. Main applications are roadbed materials, civil engineering such as bricks, and building materials, and in the end, many products have a shape.

On the other hand, in the steelmaking slag, quick lime used as an auxiliary material for converter refining and the like is not completely slagged, and so-called free CaO remains, so that reuse is suppressed. . That is, when free CaO reacts with water in the atmosphere to hydrate, the volume expands about twice and the entire converter slag collapses, so that it cannot be used for a product having a shape. Therefore, for the converter slag having such a collapse phenomenon, a way for appropriate reuse is being sought from another viewpoint.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object thereof is to provide an inexpensive waste acid treatment method that effectively utilizes the characteristics of steel slag.

[0006]

In order to achieve the above object, the inventor has focused only on the chemical properties of iron and steel slag, and in the total CaO content which is the main component thereof, the free C which still reacts with acid.
aO, 2CaO · SiO ₂ , 3CaO · SiO ₂ , 2C
The effective use of minerals such as aO.Fe ₂ O ₃ was examined. That is, the present invention is a method for treating waste acid, which comprises neutralizing the waste acid with steel slag. Further, in order to enhance the treatment efficiency, the present invention is the method for treating waste acid according to claim 1, characterized in that the iron and steel slag has a grain size of 1 mm or less. Furthermore, it is also the waste acid treatment method according to claim 1 or 2, wherein the steel slag is added to the waste acid after being preliminarily reduced.

In this case, steelmaking slag is preferably used as the steel slag, but blast furnace slag or electric furnace slag may be used. The waste acid may be any acid such as waste sulfuric acid and waste hydrochloric acid.

[0008]

In the present invention, the waste acid is neutralized with the steel slag, so that the waste acid is separated into a precipitate of metal and water.
As a result, it becomes possible to treat as industrially safe industrial wastewater and waste through the filtration process. Further, in the present invention, since the grain size of the steel slag is set to 1 mm or less, the above effect is promoted, and the processing time can be shortened in particular. Furthermore, since the iron and steel slag is preliminarily reduced and then added to the waste acid, the calcium and ferrite in the iron and steel slag are reduced to iron and free CaO, and the above effect can be further promoted.

The contents of the present invention will be described below. The neutralization reaction between CaO, which is the main component of steel slag, and waste acid is presumed to be as follows. The case of waste hydrochloric acid and waste sulfuric acid is shown as an example of waste acid. CaO + 2HCl → CaCl ₂ + H ₂ O CaO + H ₂ SO ₄ → CaSO ₄ ↓ + H ₂ O CaO + H ₂ SO ₄ + H ₂ O → CaSO ₄ · + 2H ₂ O ↓ Therefore, in carrying out the present invention, the neutralization reaction from the concentration of waste acid It suffices if CaO is used in an amount of at least the required number of moles.

The metal components that precipitate during the neutralization reaction include
There are metals contained in waste acid and metals contained in slag. These metals dissolve in the acid as ions, but as the neutralization reaction proceeds, that is, as the pH increases,
Precipitates as hydroxide. Further, the pH range in which precipitation occurs differs depending on the metal. For example, in the case of the divalent metal M, it is presumed to be as follows.

CaO + H ₂ O → Ca (OH) ₂ → Ca ²⁺ + 2OH ⁻ M ²⁺ + 2OH ⁻ → M (OH) ₂ ↓ Therefore, the molar number of CaO required for the hydroxylation of the metal component is not less than
Is required. Only water remains if the metal component is removed by precipitation, but for industrial wastewater, the pH should be 6 to 9 and the metal component subject to the wastewater standard should be at least the standard value (standard by the Water Pollution Control Law) or less. is necessary. When the metal component to be the standard is precipitated at pH ≧ 9, the pH may be adjusted with an acid after the precipitation. Further, if the metal component is not a target of the standard, it may not be precipitated.

For removing the precipitate, a known filtration method such as a press filter or an oliver filter may be used. At this time, the unreacted slag used for neutralization and the product newly formed by the reaction between the acid and the slag are simultaneously removed. In order to accelerate the neutralization reaction, it is advisable to crush the iron and steel slag in advance and to adjust the particle size. The particle size is preferably 1 mm or less, and 0.5
mm or less is suitable. Since the reaction occurs from the surface, it is advantageous to have a large specific surface area. Also, the larger the amount of steel slag, the more advantageous. The reaction is carried out by dispersing steel slag in waste acid. At that time, a uniform reaction can be continued by stirring.

