JP2013146691A - Solidification method of soil using waste gypsum - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solidification method of soil using waste gypsum in which when gypsum hemihydrate obtained by that a waste gypsum board containing fluorine is shredded and heat-treated is used to perform the solidification process of soil, the elution in soil of fluorine in gypsum can be controlled, and the curing time can be appropriately controlled.SOLUTION: A waste gypsum board spall that contains fluorine is heat-treated at a prescribed temperature and gypsum hemihydrate and a type II anhydrous gypsum are generated, the gypsum hemihydrate of fast curing and the type II anhydrous gypsum of slow curing are added/mixed to/with treatment soil at a prescribed rate and further added and mixed with portland blast furnace cement containing alumina and calcium oxide. At that time, a part of the gypsum hemihydrate of fast curing is substituted by the type II anhydrous gypsum of slow curing, thereby curing progresses comparatively slowly, and solidification can be excellently performed without starting curing at least in the solidification. Moreover, ettringite is generated also by the type II anhydrous gypsum as well as the gypsum hemihydrate, and thereby the elution to soil of fluorine is surely controlled.

Description

  The present invention relates to a method for solidifying soil, and in particular, mixing waste water gypsum board obtained by heat treatment at a predetermined temperature and type II anhydrous gypsum after crushing / sorting waste gypsum board, which is a building waste material, into soil. The present invention relates to a method for solidifying soil using waste gypsum to be solidified.

  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.

  For example, hemihydrate gypsum obtained by crushing waste gypsum board and heat-treating at a predetermined temperature is transferred to dihydrate gypsum by a hydration reaction with an appropriate amount of moisture and hardens in a very short time ( For example, it can be effectively used for solidification treatment of soft soil or the like. However, as the raw material for gypsum board, flue gas desulfurization gypsum emitted from thermal power plants, etc. is often used. Since this flue gas desulfurization gypsum contains fluorine, which is a harmful substance, it is derived from waste gypsum board. When hemihydrate gypsum is used as a soil-solidifying material as it is, there is a concern that fluorine in an amount exceeding the environmental standard (0.8 mg / l or less) is eluted in the soil.

Therefore, as disclosed in Patent Document 1 (Japanese Patent No. 4834744), the present inventors have prepared hemihydrate gypsum (CaSO ₄ · 1) obtained by crushing and heating waste gypsum board containing fluorine. / 2H ₂ O), by adding a predetermined amount of blast furnace cement containing alumina (Al ₂ O ₃ ) and calcium oxide (CaO) as additives, ettringite by hydration reaction with moisture in soft soil (3CaO · Al ₂ O ₃ · 3CaSO ₄ · 32H ₂ O) is generated, and fluorine ions eluted from the hemihydrate gypsum are taken in and fixed in the ettringite, which is suitable while suppressing the elution of fluorine into the soil. In addition, we have proposed a method for solidifying soil that enables soft soil to be solidified. The ettringite is also effective for purification of harmful substances in the soil because harmful substances such as boron, arsenic, selenium, lead, cadmium, chromium and mercury are taken in and fixed in the same manner as fluorine.

Japanese Patent No. 4834744

  However, when solidifying the soil, it is not always preferable to harden as soon as possible as in the above-mentioned conventional example, for example, if the hardening starts during the solidification of the soil, workability and There is a possibility of causing some troubles such as poor handling.

  In view of the above points, in the present invention, when the soil is solidified using hemihydrate gypsum obtained by crushing and heat-treating waste gypsum board containing fluorine, the fluorine in the gypsum elutes into the soil. It is an object of the present invention to provide a method for solidifying soil using waste gypsum that can appropriately adjust the curing time while suppressing the above.

  In order to solve the above problems, the inventors first reduced the amount of hemihydrate gypsum added to the treated soil, while increasing the amount of additives such as blast furnace cement by that amount, It was thought that the curing time could be moderately delayed without decreasing the strength and by slowing the hydration reaction. However, with this method, the amount of ettringite produced decreases as the amount of hemihydrate gypsum decreases, which not only makes it difficult to suppress the elution of fluorine ions into the soil, but also increases the amount of blast furnace cement added. There is concern about the adverse effect of increasing the pH in the soil with the increase, and from the original purpose of effective utilization of the recovered resources (gypsum), the above method that suppresses the amount of use is not very preferable. .

