RU2707811C1 - Steel-smelting slag as raw material for fertilizer, method for production of steel-smelting slag as raw material for fertilizer, method of fertilizer production and method of fertilizer application - Google Patents

Abstract

FIELD: agriculture.

SUBSTANCE: steel-smelting slag as raw material for fertilizer contains, wt%, P₂O₅: greater than or equal to 2 % and less than or equal to 8 %, MnO: greater than or equal to 3 % and less than or equal to 10 %, boron: greater than or equal to 0.005 % and less than 0.05 %, total iron: greater than or equal to 7 % and less than 15 %, CaO: greater than or equal to 38 % and less than or equal to 48 %, SiO₂: greater than or equal to 22 % and less than or equal to 30 %, sulfur: greater than or equal to 0.1 % and less than or equal to 0.6 %, MgO: greater than or equal to 1 % and less than or equal to 8 % and Al₂O₃: greater than or equal to 0.5 % and less than or equal to 3 %, wherein content of soluble P₂O₅ in P₂O₅ greater than or equal to 50 %, the fraction of citric acid soluble MnO in MnO greater than or equal to 80 %, slag basicity expressed as (CaO content / SiO₂ content), more than 1.5 and less than or equal to 2.2, and bulk density is greater than or equal to 1.9 and less than or equal to 2.8. Method of production of steel-smelting slag as raw material for fertilizer. Fertilizer production method. Use of fertilizer produced by the method. Application of fertilizer, which contains steel-smelting slag as raw material for fertilizer.

EFFECT: invention widens range of fertilizers for use in acidic soils.

19 cl, 8 tbl, 3 ex

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This application is based on and claims priority for Japanese Patent Application No. 2017-126093, filed June 28, 2017, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to steelmaking slag as a raw material for fertilizer, a method for producing steelmaking slag as a raw material for fertilizer, a method for producing fertilizer and a method for using this fertilizer.

[0002] Nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), oxygen (O), hydrogen (H), carbon (C), magnesium ( Mg), sulfur (S), iron (Fe), manganese (Mn), boron (B), zinc (Zn), nickel (Ni), molybdenum (Mo), copper (Cu) and chlorine (Cl).

[0003] Among the above elements, nitrogen (N), phosphorus (P) and potassium (K) are called three fertilizer elements and are known as elements needed by plants in large quantities. In addition, calcium (Ca), magnesium (Mg) and sulfur (S) are called secondary elements that are most needed by plants after the three elements mentioned above. In addition, iron (Fe), manganese (Mn), boron (B), zinc (Zn), molybdenum (Mo), copper (Cu) and chlorine (Cl) are necessary for plants in small quantities and are therefore called trace elements.

[0004] In addition, it has recently become clear that among the above elements, boron (B) is an element necessary for the formation of a cell membrane in the cells of plant roots. In addition, major food crops for the global population, such as rice, wheat and corn, need a lot of silicon (Si), as well as the elements mentioned above.

[0005] As a method of supplying plants with elements of Ca, P, Si, Mg, Fe, Mn, B, and C, foliar feeding is used. With foliar top dressing, for example, the following substances are used to provide the appropriate elements.

Ca: calcium chloride

P: potassium primary acid phosphate

Mg: magnesium sulfate

Fe: ferrous sulfate

Mn: Manganese Sulfate

B: boric acid

Si: potassium silicate

S: calcium sulfate (gypsum), magnesium sulfate, ferrous sulfate and manganese sulfate

[0006] However, foliar top dressing is a labor-intensive method, and therefore, a method is required that is capable of absorbing the above elements through the roots of plants without the use of foliar top dressing.

[0007] On the other hand, steelmaking slag obtained by the preliminary processing of molten iron and its decarburization, contains various minerals as its constituent components, and therefore is used as fertilizers and soil improvement materials, as disclosed in patent documents 1 -nine.

[0008] For example, Patent Document 1 describes a silicophosphate fertilizer feedstock that is collected during dephosphorization processing during pretreatment of molten blast furnace iron in a cast iron production process, as well as a method for producing a silicophosphate fertilizer feedstock.

[0009] Patent document 2 describes a method by which slag phosphate fertilizer is produced using steelmaking slag as a raw material obtained during the pre-treatment of molten iron.

[0010] Patent Document 3 reports that slag particles from steelmaking slag obtained during the production of pig iron give the effect of increasing the yield of rice paddy, as well as the effect of suppressing the formation of greenhouse gases.

[0011] Patent document 4 and patent document 5 describe a method for pre-treating molten iron, in which desiliconization and dephosphorization treatments are carried out sequentially using one converter type melting furnace, and patent document 6 describes a method by which silicon fertilizer is produced during the pre-treatment of molten cast iron in the process of cast iron production.

[0012] Patent Document 7 describes a silicon fertilizer in which the dissolution of silicic acid is achieved by mixing coal ash containing only insoluble silicic acid with molten stainless steel slag.

[0013] Patent document 8 describes a method for producing phosphoric acid-containing slag for fertilizer, and Patent document 9 describes a method for producing phosphate fertilizer feedstock obtained from a cast iron production process.

Cited Documents

Patent documents

[0014] Patent Document 1: JP 5105322B

Patent Document 2: JP 6040064B

Patent Document 3: JP 5881286B

Patent Document 4: JP 5983900B

Patent Document 5: JP 2016-29206A

Patent Document 6: JP 4246782B

Patent Document 7: JP 4040542B

Patent Document 8: JP 6119361B

Patent Document 9: JP 6011556B

SUMMARY OF THE INVENTION

Problems Solved by the Invention

[0015] The use of many types of substances containing elements such as P, Fe, Mn, Zn, Si, Ca, Mg, B, and C, in such a way that a fertilizer effect can be expected from each element, is costly and effortful. In addition, in the case when the substance containing each element is introduced into the soil, since the density of the substances is different, a substance with a low density can be washed out of the soil in regions with a large amount of rainfall or with frequent river spills. As a result, there is a fear that during the period of one vegetation, plants will be forced to grow under conditions in which the balance between the elements is lost.

[0016] In particular, leaching and lack of elements such as Fe, Mn, and B may occur in acidic soil. In addition, there is a fear that in acidic soil with a high aluminum content, it will ionize and bind to phosphoric acid, forming aluminum phosphate, and the absorption of phosphoric acid by plant roots will be inhibited.

[0017] Also, from the point of view of sustainable food supplies, it is very important that siliceous plants such as rice, wheat, and corn can be grown sustainably in acidic soils in regions where rainfall is high, as well as in regions where spills often occur. rivers

[0018] Therefore, in acidic soils in those regions where rainfall is high, and also in regions where river spills often occur, especially in acidic soils with a high aluminum content, it is assumed that among the three elements of fertilizer, P, and Fe, Mn, B, etc. will be missing among the trace elements.

[0019] Among the secondary elements, Ca and Mg are elements necessary for root growth and plant photosynthesis. In addition, Ca and Mg have alkalinity, like lime and magnesium oxide, and are also the main constituent elements of alkaline components measured in the analysis of fertilizers, etc., as well as elements that have the effect of increasing the pH of acidic soil when soil improves to pH suitable for plant cultivation.

[0020] In addition, among the secondary elements, S is an element essential for the biosynthesis of sulfur-containing amino acids, and is also an element especially necessary for the cultivation of plants of the amaryllis family or the family of lily, such as garlic, onion and potato. However, S is an element that, after it is added to the soil, can oxidize to sulfuric acid and acidify the soil, or it can be reduced by sulfate-reducing bacteria to hydrogen sulfide and cause root rot.

[0021] Si is an element necessary for the sustainable cultivation of siliceous plants such as rice, wheat and corn, and is very important in terms of sustainable food supply.

[0022] Thus, in the current situation, it is desirable to develop a fertilizer and a method for applying fertilizer that could provide many types of elements from P, Fe, Mn, Si, Ca, Mg, C, and B as fertilizer for plants easily and at a low price. even in acidic soils of those regions where rainfall is high, as well as those regions where river spills often occur, without being washed out of the soil.

[0023] Thus, the present invention has been made in view of the aforementioned problem, and an object of the present invention is to provide steelmaking slag as a raw material for fertilizer, a method for producing steelmaking slag as a raw material for fertilizer, a method for producing fertilizer, and also a method fertilizer applications, which could provide many types of elements as fertilizer for plants easily and at low cost even in acidic soils of those regions where rainfall is high, as well as s regions, where there is often spilling rivers, without washing out of the soil.

Problem Solving Tools

[0024] The inventors of the present invention conducted extensive studies in view of the aforementioned problem, and therefore, in order to provide many types of elements P, Fe, Mn, Si, Ca, Mg, B, and C, a steelmaking slag specifically designed as a raw material for fertilizers, and a method for its production, as well as a method for producing fertilizer and a method for applying fertilizer capable of supplying these elements; and thus completed the present invention.

[0025] The main points of the present invention are as follows.

[1] Steelmaking slag as a raw material for fertilizer, containing, in wt.%, P ₂ O ₅ : greater than or equal to 2% and less than or equal to 8%, MnO: greater than or equal to 3% and less than or equal to 10%, boron : greater than or equal to 0.005% and less than 0.05%, total iron: greater than or equal to 7% and less than 15%, CaO: greater than or equal to 38% and less than or equal to 48%, SiO ₂ : greater than or equal to 22% and less than or equal to 30%, sulfur: greater than or equal to 0.1% and less than or equal to 0.6%, MgO: greater than or equal to 1% and less than or equal to 8%, and Al ₂ O ₃ : greater than or equal to 0.5 % and less than or equal to 3%, wherein the proportion of soluble P ₂ O _5, P ₂ O ₅ is greater than or equal to 50%, the proportion of soluble of citric acid in a MnO MnO is greater than or equal to 80%, the slag basicity, expressed as (the content of CaO / SiO ₂ content) is greater than 1.5 and less than or equal to 2.2, and a bulk density greater than or equal to 1.9 and less than or equal to 2.8.

[2] Steelmaking slag as a raw material for fertilizer according to [1], containing a 2CaO⋅SiO ₂ -3CaO⋅P ₂ O ₅ solid solution and a solid solution based on FeO-MnO-CaO-SiO ₂ .

[3] Steelmaking slag as a raw material for fertilizer according to [1] or [2], in which the proportion of boron soluble in citric acid in boron is greater than or equal to 95%.

[4] Steelmaking slag as a fertilizer raw material according to any one of [1] to [3], in which the particle size is less than 5 mm in total, and the mass fraction of particles with sizes less than 600 μm is greater than or equal to 60% of total mass.

[5] A method for the production of steelmaking slag as a raw material for fertilizer, which produces steelmaking slag as a raw material for fertilizer according to any one of [1] to [4], which includes: casting molten blast furnace iron into a converter bucket in such a way that the clearance factor, expressed as (height of the free side of the bucket corresponding to the length from the neck to the surface of molten molten iron / internal height of the bucket corresponding to the distance from the neck to the inner bottom of the bucket), is greater than or equal to 0.5 less than or equal to 0.9; adding at least one of manganese ore, manganese-containing decarburization slag and ferromanganese to molten blast furnace iron in a converter-type ladle; blowing quicklime and / or calcium carbonate with an average particle size of less than or equal to 1 mm and oxygen into molten blast furnace iron from a lance inserted into molten blast iron; foaming slag at a temperature greater than or equal to 1300 ° C and less than or equal to 1400 ° C to perform dephosphorization treatment; and obtaining slag in such a way that the slag basicity, expressed as (CaO content / SiO ₂ content), is greater than 1.5 and less than or equal to 2.2, and the MnO content in the slag is greater than or equal to 3 wt.% and less than or equal to 10 wt.%.

[6] The method for producing steelmaking slag as a raw material for fertilizer according to [5], wherein the molten slag, after being treated with dephosphorization, is poured into a heat-resistant container plate and quickly cooled to solidify.

