JP7769566B2 - Method for producing wollastonite-containing fired product and use of said fired product - Google Patents

Description

The present invention relates to a wollastonite-containing material that is useful as a material to be mixed into cement, etc.

Wollastonite (CaSiO ₃ ), known as a silicate mineral, is used in many fields, including resins, paints, building materials, rubber, ceramics, etc. In particular, it is useful as a hardening agent in cement-based building materials and carbonated cured concrete, as it reacts with carbon dioxide to develop strength, and is also attracting attention from the perspective of CO ₂ reduction, as carbon dioxide is absorbed and fixed during this process (see Non-Patent Document 1).

Meanwhile, in recent years, various efforts by various business entities to promote the spread of renewable energy have led to a boom in the construction and operation of biomass power generation facilities. As a result, the amount of combustion ash (biomass ash) generated from biomass power generation has also increased, and there is a desire to recycle it as a resource, such as for use as a cement raw material, in the same way as incineration ash generated from municipal waste.

Hyodo et al., "CO2 absorption and fixation in cement-based materials by carbonation," Pacific Cement Research Report No. 179 (2020), pp. 15-30

Until now, there has been little knowledge about the technology for producing wollastonite using biomass ash.

The object of the present invention is to provide a wollastonite-containing material that utilizes biomass ash and is useful as a material to be blended into cement, etc.

In view of the above problems, the present inventors have conducted extensive research and have found that wollastonite (CaSiO ₃ ), a known silicate mineral, can be formed by using biomass ash as a raw material and subjecting it to a calcination treatment, thereby completing the present invention.

That is, the present invention is configured as follows.
[1] A method for producing a wollastonite-containing fired product, comprising preparing a raw material composition for firing containing 30 mass % or more of biomass ash, and firing the raw material composition for firing to form wollastonite (CaSiO ₃ ).
[2] The method for producing a wollastonite-containing fired product according to the above [1], wherein the biomass ash is a fine powder obtained by classifying raw biomass ash.
[3] The method for producing a wollastonite-containing fired product according to the above [1], wherein the biomass ash is obtained by washing raw biomass ash with water, or by classifying raw biomass ash and then washing the resulting fine powder with water.
[4] The method for producing a wollastonite-containing fired product according to any one of [1] to [3] above, wherein the CaO/ _SiO2 mass ratio of the firing raw material composition is 0.5 to 1.2.
[5] The method for producing a wollastonite-containing fired product according to any one of [1] to [4] above, wherein the raw material composition for firing is fired at 900 ° C to 1,300 ° C.
[6] The method for producing a wollastonite-containing fired product according to any one of [1] to [5] above, wherein the biomass ash has an amorphous mass of 30% by mass or more.
[7] The method for producing a wollastonite-containing fired product according to any one of [1] to [6] above, wherein the biomass ash has a silica content of 3.0 to 20.0.
[8] A method for producing a hardened product using the wollastonite-containing fired product, comprising obtaining a wollastonite-containing fired product by the production method described in any one of [1] to [7] above, preparing a hydraulic composition using the wollastonite-containing fired product as a material, adding water to the hydraulic composition and kneading them to obtain a kneaded product, and hardening the kneaded product.
[9] A method for producing a hardened product using the wollastonite-containing fired product, comprising obtaining a wollastonite-containing fired product by the production method described in any one of [1] to [7] above, preparing a hydraulic composition using the wollastonite-containing fired product as a material, preparing aggregate to be combined with the hydraulic composition using the wollastonite-containing fired product as a material, adding water to the aggregate and the hydraulic composition and kneading them to obtain a kneaded product, and hardening the kneaded product.
[10] The method for producing a hardened body according to the above [8] or [9], wherein the kneaded material is subjected to a carbonation treatment when hardening the kneaded material.
[11] A method for recycling biomass ash, comprising classifying biomass ash, calcining the fine powder obtained by the classification to obtain a wollastonite-containing calcined product, and utilizing the coarse powder obtained by the classification as a material for a hardened body made of a hydraulic composition.
[12] The method for recycling biomass ash according to the above [11], wherein the wollastonite-containing fired product is used as a material for a hardened body made of a hydraulic composition.
[13] The method for recycling biomass ash according to [11] or [12] above, wherein the coarse powder obtained by classifying the biomass ash is used as concrete aggregate, concrete admixture, cement mixture, or cement clinker raw material.
[14] The method for recycling biomass ash according to any one of [11] to [13] above, wherein the wollastonite-containing fired product is used as a concrete aggregate, a concrete admixture, or a cement admixture.
[15] The method for recycling biomass ash according to any one of [11] to [14] above, wherein the wollastonite-containing burned product and the coarse powder obtained by classifying the biomass ash are both used as common materials for a hardened body to obtain the hardened body.

According to the present invention, a process using biomass ash makes it possible to easily obtain a wollastonite-containing material that is useful as a material to be mixed into cement, etc. This also makes it possible to effectively utilize biomass ash as a resource.

FIG. 1 is a flow diagram illustrating an embodiment of the present invention. FIG. 10 is a flow diagram illustrating another embodiment of the present invention. 1 is a chart showing the results of comparing the amount of wollastonite produced depending on the raw material (levels 4, 11, 13, and 15: heating temperature 1,100°C, CaO/ _SiO2 mass ratio 0.7; and levels 8, 12, 14, and 16: heating temperature 1,100°C, CaO/ _SiO2 mass ratio 1). 1 is a diagram showing the results of comparing the amount of wollastonite produced at different heating temperatures (Levels 1 to 7: CaO/ _SiO2 mass ratio 0.7). 1 is a diagram showing the results of comparing the amount of wollastonite produced depending on the CaO/ _SiO2 mass ratio (levels 4, 8, and 9: heating temperature 1,100°C).

As shown in Figure 1, the present invention uses biomass ash as a raw material and calcines it to form wollastonite ( _CaSiO3 ), a known silicate mineral, and obtains a calcined product containing the wollastonite thus formed. As will be described later, the raw biomass ash may be washed with water before use.

Furthermore, as shown in Figure 2, in the present invention, the biomass ash used as the raw material for firing may be subjected to a classification process to adjust its particle size before use.

The present invention will be described in more detail below. Note that in this specification, unless otherwise specified, "%" refers to the percentage by mass of the total mass.

[1. Raw materials for firing]
<Biomass ash>
As used herein, "biomass ash" has the same meaning as that generally understood by those skilled in the art. That is, it refers to ash remaining after incineration or combustion of biomass consisting of organic resources derived from plants and animals (excluding fossil resources). Typical examples include ash from the incineration of plants and bamboo, and ash from food waste. It may also be combustion ash obtained by mixing biomass with coal and burning it. From the viewpoint of promoting the effective utilization of biomass, the proportion of ash derived from biomass contained in the biomass ash is preferably 50% by mass to 100% by mass, more preferably 60% by mass to 95% by mass, and particularly preferably 70% by mass to 90% by mass.

As biomass ash for use in the present invention, palm kernel shell ash (PKS ash), obtained by burning palm kernel shells as fuel, is a suitable example, among the ashes of plants and bamboo. Palm kernel shells are a by-product of palm oil production and are primarily used in the natural biomass energy industry. Palm kernel shells are a yellowish-brown fibrous material with a low ash content, with particle sizes ranging from approximately 5 mm to 40 mm, and a calorific value of approximately 4,000 kcal/kg. As such, in recent years, they have been increasingly used as fuel for biomass power generation in the production of energy using renewable resources.

