Alkali-resistant amorphous inorganic composition and its fibers

Abstract

[Problem] To develop a high added value material having excellent alkali-resistance, by effectively utilizing waste product discharged from coal-fired power plants and copper slag discharged from copper smelteries. [Solution] This inorganic composition, which has excellent alkali resistance and can be melt-spun, is obtained by preparing a noncrystalline inorganic composition containing, as main components, silica (SiO2), iron oxide (Fe2O3), alumina (Al2O3), and calcium oxide (CaO), such that i) the silica, alumina, and calcium oxide are contained in a total amount of 50-75 mass%, ii) the iron oxide is contained in an amount not less than 26 mass% but less than 40 mass%, and iii) the iron oxide is derived from a noncrystalline raw material. Raw materials for the inorganic composition can be derived mostly from coal ash and copper slag.

Description

Technical Field

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[0001] The present invention relates to an alkali-resistant amorphous inorganic composition and its fibers. More specifically, it relates to an alkali-resistant amorphous inorganic composition and its fibers that effectively utilize coal-fired power generation waste.

Background Art

[0002] After the Great East Japan Earthquake, the operation of nuclear power generation was restricted, so in Japan, the ratio of thermal power generation in energy supply has been increasing at a high rate. Among them, the ratio of coal-fired power generation is high. A large amount of coal ash (fly ash and clinker ash) is generated as waste from coal-fired power generation. As an effective use of coal ash, most of it is used as an aggregate for concrete, such as mixing it with cement (for example, see Patent Document 1). In addition, copper slag is an industrial waste for which effective use is required. Most of its uses are also as aggregates for concrete, and other uses are required.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Non-Patent Documents

[0004]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Generally, concrete exhibits a high alkalinity with a pH value of 12-13. This is because minerals (such as calcium, silicon, aluminum, and iron) contained in cement, the raw material (binder) of concrete, react with water (hydration reaction) to produce calcium hydroxide (Ca(OH)2). Thus, because concrete exhibits high alkalinity, aggregates mixed with cement require high alkali resistance. However, to the best of the inventors' knowledge, sufficient research has not been conducted to further improve the alkali resistance of aggregates. Furthermore, there appears to be little focus on developing high value-added materials that go beyond the realm of aggregates. Therefore, the inventors diligently conducted research with the aim of developing a new high-value-added material using industrial waste such as coal ash and copper slag as the main raw materials. [Means for solving the problem]

[0006] As a result, the present inventors have found that in an amorphous inorganic composition mainly composed of silica (SiO2), iron oxide (Fe2O3), alumina (Al2O3), and calcium oxide (CaO), i) silica, alumina, oxide ii) The total calcium content is 50% by mass or more and 75% by mass or less, and the iron oxide content is 2 We have discovered that an inorganic composition having an iron oxide content of 6% by mass or more and less than 40% by mass, and in which the iron oxide is derived from an amorphous raw material, exhibits excellent alkali resistance and can be processed into fibers, thus completing the present invention. The present invention will be described in detail below.

[0007] The inorganic composition of the present invention is obtained by using inorganic oxides as raw materials and melting and solidifying those raw materials. Therefore, there is no substantial difference between the component ratio in the raw material mixture and the component ratio in the material after the mixture has been melted. Thus, the component ratio in the mixture can be used as the final component ratio of the inorganic composition.

[0008] The inorganic composition of the present invention is an amorphous inorganic composition mainly composed of silica (SiO2), iron oxide (Fe2O3), alumina (Al2O3), and calcium oxide (CaO). When a crystalline phase is formed, alkaline substances can easily penetrate through the interface between the crystalline and amorphous phases, leading to a decrease in alkali resistance. In this respect, the inorganic composition of the present invention is amorphous and exhibits excellent alkali resistance. In this invention, the determination of whether an inorganic composition is amorphous or not was based on the X-ray diffraction (XRD) spectrum. Specifically, an inorganic composition was determined to be amorphous if only amorphous halos were observed in its X-ray diffraction (XRD) spectrum and no peaks of the crystalline phase were observed.

