Slag granules, slag compacts, method for producing slag compacts, and method for increasing benthic organisms

Abstract

To provide a slag granule and a slag compact, which are easily producible, and can easily increase organisms in an aqueous environment.SOLUTION: A slag granule (1) contains slag powder (2), a swelling material (3) swelling by contact with water, and a binder (4) for uniting the slag powder and the swelling material, in which the particle size of the slag granule is 20 mm or more and 50 mm or less, and the swelling material is contained in an amount of 0.5 mass% or more and 2.0 mass% or less, and further a characteristic capable of increasing open pores is provided therein.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a slag granule containing steelmaking slag. [Background technology]

[0002] In recent years, due to various factors, there has been a problem of declining fishery resources in coastal waters. In coastal fisheries, in order to ensure a stable harvest of valuable fish and shellfish from the natural world, it is important to conserve or build an ecosystem made up of diverse organisms.

[0003] Generally, steelmaking slag, a by-product generated in large quantities in the iron and steelmaking process, is mainly recycled for land applications such as roadbed material, construction materials, etc. There is a demand for expanding the recycling applications of steelmaking slag, and the development of technologies for its use in marine areas is underway (see, for example, Patent Documents 1 to 5). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 03-004988 [Patent Document 2] Japanese Patent Application Laid-Open No. 2000-078938 [Patent Document 3] Japanese Patent Publication No. 2019-170263 [Patent Document 4] Japanese Patent Application Laid-Open No. 2000-140874 [Patent Document 5] Patent Publication No. 2021-080111 Summary of the Invention [Problem to be solved by the invention]

[0005] The causes of the problem of declining fishery resources described above vary depending on the marine area and the type of organism. In order to increase the population of fishery resources in complex ecosystems, the inventions disclosed in Patent Documents 1 to 5 have room for further improvement.

[0006] There is a demand for granulated slag and molded slag that can easily promote the growth of organisms in aquatic environments. From a practical standpoint, there is also a demand for granulated slag and molded slag that are easy to manufacture. [Means for solving the problem]

[0007] In order to solve the above problems, one embodiment of the present invention provides a slag granule comprising a powder of steelmaking slag, a swelling material that expands upon contact with water, and a binder that binds the powder of steelmaking slag and the swelling material together, wherein the particle size of the slag granules is 20 mm or more and 50 mm or less, the slag granules contain 0.5 mass % or more and 2.0 mass % of the swelling material, and have the property of being able to increase open pores simply by contacting with water.

[0008] In addition, in order to solve the above-mentioned problems, one embodiment of the present invention provides a slag molded body, which comprises a powder of steelmaking slag, a swelling material that expands upon contact with water, and a binder that binds the powder of steelmaking slag and the swelling material together, and is characterized in that the swelling material is contained in an amount of 0.5 mass% to 2.0 mass%, the particle size of the slag molded body is 10 mm to 50 mm, and the open porosity is 3.0 volume% or more.

[0009] In addition, in order to solve the above-mentioned problems, one embodiment of the present invention provides a method for producing a slag molded body, which includes a preparation step of preparing a slag granule containing a powder of steelmaking slag, a swelling material that expands upon contact with water, and a binder that integrates the powder of steelmaking slag and the swelling material, and a formation step of forming a slag molded body having an open porosity greater than that of the slag granules by bringing the slag granules into contact with water and partially disintegrating them, wherein the slag granules have a particle size of 20 mm or more and 50 mm or less, contain 0.5% by mass or more and 2.0% by mass or less of the swelling material, and the slag molded body has an open porosity of 3.0% by volume or more. [Effects of the Invention]

[0010] According to one aspect of the present invention, it is possible to provide slag granules and slag molded bodies that are easy to produce and that facilitate the growth of organisms in an aquatic environment. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 2 is a schematic diagram illustrating the process of open pore generation during immersion in a water environment of a slag granulated material according to one embodiment of the present invention. [Figure 2] 1 is a flowchart showing an example of a method for producing a molded slag according to an embodiment of the present invention. [Figure 3] 3 is a flowchart showing an example of a preparation step included in a method for producing a molded slag according to an embodiment of the present invention. [Figure 4] 1 is an optical photograph showing an example of a sample (molded slag body) recovered after immersion in a Panlite water tank. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, embodiments of the present invention will be described. Note that the following description is intended to provide a better understanding of the gist of the invention, and does not limit the present invention unless otherwise specified.

[0013] In the following description, in order to facilitate understanding of the granulated slag and molded slag according to this embodiment, the new findings discovered by the present inventors will first be briefly described.

[0014] <Brief description of the findings of the invention> Conventionally, purification materials containing steelmaking slag have been proposed with the aim of enabling environmental conservation by suppressing the generation of sulfides from bottom sediments. From the viewpoint of this aim, for example, granular purification materials (see Patent Documents 1 and 2) and molded slag that disintegrate in an aqueous environment and turn into sand (see Patent Document 3) are known. Also known is a molded slag that slowly releases iron (Fe) into the seawater (see Patent Document 5).

