JP4832474B2 - Solidification method of soft soil using waste gypsum - Google Patents

Description

  The present invention relates to a method for solidifying soft soil, and in particular, waste gypsum board, which is a building waste material, is crushed and separated, mixed with hemihydrate gypsum obtained by heat treatment at a predetermined temperature and solidified by mixing with soft soil. The present invention relates to a method for solidifying soft soil using gypsum.

  Conventionally, most of the waste gypsum board that is generated in large quantities due to the dismantling of buildings has been disposed of by landfill, etc., but the waste gypsum board is managed from stable industrial waste by the revision of the Waste Disposal Law. From the viewpoint of soaring processing costs associated with the shift to industrial waste and effective utilization of resources, it is desired to separate and recover gypsum from waste gypsum board.

Gypsum is roughly classified into three types, dihydrate gypsum (CaSO ₄ · 2H ₂ O), hemihydrate gypsum (CaSO ₄ · 1 / 2H ₂ O), and anhydrous gypsum (CaSO ₄ ). When the water gypsum is heated to about 130 ° C. or higher, it is rearranged to hemihydrate gypsum, and when it is further heated to about 180 ° C. or higher, it is transferred to type II anhydrous gypsum via type III anhydrous gypsum. In addition, when hydration treatment is performed on hemihydrate gypsum, the hydration reaction proceeds rapidly and rearranges to dihydrate gypsum and hardens in a short time. Does not advance. It has been found that type III anhydrous gypsum absorbs moisture in the atmosphere strongly, so that it can be easily converted to hemihydrate gypsum if it is allowed to stand naturally.

  Gypsum such as gypsum board is in the form of dihydrate gypsum, and even if it is subjected to water treatment, hydration reaction does not occur and it does not harden. If it is rearranged to a state, it can be cured in a short time by water treatment, and for example, it can be reused sufficiently effectively as a soil-solidifying material.

  However, flue gas desulfurization gypsum discharged from thermal power plants, etc. is often used as the raw material for gypsum board, and this flue gas desulfurization gypsum contains fluorine, which is a harmful substance. When the board is crushed and separated and then heat-treated at a predetermined temperature to produce hemihydrate gypsum as it is used as a soil-solidifying material, the amount exceeding the environmental standard (0.8 mg / l or less) in the soil Fluorine may be eluted.

To solve the above problem, for example, Patent Document 1 (Japanese Patent Laid-Open No. 2008-94901) suppresses elution of fluorine by adding magnesium oxide at a predetermined ratio to hemihydrate gypsum used as a mud solidifying material. In addition, Patent Document 2 (Japanese Patent Application Laid-Open No. 2006-225475) describes a fluorine-containing material by using a solidifying material obtained by blending hemihydrate gypsum and anhydrous gypsum in a predetermined ratio. A product that suppresses elution is described.
JP 2008-94901 A JP 2006-225475 A

  As described above, some of the soil-solidifying materials mainly composed of hemihydrate gypsum regenerated from waste gypsum board and the like have been designed to suppress the elution of fluorine into the soil. In addition to this, the inventors examined whether there is a method capable of suppressing the elution of fluorine from the hemihydrate gypsum as a soil solidifying material into the soil.

  In the present invention, in view of the above points, when hemihydrate gypsum obtained by crushing and heat-treating waste gypsum board containing fluorine is mixed with soft soil and solidified, fluorine in hemihydrate gypsum is contained in the soil. It is an object of the present invention to provide a method for solidifying soft soil using waste gypsum that can be prevented from being dissolved into the soil.

As a result of intensive research to solve the above problems, the present inventors have added a predetermined amount of blast furnace cement to hemihydrate gypsum in advance and mixed it with soft soil, so that hemihydrate gypsum is mixed into the soil. It has been found that the amount of fluorine ions eluting in can be suppressed. Here, the blast furnace cement contains alumina (Al ₂ O ₃ ) and calcium oxide (CaO) components, and these components and hemihydrate gypsum (CaSO ₄ · 1 / 2H ₂ O) are contained in soft soil. causing moisture and hydration produces ettringite _{(3CaO · Al 2 O 3 ·} 3CaSO 4 · 32H 2 O), fluorine ions eluted from the hemihydrate gypsum is fixed by replacing the _SO ^{4 2-of} the ettringite It was thought that the elution of fluorine into the soil was effectively suppressed. And if suppression of the elution amount of fluorine ions in this experiment is due to the above reaction, instead of the blast furnace cement, it similarly contains alumina (Al ₂ O ₃ ) and calcium oxide (CaO) components, Blast furnace slag, coal ash, etc. can be used effectively, and these are industrial by-products similar to flue gas desulfurization gypsum, which is the raw material for waste gypsum board. It is considered advantageous.