[0009] The inorganic composition of the present invention must contain silica, alumina, calcium oxide, and iron oxide within a specific range. In the following description, the component content is expressed as an oxide equivalent. The total content of silica, alumina, and calcium oxide in the inorganic composition of the present invention is 50% by mass or more and 75% by mass or less. Of the above components, silica and alumina function to evenly disperse the iron oxide component in the inorganic composition, making the inorganic composition more amorphous, and to maintain good spinnability of the molten material even when the iron oxide content in the inorganic composition is high. Therefore, the total content of silica and alumina in the inorganic composition is preferably 40% by mass or more, more preferably 50% by mass or more, and most preferably 60% by mass or more. Furthermore, in order to further improve the spinnability of the molten material, the mass ratio of alumina to the total of silica and alumina is preferably 0.15 to 0.40. Calcium oxide affects the melt viscosity of the inorganic composition. The calcium oxide content in the inorganic composition is preferably 5% by mass or more and 20% by mass or less.

[0010] Next, the iron oxide content in the inorganic composition of the present invention must be 26% by mass or more and less than 40% by mass, and the iron oxide component must be derived from amorphous raw materials. If the iron oxide content is less than 26% by mass, alkali resistance decreases. The iron oxide content is preferably 28% by mass or more, and most preferably 30% by mass or more. On the other hand, if the iron oxide content is 40% by mass or more, the melt spinnability deteriorates. The iron oxide content is preferably 38% by mass or less, and more preferably 35% by mass or less. As stated above, it is essential that the iron oxide is derived from an amorphous raw material. In this invention, the amorphous raw material is an amorphous substance containing silica, alumina, calcium oxide, and iron oxide as essential components. Preferably, the amorphous raw material has a total content of 80% by mass or more of silica, alumina, calcium oxide, and iron oxide, and more preferably 90% by mass or more. The amorphous raw material can be an industrial product, industrial waste, or natural product. From an economic standpoint, industrial waste is preferred as the amorphous raw material, but it is not limited to this. Examples of industrial waste that meet the above requirements include copper slag and coal ash. For coal ash, the Integrated Coal Gasification Combined Cycle (AGC) method is employed. This also includes slag (IGCC slag) discharged from thermal power plants. Other natural materials include basalt and volcanic ash. In addition, iron oxide can be artificially melted and solidified together with silica, alumina, and calcium oxide to produce amorphous raw materials.

[0011] However, since none of the above-mentioned copper slag, coal ash, basalt, or volcanic ash contain iron oxide in the range of 26% by mass or more and less than 40% by mass, they alone cannot be used to form the inorganic composition of the present invention. For example, basalt is a well-known natural raw material that can be processed into fibers, with silica, alumina, calcium oxide, and iron oxide as its main components. However, its iron oxide content is 12% or less (see Non-Patent Document 1 if necessary), and therefore, it alone cannot constitute the inorganic composition of the present invention. Similarly, coal ash, which mainly consists of silica, alumina, calcium oxide, and iron oxide, can also be used as a raw material for fiber processing. However, its iron oxide content is usually 20% by mass or less, and therefore, it cannot be the inorganic composition of the present invention on its own. Basalt and coal ash, however, contain iron oxide and are rich in silica, alumina, and calcium oxide, making them extremely useful raw materials as sources of silica and alumina necessary for constructing the inorganic composition of the present invention.

[0012] The typical composition of copper slag is said to be 45-54% iron oxide, 30-36% silica, 3-6% alumina, and 2-7% calcium oxide, and it is amorphous. However, as will be explained later, copper slag has too high an iron oxide content, so its molten product lacks melt-spinning properties and cannot be the inorganic composition of the present invention on its own. Nevertheless, copper slag is a useful source of iron oxide (amorphous iron oxide source) that contains abundant, amorphous iron oxide components that are essential and important for the inorganic composition of the present invention. As mentioned above, although not economical, a raw material consisting primarily of iron oxide (approximately 50 parts by mass), to which silica, alumina, and calcium oxide are added, can be pre-melted and solidified at a high temperature and used as an amorphous iron oxide source.