[0015] The present inventors have conducted extensive research into important factors for increasing or stabilizing the populations of marine resources and have discovered the following: Bottom sediments are home to benthic organisms such as sea cucumbers, shrimp, bivalves (such as clams), and lugworms, some of which serve as food for migratory fish and shellfish such as squid. Among these benthic organisms are burrowing organisms that move vertically within the sea sand. Furthermore, because many benthic organisms undergo a planktonic larval stage during their life cycle, their sizes vary widely, from extremely small to those visible to the naked eye. The presence of a wide variety of organisms, both large and small, in the bottom sediments, including burrowing organisms, can be an important factor in securing marine resources.

[0016] Experiments conducted by the inventors have shown that benthic organisms are more likely to increase when the bottom sediment contains gravel with a diameter of approximately 10 to 50 mm. This is thought to be because sandy bottom sediment, which is suitable for sediment-dwelling organisms, can prevent the settlement of planktonic larvae if it becomes unstable due to sediment drift. Conversely, if the bottom sediment contains large particles that inhibit sediment drift, the settlement of planktonic larvae is promoted. Furthermore, it was found that if the gravel has a complex shape, the increased number of pores makes it easier for organisms to attach, thereby increasing the effect of increasing benthic organisms.

[0017] Based on the above, the inventors came up with the idea that by laying gravel-like materials with spaces (pores) of various sizes in which organisms can live in an aquatic environment, it is possible to effectively increase the number of benthic organisms, and as a result, to increase the number of organisms in the aquatic environment.

[0018] Although steelmaking slag is crushed or pulverized in the manufacturing process, it is not in a form suitable for use as bottom sediment in its original state, and is therefore processed appropriately depending on the intended use in the marine area. Until now, no material suitable for the settlement of planktonic larvae or the burrowing of organisms has been anticipated.

[0019] For example, Patent Document 4 describes a stone material whose open porosity is adjusted to 10% or more by supplying carbon dioxide to a packed tank or compact of steelmaking slag powder and solidifying it with the calcium carbonate that is produced. This type of technology can increase the open porosity of the stone material by adjusting the particle size of the raw materials.

[0020] However, adjusting the particle size of the raw materials to increase porosity results in increased voids between the raw material particles, resulting in extremely low strength immediately after molding, even with the use of binders. This makes it difficult to maintain the shape immediately after molding, and it is also difficult to mold the raw materials into pebbles before solidification by the formation of calcium carbonate. Therefore, when considering mass production of pebbles, it is necessary to carry out a long carbonation process while filling numerous molds or containers with the raw materials, resulting in poor production efficiency. Alternatively, carbonation of large-sized particles in a large-capacity container and then crushing them to pebbles is also possible, but this not only requires a large amount of energy for crushing, but also generates a large amount of dust during the manufacturing and transportation processes, making them difficult to handle.

[0021] In contrast to the conventional techniques described above, the slag granules of this embodiment contain a slag raw material (steelmaking slag) and a swelling agent. They are easy to manufacture and have the property of increasing porosity simply by contacting them with water. The slag compacts of this embodiment are produced by partially disintegrating the slag granules by contacting them with water, e.g., by immersing them in an aqueous environment. These slag compacts function like gravel in the bottom sediment and have open pores that can be used as habitats for benthic organisms. By laying the slag granules or slag compacts of this embodiment on the bottom sediment, they can be used as materials with a shape suitable for the habitat of benthic organisms, as well as for the settlement of planktonic larvae in the bottom sediment and for the burrowing of organisms.

[0022] The swelling material absorbs water and expands upon contact with water. The swelling material is a substance that promotes the disintegration of the slag granules in an aqueous environment. Stress generated inside the slag granules causes numerous cracks to form inside the slag granules. This promotes the disintegration of the slag granules. The aqueous environment in this embodiment is not particularly limited as long as it is an environment in which water is present, but is typically an environment in which slag granules or slag compacts are introduced to provide a habitat for living organisms, such as seawater, freshwater, brackish water near a river mouth, lake water, swamp water, etc.

[0023] In this embodiment, the slag granules do not disintegrate in an aqueous environment by breaking down into fine pieces, but by forming open pores. In other words, the slag granules gradually disintegrate in an aqueous environment by the function of the swelling agent, forming open pores. After the disintegration phenomenon stops (i.e., after the progress of disintegration stops), the granules change into porous slag compacts.

[0024] As described above, the inventors have discovered the following and have arrived at the present invention. Specifically, by appropriately utilizing the collapse phenomenon caused by a swelling agent, it is possible to efficiently produce slag molded bodies having a particle size of 10 mm to 50 mm and a shape that is favorable for benthic organisms to live in, including many open pores. For example, by laying a large number of slag molded bodies on the bottom sediment, it is possible to stably and efficiently increase benthic organisms in an aquatic environment. As a result, it is possible to effectively increase the number of organisms in the aquatic environment.

[0025] <Slag granules and compacted slag> An example of the slag granules and slag compacts according to one embodiment of the present invention, as well as the collapse phenomenon of the slag granules, will be described with reference to Figure 1. Figure 1 is a schematic diagram showing the process of open pore formation in a slag granule 1 according to this embodiment while immersed in a water environment. The slag granules and slag compacts are not limited to the shapes shown in Figure 1 (e.g., a substantially oblate spheroid), and may actually have an irregular shape. The slag granules may have a particle size of 20 mm or more and 50 mm or less, and the slag compacts may have a particle size of 10 mm or more and 50 mm or less.