[7] A method for producing steelmaking slag as a fertilizer feedstock according to [6], wherein the molten slag after dephosphorization is rapidly cooled by spraying water.

[8] A method for producing steelmaking slag as a raw material for fertilizer according to any one of [5] to [7], wherein the converter-type ladle is tilted to pour molten slag after dephosphorization into a slag ladle, and then molten slag in a slag ladle is poured into tiltable first heat-resistant container, water is sprayed in the first heat-resistant container for quick cooling and solidification of the molten slag, and then the solidified slag is fragmented, and the first heat-resistant container is tilted A sliding solidified slag down into the second heat-resistant container, thereby fragmenting the solidified slag.

[9] A method for producing steelmaking slag as a raw material for fertilizer according to any one of [5] to [8], wherein a 2CaO⋅SiO ₂ -3CaO⋅P ₂ O ₅ solid solution and a FeO-MnO-CaO solid solution are formed -SiO ₂ by rapid cooling.

[10] A method for producing steelmaking slag as a raw material for fertilizer according to any one of [5] to [9], wherein the slag is ground so that the particle size is less than 5 mm as a whole and the mass fraction of particles with sizes less than 600 μm was greater than or equal to 60% of the total mass.

[11] A method for the production of fertilizer, including: grinding into a powder steelmaking slag as a raw material for fertilizer according to any one of [1] - [4] or steelmaking slag as a raw material for fertilizer produced by the method of producing steelmaking slag as a raw material for fertilizers according to any one of [5] - [10].

[12] The fertilizer production method according to [11], in which a predetermined binder is added to the steelmaking slag as a raw material for fertilizer after it is pulverized, and then granulation is performed.

[13] The method for producing fertilizer according to [11] or [12], wherein the organic substance is additionally mixed with the obtained fertilizer.

[14] The method for producing fertilizer according to [13], wherein the organic matter is at least one of manure, plant residues, and compost obtained from fishery products.

[15] A method of applying fertilizer, including: applying a fertilizer that contains steelmaking slag as a raw material for fertilizer according to any one of [1] to [4], steelmaking slag as a raw material for fertilizer, produced by the method of manufacturing steelmaking slag as raw materials for fertilizer according to any one of paragraphs [5] - [10], or fertilizer produced by the method of manufacturing fertilizer according to any one of paragraphs [11] - [14], into soil in which the pH (H ₂ O) is greater than or equal to 4 and less than or equal to 6, a value expressed as (pH (H ₂ O) - pH (KCl)) is greater than or equal to but 1, and the amount of available phosphoric acid is less than or equal to 5 mg / 100 g of dry soil.

[16] The method of applying fertilizer according to [15], wherein the applied amount of fertilizer is greater than or equal to 0.05 t / ha and less than or equal to 2 t / ha of steelmaking slag as a raw material for fertilizer.

[17] The method of applying the fertilizer according to [15] or [16], wherein the fertilizer is spread on the surface of the arable layer or mixed with the arable layer before sowing or planting plants.

[18] The method of applying the fertilizer according to [15] or [16], wherein the fertilizer is spread on the surface of the arable layer next to the body of the plant being grown or mixed in the arable layer.

Effects of the invention

[0026] As described above, in accordance with the present invention, it is possible to supply many types of elements as fertilizer for plants easily and at low cost even in acidic soils of those regions where rainfall is high, as well as those regions where river spills frequently occur. without leaching from the soil.

DETAILED DESCRIPTION OF EMBODIMENTS

[0027] Next, preferred embodiments of the present invention will be described in detail.

(On the content of studies performed by the authors of the present invention)

[0028] Before describing embodiments of the present invention, the results of studies performed by the inventors of the present invention will be described in detail with respect to the requirements for the fertilizers described above and how to use them.

<Research technology disclosed in patent document 1>

[0029] Regarding the requirements described above, the silicophosphate fertilizer feedstock disclosed in the aforementioned Patent Document 1 has a relatively low basicity, the basicity expressed as (CaO content / SiO ₂ content) greater than or equal to 1.0 and less than or equal to 1.4, and therefore it is unlikely that this fertilizer will have an effect on acidic soils. In addition, the silicophosphate fertilizer feedstock disclosed in the aforementioned Patent Document 1 has a soluble CaO content of less than or equal to 30% by weight and has a low basicity, and therefore is unlikely to be effective for acidic soils.

[0030] In addition, in the aforementioned patent document 1 it is indicated that the content of Al ₂ O _{3 is} less than or equal to 10 wt.%; The examples show that the Al ₂ O ₃ content is greater than or equal to 4.84 wt.% And less than or equal to 6.33 wt.%, Which are high values in excess of 4 wt.%. Al is a substance that most likely binds to phosphate ions and is an obstacle to the absorption of phosphorus by plants; therefore, a lower Al ₂ O ₃ content is desired.

[0031] In addition, in the aforementioned patent document 1 there is neither a description of the boron content nor a description of the effect of boron on the fertilizer effect.

<Research technology disclosed in patent document 2>

[0032] In the aforementioned patent document 2, a method is disclosed by which slag phosphate fertilizer is produced using steelmaking slag as a raw material obtained from a process for the pretreatment of molten iron; however, there is no description of the method of production of steelmaking slag, which serves as raw material for slag phosphate fertilizer. In addition, from Examples of the aforementioned Patent Document 2, it can be seen that the content of phosphoric acid soluble in citric acid in the steelmaking slag serving as a raw material is greater than or equal to 2.56 wt.% And less than or equal to 2.62 wt.%, And it is possible note that the condition serving as a standard slag phosphate fertilizer that "the content of phosphoric acid soluble in citric acid should be greater than or equal to 3 wt.%" is not satisfied. In addition, in the aforementioned patent document 2 there is neither a description of the content of boron or manganese, nor a description of the effect of boron or manganese on the effect of fertilizer.

<Research technology disclosed in patent document 3>

[0033] In the aforementioned Patent Document 3, it is indicated that the amount of phosphoric acid contained is greater than or equal to 1.5 wt.% And less than or equal to 5 wt.%; however, there is no description of what proportion of this amount is soluble phosphoric acid (phosphoric acid, which dissolves with Peterman ammonium citrate solution), which can effectively affect plants.

[0034] Patent Document 3 states that the amount of CaO contained is greater than or equal to 20 wt.% And less than or equal to 50 wt.%. As a reason for such an amount, it is indicated that steelmaking slag with a CaO content of less than 20 wt.% Or more than 50 wt.% Practically does not form during the production of cast iron.

[0035] In addition, Patent Document 3 states that the steelmaking slag particles contain 10 wt.% Or more and 30 wt.% Or less SiO ₂ . Patent Document 3 indicates, as a reason for this, that when the amount of SiO ₂ is less than 10 wt.%, The amount of available dissolved silicic acid is small, and therefore, the effect of supporting the growth of diatoms that perform the production function cannot be ensured. oxygen by photosynthesis on the soil surface of a rice field covered with water. In addition, patent document 3 shows that steelmaking slag containing more than 30 wt.% SiO ₂ practically does not form during the production of cast iron, and therefore it is difficult to obtain.

[0036] In the aforementioned patent document 3, there is no description of the basicity of slag (= CaO / SiO ₂ ); therefore, a contained amount of CaO greater than or equal to 20 wt.% and less than or equal to 50 wt.%, and a contained amount of SiO ₂ greater than or equal to 10 wt.% and less than or equal to 30 wt.%, may correspond to the above, and slag basicity can vary within a very wide range, from 0.67 (CaO: 20 wt.%, SiO ₂ : 30 wt.%) to 5 (CaO: 50 wt.%, SiO ₂ : 10 wt.%). The basicity of the slag greatly affects the dissolution from fertilizer of effective components such as phosphorus, iron and manganese, and therefore it is necessary to provide a basicity suitable for dissolving these effective fertilizer elements.

[0037] In addition, Patent Document 3 states that steelmaking slag particles contain 3.5 wt.% Or more and 10 wt.% Or less MnO. Patent Document 3 indicates, as a reason for this, that when the amount of MnO contained is less than 3.5 wt.%, A sufficient amount of polyvalent manganese may not dissolve to increase the redox potential of the rice field soil. Moreover, the applied amount described in patent document 3 is from 0.5 t / ha to 5 t / ha, and it is assumed that the dissolution of a sufficient amount of polyvalent manganese to increase the redox potential of the rice field soil will occur when the applied amount is in this range. In the case when the introduced amount is less than the above range, it is necessary, apparently, to study the conditions for more efficient dissolution of manganese.

[0038] Since Patent Document 3, as mentioned above, does not describe the basicity of slag, a basicity suitable for efficiently dissolving phosphorus and manganese in the basicity range of 0.67-5, which follows from the CaO content and SiO ₂ content specified in the patent document 3, not investigated at all.

[0039] In addition, in patent document 3 there is no description of boron, and there is no description of which structure of the slag dissolves phosphorus, calcium, silicon, manganese, etc. In addition, the applied amount is set in the range of 0.5 t / ha - 5 t / ha, and a relatively large applied amount is required; therefore, it is necessary to consider some fertilizer costs and some labor costs, which reduces economic efficiency.

<Technology Studies Disclosed in Patent Document 4 and Patent Document 5>

[0040] In the method for pre-treating molten iron disclosed in Patent Document 4 and Patent Document 5, desiliconization processing and dephosphorization treatment are sequentially performed using one converter type melting furnace; thereby, the slag containing silicic acid effective for fertilizing and the slag containing phosphoric acid are collected separately. However, for fertilizer, it is preferable that both silicic acid and phosphoric acid are contained. In addition, separately performed treatment by desiliconization and dephosphorization require effort and cost in terms of obtaining slag, which serves as raw material for fertilizer. In addition, in Patent Document 4 and Patent Document 5, the composition of the dephosphorization slag produced is not disclosed at all, and there is no description of fertilizer either. Therefore, it is not possible to evaluate whether the slag disclosed in Patent Document 4 and Patent Document 5 is suitable for fertilizing or not.

[0041] The authors of the present invention believe that in order to control the composition of the produced slag in an appropriate manner, the height of the free side of the converter-type bucket (that is, the distance from the neck to the surface of molten iron) is an important condition, as described in detail below. However, in Patent Document 4, the height of the free side of the bucket when sequentially performing desiliconization processing and dephosphorization processing using one converter-type melting furnace is not disclosed at all. In addition, in Patent Document 5, a description of the proportion of the free side of the bucket is given only for desiliconization, and there is no description of the proportion of the free side of the ladle for dephosphorization processing.

<Research technology disclosed in patent document 6>

[0042] Patent Document 6 discloses a method for producing siliceous fertilizer during the pretreatment of molten cast iron in a cast iron production process, and indicates that phosphoric acid soluble in citric acid is added to the converter slag produced by pretreatment of molten cast iron to achieve a soluble content in citric acid phosphoric acid, 5 wt.% or more. In addition, patent document 6 indicates that the phosphoric acid content in the original slag is greater than or equal to 1 wt.% And less than or equal to 4 wt.%. In patent document 6 there is no description of the content of boron, nor a description of the effect of boron on the effect of fertilizer. In addition, in patent document 6 there is no description of the height of the free side of the bucket during the production of slag, and there is no description of either a method of collecting slag during unloading, or a method of cooling it.

<Research technology disclosed in patent document 7>

[0043] Patent Document 7 discloses a silicon fertilizer in which the dissolution of silicic acid is achieved by mixing coal ash containing only insoluble silicic acid with molten stainless steel slag. However, this siliceous fertilizer is stainless steel slag, and therefore contains a large amount of chromium. Therefore, if a large amount of fertilizer is used that uses this slag as a raw material, or if such fertilizer is used for a long period of time, there is a risk that the chromium content in the soil will increase. In addition, the need to mix coal ash leads to an increase in costs due to an increase in the number of operations.