[0013] This invention involves preparing a silica-alumina source, which alone has too little iron oxide content, and an amorphous iron oxide source, which alone has too much iron oxide content, so that the iron oxide content in the final inorganic composition falls within the above range, and then melting and solidifying them to create an inorganic composition with excellent alkali resistance and melt spinning properties.

[0014] The inorganic compositions of the present invention do not eliminate the inclusion of unavoidable impurities present in the raw materials. Examples of such impurities include MgO, Na2O, K2O, TiO2, and CrO2. The inorganic composition of the present invention exhibits excellent melt-spinning properties, allowing it to be processed into fibers using existing glass fiber manufacturing equipment. [Effects of the Invention]

[0015] Since the inorganic composition of the present invention is excellent in alkali resistance and also excellent in melt spinning property, it can be processed into fibers and further secondary processed into various fabrics, cloths, strand mats, etc. and used for various applications. In addition, coal ash discharged from coal-fired power plants can be effectively utilized as the main raw material. Furthermore, since copper slag can be used as the amorphous iron oxide source, the effective utilization rate of industrial waste can be further increased.

Brief Description of Drawings

[0016] [Figure 1] It is an explanatory drawing showing an outline of an evaluation test of the melt spinning property of the inorganic composition of the present invention. [Figure 2] It is an XRD spectrum of copper slag (IC-1) and iron oxide (reagent) used in Examples and Comparative Examples. [Figure 3] It is an enlarged view (microscopic photograph) of an example of the fiber obtained by the Example. [Figure 4] It is an XRD spectrum of the fiber of Example 1. [Figure 5] It is a photograph showing the sample and the test apparatus used in the alkali resistance test.

Modes for Carrying Out the Invention

[0017] Hereinafter, in the test examples (Examples and Comparative Examples) of the present invention, the following reagents and raw materials were used. <Reagent> · Iron oxide (reagent) · Silica (reagent) · Alumina (reagent) · Calcium oxide (reagent) <Amorphous raw material> · SA-1: IGCC slag · SA-2: Coal ash produced from thermal power plants in Japan · SA-3: Basalt · SA-4: Sakurajima volcanic ash · IC-1: Copper slag produced from copper smelters in Japan • IC-2: A molten solidified material (pseudo-copper slag) that mimics copper slag and has a high iron oxide content, prepared according to the procedure described below. The composition of these raw materials is shown in Table 1. Compositional analysis was performed using X-ray fluorescence analysis. XRD spectral analysis confirmed that SA-1 to SA-4, IC-1, and IC-2 are all amorphous. On the other hand, similar analytical tests revealed that the iron oxide in the reagent contains crystalline components. Figure 2 shows the XRD spectra of iron oxide (reagent) and IC-1 (copper slag). In addition, silica (reagent), alumina (reagent), and calcium oxide (reagent) are all crystalline. The above-mentioned pseudo-copper slag (IC-2) was prepared by weighing 50 parts by mass of iron oxide, 33 parts by mass of silica, 5 parts by mass of alumina, and 12 parts by mass of calcium oxide from the above-mentioned reagent, finely grinding the mixture in a mortar, transferring it to a crucible, and heating it in an electric furnace and a gas furnace at a temperature of 1,700 to 2,200°C for approximately 8 hours. It is held in place for a period of time, and the molten material is solidified in water. Of the amorphous raw materials mentioned above, SA-1 to SA-4 have a total silica and alumina content of 60% by mass or more, making them high-quality silica-alumina sources. On the other hand, IC-1 and IC-2 have an iron oxide content of 50% by mass or more in their raw materials, making them high-quality amorphous iron oxide sources. As shown in Table 1, SA-1 to SA-4, IC-1, and IC-2 are all silica, alumina, and calcium oxide. The total content of um and iron oxide is 90% by mass or more. In the table below, the content of iron oxide (Fe2O3) is abbreviated as [F], the content of silica (SiO2) as [S], the content of alumina (Al2O3) as [A], and the content of calcium oxide (CaO) as [C].