[0026] In the present invention, "particle size of A mm or more and B mm or less" means a particle size that passes through a sieve with a mesh size of B mm but does not pass through a sieve with a mesh size of A mm. Slag granules are particles that pass through a sieve with a mesh size of 50 mm but do not pass through a sieve with a mesh size of 20 mm. Slag compacts, which will be described later, are particles that pass through a sieve with a mesh size of 50 mm but do not pass through a sieve with a mesh size of 10 mm.

[0027] As shown in FIG. 1, the slag granules 1 of this embodiment include slag granules 2, which are powdered steelmaking slag, a swelling agent 3 that expands upon contact with water, and a binder 4 that binds the slag granules 2 and the swelling agent 3 together. FIG. 1 is a schematic diagram, and the slag granules 2 and the swelling agent 3 will naturally have irregular shapes in reality. The swelling agent 3 and the binder 4 may be present in the gaps between the slag granules 2, which account for the majority of the volume of the slag granules 1. For clarity, FIG. 1 shows an example in which one slag granule 1 is placed in an aqueous environment. In practice, multiple slag granules 1 may be placed in an aqueous environment.

[0028] The slag molded body 10 in this embodiment can be formed from the slag granules 1, which are easy to manufacture and handle. For example, the slag granules 1 can be placed in an aqueous environment, where they partially collapse on the bottom sediment B, forming cracks C, resulting in a porous slag molded body 10. The slag molded body 10 has a main body 11 and numerous open pores 12 formed in the main body 11. The slag molded body 10 changes into a complex shape as it becomes porous. Therefore, the slag molded body 10 has a large surface area and functions well as a settlement site for planktonic larvae and a habitat for sessile organisms. In this embodiment, the slag granules 1 are immersed in seawater W, which is an example of an aqueous environment.

[0029] The collapse phenomenon of the slag granules 1 will be explained below. When immersed in a water environment, cracks C occur in the slag granules 1. The collapse phenomenon of the slag granules 1 is a phenomenon in which the bonds between the particles of the slag raw material that made up the slag granules 1 separate in part of the slag granules 1. The collapse phenomenon also includes the phenomenon in which the slag granules 1 splits into multiple pieces.

[0030] The slag granules 1 in the aqueous environment are collected and sieved together with the fragments 20 generated by the disintegration. The progress of disintegration can be quantitatively assessed from the increase in the amount of the under-sieve (fragments 20). Specifically, the disintegration rate can be calculated by dividing the weight of the under-sieve by the weight of the slag granules 1 before disintegration. The weight of the slag granules 1 before disintegration is the weight of the slag granules 1 before they are first immersed in a liquid containing water. The mesh size of the sieve used to investigate the disintegration rate can be, for example, 10 mm. Regardless of the total length of the immersion period in the aqueous environment, if the change in the disintegration rate per week is within 3%, it is determined that the disintegration phenomenon of the slag granules 1 has stopped (the progress of disintegration has stagnated). For example, the disintegration rate is measured every week after the start of immersion in the aqueous environment, and the first disintegration rate when the change in disintegration rate per week is within 3% can be taken as the disintegration rate of the slag granules 1 in this embodiment.

[0031] The "open pores" of the slag molded body 10 are pores present in the slag molded body 10 that are open toward the outside of the slag molded body 10 and allow seawater W and living organisms to penetrate. On the other hand, the "closed pores" are pores present inside the slag molded body 10 and, unlike the open pores, are pores that do not allow seawater W and living organisms to penetrate. In other words, the open pores 12 function to increase the number of living organisms by providing habitats for benthic organisms. From the viewpoint of increasing the number of benthic organisms, the higher the open porosity, the better. A more detailed definition of open pores will be described later.

[0032] The slag molded body 10 can effectively increase benthic organisms by having an open porosity of 3.0% by volume or more. If the open porosity of the slag molded body 10 is too high, the strength of the slag molded body 10 will be significantly reduced. Therefore, the open porosity of the slag molded body 10 is preferably less than 10.0% by volume.

[0033] If the slag granules 1 are prone to collapse and split into multiple pieces (generating many large fragments 20), it is difficult to increase the open porosity of the slag molded body 10. This is because if the cracks C form a closed curve on the surface of the slag granules 1, generating relatively large fragments 20, the portions from which the fragments 20 peel off form the surface of the slag molded body 10. Note that the open pores 12 may be formed by cracks C that penetrate the slag granules 1 from the surface to the interior. However, if the cracks C completely separate the main body 11, the slag molded body 10 will split.

[0034] The open porosity of the slag molded body 10 can be measured, for example, by analyzing three-dimensional images obtained by X-ray CT (X-ray Computed Tomography). The pore size to be measured is sufficient if it is possible to measure the range of 140 μm or more, which accounts for the majority of all pores contained in the slag molded body 10. Pores with a size less than 140 μm are less useful to benthic organisms. Therefore, pores with a size less than 140 μm may be ignored (they do not need to be included in the calculation of the open porosity). The open pores 12 of the slag molded body 10 in this embodiment are voids (pores) formed in the main body 11 that are connected to the outside and have a pore size of 140 μm or more as detected by X-ray CT. The open porosity of the slag molded body 10 is measured after it is removed from the aqueous environment onto land and, for example, allowed to dry naturally. However, the open porosity of the slag molded body 10 removed onto land does not substantially change from the open porosity of the slag molded body 10 in the aqueous environment.

