Fertilizer for marine areas and method for manufacturing fertilizer for marine areas

Abstract

To provide a marine fertilizer and a method for manufacturing a marine fertilizer that can supply Fe from steelmaking slag without scattering after installation in the sea. [Solution] The marine fertilizer according to the present invention consists of a molded body obtained by mixing steelmaking slag and fermented fertilizer, wherein the molded body contains the steelmaking slag in an amount of 20 to 75% by mass relative to the total dry mass of the steelmaking slag and the fermented fertilizer, and the content of water-soluble phosphoric acid in the fermented fertilizer is in the range of 0.5 to 4.0% by mass.

Description

Technical Field

[0001] The present invention relates to a fertilizer for sea areas and a method for producing a fertilizer for sea areas. Background Art

[0002] In recent years, the reduction of seaweed beds in coastal waters has progressed nationwide, which has become a major problem leading to the decrease of fishery resources. On the other hand, like forests on land, seaweed beds absorb carbon dioxide, so they are recognized as important resources that contribute to countermeasures against global warming. However, the reduction of seaweed beds is becoming serious nationwide, and multiple causes such as water temperature rise accompanying global warming, increase of herbivores, and lack of nutrient salts are often mixed. Therefore, various countermeasures have been implemented according to the causes of seaweed bed reduction. Here, for nutrient salt deficiency, which is one of the causes of seaweed bed reduction, it is useful to supply Fe, N, and P as main nutrient salts for seaweed.

[0003] Steelmaking slag is a by-product generated in large quantities in the iron-making process (steelmaking process), and is mainly recycled for onshore uses such as roadbed materials and site preparation materials. For steelmaking slag, expansion of recycling applications is required, and the development of utilization technologies in sea areas is being promoted.

[0004] Since steelmaking slag is rich in Fe, it has attracted attention as a material related to Fe supply among the above-mentioned nutrient salts. However, although steelmaking slag is crushed and pulverized in the manufacturing process, if steelmaking slag is directly introduced into sea areas as a fertilizer, it will scatter and turbid the surrounding seawater, which may adversely affect surrounding aquatic organisms. In addition, if the installed fertilizer disappears at an early stage due to scattering, the long-term sustainability of the fertilization effect is impaired, and nutrient salts cannot be supplied efficiently. Therefore, steelmaking slag generated from the manufacturing process is not in a suitable form as a fertilizer as it is, and is required to be appropriately treated so as not to scatter and disappear immediately after or early after being installed in sea areas.

[0005] Furthermore, fermented fertilizers are also useful materials as a source of nutrients for seaweed. Fermented fertilizers refer to all fertilizers in which organic matter, such as natural materials (e.g., plants, manure, etc.), food waste, fish meal, and water treatment sludge, is decomposed or fermented by microorganisms and fungi. The above decomposition and fermentation include all processes, whether natural or artificial.

[0006] There are various types of fermented fertilizers. For example, plant-derived fertilizers include fermented fallen leaves, tree bark, or spent mushroom substrate. Livestock-derived fertilizers include animal manure from the livestock industry. Much of this is fermented to make it suitable for agricultural use and is widely distributed. These livestock-derived fermented fertilizers contain more N and P, which are useful for seaweed, compared to plant-derived fermented fertilizers, and some of the N and P are converted into inorganic substances through the fermentation process. Since these inorganic N and P are easily absorbed by seaweed, livestock-derived fermented fertilizers are also useful materials for marine fertilization.

[0007] One type of fermented fertilizer derived from livestock farming, as described above, is made from fermented chicken manure generated from poultry farming, which is then sold as fermented chicken manure. Poultry farming is a type of livestock farming that emits less carbon dioxide than other livestock farming industries. Therefore, in businesses that aim to absorb carbon dioxide by increasing seaweed beds, using fermented chicken manure derived from an industry with low carbon dioxide emissions is rational from the perspective of combating global warming. Furthermore, among fermented chicken manure products, processed poultry manure fertilizer, which is a fully fermented fertilizer, is available commercially. Because it contains a large amount of inorganic N and P due to sufficient fermentation, it can be expected to have a high fertilizing effect on seaweed.

[0008] An important role of these fermented fertilizers is to dissolve iron (Fe) from steelmaking slag. Although iron is normally insoluble in seawater, when steelmaking slag and fermented fertilizers are mixed, the organic acids in the fermented fertilizers combine with the iron in the steelmaking slag in the sea, chelating it and supplying dissolved iron to seaweed.

[0009] Furthermore, when these fermented fertilizers are used as fertilizers for marine areas, measures to prevent scattering are necessary to enhance their effectiveness, for the same reasons as with steelmaking slag. Effective fertilizers or methods for preventing scattering are publicly available as follows.

[0010] For example, Patent Document 1 discloses a method for supplying iron by laying a mixture of steelmaking slag and dredged soil containing fulvic acid in layers on the seabed. In this method, the fulvic acid promotes the leaching of Fe contained in the steelmaking slag, and it is possible to carry out construction efficiently on a large scale without scattering the dredged soil.

[0011] Furthermore, Patent Documents 2 and 3 disclose a method of supplying fulvic acid iron, which is formed by the combination of divalent iron in the steel slag and fulvic acid contained in the woody humus and marine waste, by filling a permeable bag or the like with the mixture and placing it in water. In this method, since the steel slag and the mixture are placed in a permeable bag, the fertilizer can be installed without scattering the steel slag and the mixture in the seawater.