<Research technology disclosed in patent document 8>

[0044] Patent Document 8 discloses a method for manufacturing phosphoric acid-containing slag for fertilizer, and the phosphoric acid content of this fertilizer slag is 18.32 wt.% Or more. However, this phosphoric acid content deviates significantly from the phosphoric acid content in steelmaking slag, which can be produced by pretreatment of molten iron or decarburization treatment in a conventional cast iron production process, and the aforementioned phosphoric acid containing slag for fertilizer cannot be produced by pretreatment of molten iron or by treatment decarburization in the normal cast iron production process. Therefore, for the production of such slag requires a special process, which leads to increased costs.

<Research technology disclosed in patent document 9>

[0045] Patent Document 9 also discloses a method for producing a phosphate fertilizer raw material obtained in a cast iron production process, and the phosphoric acid content of this slag serving as a phosphate fertilizer raw material is 15 wt.% Or more. However, this phosphoric acid content deviates significantly from the phosphoric acid content in steelmaking slag, which can be produced by pretreatment of molten iron or by decarburization in the normal cast iron production process, and the above slag, which serves as raw material for phosphate fertilizer, cannot be produced by pretreatment of molten cast iron. cast iron or decarburization treatment in the normal cast iron production process. Therefore, for the production of such slag requires a special process, which leads to an increase in costs.

[0046] As described in detail above, there are various problems to be resolved when the steelmaking slag of the iron production process is produced as a raw material for fertilizer, or when the steelmaking slag of the iron production process is used as raw material for a fertilizer capable of supplying various minerals.

[0047] The inventors of the present invention have carried out extensive studies of the aforementioned problems, and as a result, in order to supply many types of elements P, Fe, Mn, Si, Ca, Mg, B and C, a steelmaking slag specifically designed as a raw material for fertilizer , and the method of its production, as well as the method of producing fertilizer and the method of applying fertilizer capable of supplying these elements, have successfully obtained steelmaking slag as a raw material for fertilizer, which can supply many types of elements as fertilizer for plants more easily and at lower cost. Embodiments of the present invention will be described in detail below.

(Embodiments)

<Regarding Conventional Steelmaking Slag>

[0048] Before describing in detail steelmaking slag as a fertilizer feedstock in accordance with one embodiment of the present invention, conventional steelmaking slag will be briefly described for comparison.

[0049] Examples of steelmaking slag commonly used for fertilizer include dephosphorization slag, which is a type of steelmaking slag produced as a by-product in the pre-treatment of molten iron. Dephosphorization slag is a phosphorus-containing slag that is produced as a by-product by adding lime, iron oxide or the like. as a dephosphorizer to molten iron and blowing a gas such as oxygen into the material to remove the phosphorus contained in the molten iron, it is a type of steelmaking slag.

 [0050] The composition of a typical steelmaking slag (converter slag) is published by the Japan Slag Association (http://www.slg.jp/character.html), and a typical composition is as follows:

CaO: 45.8, SiO ₂ : 11.0, total iron: 17.4, MgO: 6.5,

Al ₂ O ₃ : 1.9, S: 0.06, P ₂ O ₅ : 1.7, MnO: 5.3 (all in wt.%).

[0051] Steelmaking slag as a fertilizer raw material in accordance with one embodiment of the present invention, described in detail below, is a kind of dephosphorization slag, and is characterized in that the amounts of P ₂ O ₅ and SiO ₂ contained therein are high and the amount contained therein the total amount of iron is low compared with the composition of the above typical steelmaking slag, which is described in more detail below. In addition, the steelmaking slag as a raw material for fertilizer in accordance with the present embodiment is characterized in that the amount of boron soluble in citric acid is high in comparison with the composition of the typical steelmaking slag mentioned above.

<About steelmaking slag as a raw material for fertilizer>

[0052] Next, steelmaking slag as a raw material for fertilizer in accordance with the present embodiment will be described in detail. The steelmaking slag as a fertilizer raw material in accordance with the present embodiment is a steelmaking slag that contains the prescribed amounts of components and is obtained by performing dephosphorization of molten blast furnace iron and contains the prescribed amounts of various elements such as Ca, P, Si, Mg, Fe, Mn, B, S, and Al.

[0053] More specifically, the steelmaking slag as a raw material for fertilizer in accordance with the present embodiment contains, in wt.%, P ₂ O ₅ : greater than or equal to 2% and less than or equal to 8%, MnO: greater than or equal to 3% and less than or equal to 10%, boron: greater than or equal to 0.005% and less than 0.05%, total iron: greater than or equal to 7% and less than 15%, CaO: greater than or equal to 38% and less than or equal to 48%, SiO ₂ : greater than or equal to 22% and less than or equal to 30%, sulfur: greater than or equal to 0.1% and less than or equal to 0.6%, MgO: greater than or equal to 1% and less than or equal to 8%, and Al ₂ O ₃ : greater than or equal to 0.5% and less than or equal to 3%. In addition, the steelmaking slag as a raw material for fertilizer in accordance with the present embodiment may contain various impurities, as well as the above components. Next, each component contained in the steelmaking slag as raw material for fertilizer in accordance with the present embodiment will be described in detail.

[CaO: greater than or equal to 38 wt.% And less than or equal to 48 wt.%]

[0054] Ca is first described. Ca is a vital fertilizer for plants. In a fertilizer or steelmaking slag, when the amount of Ca contained in it is indicated, its content is calculated on the basis of CaO oxide; thus, subsequently, the amount of Ca contained will be indicated as CaO.

[0055] CaO is an alkaline compound and has the effect of improving acidic soil. In the case where the CaO content in the steelmaking slag is less than 38 wt.%, The alkalinity is weak; therefore, in acidic soil, in which an excess of iron has appeared, there is a danger that the improvement of acidic soil will be insufficient, and that Fe contained in the steelmaking slag will only cause the excess of iron to become even worse. On the other hand, in the case where the CaO content in the steelmaking slag is more than 48 wt.%, It is too high; therefore, the content of any of P ₂ O ₅ , MnO, boron, all iron, sulfur, SiO ₂ , MgO and Al ₂ O ₃ , which are other components contained in the steelmaking slag as raw material for fertilizer in accordance with this embodiment, must be set below the desired value to make the total content, including the content of these other components, less than or equal to 100%; which means that this is not preferable. In addition, it is preferable that the steelmaking slag used in the present embodiment can be stably supplied in large quantities and can be produced in a conventional cast iron production process. And from this point of view, the CaO content in the steelmaking slag as a fertilizer feed in accordance with the present embodiment is set to be greater than or equal to 38 wt.% And less than or equal to 48 wt.%. The CaO content is preferably greater than or equal to 39 wt.% And less than or equal to 47 wt.%, And more preferably greater than or equal to 40 wt.% And less than or equal to 46 wt.%.

[0056] The amount of CaO contained can be measured, for example, by X-ray fluorescence analysis. In particular, a plurality of measurement samples are prepared in which the CaO content is known, with varying contents, and the X-ray fluorescence intensity of Ca in these prepared measurement samples is measured by an X-ray fluorescence analysis device. Based on the results of measuring the X-ray fluorescence intensity from Ca and the CaO content, a calibration curve is constructed in advance indicating the relationship between the CaO content and the X-ray fluorescence intensity. Then, for the target sample with unknown CaO content, the X-ray fluorescence intensity of Ca is measured by an X-ray fluorescence analysis apparatus, and the CaO content is determined using the obtained X-ray fluorescence intensity using this calibration curve.

[0057] In this case, a sample is taken as described below, then the target sample is prepared using the following steps, and the X-ray fluorescence intensity is measured under the following measurement conditions. The analyzed sample is placed in a vibration mill (T-100, manufactured by Kawasaki Heavy Industries, Ltd.) and ground into powder (device settings: grinding time 30 seconds, speed 1000 rpm). The powder sample is classified using a sieve with a hole size of 212 microns. Then 6 g of lithium tetraborate (flux), 0.3 g of a sample that passed through a sieve with the aforementioned hole size (212 μm), and approximately two forceps of lithium iodide (separating grease) are introduced into a platinum cup and melting is carried out under conditions 1150 ° C × 10 min × 3-4 times using a ball sampler in order to prepare glass balls. In a similar manner, the control material is also processed into glass balls. A calibration curve is created using an X-ray fluorescence analysis apparatus (ZSX PrimusII manufactured by Rigaku Corporation), and a sample that passed through a sieve with the aforementioned hole size (212 μm) is quantified and subjected to confirmatory analysis using a control material. This analytical method complies with JIS M 8205, the Japanese industry standard.

[SiO ₂ : greater than or equal to 22 wt.% And less than or equal to 30 wt.%]

[0058] Si is not a vital element for plants, but it is a very important element for siliceous plants of the grass family, such as rice, wheat and corn. Silicic acid (SiO ₂ ) makes up approximately 5% of the dry weight of the rice plant. In a fertilizer or steelmaking slag, when the amount of Si is contained therein, its content is indicated based on SiO ₂ oxide; thus, in the future, the Si content will be indicated as SiO ₂ .

[0059] The steelmaking slag as a fertilizer raw material in accordance with the present embodiment contains a large amount of SiO ₂ compared to the composition of a typical steelmaking slag, as mentioned above. The steelmaking slag as a raw material for fertilizer in accordance with the present embodiment contains a large amount of available silicic acid, effective for plants, and therefore effective for supplying Si cereal plants and the like.

[0060] In the case where the SiO ₂ content in the steelmaking slag as a fertilizer feed in accordance with the present embodiment is less than 22 wt.%, The likelihood that Si will not be able to sufficiently reach the plants increases; which means that this is not preferable. On the other hand, in the case where the SiO ₂ content is more than 30 wt.%, The CaO content is also high due to the limitation on basicity, which will be described later; therefore, the content of any of MnO, boron, all iron, sulfur, SiO ₂ , MgO, and Al ₂ O ₃ , which are other components contained in the steelmaking slag as a fertilizer feed in accordance with the present embodiment, should be set lower than desired values to make the total content, including the content of these other components, less than or equal to 100%; which means that this is not preferable. Therefore, in the steelmaking slag as a raw material for fertilizer in accordance with the present embodiment, the SiO ₂ content is set to be greater than or equal to 22 wt.% And less than or equal to 30 wt.%. The content of SiO _{2 is} preferably greater than or equal to 23 wt.% And less than or equal to 29 wt.%, And more preferably greater than or equal to 24 wt.% And less than or equal to 28 wt.%.

[0061] SiO Content₂ can be measured, for example, by x-ray fluorescence analysis. In particular, many measurement samples are prepared in which the SiO content is known.₂, with varying contents, and the X-ray fluorescence intensity of Si in these prepared measuring samples is measured by an X-ray fluorescence analysis device. Based on the results of measuring the x-ray fluorescence intensity of Si and SiO content₂a calibration curve is constructed in advance indicating the relationship between the SiO content₂ and X-ray fluorescence intensity. Then for the target sample with unknown SiO content₂ measure the x-ray fluorescence intensity of Si with an x-ray fluorescence analysis device, and the SiO content is determined from the obtained x-ray fluorescence intensity using this calibration curve₂.

[0062] Moreover, the method of preparing the target sample and the conditions for measuring the intensity of x-ray fluorescence are the same as for CaO.

[Basicity (CaO content / SiO ₂ content): greater than 1.5 and less than or equal to 2.2]

[0063] In the steelmaking slag as a fertilizer raw material in accordance with the present embodiment, the above conditions are satisfied both with respect to the CaO content and the SiO ₂ content, and in addition, basicity, expressed as (CaO content / SiO ₂ content), is greater than 1.5 and less than or equal to 2.2.

[0064] In the steelmaking slag as a raw material for fertilizer in accordance with the present embodiment, the CaO content is greater than or equal to 38 wt.% And less than or equal to 48 wt.%; and therefore, the content of SiO ₂ is set as follows depending on the basicity with a breakdown into intervals of 0.1.

