JP2015160920A - Acid soil conditioner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an acid soil conditioner which does not supply excessive alkali and can supply alkali autonomously according to change of a quality of soil and can hold a pH of the soil within a certain width steadily for a long term.SOLUTION: A powder, granular or aggregated alkali material has chitosan coating on a surface thereof. Because the chitosan coating is solid and kept stably in alkali environment, and is not solidified in acidic environment when contacting soil is acidity, alkali is supplied to neighboring by losing the solid chitosan coating and exposing the alkali material to the environment, and the acidity of the soil can be improved.

Description

  The present invention is a soil improvement material for improving acidic soil and maintaining it in a neutral region or the like, and in particular, acidic soil that can be used by controlling the alkalinity of steel slag, which is a byproduct of the steel manufacturing process. It relates to the improved material.

  Most of Japan's soils are said to be acidic soils, and it is known that some soils exhibit strong acidity in some areas. This cause is said to be due to oxidation of sulfide contained in the soil to become acidic sulfuric acid soil (for example, Materials, Vol. 53, pp. 1351-1358 (2004)). In addition, there is also knowledge that soil in planted forests is acidified depending on management conditions. In addition to this, the problem of acid rain has become apparent in recent years, and the acidification of soil due to this has also progressed.

  If the soil becomes too acidic, plant growth will be impaired, and appropriate soil improvement is required. As a typical method, there is a method of improving by supplying alkaline material to the soil, and in addition, a method of forming an acidic barrier layer by mixing alkaline soil and organic material has been proposed. In particular, the former is a simple and effective method, but if alkaline material is excessively supplied, there is a problem that the soil pH changes to the alkali side, which is counterproductive.

  Since steelmaking slag contains a large amount of calcium in its components, it can be used as an alkaline material. For example, Patent Document 1 states that acidification can be prevented and elution of heavy metals can be suppressed by supplying sized steelmaking slag to soil that may be acidified or acidified soil. However, the pH range in the present invention is 6 to 13, and it is suggested that the response to the excessive alkali supply cannot be realized only by slag sizing. Further, Patent Document 2 proposes a method in which a guest soil obtained by mixing and stirring an organic material containing converter slag and bark compost and seeds is used as an acid relaxation base material. This method is intended to work on soil structures that are dysfunctional due to significantly reduced soil pH, so it is presumed to work effectively on such soils, but not so acidic soils, It is difficult to improve soil that may become acidic in the future.

Japanese Patent Application Laid-Open No. 2000-282034 Japanese Patent No. 5179456

As described above, the method of improving acidic soil by mixing alkaline materials is the simplest and most effective, but the amount of addition directly leads to the amount of alkali supply, so the soil quality may change over time, or depending on the location There was a problem that it could not be adequately handled when there was a change in soil quality.
Therefore, the object of the present invention is to solve the above-mentioned problems of the prior art, without supplying excessive alkali, and even when the soil quality changes, the alkali can be supplied autonomously accordingly. Thus, an object of the present invention is to provide an acidic soil improving material capable of stably maintaining the pH of the soil in a certain range over a long period of time.

  The inventors of the present invention have studied the technique for solving the above-mentioned problems, and as a result, have obtained the following idea. By covering a material that is an alkali source such as steel slag (hereinafter, “steel slag” will be described as an example) with some substance, the supply of alkali is suppressed and the environment in which the environment is placed is excessively acidic. In this case, the steel slag is exposed by the collapse or dissolution of the coating, and the alkali can be supplied for the first time. In addition, when a certain amount of this is mixed in the soil, the cover is first removed and the alkali is supplied in the area where acidification has progressed, and as a result, the surrounding soil becomes neutral to weakly alkaline, The coating of the steel slag mixed with is protected and no alkali is supplied from there. Accordingly, excessive alkali is avoided, and by proceeding in stages, it becomes possible to stably maintain the pH of the soil in a certain range for a long time.

In order to realize the above, it is necessary to find a coating material that can form a stable coating on the surface of the steel slag and that disintegrates or dissolves in an excessively acidic environment. Moreover, since it is a soil material, economic rationality is also required at the same time.
Conventionally, several coating techniques for steel slag have been proposed. For example, Japanese Patent Application Laid-Open No. 2004-313818 discloses a method of coating steelmaking slag with a cement-based compound, and shows a tendency that pH increase is suppressed as compared with steelmaking slag. Since the material itself is a strongly alkaline material and always supplies an excessive amount of alkali, it is not suitable as a method for solving the problems of the present invention.

