Treatment method of gypsum-containing material, manufacturing method of calcium sulfite -containing material, manufacturing method of cement-based solidification material, and calcium silicate-containing composition

Abstract

To provide a treatment method of a gypsum-containing material that can obtain SO2 gas efficiently from gypsum by suppressing formation of sulfides.SOLUTION: A treatment method of a gypsum-containing material includes at least a mixing step of mixing a gypsum-containing material with a SiO2-containing decomposition accelerator to obtain a mixed raw material and a heating step of firing the mixed raw material and thermal decomposition of at least a part of gypsum in the gypsum-containing material for formation of SO2 gas and a residue, wherein the residue contains calcium silicate.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a method for treating a gypsum-containing substance, a method for producing a calcium sulfite-containing substance, a method for producing a cement-based solidification material, and a calcium silicate-containing composition. [Background technology]

[0002] A technique for producing a sulfur-containing composition by heating gypsum together with a carbon source is known. For example, Patent Document 1 proposes a technique for adjusting the raw material preparation conditions or the rotary kiln operating conditions by checking the amount of SO2 gas emitted from the kiln exhaust gas during a heating process in which waste gypsum board and coal gasification coke slag are heated in a rotary kiln. Patent Document 2 proposes a technique for obtaining a sulfur-containing composition containing calcium sulfide (CaS) by mixing gypsum and coal gasification coke slag so that the molar ratio of C / CaSO4 is 3 or more and calcining the mixture.

[0003] On the other hand, there is a known technology for using calcined calcium silicate containing wollastonite and anorthite in water treatment materials. For example, Patent Document 3 proposes the production of a water treatment material that exhibits pH buffering action using, as a raw material, a material that generates wollastonite and anorthite after calcination. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2023-127979 [Patent Document 2] Japanese Patent Publication No. 2022-150926 [Patent Document 3] Japanese Patent Application Laid-Open No. 2017-064597 Summary of the Invention [Problem to be solved by the invention]

[0005] As in Patent Documents 1 and 2, calcium sulfite can be produced by reacting SO2 gas, produced by thermal decomposition of gypsum, with a Ca source. Increasing the amount of SO2 gas produced can increase the amount of calcium sulfite produced. However, depending on the conditions of the thermal decomposition, the residue left after the thermal decomposition of gypsum may contain sulfides such as CaS. Contact of sulfides with acidic water generates hydrogen sulfide, which is harmful to humans, so care must be taken when handling the residue. Therefore, the present disclosure provides a method for treating a gypsum-containing material that can suppress the generation of sulfides and efficiently obtain SO2 gas from gypsum. It also provides a method for producing a calcium sulfite-containing material that can efficiently produce calcium sulfite and cement-based solidification materials. It also provides a calcium silicate-containing composition that can be used effectively for various applications. [Means for solving the problem]

[0006] One aspect of the present disclosure provides a method for treating a gypsum-containing material, the method including at least a mixing step of mixing a gypsum-containing material with a decomposition-accelerating material containing SiO to obtain a mixed raw material, and a heating step of calcining the mixed raw material to thermally decompose at least a portion of the gypsum in the gypsum-containing material and generate SO gas and a residue, the residue containing calcium silicate.

[0007] This treatment method uses a decomposition accelerator that contains SiO2 and accelerates the decomposition of gypsum. Such a decomposition accelerator is thought to accelerate the decomposition reaction, for example, as shown in the following formula (1). Therefore, it is possible to suppress the generation of sulfides and efficiently produce SO2 gas from gypsum. CaSO4+SiO2→SO2+CaSiO3+1 / 2O2(1)

[0008] One aspect of the present disclosure provides a method for producing a calcium sulfite-containing material, which includes a reaction step of reacting the SO2 gas produced by the above-mentioned treatment method with a calcium-containing material. This method for producing a calcium sulfite-containing material uses the SO2 gas produced by the above-mentioned treatment method, and therefore can efficiently produce calcium sulfite.

[0009] One aspect of the present disclosure provides a method for producing a cement-based solidification material, which includes a preparation step of obtaining a cement-based solidification material by mixing raw materials containing calcium sulfite-containing material obtained by the above-mentioned production method, cement, and gypsum. This method for producing a cement-based solidification material uses calcium sulfite obtained by the above-mentioned production method, and therefore can efficiently produce the cement-based solidification material.

