JP7496088B2 - Soil treatment and classification methods - Google Patents

Description

The present invention relates to a soil treatment method and a soil classification method.

Conventionally, soil conditioners have been added to soil to be treated for intermediate storage or disposal, making the soil easier to handle. For example, Patent Document 1 discloses that adding a bulk density adjusting material containing a water-absorbent resin and a polymer compound to target soil containing foreign matter such as grass and tree roots reduces the bulk density of the target soil, making it easier to separate the foreign matter by subsequent sieving.

On the other hand, if the target soil contains water-absorbent materials, the water-absorbent materials absorb large amounts of water when the soil is wet-classified into sand and fine particles, placing a burden on the classification and subsequent dehydration. A method is known for reducing this burden by lowering the water-absorption function of the water-absorbent materials to reduce the amount of water they absorb (see Patent Document 2).

Patent Publication No. 6401852 JP 2019-103989 A

Wet classification is originally intended to classify soil under conditions according to the desired classification point, but if the soil to be classified contains soil modifiers, etc., the coagulation and sedimentation of soil particles in water is promoted, which hinders classification based on the original particle size. Therefore, the present invention aims to provide a soil treatment method for soil containing soil modifiers, etc., to make the soil suitable for wet classification based on the original particle size. It also provides a soil classification method in which muddy water prepared by this treatment method is wet classified.

The method for treating soil according to the present invention is as follows.
[1] A method for treating soil, comprising mixing adjusted soil having an organic matter content of 1 g/kg or more and 70 g/kg or less with at least one of a water-absorbent resin and a polymer flocculant, with water and a carboxylic acid to prepare muddy water, the mass ratio of the adjusted soil to the water being 1:30 to 1:70, and the amount of the carboxylic acid mixed being 0.001 parts by mass to 2 parts by mass when the mass of the water is 100 parts by mass.

[2] A method for treating soil, comprising mixing soil having an organic matter content of 1 g/kg to 70 g/kg with at least one of a water-absorbent resin and a polymer flocculant, with water, a carboxylic acid, and hydrogen carbonate or carbon dioxide to prepare muddy water, the mass ratio of the adjusted soil to the water being 1:30 to 1:70, the amount of the carboxylic acid mixed being 0.01 parts by mass to 0.5 parts by mass when the mass of the water is 100 parts by mass, and the amount of the hydrogen carbonate or carbon dioxide mixed being 0.005 parts by mass to 10 parts by mass when the mass of the water is 100 parts by mass.

[3] A method for treating soil, comprising mixing soil having an organic matter content of more than 70 g/kg and not more than 200 g/kg with at least one of a water-absorbent resin and a polymer flocculant, with water, a carboxylic acid, and hydrogen carbonate or carbon dioxide to prepare muddy water, the mass ratio of the adjusted soil to the water being 1:30 to 1:70, the amount of the carboxylic acid mixed being 0.01 parts by mass to 0.5 parts by mass when the mass of the water is taken as 100 parts by mass, and the amount of the hydrogen carbonate or carbon dioxide mixed being 0.02 parts by mass to 0.4 parts by mass when the mass of the water is taken as 100 parts by mass.

[4] A method for treating soil, comprising mixing soil having an organic matter content of 1 g/kg or more and 70 g/kg or less with at least one of a water-absorbent resin and a polymer flocculant, with water and a carboxylic acid to prepare muddy water having a pH of 1.3 to 6.0.

[5] A method for treating soil, comprising mixing soil having an organic matter content of 1 g/kg or more and 70 g/kg or less with at least one of a water-absorbent resin and a polymer flocculant, with water, a carboxylic acid, and hydrogen carbonate or carbon dioxide to prepare muddy water having a pH of 3.0 to 8.0.

[6] A method for treating soil, comprising mixing soil having an organic matter content of more than 70 g/kg and not more than 200 g/kg with at least one of a water-absorbent resin and a polymer flocculant, with water, a carboxylic acid, and hydrogen carbonate or carbon dioxide to prepare muddy water having a pH of 4.3 to 6.3.

The water-absorbent resin and/or polymer flocculant contained in the soil promotes the aggregation and sedimentation of soil particles in water, causing the soil particles to become larger than their original particle size, which becomes an obstacle to classification based on the original particle size during wet classification. According to the soil treatment method described above, the effect of the water-absorbent resin and/or polymer flocculant can be weakened by using a carboxylic acid, or a carboxylic acid and a hydrogen carbonate or carbon dioxide, and the aggregation and sedimentation of the soil particles can be delayed. This makes it possible to ensure sufficient time for classification based on the original particle size.

The inventors have discovered conditions under which the above effects can be reliably achieved by adjusting the amount of carboxylic acid, bicarbonate, or carbon dioxide mixed depending on the amount of organic matter contained in the soil, or by mixing these to adjust the pH of the muddy water to within a predetermined range, and have completed the present invention.

In the present invention, the soil may contain radioactive cesium.

The present invention also provides a method for classifying soil, which involves wet classifying the muddy water prepared by the treatment methods [1] to [6] above.

According to the present invention, it is possible to provide a soil treatment method for soil containing soil conditioners, etc., to make the soil suitable for wet classification based on the original particle size. It is also possible to provide a soil classification method in which muddy water prepared by the treatment method is wet classified.

