KR20050025768A - Soil treatment agent and soil treating method - Google Patents

Abstract

A soil treating agent and a method of soil treatment using the same are provided to remove dioxins present in soil, especially of a cultivation area in effective way, thereby preventing soil contamination and secondary contamination of surrounding environment including crops or livestock. The soil treating agent comprises a first substance which can emit iron ions and a second substance which can emit hydrogen, wherein the first substance is at least one selected from ferrous oxide, ferric oxide, tri-iron tetraoxide, and the second substance is at least one selected from iron, sodium sulfite and sodium hydrosulfite. The soil treatment method using the same comprises mixing the soil treating agent with soil with a water content of 5-300wt% relative to the total solid content.

Description

Soil treatment agent and soil treating method

The present invention relates to a soil treatment agent and a soil treatment method, in particular, a treatment agent and a treatment method for soil containing dioxin.

Soil pollution due to dioxins in fly ash or dioxins in pesticides emitted from incineration facilities such as industrial waste and household waste has become a serious problem. Dioxins are unprecedented toxins that have the potential to cause skin and visceral disorders, as well as teratogenic or malformation. In particular, the negotiated dioxins 2,3,7,8-dibenzo-para-dioxin can be said to be one of the most toxic substances obtained by humans. In addition, in this application, the term "dioxin" refers to polychlorinated dibenzo-para-dioxin (PCDDs) and polychlorinated salts according to the provisions of Article 2 of the Japanese Act No. 105, "Special Measures for the Countermeasures against Dioxins. Dibenzofuran (PCDFs) and Coplanar polychlorinated biphenyls (Co-PCBs) are also used as meanings.

Soil contamination from these dioxins is likely to cause secondary pollution of the surrounding environment or flora and fauna. In particular, when farmland such as paddy fields or fields are contaminated with dioxin, the human body may be seriously contaminated through ingestion of crops grown in the farmland.

An object of the present invention is to effectively remove dioxins contained in the soil.

The soil treatment agent of the present invention includes a first material capable of releasing iron ions and a second material capable of releasing hydrogen. Here, the first material is one selected from the group consisting of, for example, iron oxide, ferric trioxide, and triiron tetraoxide. In addition, the second material is at least one selected from the group consisting of, for example, iron, sodium sulfite, sodium adthioate and sodium hydrogen sulfite.

The soil treatment method of the present invention includes a process of adding and mixing a soil treatment agent containing a first substance capable of releasing iron ions and a second substance capable of releasing hydrogen to the soil. In this method, it is usually preferable to set the amount of water in the mixture containing the soil and the soil treatment agent to be 5 to 300% by weight of the total solids of the mixture. In addition, the soil treatment method further includes a step of setting the pH of the mixture containing the soil and the soil treatment agent to be 7.0 or less.

In addition, the soil treatment method according to another aspect of the present invention includes a step of adding and mixing the first substance capable of releasing iron ions and the second substance capable of releasing hydrogen, respectively, in the soil. In this method, it is preferable to set the amount of water in the mixture containing the soil, the first substance and the second substance to be usually 5 to 300% by weight of the total solids of the mixture. In addition, the soil treatment method of this type further includes a step of setting the pH of the mixture containing the soil, the first substance and the second substance to be 7.0 or less.

The soil treatment agent of the present invention comprises a first substance and a second substance.

The first substance used in this soil treatment agent is a substance capable of releasing iron ions, particularly a substance capable of releasing iron ions into water. Such a first substance is not particularly limited, but a substance capable of emitting divalent or trivalent iron ions, particularly an inorganic substance, is preferable. Specific examples of such a first substance include iron oxide (FeO), ferric trioxide (Fe ₂ O ₃ ), and triiron tetraoxide (Fe ₃ O ₄ ). Among them, it is particularly preferable to use triiron tetraoxide, which can be manufactured at low cost and is easily available as waste recycling products.

Here, triiron tetraoxide is a mixture of iron oxide (FeO) and ferric trioxide (Fe ₂ O ₃ ), commonly referred to as magnetite. Although a manufacturing method etc. are not specifically limited, triiron tetraoxide is obtained as a by-product in the manufacturing process of the titanium sulfate method, for example. Specifically, the iron-containing sulfuric acid obtained in the step of producing the sulfuric acid method titanium oxide is neutralized and then concentrated / separated. The filtrate obtained by filtering the supernatant liquid at that time is neutralized and oxidized again. More specifically, sodium hydroxide is added while passing through an air stream through the filtrate, and the temperature is set at 65 ° C so as to have a pH of 6.0 to 6.3 and an oxidation rate of 75 to 80%. When the product obtained by such neutralization and oxidation treatment is separated by filtration and dried at about 120 ° C., the ratio (FeO: Fe ₂ O ₃ ) between FeO and Fe ₂ O ₃ is 10 to 30:90 to 70. Triiron tetraoxide is obtained. In addition, it is preferable to perform a final drying process in nitrogen atmosphere. In this way, it is easy to FeO and Fe ₂ O ₃ ratio between the above-described dioxins decomposition efficiency is getting higher four SAMHWA sesquioxide of the set as described.