Moreover, the method of carbonating steel slag is known, and according to this method, a film such as calcium carbonate is formed on the slag surface. Since calcium carbonate itself dissolves when it becomes acidic, it is also used to improve the acidity of the actual soil. If calcium carbonate can coat the entire surface of the slag well, it may function. Moreover, since calcium carbonate is weakly alkaline, it can be expected that a mild pH improving effect can be obtained as compared with the case of mixing ordinary steel slag. However, the carbonized film is formed by the reaction of CO ₂ gas through the water adhering to the surface of the slag, and various mineral phases exist in steel slag. In many cases, it is difficult to stably form a carbonized film on the entire slag surface due to the presence of difficult-to-form phases. As a result, the steel slag of the base material is partially exposed. The effect as a capsule material having high possibility and pH sensitivity is slightly reduced.

  In addition to the method described above, a method of forming an organic film called a biofilm has also been proposed. This method is a technique in which a biofilm is sequentially formed on the entire surface of the slag by providing nutrients, and covers the surface including dead bodies. If this technique can function effectively, it will eventually be possible to cover almost entirely even if the slag surface is not completely covered at first. However, it was found that there are not many microorganisms that can survive in an environment where the initial alkali is relatively strong, and there are many cases where it is not easy to develop a biofilm for steel slag. In addition, since whether or not the film disappears when the pH becomes acidic depends on microorganisms, there is a possibility that the influence of the use environment may increase, and a stable effect cannot be expected.

  In contrast to the prior art as described above, the present inventors have been able to form a stable film on the surface of steel slag, and as a film material that dissolves or disintegrates when it becomes acidic, chitosan, which is a polymer substance, is used. I found it promising. Chitosan is a polymer produced by processing chitin contained in crustaceans such as crabs and shrimps, and has high ecological affinity and low toxicity. For example, if a chitosan solution is dried, a film can be formed. Chitosan is weakly acidic and can be made into a solution state, but if this is shaken alkaline, gelation proceeds and solidifies. That is, when chitosan is made into a solution state and adhered to the surface of steel slag (for example, sprayed), chitosan is solidified by the action of alkali eluted from the steel slag, and the surface of the steel slag is relatively dense and effective in alkali elution. It has been found that a stable film (chitosan film) that can be suppressed is formed. Furthermore, it was found that when this film was placed in an acidic environment, the film disappeared stepwise (or gradually) and alkali was supplied from the slag.

The present invention has been made on the basis of the above-described findings and has the following gist.
[1] An acidic soil improving material having a chitosan film on the surface of a powdery or massive alkaline material.
[2] The acidic soil improvement material according to [1] above, wherein a carbonated film formed by carbonation of an alkaline material component is formed at a non-formation site of the chitosan film on the surface of the alkaline material. Improvement material.
[3] The acidic soil improver according to the above [1], which has a chitosan film on the surface of a carbonated alkaline material.

[4] The acidic soil improvement material according to any one of the above [1] to [3], wherein the alkaline material is steel slag.
[5] The acidic soil improvement material according to [4], wherein the steel slag is at least one selected from hot metal pretreatment slag and decarburization furnace slag.
[6] A method for producing an acidic soil improving material, wherein a chitosan film is formed on the surface of an alkaline material by adhering a chitosan solution to the granular or massive alkaline material.
[7] A method for producing an acidic soil improving material according to [6], wherein the alkaline material having a chitosan solution attached thereto or the alkaline material having a chitosan film formed on the surface thereof is carbonized.

[8] The method for producing an acidic soil improving material according to the above [6], wherein the alkali material having a chitosan solution attached thereto or the alkali material having a chitosan film formed on the surface is aged for 6 months or more. .
[9] The method for producing an acidic soil improving material according to the above [6], wherein the chitosan solution is attached to an alkaline material that has been previously carbonized.
[10] The method for producing an acidic soil improving material according to any one of the above [6] to [9], wherein the alkaline material is steel slag.
[11] The method for producing an acidic soil improver according to [10], wherein the steel slag is at least one selected from hot metal pretreatment slag and decarburization furnace slag.