1 is a graph showing sedimentation volumes in Experimental Examples R1 to R6. 1 is a graph showing turbidity in Experimental Examples R1 to R6. 1 is a graph showing particle size distribution in Experimental Examples R1 to R6. 1 is a graph showing sedimentation volumes in Experimental Examples R1, R2, and R7 to R16. 1 is a graph showing turbidity in Experimental Examples R1, R2, and R7 to R16. 1 is a graph showing particle size distributions in Experimental Examples R1, R2, and R7 to R16. 1 is a graph showing sedimentation volumes in Experimental Examples M1 to M6. 1 is a graph showing turbidity in Experimental Examples M1 to M6. 1 is a graph showing particle size distribution in Experimental Examples M1 to M6. 1 is a graph showing sedimentation volumes in Experimental Examples M1, M2, M4, M5, and M7 to M22. Experimental Examples This is a graph showing the turbidity in Experimental Examples M1, M2, M4, M5, and M7 to M22. 1 is a graph showing particle size distribution in Experimental Examples M1, M2, and M8 to M22. 1 is a graph showing sedimentation volumes in Experimental Examples B1 to B6. 1 is a graph showing turbidity in Experimental Examples B1 to B6. 1 is a graph showing particle size distribution in Experimental Examples B1 to B6. 1 is a graph showing sedimentation volumes in Experimental Examples B1, B2, and B7 to B16. 1 is a graph showing turbidity in Experimental Examples B1, B2, and B7 to B16. 1 is a graph showing particle size distributions in Experimental Examples B1, B2, and B7 to B16. 1 is a graph showing sedimentation volumes in Experimental Examples R17 to R21. 1 is a graph showing sedimentation volumes in Experimental Examples M23 to M27. 1 is a graph showing sedimentation volumes in Experimental Examples B17 to B20.

A preferred embodiment of the present invention will be described in detail below. The soil treatment method of this embodiment is intended for conditioned soil in which at least one of a water-absorbent resin and a polymer flocculant is mixed with soil containing organic matter. Here, "conditioned soil" refers to modified soil obtained by mixing soil containing organic matter with a soil modifier. A "soil modifier" includes at least one of a water-absorbent resin and a polymer flocculant. The soil modifier is, for example, a bulk density adjuster, which is a material that absorbs water contained in the soil to make the soil easier to handle.

The treatment method of this embodiment is performed as a pretreatment for wet classification of the adjusted soil. The soil modifier added to the adjusted soil becomes unnecessary after achieving its purpose. For example, if the soil modifier is a bulk density adjusting material, when it is added to the soil, the excess water contained in the soil is absorbed by the water-absorbing resin, adjusting the bulk density of the soil, making it easier to handle and making it easier to separate foreign matter mixed in the soil. However, if the adjusted soil is to be wet classified after the separation of foreign matter, the soil modifier promotes the aggregation and sedimentation of soil particles in water, which becomes an obstacle to classification based on the original particle size. Therefore, by carrying out the treatment method of this embodiment on the adjusted soil before wet classification, the effect of the soil modifier can be negated, and wet classification based on the original particle size can be performed. Even if the effect of the soil modifier cannot be completely negated, the time until the soil particles aggregate and settle can be delayed, so that time for classification can be secured. In addition, the wet classification mentioned here is assumed to have a classification point of 20 μm.

In the treatment method of this embodiment, the amount of the component to be mixed with the adjusted soil is changed according to the organic matter content of the soil, so that the desired effect can be reliably obtained. In this embodiment, the soil is classified into soils with an organic matter content of 1 g/kg or more and 70 g/kg or less, and soils with an organic matter content of more than 70 g/kg and 200 g/kg or less, and adjusted soils obtained by mixing at least one of a water-absorbent resin and a polymer flocculant with these soils (hereinafter, these are referred to as "first type adjusted soil" and "second type adjusted soil" respectively). The organic matter content of the soil before adding the water-absorbent resin or the polymer flocculant is a value that can be measured according to the soil organic carbon content test "JGS0231", and is the organic matter content based on the dry weight of the soil. Regardless of the value of the organic matter content, the moisture content of the soil may be 0% to 55%, 5% to 50%, or 10% to 45%, with a lower limit of 15%, 20%, 25%, or 30%, and an upper limit of 40% or 35%. The moisture content can be determined by comparing the weight of the soil before and after heating.

A water-absorbent resin is a resin that has the property of absorbing water and swelling when it comes into contact with water. Examples of water-absorbent resins include starch-based, cellulose-based, polyvinyl alcohol-based, and acrylic-based resins. A polymer flocculant is a compound that acts on the surface of soil particles in the soil to bind the soil particles together. As a polymer flocculant, an organic polymer compound is preferable, and examples thereof include polyacrylamide-based compounds. The organic polymer compound may be either an anionic or nonionic compound.

In the treatment method of this embodiment, water and a carboxylic acid are added to the target conditioned soil and mixed. Alternatively, water, a carboxylic acid, and a bicarbonate or carbon dioxide are added to the target conditioned soil and mixed. In this specification, the carboxylic acid, bicarbonate, and carbon dioxide are referred to as "conditioning agents."