In the case where the basicity is 1.8: greater than or equal to 21 wt.% And less than or equal to 27 wt.%

In the case where the basicity is 1.7: greater than or equal to 22 wt.% And less than or equal to 28 wt.%

In the case where the basicity is 1.6: greater than or equal to 24 wt.% And less than or equal to 30 wt.%

In the case where the basicity is 1.5: greater than or equal to 25 wt.% And less than or equal to 32 wt.%

In the case where the basicity is 1.4: greater than or equal to 27 wt.% And less than or equal to 34 wt.%.

[0065] As mentioned above, in the case where the basicity is in the range of 1.6-1.7, the SiO ₂ content is in the range of its content prescribed in the steelmaking slag as raw material for fertilizer in accordance with the present embodiment ( greater than or equal to 22 wt.% and less than or equal to 30 wt.%).

[0066] On the other hand, in the steelmaking slag as a raw material for fertilizer in accordance with the present embodiment, the content of SiO _{2 is} greater than or equal to 22 wt.% And less than or equal to 30 wt.%; which means that the CaO content is as follows, depending on basicity, broken down into 0.1 intervals.

In the case where the basicity is 2.1: greater than or equal to 46 wt.% And less than or equal to 63 wt.%

In the case where the basicity is 2.2: greater than or equal to 48 wt.% And less than or equal to 66 wt.%

In the case where the basicity is 2.3: greater than or equal to 51 wt.% And less than or equal to 69 wt.%.

[0067] It is in the case where the basicity is in the range of 2.1-2.2, the above result is in the range of CaO content prescribed in the steelmaking slag as raw material for fertilizer in accordance with the present embodiment (greater than or equal to 38 wt.% and less than or equal to 48 wt.%).

[0068] Therefore, it can be said that basicities greater than 1.5 and less than or equal to 2.2 are those that can satisfy the conditions for the CaO content and SiO ₂ content in the steelmaking slag as fertilizer feed in accordance with the present embodiment.

[0069] The reasons why attention is focused on the basics of about 1.4-1.8 and the basics of about 2.1-2.3 in the above description are as follows.

[0070] The sign most characterizing slag properties is basicity. CaO is a component that serves as the main factor in slag basicity. In a real cast iron production process, the usual basicities of steelmaking slag obtained by pre-treatment with dephosphorization of molten cast iron are about 1.5-1.8 and are easy to obtain. The authors of the present invention with the help of experimental studies have found that the basicity of the slag, in which the dissolution of the effective components of the fertilizer, such as silicic acid, phosphoric acid, manganese and boron, can be achieved with a better balance, there are about 1.5-1.8. Thus, in the above description, attention is focused on a basicity of about 1.4-1.8.

[0071] On the other hand, as mentioned above, most often the basicity of steelmaking slag obtained by pre-treatment of dephosphorization of molten cast iron in a real cast iron production process is about 1.5-1.8; therefore, to obtain steelmaking slag with a basicity greater than or equal to 2, an operation is performed to increase the CaO content or an operation to reduce the SiO ₂ content. Here, during an operation to increase the CaO content, the amount of lime additive added as a source of CaO increases, and this requires certain costs. Therefore, an operation can be performed to set the SiO ₂ content relatively low, and thereby the aforementioned steelmaking slag can be obtained without increasing costs. When using steelmaking slag with a basicity greater than or equal to 2 as a raw material for fertilizer, a larger amount of CaO can be included in steelmaking slag as a raw material for fertilizer. CaO is alkaline and affects the improvement of acidic soil with low pH; thus, even if an operation other than the normal cast iron production process is performed, there is a reason to achieve a basicity similar to that mentioned above. Therefore, in the above description, attention is focused on a basicity of about 2.1-2.3.

[0072] In the steelmaking slag as a fertilizer raw material in accordance with the present embodiment, when the basicity is less than or equal to 1.5, the CaO content is relatively low from the point of view of being used as a fertilizer raw material, and therefore the acid improvement effect soil is weak; which means that this is not preferable. On the other hand, in steelmaking slag as a fertilizer raw material in accordance with the present embodiment, when the basicity is more than 2.2, there is a possibility that from the point of view of using more CaO as a raw material for fertilizer, what is needed to improve acidic soil, and this will cause an increase in the cost of lime, added as a source of CaO; which means that this is not preferable. Therefore, the basicity of steelmaking slag as a raw material for fertilizer in accordance with the present embodiment is set to be greater than 1.5 and less than or equal to 2.2. If the basicity is set to be greater than 1.5 and less than or equal to 2.2, the cost of lime, which is added from the point of view of use as a raw material for fertilizer to obtain the effect of moderate improvement in acidic soil and an increase in CaO content, can be suppressed. The basicity is preferably greater than or equal to 1.6 and less than or equal to 2.1, and more preferably greater than or equal to 1.6 and less than or equal to 2.0.

[0073] Furthermore, by controlling the basicity of greater than 1.5 and less than or equal to 2.2, both the 2CaO⋅SiO ₂ -3CaO⋅P ₂ O ₅ solid solution and the solid solution based on it are easily formed in the steelmaking slag produced. FeO-MnO-CaO-SiO ₂ . In addition, as will be described in more detail below, during the production of steelmaking slag, rapid cooling can be performed during solidification of the slag, and thereby the above two types of solid solutions are formed even more easily. As will be described in detail below, these solid solutions contribute to the dissolution of not only silicic acid, but also phosphoric acid, manganese and boron; and therefore, for steelmaking slag as a raw material for fertilizer, the content of both of these solid solutions is preferred.

[P ₂ O ₅ : greater than or equal to 2 wt.% And less than or equal to 8 wt.%; soluble P ₂ O ₅ fraction: greater than or equal to 50%]

[0074] The following describes P. P is a vital element for plants, along with N and K. P is an element necessary for substances involved in energy metabolism, such as DNA and RNA, which are part of genes, and ATP, substances included in the cell membrane, etc. In addition, P is an element that acts on root growth points and influences root growth. If phosphorus is not enough, root growth is suppressed.

[0075] In a fertilizer or steelmaking slag, when the quantity P is contained therein, its content is indicated based on P ₂ O ₅ oxide; thus, in the future, the content of P will be indicated as P ₂ O ₅ .

[0076] In soil under acidic conditions, where Al and Fe tend to ionize and dissolve, it is likely that P will be converted to an insoluble form of aluminum phosphate (AlPO ₄ ) or iron phosphate (FePO ₄ ), and plant roots cannot absorb phosphate -ions (PO ₄ ^3- ) containing P. Since the steelmaking slag as a fertilizer raw material according to the present embodiment contains CaO and MgO and is alkaline, the steelmaking slag as a fertilizer raw material can improve acid soil to prevent Al ionization and Fe and washout them from the soil, and at the same time can gradually dissolve P in the form of phosphate ions (PO ₄ ^3- ).

[0077] In the steelmaking slag as a raw material for fertilizer in accordance with the present embodiment, P is present mainly in the form of a substance having the composition Ca ₂ SiO ₄ —Ca ₃ (PO ₄ ) ₂ . In the soil, P gradually dissolves in the form of PO ₄ ^3- from fertilizer containing steelmaking slag as a fertilizer feed in accordance with the present embodiment, together with Ca and Si. Consequently, P can gradually enter the plants without going into an insoluble form with Al or Fe, over a long period of time, of the order of several months, which is equivalent to one period of plant vegetation, such as rice.

[0078] In the steelmaking slag as a fertilizer raw material in accordance with the present embodiment, when the P ₂ O ₅ content is less than 2 wt.%, Effects like the ones mentioned above cannot be reliably obtained. Therefore, in the steelmaking slag as a raw material for fertilizer in accordance with the present embodiment, the content of P ₂ O _{5 is} set to be greater than or equal to 2 wt.%.

[0079] On the other hand, in the steelmaking slag as a fertilizer feed in accordance with the present embodiment, when the content of P ₂ O ₅ is more than 8 wt.%, There is a possibility that P ₂ O ₅ will be excessively to enter the soil, while the balance with nitrogen and potassium, which are the other of the three main fertilizing elements, will be lost; which means that this is not preferable. Therefore, in the steelmaking slag as a raw material for fertilizer in accordance with the present embodiment, the content of P ₂ O _{5 is} set to less than or equal to 8 wt.%.

[0080] In the steelmaking slag as a fertilizer raw material according to the present embodiment, the content of P ₂ O _{5 is} preferably greater than or equal to 3 wt.% And less than or equal to 8 wt.%, And more preferably greater than or equal to 3 wt.% And less than or equal to 6 wt.%.

[0081] The Japan Fertilizer Control Law for Slag Phosphate Fertilizers requires that the content of P ₂ O ₅ soluble in citric acid be greater than or equal to 3 wt.%. The steelmaking slag as a raw material for fertilizer in accordance with the present embodiment does not necessarily meet this standard slag phosphate fertilizer, but promises the effect of phosphoric fertilizer for the reason mentioned above. Since the content of P ₂ O ₅ in the steelmaking slag as a raw material for fertilizer in accordance with the present embodiment is greater than or equal to 2 wt.%, The content of soluble in citric acid P ₂ O _{5 is} approximately greater than or equal to 1.0 wt.%.

[0082] On the other hand, with regard to P ₂ O ₅ , which plants can actually absorb from the roots, it is known that soluble P ₂ O ₅ that dissolves in a neutral aqueous solution of ammonium citrate (Peterman ammonium citrate solution) provides a more suitable value than soluble in citric acid P ₂ O ₅ , which is soluble in a 2% aqueous solution of citric acid. The steelmaking slag as a raw material for fertilizer in accordance with the present embodiment was able to increase the proportion of soluble P ₂ O ₅ in P ₂ O ₅ contained in the slag to 50% or more by controlling the composition and structure of the slag. That is, the mass fraction of soluble P ₂ O ₅ in P ₂ O ₅ contained in the slag can be made greater than or equal to 50% by production of steelmaking slag as a raw material for fertilizer in accordance with the method of producing steelmaking slag as a raw material for fertilizer, which is described in detail below. The upper limit of the mass fraction of soluble P ₂ O ₅ in P ₂ O ₅ contained in the slag is not specifically prescribed, and is preferably as high as possible; but this mass fraction cannot be made equal to 100%, taking into account the results obtained in the actual preparation and analysis of a large number of samples of steelmaking slag, and the value of the upper limit is approximately 85%. The mass fraction of soluble P ₂ O ₅ in P ₂ O ₅ contained in the slag is preferably greater than or equal to 60%, and more preferably greater than or equal to 70%.

[0083] The content of P ₂ O ₅ can be measured, for example, by x-ray fluorescence analysis. In particular, a plurality of measurement samples are prepared in which the content of P is known, with varying contents, and the X-ray fluorescence intensity of P in these prepared measurement samples is measured by an X-ray fluorescence analysis device. Based on the results of measuring the X-ray fluorescence intensity from P and the amount of P ₂ O ₅ calculated from the P content, a calibration curve is constructed in advance that indicates the relationship between the amount of P ₂ O ₅ calculated from phosphorus and the X-ray fluorescence intensity. Then, for a target sample with an unknown content of P, the X-ray fluorescence intensity from P is measured by an X-ray fluorescence analysis device, and the P ₂ O ₅ content is determined from the obtained X-ray fluorescence intensity using this calibration curve.

[0084] Moreover, the method of preparing the target sample and the conditions for measuring the intensity of x-ray fluorescence are the same as for CaO.

[0085] The content of soluble P ₂ O ₅ can be measured using the absorption spectroscopy method of ammonium vanadomolybdate using a solution of ammonium citrate Peterman. The mass fraction of soluble P ₂ O ₅ in P ₂ O ₅ can be calculated using the contained amount of P ₂ O ₅ and the measured contained amount of soluble P ₂ O ₅ .

[MgO: greater than or equal to 1 wt.% And less than or equal to 8 wt.%]

[0086] The following describes Mg. Mg is an element necessary for plants, and is regarded as a secondary element.