In addition, some soft soils to be solidified may contain various harmful substances including heavy metals such as boron, arsenic, selenium, lead, cadmium, chromium and mercury. It is also known from the literature that it can be fixed by replacing it with Ca ²⁺ or SO ₄ ^{2- of} ettringite. In such a case, by performing the solidification treatment, fluorine from the hemihydrate gypsum into the soil can be obtained. It is considered that harmful substances in soft soil can be purified while suppressing elution.

That is, in order to solve the above-mentioned problem, the soft soil solidification method using waste gypsum according to claim 1 according to the present invention is a semi-water obtained by crushing and heating waste gypsum board containing fluorine. In a method for solidifying soft soil using waste gypsum in which gypsum is mixed with soft soil for solidification, a predetermined amount of blast furnace cement is added as an additive containing alumina and calcium oxide to the hemihydrate gypsum. And a second step of mixing and solidifying the hemihydrate gypsum added with the blast furnace cement as an additive in the first step with soft soil. (CaSO ₄ · 1 / 2H ₂ O), alumina (Al ₂ O ₃ ) and calcium oxide (CaO) contained in the blast furnace cement as an additive are hydrated using moisture in soft soil. Ettlingai (3CaO · Al ₂ O ₃ · 3CaSO ₄ · 32H ₂ O) is generated and the fluorine ions eluted from the hemihydrate gypsum are replaced with SO ₄ ^{2− of the} ettringite and fixed, and the fluorine is eluted into the soil. It is characterized in that soft soil is solidified while suppressing the amount so as not to exceed environmental standards .

Further, solidification method soft soil with gypsum according to claim 2, wherein, as the additive, and blast furnace cement and / or blast furnace slag containing a large amount of calcium oxide (CaO), alumina (Al ₂ O ₃₎ It is characterized by using coal ash containing a large amount of ash and supplementing chemical components that are lacking in ettringite production .

The method for solidifying soft soil using waste gypsum according to claim 3 is for soft soil containing one or more harmful substances selected from boron, arsenic, selenium, lead, cadmium, chromium and mercury. It is characterized in that the ions of the harmful substances in the soft soil are fixed by replacing the ettringite Ca ²⁺ or SO ₄ ²⁻ .

According to the method for solidifying soft soil using waste gypsum according to claim 1 of the present invention, hemihydrate gypsum obtained by crushing and heating waste gypsum board containing fluorine is mixed with soft soil. In the method for solidifying soft soil using waste gypsum to be solidified, a first step of adding a predetermined amount of blast furnace cement as an additive containing alumina and calcium oxide to the hemihydrate gypsum, and the first step It comprises a second step in which hemihydrate gypsum added with blast furnace cement as an additive in the step is mixed with soft soil and solidified, and at the time of the second step, hemihydrate gypsum (CaSO ₄ · 1 / 2H ₂ O), alumina (Al ₂ O ₃ ) and calcium oxide (CaO) contained in the blast furnace cement , which is an additive , are hydrated using moisture in soft soil to produce ettringite (3CaO · Al ₂ O). ₃ · 3CaSO 4 · 32H _{2 O)} to generate the fluorine ions eluted from the hemihydrate gypsum is replaced with SO ₄ ^2-of the ettringite fixed, so that the elution amount of fluorine into the soil does not exceed environmental standards Since the soft soil was solidified while restraining it, the fluorine contained in the hemihydrate gypsum regenerated as the soil solidifying material can be prevented from leaching into the soil, and the soft soil is suitably solidified. it can.