Examples of carboxylic acids include citric acid, oxalic acid, malonic acid, lactic acid, malic acid, and tartaric acid. Examples of hydrogen carbonates include sodium hydrogen carbonate (sodium bicarbonate), ammonium hydrogen carbonate, and potassium hydrogen carbonate. Carbon dioxide may be in any state, such as gas, liquid (liquefied carbon dioxide), or solid (dry ice). Among these, citric acid, oxalic acid, and sodium bicarbonate are preferred from the viewpoints of safety, versatility, and price. The amount of carboxylic acid, hydrogen carbonate, or carbon dioxide added varies depending on the amount of organic matter contained in the conditioned soil. When the organic matter content is relatively low, the pH of the muddy water can be adjusted to the desired value by adding and mixing the carboxylic acid, but when the organic matter content is relatively high, adding and mixing the hydrogen carbonate together with the carboxylic acid makes it easier to adjust the pH of the muddy water to the desired value. When hydrogen carbonate is added and mixed, the pH becomes higher than when the carboxylic acid is used alone. The difference in the dissociation constants between carboxylic acids and bicarbonates and the range of pH fluctuations caused by adding and mixing them overlap with the pH range in which soil particles in conditioned soil can be dispersed, so the combined use of carboxylic acids and bicarbonates is particularly effective in delaying the aggregation and settling of soil particles. Below, we will explain the treatment methods for different types of conditioned soil.

<Type 1 adjusted soil>
The first type of conditioned soil is a soil having an organic matter content of 1 g/kg to 70 g/kg and an conditioned soil agent mixed in. The organic matter content may be 5 g/kg to 65 g/kg, 5 g/kg to 40 g/kg, 10 g/kg to 30 g/kg, 40 g/kg to 60 g/kg, or 50 g/kg to 58 g/kg.

The moisture content of the conditioned soil may be 0% to 55%, 5% to 50%, or 10% to 45%, with a lower limit of 15%, 20%, 25%, or 30%, and an upper limit of 40% or 35%. The moisture content of the conditioned soil may be considered to be equal to the moisture content of the soil before the conditioning agent is mixed, or the moisture content of the conditioned soil may be measured again after the conditioning agent is mixed. The measurement method is the same as the measurement method for the soil before the conditioning agent is mixed.

The amount of water to be added is a solid-liquid ratio (mass ratio) of 1:30 to 1:70 relative to the mass of the first type of adjusted soil. The solid-liquid ratio may be 1:35 to 1:65, or 1:40 to 1:60. Here, the "mass of the first type of adjusted soil" refers to the mass including the water contained in the first type of adjusted soil (including water captured by the water-absorbent resin or polymer flocculant, and water not completely captured by these). In other words, the water contained in the soil from the beginning and expressed as the moisture content of the soil is considered to be part of the soil's mass.

When only carboxylic acid is added as the adjusting agent, the amount of carboxylic acid added is 0.001 to 2 parts by mass when the mass of water added is 100 parts by mass. The amount of carboxylic acid added may be 0.004 to 1.5 parts by mass, or 0.01 to 0.5 parts by mass.

The amount of carboxylic acid added is preferably adjusted so that the pH of the muddy water when the first type of adjusted soil, water, and carboxylic acid are all mixed is 1.3 to 6.0. This pH adjustment may also be made so that the pH is 1.5 to 5.0.

When both carboxylic acid and hydrogen carbonate or carbon dioxide are added as adjusting agents, the amount of carboxylic acid added is 0.01 parts by mass to 0.5 parts by mass when the mass of water to be added is 100 parts by mass. The amount of carboxylic acid added may be 0.03 parts by mass to 0.3 parts by mass, or may be 0.05 parts by mass to 0.1 parts by mass. The amount of hydrogen carbonate or carbon dioxide mixed is 0.005 parts by mass to 10 parts by mass when the mass of water to be added is 100 parts by mass. The amount of hydrogen carbonate or carbon dioxide added may be 0.03 parts by mass to 7 parts by mass, or may be 0.3 parts by mass to 3 parts by mass.

When carbon dioxide is added as a solid or liquid, the amount to be added can be determined by weighing it in a sealed container. When carbon dioxide is added as a gas, it is added by aeration, and the amount to be added can be determined by calculating the equilibrium concentration from the pH of the solution before and after addition, the partial pressure of carbon dioxide in the addition atmosphere, and the acid dissociation constant.

It is preferable to adjust the amount of adjusting agent added so that the pH of the muddy water when the first type of adjusted soil, water, and adjusting agent are all mixed is 3.0 to 8.0.

The first type of adjusted soil, water, and adjusting agent can be mixed in any order. For example, the water and adjusting agent may be added separately to the first type of adjusted soil, or the adjusting agent may be dissolved in water to prepare an aqueous solution of the adjusting agent, which is then added to the first type of adjusted soil. The first type of adjusted soil may also be added to the aqueous solution of the adjusting agent. Regardless of the mixing method used, these are thoroughly stirred to prepare a completely mixed muddy water. It is preferable to leave the adjusted muddy water to stand for 3 to 5 minutes.

The muddy water prepared in this way has the effect of the soil conditioner contained in the first adjusted soil negated. This is thought to be because the mixing of the conditioner causes the soil conditioner to expel the water it had absorbed, and the functional groups in the soil conditioner form hydrogen bonds with each other, making it difficult for soil particles to aggregate.

<Type 2 adjusted soil>
The second type of conditioned soil is a soil having an organic matter content of more than 70 g/kg and not more than 200 g/kg, to which an conditioned soil agent is mixed. The organic matter content may be 80 g/kg or more and 180 g/kg or less, or 90 g/kg or more and 160 g/kg or less.