The mode of incineration or combustion of biomass is not particularly limited, and may be, for example, a method using a stoker-type combustion furnace or a method using a fluidized-bed combustion furnace. In particular, in a fluidized-bed combustion furnace, limestone is added for the purpose of desulfurization within the combustion furnace, so calcium and sulfur are contained, and the biomass ash is mainly contained in the form of gypsum (CaSO ₄ ·2H ₂ O). When wollastonite (CaSiO ₃ ) is formed by calcination, this also acts as a CaO source. Furthermore, fly ash from a fluidized-bed combustion furnace has a fine particle size, is easy to crush and mix, and is highly calcinable. Therefore, it is preferable to use fly ash from a fluidized-bed combustion furnace as the biomass ash. Examples of fluidized-bed combustion furnaces include a circulating fluidized-bed combustion furnace and a pressurized fluidized-bed combustion furnace.

<Pretreatment of biomass ash>
The biomass ash used in the present invention may be obtained from a biomass power generation facility equipped with equipment such as a fluidized bed combustion furnace and used as is, or may be subjected to pretreatment such as classification or washing with water, as necessary.

Classification In the present invention, it is preferable to classify the raw material biomass ash and use the resulting fine powder for the following reasons.

In fluidized bed combustion furnaces, sand, primarily composed of quartz, is added as a fluidizing medium. Therefore, biomass ash contains fused and solidified or agglomerated glass, particles derived from sand (relatively coarse particles), and the aforementioned limestone- or biomass-derived particles containing alkali metals and chlorine (relatively fine particles). Therefore, biomass ash obtained from biomass power generation facilities equipped with fluidized bed combustion furnaces or similar equipment has a particle size distribution with a peak on the smaller particle size side and a peak on the larger particle size side. The biomass ash can be separated into coarse and fine particles and collected using any particle size selected between these points as the classification point.

In general, the Blaine specific surface area of biomass ash recovered from facilities such as fluidized bed combustion furnaces is typically, for example, 1,000 cm ² /g to 4,000 m ² /g, more typically 1,500 cm ² /g to 3,500 cm ² /g, and even more typically 2,000 to 3,000 cm ² /g. When this raw biomass ash is classified to collect fine powder, the Blaine specific surface area thereof is typically, for example, 2,500 cm ² /g to 7,000 cm ² /g, more typically 3,000 cm ² /g to 6,000 cm ² /g, and even more typically 4,000 cm ² /g to 5,000 cm ² /g. On the other hand, the Blaine specific surface area of the coarse powder remaining after the fine powder is collected is typically, for example, 250 cm ² /g to 2,000 cm ² /g, more typically 500 cm ² /g to 1,500 cm ² /g, and even more typically 750 cm ² /g to 1,250 cm ² /g.

The fine powder obtained by classifying raw biomass ash contains a relatively large amount of CaO, and has a good balance between the CaO source and _SiO2 source necessary for forming wollastonite ( _CaSiO3 ). Furthermore, the fine powder is highly powdery and easily calcinable without pulverization, so wollastonite can be produced at a relatively low calcination temperature or for a short calcination time. On the other hand, the powder contains relatively large amounts of chlorine and sulfur, which can be removed by washing with water as necessary, as described below, or, depending on their contents, can be volatilized and removed during calcination.

On the other hand, the coarse powder obtained by classifying raw biomass ash is high in silicon and low in chlorine and sulfur, making it suitable for use as a general cement clinker raw material, particularly as a substitute for clay and coal ash. When using it as a cement mixture, concrete admixture, or siliceous material for ALC and calcium silicate boards, it is recommended to crush it to increase its reactivity. Alternatively, the coarse powder can be used without crushing it as fine aggregate (sand) for concrete, mortar, and carbonated hardened bodies.

As described above, biomass ash can be recycled more efficiently by taking advantage of the characteristics of the components separated by classification. Specifically, the fine powder obtained by classifying raw biomass ash can be used as a raw material for forming wollastonite by calcination, and the coarse powder obtained by the classification can be used as a material for hardened hydraulic compositions, such as concrete aggregate, concrete admixture, cement mixture, and cement clinker raw material. Furthermore, the calcined product obtained by calcining the fine powder to form wollastonite can also be used as a material for hardened hydraulic compositions, such as concrete aggregate, concrete admixture, and cement mixture, after adjusting particle size and removing chlorine and sulfur, as necessary. In this case, using both the fine powder and the coarse powder as a common material for the hardened body increases the resource utilization rate of raw biomass ash per hardened body produced, resulting in greater efficiency. For example, the fired product obtained from the fine powder is used as a material for a hydraulic composition and then used to obtain a hardened body, while the coarse powder is used as aggregate for the hardened body or crushed and used as a mixture (admixture).

When classifying raw biomass ash into fine and coarse powders, the classification point can be selected from the range of preferably 10 μm to 100 μm, more preferably 30 μm to 90 μm, and particularly preferably 38 μm to 75 μm, from the viewpoint of separating the components described above.

The classification means is not particularly limited as long as it can classify biomass ash at the classification points on the order of μm as described above, but examples include sieves, gravitational settling, inertial classifiers, centrifugal classifiers, and gravity classifiers. Among these, from the perspective of classification accuracy, cyclone-type air separators, vortex-type centrifugal classifiers, and sieving devices are preferred.

In addition, when classification is done wet, chlorine dissolves in water, so even fine granules with a relatively high chlorine content have most of the chlorine removed.

Fluidized bed incinerators may also be equipped with equipment for recovering incineration ash that has settled in the boiler, air preheater, or high-temperature gas flow path, as well as equipment for recovering incineration ash using a cyclone or bag filter. The particle size of the incineration ash recovered by these recovery facilities varies depending on the facility, and biomass ash of a specific particle size can be recovered from a specific facility. Therefore, instead of classifying the raw biomass ash, biomass ash with the desired particle size can be prepared by appropriately selecting the above facilities and recovering the biomass ash.

In any non-limiting embodiment of the present invention, the biomass ash as a raw material may be washed with water before use. This washing process can remove components that are undesirable for use in materials to be incorporated into hydraulic compositions such as cement and concrete, such as chlorine, sulfur, and potassium.

The water washing method is not particularly limited and may be any conventional method. For example, the biomass ash processing method described in WO 2021/193668 may be referenced as appropriate, as explained below. However, it goes without saying that the water washing method is not limited to the specific example described below.

The treatment method includes, for example, a slurrying process in which water is added to biomass ash to form a slurry, a water-washing process in which the slurry is washed with water, and a dewatering process in which the washed slurry is dewatered. Slurrying can be carried out using a powder dissolver equipped with at least a container for holding biomass ash and water and a stirring means for mixing them to form a slurry. Water washing is carried out by leaving the slurry to stand or stirring for a predetermined period of time, resulting in a slurry in which the soluble components of the biomass ash are dissolved into the liquid phase of the slurry. The slurry in this state is discharged from the powder dissolver and dewatered using a solid-liquid separator such as a filter press.

The mass ratio (W1/M1) of biomass ash (referred to as M1) to water (referred to as W1) in the above-mentioned slurrying process is preferably 4 to 10, more preferably 4 to 7, and particularly preferably 4 to 5. If the mass ratio (W1/M1) is less than 4, the modification effect may be insufficient, such as insufficient elution of cement-repellent components such as chlorine from the biomass ash. Furthermore, if the mass ratio (W1/M1) is greater than 10, the amount of wastewater will increase.