[0012] On the other hand, Patent Document 4 discloses a marine fertilizer consisting of a compressed molded body containing fermented chicken manure, granular iron (including steelmaking slag), and magnesium oxide. Such technology is expected to be used as a fertilizer for seaweed. Furthermore, Patent Document 4 mentions that the magnesium oxide added to the compressed molded body functions as a solidifying agent, and it is expected that the magnesium oxide will contribute to preventing scattering. [Prior art documents] [Patent Documents]

[0013] [Patent Document 1] Japanese Patent Publication No. 2011-155993 [Patent Document 2] Japanese Patent Publication No. 2005-34140 [Patent Document 3] Japanese Patent Publication No. 2006-345738 [Patent Document 4] Japanese Patent Publication No. 2021-113137 [Overview of the project] [Problems that the invention aims to solve]

[0014] However, the methods disclosed in Patent Documents 1 to 4 have room for improvement in the following respects.

[0015] For example, in the method disclosed in Patent Document 1 mentioned above, although steelmaking slag is added to prevent the scattering of dredged soil, it is difficult to completely suppress turbidity immediately after application, and there is a possibility of losing a large amount of fertilizer immediately after application. Furthermore, if the solidification reaction between steelmaking slag and dredged soil is enhanced in order to completely suppress turbidity and scattering, the amount of Fe leached out decreases significantly, so there is room for improvement from the standpoint of improving the efficiency of Fe supply.

[0016] Furthermore, in the methods disclosed in Patent Documents 2 and 3, if the permeable bag is damaged or naturally decomposes in seawater, exposing the inside of the bag, the steelmaking slag and its mixture inside will scatter. As permeable bags, natural materials such as coconut husks are used with consideration for the safety of living organisms, but with natural materials, the bag material decomposes particularly quickly, and the inside of the bag is easily exposed. Therefore, there is room for improvement from the standpoint of preventing scattering.

[0017] Furthermore, in the method disclosed in Patent Document 4 mentioned above, the material is compressed and molded on land, and magnesium oxide is added as a solidifying agent, so there is no concern about scattering. However, when steelmaking slag is used as granular iron, the magnesium oxide, which is the solidifying agent, reduces the amount of Fe leached from the steelmaking slag. Therefore, there is room for improvement in terms of supplying the iron contained in the steelmaking slag to seaweed.

[0018] In view of the above-mentioned situation, the present invention aims to provide a marine fertilizer and a method for manufacturing a marine fertilizer that can supply Fe from steelmaking slag without scattering after installation in the sea. [Means for Solving the Problem]

[0019] In order to solve the above-mentioned problem, the inventor of the present invention has conducted intensive studies, and as a result, found that if fermented fertilizer contains water-soluble phosphoric acid, the water-soluble phosphoric acid reacts with steelmaking slag to generate phosphate, whereby this solidification reaction can be utilized to prevent the scattering of the fertilizer in seawater, and thus completed the present invention. The gist of the present invention, which has been completed based on the above findings, is as follows.

[0020] (1) A fertilizer for sea areas, comprising a molded product obtained by mixing steelmaking slag and fermented fertilizer, wherein the molded product contains the steelmaking slag in an amount of 20 to 75% by mass based on the total dry mass of the steelmaking slag and the fermented fertilizer, and the content of water-soluble phosphoric acid in the fermented fertilizer is in the range of 0.50 to 4.00% by mass. (2) The fertilizer for sea areas according to (1), wherein the fermented fertilizer is a processed poultry manure fertilizer. (3) The fertilizer for sea areas according to (1) or (2), wherein the steelmaking slag is contained in an amount of 30 to 55% by mass based on the total dry mass of the steelmaking slag and the fermented fertilizer. (4) The fertilizer for sea areas according to (1) or (2), wherein the molded product is a columnar molded product. (5) The fertilizer for sea areas according to (1) or (2), which is a granular molded product having a particle size of more than 0 mm and 50 mm or less. (6) A method for producing a marine fertilizer comprising steelmaking slag and fermented fertilizer, the method comprising: a mixing step of mixing said fermented fertilizer having a water-soluble phosphoric acid content in a range of 0.50 to 4.00% by mass, said steelmaking slag, and water; and a forming step of compression-molding the obtained mixture and air-drying the mixture, wherein in the mixing step, after mixing said steelmaking slag and said fermented fertilizer such that the content of said steelmaking slag is 20 to 75% by mass relative to the total dry mass of said steelmaking slag and said fermented fertilizer, when the total of the total dry mass of said steelmaking slag and said fermented fertilizer and the mass of water is taken as 100% by mass, the addition amount of said water is adjusted such that the content of said water falls within the range of 30 to 55% by mass. (7) The method for producing a marine fertilizer according to (6), wherein processed poultry manure fertilizer is used as said fermented fertilizer. (8) The method for producing a marine fertilizer according to (6) or (7), further comprising a pretreatment step of pretreating at least one of said steelmaking slag and said fermented fertilizer prior to said mixing step, wherein in said pretreatment step, phosphate is added to said fermented fertilizer to adjust the content of water-soluble phosphoric acid in said fermented fertilizer to fall within the range of 0.50 to 4.00% by mass. (9) The method for producing a marine fertilizer according to (8), wherein ammonium phosphate is used as said phosphate. (10) The method for producing a marine fertilizer according to (6) or (7), wherein in said mixing step, said steelmaking slag and said fermented fertilizer are mixed such that the content of said steelmaking slag falls within a range of 35 to 50% by mass relative to the total dry mass of said steelmaking slag and said fermented fertilizer. (11) The method for producing a marine fertilizer according to (6) or (7), wherein in said pretreatment step, the addition amount of said phosphate is adjusted such that the content of water-soluble phosphoric acid in said fermented fertilizer falls within the range of 1.00 to 2.00% by mass. Effects of the Invention

[0021] As described above, the present invention makes it possible to provide a fertilizer for marine areas and a method for manufacturing a fertilizer for marine areas that allows for the supply of Fe from steelmaking slag without scattering even after installation in the sea. [Brief explanation of the drawing]

[0022] [Figure 1] This flowchart shows an example of the process for manufacturing a marine fertilizer according to an embodiment of the present invention. [Modes for carrying out the invention]

[0023] Preferred embodiments of the present invention will be described in detail below with reference to the attached drawings. In this specification and drawings, components having substantially the same functional configuration are denoted by the same reference numerals, and redundant descriptions will be omitted.

