JP2000282034A - Method for preventing soil acidification and for stabilizing soil ph - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for properly adjusting the pH of acidic soil or soil with concern for acidification, maintaining the pH thus adjusted within a proper range, thereby stabilizing the heavy metals in the soil, preventing environmental pollution, and improving and maintaining the crop suitability of the soil as well. SOLUTION: This method comprises applying an alkaline material trimmed in granular size so as to be 30 mm in the maximum size to soil to be treated so as to prevent the soil from acidification and also stably maintaining the pH of the soil thus adjusted within a proper range over a long period; wherein the above alkaline material is characterized by being at least one kind selected from the group consisting of blast furnace slag, converter slag, coal ash, limestone and lime.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to the prevention of soil acidification using an alkaline material and stabilization of soil pH. It relates to the stabilization or immobilization of heavy metals that already exist or are imported from the outside.

[0002]

2. Description of the Related Art Soil, which is the basis of various human activities,
It is often acidified and adversely affected by a variety of factors. For example, when heavy metals are present in soil, if the soil is acidic, the heavy metals may at least partially dissolve and run off, causing secondary pollution. In such a case, the occurrence of such a problem can be prevented by controlling the degree of acidification of the soil. It is also well known that soil acidification is undesirable for most cultivated crops. Therefore, to prevent acidification of the soil, or to neutralize or alkaline acid soil,
It is desirable to be able to maintain an appropriate pH value over time.

[0003] For such a purpose, various means have been conventionally proposed and implemented. The related arts will be discussed below. (1) For waste such as incinerated ash, Notification No. 194 of the Ministry of Health and Welfare
Article No. 1 describes a cement solidification method, a chemical treatment method, an acid extraction method and a melting method. Also, a method of stabilizing heavy metals using steel slag has been proposed. But,
These methods are intended to stabilize heavy metals contained in the waste itself, such as incineration ash, and thus are difficult to apply to stabilization of heavy metals contained in soil. It has also been proposed to use iron slag as a soil conditioner, but its main purpose is to improve the physical properties of the soil, and the effect of stabilizing heavy metals has not been recognized. Is unknown.

(2) The cement solidification method is based on the principle that heavy metals are adsorbed on the surface of calcium silicate and solidified, and if this principle is applied to soil, cement is mixed into soil. Have to do
As a result, the heavy metal is immobilized, but at the same time, the soil hardens, and it is difficult to crush the once hardened soil and restore it to its original state, which is not practical.

(3) In the chemical treatment method, a heavy metal scavenger, a flocculant, an inhibitor, and the like are added to form an insoluble heavy metal complex compound, thereby stabilizing the heavy metal. The stabilizing agent stabilizes most of the metal ions, fixing even ions necessary for soil organisms, and has a serious effect on soil ecosystems. In addition, soil contamination due to these chemicals occurs and cannot be applied in practice.

(4) The acid extraction method is a technique for extracting a heavy metal by dissolving it in an aqueous solution by the action of an acid. Even if it can be applied to a soil having a small area, it is not possible to perform such extraction work on a wide range of soil. It is practically impossible. Also, it is difficult for the melting method to melt and solidify all soil in a wide range.

(5) Furthermore, several methods for stabilizing heavy metals using slag have been proposed, but all of them are difficult to apply to soil. For example, Japanese Patent Application Laid-Open No. 56-51240 proposes a treatment material for eluting heavy metals and a method of treating the same. However, since this is a method of eluting heavy metals and adsorbing them with slag,
Extraction and transportation of soil are required to implement the method on a large amount of soil over a wide area, and the soil itself becomes waste and is difficult to implement under the current method by moving the soil. JP-A-57-60074 proposes a method for detoxifying waste containing heavy metals, but it is difficult to mix a large amount of soil into molten slag for the same reason as described above. Further, in Japanese Patent Application Laid-Open No.
A treatment method for municipal waste incineration ash has been proposed, but this is a stabilization technique using cement, and it is difficult to apply this to soil treatment as described in (2) above.