[0010] One aspect of the present disclosure provides a calcium silicate-containing composition comprising gypsum and at least one of wollastonite and anorthite, wherein the total content of wollastonite and anorthite is 10% by mass or more. Such a calcium silicate-containing composition can be suitably used for various applications, such as as a raw material for cement clinker. [Effects of the Invention]

[0011] According to the present disclosure, it is possible to provide a method for treating a gypsum-containing material that can suppress the generation of sulfides and efficiently obtain SO2 gas from gypsum. It is also possible to provide a method for producing a calcium sulfite-containing material that can efficiently produce calcium sulfite and a cement-based solidifying material. It is also possible to provide a calcium silicate-containing composition that can be suitably used for various applications. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a graph showing the relationship between the blending amount of decomposition accelerator and the gypsum decomposition rate when a mixed raw material is fired at 1200°C for each type of decomposition accelerator. [Figure 2] 1 is a graph showing the relationship between the blending amount of decomposition accelerator and the gypsum decomposition rate when a mixed raw material is fired at 1150°C for each type of decomposition accelerator. [Figure 3] 1 is a graph showing the relationship between the amount of biomass ash blended and the gypsum decomposition rate for each firing temperature. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, embodiments of the present disclosure will be described. However, the following embodiments are merely examples for explaining the present disclosure and are not intended to limit the present disclosure to the following content. The symbol "to" used in a numerical range indicates a numerical range that includes the upper and lower limit values. For example, "X to Y" indicates a numerical range "greater than or equal to X and less than or equal to Y." Numerical ranges in which the upper and / or lower limits are replaced with numerical values described in the examples are also included in the content of the present disclosure. Multiple exemplified components or materials may be used alone or in combination.

[0014] In the present specification, numerical ranges in which the upper or lower limit of one numerical range is replaced with the upper or lower limit of another numerical range are also included in the present disclosure. In the present specification, numerical ranges in which the upper or lower limit of a numerical range is replaced with a value shown in the examples are also included in the present disclosure.

[0015] A method for treating a gypsum-containing material according to one embodiment includes at least a mixing step of mixing the gypsum-containing material with a decomposition-accelerating material containing SiO to obtain a mixed raw material, and a heating step of calcining the mixed raw material to thermally decompose at least a portion of the gypsum in the gypsum-containing material and generate a residue containing SO gas and calcium silicate.

[0016] The gypsum-containing material may be a gypsum-containing waste or a gypsum-containing material other than waste. The gypsum-containing waste preferably includes at least one selected from the group consisting of waste gypsum board, flue gas desulfurization gypsum (flue gas desulfurization gypsum), sulfur-containing sludge, desulfurization sludge, and desulfurization slag, and more preferably includes at least one of waste gypsum board and flue gas desulfurization gypsum. Such gypsum-containing waste is easily available in relatively large quantities, and can sufficiently reduce the production cost of the residue containing SO gas and calcium silicate.

[0017] The waste gypsum board may contain organic matter such as resin and paper adhering to the surface of the gypsum board, and inorganic impurities such as metals. The gypsum contained in the gypsum-containing material may contain at least one selected from the group consisting of gypsum dihydrate, gypsum hemihydrate, and anhydrous gypsum. In this specification, gypsum dihydrate, gypsum hemihydrate, and anhydrous gypsum are collectively referred to as gypsum. Furthermore, the gypsum content and gypsum decomposition rate are values in terms of CaSO4, which does not contain moisture, unless otherwise specified. The gypsum content in the gypsum-containing material may be 50% by mass or more, 60% by mass or more, 70% by mass or more, 80% by mass or more, 90% by mass or more, or 95% by mass or more.