  In the acidic soil improvement material of the present invention, the chitosan film formed on the surface of the alkaline material is a film that is stably maintained in a solid state in an alkaline environment and non-solidified in an acidic environment. In this case, the solid chitosan film is lost and the alkaline material is exposed to the environment, so that alkali is supplied to the surrounding area, and the acidity of the soil can be improved (for example, neutralization or weak alkalinization). In addition, when the acid soil around the soil is improved by some soil amendments due to the above mechanism, the surroundings become neutral to weakly alkaline. Is kept covered with the chitosan coating, thereby avoiding the supply of a large amount of alkali at once. For this reason, the improvement effect is exhibited only when the acidity becomes strong, and the pH of the soil can be stably maintained within a certain range for a long time.

In addition, an acidic soil improvement material obtained by subjecting an alkaline material to which a chitosan solution is adhered or an alkaline material having a chitosan film formed on the surface to carbonation treatment or atmospheric aging for a certain period of time is a non-chitosan film on the surface of the alkaline material. Since the carbonized film generated by carbonation of the alkaline material component is formed at the formation site (film defect part) and the weak part due to uneven formation of the chitosan film is strengthened, the alkali supply is controlled more appropriately. Will be.
In addition, an acidic soil improvement material in which a chitosan film is formed on the surface of an alkaline material that has been pre-carbonized is also generated by carbonation of the alkaline material component at the non-formation part (film defect part) of the chitosan film on the surface of the alkaline material. The carbonized film thus formed is formed, and the weakened part due to the uneven formation of the chitosan film is strengthened, so that the alkali supply is more appropriately controlled.

A steelmaking slag having a chitosan film formed on the surface is immersed in an aqueous solution whose initial pH is adjusted to 4.0, 5.0, or 6.5, respectively, and an elution test is performed by a tank leaching test method (JIS K0058-1). The graph which shows the result which carried out and examined the change of pH by immersion time An aqueous solution of pH 2.5 was added dropwise to a sample such as soil mixed with the soil improving material of the present invention obtained in Example 1 and soil mixed with untreated steelmaking slag, and the pH of the permeated water was measured. Graph showing the transition of the pH of the permeated water relative to the total amount of the aqueous solution charged A test in which an aqueous solution of pH 6 was added dropwise to a sample such as soil mixed with the soil improvement material of the present invention obtained in Example 2, soil mixed with untreated steelmaking slag, and the pH of the permeated water was measured. Showing the transition of the pH of the permeated water with respect to the total amount of the aqueous solution added

The acidic soil improving material of the present invention has a chitosan film on the surface of a granular or massive alkaline material such as steel slag, and such an acidic soil improving material is a chitosan on a granular or massive alkaline material. It is produced by attaching a solution and forming a chitosan film on the surface of the alkaline material.
Hereinafter, a case where the alkaline material is steel slag will be described as an example.
Steel slag contains a large amount of CaO component and MgO component, and when the surface and water come into contact with each other, these components react with water to generate OH- ions, which raise the surrounding pH. Therefore, if the surface of iron and steel slag particles can be stably covered with a material that maintains a stable solid state in an alkaline environment and dissolves in an acidic environment, the surface of the steel slag particles is autonomous depending on the soil condition, supplying alkali only in an acidic environment. It can be set as the soil improvement material which can supply alkali alkaline.

In order to investigate the performance (effect) of steel slag having a chitosan film, the following tests were conducted. A solution prepared by dissolving chitosan in an organic acid and adjusting the chitosan concentration to 1 mass% is sprayed on steelmaking slag (particle size 5 to 30 mm) having a basicity (CaO / SiO ₂ ) of 3.5, and this is applied in the atmosphere for 3 days. Cured to form a chitosan film on the surface of the slag particles. The steelmaking slag was adjusted to an aqueous solution (pH was adjusted by adding sulfuric acid to ion-exchanged water) adjusted to pH 4.0, 5.0, and 6.5 so that the liquid-solid ratio was 10: 1. An elution test by a tank leaching test method (JIS K0058-1) in which the sample was immersed and stirred at a rotational speed of 200 rpm with a stirring blade was performed, and the change in pH due to the immersion time was examined. The result is shown in FIG.

  According to FIG. 1, when the initial pH of the aqueous solution exceeds 6 (pH 6.5), the pH only rises to a level slightly exceeding pH 9. This is considered to be because a trace amount of alkali is eluted at the initial stage of immersion, but thereafter the elution of alkali is suppressed by the chitosan film. In addition, the elution of a trace amount of alkali components at the initial stage of immersion is because the chitosan film contains alkali components such as calcium diffused from the slag during the formation of the chitosan film, and this alkaline component dissolves at the initial stage of immersion. Conceivable. On the other hand, in the case of an acidic environment such as the initial pH 4.0 or 5.0 of the aqueous solution, the pH does not drop accordingly, but conversely the pH rises to about 11. This is considered to be because the film is removed by exposing the chitosan film to an acidic environment, the steelmaking slag inside is in direct contact with water, and alkali is supplied to the outside.

