JP7260114B2 - Soil dissolution method and classification method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a soil dissolution method and a soil classification method.

Conventionally, soil is pulverized with a drum washer or a ball mill (see Patent Documents 1 and 2, for example). Grinding and subsequent classification generally aims to separate the soil at the desired particle size as the classification point.

JP 2016-138846 A JP 2014-142311 A

If the soil to be pulverized and classified contains organic matter, the soil tends to aggregate, and it may not be possible to achieve the desired pulverization (demulsification), pulverization, and classification. . In addition, with the methods of Patent Documents 1 and 2, it is not easy to pulverize the soil to a size of about several μm, and it is difficult to meet the demand for obtaining soil with a particle size of about several μm.

INDUSTRIAL APPLICABILITY According to the present invention, even if the soil contains organic matter and forms aggregates, the soil can be reliably disintegrated and pulverized, and the soil containing soil particles having a particle size of about several μm can be obtained. The purpose is to provide a desludging method. Another object of the present invention is to provide a method for classifying soil using the demulsification method.

The present invention provides a soil thawing method in which soil containing organic matter is pulverized by a wet mill, and the pulverization media used in the wet mill have a particle size of 2 to 18 mm.

Soil containing organic matter tends to be aggregated, and when grinding media with a particle size of several tens of millimeters is used in a wet mill, it is difficult to grind aggregates with a predetermined particle size or less. . Here, by using a grinding medium having a particle size of 2 to 18 mm, it becomes easy to grind aggregated grains having a similar size. According to this, the soil can be pulverized to particles of about several μm.

The soil may contain radioactive cesium. Radioactive cesium is generally attached to clay with particle sizes ranging from a few μm to 20 μm. Therefore, if the pulverization described above can be achieved, the clay particles of several μm to 20 μm, which have a high concentration of radioactive cesium, can be separated from other portions having a large particle size, thereby contributing to volume reduction of the radioactive material to be treated.

The grinding media may be sand or gravel.

The soil may be soil derived from agricultural land and containing humus. Agricultural land-derived soil is particularly suitable for application of the present invention because it tends to be aggregated.

In the present invention, it is preferable to adjust the pH of the contents in the wet mill to 9 to 13 when pulverizing with the wet mill. It is also preferable to mix the soil with water and keep it at 25 to 100° C. for a predetermined period of time before wet milling. According to these, the desludging speed increases.

Further, the present invention provides a classification method for solid-liquid separation by solid-liquid separation means after dissolving mud water by the above-described desludging method. According to this, it is possible to classify clay having a particle size of about several μm from the target soil.

According to the present invention, even if the soil contains organic matter and forms aggregates, the soil can be reliably disintegrated and pulverized, and the soil containing soil particles having a particle size of about several μm can be obtained. , can provide a soil thaw method. In addition, it is possible to provide a method for classifying soil using the desludging method.

4 is a graph showing the results of Examples 1-3.

Preferred embodiments of the present invention are described in detail below. In the soil dissolution method and the soil classification method of the present embodiment, soil containing organic matter is pulverized by a wet mill. In the following, soil derived from agricultural land containing radioactive cesium will be described.

Soil derived from agricultural land contains a lot of organic matter. Here, organic matter includes, for example, humus, fungi, microorganisms, root hairs, and humus-resistant cellulose. Humus is a substance produced by the decomposition of organic matter derived from plants and animals, and its size varies from several nanometers to several centimeters.

In the soil containing organic matter, the organic matter tends to bind soil particles together and form aggregates. Agglomerates resist forces tending to break up the soil, and therefore may not be able to achieve the desired pulverization with any pulverizing device. Therefore, it is desirable to eliminate the aggregated state (this is called "demulsification") when the soil is pulverized and further classified.

In the desludging method of the present embodiment, first, the target soil is mixed with water to obtain muddy water. Next, this muddy water is sieved to remove sand and gravel with a large particle size (for example, 2 mm or more). The muddy water that has passed through the sieve is put into the wet mill, and the wet mill is operated to pulverize the soil.