The time required for the water washing process is preferably 30 minutes or more, more preferably 45 minutes or more, to ensure that the biomass ash is thoroughly treated with water. Furthermore, the higher the temperature, the more efficient the elution of repellent components such as chlorine from the biomass ash. However, from the perspective of processing costs, a temperature of 5°C to 50°C is preferred, more preferably 25°C to 50°C.

During the dehydration process, to prevent repellent components such as chlorine contained in the slurry from remaining in the liquid phase, the moisture content of the dehydrated product is preferably 20% to 90% by mass, and more preferably 30% to 70% by mass. If necessary, fresh water can be added to the dehydrated product and it can be dehydrated again. This is preferable because it replaces most of the liquid phase of the slurry with water.

In the above treatment method, the pH during water washing is preferably adjusted to the acidic side. In other words, by reducing the pH, chlorine can be removed more efficiently than when the pH is not adjusted. The pH adjuster is not particularly limited as long as it can reduce the pH of the slurry. Examples include acid solutions and _CO2- containing gases. For example, combustion exhaust gases from rotary kilns in cement manufacturing facilities and combustion exhaust gases from biomass incineration facilities and biomass power plants contain carbon dioxide ( _CO2 ). Therefore, by injecting this combustion exhaust gas into the slurry, the pH can be reduced to a weak alkaline state. While the _CO2- containing gas may contain carbon dioxide, a carbon dioxide concentration of 10% by volume or more is preferred, and 20% by volume is more preferred, in order to promote efficient carbonation. Furthermore, since harmful gases such as sulfur oxides (SOx) are contained in combustion exhaust gases, particularly after capturing chlorine bypass dust from cement manufacturing facilities, the effect of immobilizing these gases can also be expected.

The pH condition for washing the slurry with water is preferably between pH 4 and 12.5, and more preferably between pH 5 and 12.

Dry Ash In any non-limiting embodiment of the present invention, dry ash may be used as the raw biomass ash. Dry ash refers to ash that has never been sprayed with water, is not granulated, and does not form hydrates. In contrast, if water is sprayed once and the ash becomes granulated, or chlorine is incorporated into the formed hydrates, it may be difficult to separate the characteristic components by classification or water washing as described above. Therefore, when dry ash is used as the raw biomass ash and the classification and water washing processes are performed as described above, it is preferable to perform the classification process before the water washing process, for example, to obtain a fine powder, which is then washed with water.

For example, it is preferable that the dried ash does not contain hydrated Friedel's salt or ettringite, as detected by powder X-ray diffraction. The moisture content is preferably 10% or less, more preferably 5% or less. The loss on ignition is preferably 10% or less. The moisture content can be determined as the mass loss rate when dried at 105°C. The loss on ignition can be determined as the mass loss rate when an object dried at 105°C is heated at 975°C.

<Composition characteristics of biomass ash>
Below, typical compositional characteristics of biomass ash used as a raw material for firing will be described, although not limited thereto.

The proportion of CaO in the biomass ash used as the raw material for calcination (based on ignition raw material) is preferably 10% by mass to 40% by mass, more preferably 15% by mass to 35% by mass. If the proportion of CaO is within this range, the amount of CaO source required to form wollastonite (CaSiO ₃ ) is reduced or becomes unnecessary when classification is performed, which makes it possible to reduce the cost of adding additional equipment and chemicals required for addition.

The silicic acid ratio (S.M.) of biomass ash used as a raw material for firing is preferably 3.0 to 20.0, more preferably 4.0 to 18.0, even more preferably 5.0 to 16.0, and particularly preferably 8.0 to 13.0. If the silicic acid ratio is within the above range, the total amount of Al ₂ O ₃ and Fe ₂ O ₃ relative to SiO ₂ can be kept low, thereby increasing the amount of wollastonite produced. Therefore, when the fired product is used as a material for a hydraulic composition, its strength development can be further improved. On the other hand, if the silicic acid ratio exceeds the above range, it may be difficult to ensure the amount of ash derived from the biomass.

The proportion of _Al2O3 in the biomass _ash used as the raw material for firing (based on ignition raw material) is preferably 10 mass% or less, more preferably 5 mass% or less, and particularly preferably 3 mass% or less. If the proportion of _Al2O3 exceeds the above range, a large amount of non-reactive melilite may be produced during firing. Note that biomass ash is preferable because _it has a lower proportion of _Al2O3 than general coal _ash .

From the viewpoint of the wollastonite production rate, the amorphous content of the biomass ash used as the raw material for firing is preferably 30% by mass or more, more preferably 35% by mass or more, and particularly preferably 40% by mass or more.

The proportion of alkali metals in the biomass ash used as the raw material for firing (based on ignition raw material) is preferably 1.0% by mass to 5.0% by mass, more preferably 1.5% by mass to 4.0% by mass, calculated as oxide (R ₂ O). If the proportion of alkali metals is below this range, the rate of wollastonite production may be slow. On the other hand, if the proportion of alkali metals exceeds this range, the firing process may produce a large amount of non-reactive feldspars, or the material may melt during firing or large lumps may be easily generated, making firing in a kiln difficult. Furthermore, when the fired product is used as a cement admixture, concrete admixture, or concrete aggregate, there is a risk of alkali-aggregate reaction occurring.

The proportion of alkali metal (R) converted to oxide (R ₂ O) can be calculated from the proportions (mass %) of Na ₂ O and K ₂ O in the sample using the following formula (1).
_R2O = _Na2O + _0.658K2O ...(1)

<Raw material composition for firing>
Biomass ash contains both the CaO source and the _SiO2 source necessary for the formation of wollastonite. Therefore, the obtained biomass ash or the pretreated biomass ash may be used for firing as is. That is, for example, the raw material composition for firing may contain 100% by mass of biomass ash.

On the other hand, other raw materials may be added to the biomass ash as appropriate to form a raw material composition for firing. However, from the perspective of efficiently producing wollastonite, the content of biomass ash in the raw material composition for firing should be at least 30% by mass. The content of biomass ash in the raw material composition for firing is preferably 40% by mass or more, more preferably 50% by mass or more, even more preferably 60% by mass or more, even more preferably 75% by mass or more, and particularly preferably 90% by mass or more.

Other raw materials that can be used as the _SiO2 source include, for example, construction waste soil (soil, earth and sand, surplus soil, waste soil, and construction sludge that are generated secondarily at construction sites and other work sites), volcanic ash and other volcanic-derived materials, silica stone, clay, etc. These may be used alone or in combination of two or more.

Other raw materials that can be used as CaO sources include, for example, limestone, quicklime, slaked lime, shells, and calcium-containing industrial or general waste. Examples of calcium-containing industrial waste include raw concrete sludge, various sludges (e.g., sewage sludge, water purification sludge, steelmaking sludge, etc.), construction waste, concrete waste, various incineration ashes (e.g., biomass ash, coal ash, chicken manure ash, livestock manure ash, sludge incineration ash), foundry sand, rock wool, waste glass, secondary blast furnace ash, various by-products, and unused resources (unused remaining materials, etc.). Examples of calcium-containing general waste include, for example, dried sewage sludge powder and municipal solid waste incineration ash. These may be used alone or in combination of two or more.

The calcination raw material composition may contain, as appropriate, raw materials commonly used in the production of cement clinker, provided that the effects of the present invention are not impaired. Examples of such raw materials include aluminum-containing raw materials ( _{Al2O3 sources} ) such as clay, and iron-containing raw materials ( _{Fe2O3 sources} ) such as iron slag and iron cake.