(6) For soil improvement, various soil amendments have been proposed, but these are mainly used for the purpose of improving the physical properties of the soil and stabilize heavy metals in the soil. It is not intended. For example, JP
Japanese Patent No. 3-17157 discloses a soil improvement material for turf, which is mainly composed of granulated blast furnace slag. The purpose is to improve the physical properties of the topsoil as a lawn soil, and to control soil pH. Is not intended, and its effect is unknown. JP-A-60-5088 discloses that chromium ore is used as a main raw material, carbonaceous material and flux are added thereto, and chromium and iron are reduced and melted and separated.
1.39 MgO) / (SiO ₂ +1.18 Al ₂ O ₃ ) =
A soil amendment material for slag manufactured to satisfy the component conditions of 0.7 to 1.2 and Al2O3 = 17 to 22% is disclosed. There is a problem that the cost is high, the effect of adjusting the soil pH is unknown, and the high content of Al2O3 causes the root rot of the crop due to elution of a high concentration of aluminum ions, and may further promote the acidification of the soil. Also, JP-A-1-168
No. 791 discloses a soil improvement material for turfgrass in which an acidifying agent is mixed with steel slag. However, since the acidifying agent is mixed, the alkali properties of the steel slag disappear and are neutralized. Therefore, it is not suitable for adjusting the pH of acid soils often found in Japan and the like.

[0009]

[Problems to be solved by the invention] Most of the soil in Japan is
Due to the formation of volcanic ash due to weathering and the climatic conditions of warm rain in Japan, it usually exhibits weak acidity. In addition, several mechanisms promote soil acidification. Acidification of soil by acid rain, acidification of soil by weathering of soil, acidification of soil caused by improper ion balance as a result of continuous cropping using chemical fertilizer, and sulfuric acid generated by oxidation of sulfur compounds by soil microorganisms Soil acidification (see Figure 2) caused by
The area tends to increase year by year.

When the soil becomes acidic, heavy metals such as manganese, zinc, arsenic, cadmium, nickel, and lead, which are originally present in the soil, elute, tending to cause environmental pollution and growth inhibition of crops. Become like In addition, environmental pollution of soil due to heavy metals contained in wastewater from waste disposal sites, factories that refine or use heavy metals, and the like has become a problem.

Once a wide range of soil is contaminated, it is difficult to purify and remove heavy metals. At present, various methods for treating heavy metals in wastes such as incineration ash have been proposed, but as described above, they cannot be applied to the treatment of soil that is widely contaminated.

For soil contaminated with heavy metals as described above, the pH is appropriately adjusted for heavy metals,
It is desirable to maintain H for a long period of time so that heavy metals are insolubilized as hydroxide salts and stabilized.

[0013]

Means for Solving the Problems The present inventors have developed a method for preventing acidification of soil with less adverse effect and / or an appropriate method for preventing soil acidification.
We have been diligently studying and studying the H adjustment method and, finally, the method of stabilizing heavy metals.

Thus, the present invention is to prevent acidification of soil which may be acidified by various factors, or to properly adjust the pH of acidified or weakly acidic soil and maintain it for a long period of time. Providing a method comprising: In this method, when the soil contains a heavy metal naturally or naturally or contains a heavy metal imported from the outside, the heavy metal is insolubilized, and the outflow from the soil and the occurrence of secondary pollution are effectively prevented. In addition, soil unsuitable for crop cultivation due to the influence of heavy metals can be recovered so that crop cultivation is possible.
More specifically, the present invention relates to the above method comprising applying an effective amount of alkali materials (blast furnace slag, converter slag, coal ash, limestone and lime) whose particle size has been adjusted to the soil.

[0015] In one embodiment of the present invention, acidification of the soil is performed by applying an alkali material sized so that the maximum particle size is 30 mm to the soil which may be acidified or the acidified soil. A method for preventing and stabilizing soil pH for a long time, wherein the alkaline material is at least one selected from the group consisting of blast furnace slag, converter slag, coal ash, limestone, and lime. The above method is provided.