Here, the grinding media used in the wet mill may be metal spheres, alloy spheres, metal oxide spheres, metal composite oxide spheres, or the like, and may be sand or gravel. Examples of metals include iron and aluminum, examples of alloys include stainless steel, and examples of metal oxides and metal composite oxides include oxides of iron, oxides of aluminum and zircon, and composite oxides. As the sand or gravel, sand or gravel prepared separately from the target soil may be used, or the sand or gravel separated by the sieve may be washed and used. The latter case is economical because the particles contained in the same soil are reused. The density of the grinding media is preferably 2.0-8.0 g/cm ³ , more preferably 2.2-6.0 g/cm ³ , and more preferably 2.4-3.6 g/cm ³ . It is even more preferable to have

The grinding media used in the wet mill have a particle size of 2-18 mm. The particle size is preferably 3 to 14 mm, more preferably 4 to 12 mm. Since the size of soil aggregates is often within these ranges, the efficiency of pulverizing the aggregates is high when the particle size of the grinding media is within these ranges. In addition, when the grain size is sand or gravel as the grinding medium, the grain size is measured by the wet vibration sieving method or the elutriation tilt method.

The peripheral movement distance of the wet mill (that is, the value obtained by multiplying the peripheral speed by the dissolution time or retention time) is preferably 80 m or more, more preferably 240 m or more, from the viewpoint of sufficient desludging. , 390 m or more.

When the soil is thawed by the above method, the particle size distribution of the soil is biased toward smaller particle sizes. After that, muddy water is taken out from the wet mill and sieved to remove soil having a predetermined particle size or more (for example, 75 μm or more). Further, for example, using a classifier such as a cyclone, soil having a particle size of 30 μm or more, 20 μm or more, or 10 μm or more is removed.

Then, the muddy water remaining after the classification is solid-liquid separated by solid-liquid separation means. Microbubble flotation or coagulation sedimentation can be used as solid-liquid separation means. Microbubble flotation is a method of separating predetermined fine particles in a suspension using bubbles (microbubbles) having a size of about μm. Since the microbubbles adhere to the predetermined fine particles and float on the water surface, the separation of the clay particles having a particle size of μm level is achieved by recovering the microbubbles.

On the other hand, the coagulation-sedimentation method is a method in which a coagulant is added to form aggregates to increase the sedimentation rate, and the principle is to neutralize the surface charge of particles or to render the surface hydrophobic. As the aggregating agent, salts of polyvalent metal ions are particularly preferred for the purpose of neutralizing surface charges, and polyaluminum chloride (PAC), ammonium sulfate, iron chloride, iron sulfate and the like are preferred. A surfactant can be used for the purpose of making the surface hydrophobic.

Clay having a particle size of about several micrometers can be separated from the soil containing organic matter by the dissolution method and the classification method described above.

In the desludging method of this embodiment, since the particle size of the grinding media is 2 to 18 mm, it is suitable for pulverizing soil aggregated to approximately the same particle size. When the particle diameters of the grinding media and the aggregated particles are in such a relationship, grinding so as to scrape off the surface of the soil particles (surface grinding) and dividing the soil particles into a plurality of small particles of the same size Pulverization to divide (volumetric pulverization) occurs in a well-balanced manner, and the organic aggregate particles in the soil are efficiently reduced.

A large amount of radioactive cesium generally adheres to clay particles with a particle size of 20 μm or less, particularly clay particles with a particle size of several hundred nm to 20 μm. Therefore, according to the desludging method and the classification method described above, the clay particles with a high concentration of radioactive cesium can be separated from other portions with a large particle size. As a result, the other part (for example, soil with a particle size of 20 μm or more) can be reused as a material, and the part containing radioactive cesium can be concentrated, and the volume of the radioactive material to be treated can be reduced. will be invested.

Although the preferred embodiments of the present invention have been described above, the present invention is not limited to the above embodiments. For example, in the above embodiment, the muddy water is put into the wet mill immediately after sand or gravel with a relatively large particle size (for example, 2 mm or more) is removed, but the muddy water is put into the wet mill before the classification. Conversely, it may be further classified (for example, 75 μm or more) using a sieve with a small mesh, and then charged into a wet mill. The fact that the soil is agglomerated means that even particles that normally pass through the sieve due to their small particle size may not pass through the sieve due to the increased particle size due to the agglomeration. In this case, since clay particles containing radioactive cesium may remain on the sieve, it is preferable to perform desludging by a wet mill at an early stage in the entire classification process in order to avoid this.