[0018] The decomposition accelerator may contain SiO2 and accelerate the decomposition of gypsum upon heating. The decomposition accelerator preferably contains at least one selected from the group consisting of coal ash, silica sand, silica stone, bentonite, biomass ash, municipal solid waste incineration ash, blast furnace slag, and waste glass. Such decomposition accelerators are easily available in relatively large quantities and can significantly reduce the production cost of residues containing SO2 gas and calcium silicate. Furthermore, the use of coal ash, biomass ash, municipal solid waste incineration ash, blast furnace slag, and waste glass enables effective waste utilization. In recent years, the use of carbon-neutral biomass has expanded to prevent global warming. Since much of the combustion ash (biomass ash) generated by biomass combustion is disposed of in landfills, there is a need for its effective utilization. The treatment method of this embodiment can also meet such needs. Examples of biomass ash include combustion ash from plants and sewage sludge.

[0019] From the viewpoint of accelerating the thermal decomposition of gypsum, the decomposition accelerator may contain at least one selected from the group consisting of coal ash, silica sand, silica stone, and bentonite, and may contain coal ash.

[0020] From the viewpoint of sufficiently promoting the thermal decomposition of gypsum, the SiO2 content in the decomposition accelerator is preferably 20% by mass or more, more preferably 30% by mass or less, even more preferably 40% by mass or less, and particularly preferably 50% by mass or more. The SiO2 content in the decomposition accelerator may be 85% by mass or less, 80% by mass or less, or 70% by mass or less. This allows the decomposition accelerator to contain a sufficient amount of Al2O3 in addition to SiO2. The Al2O3 content in the decomposition accelerator is preferably 10% by mass or more, more preferably 20% by mass or more. The Al2O3 content in the decomposition accelerator may be 40% by mass or less, 30% by mass or less, or 25% by mass or less. An example of the decomposition accelerator may have an SiO2 content of 20 to 85% by mass and / or an Al2O3 content of 10 to 40% by mass. The decomposition accelerator may contain CaO, Na2O, C (carbon), etc. as components other than SiO2.

[0021] The total content of Na and K in the decomposition accelerator, calculated as the oxides (NaO, KO), is preferably 7% by mass or less, more preferably 6% by mass or less, and even more preferably 5% by mass or less. This prevents the decomposition accelerator from melting and adhering to the inside of the heating device used in the heating step, and improves the handleability of the residue.

[0022] In the mixing step, at least the gypsum-containing material and the decomposition accelerator are mixed to obtain a mixed raw material. Raw materials other than the gypsum-containing material and the decomposition accelerator may also be mixed. The mixing method is not particularly limited, and mixing may be performed using a conventional mixer. Examples of the mixer include a high-speed mixer, a planetary mixer, a homogenizer, a ribbon blender, a paddle mixer, a tumbler mixer, and a jet mixer.

[0023] In the mixing step, the gypsum-containing material and the decomposition accelerator are mixed so that the molar ratio of SiO2 to CaSO4 contained in the mixed raw material is preferably 0.2 or more, more preferably 0.4 or more, even more preferably 0.6 or more, and particularly preferably 0.8 or more. This allows the thermal decomposition of gypsum to be sufficiently accelerated. From the viewpoint of reducing the production cost of SO2 gas, the molar ratio of SiO2 to CaSO4 contained in the mixed raw material may be 5.0 or less, 4.0 or less, or 3.0 or less.

[0024] In the heating step, the mixed raw material is calcined to thermally decompose at least a portion of the gypsum in the gypsum-containing material, thereby generating SO2 gas and a residue. The heating step may be performed using a conventional heating device. The heating device may be a continuous type or a batch type. Either an externally heated type or an internally heated type may be used as the heating method. The heat source is not particularly limited, and may be, for example, heavy oil, pulverized coal, or electricity. Specific examples of heating devices include a rotary kiln, a fluidized bed furnace, and an electric furnace. However, the present invention is not limited to these. The atmosphere in which the mixed raw material is calcined is not particularly limited, and is preferably an air atmosphere from the viewpoint of simplifying the device configuration.