[0018] [Table 1]

[0019] Prior to conducting a series of alkali resistance tests, melt spinning and alkali resistance tests were performed on the raw materials themselves, namely the silica-alumina source and the amorphous iron oxide source. <Fat Spinning Test> An evaluation of melt spinning properties (hereinafter simply referred to as "spinning properties test") was conducted using an electric furnace. A schematic of the test is shown in Figure 1. In Figure 1, the electric furnace (1) has a height (H) of 60 cm and an outer diameter (D) of 50 cm, and is equipped with an opening (4) with a diameter (d) of 10 cm in the center. On the other hand, 30 g of the mixture is placed in a Tammann tube (2) with an inner diameter (φ) of 2.1 cm and a length of 10 cm. A hole with a diameter of 2 mm is made in the center of the bottom of the Tammann tube (2). During the melting test, the Tammann tube (2) is held in a predetermined position inside the opening (4) of the electric furnace by a suspension rod (3). When heated, the mixture melts, and due to its own weight, it flows down from the bottom of the Tammann tube, solidifies upon contact with the outside air, and becomes a thread (fiber). The electric furnace is heated according to a predetermined heating program, with the maximum temperature to reach the furnace set at 1350°C. It has been pre-confirmed that the temperature inside the Tammann tube (molten material) follows approximately 50°C lower than the furnace temperature. In this invention, as an indicator for evaluating melt spinnability, the acceptable level was defined as the molten material flowing and falling to form a thread before the furnace temperature reached 1350°C, that is, the melting temperature of the sample being 1300°C or lower, and the molten material having a suitable melt viscosity for forming a thread (fiber). The melt spinnability of the sample was ranked in three stages from A to C according to its melting behavior. . A: It becomes thread (fiber). B: The sample does not begin to melt, or the molten material is too viscous, so nothing comes out of the bottom of the Tammann tube. C: The sample melts, but the viscosity of the molten material is too low, so it only drops out as droplets and does not form threads (fibers).

[0020] <Alkali resistance test> During the spinning test, when the inorganic composition melts and solidifies, either a fiber with an ellipsoidal solid at the tip or a simple ellipsoidal solid is formed (black solid (X) in Figure 5(a)). Separately, a 10% by mass NaOH solution (pH approximately 13) is prepared and placed in a test tube (W), and the above solid (weight Immerse the sample in quantity W1), keep the test tube (W) at 90°C using a sand heater, and leave for 30 days. The process was continued. Next, the sample was collected using a mesh and its weight (W2) after drying was measured. The weight loss rate (%) was calculated using the following formula (1). Weight reduction rate (%)=(1-W2 / W1)×100...(1)

[0021] Table 2 shows the results of melt spinning and alkali resistance tests for the raw materials obtained by the above procedure, namely the silica-alumina source and the amorphous iron oxide source. From this, it was confirmed that fibers can be obtained using coal ash and basalt as raw materials, as in conventional technology. It was also confirmed that the alkali resistance was at the level shown in Table 2. A comparison of the absolute values ​​of alkali resistance of SA-1 and SA-3 showed a tendency for alkali resistance to improve as the iron oxide content in the inorganic composition increased. On the other hand, although fibers could not be obtained from copper slag and pseudo-copper slag, the alkali resistance of the molten solidified material was extremely high (both showed a weight loss of 0.00%). These results suggest that it is possible to create fibers superior to existing fly ash fibers and basalt fibers by increasing the iron oxide content in the inorganic composition.