The moisture content of the conditioned soil may be 0% to 55%, 5% to 50%, or 10% to 45%, with a lower limit of 15%, 20%, 25%, or 30%, and an upper limit of 40% or 35%. The moisture content of the conditioned soil may be considered to be equal to the moisture content of the soil before the conditioning agent is mixed, or the moisture content of the conditioned soil may be measured again after the conditioning agent is mixed. The measurement method is the same as the measurement method for the soil before the conditioning agent is mixed.

The amount of water to be added is a solid-liquid ratio of 1:30 to 1:70 relative to the mass of the second type of adjusted soil. The solid-liquid ratio may be 1:35 to 1:65, or 1:40 to 1:60. Here, the "mass of the second type of adjusted soil" refers to the mass including the water contained in the second type of adjusted soil (including water captured by the water-absorbent resin or polymer flocculant, and water not completely captured by these). In other words, the water contained in the soil from the beginning and expressed as the moisture content of the soil is considered to be part of the soil's mass.

As the adjusting agent, both carboxylic acid and hydrogen carbonate or carbon dioxide are added. The amount of carboxylic acid added is 0.01 parts by mass to 0.5 parts by mass when the mass of water to be added is 100 parts by mass. The amount of carboxylic acid added may be 0.02 parts by mass to 0.3 parts by mass, or may be 0.05 parts by mass to 0.1 parts by mass. The amount of hydrogen carbonate or carbon dioxide mixed is 0.02 parts by mass to 0.4 parts by mass when the mass of water to be added is 100 parts by mass. The amount of hydrogen carbonate or carbon dioxide added may be 0.03 parts by mass to 0.3 parts by mass, or may be 0.05 parts by mass to 0.2 parts by mass.

When carbon dioxide is added as a solid or liquid, the amount to be added can be determined by weighing it in a sealed container. When carbon dioxide is added as a gas, it is added by aeration, and the amount to be added can be determined by calculating the equilibrium concentration from the pH of the solution before and after addition, the partial pressure of carbon dioxide in the addition atmosphere, and the acid dissociation constant.

It is preferable to adjust the amount of adjusting agent added so that the pH of the muddy water when the second type of adjusted soil, water, and adjusting agent are all mixed is 4.3 to 6.3.

The second type of adjusted soil, water, and adjusting agent can be mixed in any order. For example, the water and adjusting agent may be added separately to the second type of adjusted soil, or the adjusting agent may be dissolved in water to prepare an aqueous solution of the adjusting agent, which is then added to the second type of adjusted soil. Alternatively, the second type of adjusted soil may be added to the aqueous solution of the adjusting agent. Regardless of the method used for mixing, these are thoroughly stirred to prepare a completely mixed muddy water. It is preferable to leave the adjusted muddy water to stand for 3 to 5 minutes.

The muddy water prepared in this way has the effect of the soil conditioner contained in the second adjusted soil negated. This is thought to be because the mixing of the conditioner causes the soil conditioner to expel the water it had absorbed, and the functional groups in the soil conditioner form hydrogen bonds with each other, making it difficult for soil particles to aggregate.

<How to confirm the effect>
In the treatment method of this embodiment, whether or not the effect of the soil modifier contained in the conditioned soil has been counteracted can be confirmed by measuring, for example, the following indicators.

・Sedimentation volume: The muddy water prepared by adding and mixing the adjusting agent is left to stand, and the volume of the supernatant liquid is measured at specified intervals. It is easier to measure the volume if a transparent container with graduations, such as a graduated cylinder, is used. If the soil conditioner is effective, the sedimentation volume will increase quickly, and if the effect of the soil conditioner is negated, the sedimentation volume will increase slowly.

- Turbidity: The muddy water prepared by adding and mixing the adjusting agent is left to stand and the supernatant liquid is collected at specified intervals. The turbidity of the collected supernatant liquid is measured with a turbidimeter. The turbidity value is shown as turbidity (FTU) using, for example, a formazin standard solution. If the soil conditioner is effective, the turbidity decreases quickly, and if the effect of the soil conditioner is negated, the turbidity decreases slowly.

・Particle size distribution...The muddy water prepared by adding and mixing the adjusting agent is left to stand, and the supernatant liquid is collected after a specified time. The particle size distribution of the collected supernatant liquid is measured using the laser diffraction and scattering method. A laser diffraction particle size distribution measuring device can be used. When the soil conditioner is effective, there are many soil particles with small particle sizes, and when the effect of the soil conditioner is negated, there are many soil particles with large particle sizes. These measurements can be made in accordance with "JIS Z8825:2013 Particle size analysis - laser diffraction and scattering method -" and "JIS A1204:2020 Soil particle size test (particle size accumulation curve)".

<Wet classification>
The muddy water prepared by the treatment method of this embodiment is then wet classified. Any of the conventionally known methods may be used for the wet classification. If time has passed since the preparation of the muddy water, it is preferable to remix the muddy water to make it uniform just before starting the classification. The classification point may be within the range of 50 μm to 100 μm (e.g., 75 μm), or may be within the range of 10 μm to 40 μm (e.g., 20 μm). In this classification method, particularly when the classification point is set to 20 μm, the clay to which the radioactive cesium is adsorbed can be classified, migrated, and concentrated so that it is more contained in the fine grain fraction, which is preferable because the volume of the radioactive cesium-containing soil that needs to be specially treated can be reduced.