[0025] In the heating step, for example, the reaction shown in formula (1) below occurs. This produces a residue containing SO2 gas and calcium silicate. The gas generated in the heating step may contain other gases in addition to SO2 gas. The calcium silicate contained in the residue is not limited to wollastonite, and may contain other calcium silicates. Examples of such calcium silicates include belite, and when the decomposition accelerator contains Al2O3, anorthite can be used. CaSO4+SiO2→SO2+CaSiO3+1 / 2O2(1)

[0026] If the amount of C contained in the mixed raw material is too high, much of the oxygen in the firing atmosphere is consumed in the reaction with C, which can result in an extremely low-oxygen atmosphere. In such a case, the reaction shown in formula (3) below is more likely to proceed. Furthermore, CO produced by the reaction between oxygen and C also contributes to the production of CaS, as shown in formula (2), thereby promoting the overall production of CaS. As these reactions proceed, the amount of SO2 gas produced decreases accordingly. Therefore, the molar ratio of C (carbon) to CaSO4 contained in the mixed raw material is preferably 0.2 or less, more preferably 0.15 or less, even more preferably 0.1 or less, and particularly preferably 0.09 or less. This further suppresses the production of CaS and sufficiently increases the amount of SO2 gas produced. The C (carbon) contained in the mixed raw material may be derived from, for example, waste gypsum board or from a decomposition accelerator. From the perspective of reducing the amount of C (carbon) contained in the mixed raw material, it is preferable to reduce the amount of waste plastics and the like used, and the mixed raw material may not contain plastics. CaSO4+4CO→CaS+4CO2(2) CaSO4+2C→CaS+2CO2(3)

[0027] The calcination temperature of the mixed raw material is preferably above 1100°C, more preferably 1150°C or higher, and even more preferably 1200°C or higher. By setting the calcination temperature at such a temperature, the amount of SO2 produced can be sufficiently increased. If the calcination temperature of the mixed raw material is too high, when a decomposition accelerator with a high content of alkaline components is used, these components tend to melt and adhere to the inside of the heating device. Therefore, the calcination temperature of the mixed raw material may be 1600°C or lower, 1500°C or lower, or 1450°C or lower. This can improve fuel efficiency. An example of the calcination temperature range is 1100 to 1600°C.

[0028] The calcination time of the mixed raw material may be 0.1 to 10 hours, 0.5 to 5 hours, or 0.7 to 3 hours. Longer calcination times of the mixed raw material tend to increase the gypsum decomposition rate, and the calcium silicate content in the residue tends to increase, resulting in a lower gypsum content. The gypsum decomposition rate in the heating step (gypsum decomposition rate) may be 3% or more, 5% or more, 10% or more, 15% or more, or 20% or more. The gypsum decomposition rate can be determined by the method described in the Examples. There is no particular upper limit to the gypsum decomposition rate, and it may be, for example, 80% or less, 60% or less, or 50% or less.

[0029] According to the method for treating a gypsum-containing material of this embodiment, gypsum can be thermally decomposed to efficiently obtain a residue containing SO2 and calcium silicate. The SO2 may be used for producing calcium sulfite. The calcium silicate-containing residue may be used as a raw material for cement clinker. Gypsum may remain in the residue.

[0030] Since the residue contains calcium silicate, it can also be called a calcium silicate-containing composition. The calcium silicate in the residue may include at least one of wollastonite and anorthite. When the purpose is to produce SO2 gas, such a residue can also be called a by-product. The residue can be suitably used as a raw material for cement clinker, a water treatment material, etc.

[0031] The total content of wollastonite and anorthite in the residue is preferably 10% by mass or more, more preferably 15% by mass or more, even more preferably 20% by mass or more, and particularly preferably 25% by mass. Such a residue can be more suitably used as a raw material for cement clinker. The total content of wollastonite and anorthite in the residue may be, for example, 90% by mass or less, 80% by mass or less, or 70% by mass or less. An example of the total content of wollastonite and anorthite in the residue is 10 to 90% by mass.

[0032] The gypsum content in the residue may be 90% by mass or less, 80% by mass or less, 70% by mass or less, 60% by mass or less, or 50% by mass or less. This allows the amount of SO2 generated in the heating step to be sufficiently large. The gypsum content in the residue may be 5% by mass or more, 10% by mass or more, or 20% by mass or more. An example of the gypsum content in the residue is 10 to 90% by mass.