Further, a desludging aid may be added during desludging in the wet mill. Examples of desludging aids include pH adjusters and dispersants. Examples of the pH adjusting material include those that make the liquid alkaline, such as calcium hydroxide (slaked lime) and sodium hydroxide. When the target soil exhibits acidity or neutrality, calcium ions are added to the mud to be demulsified by the wet mill to adjust the pH of the mud to 9 to 13, or 10 to 12, or 10. It may be adjusted to about 5 to 11.5. This increases the desludging speed. Calcium hydroxide (slaked lime) is preferable as a calcium ion supply source, and the amount of the calcium ion supply source added is 2.3× as the amount of calcium ions (Ca ²⁺ ) per 1 g of soil (original soil). It is preferably 10 ⁻⁶ to 5.0×10 ⁻³ mol, more preferably 2.3×10 ⁻⁵ to 2.3×10 ⁻³ mol, and more preferably 5.0×10 ⁻⁵ to 1 .0×10 ⁻³ mol is more preferable, 1.0×10 ⁻⁴ to 8.0×10 ⁻⁴ mol is even more preferable, and 2.3×10 ⁻⁴ to 3.0× 10 ⁻⁴ mol is particularly preferred.

Alternatively, the target soil may be mixed with water before being pulverized by the wet mill, and after this is maintained at 25 to 100° C. for a predetermined time, the wet mill may be pulverized. The lower limit of this temperature may be 30°C or 35°C. The upper limit of this temperature may be 80°C or 60°C. The upper limit is preferably 45° C. from the viewpoint of the temperature standard for waste water. The time for keeping the temperature may be 5 to 60 minutes, or 10 to 50 minutes. During this time the temperature may fluctuate within the above range. If the desludging is performed after performing the treatment that satisfies these conditions, the desludging rate will be further increased, and the final particle size after desludging will further increase the proportion of soil particles having a smaller particle size. In addition, when this treatment is performed, the temperature at the time of desludging does not matter, and desludging may be performed at room temperature.

In the above embodiment, soil derived from agricultural land containing radioactive cesium was targeted, but soil derived from agricultural land may be targeted as long as it contains organic matter.

EXAMPLES The content of the present invention will be described in more detail below with reference to examples. In addition, the present invention is not limited to the following examples. In the description of the examples, the term "grinding" refers to the action performed in the wet mill, and refers to both "grinding" and "demulsification" that actually occur inside.

<Examples 1 to 4>
A commercially available 900 mL container magnetic pod mill (outer diameter 130 mm) as a grinding vessel, alumina balls with a diameter of 6 mm or 10 mm (specific gravity 3.6) as grinding media, and mulching stone (specific gravity 2.5 to 2.7; main component prepared limestone (calcium carbonate). As soil containing humus, 107 g of Kanuma Kuroboku soil (average moisture content of 31%), 500 mL of water, and 300 mL of grinding media are put into a magnetic pod, and this is ground under the following conditions with a commercially available tabletop ball mill stand. was performed (see also Table 1).
· Common conditions ... Rotation speed: 24 rpm; mill peripheral speed: 16.3 cm / sec; room temperature (about 20 ° C.)
・(Original soil)…Pulverization time: 0 minutes (that is, no pulverization)
Example 1 Grinding time: 10 minutes Grinding media: 10 mm diameter alumina balls Example 2 Grinding time: 40 minutes Grinding media: 10 mm diameter alumina balls Example 3 Grinding time: 40 minutes Grinding media: 6 mm diameter alumina balls Example 4 ... Grinding time: 40 minutes; Grinding media: 5 mm diameter mulching stone

The ground product was removed from the magnetic pod mill and classified by wet vibration sieving. At this time, a JIS standard stainless sieve was used as the sieve of 38 μm or more, and a plastic sieve manufactured by Ito Seisakusho was used as the sieve of 20 μm or less. The results of the particle size distribution (frequency distribution) of the original soil and Examples 1 to 3 are shown in FIG.

From the graph shown in FIG. 1, it can be seen that in Examples 1 to 3, the dissolution of the black soil progressed and the particle size became smaller. As the pulverization time (dissolution time) was lengthened, or the diameter of the alumina balls was reduced from 10 mm to 6 mm, the frequency peak on the coarse grain side tended to shift toward finer grain sizes.