[0022] [Table 2]

[0023] [Example 1] Based on the findings obtained from the preliminary tests above, SA-2 was used as the silica-alumina source so that the iron oxide content of the final composition would be higher than that of IGCC slag (SA-1) and basalt (SA-3). The raw materials used were 20 parts by mass of SA-3, 20 parts by mass of SA-4, and 30 parts by mass of IC-1 as an iron oxide source. The oxide abundance ratio in the raw materials (oxide composition ratio of the final inorganic composition) was iron oxide:28 parts by mass. Amount %, Silica: 47% by mass, Alumina: 11% by mass, Calcium oxide: 9% by mass, Others The iron oxide content is 5% by mass. All iron oxide components are derived from amorphous raw materials. The total amount of silica and alumina in the composition is 58% by mass, and the ratio of alumina to the total amount of silica and alumina is 0.19. When melt spinning was attempted using the same procedure as in the preliminary test described above, fibers were obtained (Figure 3). The molten solidified material was amorphous. Furthermore, the molten solidified material also exhibited excellent alkali resistance (weight loss rate of 0.00%). The results are shown in Table 3. For comparison purposes, the evaluation results for SA-1 in the preliminary test are presented again as Comparative Example 1, and the evaluation results for SA-3 are presented again as Comparative Example 2.

[0024] [Comparative Example 3] SA-2: 66 parts by mass, Iron oxide (reagent): 8 parts by mass, Silica (reagent): 9 parts by mass 15 parts by mass of calcium oxide (reagent) were weighed and a spinning test was performed in the same manner as in Example 1, yielding fibers. XRD spectral analysis revealed crystal peaks. Alkali resistance test results showed a weight loss rate of 0.20%. The results are shown in Table 3. [Comparative Examples 4 and 5] In the hope of improving alkali resistance, the mixing ratios of SA-2, iron oxide (reagent), silica (reagent), and calcium oxide (reagent) were changed to increase the iron oxide content of the composition of Comparative Example 3, and the same tests were conducted (Comparative Examples 4 and 5). The results are shown in Table 3, along with the raw material mixing ratio, oxide composition ratio, total amount of silica and alumina in the composition, and the ratio of alumina to the total amount of silica and alumina. As a result, good fibers were obtained in both Comparative Examples 4 and 5, but contrary to expectations, alkali resistance actually worsened despite having a higher iron oxide content than Comparative Example 3. The molten solidified product was amorphous. Comparative Examples 3-5 suggest that if iron oxide (reagent, crystalline) is included in the raw materials, the alkali resistance decreases even if the final inorganic composition is amorphous.

[0025] [Example 2] The raw materials were prepared in the same manner as in Example 1, except that IC-2 was used instead of the amorphous iron oxide source IC-1. The spinnability test was performed in the same manner as in Example 1. As a result, fibers were obtained. The molten solidified material was amorphous. The alkali resistance test showed a weight loss rate of 0.00%. The results are shown in Table 3.

[0026] [Table 3]

[0027] [Example 3] The spinning test was performed in the same manner as in Example 1, except that SA-1: 50 parts by mass was used as the silica-alumina source and IC-1: 50 parts by mass was used as the amorphous iron oxide source. In this study, the iron oxide content in the raw materials (iron oxide content of the final inorganic composition) was 32% by mass, and all iron oxide components originated from amorphous raw materials. Spinning tests yielded fibers. The molten solidified material was amorphous. Alkali resistance tests showed a weight loss rate of 0.00%. The results are shown in Table 4. For reference, Comparative Example 1 is reproduced again in Table 4.

[0028] [Example 4] The test was carried out in the same manner as in Example 3, except that IC-2 was used instead of IC-1. In this example, the iron oxide content in the raw materials (iron oxide content of the final inorganic composition) was 30% by mass, and all iron oxide components originated from amorphous raw materials. As a result of the spinnability test, fibers were obtained. The molten solidified product was amorphous. As a result of the alkali resistance test, the weight loss rate was 0.00%. The results are shown in Table 4.