[0035] By immersing the slag granules 1 in an aqueous environment and disintegrating them appropriately without breaking them into multiple pieces, a slag compact 10 with increased open porosity can be formed. For this reason, the slag granules 1 contain 0.5% by mass or more of the swelling agent 3. Furthermore, if the slag granules 1 continue to disintegrate in an aqueous environment and the disintegration rate becomes excessively high, most of the slag granules 1 will turn into small-grained sand. In this case, it is difficult to efficiently produce slag compacts 10 with grain sizes of 10 mm or more. Therefore, the slag granules 1 contain 2.0% by mass or less of the swelling agent 3 in order to keep the disintegration rate due to immersion in an aqueous environment low. The disintegration rate of the slag granules 1 when immersed in an aqueous environment is 10% to 60%.

[0036] The content of the swelling material 3 in the slag molded body 10 of this embodiment is equivalent to the content of the swelling material 3 in the slag granules 1. Therefore, the slag molded body 10 may contain the swelling material 3 in an amount of 0.5 mass % or more and 2.0 mass % or less.

[0037] In this embodiment, if the particle size of the slag granules 1 is excessively large, handling becomes difficult and it takes time for the granules to disintegrate after immersion in an aqueous environment. In this case, production efficiency decreases. Furthermore, if the particle size of the slag granules 1 is excessively small, the size of the granules decreases due to disintegration. In this case, it is difficult to maintain the particle size of the slag molded body 10 at 10 mm or more. Therefore, the granules 1 may have a particle size of 20 mm or more and 50 mm or less.

[0038] The slag molded bodies 10 function as gravel in an aquatic environment. Therefore, the slag molded bodies 10 may have a particle size of 10 mm or more and 50 mm or less. If the particle size of the slag molded bodies 10 is less than 10 mm, they have a particle size similar to that of sea sand and are easily dispersed by tidal currents, making it difficult to efficiently increase benthic organisms. If the particle size of the slag molded bodies 10 exceeds 50 mm, they are stably located in the bottom sediment B, and may function as a useful attachment site for seaweed, but their contribution to the increase of benthic organisms, which is their original purpose, is reduced. This is because it becomes difficult for benthic organisms to push aside the slag molded bodies 10, reducing the mobility of benthic organisms in the bottom sediment B.

[0039] As described above, the slag granules 1 according to this embodiment have the property of increasing the open pores simply by contacting them with water. When the slag granules 1 are immersed in a water environment to allow the collapse phenomenon to progress, the open porosity after the increase in the collapse rate stagnates becomes 3.0% by volume or more. This allows the formation of a slag molded body 10.

[0040] The slag molded bodies 10 in this embodiment have the above-described configuration and function as a habitat for benthic organisms of various sizes, from microscopic to visible in an aquatic environment, thereby contributing to the increase of marine resources. For example, by introducing a large number of slag granules 1 or slag molded bodies 10 into an aquatic environment, it is possible to construct a substrate (substrate) on the bottom sediment. This method of increasing benthic organisms (method for increasing benthic organisms) is also included in the scope of the present invention.

[0041] In addition, without being limited to the example of this embodiment, the slag molded body 10 may be formed by immersing the slag granulated material 1 in water such as an aquarium on land, or a pre-formed slag molded body 10 may be introduced into an aquatic environment in which it is desired to increase the number of living organisms.

[0042] <Method of manufacturing granulated slag and compacted slag> An example of a method for producing the granulated slag 1 and the molded slag 10 according to one embodiment of the present invention will be described.

[0043] First, the raw materials and mixtures used for the granulated slag 1 and the molded slag 10 will be described below.

[0044] (Slag granular material) The slag powder 2 is a powder of steelmaking slag. Steelmaking slag is a preferred slag used as a raw material for the slag granules 1 and the slag molded bodies 10, and is a by-product generated in large quantities in the steelmaking process. Examples of steelmaking slag include converter slag, electric furnace slag, pre-treated slag, decarburized slag, desulfurized slag, dephosphorized slag, desiliconized slag, electric furnace oxidized slag, electric furnace reduced slag, secondary refining slag, and ingot casting slag. The slag powder 2 may also be a powder of a mixture of these slags.

[0045] The slag granules 2 contain elements such as iron (Fe), manganese (Mn), calcium (Ca), magnesium (Mg), silicon (Si), and phosphorus (P). The slag molded body 10 contains the slag granules 2, and thus has the function of eluting iron, which is useful for living organisms, in the aquatic environment. The slag granules 1 and the slag molded body 10 may also have the function of eluting components other than iron among the above elements in order to improve the aquatic environment. In particular, P can effectively contribute as a nutrient for phytoplankton and seaweed.