  Therefore, as a result of intensive studies, as with hemihydrate gypsum, ettringite is produced by hydration reaction with alumina and calcium oxide contained in blast furnace cement, etc. Anhydrous gypsum that has the property of slowing down after being dislocated (slow-hardening) can be replaced with a part of hemihydrate gypsum to ensure a sufficient curing time while ensuring sufficient ettringite production. I thought it could be delayed.

  Anhydrous gypsum can be produced by heat-treating gypsum such as waste gypsum board in the form of dihydrate gypsum at a predetermined temperature, and hemihydrate gypsum is produced at a temperature range of about 130 to 180 ° C. In the higher temperature range of about 180 to 350 ° C., it is converted into type III anhydrous gypsum, in the temperature range of about 350 to 1000 ° C., type II anhydrous gypsum, and further to about 1100 ° C. Each is supposed to be dislocated. Among these, type III anhydrous gypsum absorbs moisture in the atmosphere strongly, and if left undisturbed, it is very easily transferred to hemihydrate gypsum, so it is not suitable for replacing hemihydrate gypsum. . In addition, type I anhydrous gypsum is considered disadvantageous in terms of cost because heat treatment requires a high temperature of 1100 ° C. or higher. On the other hand, type II anhydrous gypsum has a heat treatment temperature that is not so high compared to hemihydrate gypsum and can reduce the processing cost. It was.

  Based on the above assumption, the present inventors added a predetermined amount of water to a mixture of hemihydrate gypsum having fast hardening and type II anhydrous gypsum having slow hardening in an appropriate ratio, and hydration reaction As a result, it has been found that the setting time varies depending on the mixing ratio of both, for example, to the treated soil, hemihydrate gypsum and type II anhydrous gypsum were added at an appropriate ratio, respectively, blast furnace cement, etc. When an appropriate amount of these additives were added and mixed, the curing time could be adjusted appropriately while sufficiently producing ettringite that fixes fluorine, and a suitable solidification treatment could be achieved.

  That is, in order to solve the above-mentioned problem, the soil solidification method using the waste gypsum according to claim 1 according to the present invention is a semi-water gypsum obtained by crushing and heating a waste gypsum board containing fluorine. On the other hand, in order to generate ettringite that fixes fluorine ions by reaction with the gypsum component in the hemihydrate gypsum, after adding a predetermined amount of blast furnace cement containing alumina and calcium oxide as an additive, the treated soil and The waste gypsum board is crushed and heat-treated in the method for solidifying soil using waste gypsum that is mixed and generated to fix the soil while fixing fluorine ions eluted from gypsum. The type II anhydrous gypsum obtained in this way is mixed with a part of the hemihydrate gypsum and mixed, and the mixing ratio of the fast-curing hemihydrate gypsum and the slow-hardening type II anhydrous gypsum is adjusted. This is characterized in that the setting time is adjusted to prevent hardening from starting during at least the solidification of the treated soil.

  The soil solidification method using waste gypsum according to claim 2 is characterized in that the type II anhydrous gypsum is substituted with half or more of the half-water gypsum and mixed.

  The soil solidification method using waste gypsum according to claim 3 is characterized in that the mixing ratio of hemihydrate gypsum to type II anhydrous gypsum is adjusted to 30 wt% or less.

  Further, in the method for solidifying soil using waste gypsum according to claim 4, blast furnace cement and / or blast furnace slag containing a large amount of calcium oxide and coal ash containing a large amount of alumina are used as the additive. It is characterized by supplementing chemical components that are insufficient for ettringite production.

  Moreover, the soil solidification method using the waste gypsum according to claim 5 is a method for treating soil containing one or more harmful substances selected from boron, arsenic, selenium, lead, cadmium, chromium and mercury. It is characterized in that ions of the harmful substance therein are fixed with the ettringite.

  According to the method for solidifying soil using waste gypsum according to claim 1 of the present invention, fluoric acid cement is fixed by adding blast furnace cement to hemihydrate gypsum obtained by crushing and heating waste gypsum board. While ettringite is produced, type II anhydrous gypsum obtained by crushing and heat-treating the waste gypsum board is replaced with part of the hemihydrate gypsum, and hardening does not start at least during the solidification treatment of the soil As described above, the setting time was adjusted by adjusting the mixing ratio of slow-hardening type II anhydrous gypsum to fast-setting hemihydrate gypsum. It is possible to suitably solidify the treatment at an arbitrary curing time.