Further, according to the solidification method of soft soil with gypsum according to claim 2, as the additive, and blast furnace cement and / or blast furnace slag containing a large amount of calcium oxide (CaO), alumina (Al ₂ O ₃ ) Coal ash containing a large amount of ash is used to compensate for the chemical components that are deficient in ettringite formation, which is advantageous in that the amount of additive can be reduced to keep processing costs low. In addition, blast furnace slag and coal ash, which are industrial by-products, can be used effectively, which is beneficial in terms of environment.

According to the method for solidifying soft soil using waste gypsum according to claim 3, soft soil containing one or more harmful substances selected from boron, arsenic, selenium, lead, cadmium, chromium, and mercury is used. On the other hand, since the ions of the harmful substances in the soft soil are replaced with Ca ²⁺ or SO ₄ ^{2− of the} ettringite and fixed, the purification treatment of the harmful substances in the soil is performed together with the solidification treatment of the soft soil. Can also be performed.

In the method for solidifying soft soil using the waste gypsum of the present invention, first, the waste gypsum board containing fluorine is crushed into a predetermined size and separated from paper or the like, and dihydrate gypsum as a main component Then, the dihydrate gypsum is heat-treated at a predetermined temperature to form hemihydrate gypsum, and is adjusted to a state suitable as a soil solidifying material. Then, a predetermined amount of additives such as blast furnace cement, blast furnace slag, and coal ash containing alumina (Al ₂ O ₃ ) and calcium oxide (CaO) components were added to the hemihydrate gypsum thus obtained. Then, it is mixed with soft soil and solidified.

At this time, the fluorine ions contained in the hemihydrate gypsum try to elute into the soil, but the elution amount is greatly reduced as compared with the case of hemihydrate gypsum alone. This is due to the fact that hemihydrate gypsum (CaSO ₄ · 1 / 2H ₂ O), alumina (Al ₂ O ₃ ), and calcium oxide (CaO) undergo hydration reaction due to a large amount of moisture present in soft soil, resulting in ettringite. (3CaO · Al ₂ O ₃ · 3CaSO ₄ · 32H ₂ O) is generated, and the fluorine ions eluted from the hemihydrate gypsum are replaced with SO ₄ ^{2− of the} ettringite and fixed to fix the fluorine in the soil. This is thought to be due to suppression.

  Thus, it is possible to effectively suppress the fluorine contained in the hemihydrate gypsum regenerated as a soil solidifying material from being eluted into the soil, and soft soil can be solidified suitably in terms of environment. In addition, when blast furnace slag, coal ash, etc. are used as additives to be added to hemihydrate gypsum, these are industrial by-products, like flue gas desulfurization gypsum, which is a raw material for gypsum board, so that the processing cost is relatively In addition to being able to keep the cost low, it is considered that it is very beneficial in terms of the environment to be able to use these effectively.

In addition, the soft soil to be treated may contain various harmful substances including heavy metals such as boron, arsenic, selenium, lead, cadmium, chromium and mercury. It is considered that the ettringite can be fixed by being replaced with Ca ²⁺ or SO ₄ ^{2− of the} ettringite. Therefore, it is preferable that the solidification treatment is performed so that the toxic substances in the soil can be purified at the same time while suppressing the elution of fluorine from the hemihydrate gypsum.

  In addition, by actively utilizing such properties of ettringite, for example, even when hemihydrate gypsum that does not contain fluorine is used as a soil solidifying material, blast furnace cement, blast furnace slag, coal ash, etc. are added. The ettringite may be generated by solidification treatment, and the ettringite may be subjected to purification treatment of harmful substances in the soil exclusively. Also, even if it is not soft soil that requires solidification treatment, an appropriate amount of hemihydrate gypsum and blast furnace cement, blast furnace slag, coal ash, etc. are added to the soil contaminated with the above harmful substances. It is also possible to generate ettringite by spraying tap water necessary for the hydration reaction and to purify harmful substances in the soil.

  Hereinafter, an embodiment of the present invention will be described in detail.

  First, the waste gypsum board containing fluorine is finely crushed and separated from paper, etc. to recover the main component dihydrate gypsum, and then the dihydrate gypsum is heated at about 130 to 180 ° C. Hemihydrate gypsum was obtained. The blast furnace cement was added to 140% by weight of water added to 100% by weight of MC clay (trademark) manufactured by Sanyo Clay Industry Co., Ltd. instead of soft soil to be solidified, and 0, 5, 10% by weight Then, 0 to 50% by weight of the hemihydrate gypsum was added and sufficiently stirred and mixed, and then cured for 28 days.