[0033] The CaS content in the residue is preferably 10% by mass or less, more preferably 5% by mass or less, even more preferably 3% by mass or less, and particularly preferably 1% by mass or less. This allows the amount of SO2 gas generated in the heating step to be sufficiently large. The CaO content in the residue may be 5% by mass or less, 3% by mass or less, or 1% by mass or less. In addition to the above components, the residue may also contain SiO2. The content of each component in the residue can be measured by X-ray diffraction. The composition of the residue can be adjusted, for example, by changing the type of decomposition accelerator.

[0034] The method for treating a gypsum-containing material may include a carbonation step in which the residue is contacted with a CO2-containing gas to carbonate the Ca compounds contained in the residue. From the viewpoint of efficiently promoting carbonation, the residue may contain water. The moisture content of the residue may be, for example, more than 0% by mass but not more than 30% by mass, i.e., moist, or may be in a slurry state exceeding 30% by mass. The carbonation step may involve storing the residue in a sealed facility and stirring the residue while flowing a CO2-containing gas through it to promote carbonation. Alternatively, the residue may be spread out in a yard or the like, and a CO2-containing gas may be continuously flowed therethrough, with the residue being periodically turned over to promote carbonation over a period of about one month. Alternatively, the residue may be contacted with a CO2-containing gas while molded into a formwork. Furthermore, the residue may be contacted with a CO2-containing gas while being heated. The CO2-containing gas used in the carbonation step may be, for example, exhaust gas containing CO2 discharged from a cement clinker manufacturing apparatus. Carbonation may be carried out by using a CO2-containing gas in a high-pressure state or in a supercritical state. Alternatively, dry ice may be used in the form of particles.

[0035] Among the components contained in the residue, those that can be carbonated include CaO produced by the decomposition of gypsum, Ca(OH)2 produced by the reaction of CaO with water, wollastonite, CSH, etc. The residue that has undergone the carbonation process contains CaCO3. Such residue may be used as a cement clinker raw material, or may be mixed with produced cement clinker to be used as an admixture for producing cement. It may also be used as a roadbed material, etc.

[0036] A method for producing a calcium sulfite-containing material according to one embodiment includes a reaction step of reacting a calcium-containing material with the SO gas generated in the heating step of the above-described method for treating a gypsum-containing material. Examples of calcium-containing materials include calcium carbonate, calcium hydroxide, and calcium oxide. In the reaction step, calcium sulfite may be obtained by, for example, the reaction of the following formula (4) or (5):

[0037] Ca(OH)2+SO2→ CaSO3+H2O (4) CaCO3+SO2 → CaSO3+CO2(5)

[0038] The reactions of formulas (4) and (5) may be carried out by passing SO gas through a slurry containing Ca(OH) or CaCO. The reaction of formula (5) may also be carried out by contacting powdered CaCO with heated SO gas. The SO gas may be passed through the slurry as a mixed gas with other gases, or may be brought into contact with powdered CaCO. In this way, a calcium sulfite-containing material containing calcium sulfite can be obtained.

[0039] The calcium sulfite content of the calcium sulfite-containing material may be 5% by mass or more, 10% by mass or more, 20% by mass or more, or 30% by mass or more. The calcium sulfite-containing material may be in the form of a slurry or a granular solid containing calcium sulfite hemihydrate. The calcium sulfite-containing material may contain calcium bisulfite (Ca(HSO3)2), a double salt of calcium sulfite and calcium sulfate, or calcium sulfate.

[0040] This method for producing a calcium sulfite-containing material uses SO2 gas generated in the heating step of the method for treating a gypsum-containing material, so that the calcium sulfite-containing material can be produced efficiently at low production cost. The calcium sulfite-containing material may be used in the production of cement compositions and cement-based solidifying materials.

[0041] A method for producing a cement-based solidification material according to one embodiment includes a preparation step of mixing raw materials including a calcium sulfite-containing material obtained by the above-described method for producing a calcium sulfite-containing material, cement, and gypsum to obtain a cement-based solidification material.

[0042] The cement may be any of the various Portland cements specified in JIS R5210:2003 "Portland Cement." The cement may be cement clinker. The gypsum may be any of gypsum dihydrate, gypsum hemihydrate, and anhydrous gypsum. From the viewpoint of strength development of the cement composition, gypsum dihydrate or anhydrous gypsum may be contained.