  Further, according to the method for solidifying soil using waste gypsum according to claim 2, since type II anhydrous gypsum is substituted with more than half of hemihydrate gypsum and mixed, slow hardening type II anhydrous gypsum Thus, a relatively slow solidification treatment mainly composed of can be achieved, and a suitable delay adjustment of the curing time can be expected.

  Further, according to the method for solidifying soil using waste gypsum according to claim 3, since the mixing ratio of hemihydrate gypsum to type II anhydrous gypsum is adjusted to 30 wt% or less, most of the hardened II In the state where it is replaced with type anhydrous gypsum, a more gradual solidification treatment becomes possible, and a suitable delay adjustment of the curing time becomes possible.

  Further, according to the method for solidifying soil using waste gypsum according to claim 4, blast furnace cement and / or blast furnace slag containing a large amount of calcium oxide and coal ash containing a large amount of alumina are used as additives. The chemical components that are lacking in ettringite production are compensated for each other, so that the amount of additive can be reduced and the processing cost can be kept low, and the blast furnace slag and coal ash, which are industrial byproducts, can be reduced. It can be used effectively and is also beneficial in terms of the environment.

  Moreover, according to the solidification processing method of the soil using the waste gypsum according to claim 5, for the soil containing one or more harmful substances selected from boron, arsenic, selenium, lead, cadmium, chromium, mercury, Since the ions of the harmful substances in the soil are fixed by the ettringite, the purification of the harmful substances in the soil can be performed together with the solidification treatment of the soil.

It is a graph which shows the relationship of the hardening time at the time of a hydration reaction with respect to hemihydrate gypsum / type II anhydrous gypsum.

  In the method for solidifying soil using waste gypsum of the present invention, dihydrate gypsum recovered from fluorine-containing waste gypsum board is heat-treated at a predetermined temperature, for example, a temperature range of about 130 to 180 ° C. Heat treatment is carried out on hemihydrate gypsum and in the temperature range of about 350 to 1000 ° C., respectively, to be transferred to type II anhydrous gypsum. Then, hemihydrate gypsum obtained by the heat treatment and type II anhydrous gypsum are respectively added to the treated soil at a predetermined ratio, and further containing alumina and calcium oxide, for example, blast furnace cement or blast furnace slag Then, an additive such as coal ash and a predetermined amount of water are added as necessary, and the mixture is agitated and mixed using an appropriate agitation / mixing means such as a continuous mixer and solidified. In addition, it is not always necessary to use a mixer. For example, after each material is sprayed on the treated soil, it may be solidified by directly stirring and mixing with the soil using a backhoe or the like.

  At this time, if it is a fast-setting hemihydrate gypsum alone, it will harden in a very short time due to a rapid hydration reaction with moisture in the treated soil and water added as necessary. However, in the present invention, a part of hemihydrate gypsum is treated with slow-hardening type II anhydrous gypsum. Since it is substituted, the hydration reaction can be made relatively slow, the curing time can be delayed, and at least during the solidification treatment, the above problem can be prevented by adjusting so that curing does not start. It can be prevented.

  As the ratio of type II anhydrous gypsum to hemihydrate gypsum increases, the curing time can be further delayed.For example, type II anhydrous gypsum is replaced with more than half of hemihydrate gypsum, that is, type II anhydrous gypsum. By adjusting the amount of gypsum to be larger than that of hemihydrate gypsum, it is possible to perform a relatively slow solidification treatment mainly consisting of slow-hardening type II anhydrous gypsum, and it is possible to suitably adjust the setting time with delay. It becomes. In addition, if the relationship of the setting time to the ratio of hemihydrate gypsum and type II anhydrous gypsum is confirmed in advance by testing or the like, it is possible to arbitrarily adjust the setting time with reference to the test data, for example, In addition, it is possible to quickly cure after completion of the treatment so as to obtain a desired strength while reliably preventing the curing during the solidification treatment.