The raw material composition for firing can be prepared by appropriately mixing predetermined amounts of the above-mentioned biomass ash and other raw materials such as a CaO source and a _SiO2 source. The raw materials may be pulverized as needed. The means for blending the raw materials is not particularly limited, and a conventional device such as a mixer may be used. A conventional device such as a ball mill may be used as the pulverizing means.

<Compositional characteristics of raw material composition for firing>
Hereinafter, typical compositional characteristics of the raw material composition for firing will be described, although the composition is not limited thereto.

The mass ratio of CaO to SiO ₂ (CaO/SiO ₂ ) in the raw material composition for firing is preferably 0.5 to 1.2, more preferably 0.5 to 1.1, even more preferably 0.6 to 1.0, and particularly preferably 0.7 to 0.9, from the viewpoint of the amount of wollastonite produced.

The silicic acid ratio (S.M.) of the raw material composition for firing is preferably 3.0 to 20.0, more preferably 4.0 to 19.0, even more preferably 5.0 to 18.0, even more preferably 8.0 to 17.0, particularly preferably 10.0 to 17.0, and most preferably 12.0 to 17.0. If the silicic acid ratio is within the above range, the total amount of Al ₂ O ₃ and Fe ₂ O ₃ relative to SiO ₂ can be kept low, thereby increasing the amount of wollastonite produced. Therefore, when the fired product is used as a material for a hydraulic composition, its strength development can be further improved. On the other hand, if the silicic acid ratio exceeds the above range, it may be difficult to ensure the amount of ash derived from biomass.

The proportion of Al ₂ O ₃ in the raw material composition for firing (based on ignition raw material) is preferably 1.0 to 7.0 mass%, more preferably 1.5 to 5.0 mass%, and particularly preferably 2.0 to 3.0 mass%. If the proportion of _{Al 2} O ₃ is within the above range, the amount of wollastonite produced can be increased. However, if the proportion of Al ₂ O ₃ exceeds the above range, a large amount of non-reactive melilite may be produced by firing.

The proportion of alkali metal in the raw material composition for firing (based on ignition raw material), calculated as oxide (R ₂ O), is preferably 0.3 to 4.0% by mass, more preferably 1.1 to 3.0% by mass, and particularly preferably 1.2 to 2.5% by mass. If the proportion of alkali metal is below this range, the rate of wollastonite formation may be slow. On the other hand, if the proportion of alkali metal exceeds this range, the firing process may produce a large amount of non-reactive feldspar, or the composition may melt during firing or large lumps may be easily generated, making firing in a kiln difficult. Furthermore, when the fired product is used as a cement admixture, concrete admixture, or concrete aggregate, there is a risk of alkali-aggregate reaction occurring.

The proportion of alkali metal (R) converted to oxide (R ₂ O) can be calculated using the above-mentioned formula (1). When the proportion of alkali metal (R ₂ O) in the raw material composition for firing is high or when it is desired to reduce the alkali metal in the fired product, chlorine may be added and firing as described below may be performed to salt the alkali metal, which may then be removed by volatilization or by washing the product with water.

2. Firing
In the present invention, the raw material composition for firing described above is subjected to firing treatment to obtain a fired product containing wollastonite (CaSiO ₃ ), which is known as a silicate mineral.

<Firing treatment>
The firing conditions are not particularly limited as long as they allow the formation of wollastonite using biomass ash as a raw material, but the above-mentioned raw material composition for firing may be fired preferably under temperature conditions of 900°C to 1,300°C, more preferably 1,000°C to 1,250°C, and even more preferably 1,100°C to 1,200°C.

The calcination method is not particularly limited, and conventional equipment such as a rotary kiln can be used. When calcining using a rotary kiln, alternative fuel waste materials such as waste oil, waste tires, and waste plastics can also be used.

<Wollastonite-containing burned material>
The fired product obtained by the above-described firing treatment contains wollastonite (CaSiO ₃ ), a silicate mineral. Wollastonite is known to exist in two forms: wollastonite (α-type, low-temperature type) and pseudowollastonite (β-type, high-temperature type). The wollastonite-containing fired product provided by the present invention may contain either one of these forms alone or a combination of multiple forms. The wollastonite content (when multiple forms are contained in combination, the total content) is preferably 10% by mass or more, more preferably 20% by mass or more, and particularly preferably 30% by mass or more. Note that pseudowollastonite has a higher carbon dioxide absorption activity. Therefore, when the wollastonite-containing fired product provided by the present invention is used for carbon dioxide absorption, it is preferable that the pseudowollastonite form accounts for a majority of the wollastonite, and more preferably, it accounts for more than half of the wollastonite form.

The fired product obtained by the above-mentioned firing process may contain other mineral components in addition to wollastonite. For example, rankinite (3CaO·2SiO ₂ ) can be mentioned. Rankinite is reactive with carbon dioxide and exhibits strength development through this reaction. However, from the viewpoint of ensuring the wollastonite content, the rankinite content in the wollastonite-containing fired product provided by the present invention is preferably 20% by mass or less, and more preferably 10% by mass or less. Other examples include melilites. _That is, akermanite component ( _Ca2MgSi2O7 ), ferroakermanite component ( _{Ca2FeSi2O7 )} , gehlenite component ( _Ca2Al2SiO7 ), sodamelite component ( _CaNaAlSi2O7 ), _hardystonite component ( _Ca2ZnSi2O7 ), gougiaite component ( _{Ca2BeSi2O7 )} , _Okayamaite component ( _Ca2B2SiO7 ), _{ferrighelenite} component ( _{Ca2Fe3 + 2SiO7 )} , and _{ferrialumingehlenite} component ( _Ca2Fe3 + _{AlSiO7 ) . Here} , melilites have _poor reactivity with carbon dioxide and _exhibit poor strength development _through this reaction. Therefore, in the wollastonite-containing fired product provided by the present invention, the content of melilites is preferably 20% by mass or less, and more preferably 10% by mass or less.

The fired product obtained by the above-mentioned firing treatment may contain belite (2CaO·SiO ₂ ) as an intermediate reaction mineral component. Alternatively, it may contain quicklime, quartz, feldspars, amorphous phases, etc. as unreacted mineral components. From the viewpoint of ensuring the wollastonite content, the wollastonite-containing fired product provided by the present invention preferably has a quicklime content of 2% by mass or less, a quartz content of 8% by mass or less, and a feldspar content of 8% by mass or less. The amorphous content is preferably 45% by mass or less, more preferably 35% by mass or less, and most preferably 25% by mass or less. The total amount of the intermediate reaction mineral component and unreacted mineral component is preferably 50% by mass or less, more preferably 40% by mass or less, and most preferably 30% by mass or less.

In this specification, the term "mineral" refers not only to minerals formed geologically as natural products, but also to artificial minerals formed by processes such as the firing described above, which have similar component compositions and crystalline structures to natural minerals. The morphology of mineral components can be measured using standard methods, such as powder X-ray diffraction, microscopic observation, and electron backscatter diffraction (EBSD). The content of mineral components can be measured by the Rietveld method in the case of powder X-ray diffraction, and by point counting in the case of microscopic observation and electron backscatter diffraction.

[3. Uses of fired products]
The wollastonite-containing fired product provided by the present invention can be used as it is, or after particle size adjustment such as coarse crushing, as civil engineering materials such as roadbed materials and backfill materials. It can also be used as aggregate for mortar and concrete. In other words, the wollastonite-containing fired product can be used in place of sand and gravel, which are usually used as fine and coarse aggregates, respectively.