Although the preferred embodiment of the present invention has been described above, the present invention is not limited to the above embodiment. For example, the above describes a case where an adjustment agent is mixed with the adjusted soil, but other agents may be mixed in addition to the adjustment agent as necessary. In this case, it is preferable that the pH of the muddy water after mixing is within the pH range shown above.

The present invention will be explained in more detail below with reference to experimental examples. Note that the present invention is not limited to the following experimental examples.

The materials used and the various measuring methods are as follows.
<Soil>
Soil R: soil with an organic matter content of 13.0 g/kg and a moisture content of about 50%.
Soil M: soil with an organic matter content of 56.7 g/kg and a moisture content of about 50%.
Soil B: soil with an organic matter content of 97.9 g/kg and a moisture content of about 50%.

<Soil conditioner>
The material contains 90% by mass or more of Green Tough, approximately 5% by mass of water absorbent resin, and 1% by mass or less of polyacrylamide.

<Modified soil>
The soil modifier was added at 25 g/kg and mixed into soil R, soil M, and soil B. The modified soils thus prepared are called modified soil R, modified soil M, and modified soil B, respectively.

<Method of measuring pH>
The pH of the muddy water was measured using a glass electrode pH meter (MM-50R, manufactured by DKK-TOA Corporation).

<Method of measuring sedimentation volume>
The muddy water was placed in a stoppered graduated cylinder, shaken, and then allowed to stand before starting a stopwatch. The sedimentation length (vertical length of the supernatant) was visually confirmed at each specified time by checking the graduations on the graduated cylinder. The sedimentation volume was calculated by multiplying the bottom area of the graduated cylinder by its length.

<Method of measuring turbidity>
The muddy water was placed in a stoppered measuring cylinder, shaken, and then allowed to stand before starting a stopwatch. The supernatant was collected at predetermined intervals in a plastic bottle and measured. A portable turbidity sensor (TD-M500, manufactured by OPTEX) was used as the turbidity meter.

<Method of measuring particle size distribution>
The muddy water was placed in a stoppered graduated cylinder, shaken, and allowed to stand before starting a stopwatch. After 10 minutes, the supernatant was directly collected and approximately 5 g was added to the sample layer of a laser diffraction particle size distribution analyzer (SALD-3100, manufactured by Shimadzu Corporation) for measurement. The particle size distribution of the soil particles was determined using the laser diffraction particle size distribution analyzer, and the vertical axis of the particle size accumulation curve was expressed as the relative particle amount (accumulation).

The experiment was carried out according to the following procedure.
<Experiment using citric acid and sodium bicarbonate as adjusting agents>
(Experimental Example R1)
Muddy water was prepared by mixing 4 g of soil R with 200 ml of water. The muddy water was placed in a stoppered graduated cylinder, shaken, and allowed to stand. The sedimentation volume, turbidity, and particle size distribution were measured at predetermined intervals. The pH of the supernatant was also measured.

(Experimental Example R2)
Muddy water was prepared by mixing 4 g of modified soil R with 200 ml of water. The muddy water was placed in a measuring cylinder with a stopper, shaken, and allowed to stand. The sedimentation volume, turbidity, and particle size distribution were measured at predetermined intervals. The pH of the supernatant was also measured.

(Experimental Example R3)
Citric acid was added to 200 ml of water in an amount of 0.004 parts by mass when the mass of the water was 100 parts by mass to prepare an aqueous solution. The pH of this aqueous solution was measured. 4 g of modified soil R was mixed with this aqueous solution to prepare muddy water. The muddy water was placed in a stoppered graduated cylinder, shaken, and allowed to stand. The sedimentation volume, turbidity, and particle size distribution were measured at predetermined intervals. The pH of the supernatant was also measured.

(Experimental Examples R4 to R6)
The sedimentation volume, turbidity, particle size distribution, and pH were measured in the same manner as in Experimental Example R3, except that the amount of citric acid added was changed as shown in Table 1.

Graphs of the measured sedimentation volume, turbidity, and particle size distribution for experimental examples R1 to R6 are shown in Figures 1 to 3. It can be seen that in all cases of sedimentation volume, turbidity, and particle size distribution, the graphs for when citric acid was added are located between the graphs for soil R alone (R1) and the graphs for modified soil R alone (R2). In other words, it can be seen that the effects of the soil modifier are cancelled out by the addition of citric acid.

(Experimental Example R7)
Citric acid was added to 200 ml of water in an amount of 0.05 parts by mass when the mass of the water was 100 parts by mass, and sodium bicarbonate was added in an amount of 0.01 parts by mass to prepare an aqueous solution. The pH of this aqueous solution was measured. 4 g of modified soil R was mixed with this aqueous solution to prepare muddy water. The muddy water was placed in a stoppered graduated cylinder, shaken, and allowed to stand. The sedimentation volume and turbidity were measured at predetermined intervals. The pH of the supernatant was also measured.

(Experimental Examples R8 to R16)
The sedimentation volume, turbidity, and pH were measured in the same manner as in Experimental Example R7, except that the amounts of citric acid and sodium bicarbonate added were changed as shown in Table 1. For Experimental Examples R12 to R16, the particle size distribution was also measured.