The first substance as described above is preferably in the form of a powder, but the particle form thereof is not particularly limited. In general, however, the smaller the particles, the higher the contact efficiency with the dioxins contained in the soil, and thus the higher the decomposition efficiency of the dioxins, and the smaller the particles, the higher the cost. What was manufactured using the line can be used as it is. Therefore, 0.2-50 micrometers is preferable and, as for the average particle diameter of the 1st substance which is a powder form, 0.3-10 micrometers is more preferable.

In addition, when the first substance is triiron tetraoxide, the method and conditions for making it into powder form are not particularly limited, but in general, ferric tetraoxide is anhydrous in order to avoid the degradation of dioxins by the reaction of triiron tetraoxide with water and oxygen. It is preferable to grind and dry under an inert gas stream of nitrogen (for example, under a nitrogen stream).

In addition, the second substance used in the soil treatment agent of the present invention is a substance capable of releasing hydrogen, particularly a substance capable of releasing hydrogen into water. Although the second material is not particularly limited, a material capable of releasing hydrogen in an ionic state, particularly an inorganic material capable of releasing hydrogen in an ionic state is preferable. Specific examples of such a second substance include, for example, iron, sodium sulfite (Na ₂ SO ₃ ), sodium adithioate (Na ₂ S ₂ O ₄ ), sodium hydrogen sulfite (NaHSO ₃ ), and sodium thiosulfate (Na ₂ S _2). O ₃ ) and sodium borohydride (NaBH ₄ ). These substances may be used in combination of two or more as appropriate.

Preferred as the second material are at least one of iron, sodium sulfite, sodium adthioate and sodium hydrogen sulfite because of its low cost and easy handling when stored.

Since the second material as described above can be uniformly mixed with the first material, and the contact efficiency with the dioxins contained in the soil can be enhanced, the second material is preferably in the form of a powder. More specifically, a powder form having an average particle diameter of 0.2 to 50 µm is preferable, and a powder form having an average particle diameter of 0.3 to 10 µm is more preferable. However, the particle form is not particularly limited.

It is preferable that the soil treating agent of the present invention usually contains the second substance at a ratio of 1 to 300 parts by weight relative to 100 parts by weight of the first substance. Moreover, 1-30 weight part is more preferable, and, as for the ratio of the 2nd substance with respect to a 1st substance, 5-20 weight part is more preferable. If the ratio of the second substance is less than 1 part by weight, the function of releasing hydrogen may be impaired by other substances, which may make it difficult to effectively decompose and remove dioxins in the soil. On the contrary, when the ratio of the second substance exceeds 300 parts by weight, the ratio of the first substance in the soil treatment agent becomes small, so that it is difficult to effectively decompose and remove dioxins in the soil.

The soil treating agent of the present invention may contain a compound containing silicon, titanium, aluminum, calcium, or the like as impurities in addition to the above-mentioned first substance and second substance within a range that does not impair the desired effect thereof.

The soil treating agent of the present invention can be prepared by mixing the first substance and the second substance in the above-mentioned ratios and stirring sufficiently.

Referring to the soil treatment method of the present invention. This soil treatment method is a method for removing dioxins contained in the soil, and the soil to be treated is not particularly limited, but is, for example, fly ash mixed soil, sludge, paddy soil, and field soil. .

In the first aspect of the soil treatment method of the present invention, the above-described soil treatment agent is first added to the soil to be treated and sufficiently mixed. At this time, it is preferable to set the mixing ratio of the soil treating agent to 1 to 50 parts by weight, and more preferably to 5 to 25 parts by weight with respect to 100 parts by weight of the soil. If the proportion of the soil treatment agent is less than 1 part by weight, it may be difficult to effectively decompose and remove dioxins contained in the soil. On the contrary, if the amount exceeds 50 parts by weight, the first substance may remain excessively in the treated soil, and if the soil is used as agricultural soil, it may adversely affect the growth of plants such as crops. In addition, the mixing ratio of the soil treating agent here is the ratio which converted the total amount of a 1st substance and a 2nd substance.