[0046] In one embodiment of the present invention, the slag powder 2 used as the raw material for the slag granules 1 and slag molded bodies 10 is preferably in a powdered form. The particle size of the slag powder 2 may be adjusted appropriately, taking into consideration the strength, collapsibility, and particle size of the fragments 20 of the slag molded body 10. When the slag powder 2 is in a powdered form, an excessively large particle size reduces the strength of the slag granules 1 and slag molded bodies 10, so the particle size of the slag powder 2 may be adjusted to 7.0 mm or less, or 5.0 mm or less. When the slag powder 2 is in a powdered form, there is no particular restriction on the lower limit of the particle size of the slag powder 2. Considering the need to allow the fragments 20 generated when the slag granules 1 disintegrate in an aqueous environment to function as sea sand, the yield of the manufacturing process for the slag granules 1 (the moldability of the powder granules), and the strength of the slag granules 1, it is desirable that the slag granules 1 contain slag powder granules 2 with a particle size of 1.0 mm or less.

[0047] Furthermore, the slag powder 2 used as the raw material may be used in a state where alkali elution in an aqueous environment is suppressed by, for example, aging treatment before or after particle size adjustment, as necessary. Slag powder 2 that has been subjected to a carbonation treatment or a treatment of immersion in hydrochloric acid or sulfuric acid may also be used. Preferably, slag powder 2 that has been subjected to a carbonation treatment after particle size adjustment may also be used. Furthermore, since carbonation treatment of the slag granules 1 solidifies the granules and inhibits disintegration, it is preferable to perform the carbonation treatment on the powdered slag raw material before producing the granules 1.

[0048] (swelling material) The swelling material 3 has the property of expanding in volume upon contact with water, and is mixed with the slag granules 2 and contained in the slag granules 1 for the purpose of imparting disintegration properties to the slag granules 1 .

[0049] In one embodiment of the present invention, the slag granules 1 and the slag molded body 10 contain 0.5% by mass or more and 2.0% by mass or less of the swelling material 3. The slag granules 1 and the slag molded body 10 may contain one type of swelling material 3 or multiple types of swelling materials 3.

[0050] The volume expansion ratio can be used to evaluate the function of the swelling material 3. The volume expansion ratio of the swelling material 3 is preferably 4.0 or more from the viewpoint of efficiently imparting collapsibility. By adjusting the mixing ratio of the swelling material 3 with the slag granular material 2, it is possible to impart appropriate collapsibility. If the volume expansion ratio of the swelling material 3 is too high, it becomes difficult to control the collapse behavior, so the volume expansion ratio of the swelling material 3 is preferably 10.0 or less.

[0051] Here, the volume expansion ratio is calculated based on the change in volume of the swelling material 3 when it is immersed in a sufficient amount of water. Specifically, for example, it is as follows. The unit volume mass of the swelling material 3 before and after immersion is measured in accordance with JIS A 1104 (unit volume mass of aggregate). The weight of the swelling material 3 includes the weight of water. Therefore, the weight (mass) of the swelling material 3 in a dried state before immersion (for convenience of explanation, referred to as "dry swelling material D") is used to calculate the unit volume mass. The volume per unit mass is calculated by taking the reciprocal of the unit volume mass using the mass of the dry swelling material D. The volume expansion ratio is calculated as the ratio of the following values ​​A and B: Value A: Volume of swelling material 3 before immersion in water ÷ Mass of dry swelling material D Value B: Volume of swelling material 3 after immersion in water ÷ mass of dry swelling material D.

[0052] The weight of the dry swelling material D can also be determined from the weight and moisture content of the swelling material 3 after immersion. The volume expansion ratio can also be calculated based on the dry base density (unit volume mass) of the swelling material 3 before and after immersion using the mass of the dry swelling material D.

[0053] The swelling material 3 is preferably immersed in a sufficient amount of water, with a weight of at least 100 times the dry weight of the swelling material 3 (the weight of the above-mentioned dry swelling material D). The water in which the swelling material 3 is immersed is preferably the same as the water environment in which the slag granules 1 and slag molded bodies 10 are used. For example, the water in which the swelling material 3 is immersed is preferably seawater when the slag granules 1 and slag molded bodies 10 are used in the sea, and freshwater when they are used in rivers or lakes. The immersion time of the swelling material 3 is the time until the moisture content of the swelling material 3 reaches saturation.

[0054] If the content of swelling agent 3 when mixed exceeds 2.0% by mass, the strength of the slag granules 1 may be reduced more than necessary, and the slag granules 1 may completely disintegrate and become only sandy during immersion in a water environment. Therefore, the content of swelling agent 3 may be 2.0% by mass or less, or may be 1.5% by mass or less.

[0055] In the present invention, unless otherwise specified, the content of the swelling agent 3 refers to the ratio of the weight of the swelling agent 3 (in a dry state) to the total weight of the slag granules 2 and the swelling agent 3 (in a dry state). Therefore, the content of the swelling agent 3 in the slag granules 1 can be determined, for example, as follows: The binder 4 and the like are removed from the slag granules 1 to obtain a mixture of the slag granules 2 and the swelling agent 3. The mixture is then dried. The ratio of the weight of the swelling agent 3 (in a dry state) in the mixture to the weight of the mixture after drying is calculated. The same applies to the slag molded body 10.