Fluorine ions contained in the above-mentioned hemihydrate gypsum and type II anhydrous gypsum are hemihydrate gypsum (CaSO ₄ · 1 / 2H ₂ O), alumina (Al ₂ O ₃ ) and calcium oxide (CaO) in blast furnace cement. Can be effectively fixed by ettringite (3CaO · Al ₂ O ₃ · 3CaSO ₄ · 32H ₂ O) produced from the reaction with yttrium gypsum, but also with type II anhydrous gypsum (CaSO ₄ ) in the same manner as hemihydrate gypsum. Therefore, the elution of fluorine from the gypsum to the soil can be reliably suppressed while adjusting the setting time by substituting part of the hemihydrate gypsum with type II anhydrous gypsum.

  Thus, from the fluorine-containing waste gypsum board, reprocessing the hemihydrate gypsum and type II anhydrous gypsum according to the heat treatment temperature, the fast-curing hemihydrate gypsum and the slow-hardening type II anhydrous gypsum obtained in this way, And by adding and mixing alumina and calcium oxide-containing blast furnace cement in appropriate amounts to the soil, the curing time is set appropriately while generating the amount of ettringite necessary to fix the fluorine eluted from the gypsum without a shortage. Therefore, a suitable solidification treatment according to the properties and uses of each soil is possible.

  Also, as the additive, the blast furnace cement alone has a relatively small alumina component, so an appropriate amount of coal ash rich in alumina component is added to the blast furnace cement, or a part or all of the blast furnace cement is calcium oxide. It may be replaced with blast furnace slag rich in components and coal ash rich in alumina components. In that case, blast furnace slag and coal ash are industrial by-products as with flue gas desulfurization gypsum which is the raw material of gypsum board. Therefore, it is considered that it is very beneficial in terms of the environment that the processing cost can be kept relatively low and these can be used effectively.

The ratio of blast furnace slag and coal ash to replace blast furnace cement is the amount of hemihydrate gypsum and type II anhydrous gypsum, taking into account the amount of calcium oxide contained in blast furnace slag and the amount of alumina contained in coal ash. On the other hand, it is preferable to adjust the amount of calcium oxide and the amount of alumina suitable for efficiently generating ettringite. For example, the chemical equivalent ratio (mol ratio) of alumina, calcium oxide and gypsum is alumina (Al ₂ When adjusted so that O ₃ ): calcium oxide (CaO): gypsum (CaSO ₄ ) = 1: 3: ₃ , ettringite (3CaO · Al ₂ O ₃ · 3CaSO ₄ · 32H ₂ O) is efficiently produced. Is done.

  In addition, soil to be treated may contain various harmful substances including heavy metals such as boron, arsenic, selenium, lead, cadmium, chromium, mercury, etc. It can be fixed with ettringite, and by applying the above-mentioned solidification treatment, it is preferable that the toxic substance in the soil can be purified at the same time while suppressing elution of fluorine from hemihydrate gypsum and type II anhydrous 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 the soil does not require solidification treatment, an appropriate amount of hemihydrate gypsum, type II anhydrous gypsum, blast furnace cement, blast furnace slag, coal ash, etc. It is also possible to produce ettringite by spraying as much water as necessary for the hydration reaction and purifying the harmful substances in the soil.

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

  First, after crushing the waste gypsum board containing fluorine finely, collecting the dihydrate gypsum which is the main component by separating from paper and the like, this dihydrate gypsum, for example, using a heating device such as a rotary kiln, Heat treatment is performed in a temperature range of about 130 to 180 ° C. to obtain fast-setting hemihydrate gypsum, and heat treatment is performed in a temperature range of about 350 to 1000 ° C. to obtain slow-hardening type II anhydrous gypsum.

  Then, the soil to be solidified, for example, soft soil, or a soil material such as roadbed, roadbed, and embankment, is charged into a continuous mixer such as a stabilizer, while the half-water gypsum obtained by the heat treatment is used. And type II anhydrous gypsum are supplied to the mixer at predetermined ratios, and contain alumina and calcium oxide, for example, blast furnace cement, blast furnace slag, coal ash and other additives, and a predetermined amount as required. Water is added, and the materials are stirred and mixed in a mixer for solidification treatment.

  At this time, if it is a fast-curing hemihydrate gypsum alone, curing may start unnecessarily quickly.For example, if curing occurs during the solidification process, it may lead to deterioration in workability and handling properties. However, by replacing part of hemihydrate gypsum with slow-hardening type II anhydrous gypsum, it is possible to appropriately delay the curing time and avoid the above-mentioned problems, enabling suitable solidification treatment It is said. In addition, since ettringite is produced by II-type anhydrous gypsum as well as hemihydrate gypsum, fluorine that is likely to be eluted from gypsum can be stably fixed and reliably suppressed.