At this time, the amount of water in the mixture containing the soil and the soil treatment agent is preferably set to 5 to 300% by weight of the total solids of the mixture. Moreover, it is more preferable to set this moisture content to 30 to 200 weight% of a total solid, and it is more preferable to set to 50-100 weight%. When this moisture content is less than 5 weight%, since the solubility of a 1st material and a 2nd material decreases, there exists a possibility that it may become difficult to remove dioxins in soil. On the contrary, if it exceeds 300% by weight, the soil particles are likely to settle in water, so that the contact rate between the soil particles and water is lowered, which may require a long time until the dioxins in the soil are removed. Moreover, it is preferable to set so that water content may increase in proportion to the quantity of the 2nd substance normally contained in a soil treatment agent.

In addition, in this type of soil treatment method, the pH of the mixture containing the soil and the soil treatment agent is preferably set to be usually 7.0 or less as necessary. When the pH of this mixture is larger than 7.0, hydroxides adhere to the surface of the first substance, which may make it difficult to proceed with decomposition of dioxins. This pH can usually be adjusted by adding acid to the mixture containing soil and soil treatment. The acid usable here is usually an inorganic acid such as hydrochloric acid or sulfuric acid or an organic acid such as oxalic acid or acetic acid.

Then, the soil mixed with the soil treatment agent is left. As a result, dioxins contained in the soil are decomposed by the soil treatment agent, thereby obtaining soil from which the dioxins have been removed. The length of the standing period here is preferably longer, but is usually 7 days or more, preferably 10 days or more. If it is left for less than 7 days, there is a possibility that the dioxins contained in the soil cannot be sufficiently removed from the soil.

In the second aspect of the soil treatment method of the present invention, the first substance and the second substance are added to the soil to be treated first and mixed sufficiently. Mixing here can be performed using a commercially available biaxial mixer or rod mill, for example. Moreover, it is preferable to set so that the ratio of a 1st material and a 2nd material at the time of this mixing may become the same as the mixing in the above-mentioned soil treatment agent. The total amount of the first substance to be added to the soil and the second substance is preferably set to 1 to 50 parts by weight, more preferably 5 to 25 parts by weight with respect to 100 parts by weight of the soil. When the ratio of the total amount is less than 1 part by weight, it may be difficult to efficiently decompose and remove dioxins contained in the soil. On the contrary, if it exceeds 50 parts by weight, the first substance may remain excessively in the treated soil, and thus, if the soil is used as agricultural soil, it may adversely affect the growth of plants such as crops.

In the soil treatment method of this type, the amount of water in the mixture containing the soil, the first substance and the second substance is preferably set to 5 to 300% by weight of the total solids of the mixture. Moreover, it is more preferable to set this moisture content to 30 to 200 weight% of a total solid, and it is more preferable to set to 50-100 weight%. When this moisture content is less than 5 weight%, since the solubility of a 1st material and a 2nd material decreases, there exists a possibility that it may become difficult to remove dioxins in soil. On the contrary, if it exceeds 300% by weight, the soil particles are likely to settle in water, so the contact rate between the soil particles and water is lowered, which may require a long time until the dioxins in the soil are removed. Moreover, it is preferable to set so that water content may increase in proportion to the quantity of the 2nd substance normally contained in a mixture.

In the soil treatment method of this aspect, it is preferable to set the pH of the mixture containing the soil, the first substance and the second substance to be 7.0 or less, as necessary. When the pH of this mixture is larger than 7.0, hydroxides are produced, which may inhibit dechlorination of dioxins, that is, decomposition of dioxins. This pH can usually be adjusted by adding acid to the mixture comprising the soil, the first material and the second material. The acid available here is the same as for the soil treatment method according to the first form.

Subsequently, the soil mixed with the first material and the second material is left. As a result, the first substance and the second substance act to decompose the dioxins contained in the soil, thereby obtaining a soil from which the dioxins have been removed. It is preferable to set the leaving period here like the case of the soil treatment method which concerns on 1st aspect mentioned above.

The soil to which the soil treatment method of the present invention is applied is effectively decomposed and removed dioxin contained in the soil. In addition, the soil has a low alkaline to acidity suitable for the growth of the crop, the pH is maintained, and the electrical conductivity can be maintained at about 500 to 800μS suitable for the growth of the crop. Therefore, in the case where the soil treatment method of the present invention is performed on paddy soil or field soil, the soil after treatment can be reused as it is as soil for cultivation of crops without additional treatment. In addition, since the first substance and the second substance used in this treatment method are less likely to adversely affect the crop or the surrounding environment, the soil after the treatment is safe for the crop or the surrounding environment.