[0056] The swelling material 3 contained in the slag molded body 10 is preferably biodegradable to reduce the burden on the environment. For example, the swelling material 3 may include plant residues generated in food and beverage factories, discarded agricultural crops, and materials containing dietary fiber, such as marine algae harvested or collected as waste. To reduce procurement costs, it is preferable to use plant residues generated in food and beverage factories. Examples of materials that can be used as the swelling material 3 include wakame seaweed stems, citrus peels, and coffee grounds. In this case, the volume expansion ratio of the swelling material 3 is approximately 3 to 6.

[0057] (binder) The binder 4 is mixed with the granulated slag 1 in order to improve the yield when the granulated slag 1 is molded and to increase the strength after molding.

[0058] Examples of binders 4 include lignosulfonic acid, metal salts of lignosulfonic acid, molasses, and starch. When lignosulfonic acid or molasses is added, the amount of binder 4 added is preferably 2% by mass or more and 10% by mass or less of the total mass of the slag granules 2 and the swelling material 3, taking into consideration the cost and the strength of the slag granules 1.

[0059] Lignin sulfonic acid and its metal salts are suitable for use as binders due to their excellent dispersibility and caking properties. Lignin sulfonic acid and its metal salts have iron chelating properties, which increase the amount of iron eluted from the slag granules 2, the raw material for the slag compacts 10, in an aqueous environment. Iron is an essential element for the growth of many living organisms, and it is therefore preferable to use lignin sulfonic acid to supply iron to these organisms.

[0060] When a metal salt of lignosulfonic acid is used, the type of metal element may be appropriately selected, and may be, for example, metals such as sodium (Na) or potassium (K), with Mg, Ca, or Na being preferred in consideration of ease of handling and cost.

[0061] The form of lignosulfonic acid and its metal salts can be selected appropriately, and they can be added in the form of a powder or an aqueous solution during the production process.

[0062] (manufacturing process) The manufacturing process of the molded slag 10 will be described with reference to FIGS.

[0063] As shown in FIG. 2, an example of a method for manufacturing the slag molded body 10 in this embodiment includes a preparation step S1 for preparing the slag granulated material 1, and a formation step S2 for forming the slag molded body 10 by bringing the slag granulated material 1 into contact with water to partially disintegrate it.

[0064] In the preparation step S1, it is sufficient to prepare the slag granules 1, and the specific method for preparing the slag granules 1 is not particularly limited. For example, the slag granules 1 may be prepared by obtaining manufactured slag granules 1. Alternatively, the slag granules 1 may be manufactured. In this case, an example of a method for manufacturing the slag molded body 10 in this embodiment may include a raw material mixing step S11 for mixing raw materials and a slag granule molding step S12 for producing the slag granules 1, as shown in FIG. 3 .

[0065] In the raw material mixing step S11, the slag powder 2 is mixed with a swelling agent 3 and a binder 4. The equipment used for mixing is not specifically limited, but can be appropriately selected from, for example, a kneader, a paddle mixer, etc. Considering production efficiency and the strength of the granulated slag, it is preferable to use a kneader.

[0066] In the slag granule forming step S12, the mixture obtained in the raw material mixing step S11 is granulated and formed to produce slag granules 1. The equipment used for forming is not specifically limited, but can be appropriately selected from, for example, a briquetting machine, pan pelletizer, drum mixer, rotary mixer, compression molding press, etc. Considering production efficiency and the strength of the slag granules, it is preferable to use a briquetting machine.

[0067] In the forming step S2, for example, the slag granules 1 are immersed in an aqueous environment. Alternatively, the slag molded bodies 10 may be formed on land in advance and then introduced into the aqueous environment. For example, the slag granules 1 may be immersed in water having the same or different composition as the aqueous environment in which the slag molded bodies 10 are to be placed to form the slag molded bodies 10, and then the slag molded bodies 10 may be introduced into the aqueous environment.

[0068] In order to improve the effect of increasing the number of living organisms in the slag molded bodies 10, environmental water identical to the environment in which the slag molded bodies 10 are placed may be poured over the slag molded bodies 10, so that floating larvae originating from the environmental water can be allowed to settle and grow on the bottom of the slag molded bodies 10 in advance. The solid-liquid ratio (ratio of the volume of liquid to the volume of the slag granules 1) in the formation step S2 is preferably 3 or more, more preferably 5 or more. When the immersion treatment is carried out in a land-based water tank, a high solid-liquid ratio requires a large amount of space for the immersion treatment, so the solid-liquid ratio for the immersion treatment is preferably 10 or less.

[0069] To understand the disintegration behavior of the slag granules 1 in the forming step S2, an indoor immersion test may be performed in advance. For example, the slag granules 1 may be immersed in a solvent similar to the aqueous environment to which they will be introduced at a solid-liquid ratio of 5. By performing this immersion test multiple times and investigating the change in the disintegration rate, it is possible to understand in advance the time until the disintegration of the slag granules 1 stops.

[0070] The manufacturing method of this embodiment makes it possible to manufacture a molded slag body 10, which is a molded body in which the slag granules 1 are partially disintegrated by contact with water and the disintegration phenomenon has stopped. The molded slag body 10 has a porous shape.