  Therefore, when steel slag with a chitosan film comes into contact with acidic soil or when it is strongly affected by acidic soil, the solid chitosan film of the steel slag is lost and the steel slag is exposed to the environment. Alkali is supplied to the surrounding area, and the acidity of the soil can be improved (for example, neutralization or weak alkalinization). In addition, when some soil amendments improve the surrounding acidic soil, other soil amendments present in the vicinity are maintained once the steel slag is covered with the chitosan film. It is avoided that a large amount of alkali is supplied. For this reason, the improvement effect is exhibited only when the acidity becomes strong, and it becomes possible to stabilize the pH of the soil in a certain range over a long period of time.

In the present invention, the alkaline material for forming the chitosan film is not particularly limited in type as long as it has an ability to supply alkali such as Ca ions and Mg ions and is in the form of particles or lumps. Examples include, but are not limited to, limestone, calcium carbonate, concrete glass (waste material), shells, sawdust, and steel slag. One or more of these alkaline materials can be used. In particular, steel slag is known to be effective as a soil fertilizer because it contains various trace components, and is more desirable.
Since steel slag is only required to be supplied with alkali, both blast furnace slag and steelmaking slag are targeted. However, when considering the alkali improvement effect of the soil, steelmaking slag having a higher basicity (CaO / SiO ₂ ) is desirable.

Examples of steelmaking slag include hot metal pretreatment slag (dephosphorization slag, desulfurization slag, etc.), decarburization slag generated in decarburization furnaces such as converters, electric furnace slag, secondary refining slag, ingot slag, etc. However, it is not limited to these. One or more of these steelmaking slags can be used. Of these, those having a basicity (CaO / SiO ₂ ) of more than 3 often contain free CaO and have a large ability to supply alkali to the periphery, and therefore are suitable as the object of the present invention. . However, when the basicity exceeds 5, it is difficult to ensure volume stability regardless of the presence or absence of the chitosan film, so the basicity of the steelmaking slag is preferably 5 or less.

Also, among steelmaking slag, it is produced as a lump or powder material suitable for earthwork materials, etc., and the basicity is relatively stable. Furnace slag is preferred, and one or more of these are preferably used.
The steelmaking slag may be either granular or lump-shaped, but considering that the soil improvement material becomes part of the soil as it is, the particle size is preferably 30 mm or less, and more preferably 5 mm or less. The same applies to other alkaline materials.

In the acidic soil improving material of the present invention, the chitosan film on the surface of steel slag (alkaline material) can be obtained by attaching a chitosan solution to a granular or massive steel slag. Usually, after the chitosan solution is attached, curing is usually performed.
The method of supplying the chitosan solution to the steel slag and adhering it to the slag surface (wetting the slag surface) is arbitrary, but usually the method of spraying the chitosan solution on the steel slag or immersing the steel slag in the chitosan solution is adopted. It is done. As for the chitosan concentration of the chitosan solution, if the concentration is too low, the coating degree of the film cannot be secured sufficiently. From this viewpoint, the chitosan concentration is preferably 0.1 mass% or more. On the other hand, the higher the chitosan concentration of the solution, the more the film thickness can be secured. However, when the concentration is too high, the viscosity increases and it is difficult to efficiently form the film. From this viewpoint, the chitosan concentration is preferably 3 mass% or less, and more preferably 1 mass% or less.

The amount of chitosan solution applied to the steel slag is desirably such that the surface of the slag is almost stably covered with the chitosan solution, and the mass of the solution is preferably 1 mass% or more of the steel slag. In particular, about steel slag with much powder content, about 1 mass% may not be enough, and in that case, 3 mass% or more is desirable. Although there is no particular upper limit, a solution that does not participate in the reaction remains in the periphery even if there is a surplus, so about 15 mass% is a good guideline.
Further, in the method in which the chitosan solution is sprayed on the steel slag, the steel slag after the solution spraying may be stirred with a mixer or a stirrer so that the chitosan solution is spread over the entire slag.