[0024] (Outline of a marine fertilizer and its manufacturing method according to an embodiment of the present invention) The marine fertilizer according to an embodiment of the present invention (hereinafter abbreviated as "fertilizer") consists of a molded body obtained by mixing steelmaking slag and fermented fertilizer. In the fertilizer according to this embodiment, water-soluble phosphoric acid contained in the fermented fertilizer reacts with calcium in the steelmaking slag, causing a solidification reaction by producing calcium phosphate. Therefore, it has the characteristic of not scattering even after being placed in seawater and easily maintaining its shape for a long period of time.

[0025] Furthermore, in the method for producing a marine fertilizer according to the embodiment of the present invention, the content of water-soluble phosphorus in the fermented fertilizer is adjusted to a desired state, and then the steelmaking slag and fermented fertilizer are mixed with water in a desired ratio. Next, the resulting mixture is compressed and molded, and then air-dried to form a molded body. The resulting molded body can be used as a marine fertilizer. The fertilizer produced as described above is installed in the sea after the solidification reaction is completed.

[0026] In the method for manufacturing marine fertilizer according to the embodiment of the present invention, it is possible to increase the strength of the fertilizer before installation in the sea by utilizing a solidification reaction. Therefore, it can be efficiently transported on land without generating dust, and after being introduced into the sea, it can be used to fertilize seaweed without scattering.

[0027] Furthermore, in the method for manufacturing fertilizer for marine areas according to the embodiment of the present invention, it is possible to process the fertilizer into any shape by changing the shape of the mold of the molding machine used during molding.

[0028] Based on the findings described above, a fertilizer for marine areas and a method for manufacturing a fertilizer for marine areas according to an embodiment of the present invention will be described in detail below.

[0029] (Regarding fertilizers for marine areas) The marine fertilizer according to this embodiment consists of a molded body obtained by mixing steelmaking slag and fermented fertilizer. The molded body contains steelmaking slag in an amount of 20 to 75% by mass relative to the total dry mass of the steelmaking slag and fermented fertilizer, and the water-soluble phosphoric acid content in the fermented fertilizer is in the range of 0.50 to 4.00% by mass.

[0030] <About steelmaking slag> The steelmaking slag used in the fertilizer according to this embodiment is a by-product generated in the steelmaking process, and its properties are granular. There are no particular restrictions on the type of steelmaking slag, and various known types of steelmaking slag can be used. Examples of such 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-forming slag. In addition, in this embodiment, it is also possible to use a mixture of multiple types of the above-mentioned slags.

[0031] Furthermore, the steelmaking slag used in this embodiment may be any type of steelmaking slag that has been subjected to carbonation treatment (so-called carbonated slag). Here, the carbonation treatment conditions for obtaining carbonated slag are not particularly limited. Such carbonated slag may be obtained by stirring steelmaking slag in a carbon dioxide atmosphere, by contacting steelmaking slag with water containing carbon dioxide to carbonate it, or by aging steelmaking slag outdoors for a long period of time to carbonize it.

[0032] <About fermented fertilizers> The fermented fertilizer focused on in this embodiment is obtained by decomposing or fermenting organic matter, such as natural materials (e.g., plant-derived materials, manure, etc.), food waste, fish meal, or water treatment sludge, using microorganisms or fungi. Furthermore, the above decomposition or fermentation may occur as a natural phenomenon or may be artificially induced.

[0033] The fermented fertilizer used in this embodiment is not particularly limited as long as it is one of the above-mentioned types. The "organic matter-based substance" that forms the basis of the fermented fertilizer can be selected from, for example, leaf mold, tree bark, spent mushroom substrate, fish meal, water treatment sludge, livestock manure (cattle, chicken, pig, horse, etc.).

[0034] The fermented fertilizer used in this embodiment preferably contains a large amount of organic acids that promote the elution of Fe from steelmaking slag. Furthermore, it is preferable that the fermented fertilizer has been fermented beforehand.

[0035] The fermented fertilizers described above may be commercially available or may be manufactured by oneself using various known manufacturing methods.

[0036] [Processed poultry manure fertilizer] As the fermented fertilizer described above, it is preferable to use processed poultry manure fertilizer, which is a fertilizer made by processing poultry manure such as chicken manure, using poultry manure as the raw material. There are various types of processed poultry manure fertilizers, such as (a) those made by mixing sulfuric acid or the like with the raw material and drying it by heat, (b) those made by heating and steaming the raw material and then drying it, (c) those made by simultaneously drying with hot air and crushing, and (d) those made by fermentation and drying. In this embodiment, it is possible to use any of the above types of processed fertilizers as the fermented fertilizer.

[0037] Among the processed poultry manure fertilizers described above, it is more preferable to use fermented and fully matured fertilizer, and even more preferable to use processed poultry manure fertilizer made from fully matured and fermented chicken manure. Here, the fermented and fully matured fertilizer described above is a fertilizer in which the decomposition of organic matter by fermentation has been completed and it has become sufficiently decomposed.

[0038] Among the fermented and matured fertilizers described above, it is particularly preferable to use a fermented and matured fertilizer made from fully fermented chicken manure. Fermented and matured fertilizer made from fully fermented chicken manure contains a large amount of inorganic N and P elution due to sufficient fermentation, and also contains a large amount of water-soluble phosphate. Since water-soluble phosphate is a substance that contributes to the hydration and solidification reaction that proceeds in the fertilizer according to this embodiment, processed poultry manure fertilizer derived from fermented chicken manure that contains a large amount of water-soluble phosphate is particularly useful in terms of hydration and solidification reactivity.