[0043] The calcium sulfite-containing material may be in a solid form or in a slurry form. The calcium sulfite-containing material, cement, and gypsum may be mixed using a cement mill such as a vertical mill or a ball mill. If the calcium sulfite-containing material is in a slurry form, the temperature rise in the cement mill can be sufficiently suppressed. The raw materials for the cement-based solidification material may contain other components. Examples of other components include slag, calcium carbonate, clinker dust, fly ash, silica fume, and metakaolin.

[0044] This method for producing cement-based solidification material uses calcium sulfite-containing material obtained using SO2 gas generated in the heating process of the method for treating gypsum-containing material, so cement-based solidification material can be produced efficiently and at low production costs.

[0045] A calcium silicate-containing composition according to one embodiment includes gypsum and at least one of wollastonite and anorthite, with the total content of wollastonite and anorthite being 10% by mass or more. This calcium silicate-containing composition may be a residue obtained in a calcination step in a method for treating a gypsum-containing material. That is, it may be a reaction product of a mixed raw material containing gypsum and a decomposition accelerator, or it may contain the reaction product. The description of the composition and components of the residue may also apply to the calcium silicate-containing composition of this embodiment. However, the calcium silicate-containing composition is not limited to the residue obtained in the method for treating a gypsum-containing material. For example, the calcium silicate-containing composition may be produced by a different method or by blending the residue with other components. The calcium silicate-containing composition is suitable for use as a raw material for cement clinker, a water treatment material, or the like.

[0046] Although the embodiments of the present disclosure have been described above, the present disclosure is not limited to the above-described embodiments. For example, the present disclosure includes the following [1] to

[11] .

[0047] [1] A mixing step of mixing at least a gypsum-containing material and a decomposition accelerator containing SiO2 to obtain a mixed raw material; a heating step of calcining the mixed raw material to thermally decompose at least a portion of the gypsum in the gypsum-containing material and generate SO gas and a residue, The method for treating a gypsum-containing material, wherein the residue contains calcium silicate. [2] The method for treating a gypsum-containing material according to [1], further comprising a carbonation step of contacting the residue with a CO2-containing gas to carbonate Ca compounds contained in the residue. [3] The treatment method according to [1] or [2], wherein in the mixing step, the gypsum-containing material and the decomposition-accelerating material are mixed so that the molar ratio of SiO2 to CaSO4 contained in the mixed raw material is 0.2 or more. [4] The treatment method according to any one of [1] to [3], wherein the molar ratio of C to CaSO4 contained in the mixed raw material is 0.2 or less. [5] The treatment method according to any one of [1] to [4], wherein the calcium silicate contains at least one of wollastonite and anorthite. [6] The treatment method according to any one of [1] to [5], wherein the content of CaS in the residue is less than 1 mass %. [7] The treatment method according to any one of [1] to [6], wherein the decomposition accelerator comprises at least one selected from the group consisting of coal ash, silica sand, silica stone, bentonite, biomass ash, municipal solid waste fly ash, blast furnace slag, and waste glass. [8] The method according to any one of [1] to [7], wherein the gypsum-containing material includes at least one of waste gypsum board and discarded gypsum. [9] A method for producing a calcium sulfite-containing material, comprising a reaction step of reacting the SO2 gas produced by the treatment method according to any one of [1] to [8] above with a calcium-containing material.

[10] A method for producing a cement-based solidification material, comprising a preparation step of mixing raw materials containing the calcium sulfite-containing material obtained by the production method described in [9] above, cement, and gypsum to obtain a cement-based solidification material.

[11] A calcium silicate-containing composition comprising gypsum and at least one of wollastonite and anorthite, wherein the total content of the wollastonite and the anorthite is 10% by mass or more.

[12] The calcium silicate-containing composition according to

[11] , wherein the CaS content is 10% by mass or less. [Example]

[0048] The present disclosure will be described in detail below with reference to examples and comparative examples, but the present disclosure is not limited to the following examples.