  After the curing, each sample is subjected to a fluorine elution test in accordance with the Environmental Agency Notification No. 13 method, and the concentration of the eluted fluorine ion is measured in accordance with the method listed in Table 6 of the Water Quality Environmental Standard Notification. The measurement results are shown in the graph of FIG.

  As a result, as can be seen from the graph of FIG. 1, when no blast furnace cement is added (dotted line), the amount of fluorine elution is all environmental standards (0.8 mg / l) regardless of the amount of hemihydrate gypsum added. In contrast, for blast furnace cement with 5 wt% (double-dot chain line) or 10 wt% (single-dot chain line) added, all of the fluorine elution amount is environmental standards regardless of the amount of hemihydrate gypsum added. (0.8 mg / l). In the graph, elution of fluorine is observed even when hemihydrate gypsum is not added, but this is due to the fluorine originally contained in the MC clay.

  And in order to confirm presence of ettringite about each said specimen, when each specimen was analyzed by the powder X-ray diffraction method, as shown in FIG. 2, from which the blast furnace cement was not added (FIG. 2a) No peak identifying the ettringite (circled portion in FIG. 2a) was found, and no ettringite was produced, but from which blast furnace cement was added at 5% by weight or 10% by weight (FIG. 2b) In addition, a peak identifying the ettringite (circled portion in FIG. 2b) was observed, confirming the presence of ettringite.

  From the above results, by adding an appropriate amount of hemihydrate gypsum and an additive such as blast furnace cement to the soil in the presence of sufficient moisture, hydration reaction occurs and ettringite is produced. It was confirmed that fluoride ions eluted from hemihydrate gypsum were fixed by ettringite and the dissolution into the soil could be suppressed.

It is a graph which shows the result of the elution test of the fluorine regarding the solidification processing method of the soft soil using the waste gypsum concerning this invention. It is a figure which shows the result of the powder X-ray diffraction regarding the solidification processing method of the soft soil using the waste gypsum which concerns on this invention, When a did not add a blast furnace cement, b showed the case where a blast furnace cement was added. Is.

Claims (3)

In the method for solidifying soft soil using waste gypsum in which hemihydrate gypsum obtained by crushing and heat-treating waste gypsum board containing fluorine is mixed with soft soil, in the method for solidifying treatment of soft soil, alumina is used for the hemihydrate gypsum A first step of adding a predetermined amount of blast furnace cement as an additive containing calcium oxide, and a mixture of hemihydrate gypsum added with blast furnace cement as an additive in this first step is mixed with soft soil and solidified. It consists of a second step, wherein the time of the second step, the hemihydrate gypsum _{(CaSO 4 · 1 / 2H 2} O), alumina _(Al 2 _{O 3)} and calcium oxide contained in the blast furnace cement is added material ( fluorine ion to the CaO), by utilizing the moisture of soft soil by hydration reaction to produce ettringite _{(3CaO · Al 2 O 3 ·} 3CaSO 4 · 32H 2 O), eluted from hemihydrate gypsum The emissions were fixed SO ₄ ^2-a is substituted the ettringite, characterized in that the elution amount of fluorine into the soil is such that solidification of soft soil while suppressing so as not to exceed environmental standards waste A method for solidifying soft soil using plaster. As the additive material, and blast furnace cement and / or blast furnace slag containing a large amount of calcium oxide (CaO), using a coal ash containing a large amount of alumina (Al 2 _{O 3),} the chemical components to be insufficient to each formation of ettringite The method for solidifying soft soil using the waste gypsum according to claim 1, wherein the soil is supplemented . With respect to soft soil containing one or more kinds of harmful substances selected from boron, arsenic, selenium, lead, cadmium, chromium and mercury, ions of the harmful substances in the soft soil are converted into Ca ²⁺ or SO ₄ ^{2 of the} ettringite. ^The method for solidifying soft soil using waste gypsum according to claim 1 or 2, wherein the solidified by replacing with-.

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