[0039] <Regarding the steelmaking slag content> In the fertilizer according to this embodiment, the content of steelmaking slag and the content of water-soluble phosphoric acid, described later, are adjusted in order to control the hydration solidification reaction and the amount of Fe elution, respectively. The fertilizer according to this embodiment contains steelmaking slag in an amount of 20 to 75% by mass relative to the total dry mass of the steelmaking slag and the fermented fertilizer.

[0040] In the fertilizer according to this embodiment, steelmaking slag is a raw material that serves as a source of Fe elution. In the fertilizer according to this embodiment, if the steelmaking slag content is less than 20% by mass relative to the total dry mass of the steelmaking slag and fermented fertilizer, the solidification reaction will not proceed sufficiently in the fertilizer, and it will not be possible to prevent the scattering of the fertilizer in the sea. By setting the steelmaking slag content to 20% by mass or more relative to the total dry mass of the steelmaking slag and fermented fertilizer, the solidification reaction can proceed sufficiently in the fertilizer, and it will be possible to prevent the scattering of the fertilizer in the sea. The steelmaking slag content is preferably 30% by mass or more, and more preferably 35% by mass or more, relative to the total dry mass of the steelmaking slag and fermented fertilizer.

[0041] On the other hand, in the fertilizer according to this embodiment, if the steelmaking slag content exceeds 75% by mass of the total dry mass of the steelmaking slag and fermented fertilizer, the content of fermented fertilizer, which is a raw material that promotes the leaching of Fe, will be insufficient, leading to a decrease in the amount of Fe leached. By setting the steelmaking slag content to 75% by mass or less of the total dry mass of the steelmaking slag and fermented fertilizer, it is possible to ensure a sufficient amount of Fe leached. The steelmaking slag content is preferably 55% by mass or less, and more preferably 50% by mass or less, of the total dry mass of the steelmaking slag and fermented fertilizer.

[0042] <Regarding the content of water-soluble phosphorus in fermented fertilizers> In the fermented fertilizer used in this embodiment, the content of water-soluble phosphorus in the fermented fertilizer is within the range of 0.50 to 4.00% by mass. Here, this content refers to the ratio of water-soluble phosphorus to the dry mass of the fermented fertilizer.

[0043] When the content of water-soluble phosphoric acid in the fermented fertilizer is less than 0.50 mass%, the solidification reaction does not proceed sufficiently in the fertilizer, and scattering of the fertilizer in the sea area cannot be prevented. By setting the content of water-soluble phosphoric acid in the fermented fertilizer to 0.50 mass% or more, the solidification reaction can be sufficiently progressed in the fertilizer, and scattering of the fertilizer in the sea area can be prevented. The content of water-soluble phosphoric acid in the fermented fertilizer is preferably 1.00 mass% or more.

[0044] On the other hand, when the content of water-soluble phosphoric acid in the fermented fertilizer exceeds 4.00 mass%, the water-soluble phosphoric acid reacts with Fe in steelmaking slag to generate iron phosphate and insolubilize it, which reduces the Fe elution amount of the fertilizer. Therefore, the content of water-soluble phosphoric acid in the fermented fertilizer is set to 4.00 mass% or less. The content of water-soluble phosphoric acid in the fermented fertilizer is preferably 2.00 mass% or less.

[0045] The content of water-soluble phosphoric acid in the fermented fertilizer as described above can be quantified by the method specified in Item 4.2.4 "Water-soluble phosphoric acid" in "Official Test Methods for Fertilizers etc. (Test Methods for Fertilizers etc. (2024))" established by the Food and Agricultural Materials Inspection Center, Incorporated Administrative Agency. In the above test method, ammonium vanadomolybdate absorptiometry, quinoline gravimetry, and ICP emission spectrometry are described as measurement methods capable of quantifying the concentration of water-soluble phosphoric acid. As long as no problematic measurement error occurs, any one of the above three types of measurement methods can be selected and implemented to quantify the water-soluble phosphorus concentration in the fermented fertilizer. Based on the water-soluble phosphorus concentration in the fermented fertilizer obtained by the above quantification method, it can be converted into phosphoric acid (P2O5) concentration, and the obtained phosphoric acid concentration can be used as the content of water-soluble phosphoric acid in the fermented fertilizer.

[0046] <Regarding the content of MgO> It is preferable that the fertilizer for sea areas according to the present embodiment does not contain MgO as its chemical component. Since the fertilizer for sea areas according to the present embodiment does not contain MgO, when the fertilizer is placed in the sea area, Fe can be eluted from the fertilizer over a longer period of time.

[0047] <Regarding the shape of the fertilizer material as a molded product> The shape of the molded body of the fertilizer material for marine use according to this embodiment is not particularly limited, and the molded body may have various shapes as long as it is advantageous for handling when introducing the fertilizer material according to this embodiment into the sea or when installing it in the sea. For example, the fertilizer material according to this embodiment may be a columnar molded body such as a cylinder or polygonal prism, or it may be a granular molded body having a predetermined particle size.

[0048] In this embodiment, when a granular fertilizer is preferred, there are no specific requirements regarding the particle size of the granular fertilizer. However, from the viewpoint of ease of handling the granular fertilizer, it is preferable to adjust the particle size by appropriately crushing the fertilizer.

[0049] In this embodiment, it is preferable that the particle size of the granular fertilizer is greater than 0 mm and less than or equal to 50 mm (in other words, the particle size below sieving is greater than 0 mm and less than or equal to 50 mm). When aiming for granular fertilizer, by keeping the particle size of the fertilizer identified by sieving within the above range, it is possible to prevent an increase in the cost required for crushing and a decrease in handling (workability) due to dust generation during transportation. From the viewpoint of increasing the specific surface area of ​​the molded body and efficiently dissolving Fe, the smaller the particle size of the fertilizer, the better, and the lower limit is greater than 0 mm. However, if the particle size is made excessively small, the increase in the cost required for crushing and the decrease in handling (workability) due to dust generation during transportation will be significant. Therefore, in substance, it is preferable that the particle size of the fertilizer identified by sieving is at least within the range of greater than 0 mm and less than or equal to 30 mm (the particle size below sieving is greater than 0 mm and less than or equal to 30 mm).