In addition, Table 1 shows the proportions of particles of 0 to 20 μm, 20 to 75 μm, and 75 μm or more in the original soil and the pulverized products of Examples 1 to 4 (wt %; based on recovered dry soil). According to this, it can be seen that selective disaggregation to a particle size of 20 μm or less is performed in each example.

<Examples 5 to 7>
A commercially available 4800 mL magnetic pod mill (outer diameter: 215 mm) was prepared as a pulverization vessel, and Asake sand (specific gravity: 2.6) with a diameter of 5 mm was prepared as a pulverization medium. As soil containing humus, Ibaraki Daigo rice field soil (average moisture content 36%) was prepared, and the amount of target soil, water, and Asake sand in the amount shown in Table 2 was put into the magnetic pod, and this was placed. Pulverization was performed with a commercially available tabletop ball mill stand under the following conditions.

In Examples 6 and 7, slaked lime was added to bring the pH to 11.5. Furthermore, in Example 7, after mixing the target soil, water, morning ash, and slaked lime, the mixture was allowed to stand in a constant temperature bath at 45° C. for 10 minutes, and then pulverized with a mill. Table 2 shows the particle undersize of the pre-milled and milled products in Examples 5-7. This undersize was measured by a particle size distribution analyzer.

From the results shown in Table 2, it can be seen that even when the soil from the fields of Ibaraki Daigo was targeted, it was possible to effectively disaggregate to a particle size of 10 μm or less (Example 5). In addition, it can be seen that by adjusting the pH to 11.5 by adding slaked lime during pulverization (during dissolution), the size of the particles after pulverization became smaller than when slaked lime was not added. (Example 6). In addition, it can be seen that the size of the particles after pulverization was further reduced by heating the target soil at pH 11.5 before pulverization (Example 7).

<Examples 8 to 16>
Instead of the Kuroboku soil of Example 1, field soil from Ibaraki (average moisture content: 21%) was used. As shown in Table 3, pulverization was performed by changing the pulverization time, rotation speed, mill peripheral speed, alumina ball (or Asake sand (granitic, specific gravity 2.6), mulching stone) diameter. Slaked lime was added into the magnetic pods in the amounts shown in Table 3 during the grinding. Table 3 shows the particle size ratios in the original soil and the pulverized product.

From the results shown in Table 3, it can be seen that even in the case of field soil from Ibaraki, it was possible to effectively disintegrate to a grain size of 20 μm or less.

<Examples 17 to 19>
A commercially available 4800 mL magnetic pod mill (outer diameter: 215 mm) was prepared as a pulverization vessel, and Asake sand (specific gravity: 2.6) with a diameter of 5 mm was prepared as a pulverization medium. As soil containing humus, the same Ibaraki field soil (average moisture content 21%) as in Examples 8 to 16, or Ibaraki Daigo field soil (average moisture content 36%) was prepared. The indicated amounts of target soil, water, and dawn sand were put into a magnetic pod and pulverized with a commercially available tabletop ball mill stand under the following conditions. Table 4 shows the particle size ratio in the pulverized product.

From the results shown in Table 4, it can be seen that even when the soil of the Ibaraki Daigo rice field was targeted, the sludge could be effectively disintegrated.

INDUSTRIAL APPLICABILITY The present invention can be used to demulsify and classify aggregated soil.

Claims (6)

The soil containing organic matter is pulverized with a wet mill,
The grinding media used in the wet mill have a particle size of 2 to 18 mm,
The method for dissolving soil, wherein the soil is soil derived from agricultural land and contains humus . 2. The method of dissolving soil according to claim 1, wherein said soil contains radioactive cesium. 3. The method of dissolving soil according to claim 1, wherein said grinding media are sand or gravel. 4. The method of dissolving soil according to claim 1, wherein the pH of the content in the wet mill is adjusted to 9 to 13 when pulverizing in the wet mill. The method of dissolving soil according to any one of claims 1 to 4 , wherein the soil is mixed with water and kept at 25 to 100°C for a predetermined time before the pulverization. A method for classifying soil, comprising solid-liquid separation by means of solid-liquid separation means after dissolving mud water by the method for dissolving soil according to any one of claims 1 to 5 .

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