[0029] [Example 5] The spinnability test was performed in the same manner as in Example 4, except that SA-1 was used in 37 parts by mass and IC-2 in 63 parts by mass. In this example, the iron oxide content in the raw materials (iron oxide content of the final inorganic composition) was 35% by mass, and all iron oxide components originated from amorphous raw materials. The spinnability test yielded good fibers. The molten solidified product was amorphous. The alkali resistance test showed a weight loss rate of 0.00%. The results are shown in Table 4.

[0030] [Comparative Example 6] The spinnability test was performed in the same manner as in Example 4, except that SA-1 was used in 25 parts by mass and IC-2 in 75 parts by mass. In this example, the iron oxide content in the raw materials (iron oxide content of the final inorganic composition) was 40% by mass, and all iron oxide components originated from amorphous raw materials. As a result of the spinnability test, the molten material only dripped from the crucible, and no fibers were obtained. The solidified molten material was amorphous. The alkali resistance of the solidified molten material was good (weight loss rate 0.00%). The results are shown in Table 4.

[0031] [Comparative Example 7] The spinnability test was performed in the same manner as in Example 4, except that SA-1 was used in 12 parts by mass and IC-2 in 88 parts by mass. In this example, the iron oxide content in the raw materials (iron oxide content of the final inorganic composition) was 45% by mass, and all iron oxide components originated from amorphous raw materials. As a result of the spinnability test, the molten material only dripped from the crucible, and no fibers were obtained. The solidified molten material was amorphous. The alkali resistance of the solidified molten material was good (weight loss rate 0.00%). The results are shown in Table 4. Table 4 shows that while iron oxide components derived from amorphous raw materials contribute to improving the alkali resistance of inorganic compositions, melt spinning performance deteriorates when their content exceeds 40% by mass.

[0032] [Table 4]

[0033] [Example 6] The same method as in Example 1, except that SA-2: 20 parts by mass, SA-3: 20 parts by mass, SA-4: 30 parts by mass were used as silica-alumina sources, and IC-2: 30 parts by mass was used instead of amorphous iron oxide source IC-1. A spinning test was conducted in the same manner. In this test example, the iron oxide content in the raw material (iron oxide content of the final inorganic composition) was 26% by mass, and all iron oxide components originated from amorphous raw materials. As a result of the spinning test, fiber was obtained. The molten solidified material was amorphous. As a result of the alkali resistance test, the weight loss rate was 0.00%. The results are shown in Table 5. For reference, Comparative Example 2 is reproduced again in Table 5.

[0034] [Example 7] Spinning tests were conducted in the same manner as in Example 1, except that SA-3: 65 parts by mass was used as the silica-alumina source and IC-2: 35 parts by mass was used as the amorphous iron oxide source. In this study, the iron oxide content in the raw materials (iron oxide content of the final inorganic composition) was 30% by mass, and all iron oxide components originated from amorphous raw materials. Spinning tests yielded fibers. The molten solidified material was amorphous. Alkali resistance tests showed a weight loss rate of 0.00%. The results are shown in Table 5.

[0035] [Example 8] The same as in Example 7, except that SA-3: 50 parts by mass and IC-2: 50 parts by mass were used. A spinning test was conducted in the manner described above. In this test example, the iron oxide content in the raw material (iron oxide content of the final inorganic composition) was 35% by mass, and all iron oxide components originated from amorphous raw materials. As a result of the test, fibers were obtained. The molten solidified material was amorphous. In the alkali resistance test, the weight loss rate was 0.00%. The results are shown in Table 5.