  Chitosan is a polymer produced by processing chitin contained in crustaceans such as crabs and shrimps, but chitosan itself is almost insoluble in water, and chitosan solution is made of acid (weakly acidic). A solution obtained by dissolving in (solution) is used. The acid can be any of inorganic acids such as hydrochloric acid and nitric acid, and organic acids such as acetic acid, lactic acid, gluconic acid and malic acid. However, the organic acid is used because the Ca concentration in the solution can be kept high. More desirable. Of organic acids, acetic acid and lactic acid are particularly preferred.

After supplying chitosan solution to steel slag and attaching it to the slag surface, it is usually cured, but this curing method can be performed by curing in the air, carbonation curing (carbonation treatment) described later, etc. it can. In order to stabilize the chitosan film, the curing period is preferably 3 days or longer, preferably 7 days or longer in the atmosphere. When drying proceeds due to gas distribution effect such as carbonation treatment, it may be about 6 hours.
By the solution treatment and curing as described above, a chitosan film is formed on the surface of each slag particle of the steel slag. This chitosan film is formed by solidifying chitosan adhering to the slag surface by the effect of alkali eluted from this steel slag, and it is a relatively dense film that can effectively suppress alkali elution. It is. The same applies even when the alkaline material is a material other than steel slag.

Steel slag (particularly steelmaking slag) contains free CaO and the like, and therefore has the potential to increase the pH to 12 or more when it comes into contact with water. In the acidic soil improvement material of the present invention, the chitosan film covering the steel slag in the acidic soil gradually collapses, and the alkaline soil is improved by eluting the alkali. Therefore, the chitosan film is formed without pretreatment of the steel slag. Although there is no particular problem even if it has been made, in this case, there is a possibility that the portion immediately adjacent to the slag becomes a slightly higher alkali. In order to avoid such a condition, it is preferable to carbonize steel slag in advance and form a chitosan film on the carbonized steel slag. If the steel slag is carbonated in advance, the free CaO content is CaCO _3, and thereby the alkali supply is more appropriately controlled (suppressed). For this reason, the alkali of the immediate vicinity of slag does not become so high, and the rapid change of soil can be relieved.

  A more desirable method is a method in which an alkaline material to which a chitosan solution is adhered or an alkaline material in which a chitosan film is formed on the surface is carbonized, whereby a chitosan film is not formed on the surface of the steel slag (film). It becomes an acidic soil improvement material in which a carbonized film generated by carbonation of steel slag components is formed (filled) in the defective part). In the case of steel slag, calcium carbonate and / or magnesium carbonate is produced by the carbonation reaction of Ca or / and Mg, which is a slag component, and this product (carbonized film) is a non-formation part (film defect part) of the chitosan film. Is coated (filled). As a result, a film in which a chitosan film and a carbonate are combined (an organic-inorganic composite film mainly composed of chitosan and combined with calcium carbonate and / or magnesium carbonate) is formed. This organic-inorganic composite film is a more stable film, and the alkali supply rate can be slightly reduced by relaxing the decomposition of the film. That is, since the weakened part due to the uneven formation of the chitosan film is reinforced with the carbonate, the alkali supply is more appropriately controlled (suppressed).

Further, since carbonation proceeds by carrying out air curing for a certain period or longer, an alkali material having a chitosan solution attached or an alkali material having a chitosan film formed on the surface may be subjected to air aging for a certain period or longer. As a result, the acid soil improvement material almost the same as the carbonation treatment, that is, the carbonized film formed by carbonation of the steel slag component is formed on the non-formation part (film defect part) of the chitosan film on the steel slag surface ( It becomes an acidic soil improvement material having a composite film filled.
Atmospheric aging causes a certain degree of carbonation to progress in 2 months or more, but in order to form a more stable composite film, atmospheric aging of 6 months or more is preferable.

When carbonizing steel slag in advance, or when carbonating steel slag that has been treated with chitosan, the carbonation should be performed with an appropriate amount of water (preferably the amount of water having surface adhering water). It is done by supplying the CO ₂ containing gas to the adjusted steel slag. Specific methods include, for example, a method in which CO ₂ -containing gas is blown into a slag pile, a method in which slag is housed in a container and CO ₂ -containing gas is blown into the slag in the container from the bottom of the container, and steel slag is stirred. However, a method such as a method of blowing CO ₂ into the container can be employed. Further, by immersing the steel slag in water, a method of blowing CO ₂ containing gas to the water it is also possible. As the CO ₂ -containing gas, for example, exhaust gas discharged from various facilities in the steelworks can be used.
Although the case where the alkaline material is steel slag has been described above as an example, the same applies to other materials.