[0087] In general, the MgO content in the steelmaking slag is significantly lower than the CaO content. The Mg contained in the steelmaking slag originates mainly from Mg added during sintering or dissolving from the refractory bricks of the converter wall. In a fertilizer or steelmaking slag, when the amount of Mg contained therein is indicated, its content is indicated based on MgO oxide; thus, in the future, the Mg content will be indicated as MgO.

[0088] MgO is alkaline and has the effect of improving acidic soil, like CaO. In the steelmaking slag as a fertilizer raw material in accordance with the present embodiment, when the MgO content is less than 1 wt.%, The aforementioned acid soil improvement effect cannot be exhibited. On the other hand, an ideal ratio of lime / magnesium oxide is considered approximately 2.5-6 from the point of view of use as a raw material for fertilizer. In the steelmaking slag as a raw material for fertilizer in accordance with the present embodiment, the CaO content is high, from 38% to 48%; and therefore, in order to satisfy the lime / magnesium oxide ratio mentioned above, the content of magnesium oxide is, for example, 6.3-8%, even when the lime / magnesium oxide ratio is at most 6. However, if in the actual process of cast iron production a MgO source is added, it is difficult to make the MgO content of more than 8 wt.%. Therefore, in the steelmaking slag as a raw material for fertilizer in accordance with the present embodiment, the MgO content is set to be greater than or equal to 1 wt.% And less than or equal to 8 wt.%. The MgO content is preferably greater than or equal to 2 wt.% And less than or equal to 8 wt.%, And more preferably greater than or equal to 3 wt.% And less than or equal to 8 wt.%.

[0089] The MgO content can be measured, for example, by X-ray fluorescence analysis. In particular, a plurality of measurement samples are prepared in which the Mg content is known, with varying contents, and the X-ray fluorescence intensity of Mg in these prepared measurement samples is measured by an X-ray fluorescence analysis device. Based on the results of measuring the X-ray fluorescence intensity from Mg and the MgO amount calculated from the Mg content, a calibration curve is constructed in advance indicating the relationship between the MgO amount calculated from magnesium and the X-ray fluorescence intensity. Then, for the target sample with unknown Mg content, the X-ray fluorescence intensity of Mg is measured by an X-ray fluorescence analysis apparatus, and the MgO content is determined from the obtained X-ray fluorescence intensity using this calibration curve.

[0090] Moreover, the method of preparing the target sample and the conditions for measuring the intensity of x-ray fluorescence are the same as for CaO.

[Total iron: greater than or equal to 7 wt.% And less than 15 wt.%]

[0091] The following describes Fe. Fe is a trace element necessary for plants, and iron-containing substances are used as special fertilizers. However, in acidic soil, Fe can cause an excess of iron for plants, and therefore is also an element that can be harmful to plants.

[0092] The steelmaking slag as a fertilizer raw material in accordance with the present embodiment contains CaO in an amount greater than or equal to 38 wt.% And less than or equal to 48 wt.% And contains MgO in an amount greater than or equal to 1 wt.% And less than or equal to 8 wt.%, and therefore is alkaline; in addition, as will be described later, it contains a relatively low total amount of iron greater than or equal to 7 wt.% and less than 15 wt.%; which means that it can supply Fe as a trace element for plants even in soil in which there is concern about an excess of iron in acidic soil.

[0093] A sign of a fertilizer containing steelmaking slag as a raw material for fertilizer in accordance with this embodiment is a sign of a high bulk density, and therefore it is not washed out by rainwater, but remains after it and allows each element with the effect of fertilizer to dissolve within a long period of time. Fe is also an important element in terms of increasing the bulk density of a fertilizer containing steelmaking slag as a fertilizer feed in accordance with the present embodiment.

[0094] Fe is an element inevitably contained in various types of steelmaking slag. In the steelmaking slag as a fertilizer raw material in accordance with the present embodiment, when the total iron content is less than 7 wt.%, The bulk density is small, and the probability that the fertilizer containing steelmaking slag as a raw material for fertilizer in accordance with the present embodiment, will be washed away by rainwater, increases. On the other hand, if the total iron content is greater than or equal to 15 wt.%, The likelihood that an excess of iron is formed for plants in acidic soil increases; which means that this is not preferable. Therefore, the total iron content in the steelmaking slag as a raw material for fertilizer in accordance with the present embodiment is set to be greater than or equal to 7 wt.% And less than 15 wt.%. The total iron content is preferably greater than or equal to 8 wt.% And less than or equal to 14 wt.%, And more preferably greater than or equal to 9 wt.% And less than or equal to 13 wt.%.

[0095] When the steelmaking slag as a raw material for fertilizer in accordance with the present embodiment is analyzed using an X-ray diffractometer, a peak of a mineral belonging to the FeO-CaO-SiO ₂ system is observed. On the other hand, when the steelmaking slag as a raw material for fertilizer in accordance with the present embodiment is immersed in water for a long period of time, and then the structure is studied using an electronic microprobe analyzer (EPMA), there is a trace of a decrease in concentration in the part where Fe and Mn overlap. Based on this, it is assumed that during the formation of a solid solution based on FeO-MnO-CaO-SiO ₂ , in which MnO and FeO are dissolved together as a solid solution, the dissolution of Mn together with Fe is accelerated. Such an oxidation state of Fe is obtained by producing steelmaking slag as a raw material for fertilizer in accordance with the method for producing steelmaking slag as a raw material for fertilizing described below. The term "solid solution" in the present embodiment specifically describes the basic chemical components and may include, in terms of its properties, also components that are not specifically described. For example, a FeO — MnO — CaO — SiO ₂ based solid solution may include one in which MgO is in the form of a solid solution.

[0096] In the production of steelmaking slag as a raw material for fertilizer in accordance with the method for producing steelmaking slag as a raw material for fertilizer described in detail below, in the steelmaking slag produced as a raw material for fertilizer, the total iron content becomes lower than in steelmaking slag of a conventional converter process , and a content range such as the one mentioned above is achieved, and an Fe oxidation state such as the one mentioned above is obtained.

[0097] The total iron content can be measured, for example, by x-ray fluorescence analysis. In particular, a plurality of measurement samples are prepared in which the total iron content is known, with varying contents, and the X-ray fluorescence intensity of Fe in these prepared measurement samples is measured by an X-ray fluorescence analysis device. Based on the results of measuring the x-ray fluorescence intensity of Fe and the total iron content, a calibration curve is constructed in advance indicating the relationship between the total iron content and the X-ray fluorescence intensity. Then, for the target sample with unknown total iron content, the X-ray fluorescence intensity of Fe is measured by an X-ray fluorescence analysis device, and the total iron content is determined from the obtained X-ray fluorescence intensity using this calibration curve.

[0098] Moreover, the method of preparing the target sample and the conditions for measuring the intensity of x-ray fluorescence are the same as for CaO.

[MnO: greater than or equal to 3 wt.% And less than or equal to 10 wt.%; soluble manganese in citric acid: greater than or equal to 80%]

[0099] The following describes Mn. Mn is also an element with a fertilizer effect for plants as a trace element. In a fertilizer or steelmaking slag, when the amount of Mn contained in it is indicated, its content is calculated on the basis of MnO oxide; thus, hereinafter, the content of Mn will be indicated as MnO.

[0100] In the steelmaking slag as a raw material for fertilizer in accordance with the present embodiment, when the MnO content is less than 3 wt.%, It is small; therefore, the dissolution of Mn from a fertilizer containing steelmaking slag as a fertilizer feed in accordance with the present embodiment is insufficient, and the effect of fertilizer Mn cannot be exhibited. On the other hand, when the MnO content is more than 10 wt.%, An excess of manganese is formed for plants, especially in acidic soil; which means that this is not preferable. Therefore, in the steelmaking slag as a raw material for fertilizer in accordance with the present embodiment, the MnO content is set to be greater than or equal to 3 wt.% And less than or equal to 10 wt.%. The content of MnO is preferably greater than or equal to 4 wt.% And less than or equal to 9 wt.%, And more preferably greater than or equal to 5 wt.% And less than or equal to 8 wt.%.

[0101] When forming a solid solution of 2CaO⋅SiO ₂ -3CaO⋅P ₂ O ₅ and a solid solution based on FeO-MnO-CaO-SiO ₂ in steelmaking slag as a raw material for fertilizer in accordance with the present embodiment, the dissolution of Mn like the above accelerates, and in addition, the dissolution of silicic acid, phosphoric acid and boron can be accelerated.

[0102] It is known that plants secrete organic acid from the roots, and in this respect, citric acid soluble manganese, which is manganese soluble in a 2% aqueous citric acid solution, is an indicator of the manganese used by plants. In the steelmaking slag as a fertilizer raw material according to the present embodiment, it was possible to provide an amount of citric acid soluble MnO of 80% or more of the total MnO contained in the steelmaking slag by controlling its composition and structure. That is, the mass fraction of citric acid soluble MnO in the MnO contained in the slag can be made greater than or equal to 80% by producing steelmaking slag as a raw material for fertilizer in accordance with a method for producing steelmaking slag as a raw material for fertilizer, which will be described in detail below. . The upper limit of the mass fraction of citric acid soluble MnO in the MnO contained in the slag is not specifically prescribed, and is preferably as high as possible; but this mass fraction cannot be made equal to 100%, taking into account the results obtained in the actual preparation and analysis of a large number of samples of steelmaking slag, and the value of the upper limit is approximately 95%. The mass fraction of citric acid soluble MnO in the MnO contained in the slag is preferably greater than or equal to 85%, and more preferably greater than or equal to 90%.

[0103] The content of MnO can be measured, for example, by x-ray fluorescence analysis. In particular, a plurality of measurement samples are prepared in which the content of Mn is known, with varying contents, and the X-ray fluorescence intensity of Mn in these prepared measurement samples is measured by an X-ray fluorescence analysis device. Based on the results of measuring the X-ray fluorescence intensity from Mn and the amount of MnO calculated from manganese, a calibration curve is constructed in advance that indicates the relationship between the MnO content calculated from manganese and the X-ray fluorescence intensity. Then, for a target sample with an unknown Mn content, the X-ray fluorescence intensity of Mn is measured by an X-ray fluorescence analysis apparatus, and the MnO content is determined from the obtained X-ray fluorescence intensity using this calibration curve.

[0104] Moreover, the method of preparing the target sample and the conditions for measuring the intensity of x-ray fluorescence are the same as for CaO.

[0105] The content of citric acid soluble MnO can be measured using the Leaching Method described in Testing Methods for Fertilizers (2016) using a 2% aqueous citric acid solution and the flame atomic absorption spectroscopy method prescribed by the Food and agricultural materials (Food and Agricultural Materials Inspection Center, FAMIC). The mass fraction of citric acid soluble MnO in MnO can be calculated using the contained amount of MnO and the measured amount of citric acid soluble MnO.

[Boron: greater than or equal to 0.005 wt.% And less than 0.05 wt.%; the proportion of boron soluble in citric acid: greater than or equal to 95%]

[0106] The following describes boron. Boron is a trace element necessary for plants; it is known that if boron is not enough, then plants have a deficiency of boron. Boron is an element necessary for the synthesis of the membrane of plant cells.

[0107] On the other hand, it is known that when the boron content in the soil is more than 5 mg / kg, an excess of boron may occur in the plants. A boron content of 5 mg / kg is a very low value. Examples of a commercially available fertilizer containing boron include a borate fertilizer (boron in citric acid: greater than or equal to 35%), fused boron fertilizer (soluble in citric acid boron: approximately 24%), and a composite fertilizer with fused trace elements (FTE) (boron soluble in citric acid: 5-9%); however, they all contain large amounts of boron, and therefore there is a concern that excessive use of these fertilizers will result in an excess of boron. When these commercially available fertilizers are applied to the soil, it is difficult to make the boron content in the soil less than or equal to 5 mg / kg.