The wollastonite-containing fired product provided by the present invention can also be used as a filler for reinforcing resins, a cement admixture, a concrete admixture, or a siliceous material for ALC/calcium silicate boards. In this case, it is recommended to adjust the particle size appropriately by subjecting it to grinding or classification treatment as necessary. For example, the Blaine specific surface area is preferably 2,500 to 10,000 cm ² /g, more preferably 3,000 to 9,000 cm ² /g. During grinding, conventional gypsum or grinding aids may be added. The grinding means is not particularly limited, and conventional devices such as a ball mill can be used. The classification means is not particularly limited, and conventional devices such as a centrifugal air classifier with rotating blades can be used.

When the wollastonite-containing fired product provided by the present invention is used as a cement admixture, concrete admixture, etc. after adjusting the particle size appropriately as described above, it is expected to have effects such as reduced bleeding, improved fluidity, and reduced heat of hydration when mixed with water and hardened.

Furthermore, by adjusting the particle size appropriately as described above, and then mixing the wollastonite-containing fired product provided by the present invention with high-early-strength Portland cement, high-early-strength Portland cement clinker, high-C3A cement (e.g., C3A content of 10% to 15% by mass), or high-C3A cement clinker (e.g., C3A content of 10% to 15% by mass) in an amount that is 5 to 25 parts by mass per 100 parts by mass of conventional cement, cement of equivalent quality to ordinary Portland cement can be obtained.

The wollastonite-containing calcined product provided by the present invention can be produced using a smaller amount of limestone as a raw material and at a lower calcination temperature than conventional cements such as Portland cement. Therefore, by using it as a material for hydraulic compositions in place of cement, as described below, the overall carbon dioxide emissions associated with cement production can be reduced.

<Hydrocurable composition>
As described above, the wollastonite-containing fired product provided by the present invention can be used as a material for hydraulic compositions such as cement, mortar, and concrete. Herein, the term "hydraulic composition" has the same meaning as that generally understood by those skilled in the art. That is, it refers to a composition that hardens when mixed with water and kneaded. Usually, such a composition is prepared in a powder form before being mixed with water.

When the wollastonite-containing fired product provided by the present invention is used as a material for a hydraulic composition, it is recommended to adjust the particle size appropriately by subjecting it to pulverization or classification as necessary. For example, the Blaine specific surface area is preferably 2,500 cm ² /g to 10,000 cm ² /g, more preferably 3,000 cm ² /g to 9,000 cm ² /g. If the Blaine specific surface area is 2,500 cm ² /g or more, the strength of the resulting hardened body will be greater. On the other hand, if the Blaine specific surface area is 10,000 cm ² /g or less, the energy required for pulverization can be kept low from the standpoint of production costs.

The grinding means is not particularly limited, and conventional devices such as a ball mill can be used. The classification means is not particularly limited, and conventional devices such as a centrifugal air classifier with rotating blades can be used.

Cement When the wollastonite-containing calcined product provided by the present invention is used as a material for a hydraulic composition, it is preferable for the hydraulic composition to contain a conventional cement in order to increase the strength of the resulting hardened body. Such cements are not particularly limited, and examples include various Portland cements such as ordinary Portland cement, high-early-strength Portland cement, moderate-heat Portland cement, and low-heat Portland cement, as well as ecocement, rapid-hardening cement, and ultra-rapid-hardening cement. These may be used alone or in combination of two or more. Among these, at least one of ordinary Portland cement and high-early-strength Portland cement is preferred from the viewpoints of strength development and cost. When the wollastonite-containing calcined product is used as a material for a hydraulic composition, the content may be, for example, 5 to 50 parts by mass, 10 to 35 parts by mass, or 15 to 25 parts by mass per 100 parts by mass of the cement composition. Furthermore, when a carbonated hardened body is produced from the hydraulic composition, the proportion of the burned product contained in the hydraulic composition may be, for example, 20 parts by mass or more, 30 parts by mass or more, 50 parts by mass or more, or 75 parts by mass or more, based on 100 parts by mass of the cement composition, from the viewpoints of increasing the amount of carbon dioxide absorbed and increasing the strength of the resulting hardened body. On the other hand, from the viewpoints of increasing the strength of the hardened body when demolding is performed or accelerating the timing of demolding and thereby improving the production efficiency of products made from the hardened body, the upper limit of the proportion may be, for example, 95 parts by mass or less, 90 parts by mass or less, more preferably 75 parts by mass or less, 60 parts by mass or less, or 50 parts by mass or less, based on 100 parts by mass of the cement composition.

The hydraulic composition may be in an embodiment that does not contain a conventional cement, and for example, the wollastonite-containing fired product provided by the present invention may be used as is. That is, for example, the hydraulic composition may contain 100 mass% of the wollastonite-containing fired product provided by the present invention. However, when using such an embodiment that does not contain a conventional cement or contains only a small amount of cement, from the viewpoint of strength development, it is preferable to perform at least one of the following: pulverizing the product to increase the Blaine specific surface area to, for example, 8,000 cm ² /g to 12,000 cm ² /g, or heat curing the product when kneading it with water and hardening it.

Gypsum The hydraulic composition may contain gypsum as a material from the viewpoint of the fluidity and workability of the kneaded product before hardening. The gypsum is not particularly limited, and examples thereof include natural gypsum dihydrate, flue gas desulfurization gypsum, phosphate gypsum, titanic gypsum, and hydrofluoric gypsum. Examples of the form of gypsum include gypsum dihydrate, gypsum hemihydrate, and anhydrous gypsum. These may be used alone or in combination of two or more.

The amount of gypsum to be added is preferably 1 to 6 parts by mass, and more preferably 3 to 5 parts by mass, per 100 parts by mass of the hydraulic composition (powder), from the standpoint of the fluidity and workability of the kneaded product before hardening.

The gypsum to be blended into the hydraulic composition as a material may be pre-ground gypsum powder, or the gypsum may be ground together with the wollastonite-containing fired product provided by the present invention when it is ground to an appropriate particle size, so that the gypsum is contained in the hydraulic composition.

Amines Amines may be blended into the hydraulic composition as a material thereof. Amines are known to have the effect of reacting with carbon dioxide to promote the generation of carbonate ions, and when the hydraulic composition contains amines, the carbonation of the calcium component contained in the hydraulic composition proceeds more efficiently, thereby increasing the strength of the carbonated hardened body described below.

The amines may be any amine having an amino group and a hydroxyl group in the molecule, and are not particularly limited. Examples include monoethanolamine (MEA), diethanolamine (DEA), triethanolamine (TEA), diglycolamine (DGA), diisopropanolamine (DIPA), methyldiethanolamine (MDEA), and triisopropanolamine (TIPA). These amines are generally known as grinding aids. Alternatively, the amines may be waste liquid containing used amines recovered from amine-based carbon dioxide recovery systems used to recover carbon dioxide from exhaust gases from factories, etc. In other words, such used amines, which are typically disposed of as waste liquid, can be effectively reused by using them as the above-mentioned amines.

The amount of amines to be added is preferably 0.002 to 1 part by mass, and more preferably 0.01 to 0.1 part by mass, per 100 parts by mass of the hydraulic composition (powder form), from the perspective of accelerating the carbonation of the hardened body or, for example, improving the strength development when carbonation curing is performed.

The amines may also be used as grinding aids when grinding the wollastonite-containing fired material provided by the present invention to an appropriate particle size, and the amines may be contained in the hydraulic composition.