[0050] The fertilizer for marine areas according to this embodiment has been described in detail above.

[0051] (Regarding the manufacturing method of fertilizers for marine areas) Next, with reference to Figure 1, the method for manufacturing the marine fertilizer according to this embodiment will be described in detail. Figure 1 is a flowchart showing an example of the flow of the manufacturing method for the marine fertilizer according to this embodiment.

[0052] The method for manufacturing a marine fertilizer according to this embodiment is a method for manufacturing a marine fertilizer comprising steelmaking slag and fermented fertilizer. The method for manufacturing a marine fertilizer according to this embodiment includes a mixing step (step S13) and a molding step (step S15), as schematically shown in Figure 1. Furthermore, it is preferable that the method for manufacturing a marine fertilizer according to this embodiment further includes a pretreatment step (step S11) prior to the mixing step (step S13). These steps will be described in detail below.

[0053] <Pre-treatment process (Step S11)> The pretreatment step (step S11) in the method for manufacturing fertilizer for marine areas according to this embodiment is a step that is performed as necessary prior to the mixing step (step S13) described later.

[0054] The pretreatment step (step S11) according to this embodiment is a step of applying pretreatment to at least one of steelmaking slag or fermented fertilizer as necessary. One such pretreatment is a pretreatment to adjust the content of water-soluble phosphoric acid in the fermented fertilizer used as a raw material.

[0055] In the fertilizer according to this embodiment, the water-soluble phosphorus contained in the fermented fertilizer mainly originates from the raw materials originally present in the fermented fertilizer. However, if the water-soluble phosphorus content in such fermented fertilizer is less than 0.50% by mass, it is preferable to perform a pretreatment to adjust the water-soluble phosphorus content.

[0056] More specifically, in the pretreatment step (step S11) according to this embodiment, if the water-soluble phosphorus content of the fermented fertilizer used as one of the raw materials is less than 0.50% by mass, it is preferable to add a phosphate to the fermented fertilizer to adjust the water-soluble phosphorus content in the fermented fertilizer to be within the range of 0.50 to 4.00% by mass.

[0057] Here, the phosphate, which is added to the fermented fertilizer as a water-soluble phosphate regulator, may be added in the subsequent mixing step (step S13) at the time when the steelmaking slag and the fermented fertilizer are mixed. However, as a pretreatment step (step S11) according to this embodiment, by adding the phosphate to the fermented fertilizer and stirring it well prior to mixing with the steelmaking slag, it becomes possible to uniformly disperse the phosphate, which functions as water-soluble phosphate, in the fermented fertilizer. As a result, it becomes possible to more stabilize the increase in strength due to the hydration solidification reaction in the fertilizer according to this embodiment.

[0058] The phosphate additive used in the pretreatment step (step S11) according to this embodiment is not particularly limited as long as it functions as a water-soluble phosphate in the fermented fertilizer, and various known phosphate-containing compounds can be used. Examples of such phosphate-containing compounds include sodium phosphate, ammonium phosphate, potassium phosphate, and superphosphate. Among these, ammonium phosphate is a phosphate that is water-soluble and contains ammoniacal nitrogen. Since ammoniacal nitrogen can be supplied as a necessary nutrient for seaweed, it is more preferable to use ammonium phosphate as a phosphate additive from the viewpoint of the water-soluble phosphate content and the supply of N and P to seaweed.

[0059] On the other hand, if the water-soluble phosphate content in the fermented fertilizer used as a raw material exceeds 4.00% by mass, the water-soluble phosphate content can be adjusted to 4.00% by mass or less by masking. Masking can be performed by a treatment that converts a portion of the water-soluble phosphate into an insoluble form, by adding a substance that reacts with water-soluble phosphate to produce an insoluble solid as a water-soluble phosphate adjusting agent.

[0060] Examples of substances added for masking include alkaline salts of alkaline earth metal elements, oxides or hydroxides of alkaline earth metal elements. Here, from the viewpoint of reducing the amount of Fe leached, it is preferable to use an element other than Mg as the alkaline earth metal element. More specifically, as a substance added for masking, it is preferable to add slaked lime (Ca(OH)2) or quicklime (CaO), which are readily available and have little effect on the amount of Fe leached.

[0061] The amount of alkaline earth metal-containing compound added should be appropriately determined considering the molar ratio of alkaline earth metal to phosphorus in the phosphate produced by masking, and the amount of excess water-soluble phosphorus in the fermented fertilizer. For example, 1.0 to 2.0 times the number of moles of alkaline earth metal relative to the number of moles of phosphorus relative to the excess water-soluble phosphorus should be added. However, even if 1.0 to 2.0 times the number of moles of alkaline earth metal is added as described above, the reactivity of water-soluble phosphorus may decrease due to the reaction of the alkaline earth metal with silicon and sulfur-based chemical species, making it difficult to adjust the water-soluble phosphorus content to 4.00% by mass or less. In such cases, 2.0 times or more the number of moles of alkaline earth metal relative to the number of moles of phosphorus relative to the excess water-soluble phosphorus should be added.

[0062] If the fermented fertilizer contains a large amount of highly reactive alkaline earth metal elements and is neutral or acidic, the fermented fertilizer may be adjusted to be alkaline to mask the water-soluble phosphorus. The method for adjusting to alkalinity is not particularly limited; for example, seawater or hydroxides may be added, or caustic soda (NaOH) or caustic potash (KOH) may be added.