Graphs of the measured sedimentation volume, turbidity, and particle size distribution for experimental examples R7 to R16 are shown in Figures 4 to 6. It can be seen that the graphs for the cases where citric acid and sodium bicarbonate were added are located between the graphs for soil R alone (R1) and the graphs for modified soil R alone (R2). In other words, it can be seen that the effects of the soil modifier are negated by the addition of citric acid and sodium bicarbonate.

(Experimental Example M1)
Muddy water was prepared by mixing 4 g of soil M with 200 ml of water. The muddy water was placed in a measuring cylinder with a stopper, shaken, and allowed to stand. The sedimentation volume, turbidity, and particle size distribution were measured at predetermined intervals. The pH of the supernatant was also measured.

(Experimental Example M2)
Muddy water was prepared by mixing 4 g of modified soil M with 200 ml of water. The muddy water was placed in a stoppered graduated cylinder, shaken, and allowed to stand. The sedimentation volume, turbidity, and particle size distribution were measured at predetermined intervals. The pH of the supernatant was also measured.

(Experimental Example M3)
Citric acid was added to 200 ml of water in an amount of 0.004 parts by mass when the mass of the water was 100 parts by mass to prepare an aqueous solution. The pH of this aqueous solution was measured. 4 g of modified soil M was mixed with this aqueous solution to prepare muddy water. The muddy water was placed in a stoppered graduated cylinder, shaken, and allowed to stand. The sedimentation volume, turbidity, and particle size distribution were measured at predetermined intervals. The pH of the supernatant was also measured.

(Experimental Examples M4 to M6)
The sedimentation volume, turbidity, particle size distribution, and pH were measured in the same manner as in Experimental Example M3, except that the amount of citric acid added was changed as shown in Table 2.

Graphs of the measured sedimentation volume, turbidity, and particle size distribution for experimental examples M1 to M6 are shown in Figures 7 to 9. It can be seen that in all cases of sedimentation volume, turbidity, and particle size distribution, the graphs for when citric acid was added are located between the graphs for soil M alone (M1) and the graphs for improved soil M alone (M2). In other words, it can be seen that the effects of the soil improver are cancelled out by the addition of citric acid.

(Experimental Example M7)
Citric acid was added to 200 ml of water in an amount of 0.05 parts by mass when the mass of the water was 100 parts by mass, and sodium bicarbonate was added in an amount of 0.01 parts by mass to prepare an aqueous solution. The pH of this aqueous solution was measured. 4 g of modified soil R was mixed with this aqueous solution to prepare muddy water. The muddy water was placed in a stoppered graduated cylinder, shaken, and allowed to stand. The sedimentation volume and turbidity were measured at predetermined intervals. The pH of the supernatant was also measured.

(Experimental Examples M8 to M22)
The sedimentation volume, turbidity, and pH were measured in the same manner as in Experimental Example M7, except that the amounts of citric acid and sodium bicarbonate added were changed as shown in Table 2. For Experimental Examples M8 to M14 and M16 to M22, the particle size distribution was also measured.

Graphs of the measured sedimentation volume, turbidity, and particle size distribution for experimental examples M7 to M22 are shown in Figures 10 to 12. It can be seen that the graphs for the cases where citric acid and sodium bicarbonate were added are located between the graphs for soil M alone (M1) and the graphs for modified soil M alone (M2). In other words, it can be seen that the effects of the soil modifiers are cancelled out by the addition of citric acid and sodium bicarbonate.

(Experimental Example B1)
Muddy water was prepared by mixing 4 g of soil B with 200 ml of water. The muddy water was placed in a stoppered graduated cylinder, shaken, and allowed to stand. The sedimentation volume, turbidity, and particle size distribution were measured at predetermined intervals. The pH of the supernatant was also measured.

(Experimental Example B2)
Muddy water was prepared by mixing 4 g of modified soil B with 200 ml of water. The muddy water was placed in a stoppered graduated cylinder, shaken, and allowed to stand. The sedimentation volume, turbidity, and particle size distribution were measured at predetermined intervals. The pH of the supernatant was also measured.

(Experimental Example B3)
Citric acid was added to 200 ml of water in an amount of 0.004 parts by mass when the mass of the water was 100 parts by mass to prepare an aqueous solution. The pH of this aqueous solution was measured. 4 g of modified soil B was mixed with this aqueous solution to prepare muddy water. The muddy water was placed in a stoppered graduated cylinder, shaken, and allowed to stand. The sedimentation volume, turbidity, and particle size distribution were measured at predetermined intervals. The pH of the supernatant was also measured.

(Experimental Examples B4 to B6)
The sedimentation volume, turbidity, particle size distribution, and pH were measured in the same manner as in Experimental Example B3, except that the amount of citric acid added was changed as shown in Table 3.

Graphs of the measured sedimentation volume, turbidity, and particle size distribution for Experimental Examples B1 to B6 are shown in Figures 13 to 15. It can be seen that in all cases of sedimentation volume, turbidity, and particle size distribution, the graphs for when citric acid was added are not necessarily located between the graphs for soil B alone (B1) and the graphs for improved soil B alone (B2). In other words, it is difficult to say that the effects of the soil improver are cancelled out by the addition of citric acid.