Other Materials The hydraulic composition may contain other materials as needed, provided that the object of the present invention is not impaired. Examples of such other materials include various additives such as water-reducing agents, antifoaming agents, and shrinkage-reducing agents, as well as various admixtures such as fly ash, silica fume, ground granulated blast furnace slag, and ground limestone. Rapid hardening agents and hardening accelerators may also be added to increase early strength and improve handling. The proportion of such other materials in the hydraulic composition varies depending on the type of material, but is typically, for example, 20% by mass or less, and preferably 10% by mass or less.

Gypsum and free lime content The gypsum content in the hydraulic composition is preferably 5.0% by mass or less, more preferably 1.0% by mass to 4.0% by mass, calculated as SO _3. If the gypsum content is within the above range, the fluidity of the kneaded material before hardening is further improved.

The proportion of free lime in the hydraulic composition is preferably 2.0% by mass or less, and more preferably 0.2 to 1.5% by mass, from the viewpoint of strength development in the carbonation curing process described below.

In addition, if the hydraulic composition is formulated with materials other than the wollastonite-containing fired product provided by the present invention, the gypsum and free lime contents mentioned above include the gypsum and free lime derived from those materials.

<Cured body>
By mixing the hydraulic composition with water, kneading, and curing the mixture, a cured product using the wollastonite-containing burned material can be obtained.

Water: The water used to obtain the hardened body is not particularly limited, and examples include tap water and sludge water. The mass ratio of water to the hydraulic composition (powdered) (water/powdered hydraulic material) is preferably 0.3 to 1.0, more preferably 0.4 to 0.7. If the ratio is 0.3 or more, breathability is ensured and the carbon dioxide absorption effect is enhanced. In addition, the workability of the kneaded hydraulic composition is improved. If the ratio is 1.0 or less, the strength of the hardened body can be ensured.

Aggregate: When the hydraulic composition is hardened, aggregate may be used to form the body of the resulting hardened product. Examples of fine aggregate include river sand, mountain sand, land sand, sea sand, crushed sand, silica sand, slag, lightweight fine aggregate, recycled aggregate, artificially fired aggregate, and mixtures thereof. Examples of coarse aggregate include river gravel, mountain gravel, land gravel, crushed stone, slag, lightweight coarse aggregate, recycled aggregate, artificially fired aggregate, and mixtures thereof.

The wollastonite-containing fired product provided by the present invention may be used as the aggregate used when hardening the hydraulic composition (hereinafter, when the wollastonite-containing fired product provided by the present invention is used as aggregate, it may be referred to as "fired aggregate"). In this case, wollastonite is present on most of the surface of the fired aggregate, and when this wollastonite is carbonated, the total amount of carbon dioxide absorbed into the hardened body can be increased, and the interface between the cement paste and the aggregate can be densified by the carbonation reaction, thereby increasing the strength of the hardened body.

When the above-mentioned sintered aggregate is used in the above-mentioned hydraulic composition, it can be used as at least one of fine aggregate and coarse aggregate. In this case, the wollastonite-containing sintered product provided by the present invention can be crushed or sized appropriately to obtain a particle size suitable for use as the desired aggregate (fine aggregate, coarse aggregate, etc.), and the sintered aggregate prepared in this manner can be used.

When the burned aggregate is used in the hydraulic composition, for example, if the set product of the hydraulic composition resembles conventional mortar, it may be included as a substitute for the fine aggregate normally used in such mortar, or if the set product of the hydraulic composition resembles conventional concrete, it may be included as a substitute for at least one of the fine aggregate and coarse aggregate normally used in such concrete. However, from the perspective of increasing the total amount of carbon dioxide absorbed by the set product, it is preferable that it be included as a substitute for the fine aggregate normally used.

When the above-mentioned sintered aggregate is used in the above-mentioned hydraulic composition, other aggregates may be used in addition to the above-mentioned sintered aggregate. As for aggregate, as described above, examples of fine aggregate include river sand, mountain sand, land sand, sea sand, crushed sand, silica sand, slag, lightweight fine aggregate, recycled aggregate, artificially sintered aggregate, and mixtures thereof. Examples of coarse aggregate include river gravel, mountain gravel, land gravel, crushed stone, slag, lightweight coarse aggregate, recycled aggregate, artificially sintered aggregate, and mixtures thereof.

When the sintered aggregate is used in the hydraulic composition, the proportion of the sintered aggregate in the total amount of aggregate used may preferably be, as a lower limit, 20% by mass or more, 25% by mass or more, 30% by mass or more, 50% by mass or more, 70% by mass or more, 90% by mass or more, or 100% by mass. If the proportion of the sintered aggregate in the total amount of aggregate used is above the above range, the total amount of carbon dioxide that can be absorbed by the resulting hardened body can be increased, and the strength of the resulting hardened body can be increased, compared to when general aggregate is used.

Furthermore, when the sintered aggregate is fine aggregate, the proportion of the sintered aggregate in the total amount of fine aggregate may preferably be, as a lower limit, 20% by mass or more, 25% by mass or more, 30% by mass or more, 50% by mass or more, 70% by mass or more, 90% by mass or more, or 100% by mass. If the proportion of the sintered aggregate in the total amount of fine aggregate used is above the above range, the total amount of carbon dioxide that the resulting hardened body can absorb can be increased, and the strength of the resulting hardened body can be increased, compared to when general aggregate is used.

When aggregate is used in the hydraulic composition, the amount of aggregate (the total amount when fine aggregate and coarse aggregate are used in combination) is preferably 200 to 700 parts by mass, and more preferably 200 to 600 parts by mass, per 100 parts by mass of the hydraulic composition (powdered). If the amount of aggregate is within the above range, the strength of the resulting hardened body will be good, while the shrinkage rate will be kept low.

When a combination of fine aggregate and coarse aggregate is used in the hydraulic composition, the fine aggregate ratio (the percentage of the mass of fine aggregate relative to the total mass of aggregate) is preferably 5% to 60%. A fine aggregate ratio within this range improves the workability and ease of molding of the kneaded product. The coarse aggregate ratio is preferably 1.0 to 7.0, more preferably 1.5 to 6.5.

<Carbonated hardened body>
By combining the hydraulic composition with water, kneading, and curing the composition, a hardened body using the wollastonite-containing burned material can be obtained. Furthermore, by subjecting the composition to a carbonation treatment during curing, a carbonated hardened body can be obtained, which absorbs carbon dioxide. Here, "carbonation" in this specification refers to the reaction of an alkaline component in a hardened body of the hydraulic composition with carbon dioxide, thereby lowering the pH of the alkaline component.

As an example, the following describes a method in which (A) a hydraulic composition (powdered), (B) water, and (C) aggregate are mixed to prepare a hydraulic composition mixture, which is then poured into a formwork and cured to obtain a carbonated hardened body.

[Kneaded material preparation step]
This step is a step of kneading the above-mentioned (A) hydraulic composition (powder form), (B) water, and (C) aggregate materials to prepare a kneaded mixture.

There are no particular limitations on the method for kneading the materials. Furthermore, there are no particular limitations on the equipment used for kneading; for example, conventional mixers such as an omnimixer, pan mixer, twin-screw mixer, or tilting mixer can be used.

[Pouring process]
This step is a step of casting the kneaded material obtained in the above step into a formwork.

There are no particular limitations on the casting method, and conventional methods such as pour molding can be used.

The curing method used after the mixture is poured into the formwork and before it is removed from the formwork is not particularly limited, and common curing methods such as air curing, moist air curing, underwater curing, and steam curing can be used.

[Demolding process]
This step is a step in which, after the kneaded material in the formwork has hardened, the hardened hydraulic composition obtained by the hardening of the kneaded material is removed from the formwork.