[0063] The substance used to promote the masking described above may be in liquid or solid form. However, from the viewpoint of efficiently promoting the masking reaction, when adding a solid substance, it is preferable to use a powder with small particle size, and it is even more preferable to add water together with the powder and mix them uniformly. Furthermore, when using powder, it is preferable to add water equivalent to 10 to 20% by mass of the fermented fertilizer mass together with powder with a particle size of 1 mm or less and mix them uniformly.

[0064] <Mixing process (Step S13)> The mixing step (step S13) in the method for producing a fertilizer for marine areas according to this embodiment is a step of mixing a fermented fertilizer having a water-soluble phosphoric acid content in the range of 0.50 to 4.00% by mass, steelmaking slag, and water to obtain a mixture.

[0065] More specifically, the mixing step (step S13) according to this embodiment involves mixing steelmaking slag and fermented fertilizer so that the steelmaking slag content is 20 to 75% by mass relative to the total dry mass of the steelmaking slag and fermented fertilizer. Subsequently, the amount of added water is adjusted so that the water content is within the range of 30 to 55% by mass when the sum of the total dry mass of the steelmaking slag and fermented fertilizer and the mass of water is taken as 100% by mass.

[0066] The reason for setting the steelmaking slag content at 20-75% by mass relative to the total dry mass of the steelmaking slag and fermented fertilizer is as mentioned earlier, so a detailed explanation will be omitted below.

[0067] In the mixing step (step S13) according to this embodiment, the amount of water added is adjusted so that the water content is within the range of 30 to 55% by mass, when the total dry mass of the steelmaking slag and fermented fertilizer and the mass of water are taken as 100% by mass. If the amount of water added is less than 30% by mass, sufficient compressibility cannot be obtained in the subsequent molding step (step S15), which is undesirable. By adding 30% by mass or more of water, the resulting mixture will exhibit excellent compressibility in the subsequent molding step (step S15). In the mixing step (step S13) according to this embodiment, the amount of water added is preferably 35% by mass or more.

[0068] On the other hand, in the mixing step (step S13) according to this embodiment, if the water content exceeds 55% by mass, the resulting mixture will have too much water, which reduces the solidification reactivity of the fertilizer produced and is therefore undesirable. By limiting the amount of water added to 55% by mass or less, it is possible to improve the compressibility in the subsequent molding step (step S15) while maintaining good solidification reactivity of the fertilizer produced. In the mixing step (step S13) according to this embodiment, the amount of water added is preferably 50% by mass or less.

[0069] Furthermore, in order to achieve the above-mentioned moisture content, the lower the moisture content (moisture concentration) of the steelmaking slag and fermented fertilizer used as raw materials, the more preferable it is from the viewpoint of facilitating control of solidification reactivity.

[0070] Furthermore, the mixing apparatus used in the mixing step (step S13) according to this embodiment is not particularly limited, and various known apparatuses can be used. Examples of such apparatuses include kneaders, paddle mixers, drum mixers, rotary mixers, and the like.

[0071] <Molding process (Step S15)> In the manufacturing method of fertilizer for marine areas according to this embodiment, the molding step (step S15) is a step in which the mixture obtained in the mixing step (step S13) is compressed into a desired shape and then air-dried.

[0072] The molding method used in the molding process (step S15) according to this embodiment, and the shape of the molded article obtained in such molding process, are not particularly limited.

[0073] For example, in the molding process (step S15) according to this embodiment, the material may be molded into a columnar shape with a height of 10 to 30 cm and a width of 15 to 30 cm using various known compression presses. When molding into a columnar shape, the area / volume ratio is preferably about 0.1 to 0.9, and more preferably about 0.2 to 0.5. The compression molding pressure is not particularly specified, but for example, it is preferably 300 kgf (1 kgf is approximately 9.8 N) or more per 0.4 square meters. When molding into a granular shape, it is preferable to mold it so that the particle size distribution is greater than 0 mm and less than or equal to 50 mm.

[0074] Furthermore, in the molding process (step S15) according to this embodiment, the compression molding method is not limited to the method using the compression press described above. For example, the raw material mixture may be placed in a metal mold and compacted manually using a rod-shaped jig, or various extrusion molding machines and briquetting machines may be used.

[0075] Furthermore, in the molding process (step S15) according to this embodiment, after obtaining a molded body of the desired shape, the obtained molded body is left to stand and air-dry until the hydration solidification reaction is completed. There are no particular restrictions on the method of air-drying. However, it is preferable that the ambient temperature for air-drying is appropriately adjusted in order to efficiently promote the hydration solidification reaction. For example, the ambient temperature for air-drying is preferably in the range of 10 to 30°C, and more preferably in the range of 20 to 25°C.

[0076] Furthermore, there are no particular limitations on the duration of natural drying. However, from the viewpoint of the strength of the molded body, it is preferable to allow for a period during which most of the moisture has evaporated and the hydration solidification reaction is nearing completion. For example, for a molded body with a height of 10 cm or less, the natural drying period is preferably 3 days or more, and more preferably 2 weeks or more. Also, when a columnar shape with a height of 10 to 30 cm and a width of 15 to 30 cm is formed using a compression press, the natural drying period is preferably 3 weeks or more, and more preferably 4 weeks or more.

[0077] By following the above-described process, it becomes possible to manufacture the marine fertilizer according to this embodiment.

[0078] The above describes in detail an example of a method for manufacturing a marine fertilizer according to this embodiment, with reference to Figure 1.

[0079] Furthermore, when storing the fertilizer material for marine use according to this embodiment before installation in the marine area, it is preferable to store it in a place with low humidity (including condensation) to maintain a moisture content of 10% by mass or less, from the viewpoint of maintaining consistent quality. More specifically, it is preferable to completely remove moisture from the fertilizer material to be stored by heat drying treatment at 60-100°C beforehand, and then seal it in packaging material such as a flexible container bag to maintain a moisture content close to 0% by mass. [Examples]

[0080] The following sections will provide a detailed explanation of the marine fertilizer and its manufacturing method according to this embodiment, with reference to examples and comparative examples. Note that the following examples are merely illustrative of the marine fertilizer and its manufacturing method according to this embodiment, and the marine fertilizer and its manufacturing method according to this embodiment are not limited to the examples below.