[0071] [Additional notes] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in the above description are also included in the technical scope of the present invention. [Example]

[0072] Examples of granulated slag and molded slag according to one embodiment of the present invention will be described below, but the present invention is not limited to these examples.

[0073] The chemical compositions of the steelmaking slag, swelling agent, and binder used as raw materials are shown in Table 1. The chemical compositions of various swelling agents and binders were measured in the dry state.

[0074] [Table 1]

[0075] The steelmaking slag and swelling agent were pretreated as shown in Table 2. For the steelmaking slag, pulverized and classified to 5 mm or less was carbonated for 1 hour and used as the raw material.

[0076] [Table 2]

[0077] The pretreated slag powder, various swelling agents, and binders were mixed to the mixing ratios shown in Table 3, and mixed for 5 minutes using a kneader while adding water as needed. The swelling agents were dried at 60°C for 12 hours or more before mixing, crushed to 5 mm or less, and passed through a 5 mm sieve. The under-sieve material was used as the mixing material.

[0078] In Table 3, the "addition amount [included]" of the swelling agent is the weight of the swelling agent divided by the total amount of the slag powder and swelling agent, expressed as a percentage (mass %). The "addition ratio [excluded from the total weight of the slag and swelling agent]" of the binder is the weight of the binder divided by the total amount of the slag powder and swelling agent, expressed as a percentage (mass %). For example, in Example No. 1 in Table 3, "slag powder + swelling agent" is 100 mass%, and the blending ratio is (slag powder: swelling agent): binder = (99:1):10.

[0079] Each mixed sample was shaped into particles of 30 mm, 45 mm, or 60 mm using a briquette machine, and the resulting slag granules were dried at 105°C for 12 hours.

[0080] (Indoor immersion test) An indoor immersion test was conducted on the obtained slag granules of each Example and Comparative Example. They were immersed for four weeks in a beaker containing artificial seawater to achieve a solid-liquid ratio of 5, and the disintegration rate was measured every week. The disintegration rate was calculated by dividing the weight of the granules that had passed through a 10 mm sieve by the weight of the granules that had not passed through the sieve. The test results are shown in Table 3. In all Examples, the disintegration rate of the granules remained within 3% from the third to fourth week, and it was determined that the disintegration phenomenon had stopped within four weeks. In Comparative Examples, when the amount of swelling agent added was 3% or more, the disintegration rate exceeded 70% after the second or third week, resulting in low production of slag compacts. In the other Comparative Examples, the disintegration phenomenon stopped within four weeks.

[0081] [Table 3]

[0082] (Panlite water tank immersion test) The resulting granulated slag of each of the Examples and Comparative Examples was subjected to a Panlite water tank immersion test.

[0083] A Panlite tank of approximately 1000 L filled with seawater was prepared, and 100 kg of granulated slag was placed in a plastic container and immersed in the tank for 4 weeks without changing the water, producing a slag compact.

[0084] After immersion in the Panlite tank, all immersion samples were sieved through a 10 mm sieve to determine their disintegration rates. The disintegration rates after immersion in the Panlite tank were similar to those of the results of the above-mentioned indoor immersion test (the disintegration rate at the point when the disintegration phenomenon stopped). In the comparative examples, where the disintegration rate exceeded 60% after immersion in the Panlite tank, satisfactory slag compacts were not obtained. Therefore, as described below, an actual seawater immersion test was conducted using the slag granules of the examples and comparative examples, which had disintegration rates of 60% or less.

[0085] Figure 4 is an optical photograph showing an example of a sample (slag compact) recovered after immersion in a Panlite water tank. Approximately 200 g of each immersion sample (slag compact) from each Example and Comparative Example was collected from the Panlite water tank and air-dried. Each immersion sample was then placed in a plastic container and subjected to open porosity measurement using X-ray CT. The X-ray CT measurement device used was a TDM3000H-FP (Yamato Scientific Co., Ltd.). The radiation source was white X-rays, the X-ray tube voltage was adjusted to 250 kV, and the measurement focal size was adjusted to φ4 μm. X-ray CT images of the test materials were analyzed using 3D image analysis software (VGSTUDIO MAX, Volume Graphics Co., Ltd.). The total volume of open pores and the total volume of the slag compact (including open and closed pores) were calculated, and the open porosity was calculated by dividing the total volume of open pores by the total volume of the slag compact. The lower limit of particle size (pore size) for open porosity using this method is 140 μm. Table 4 shows the measurement results of the disintegration rate of the slag granules after immersion in the Panlite water tank, the open porosity of the slag granules before immersion in the Panlite water tank, and the open porosity of the slag compacts after immersion in the Panlite water tank in the Panlite water tank.

[0086] (Actual seawater immersion test) Of the slag granules obtained in each example and comparative example, those in examples 1 to 5 and comparative examples 7, 8, 11, 12, and 16, which showed a disintegration rate of 60% or less in the Panlite tank immersion test described above, were released into an actual sea area to test for the growth of benthic organisms. The target sea area was the Seto Inland Sea, where the tidal currents are gentle and the bottom sediment is nearly sandy. 40 kg of slag granules were placed in a rectangular polypropylene container with a fully open top and placed on the seabed. The slag granules were placed in a range of 5 to 10 m from the coast toward the open sea, at a depth of approximately 3 to 4 m, and immersed for approximately one year.