[High strength curing process]
This step is optionally performed between the demolding step and the carbonation curing step, and is a step for increasing the strength of the hardened product of the hydraulic composition.

In this step, the hardened hydraulic composition released from the formwork is cured until its compressive strength reaches preferably 3 N/ ^mm2 or more, more preferably 5 N/ ^mm2 or more, and particularly preferably 10 N/ ^mm2 or more, thereby increasing the strength of the carbonated hardened body after carbonation curing (for example, the compressive strength of mortar or concrete).

The curing method is not particularly limited, and general curing methods such as air curing, moist air curing, underwater curing, and steam curing can be used. Note that "curing" in the high-strength curing process does not include carbonation curing.

[Carbonation curing process]
This step is a step of carbonating and curing the hardened hydraulic composition released from the formwork to obtain a carbonated hardened body by carbonating the hardened hydraulic composition.

The concentration of carbon dioxide gas used for carbonation curing in this process is preferably 1% by volume or more, more preferably 3% by volume or more, even more preferably 10% by volume or more, even more preferably 50% by volume or more, and particularly preferably 60% by volume or more. A concentration of 1% by volume or more can increase the amount of carbon dioxide absorbed during the carbonation curing process.

There is no particular upper limit to the carbon dioxide gas concentration; the higher the carbon dioxide gas concentration, the greater the amount of carbon dioxide absorbed. However, from the perspective of reducing the cost of curing equipment, etc., the upper limit is preferably 90% by volume or less, more preferably 70% by volume or less, and particularly preferably 50% by volume or less.

The temperature during the carbonation curing process is not particularly limited, but is preferably 5°C to 100°C, more preferably 10°C to 50°C, and especially preferably 15°C to 35°C. If the temperature during carbonation curing is within the above range, the strength of the carbonated hardened body can be increased. Furthermore, the productivity of products made from the carbonated hardened body is improved.

Furthermore, the carbonated hardened body of the present invention is highly effective in reducing carbon dioxide emissions even when carbonation curing is performed at relatively low temperatures (e.g., 5°C to 30°C).

The relative humidity in this process is not particularly limited, but is preferably 20% to 90%, more preferably 30% to 80%, and especially preferably 40% to 70%. A relative humidity of 20% or higher improves the productivity of the carbonated hardened body and increases the strength of the carbonated hardened body. It is difficult to achieve a relative humidity of more than 90%, and the costs for equipment, etc. would be excessive.

In the carbonation curing process, it is preferable to carry out carbonation curing so that the carbonation depth from the surface of the carbonated hardened body is preferably 2 mm or more, more preferably 5 mm or more, even more preferably 8 mm or more, and particularly preferably 10 mm or more. By carrying out carbonation curing so that the carbonation depth is 2 mm or more, more carbon dioxide can be absorbed into the carbonated hardened body. Specifically, the carbonation depth can be made 2 mm or more by appropriately adjusting the carbon dioxide gas concentration, temperature, and relative humidity values, as well as the curing time, in the carbonation curing process described above.

Furthermore, from the viewpoint of absorbing carbon dioxide in a short period of time, it is preferable to carry out carbonation curing so that the carbonation depth is 2 mm or more, preferably when the material is 1 day old (after demolding), and more preferably when the material is 3 days old (after demolding).

The "carbonation depth from the surface of the carbonated hardened body" can be measured in accordance with "JIS A 1152:2018 (Method for measuring carbonation depth of concrete)."

The resulting carbonated hardened material can be used as roadbed material, interlocking blocks, etc. Furthermore, even after installation as roadbed material, etc., it can continue to absorb and fix carbon dioxide.

Furthermore, when the hydraulic composition contains sintered aggregate (aggregate made from the sintered product described above), the sintered aggregate may be subjected to a carbonation treatment before the kneaded product preparation step in order to densify it and increase its strength. Carbonation treatment can be carried out, for example, by moistening the aggregate and leaving it to stand in the presence of carbon dioxide gas. Note that if the sintered aggregate is excessively carbonated in this case, the carbonation reaction will not occur during carbonation curing, and the strength of the carbonated hardened body after carbonation curing may not be improved.

The carbonated hardened body obtained by the above manufacturing method emits less carbon dioxide during production than when ordinary Portland cement is used instead of the pulverized sintered product (the pulverized sintered product described above), or when ordinary aggregate is used instead of the sintered aggregate, by preferably 15% or more, more preferably 20% or more, even more preferably 30% or more, and particularly preferably 40% or more. Furthermore, the reduction in strength (e.g., compressive strength) of the carbonated hardened body is preferably 50% or less, more preferably 40% or less.

The present invention will be explained in more detail below using test examples. However, the scope of the present invention is not limited to these test examples.

1. Test Samples
Biomass ash raw powder: Fly ash generated from a biomass power plant (furnace type: circulating fluidized bed boiler (CFB), fuel: coconut shells (PKS) 100%) (hereinafter referred to as "raw powder")
・Biomass ash coarse powder*: Raw powder sieved to 53 μm (hereinafter referred to as "coarse powder")
・Biomass ash fine powder*: Raw powder passed through a 53 μm sieve (hereinafter referred to as "fine powder")
・Silica sand: Kashima No. 6 silica sand (hereinafter referred to as "silica sand")
Calcium carbonate: Special grade (95.5% or more) _CaCO3 powder, used as a CaO concentration adjuster *Classification device: Spin Air Sieve (SAR-75) (manufactured by Seishin Enterprise Co., Ltd.)

[2. Analysis method]
Chemical composition of biomass ash (before washing): Fluorescent X-ray analyzer (Rigaku Corporation, "ZSX Primus II") was used (calibration curve (clay) method)
Chemical composition of biomass ash (after washing) and chemical composition of burned product: Fluorescent X-ray analyzer (Rigaku Corporation, "ZSX Primus II") was used (FP method: Fundamental Parameter Method)
Mineral content: Using a sample to which 10% corundum (Al ₂ O ₃ ) was added as an internal standard substance, the X-ray diffraction pattern was measured with an X-ray diffractometer (D8 ADVANCE A-25 manufactured by Bruker AXS).

The X-ray diffraction measurement conditions were CuKα radiation, tube voltage 50 kV, tube current 40 mA, scan range 10° to 65° (2θ), step width 0.0234, and scan speed 0.13 sec/step. Next, using the obtained diffraction pattern, Rietveld analysis was performed using software (TOPAS Ver. 6.0 manufactured by Bruker A.X.) to obtain quantitative results for the mineral composition. From the obtained results, the amorphous mass was calculated from the quantitative corundum value using the following formula (2).

G=100・(AR)/{A・(100−R)/100}…(2)
In the formula (2), G is the amorphous mass (%), R is the mixing ratio of Al ₂ O ₃ (%), and A is the quantitative value of Al ₂ O ₃ (%).

The quantitative results obtained from Rietveld analysis were then standardized so that the total amount of the composition, excluding the quantitative value of corundum, was 100%, and this value was then further standardized by the proportion excluding the amorphous mass to determine the mineral composition of each biomass ash.

3. Characteristics of test samples
Table 1 shows the chemical compositions of the test samples.

Table 2 shows the results of the XRD qualitative analysis of the test samples.

Table 3 shows the XRD/Rietveld analysis results of the test samples.

Table 4 shows the Blaine specific surface area and CaO/ _SiO2 mass ratio of the test samples.