In another embodiment of the present invention, at least one of blast furnace slag, converter slag, coal ash, limestone and lime sized to have a maximum particle size of 30 mm,
Applying an alkaline material containing calcium as a main component and releasing it to prevent acidification of the soil, and furthermore, pH 6-1 of the soil
By adjusting to a target value within the range of 3 and stabilizing the soil pH for a long period of time, it is possible to obtain soil from a site containing naturally high concentrations of heavy metals, waste disposal sites, and factories that refin or use heavy metals. A method is provided for stabilizing heavy metals in soils that are contaminated with wastewater and contain high concentrations of heavy metals.

In the present invention, prevention of soil acidification and / or
Or stabilization of heavy metals by appropriate soil pH adjustment,
By applying an effective amount of an alkali material having a particle size adjusted to 30 mm or less, heavy metals can be insolubilized by the effect of ions such as iron, calcium, and magnesium that are gradually and long-term eluted according to soil pH. The pH value required for insolubilization (stabilization) of heavy metals differs depending on the type of heavy metals, and for the purpose of the present invention, it is necessary to adjust the pH to an appropriate range of pH 6 or more. Further, in order to adjust the pH to 13 or more, a large amount of alkali material is required, which is not practical.

Regarding the pH value in the present invention, it is necessary to adjust the soil pH to 8 or more for stabilization depending on the type of heavy metal. A pH of 8 or higher can lead to environmental pollution, but the pH rises in the immediate soil applied, but is neutralized by the effect of soil interference, and therefore in most cases is several tens of centimeters away In the place, the effect of environmental pollution does not substantially occur in the present invention since the place is almost neutralized.

The maximum particle size of the alkaline material in the present invention is 30 mm, because if the maximum particle size exceeds 30 mm, mixing of the alkaline material into the soil by heavy equipment, other equipment, and tools is hindered. is there. If alkaline materials are used in a crushed form, as in the case of lime application, the pH rapidly rises due to the rapid and excessive elution of the alkaline components calcium, iron, magnesium, etc. May have serious adverse effects on microorganisms. In such a case, the long-term effect cannot be expected because the persistence of the elution of the alkali component is poor. Since each alkali component shows different elution behavior and exhibits a different stabilizing action for each heavy metal, by appropriately combining two or more alkali materials (different alkali component compositions) as necessary. ,
The most effective action can be obtained for each soil. Such a combination can be easily set by those skilled in the art by considering the composition characteristics of the alkaline material, the characteristics of the soil, and the like. In particular, converter slag contains phosphoric acid together with iron, calcium, and magnesium ions, and thus has the advantage that the effect of insolubilizing heavy metals is enhanced.

The heavy metal ions combine with the hydroxide ions in a pH-dependent manner (particularly at the alkaline pH) to form insoluble salts. The present invention is based on stabilizing (fixing) heavy metals by adjusting the soil pH using an alkaline material and maintaining the pH value in an appropriate range for a long period of time.

Table 1 shows that the solubility products of the main heavy metals and the hydroxide ions, the equilibrium constants of the complex ions of the amphoteric hydroxide and the hydrogen ions, and the dissolution concentrations of the main heavy metals are 10-5 m.
Shows data on the pH range below ol / l. The equation of the solubility product of heavy metal and hydroxide ion explains the decrease in the concentration of heavy metal dissolved with increasing pH (= increase in hydroxide ion concentration). Some heavy metals redissolve when the alkalinity becomes too high, and this phenomenon is explained by the equilibrium constant between the complex ion of amphoteric hydroxide and hydrogen ion.

[0022]

[Table 1]

For reference, Table 2 shows the results of chemical composition analysis of various alkali materials.

[0024]

[Table 2]

EXAMPLES As test samples, acidic soil (pH 5.1) of Amami Oshima was used. Various alkali materials were mixed with the sample soil at the ratios shown in Table 3 (weight percentage w / w percent), and the pH of each mixed sample was measured. In this operation, a predetermined amount of an alkaline material is mixed with the dried soil. For example, in (8), 20% of granulated blast furnace slag and 10% of converter slag are used for 70% of dry soil. -Cent mixing and the pH of this mixture was determined by a dissolution test. Table 3 shows the results of the tests (1) to (13). As shown in Tests (2) to (6), as the mixing ratio of the converter slag increased, the soil pH increased. Similarly, the soil pH rises in proportion to the mixing ratio of each alkaline material, and thus, by increasing or decreasing the mixing ratio, the soil p
H can be freely controlled between about 6 and 13.