[0108] For example, in the case where a fertilizer with a boron content of 5% is applied per 1 kg of soil, assuming that the boron is not contained in this soil, an attempt to make the boron content in the soil less than or equal to 5 mg / kg requires uniform mixing with the soil a very small amount of fertilizer applied, less than or equal to 100 mg. Therefore, with conventional application methods, there is great concern that boron will be introduced in large excess. In order to uniformly apply small amounts of these fertilizers containing large amounts of boron, you can pre-dissolve or disperse the fertilizers in water and apply them; but it is assumed that conventional fertilizers will most likely be washed away by rainwater, etc. Therefore, it is assumed that, from the point of view of optimal soil supply with boron, a fertilizer with a low boron content that is not susceptible to rapid leaching is preferred.

[0109] In the steelmaking slag as a fertilizer raw material according to the present embodiment, when the boron content is less than 0.005 wt.% (= 50 mg / kg), even when fertilizer containing steelmaking slag as raw materials for fertilizer in accordance with the present embodiment, the effect of fertilizer with boron for plants cannot be manifested, because the amount of boron introduced is small. On the other hand, in a normal cast iron production process, steelmaking slag is obtained in which the boron content is greater than or equal to 0.05 wt.%; and the difficulty of additionally adding a source of boron, such as borax, to increase the boron content is a factor in increasing cost, which means it is not preferred. The steelmaking slag as a fertilizer feed in accordance with the present embodiment has a much higher proportion of boron soluble in citric acid in the boron contained than conventional boron fertilizers, and therefore has approximately the same ability to supply boron as conventional fertilizers based on boron, even when the boron content in it is less than 0.05 wt.%. Therefore, in the steelmaking slag as a raw material for fertilizer in accordance with the present embodiment, the boron content is set to be greater than or equal to 0.005 wt.% And less than 0.05 wt.%. The boron content is preferably greater than or equal to 0.01 wt.% And less than or equal to 0.05 wt.%, And more preferably greater than or equal to 0.02 wt.% And less than or equal to 0.05 wt.%.

[0110] It is known that plants secrete organic acid from the roots, as mentioned above, and in this regard, boron soluble in citric acid, which is boron that dissolves in a 2% aqueous citric acid solution, is an indicator of the boron used by plants . In the steelmaking slag as a raw material for fertilizer in accordance with the present embodiment, it was possible to include boron in its composition, which is easily soluble in the soil, and it was possible to provide an amount of boron soluble in citric acid of 95% or more of the total boron contained in the steelmaking slag by its structure, the control by setting the basicity, that is the ratio between the amounts contained CaO and SiO ₂ in a range more than 1.5 and less than or equal to 2.2, as well as adequately first select the temperature during the production of the molten slag and cooling process during the solidification time of the slag, thereby obtaining the boron in the form of, for example, compounds in which a portion of SiO ₂ in the compound is replaced by SiO ₂ B ₂ O ₃ or the like That is, the mass fraction of boron soluble in citric acid in boron contained in the slag can be made greater than or equal to 95% by production of steelmaking slag as a raw material for fertilizer in accordance with the method of producing steelmaking slag as a raw material for fertilizer, which will be described in detail below . By increasing the proportion of boron soluble in citric acid, one can obtain a high fertilizing effect, despite the fact that the amount of boron contained in steelmaking slag as a raw material for fertilizer is low.

[0111] The boron content can be measured, for example, using an inductively coupled plasma atomic emission spectroscopy (ICP) method. In particular, 0.5 g of the sample and reagent (2 g of sodium carbonate and 3 g of sodium peroxide) are placed in a nickel (Ni) crucible and alkaline melting is performed (burner heating). After alkaline melting, the nickel crucible is placed in a beaker, water and hydrochloric acid are poured into it (1: 9), the nickel crucible is taken out after its contents have dissolved, and the beaker is heated; thus the sample is dissolved. The resulting dissolved sample was introduced into inductively coupled plasma (device: SPS3100 manufactured by Hitachi High-Tech Science Corporation), light emission due to boron was measured at a wavelength of 249.753 nm; Thus, boron is quantified. This analytical method complies with Appendix A of JIS 5011-3.

[0112] The content of boron soluble in citric acid can be measured by using the leaching method described in Testing Methods for Fertilizers (2016) using a 2% aqueous citric acid solution and the azomethine H method prescribed by the Food and Agricultural Inspection Center materials (FAMIC). The mass fraction of boron soluble in citric acid in the boron contained can be calculated using the amount of boron contained and the measured amount of boron soluble in citric acid.

[Sulfur: from 0.1 wt.% To 0.6 wt.%]

[0113] Sulfur is further described. Sulfur is an element necessary for the biosynthesis of sulfur-containing amino acids, such as cysteine and methionine, as well as for the biosynthesis of proteins, and is an element essential for the growth of batun, onions, garlic, etc.

[0114] In the case where the sulfur content in the steelmaking slag as a raw material for fertilizer in accordance with the present embodiment is less than 0.1 wt.%, Even when fertilizer is applied to the soil using steelmaking slag as a raw material for fertilizer in accordance with the present embodiment, it is likely that the effect of sulfur fertilizer for plants cannot be exhibited because the amount of sulfur is small. On the other hand, in the case where the sulfur content in the steelmaking slag as a fertilizer feed in accordance with the present embodiment is more than 0.6 wt.%, There may be a problem of the formation of hydrogen sulfide in the soil from the sulfur supplied by the fertilizer and, as a result, rotting of roots, and similar problems. Therefore, the sulfur content in the steelmaking slag as a raw material for fertilizer in accordance with the present embodiment is set to be greater than or equal to 0.1 wt.% And less than or equal to 0.6 wt.%. The sulfur content is preferably greater than or equal to 0.2 wt.% And less than or equal to 0.6 wt.%, And more preferably greater than or equal to 0.3 wt.% And less than or equal to 0.6 wt.%.

[0115] The sulfur content can be measured, for example, using an alkaline melting method and ICP atomic emission spectroscopy. In particular, 0.5 g of the sample and reagent (2 g of sodium carbonate and 3 g of sodium peroxide) are placed in a nickel crucible and alkaline melting is performed (heating by a burner). After alkaline melting, the nickel crucible is placed in a beaker, water and hydrochloric acid (1: 9) are poured into it, the crucible is taken out after its contents have dissolved, and the beaker is heated; thus the sample is dissolved. The resulting dissolved sample was introduced into inductively coupled plasma (device: SPS3100 manufactured by Hitachi High-Tech Science Corporation), the light emission due to sulfur was measured at a wavelength of 182.036 nm; thus, sulfur is quantified. This analytical method complies with Appendix A of JIS 5011-3.

[Al ₂ O ₃ : greater than or equal to 0.5 wt.% And less than or equal to 3 wt.%]

[0116] The following describes Al. In a fertilizer or steelmaking slag, when the amount of Al contained therein is indicated, its content is indicated based on Al ₂ O ₃ oxide; thus, in the future, the Al content will be indicated as Al ₂ O ₃ .

[0117] In acidic soil, Al is converted to an aluminum ion, Al ³⁺ , and binds to a phosphate ion, PO ₄ ^3- ; which means that Al suppresses the uptake of P by plant roots. Therefore, the content of Al ₂ O ₃ in the steelmaking slag as a fertilizer feed in accordance with the present embodiment should preferably be as low as possible.

[0118] In the case where the content of Al ₂ O ₃ in the steelmaking slag as a fertilizer raw material in accordance with the present embodiment is more than 3 wt.%, The dissolution of P from a fertilizer containing steelmaking slag as a fertilizer raw material in accordance with the present embodiment, is suppressed for the above reason. On the other hand, when dephosphorization is performed on molten cast iron, Al ₂ O _{3 is} inevitably mixed in the slag, which means that it is difficult to make the Al ₂ O ₃ content less than or equal to 0.5 wt%. Therefore, in the steelmaking slag as a fertilizer raw material in accordance with the present embodiment, the Al ₂ O ₃ content is set to be greater than or equal to 0.5 wt.% And less than or equal to 3 wt.%. The content of Al ₂ O _{3 is} preferably greater than or equal to 0.5 wt.% And less than or equal to 2.5 wt.%, And more preferably greater than or equal to 0.5 wt.% And less than or equal to 2 wt.%.

[0119] The Al ₂ O ₃ content can be measured, for example, by X-ray fluorescence analysis. In particular, a plurality of measurement samples are prepared in which the Al content is known with varying contents, and the X-ray fluorescence intensity of Al in these prepared measurement samples is measured by an X-ray fluorescence analysis device. Based on the results of measuring the X-ray fluorescence intensity from Al and the amount of Al ₂ O ₃ calculated from the aluminum content, a calibration curve is constructed in advance indicating the relationship between the Al ₂ O ₃ content and the X-ray fluorescence intensity. Then, for the target sample with unknown Al content, the X-ray fluorescence intensity from Al is measured by an X-ray fluorescence analysis device, and the Al ₂ O ₃ content is determined using the obtained X-ray fluorescence intensity using this calibration curve.

[0120] Moreover, the method of preparing the target sample and the conditions for measuring the intensity of x-ray fluorescence are the same as for CaO.

[Bulk density: greater than or equal to 1.9 and less than or equal to 2.8]

[0121] In the presence of a composition such as the one mentioned above, the steelmaking slag as a fertilizer feed in accordance with the present embodiment has a bulk density (more specifically, free bulk density) of greater than or equal to 1.9 and less than or equal to 2.8. In the case when the bulk density is less than 1.9, the likelihood of leaching of fertilizer increases with a large amount of rainfall; which means that this is not preferable. On the other hand, when the bulk density is more than 2.8, the fertilizer worker feels heavier, which means that this is not preferable. The bulk density of the steelmaking slag as a fertilizer feed in accordance with the present embodiment is preferably greater than or equal to 2.0 and less than or equal to 2.7, and more preferably greater than or equal to 2.1 and less than or equal to 2.6.

[0122] The bulk density of steelmaking slag as a raw material for fertilizer can be measured, for example, by the following method. Namely, bulk density (free bulk density) can be obtained by dividing a mass that easily fills a certain volume by this volume. In this case, the slag used for measurement has a particle size corresponding to MS-25 prescribed in JIS A5015, and mass per unit volume (= bulk density) is measured in accordance with JIS A1104.

[About the structure of steelmaking slag as a raw material for fertilizer]

[0123] The steelmaking slag as a fertilizer raw material in accordance with the present embodiment preferably contains a 2CaO⋅SiO ₂ -3CaO⋅P ₂ O ₅ solid solution and a FeO-MnO-CaO-SiO ₂ solid solution in its structure. These solid solutions can be formed with better efficiency by rapidly cooling the slag when it solidifies from the molten state during the production of steelmaking slag as a raw material for fertilizer, as will be described below.

[0124] In soil, in addition to calcium and silicic acid, phosphoric acid dissolves more efficiently from a 2CaO⋅SiO ₂ -3CaO⋅P ₂ O ₅ solid solution. In addition, in soil, iron and manganese dissolve more efficiently from a solid solution based on FeO-MnO-CaO-SiO ₂ . Therefore, due to the content in the steelmaking slag as a fertilizer raw material in accordance with the present embodiment of both of these solid solutions in its structure, elements with a fertilizer effect, such as calcium, silicic acid, phosphoric acid, iron and manganese, can be more efficient dissolved in the soil. In addition, in steelmaking slag as a raw material for fertilizer produced by the production method described below, part of the SiO ₂ in these solid solutions is likely to be replaced with B ₂ O ₃ for some unclear reason; therefore, when both of these solid solutions are present, boron can also dissolve.

[0125] The existence of the aforementioned 2CaO⋅SiO ₂ -3CaO⋅P ₂ O ₅ solid solution and a FeO-MnO-CaO-SiO ₂ solid solution can be verified by a method such as shown below.