Further, since the steel slag contains CaO in various mineral forms as described above, it is effective to reduce it in advance to increase free CaO. The reduction is not particularly limited, but utilization of various exhaust gases generated in a steel mill or the like is free in terms of energy and cost. Further, the temperature of the neutralization treatment may be room temperature or higher, but it has been confirmed that the treatment effect is enhanced by heating up to 200 ° C. for sulfuric acid and less than 100 ° C. for hydrochloric acid.

The type and concentration of waste acid are not particularly limited.

[0015]

【Example】

Example 1 An experiment was conducted to which the method according to the present invention was applied, using waste sulfuric acid generated from a drawn steel pipe production line of an iron mill. The concentration of waste sulfuric acid is 10%, and the contained metal components are shown in Table 1. Converter slag was prepared as steel slag used for neutralization. Table 2 shows the chemical composition of the slag.

[0016]

[Table 1]

[0017]

[Table 2]

After smashing the slag to 1 mm under and sizing, the first neutralization experiment was a waste sulfuric acid of 5000 gr.
(About 4750 cc) was processed. At that time, an amount of slag equivalent to 5 times the equivalent amount of CaO required for neutralization was added.
In the experimental process, as shown in FIG. 1, slag was added while stirring the waste sulfuric acid at room temperature, and when the waste acid reached a predetermined pH, the precipitate was suction filtered and the filtrate was quantitatively analyzed. . The experimental results are shown in Table 3.

[0019]

[Table 3]

From Table 3, it can be judged that almost all metal components other than Mn, which is the target metal component of industrial wastewater standards, were precipitated at pH ≦ 9, and almost all Mn was precipitated at pH 11. Even if Mg remains, there is no problem in industrial wastewater. Therefore, if a reagent sulfuric acid is added to the filtrate having a pH of 11 to adjust the pH to 6 to 9, since each metal component is within the above-mentioned industrial wastewater standard, industrial wastewater can be produced.

The cake remaining as a filtration residue was a slag particle having a precipitate of metal components and white gypsum scraps on the surface, which could be discarded. Example 2 As a waste acid, a waste hydrochloric acid generated from a bar steel line was prepared. The concentration of waste hydrochloric acid is 20%, and the metal components contained are shown in Table 4.

[0022]

[Table 4]

The steel slag used was heated and reduced in a laboratory electric furnace for 30 minutes under a CO gas atmosphere and a temperature of 800 ° C. Then, the reduced slag cooled to 100 ° C. was used as a neutralizing agent in an experiment similar to that in Example 1. As a result, the slag used for neutralization was 2.3 times the CaO equivalent, which was smaller than that in Example 1, and the same results as in Table 3 were obtained. As in Example 1, the pH of the filtrate was adjusted to produce industrial wastewater. The cake remaining as the filtrate was slag particles that remained unreacted with the precipitate of the metal component and was discarded.

[0024]

EFFECTS OF THE INVENTION According to the present invention, CaO, which is the main component of the slag, can function as a neutralizing agent and can neutralize the waste acid by immersing the steelmaking slag in the waste acid and reacting it with the wastewater. Can be divided into waste. As aforementioned,
Since slag is an industrial waste, if it can be applied as a neutralizing agent, it is not necessary to purchase a commercially available neutralizing agent, the waste acid treatment cost can be reduced, and so-called two birds with one stone can be obtained. In this neutralization reaction, CaO contributes to the neutralization reaction regardless of the basicity of the steelmaking slag.
Therefore, the reuse is not suppressed, so that the reuse rate of the steelmaking slag can be remarkably improved. The neutralization reaction of the present invention can be applied not only to steelmaking slag but also to all steel slag containing CaO.

The reaction conditions such as the amount of slag, the particle size of slag, the concentration of waste acid, the metal components contained in the waste acid and the reaction temperature in the neutralization reaction of the present invention are not particularly limited, and the waste acid is neutralized. It can be controlled within a range where it can be separated into industrial wastewater and waste.

[Brief description of drawings]

FIG. 1 is a diagram showing a step in which a method for treating a waste acid according to the present invention is performed.

Claims (3)

[Claims] 1. A method for treating waste acid, which comprises neutralizing the waste acid with steel slag. 2. The method for treating waste acid according to claim 1, wherein the steel slag is 1 mm or less. 3. The method for treating waste acid according to claim 1, wherein the steel slag is added to the waste acid after being preliminarily reduced.