[0026]

[Table 3]

Next, the effect of the pH value on the stabilization of heavy metals will be clarified. Converter slag was added to the acidic soil (pH 5.1) at 0, 5, 10, 15, 20, and 30 percent to adjust the soil pH as shown in Table 3. 0.005 m for each soil 1.0 g thus treated
ol / l ZnSO4, 0.005 mol / l MnS
An aqueous solution containing O4 was added, shaken for 4 hours, allowed to stand, and the concentrations of zinc and manganese in the supernatant were measured. The results of a series of these experiments are summarized in Table 4 and FIG.

[0028]

[Table 4]

The zinc concentration in the supernatant began to drop at pH 7.8 and reached a minimum at pH 8.9. This decrease in concentration is due to the solubility product of zinc ions [Zn] [OH] ₂ = 1.2 × 1
It is described by 0-17. Following the minimum above,
The zinc concentration increased again with increasing pH. This is because zinc formed a complex ion of the amphoteric hydroxide and redissolved. Its solubility product is [HZnO ₂ ] [H] = 10-17, which explains the concentration of zinc in the supernatant. The concentration in the manganese supernatant begins to decrease from around pH 7.8 and is low and stable above pH 10.4. This is the solubility product of manganese ions, as with zinc.
[HZnO ₂ ] = 1.9 × 10−13. Since manganese has a higher solubility product of complex ions of amphoteric hydroxide than zinc in a high pH range, no re-dissolution was observed in this high pH range. From these results, it was found that the soil (especially, the soil which may be acidified, the acidified soil) using the alkaline material such as the slag described above was used.
H can be adjusted effectively and practically, and its pH
It is clear that the implementation of the adjustment can stabilize the heavy metals present in the soil for a long period of time, prevent their elution and eliminate the occurrence of secondary contamination. The same tendency was observed in the results of repeated field experiments in soil areas having various pH characteristics, and from the results of these numerous field experiments, the soil pH adjustment effect achieved by the alkali material of the present invention was several It has been ascertained or assumed to be maintained for a year, for example, about 2-5 years, or even longer. The effects of the present invention are listed below as examples. (1) Ca eluted from alkaline materials according to soil pH
Thereby, soil acidification prevention and / or adjustment of soil pH and maintenance of pH within an appropriate range can be achieved in a long term. (2) The above actions stabilize heavy metals that are already present in the soil or that are imported from the outside,
Since the heavy metals are kept in place, adverse effects on the environment are prevented. (3) Suitable pH adjustment for a specific type of metal can be easily performed depending on the type and mixing ratio of the alkali material. At this time, various data such as solubility product of heavy metal and hydroxide ion, equilibrium constant of complex ion of amphoteric hydroxide (if formed) and hydrogen ion, and relationship between solubility and pH value are considered. By performing a simple preliminary test when necessary, an appropriate prescription can be set more easily. (4) Even if the present invention is applied to agricultural land, since the particle size of the alkaline material used is adjusted to 30 mm or less, it does not substantially hinder agricultural work. (5) According to the present invention, it is possible to effectively prevent or prevent the elution of heavy metals which may cause an environmental pollution problem near a waste disposal site and the secondary contamination. (6) According to the present invention, since a relatively large amount of slag and the like is consumed, effective use of the slag and the like is achieved and promoted.

[Brief description of the drawings]

FIG. 1 is a graph of Zn and Mn elution concentrations at various pH values.

FIG. 2 is a conceptual diagram showing an example of an acidification process of soil due to microbiological factors.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) // C09K 101: 00 109: 00

Claims (2)

[Claims] An alkaline material sized to have a maximum particle size of 30 mm is applied to soil that is likely to be acidified or acidified soil to prevent acidification of the soil and to adjust soil pH. A method for stabilizing for a long time, wherein the alkaline material is at least one selected from the group consisting of blast furnace slag, converter slag, coal ash, limestone and lime. 2. The method according to claim 1, wherein when the heavy metal is present in the soil or is introduced, the heavy metal is stabilized in the soil by the action of preventing acidification and stabilizing the pH.