[0126] For example, steelmaking slag as a fertilizer raw material according to the present embodiment is pulverized and then X-ray diffracted using a conventional X-ray diffractometer (eg, SmartLab manufactured by Rigaku Corporation) by focusing (θ-2θ measurement), in which Co-Kα (λ = 1.7902 Å) is used as the X-ray source, the load power of the X-ray source (tube voltage / tube current) is 5.4 kW (40 kV / 135 mA), using a scintillation counter is used, and the scanning speed is 1.5 ° / min in order to study the 2CaO⋅SiO ₂ crystal, the FeO⋅CaO⋅SiO ₂ crystal, etc. In addition, the steelmaking slag as a fertilizer raw material according to the present embodiment is embedded in a known resin such as epoxy, and then grinding and polishing are performed to expose a smooth cut of the steelmaking slag as a fertilizer raw material, and a map of the distribution of structural elements is obtained slag observed in the section at an accelerating voltage of 15 kV using a conventional EPMA device (for example, JXA-8100 manufactured by JEOL Ltd.). In the slag structure, in which all of Ca, Si, O, and P are observed, and in the slag structure, in which all of Fe, Mn, Ca, Si, and O are observed in the measurement region narrowed to a diameter of 100 μm, EPMA calculation of each the element is analyzed and determined semi-quantitatively using the ZAF method; thereby, it can be checked whether a solid solution of 2CaO⋅SiO ₂ -3CaO⋅P ₂ O ₅ or a solid solution based on FeO-MnO-CaO-SiO ₂ exists.

[About the particle size of steelmaking slag as a raw material for fertilizer]

[0127] In the present embodiment, the steelmaking slag as a fertilizer raw material, such as described above, can suitably be used as a fertilizer raw material when brought to the appropriate particle size by grinding or the like. Known products, such as a jaw crusher, a hammer crusher, a core mill, a ball mill, and a roller mill, can be used as grinding raw materials for grinding steelmaking slag.

[0128] Using a grinding method, such as the one mentioned above, steelmaking slag as a raw material for fertilizer is preferably adjusted to a particle size of less than 5 mm, and more preferably to a particle size of less than 600 μm. These particle sizes are determined by a sieve screening method in accordance with JIS Z8801. In the case where the particle size of the steelmaking slag as a raw material for fertilizer is greater than or equal to 5 mm, the specific surface area of the steelmaking slag as a raw material for fertilizer is too small, and the dissolution efficiency of each fertilizer element may decrease. When the particle size of the steelmaking slag as a raw material for fertilizer is less than 600 microns, the specific surface area of the steelmaking slag as a raw material for fertilizer increases, and the dissolution efficiency of each fertilizer element can improve.

[0129] In the steelmaking slag as a fertilizer raw material in accordance with the present embodiment, the mass fraction of particles with sizes less than 600 microns is preferably greater than or equal to 60% of the total mass. If the mass fraction of particles with sizes less than 600 microns is greater than or equal to 60%, the dissolution efficiency of each fertilizer element can be further improved. The mass fraction of particles with sizes less than 600 microns is more preferably greater than or equal to 80%.

[0130] Steel smelting slag as a raw material for fertilizer in accordance with the present embodiment has been described in detail.

<About the method of production of steelmaking slag as a raw material for fertilizer>

[0131] A method for producing steelmaking slag as a raw material for fertilizer in accordance with the present embodiment will be described in detail below. Steelmaking slag as a raw material for fertilizer in accordance with the present embodiment is produced by performing a special dephosphorization treatment of molten blast furnace iron, such as described below.

[0132] Steelmaking slag as a fertilizer raw material in accordance with the present embodiment, such as described above, is produced (1) by pouring molten blast furnace iron into a converter-type ladle so that the clearance coefficient, expressed as (free height of the bead, corresponding to the length from the neck to the surface of the molten molten iron / inner bucket height corresponding to the distance from the neck to the inner bottom of the bucket) was greater than or equal to 0.5 and less than or equal to 0.9; (2) adding at least one of manganese ore, manganese-containing decarburization slag, and ferromanganese to molten blast furnace iron in a converter-type ladle; and (3) blowing quicklime and / or calcium carbonate with an average particle size of less than or equal to 1 mm and oxygen into molten blast furnace iron from a lance inserted into molten blast furnace iron and foaming the slag at a temperature greater than or equal to 1300 ° C and less than or equal to 1400 ° C in order to perform dephosphorization treatment, and thus obtaining a slag such that the slag basicity, expressed as (CaO content / SiO ₂ content), is greater than 1.5 and less than or equal to 2.2, and the MnO content in slag greater than or equal to 3 wt.% and less than or equal to 10 wt.%.

[1: The process of casting molten cast iron]

[0133] The process for casting molten cast iron, shown in paragraph (1) above, is a process in which molten cast iron obtained in a blast furnace is poured into a converter bucket. In the case where the clearance coefficient, expressed as (bucket free height / internal bucket height), is less than 0.5 when casting molten blast furnace iron into a converter bucket, the bucket free height is too small, and therefore, the gap existing above the surface of molten molten iron is too narrow; and therefore, it is difficult to sufficiently melt the molten blast furnace iron, and the dephosphorization reaction cannot be carried out sufficiently; so this is not preferred. On the other hand, when the clearance coefficient, expressed as (bucket free height / bucket internal height), is more than 0.9, the amount of dephosphorized molten iron is small, which is inefficient; which means that this is not preferred; in addition, since only a small amount of molten blast furnace iron is poured into a converter bucket, productivity is reduced. The clearance factor, expressed as (bucket free height / bucket internal height), is preferably greater than or equal to 0.5 and less than or equal to 0.8, and more preferably greater than or equal to 0.6 and less than or equal to 0.8.

[2: The process of introducing additional material]

[0134] The introduction process of the additive material shown in paragraph (2) above is a process in which at least one of manganese ore, manganese-containing decarburization slag and ferromanganese are introduced into molten cast iron in a converter-type ladle in order to obtain the desired grade MnO in the slag (i.e., so that the MnO content in the slag is greater than or equal to 3 wt.% And less than or equal to 10 wt.%). However, it is not specifically limited how much of which additive material from the abovementioned additive materials to be introduced, and this can be determined in accordance with the desired MnO content in the slag according to the circumstances.

[3: Dephosphorization Processing Process]

[0135] The dephosphorization treatment process shown in paragraph (3) above is a process in which a source of calcium and oxygen is blown into molten cast iron with an adjusted MnO content and foamed slag at a prescribed temperature in order to dephosphorize the molten cast iron.

[0136] In this case, at least one of quicklime and calcium carbonate with an average particle size of less than or equal to 1 mm is used as a source of calcium used for dephosphorization treatment. Quicklime and calcium carbonate with an average particle size of less than or equal to 1 mm can be obtained using industrial sieves in accordance with JIS Z8801. In the case where quicklime is used as a source of calcium, when the average particle size is more than 1 mm, unreacted quicklime may remain; which means that this is not preferable. In the case where the average particle size of quicklime and calcium carbonate is more than 1 mm, the lance may be damaged by blowing, and its service life may be reduced; which means that this is not preferable. Here, the average particle size of quicklime and calcium carbonate refers to the size of the particles with an aggregate value of 50 wt.% On the size distribution of particles passing through industrial sieves in accordance with JIS Z8801. The amount of injected calcium source is set so that at the end of the dephosphorization process, the desired basicity is obtained (i.e., greater than 1.5 and less than or equal to 2.2).

[0137] The temperature of the slag during foaming is set to be greater than or equal to 1300 ° C and less than or equal to 1400 ° C. When the temperature of the slag is less than 1300 ° C, the dephosphorization reaction does not proceed; which means it is not preferable. On the other hand, when the temperature of the slag is more than 1400 ° C, there is a possibility of refosphoration, in which phosphorus is again melted with molten steel; which means it is not preferable. The temperature of the slag during foaming is preferably greater than or equal to 1310 ° C and less than or equal to 1390 ° C, and more preferably greater than or equal to 1320 ° C and less than or equal to 1380 ° C. Slag temperature can be measured using a thermocouple or optical pyrometer.

[0138] The dephosphorization treatment, such as the one mentioned above, is performed so that the basicity of the slag is greater than 1.5 and less than or equal to 2.2, and the MnO content in the slag is greater than or equal to 3 wt.% And less than or equal to 10 wt. %, and dephosphorization treatment ends when the slag basicity and MnO content fall within ranges such as those mentioned above.

[0139] When performing a dephosphorization treatment such as described above, the components of the obtained steelmaking slag acquire characteristics such as those described above, and the density of the produced steelmaking slag falls into the range described above.

[0140] After the dephosphorization treatment process described above, the slag solidification process described below (4) and (5) the slag grinding process are preferably performed.

[4: Slag solidification process]

[0141] The slag solidification process shown in paragraph (4) above is a process in which molten slag solidifies after dephosphorization by a prescribed method.

[0142] The slag solidification process may be, for example, a process in which solidification of the molten slag after dephosphorization is caused by pouring the molten slag after dephosphorization into a heat-resistant container and performing rapid cooling. In this case, in order to more effectively cool the molten slag, it is preferably distributed with a thin layer in a heat-resistant dish-shaped container, and additional spraying of water onto the molten slag distributed by a thin layer is preferably performed for quick cooling.

[0143] In addition to the above method, the following method may also be used as the slag solidification process. Namely, (a) the converter-type bucket is tilted to pour molten slag after dephosphorization into the slag ladle, and then the molten slag in the slag ladle is tilted into a tiltable first heat-resistant container, (b) water is sprayed in the first heat-resistant container for quick cooling the molten slag to a temperature of, for example, about 600 ° C, with its hardening, and then the molten slag is fragmented, and (c) the first heat-resistant container is tilted to slip the solidified slag down into the second heat-resistant container and thereby fragmenting the solidified slag.

[0144] In both types of slag solidification processes, such as those mentioned above, it is preferable to spray water or the like. during solidification of molten slag for quick cooling. With rapid cooling of molten slag, both a solid solution of 2CaOiSiO ₂ -3CaO⋅P ₂ O ₅ and a solid solution based on FeO-MnO-CaO-SiO ₂ can be formed more reliably in it.

[5. The process of grinding slag]

[0145] The slag grinding process shown in paragraph (5) above is a process in which the steelmaking slag hardened in the above manner is crushed to a desired particle size.

[0146] In the process of grinding the slag, solid steel slag is fragmented and crushed to the desired particle size using, for example, a known means such as a jaw crusher, hammer mill, rod mill, ball mill or roller mill. In this case, the fragmentation and grinding is preferably performed so that all particles of steelmaking slag have a size of less than 5 mm and the mass fraction of particles with sizes less than 600 microns is greater than or equal to 60% of the total mass, as mentioned above.

[0147] Through processes such as those described above, steelmaking slag is produced as a raw material for fertilizer in accordance with the present embodiment.

<About the method of fertilizer production>

[0148] A method for producing fertilizer using steelmaking slag as raw material for fertilizer in accordance with the present embodiment will be briefly described below. Steelmaking slag as a raw material for fertilizer in accordance with the present embodiment, such as described above, can be used as fertilizer as it is, by bringing its particle size to a predetermined range (for example, all particle sizes are approximately less than 600 μm). That is, the fertilizer production method in accordance with the present embodiment is a pulverization of steelmaking slag as a raw material for fertilizer produced by a method of producing steelmaking slag as a raw material for fertilizer, such as mentioned above, using known means.

[0149] Although steelmaking slag as a raw material for fertilizer after grinding into powder can be used as fertilizer directly in the form as it is, as mentioned above, granulation can be performed after adding the prescribed binder. However, the binder used during granulation is not particularly limited; for example, molasses, lignin, metal lignin sulfonate, starch, polyvinyl alcohol, carboxymethyl cellulose, etc. can be used.

[0150] Organic fertilizer can be further mixed with fertilizer obtained by a method such as the one mentioned above. Such organic matter may be, for example, at least one of manure, such as cattle manure, pig manure and bird droppings, plant debris and compost obtained from fishery products. By further mixing such organic matter, the fertilizing effect of a fertilizer containing steelmaking slag as a raw material for fertilizer in accordance with the present embodiment can be further improved.