[Example 1]
A chitosan solution was sprayed on steelmaking slag (decarburization furnace slag, basicity (CaO / SiO ₂ ): 3.5, particle size: 0-25 mm) and then cured to obtain a soil improvement material of the present invention. Curing was performed by carbonation curing. The carbonation curing was treated with chitosan, placed in a container, and treated with 1 atm CO ₂ for 6 hours.
The soil improvement material of the present invention obtained as described above is mixed with soil (Kanto loam) and packed in a φ150 mm mold to a thickness of 150 mm so that the filling rate is about 80%. It was set as the sample of this. An aqueous solution adjusted to pH 2.5 with an acid in which sulfuric acid and nitric acid were mixed at a ratio of 2: 1 was dropped, and the pH of the permeated water was measured. For comparison, the same test was performed on a sample of only soil (Kanto Loam) and a sample of only untreated steel slag.

  FIG. 2 shows the pH transition of the permeate with respect to the total amount of the aqueous solution charged. In the case of the soil-only sample, the pH decreases as the total amount of the aqueous solution added increases and falls below pH 5, whereas in the case of the sample of the present invention material, although the pH is slightly lower at the beginning, it passes a certain amount of water. After that, it rises to around pH 7 and is stable. On the other hand, in the case of a sample made of only untreated steelmaking slag, the pH is close to 10, which is an excessive alkaline environment.

[Example 2]
A chitosan solution was sprayed on steelmaking slag (decarburization furnace slag, basicity (CaO / SiO ₂ ): 3.5, particle size: 0-25 mm) and then cured to obtain a soil improvement material of the present invention. Curing was performed by carbonation curing. The carbonation curing was treated with chitosan, placed in a container, and treated with 1 atm CO ₂ for 6 hours.
The soil improvement material of the present invention obtained as described above is mixed with soil (Kanto loam) and packed in a φ150 mm mold to a thickness of 150 mm so that the filling rate is about 80%. It was set as the sample of this. Here, ion exchange water having pH 6 was dropped, and the pH of permeate was measured. For comparison, a similar test was performed on a sample containing only soil (Kanto Loam), a sample containing only untreated steel slag, and a sample obtained by mixing untreated steel slag with soil (Kanto Loam).

  FIG. 3 shows the pH transition of the permeated water relative to the total amount of water input. In the case of a sample in which untreated steelmaking slag is mixed with soil (Kanto loam), it is initially in the vicinity of pH 7, but when the amount of permeate increases, the alkali starts to rise rapidly. On the other hand, in the case of the sample of the present invention material, it is maintained in the vicinity of pH 7 for a long time, and it can be confirmed that even when neutral water is dripped, it can be prevented from becoming a strong alkali.

Claims (11)

  An acidic soil improvement material characterized by having a chitosan film on the surface of a powdery or massive alkaline material.   The acidic soil improvement material according to claim 1, wherein a carbonized film generated by carbonation of an alkaline material component is formed at a non-formation site of the chitosan film on the surface of the alkaline material.   The acidic soil improvement material according to claim 1, which has a chitosan film on the surface of a carbonized alkaline material.   The acidic soil improvement material according to any one of claims 1 to 3, wherein the alkaline material is steel slag.   The acidic soil improvement material according to claim 4, wherein the steel slag is at least one selected from hot metal pretreatment slag and decarburization furnace slag.   A method for producing an acidic soil improving material, wherein a chitosan film is formed on a surface of an alkaline material by adhering a chitosan solution to a granular or massive alkaline material.   The method for producing an acidic soil improvement material according to claim 6, wherein an alkaline material having a chitosan solution attached thereto or an alkaline material having a chitosan film formed on the surface thereof is carbonized.   The method for producing an acidic soil amendment according to claim 6, wherein the alkali material having a chitosan solution attached thereto or the alkali material having a chitosan film formed on the surface thereof is subjected to air aging for 6 months or more.   The method for producing an acidic soil improvement material according to claim 6, wherein a chitosan solution is attached to an alkaline material that has been carbonized in advance.   The method for producing an acidic soil improvement material according to any one of claims 6 to 9, wherein the alkaline material is steel slag.   The method for producing an acidic soil improvement material according to claim 10, wherein the steel slag is at least one selected from hot metal pretreatment slag and decarburization furnace slag.

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