(Experimental Example B7)
Citric acid was added to 200 ml of water in an amount of 0.05 parts by mass when the mass of the water was taken as 100 parts by mass, and sodium bicarbonate was added in an amount of 0.01 parts by mass to prepare an aqueous solution. The pH of this aqueous solution was measured. Muddy water was prepared by mixing 4 g of modified soil B with this aqueous solution. The muddy water was placed in a stoppered graduated cylinder, shaken, and allowed to stand. The sedimentation volume, turbidity, and particle size distribution were measured at predetermined intervals. The pH of the supernatant was also measured.

(Experimental Examples B8 to B16)
The sedimentation volume, turbidity, particle size distribution, and pH were measured in the same manner as in Experimental Example B7, except that the amounts of citric acid and sodium hydrogen carbonate to be added were changed as shown in Table 3.

Graphs of the measured sedimentation volume, turbidity, and particle size distribution for Experimental Examples B7 to B16 are shown in Figures 16 to 18. In Figure 16 (sedimentation volume), it can be seen that the graph when citric acid and sodium bicarbonate are added is located between the graph when only soil B is used (B1) and the graph when only modified soil B is used (B2). In other words, it can be seen that the effect of the soil modifier is canceled by the addition of citric acid and sodium bicarbonate. In Figures 17 (turbidity) and 18 (particle size distribution), it can be seen that the graph when citric acid and sodium bicarbonate are added is located between the graph when only soil B is used (B1) and the graph when only modified soil B is used (B2) at a certain concentration. It can also be seen that the graph is not located between the graph when only soil B is used (B1) and the graph when only modified soil B is used (B2) at another concentration. In other words, it can be seen that the effect of the soil modifier is canceled by adding citric acid and sodium bicarbonate in a specific concentration range.

<Experiment using oxalic acid and sodium bicarbonate as adjusting agents>
(Experimental Example R17)
Muddy water was prepared by mixing 4 g of soil R with 200 ml of water. The muddy water was placed in a stoppered graduated cylinder, shaken, and allowed to stand. The sedimentation volume was measured at predetermined intervals.

(Experimental Example R18)
Muddy water was prepared by mixing 4 g of modified soil R with 200 ml of water. The muddy water was placed in a stoppered graduated cylinder, shaken, and allowed to stand. The sedimentation volume was measured at predetermined intervals.

(Experimental Example R19)
An aqueous solution was prepared by adding oxalic acid in an amount of 0.5 parts by mass when the mass of the water was 100 parts by mass to 200 ml of water. The pH of this aqueous solution was measured. 4 g of modified soil R was mixed with this aqueous solution to prepare muddy water. The muddy water was placed in a stoppered graduated cylinder, shaken, and allowed to stand. The sedimentation volume was measured at predetermined intervals. The pH of the supernatant was also measured.

(Experimental Example R20)
The sedimentation volume and pH were measured in the same manner as in Experimental Example R19, except that the amount of citric acid added was changed as shown in Table 4.

(Experimental Example R21)
To 200 ml of water, oxalic acid was added in an amount of 0.05 parts by mass when the mass of the water was 100 parts by mass, and sodium bicarbonate in an amount of 0.01 parts by mass was added to prepare an aqueous solution. The pH of this aqueous solution was measured. 4 g of modified soil R was mixed with this aqueous solution to prepare muddy water. The muddy water was placed in a stoppered graduated cylinder, shaken, and allowed to stand. The sedimentation volume was measured at predetermined intervals. The pH of the supernatant was also measured.

Figure 19 shows a graph of the measured sedimentation volume for experimental examples R17 to R21. It can be seen that the graphs for when only oxalic acid was added (R19 and R20) and when oxalic acid and sodium bicarbonate were added (R21) are located between the graph for when only soil R was used (R17) and the graph for when only modified soil R was used (R18). In other words, it can be seen that the effect of the soil modifier was negated by the addition of only oxalic acid, or the addition of oxalic acid and sodium bicarbonate.

(Experimental Example M23)
Muddy water was prepared by mixing 4 g of soil M with 200 ml of water. The muddy water was placed in a stoppered graduated cylinder, shaken, and allowed to stand. The sedimentation volume was measured at predetermined intervals.

(Experimental Example M24)
Muddy water was prepared by mixing 4 g of modified soil M with 200 ml of water. The muddy water was placed in a stoppered graduated cylinder, shaken, and allowed to stand. The sedimentation volume was measured at predetermined intervals.

(Experimental Example M25)
An aqueous solution was prepared by adding oxalic acid in an amount of 0.5 parts by mass when the mass of the water was 100 parts by mass to 200 ml of water. The pH of this aqueous solution was measured. 4 g of modified soil M was mixed with this aqueous solution to prepare muddy water. The muddy water was placed in a stoppered graduated cylinder, shaken, and allowed to stand. The sedimentation volume was measured at predetermined intervals. The pH of the supernatant was also measured.

(Experimental Example M26)
The sedimentation volume and pH were measured in the same manner as in Experimental Example M25, except that the amount of citric acid added was changed as shown in Table 4.

(Experimental Example M27)
To 200 ml of water, oxalic acid was added in an amount of 0.05 parts by mass when the mass of the water was taken as 100 parts by mass, and sodium bicarbonate in an amount of 0.01 parts by mass was added to prepare an aqueous solution. The pH of this aqueous solution was measured. 4 g of modified soil M was mixed with this aqueous solution to prepare muddy water. The muddy water was placed in a stoppered graduated cylinder, shaken, and allowed to stand. The sedimentation volume was measured at predetermined intervals. The pH of the supernatant was also measured.