[0049] [Preparing raw materials] Crushed waste gypsum board with the composition shown in Table 1 and three types of decomposition accelerators with the compositions shown in Table 2 were prepared. The gypsum dihydrate content was analyzed by measuring the SO3 content using an X-ray fluorescence analyzer and a carbon / sulfur analyzer, and converting this measurement value to CaSO4. The composition of each decomposition accelerator in Table 2 was determined by measurement using an X-ray fluorescence analyzer and a carbon / sulfur analyzer.

[0050] [Table 1]

[0051] [Table 2]

[0052] [Disposal of waste gypsum board] (Example 1-1) Crushed waste gypsum board and coal ash were blended in a ratio of 100 parts by weight of crushed waste gypsum board to 20 parts by weight of coal ash and mixed in a bag to obtain a mixed raw material. The molar ratio of C to CaSO4 contained in the mixed raw material and the molar ratio of SiO2 to CaSO4 contained in the mixed raw material were as shown in Table 3. The obtained mixed raw material was fired in a box-type electric furnace (manufactured by Motoyama, product name: Superburn SB20350) under the firing conditions shown in Table 3 to produce a gas containing SO2 and a residue. The firing was carried out in the open air.

[0053] (Examples 1-2 to 1-5, 2-1 to 2-6, 3-1 to 3-16, Comparative Examples 3-1 to 3-5) The mixed raw material was fired in the same manner as in Example 1-1, except that the type of decomposition accelerator, the blending ratio (mass parts of decomposition accelerator per 100 mass parts of the total of crushed waste gypsum board and decomposition accelerator), the molar ratio of C to CaSO4 contained in the mixed raw material, the molar ratio of SiO2 to CaSO4 contained in the mixed raw material, and the firing conditions were as shown in Table 3, and a gas containing SO2 and a residue were produced.

[0054] (Comparative Examples 4-1 to 4-4) The crushed waste gypsum board was fired in the same manner as in Example 1-1, except that no decomposition accelerator was added, only the crushed waste gypsum board prepared in Example 1-1 was used instead of the mixed raw material, and the firing conditions were as shown in Table 3, to produce a gas containing SO2 and a residue.

[0055] [Table 3]

[0056] [Residue analysis] The crystalline components contained in the residue (CaSO4, CaO, CaSiO3, CaAl2Si2O8, CaS) were quantified using an XRD-Rietveld method with an X-ray diffractometer (Bruker A.X., accelerating voltage: 30 kV, current: 10 mA, tube: Cu). Analysis software (Bruker A.X., Topas) was used for Rietveld analysis. The results are shown in Table 4. In addition, the gypsum decomposition rate was calculated using the following formula using the data on the CaSO4 content in the mixed raw material and the CaSO4 content in the residue. The results are shown in Table 4. A gypsum decomposition rate of 100% means that all of the gypsum contained in the mixed raw material was decomposed.

[0057] Gypsum decomposition rate [%] = (mass of CaSO4 contained in the mixed raw material - mass of CaSO4 contained in the residue) / mass of CaSO4 contained in the mixed raw material

[0058] [Evaluation of handling] After firing in each example and comparative example, the crucible container containing the sample was visually inspected. A case in which a portion of the mixed raw material melted during firing and adhered to the crucible container after firing was evaluated as "B." On the other hand, a case in which no adhered material remained on the crucible container after firing was evaluated as "A." The evaluation results are shown in Table 4. A "-" in Table 4 indicates that the sample was not subjected to Rietveld analysis. This is because, even if a component indicated by a "-" is present, it is present in trace amounts, and therefore, priority was given to ensuring the accuracy of the Rietveld analysis. On the other hand, a component indicated by a "0" in Table 4 indicates that the component was subjected to Rietveld analysis but was not detected.

[0059] [Table 4]

[0060] In the comparative example in which no decomposition accelerator was added to the mixed raw material, gypsum was not sufficiently decomposed. In comparative example 4-1 in which the firing temperature was 1200°C, gypsum did not decompose at all, whereas in examples 1-1 to 1-5, 2-4 to 2-6, and 3-2 in which the firing temperature was 1200°C, some of the gypsum decomposed. These results confirmed that the addition of a decomposition accelerator accelerates the decomposition of gypsum.