(Example)

Example 1

90 parts by weight of a commercially available triiron tetraoxide (iron purity of 95% or more) powder and 10 parts by weight of sodium hydrogen sulfite (reagent) were sufficiently mixed to obtain a soil treatment agent. Subsequently, 200 g of the soil treatment agent was mixed with 1 kg of non-crop soil contaminated with dioxins, and 1000 ml of water was further added and mixed. The non-cropland soil thus treated was left as it was, and the dioxins content (total amount of PCDDs, PCDFs and Co-PCBs), pH and electrical conductivity were examined after 1 day, 7 days, 14 days and 30 days. Here, dioxins were investigated according to the method for measuring soil dioxins, as defined in the Soil Survey and Measurement Manual for Dioxins, which was enacted in 2000 by the Japan Environment Agency. In addition, pH was measured using a pH meter, and electrical conductivity was measured using an electrical conductivity meter. The results are shown in Table 1. In addition, in Table 1, dioxins removal rate is calculated | required by the following formula | equation. This is also the same in the following examples. In addition, in formula, A represents the amount of dioxins contained in the soil before treatment, and B represents the amount of dioxins contained in the soil at the time of measurement.

Dioxins content (pgTEQ / g per dry weight) Dioxin removal rate (%) pH Electrical Conductivity (μS) Before treatment 1300 - 6.5 750 1 day later 450 65.4 6.3 758 7 days later 250 80.8 6.3 800 14 days later 135 89.6 6.4 759 30 days later 110 91.5 6.3 760

Example 2

To 1 kg of air-dried sludge contaminated with dioxin, 100 g of the soil treatment agent obtained in Example 1 was mixed, and 1000 ml of water was further added and mixed. This sludge was left as it was, and the dioxins content, pH, and electrical conductivity of 1 day, 7 days, 14 days, and 30 days were examined in the same manner as in Example 1. The results are shown in Table 2.

Dioxins content (pgTEQ / g per dry weight) Dioxin removal rate (%) pH Electrical Conductivity (μS) Before treatment 1350 - 6.5 950 1 day later 1270 5.9 6.5 1050 7 days later 710 47.4 6.4 980 14 days later 500 63.0 6.5 960 30 days later 480 64.4 6.4 780

Examples 3 to 5

To 1000 parts by weight of the same air-dried (naturally dried) sludge as used in Example 2, the soil treatment agent obtained in Example 1 was mixed in the ratio shown in Table 3, and water was further added in the amount shown in Table 3 and mixed. . This sludge was left as it was, and the dioxins content after 7 days was investigated similarly to the case of Example 1. The results are shown in Table 3. According to Table 3, it can be seen that the dioxins contained in the sludge can be more effectively removed by increasing the soil treatment agent mixed in the sludge.

Sludge before treatment Example 3 Example 4 Example 5 Soil treatment amount added (part by weight) - 200 300 500 Water addition amount (ml) - 200 300 500 Dioxins content (pgTEQ / g dry weight) 1350 400 250 210 Dioxin removal rate (%) - 70.4 81.5 84.4

Since the soil treating agent of the present invention includes a first substance capable of releasing iron ions and a second substance capable of releasing hydrogen, it is effective to remove dioxins contained in the soil when added to the soil and mixed. Can be.

In the soil treatment method of the present invention, the soil treatment agent of the present invention is added to the soil and mixed, or the first substance capable of releasing iron ions and the second substance capable of releasing hydrogen are added to the soil and mixed. This can effectively remove dioxins contained in the soil.

Claims (8)

A first material capable of releasing iron ions, A soil treating agent comprising a second substance capable of releasing hydrogen. The method of claim 1, wherein the first material is any one selected from the group consisting of iron oxide, ferric trioxide and triiron tetraoxide and the second material is at least any one selected from the group consisting of iron, sodium sulfite, sodium adthioate and sodium bisulfite. One soil treatment agent. A soil treating method comprising the step of adding and mixing a soil treating agent containing a first substance capable of releasing iron ions and a second substance capable of releasing hydrogen to the soil. The soil treatment method according to claim 3, wherein the amount of water in the mixture containing the soil and the soil treatment agent is set to be 5 to 300% by weight of the total solids of the mixture. The soil treatment method according to claim 3 or 4, further comprising a step of setting the pH of the mixture containing the soil and the soil treatment agent to be 7.0 or less. And a process of adding and mixing the first substance capable of releasing iron ions and the second substance capable of releasing hydrogen, respectively, to the soil. The soil treatment method according to claim 6, wherein the amount of water in the mixture comprising the soil, the first substance and the second substance is set to 5 to 300% by weight of the total solids of the mixture. The soil treatment method according to claim 7, further comprising the step of setting the pH of the mixture including the soil, the first substance, and the second substance to be 7.0 or less.