3. Characteristics of test samples
(Washing treatment)
The chlorine contained in the raw powder, coarse powder, and fine powder was removed in advance by washing with water.
Washing ratio: 1:4 (400g of water to 100g of biomass ash)
Stirring conditions: rotation speed 400 rpm, time 30 minutes, water temperature at room temperature Cake washing water ratio: 1:4 (400g of water to 100g of biomass ash)

(powderness adjustment)
To eliminate the influence of fineness during firing, the Blaine values of the raw powder/water-washed product, coarse powder/water-washed product, and silica sand were adjusted using a fine grinder (disc mill) so that they were equivalent to the Blaine value of the fine powder/water-washed product.

Table 5 shows the chemical composition of the pretreated sample.

Table 6 shows the results of the XRD qualitative analysis of the pretreated samples.

Table 7 shows the XRD Rietveld analysis results of the pretreated sample.

Table 8 shows the Blaine specific surface area and CaO/ _SiO2 of the pretreated samples.

[4. Test conditions and standards]
In order to investigate the conditions for producing wollastonite, various levels were set for the firing temperature and the CaO/ _SiO2 mass ratio.

Table 9 shows the test levels.

Table 10 shows the formulation for the test levels.

Table 11 shows the chemical composition of the samples after adjusting the formulation for the test levels.

5. Heat treatment and results
(Heating conditions)
Furnace used for heating: Box-type electric furnace (Motoyama S7-2035D-OP)
Heating temperature: As per test standard Heating time: 60 minutes

Table 12 shows the XRD Rietveld analysis results for the heat-treated product.

Table 13 shows the chemical composition of the heat-treated product.

Furthermore, FIG. 3 shows the results of comparing the amount of wollastonite produced depending on the raw material (Levels 4, 11, 13, and 15: heating temperature 1,100°C, CaO/ _SiO2 mass ratio 0.7; and Levels 8, 12, 14, and 16: heating temperature 1,100°C, CaO/ _SiO2 mass ratio 1).

As shown in Tables 12, 13, and Figure 3, when raw biomass ash powder or fine or coarse powder obtained by classification was heat-treated, the amount of wollastonite ( _CaSiO3 ) increased compared to silica sand. Therefore, it can be seen that using biomass ash as a raw material accelerates the wollastonite production reaction and makes it easy to obtain a wollastonite-containing fired product. In particular, those made from fine powder as a raw material have a high amount of wollastonite ( _CaSiO3 ), low amounts of intermediately reacted mineral components and unreacted mineral components, and a fast sintering reaction. Furthermore, those made from coarse powder as a raw material have a low amount of wollastonite ( _CaSiO3 ) and a slower wollastonite production rate, but after heating, the CaO and _SiO2 content is higher (low SM, low _R2O , low MgO, low _SO3 ) than those made from raw ash or fine powder. Therefore, it is believed that the wollastonite content can be further increased by firing at a higher temperature or for a longer period of time.

Figure 4 shows the results for levels 1 to 7, comparing the wollastonite content in the heated products at different heating temperatures.

As shown in Figure 4, temperatures above 1,000°C are thought to be preferable for forming wollastonite using biomass ash as a raw material. In particular, at temperatures above 1,200°C, pseudowollastonite increases, while intermediately reacted mineral components and unreacted mineral components decrease.

FIG. 5 shows the results for levels 4, 8, and 9, and compares the wollastonite content in the heated product depending on the CaO/SiO ₂ mass ratio in the raw material composition for firing.

As shown in Figure 5, when wollastonite is formed using biomass ash as a raw material, it is believed that good results can be obtained if the CaO/ _SiO2 mass ratio in the raw material composition for firing is in the range of approximately 0.5 to 1.2. Note that the higher the CaO/ _SiO2 mass ratio, the lower the wollastonite content and the slower the wollastonite formation rate, but it is believed that the wollastonite content can be increased by firing at a higher temperature or for a longer period of time.

Table 14 shows the results of comparing the minerals produced when the fine powder was washed with or without water (levels 4 and 10) (heating temperature 1,100°C).

Table 15 also shows the results of comparing the chemical composition of fine powders with and without water washing (levels 4 and 10) (heating temperature 1,100°C).

As shown in Tables 14 and 15, the heat-treated product obtained by washing fine biomass ash powder with water and then heat-treating it produced the same amount of wollastonite and had a lower chlorine content than the product obtained without water washing.

Claims (14)

A method for producing a wollastonite-containing fired product, comprising: preparing a raw material composition for firing containing 30% by mass or more of biomass ash; and firing the raw material composition for firing at 1,050°C to 1,300°C to form wollastonite (CaSiO ₃ );
The production method as described above, wherein the proportion of Al ₂ O ₃ in the raw material composition for firing (based on ignition raw material) is 1.0 mass % to 7.0 mass % . The method for producing a wollastonite-containing fired product according to claim 1, wherein the biomass ash is a fine powder obtained by classifying raw material biomass ash at a classification point in the range of 10 μm to 100 μm . The method for producing a wollastonite-containing fired product according to claim 1, wherein the biomass ash is obtained by washing raw biomass ash with water, or by classifying the raw biomass ash at a classification point in the range of 10 μm to 100 μm , and then washing the resulting fine powder with water. The method for producing a wollastonite-containing fired product according to any one of claims 1 to 3, wherein the CaO/ _SiO2 mass ratio of the firing raw material composition is 0.5 to 1.2. The method for producing a wollastonite-containing fired product according to any one of claims 1 to 4 , wherein the biomass ash has an amorphous content of 30 mass% or more. The method for producing a wollastonite-containing fired product according to any one of claims 1 to 5 , wherein the biomass ash used has a silica content of 3.0 to 20.0. A method for producing a hardened product using the wollastonite-containing fired product, comprising obtaining a wollastonite-containing fired product by the production method according to any one of claims 1 to 6 , preparing a hydraulic composition using the wollastonite-containing fired product as a material, adding water to the hydraulic composition and kneading the mixture to obtain a kneaded product, and hardening the kneaded product. A method for producing a hardened body using the wollastonite-containing sintered product, comprising the steps of obtaining a wollastonite-containing sintered product by the production method according to any one of claims 1 to 6 , preparing a hydraulic composition using the wollastonite-containing sintered product as a material, preparing aggregate to be combined with the hydraulic composition using the wollastonite-containing sintered product as a material, adding water to the aggregate and the hydraulic composition and kneading them to obtain a kneaded product, and hardening the kneaded product. 9. The method for producing a hardened product according to claim 7 , wherein the kneaded material is subjected to a carbonation treatment when hardening the kneaded material. A method for recycling biomass ash, comprising: classifying biomass ash at a classification point within a range of 10 μm to 100 μm; calcining the fine powder obtained by the classification at 1,050°C to 1,300°C to obtain a wollastonite-containing calcined product; and utilizing the coarse powder obtained by the classification as a material for a hardened body made of a hydraulic composition ,
The above resource recovery method, wherein the proportion of Al ₂ O ₃ in the biomass ash (based on ignition raw material) is 5.0 mass % or less . The method for recycling biomass ash according to claim 10 , wherein the wollastonite-containing burned material is used as a material for a hardened body made of a hydraulic composition. The method for recycling biomass ash according to claim 10 or 11 , wherein the coarse powder obtained by classifying the biomass ash is used as concrete aggregate, concrete admixture, cement mixture, or cement clinker raw material. The method for recycling biomass ash according to any one of claims 10 to 12 , wherein the wollastonite-containing fired product is used as a concrete aggregate, a concrete admixture, or a cement admixture. The method for recycling biomass ash according to any one of claims 10 to 13, wherein the wollastonite-containing burned product and the coarse powder obtained by classifying the biomass ash are both used as common materials for a hardened body to obtain the hardened body.