[0081] <1. Preparation of steelmaking slag> Steelmaking slag (manufactured by Nippon Steel Corporation) with a particle size of 0-25 mm, which is discarded during the steelmaking process of the steelmaking business and then crushed and particle size adjusted at the plant, was collected and then particle size adjusted by sieving. The raw material with a particle size of 0-25 mm that had not undergone particle size adjustment was designated as "Steelmaking Slag 1", the raw material adjusted to a particle size of 0-10 mm by sieving was designated as "Steelmaking Slag 2", and the raw material adjusted to a particle size of 0-5 mm was designated as "Steelmaking Slag 3". The obtained Steelmaking Slag 1 to Steelmaking Slag 3 were dried in a dryer set to 105°C for 6 hours to remove moisture.

[0082] <2. Preparation of fermented fertilizer> Six types of fermented fertilizers were dried in a dryer set to 105°C for 6 hours. After drying, the samples were passed through a 9.5 mm mesh sieve, and the sediment was collected to obtain fermented fertilizer samples. To a portion of the collected sediment, 1.5 to 17.0% by mass of agricultural ammonium phosphate fertilizer or 4 to 30% by mass of magnesium oxide reagent was added, and then mixed in a mortar mixer. The capacity of the mortar mixer was 0.1 m³. 3 The stirring speed was set to 48 rpm. Ammonium phosphate fertilizer was added to increase the amount of water-soluble phosphorus, and magnesium oxide reagent was added to understand its effect on the amount of Fe eluted.

[0083] The water-soluble phosphorus (P2O5 equivalent) content was quantified for each fermented fertilizer sample obtained. The water-soluble phosphorus content was quantified by the ammonium vanadomolybdate method in accordance with the method specified in item 4.2 "Phosphorus (Phosphoric Acid)" of the "Fertilizer Analysis Methods (1992 Edition)" of the National Institute for Agro-Environmental Sciences, Ministry of Agriculture, Forestry and Fisheries.

[0084] Details of the prepared fermented fertilizer samples are summarized in Table 1 below.

[0085] [Table 1]

[0086] <3. Preparation of fertilizer materials> The above fermented fertilizer samples were added to the above steelmaking slags 1 to 3 and mixed in a mortar mixer for 10 minutes. The capacity of the mortar mixer was 0.1 m³. 3 The stirring speed was set to 48 rpm. During stirring, the moisture level was visually checked, and water was added in the amounts shown in Table 2 below relative to the total mass of the steelmaking slag and fermented fertilizer sample while stirring was performed.

[0087] The resulting mixture was molded to a diameter of 50 mm and a height of 100 mm in accordance with the Cement Association Standard Test Method JCAS L-01:2006. More specifically, the mixed mixture was poured into the mold in three separate batches (three layers), and each layer was compressed 12 times using a 1.5 kg rammer (tamping rod) to form the cylindrical sample. The prepared cylindrical sample was air-dried at room temperature (18-25°C) for one week.

[0088] The manufacturing conditions for each molded product obtained are summarized in Table 2 below.

[0089] [Table 2]

[0090] <4. Evaluation Test Methods for Fertilizer Materials> The prepared cylindrical samples were placed in 80mm diameter x 50mm height plastic containers and immersed in 10 times the sample mass of artificial seawater (pH 8.0) in a 2L beaker. The artificial seawater was continuously stirred with a magnetic stirrer set to 200rpm and replaced every 24 hours. After 24 hours and 2 weeks, eluates were collected, filtered through a 0.45μm pore size filter, and the Fe concentration was measured by inductively coupled plasma mass spectrometry (ICP-MS). Hydrochloric acid was used for acid decomposition, and ICP-MS measurements were performed using a Shimadzu Corporation ICPMS-2030.

[0091] When the prepared cylindrical sample was immersed in artificial seawater, the amount of Fe leached was high on the first day of immersion, but decreased as the number of immersion days increased. According to the inventors' findings, after two weeks from immersion, the change in the amount of Fe leached over time decreased, and the amount of Fe leached stabilized. Therefore, in this example, conditions in which Fe leaching continued and the amount of Fe leached after two weeks was 10 μg / L or more were judged to be good Fe leaching properties.

[0092] Furthermore, the appearance of the cylindrical samples was checked two weeks later to see if there were any cracks or collapses. Samples without cracks or collapses were given a score of "A," and were judged to be in good condition with a low risk of scattering in the sea area. Samples that cracked but did not collapse were given a score of "B," and those that collapsed were given a score of "C."

[0093] The results obtained are summarized in Table 3 below.

[0094] [Table 3]

[0095] Although preferred embodiments of the present invention have been described in detail above with reference to the attached drawings, the present invention is not limited to these examples. It is clear to any person with ordinary skill in the art to which the present invention belongs that various modifications or alterations can be conceived within the scope of the technical idea described in the claims, and these are also understood to fall within the technical scope of the present invention.

[0096] The embodiments disclosed herein are illustrative and not restrictive in all respects. The embodiments described above may be omitted, replaced, or modified in various ways without departing from the appended claims, the technical scope of the invention as described later, and the spirit thereof. For example, the constituent elements of the embodiments described above can be combined in any way without impairing their effects. Furthermore, such any combination will naturally yield the effects and benefits of each constituent element in the combination, as well as other effects and benefits that will be obvious to those skilled in the art from the description herein.

[0097] Furthermore, the effects described herein are merely descriptive or illustrative, and not limiting. In other words, the technology according to the present invention may produce other effects that will be apparent to those skilled in the art from the description herein, in addition to or instead of the effects described above.