Figure 20 shows a graph of the measured sedimentation volume for experimental examples M23 to M27. It can be seen that the graphs for the cases where only oxalic acid was added (M25 and M26) and where oxalic acid and sodium bicarbonate were added (M27) are located between the graph for soil M only (M23) and the graph for modified soil M only (M24). In other words, it can be seen that the effect of the soil modifier is negated by the addition of only oxalic acid, or the addition of oxalic acid and sodium bicarbonate.

(Experimental Example B17)
Muddy water was prepared by mixing 4 g of soil B with 200 ml of water. The muddy water was placed in a stoppered graduated cylinder, shaken, and allowed to stand. The sedimentation volume was measured at predetermined intervals.

(Experimental Example B18)
Muddy water was prepared by mixing 4 g of modified soil B with 200 ml of water. The muddy water was placed in a stoppered graduated cylinder, shaken, and allowed to stand. The sedimentation volume was measured at predetermined intervals.

(Experimental Example B19)
To 200 ml of water, oxalic acid was added in an amount of 0.025 parts by mass when the mass of the water was taken as 100 parts by mass, and sodium bicarbonate in an amount of 0.05 parts by mass was added to prepare an aqueous solution. The pH of this aqueous solution was measured. 4 g of modified soil B was mixed with this aqueous solution to prepare muddy water. The muddy water was placed in a stoppered graduated cylinder, shaken, and allowed to stand. The sedimentation volume was measured at predetermined intervals. The pH of the supernatant was also measured.

(Experimental Example B20)
The sedimentation volume and pH were measured in the same manner as in Experimental Example R19, except that the amount of oxalic acid added was changed as shown in Table 4.

Figure 21 shows a graph of the measured sedimentation volume for experimental examples B17 to B20. It can be seen that the graphs for cases where oxalic acid and sodium bicarbonate were added (B19 and B20) are located between the graph for soil B alone (B17) and the graph for modified soil B alone (B18). In other words, it can be seen that the effect of the soil modifier is cancelled out by the addition of oxalic acid and sodium bicarbonate.

The present invention can be used for pretreatment of soil for wet classification.

Claims (8)

an adjusted soil obtained by mixing at least one of a water-absorbent resin and a polymer flocculant with soil having an organic matter content of 1 g/kg or more and 70 g/kg or less;
water and,
A muddy water is prepared by mixing a carboxylic acid and
The mass ratio of the adjusted soil to the water is 1:30 to 1:70;
The method for treating soil, wherein the amount of the carboxylic acid mixed is 0.001 parts by mass to 2 parts by mass per 100 parts by mass of the water. an adjusted soil obtained by mixing at least one of a water-absorbent resin and a polymer flocculant with soil having an organic matter content of 1 g/kg or more and 70 g/kg or less;
water and,
Carboxylic acid,
A muddy water is prepared by mixing with hydrogen carbonate or carbon dioxide.
The mass ratio of the adjusted soil to the water is 1:30 to 1:70;
the amount of the carboxylic acid mixed is 0.01 parts by mass to 0.5 parts by mass relative to 100 parts by mass of the water,
A method for treating soil, wherein the amount of the hydrogen carbonate or the carbon dioxide mixed is 0.005 parts by mass to 10 parts by mass per 100 parts by mass of the water. an adjusted soil in which at least one of a water-absorbent resin and a polymer flocculant is mixed into soil having an organic matter content of more than 70 g/kg and not more than 200 g/kg;
water and,
Carboxylic acid,
A muddy water is prepared by mixing with hydrogen carbonate or carbon dioxide.
The mass ratio of the adjusted soil to the water is 1:30 to 1:70;
the amount of the carboxylic acid mixed is 0.01 parts by mass to 0.5 parts by mass relative to 100 parts by mass of the water,
A method for treating soil, wherein the amount of the hydrogen carbonate or the carbon dioxide mixed is 0.02 to 0.4 parts by mass per 100 parts by mass of the water. an adjusted soil obtained by mixing at least one of a water-absorbent resin and a polymer flocculant with soil having an organic matter content of 1 g/kg or more and 70 g/kg or less;
water and,
A method for treating soil, comprising mixing a carboxylic acid with the soil to prepare muddy water having a pH of 1.3 to 6.0. an adjusted soil obtained by mixing at least one of a water-absorbent resin and a polymer flocculant with soil having an organic matter content of 1 g/kg or more and 70 g/kg or less;
water and,
Carboxylic acid,
A method for treating soil, comprising mixing with hydrogen carbonate or carbon dioxide to prepare muddy water having a pH of 3.0 to 8.0. an adjusted soil in which at least one of a water-absorbent resin and a polymer flocculant is mixed into soil having an organic matter content of more than 70 g/kg and not more than 200 g/kg;
water and,
Carboxylic acid,
A method for treating soil, comprising mixing with hydrogen carbonate or carbon dioxide to prepare muddy water having a pH of 4.3 to 6.3. The method for treating soil according to any one of claims 1 to 6, wherein the soil contains radioactive cesium. A method for classifying soil, comprising wet classifying the muddy water prepared by the method for treating soil according to any one of claims 1 to 7.

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