[0061] Fig. 1 is a graph showing the relationship between the amount of decomposition accelerator and the gypsum decomposition rate for each type of decomposition accelerator in Examples and Comparative Examples fired at a firing temperature of 1200°C. As shown in Fig. 1, it was confirmed that the gypsum decomposition rate tends to increase when the amount of decomposition accelerator is increased. Furthermore, it was confirmed that when the amount of decomposition accelerator is the same, the gypsum decomposition rate is highest when coal ash is used.

[0062] Fig. 2 is a graph showing the relationship between the amount of decomposition accelerator and the gypsum decomposition rate for each type of decomposition accelerator in Examples and Comparative Examples fired at a firing temperature of 1150°C. Fig. 2 also confirms that increasing the amount of decomposition accelerator tends to increase the gypsum decomposition rate. A comparison of Fig. 1 and Fig. 2 confirms that increasing the firing temperature improves the gypsum decomposition rate.

[0063] As shown in Table 4, when coal ash was used, anorthite was confirmed to be formed in the residue (Examples 1-1 to 1-5). This is thought to be due to the fact that the Al2O3 content of coal ash is higher than that of other decomposition accelerators. On the other hand, almost no wollastonite was formed. Furthermore, when silica sand was used, wollastonite was confirmed to be formed in the residue (Examples 2-1 to 2-6). This is thought to be due to the fact that silica sand has a lower Al2O3 content and a higher SiO2 content than the other decomposition accelerators. It was confirmed that when biomass ash was used, a residue containing both anorthite and wollastonite was obtained. In some examples, a residue with a total content of anorthite and wollastonite exceeding 50% by mass was obtained. Furthermore, none of the residues contained CaS.

[0064] Figure 3 is a graph showing the relationship between the amount of biomass ash blended and the gypsum decomposition rate for each firing temperature. It was confirmed that the gypsum decomposition rate improved as the temperature increased and as the amount of biomass ash blended increased.

[0065] The evaluation results of the handling properties confirmed that when coal ash and silica sand were used, the molten material did not adhere to the inner wall of the crucible, and that the handling properties were excellent. Therefore, it can be said that coal ash and silica sand are excellent in productivity, especially when the scale is increased.

Claims

1. At least, gypsum content and SiO ２ a mixing step of mixing the raw material with a decomposition promoter containing the compound; The mixed raw material is calcined to thermally decompose at least a portion of the gypsum in the gypsum-containing material, and SO ２ a heating step to produce a gas and a residue; The method for treating a gypsum-containing material, wherein the residue contains calcium silicate.

2. The residue and CO ２ The method for treating a gypsum-containing material according to claim 1, further comprising a carbonation step of contacting the residue with a gypsum-containing gas to carbonate the Ca compounds contained in the residue.

3. In the mixing step, CaSO contained in the mixed raw material ４ SiO ２ The treatment method according to claim 1, wherein the gypsum-containing material and the decomposition-accelerating material are mixed so that the molar ratio of

4. CaSO contained in the mixed raw material ４ 2. The method of claim 1, wherein the molar ratio of C to SiO is 0.2 or less.

5. The method of claim 1 , wherein the calcium silicate comprises at least one of wollastonite and anorthite.

6. 2. The method according to claim 1, wherein the residue contains less than 1% by mass of CaS.

7. 2. The treatment method according to claim 1, wherein the decomposition accelerator comprises at least one selected from the group consisting of coal ash, silica sand, silica stone, bentonite, biomass ash, municipal solid waste fly ash, blast furnace slag, and waste glass.

8. The method according to claim 1 , wherein the gypsum-containing material comprises at least one of waste gypsum board and discarded gypsum.

9. The SO produced by the treatment method according to any one of claims 1 to 8 ２ A method for producing a calcium sulfite-containing material, comprising a reaction step of reacting a gas with a calcium-containing material.

10. A method for producing a cement-based solidification material, comprising a preparation step of mixing raw materials containing the calcium sulfite-containing material obtained by the production method according to claim 9, cement, and gypsum to obtain a cement-based solidification material.

11. A calcium silicate-containing composition comprising gypsum and at least one of wollastonite and anorthite, wherein the total content of the wollastonite and the anorthite is 10 mass% or more.

12. The calcium silicate-containing composition according to claim 11, wherein the CaS content is 10% by mass or less.

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