[0098] Furthermore, the following configurations also fall within the technical scope of the present invention. (1) It consists of a molded body made by mixing steelmaking slag and fermented fertilizer. The aforementioned molded body is The steelmaking slag is contained in an amount of 20 to 75% by mass relative to the total dry mass of the steelmaking slag and the fermented fertilizer. A fertilizer for marine areas, wherein the fermented fertilizer contains water-soluble phosphorus in the range of 0.50 to 4.00% by mass. (2) The fermented fertilizer is a processed poultry manure fertilizer, as described in (1) for use in marine areas. (3) The fertilizer for marine areas according to (1) or (2), wherein the steelmaking slag is contained in an amount of 30 to 55% by mass relative to the total dry mass of the steelmaking slag and the fermented fertilizer. (4) The molded body is a columnar molded body, and is a marine fertilizer as described in any one of (1) to (3). (5) A granular molded body having a particle size greater than 0 mm and less than or equal to 50 mm, which is a marine fertilizer as described in any one of (1) to (3). (6) A method for producing a fertilizer for marine areas, comprising steelmaking slag and fermented fertilizer, A mixing step of mixing the fermented fertilizer having a water-soluble phosphoric acid content in the range of 0.50 to 4.00% by mass, the steelmaking slag, and water. The resulting mixture is compressed and molded, and then air-dried in a molding process, It has, In the aforementioned mixing step, After mixing the steelmaking slag and the fermented fertilizer, the amount of steelmaking slag contained in the mixture is 20 to 75% by mass of the total dry mass of the steelmaking slag and the fermented fertilizer. A method for producing a fertilizer for marine areas, comprising adjusting the amount of added water so that, when the total dry mass of the steelmaking slag and the fermented fertilizer, plus the mass of water, is taken as 100% by mass, the water content is within the range of 30 to 55% by mass. (7) A method for producing a marine fertilizer as described in (6), wherein processed poultry manure fertilizer is used as the fermented fertilizer. (8) Prior to the mixing step, the process further includes a pretreatment step in which at least one of the steelmaking slag or the fermented fertilizer is pretreated. The method for producing a marine fertilizer according to (6) or (7), wherein in the pretreatment step, a phosphate salt is added to the fermented fertilizer to adjust the content of water-soluble phosphorus in the fermented fertilizer to be within the range of 0.50 to 4.00% by mass. (9) A method for producing a marine fertilizer according to (8), wherein ammonium phosphate is used as the phosphate. (10) A method for producing a marine fertilizer according to any one of (6) to (9), wherein in the mixing step, the steelmaking slag and the fermented fertilizer are mixed such that the content of the steelmaking slag is within the range of 35 to 50% by mass of the total dry mass of the steelmaking slag and the fermented fertilizer. (11) A method for producing a marine fertilizer according to any one of (6) to (10), wherein in the pretreatment step, the amount of phosphate added is adjusted so that the content of water-soluble phosphorus in the fermented fertilizer is within the range of 1.00 to 2.00% by mass.

Claims

1. It consists of a molded body made by mixing steelmaking slag and fermented fertilizer. The aforementioned molded body is The steelmaking slag is contained in an amount of 20 to 75% by mass relative to the total dry mass of the steelmaking slag and the fermented fertilizer. A fertilizer for marine areas, wherein the content of water-soluble phosphorus in the fermented fertilizer is in the range of 0.50 to 4.00% by mass.

2. The fermented fertilizer is processed poultry manure fertilizer, as described in claim 1, for use in marine areas.

3. The marine fertilizer according to claim 1 or 2, wherein the steelmaking slag is contained in an amount of 30 to 55% by mass relative to the total dry mass of the steelmaking slag and the fermented fertilizer.

4. The molded body is a columnar molded body, as described in claim 1 or 2, for use as a fertilizer for marine areas.

5. The fertilizer for marine areas according to claim 1 or 2, wherein the molded body is a granular molded body having a particle size of more than 0 mm and less than or equal to 50 mm.

6. A method for producing a fertilizer for marine areas, comprising steelmaking slag and fermented fertilizer, A mixing step of mixing the fermented fertilizer having a water-soluble phosphoric acid content in the range of 0.50 to 4.00% by mass, the steelmaking slag, and water. The resulting mixture is compressed and molded, and then air-dried in a molding process, It has, In the aforementioned mixing step, After mixing the steelmaking slag and the fermented fertilizer, the amount of steelmaking slag contained in the mixture is 20 to 75% by mass of the total dry mass of the steelmaking slag and the fermented fertilizer. A method for producing a fertilizer for marine areas, comprising adjusting the amount of added water so that, when the total dry mass of the steelmaking slag and the fermented fertilizer, plus the mass of water, is taken as 100% by mass, the water content is within the range of 30 to 55% by mass.

7. A method for producing a fertilizer for marine areas according to claim 6, wherein processed poultry manure fertilizer is used as the fermented fertilizer.

8. Prior to the mixing step, the process further includes a pretreatment step in which at least one of the steelmaking slag or the fermented fertilizer is pretreated. The method for producing a marine fertilizer according to claim 6 or 7, wherein in the pretreatment step, a phosphate is added to the fermented fertilizer to adjust the content of water-soluble phosphorus in the fermented fertilizer to be within the range of 0.50 to 4.00% by mass.

9. A method for producing a marine fertilizer according to claim 8, wherein ammonium phosphate is used as the phosphate.

10. The method for producing a fertilizer for marine areas according to claim 6 or 7, wherein in the mixing step, the steelmaking slag and the fermented fertilizer are mixed such that the content of the steelmaking slag is within the range of 35 to 50% by mass of the total dry mass of the steelmaking slag and the fermented fertilizer.

11. The method for producing a marine fertilizer according to claim 6 or 7, wherein in the pretreatment step, the amount of phosphate added is adjusted so that the content of water-soluble phosphorus in the fermented fertilizer is within the range of 1.00 to 2.00% by mass.

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