[0036] [Comparative Example 8] The same as in Example 7, except that SA-3 was 30 parts by mass and IC-2 was 70 parts by mass. A spinning test was conducted in the manner described above. In this test example, the iron oxide content in the raw material (iron oxide content of the final inorganic composition) was 41% by mass, and all iron oxide components originated from amorphous raw materials. As a result of the spinning test, the molten material only dripped from the crucible, and no fibers were obtained. The solidified molten material was amorphous. The alkali resistance of the solidified molten material was good (weight loss rate 0.00%). The results are shown in Table 5.

[0037] [Comparative Example 9] The same as in Example 7, except that SA-3 was 15 parts by mass and IC-2 was 85 parts by mass. A spinning test was conducted in the manner described above. In this test example, the iron oxide content in the raw material (iron oxide content of the final inorganic composition) was 45% by mass, and all iron oxide components originated from amorphous raw materials. As a result of the spinning test, the molten material only dripped from the crucible, and no fibers were obtained. The solidified molten material was amorphous. The alkali resistance of the solidified molten material was good (weight loss rate 0.00%). The results are shown in Table 5. Table 5 shows that the same results as in Table 4 were obtained when basalt was used as the raw material instead of IGCC slag.

[0038] [Table 5]

[0039] [Example 9] 50 parts by mass of IC-1 (copper slag), 28 parts by mass of silica (reagent), 7 parts by mass of alumina (reagent), and 15 parts by mass of calcium oxide (reagent) were weighed and ground in a mortar to prepare the raw materials. The oxide composition of the raw materials was as follows: iron oxide: 28% by mass, silica: 46% by mass, alumina: 10% by mass, calcium oxide: 16% by mass, and others: 2% by mass. The iron oxide content in the raw materials (iron oxide content of the final inorganic composition) was entirely derived from copper slag, i.e., from amorphous raw materials. On the other hand, the other oxides, namely silica, alumina, and calcium oxide, were reagents (crystalline). When the raw materials thus prepared were subjected to a spinnability test, fibers were obtained. The molten solidified material was amorphous. The alkali resistance of the molten solidified material was good (weight loss rate 0.00%). This example demonstrates that, as long as the iron oxide component is derived from amorphous raw materials, silica, alumina, and calcium oxide may all contain components derived from crystalline raw materials. In other words, it is clear that the origin of the iron oxide component in the inorganic composition from amorphous raw materials is important for improving alkali resistance.

[0040] From the comparison between Examples 1-9 and Comparative Examples 1-9, silica, iron oxide, alumina and calcium oxide were found to be present. It has been revealed that in an amorphous inorganic composition mainly composed of um, by using an iron oxide component derived from amorphous raw materials and setting its content to 26% by mass or more and less than 40% by mass, an inorganic composition and its fibers with excellent alkali resistance can be obtained. [Industrial applicability]

[0041] Since the inorganic composition of the present invention has excellent alkali resistance, it can be used not only as an aggregate but also further processed into alkali-resistant inorganic fibers for concrete reinforcement.

Claims

1. A method for producing amorphous inorganic fibers by melt-spinning raw materials consisting mainly of silica, alumina, calcium oxide, and iron oxide, and consisting only of industrial waste or natural products, The aforementioned raw materials are a) An iron oxide source derived from industrial waste, wherein the iron oxide content in the iron oxide source is 45% by mass or more and 54% by mass or less, b) A silica-alumina source derived from industrial waste or natural products, wherein the silica-alumina source has an iron oxide content of 20% by mass or less, In the aforementioned raw materials, i) The total content of silica, alumina, calcium oxide, and iron oxide is 80% by mass or more, ii) The total content of silica, alumina, and calcium oxide is 50% by mass or more and 75% by mass or less, iii) A method for producing amorphous inorganic fibers, wherein the iron oxide content is 26% by mass or more and 35% by mass or less.

2. The method for producing amorphous inorganic fibers according to Claim 1, wherein the iron oxide source is copper slag, and the silica-alumina source is coal ash (provided that the coal ash includes IGCC slag) or basalt.

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