  The mixing ratio of the hemihydrate gypsum and type II anhydrous gypsum may be determined as appropriate. For example, a plurality of samples in which the mixing ratio of hemihydrate gypsum and type II anhydrous gypsum is changed little by little are prepared. Preliminarily conducted a test such as adding and mixing an appropriate amount of water to each sample and measuring the time until hardening occurs in each sample. Based on this test data, mixing hemihydrate gypsum with type II anhydrous gypsum You may make it adjust a ratio.

  As the above test, a sample prepared by mixing commercially available hemihydrate gypsum and type II anhydrous gypsum at a predetermined ratio is prepared (semihydrate gypsum / type II anhydrous gypsum: prepared in a range of about 10 to 55 wt%). ) After adding and mixing tap water to each sample so that the water content is about 66 wt% and mixing it, the rod is inserted near the center of the mixture, and the rod is self-supporting as it is. The measurement is carried out with the time until it becomes possible to be the time until curing starts, and the result is shown in the graph of FIG.

  As a result, as can be seen from the graph of FIG. 1, when the ratio of hemihydrate gypsum to type II anhydrous gypsum is more than about 30 wt%, curing started in about several minutes, but when it becomes about 30 wt% or less. The curing time is gradually delayed. When the ratio is about 15 wt%, the curing time is about 5000 seconds (about 1.5 hours), and when the ratio is about 10 wt%, the curing time is about 9000 seconds. It was confirmed that it was delayed to the extent (about 2.5 hours).

  In this way, as the proportion of type II anhydrous gypsum increases, the curing time can be gradually delayed, but type II anhydrous gypsum is replaced with at least half of half water gypsum, and type II anhydrous gypsum is hemihydrate gypsum. More preferably, the ratio of hemihydrate gypsum to type II anhydrous gypsum is about 30 wt% or less, and most of the amount is adjusted so that type II anhydrous gypsum occupies, A relatively slow solidification treatment mainly composed of slow-hardening type II anhydrous gypsum is possible, and the curing time can be suitably adjusted for delay.

  In addition, if the mixing ratio of hemihydrate gypsum and type II anhydrous gypsum is determined based on the test data, the adjustment of the curing time becomes relatively easy, and at least curing during the solidification process is surely avoided. In addition, it is possible to quickly cure after the solidification treatment so as to obtain a desired strength.

Claims (5)

  In order to produce ettringite that fixes fluorine ions by reaction with gypsum components in the hemihydrate gypsum obtained by crushing and heat treating waste gypsum board containing fluorine, alumina and calcium oxide are used. After adding a predetermined amount of contained blast furnace cement as an additive, it is stirred and mixed with the treated soil, and the waste gypsum is solidified while fixing fluorine ions eluted from the gypsum with the generated ettringite In the method for solidifying soil using a mixture, type II anhydrous gypsum obtained by crushing and heat-treating the waste gypsum board is substituted for part of the hemihydrate gypsum and mixed, and fast-setting hemihydrate gypsum and The setting time was adjusted by adjusting the mixing ratio with slow-hardening type II anhydrous gypsum, so that hardening did not start at least while the treated soil was solidified. A method for solidifying soil using waste gypsum characterized by the above.   The solidification method of soil using waste gypsum according to claim 1, wherein type II anhydrous gypsum is substituted with more than half of hemihydrate gypsum and mixed. Processing method.   The method for solidifying soil using waste gypsum according to claim 1, wherein the mixing ratio of hemihydrate gypsum to type II anhydrous gypsum is adjusted to 30 wt% or less. Solidification method.   The soil solidification processing method using the waste gypsum according to any one of claims 1 to 3, wherein, as the additive, blast furnace cement and / or blast furnace slag containing a large amount of calcium oxide, and coal ash containing a large amount of alumina. A method for solidifying soil using waste gypsum characterized in that the chemical components that are lacking in ettringite production are compensated for each other.   In the solidification processing method of the soil using waste gypsum in any one of Claims 1 thru | or 4, in the soil containing 1 or more types of harmful substances selected from boron, arsenic, selenium, lead, cadmium, chromium, mercury On the other hand, a method for solidifying soil using waste gypsum characterized in that ions of the harmful substances in the soil are fixed by the ettringite.

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