[0087] After immersion in the actual sea, the slag compacts were pulled up together with the case, and any rubbish or migratory fish and shellfish that had become mixed in the case were removed to obtain a recovered sample. After measuring the bulk density and weight of the recovered sample, the organisms in the recovered sample, including those attached to the slag compacts, were sieved through a 1 mm sieve, and the weight of the organisms on the sieve was measured. The weight of the organisms per bulk volume (kg / m) was calculated from the weight, bulk density, and organism weight of the recovered sample. 3 ) was sought.

[0088] Table 4 shows the results of the survey on the increase of benthic organisms in the actual seawater immersion test.

[0089] [Table 4]

[0090] As shown in Table 4, in the examples where the open porosity of the slag compacts was 3.0% by volume or more and the particle size of the slag compacts (similar to the particle size of the granulated slag introduced into actual marine areas) was 50 mm or less, the biological weight (benthos) was higher than in the comparative examples, indicating the presence of abundant benthic organisms, and that these are good bottom sediment materials. The higher the open porosity of the slag compacts, the higher the benthic organism weight tends to be, indicating that increasing the open porosity can increase the benthic organisms. It can be seen that the slag compacts of the examples are capable of efficiently increasing the benthic organisms.

[0091] On the other hand, in the comparative examples in which the open porosity of the slag molded body was less than 3.0% or the particle size exceeded 50 mm, the presence of benthic organisms was observed, but the organism weight was lower than in the examples. [Explanation of symbols]

[0092] 1. Slag granules 2. Slag powder (steelmaking slag powder) 3 Swelling material 4. Binder 10. Slag compact 11 Main body 12 Open pores 20 Fragments B. Bottom sediment C Crack W Seawater

Claims

1. A slag granule, The composition comprises a powder of steelmaking slag, a swelling material that expands upon contact with water, and a binder that binds the powder of steelmaking slag and the swelling material together, The particle size of the slag granules is 20 mm or more and 50 mm or less, The ratio of the swelling agent to the total mass of the steelmaking slag powder and the swelling agent is 0.5 mass% or more and 2.0 mass% or less, The ratio of the binder to the total mass of the steelmaking slag powder and the swelling material is 6% by mass or more and 10% by mass or less, A granulated slag characterized by its ability to increase open pores simply by contacting it with water.

2. The open pores are pores that are open to the outside and have a pore size detected by X-ray CT of 140 μm cubed [μm 3 ] or more; 2. The slag granules according to claim 1, characterized in that when the granules are immersed in an aqueous environment to allow the disintegration phenomenon to progress, the open porosity after the increase in the disintegration rate stagnates is 3.0% by volume or more.

3. A slag granule as described in claim 1, wherein the ratio of the swelling material to the total mass of the steelmaking slag powder and the swelling material is 0.5 mass% or more and 1.5 mass% or less.

4. 3. The slag granules according to claim 2, wherein the binder is one or more selected from the group consisting of lignosulfonic acid, metal salts of lignosulfonic acid, molasses, and starch.

5. 3. The slag granules according to claim 2, wherein the disintegration rate when immersed in a water environment is 10% or more and 60% or less.

6. A slag molded body, The composition comprises a powder of steelmaking slag, a swelling material that expands upon contact with water, and a binder that binds the powder of steelmaking slag and the swelling material together, The ratio of the swelling agent to the total mass of the steelmaking slag powder and the swelling agent is 0.5 mass% or more and 2.0 mass% or less, The particle size of the slag molded body is 10 mm or more and 50 mm or less, The ratio of the binder to the total mass of the steelmaking slag powder and the swelling material is 6% by mass or more and 10% by mass or less, A slag molded body having an open porosity of 3.0% by volume or more.

7. A method for producing a slag molded body, a preparation step of preparing a slag granule containing steelmaking slag powder, a swelling material that expands upon contact with water, and a binder that integrates the steelmaking slag powder and the swelling material; and a forming step of forming a slag molded body having an open porosity increased compared to the slag granules by bringing the slag granules into contact with water and partially disintegrating the slag granules, The slag granules have a particle size of 20 mm or more and 50 mm or less, a ratio of the swelling agent to the total mass of the steelmaking slag powder and the swelling agent is 0.5 mass% or more and 2.0 mass% or less, and a ratio of the binder to the total mass of the steelmaking slag powder and the swelling agent is 6 mass% or more and 10 mass% or less, The method for producing a molded slag body, wherein the molded slag body has an open porosity of 3.0% by volume or more.

8. The preparation step includes: a raw material mixing step of mixing the binder and 0.5% by mass or more and 2.0% by mass or less of the swelling material with the steelmaking slag powder; 8. The method for producing a molded slag body according to claim 7, further comprising a slag granule molding step of granulating and molding the mixture obtained in the raw material mixing step to produce the slag granules.

9. A method for increasing benthic organisms, comprising laying the granulated slag according to any one of claims 1 to 5 or the molded slag according to claim 6 in an aqueous environment.

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