[0151] Using the above fertilizer in accordance with the present embodiment, many types of elements are phosphorus (P), iron (Fe), manganese (Mn), silicon (Si), calcium (Ca), magnesium (Mg), boron (B ) and sulfur (S) - can be supplied more efficiently.

<About the method of fertilizer application>

[0152] Next, a method for using a fertilizer containing steelmaking slag as a raw material for fertilizer in accordance with the present embodiment will be described. Fertilizer containing steelmaking slag as a raw material for fertilizer, such as described above, can easily supply many types of elements as plant fertilizer at a low price even to acidic soils in regions where rainfall is high, as well as in regions where it often occurs spill of rivers, without leaching from the soil. More specifically, by applying this fertilizer to a specific acidic soil in a manner such as described below, the soil can be alkalized and many kinds of elements can be supplied as fertilizer more efficiently for those plants that are intended to be grown.

[0153] That is, in the method of applying the fertilizer according to the present embodiment, the fertilizer containing steelmaking slag as a raw material for the fertilizer, or a fertilizer such as the one mentioned above, is applied to the soil in which (i) the pH (H ₂ O) greater than or equal to 4 and less than or equal to 6, (ii) a value expressed as (pH (H ₂ O) - pH (KCl)) is greater than or equal to 1, and (iii) the amount of available phosphoric acid is less than or equal to 5 mg / 100 g of dry soil.

[0154] Here, the pH (H ₂ O) refers to the pH of the suspension obtained by adding water to the soil in a predetermined ratio, and the pH (KCl) refers to the pH of the suspension obtained by adding a solution of potassium chloride to the soil in a predetermined ratio. H ⁺ hydrogen ions present in the soil include two types, that is, dissolved in soil water and electrically adsorbed on the surfaces of colloidal soil particles (e.g. clay, humus, etc.). The pH value (H ₂ O) indicates the concentration of H ⁺ ions dissolved in soil water, and the pH value (KCl) indicates the total concentration of H ⁺ ions dissolved in soil water and H ⁺ ions adsorbed on colloidal particles of the soil. It is said that pH (H ₂ O) indicates the strength and weakness of the soil acidity (active acidity), which is directly related to the growth of plant roots, and on the other hand, pH (KCl) indicates the potential acidity held by the soil (potential acidity).

[0155] The value shown in paragraph (ii) above can be used as an indicator of how much Al is present in the soil. The available phosphoric acid shown in paragraph (iii) indicates the amount of phosphoric acid absorbed by the plants and can be measured by a known method for testing fertilizers, etc., such as the Truog method, using a solution of sulfuric acid with a pH of about 3. Soil, in of which the amount of phosphoric acid available is less than or equal to 5 mg / 100 g of dry soil, is soil with a very small amount of phosphoric acid coming from the soil. For example, in Japan, the recommended value of available phosphoric acid in farmland soils recommended by the Ministry of Agriculture, Forestry and Fisheries is 10-75 mg / 100 g of dry soil. In acidic soil, in which the pH (H ₂ O) - pH (KCl) is large and the amount of Al is large, there is a fear that the phosphate ion will bind to the Al ion, turning into an insoluble form of AlPO ₄ , and phosphorus absorbed by plants acid will be missed. The fertilizer in accordance with the present embodiment can supply phosphoric acid to a soil in which there is a lack of available phosphoric acid and exhibits a fertilizing effect.

[0156] it Should be noted that the above pH (H ₂ O) and pH (KCl) can be measured by placing 20 g of air-dried soil in a shake bottle with a capacity of 100 ml, adding 50 ml of distilled water or 50 ml of a normal solution of KCl shaking for 30 minutes and then measuring the pH of the aqueous solution using a glass pH electrode. In addition, the content of available phosphoric acid can be measured by the Truog method.

[0157] In regions with heavy rainfall, where each element with a fertilizer effect may be washed away and become insufficient, the fertilizer according to the present embodiment exhibits an excellent fertilizer effect of a particular acidic soil, such as the one mentioned above.

[0158] The applied amount of fertilizer in accordance with the present embodiment is preferably greater than or equal to 0.05 t / ha and less than or equal to 2 t / ha in terms of steel slag as raw material for fertilizer. In the case where the applied amount is less than 0.05 t / ha, it is too small, and it is likely that the fertilizer effect according to the present embodiment, containing a plurality of elements with the fertilizer effect, cannot be clearly manifested. On the other hand, when the applied amount is more than 2 t / ha, costs are increased due to the use of a large amount of fertilizer in accordance with the present embodiment. A more preferred application amount is greater than or equal to 0.1 t / ha and less than or equal to 1 t / ha.

[0159] In the method of applying the fertilizer according to the present embodiment, the fertilizer according to the present embodiment, such as the one mentioned above, can be spread on the surface of the arable layer or mixed with the arable layer before sowing or planting the plants. In addition, a fertilizer in accordance with the present embodiment, such as the one mentioned above, may be scattered on the surface of the arable layer near the body of the plant being grown or may be mixed into the arable layer.

[0160] The target plant for fertilizer in accordance with the present embodiment, such as the one mentioned above, can be, for example, a plant that falls under any of the cereal plants, sedimentary plants, melons, legumes, amaryllis plants, lily plants, nightshade plants , cruciferous plants, flowering plants, banana plants, palm plants, grape plants, aroid plants, orchid plants, bindweed plants, aster plants, sesame plants, calendula plants ny, plants of the poppy family, rue plants, umbrella plants, pepper plants, madder plants, nettle plants, etc. The steelmaking slag as a raw material for fertilizer in accordance with the present embodiment tends to release three elements, secondary elements and trace elements of the fertilizer, and a fertilizer using steelmaking slag as a raw material for fertilizer has demonstrated its effect on paddy rice, which is a typical cereal plant as shown in the Examples below; therefore, one can expect to obtain the effect in the plants mentioned above, as well as in cereal plants. It goes without saying that the fertilizer in accordance with the present embodiment can also be used for plants other than those mentioned above.

[0161] The method for applying fertilizer according to the present embodiment has been briefly described.

[ Examples ]

[0162] Next, steelmaking slag as a raw material for the fertilizer of the present invention, as well as fertilizer and method of applying fertilizer using steelmaking slag will be described specifically with examples and Comparative examples. The following examples are merely examples, and the present invention is not limited to these examples.

(Example 1)

[0163] Pieces of steelmaking slag as a raw material for fertilizer were produced by the following method. Namely, the manganese-containing decarburization slag was additionally introduced into ordinary molten blast furnace iron in a converter in which the clearance coefficient, expressed as (bucket free height / bucket internal height), was 0.7, then quicklime with an average particle size of less than or equal to 1 mm, and oxygen was blown out from the lance inserted into the molten iron; and dephosphorization treatment was performed during foaming at 1350 ° C. After draining the steel, two cooling treatments were performed on the produced slag. In one cooling treatment, the converter was tilted, releasing slag into a heat-resistant container plate, and the slag was distributed in a thin layer and water was sprayed; thus, the slag was rapidly cooled. In another cooling treatment, the converter was tilted, releasing slag into a slag ladle; after 30 minutes, the slag ladle was tilted at the place of unloading of slag for unloading, and the slag was allowed to cool; thus, the slag was slowly cooled to normal temperature.

[0164] The rapidly cooled steelmaking slag and the slowly cooled steelmaking slag obtained by the aforementioned process were ground so that all particles were smaller than 5 mm and the mass fraction of particles smaller than 600 μm was 60% or more. The resulting samples of steelmaking slag were analyzed in accordance with the method described above; The results of the analysis of the rapidly cooled steelmaking slag are shown in Table 1. The X-ray fluorescence analysis device used was the Zig Primus II manufactured by Rigaku Corporation, and the ICPS-8100 manufactured by Shimadzu Corporation was used as an atomic emission spectroscopy instrument with ICP.

[0165] The chemical components of the rapidly cooled steelmaking slag and the slowly cooled steelmaking slag were the same. In addition, the mass fraction of soluble P ₂ O ₅ , the mass fraction of citric acid soluble MnO, and the mass fraction of boron soluble in citric acid in slowly cooled steelmaking slag were 60%, 65%, and 75%, respectively.

[0166] Moreover, in Table 1 below, the units of all indicators, except basicity or density, are wt.%, And the values of soluble P ₂ O ₅ , soluble in citric acid MnO and soluble in citric acid boron are given based on the total content relevant components. In addition, in Table 1, alkalinity indicates the ability of an appropriate fertilizer to neutralize soil acidity and shows the value measured by the ethylenediaminetetraacetate method described in Testing Methods for Fertilizers (2016) prescribed by the Food and Agricultural Material Inspection Center (FAMIC).

[0167] From Table 1 it is seen that in rapidly chilled pieces of steelmaking slag, the soluble P ₂ O ₅ mass fraction is 80%, the mass fraction of MnO soluble in citric acid is 83%, and the mass fraction of boron soluble in citric acid is 100%. In addition, in the obtained pieces of steelmaking slag, the total content of CaO, P ₂ O ₅ , SiO ₂ , MgO, Al ₂ O ₃ , all iron, MnO, boron and sulfur was 97.761 wt.%, And the rest was impurities.

[0168] [Table 1] Table 1. Analysis of steelmaking slag

CaO P ₂ O ₅ Soluble P ₂ O ₅ SiO ₂ MgO Al ₂ O ₃ Total iron MnO MnO Citric Acid Soluble Alkalinity Boron Boron Soluble in Citric Acid Sulfur Basicity Density 43 5.5 4.4 26 4,5 1.3 eleven 6 5 46 0.011 0.011 0.45 1.7 2.2

[0169] In addition, the substances forming the crystalline phase of each of the rapidly cooled steelmaking slag and the slowly cooled steelmaking slag were investigated using X-ray diffraction (SmartLab X-ray diffractometer manufactured by Rigaku Corporation) and EPMA (JXA-8100 manufactured by JEOL Ltd.) in accordance with the method described above; the results obtained are shown in Table 2 below. In Table 2, “observed” means that this solid solution is observed, and “not observed” means that this solid solution is not observed. As can be seen from Table 2, the existence of both of the 2CaO существованиеSiO ₂ -3CaO⋅P ₂ O ₅ solid solution and the FeO-MnO-CaO-SiO ₂ solid solution was observed in rapidly cooled steelmaking slag; on the other hand, in a slowly cooled steelmaking slag, the existence of a 2CaO⋅SiO ₂ -3CaO⋅P ₂ O ₅ solid solution was observed, and the existence of a solid solution based on FeO-MnO-CaO-SiO _{2 was} not observed.

[0170] [Table 2]

Table 2. Solid solutions contained in steelmaking slag

Solid solution
2CaO⋅SiO ₂ -3CaO⋅P ₂ O ₅ Solid solution based on FeO-MnO-CaO-SiO ₂ Quickly cooled steelmaking slag Observed Observed Slowly cooled steelmaking slag Observed Not visible

(Example 2)

[0171] Using fertilizers such as those mentioned above, a paddy rice cultivation test was conducted in soil, the analysis of which is shown in Table 3 below. In this soil, pH (H ₂ O), pH (KCl) and the content of available phosphoric acid measured by the methods described above; the pH value (H ₂ O) was in the range greater than or equal to 4 and less than or equal to 6, the pH value (H ₂ O) - pH (KCl) was greater than or equal to 1, and the content of available phosphoric acid was less than or equal to 5 mg / 100 g of dry soil.

[0172] [Table 3]

Table 3. Soil analysis results

pH
(H ₂ O) pH
(KCl) Available phosphoric acid
(mg / 100 g dry soil) 5.3 4.1 2

[0173] More specifically, the test of the fertilizer effect in paddy rice was carried out for cases where fertilizer was applied using the rapidly cooled steelmaking slag and the slowly cooled steelmaking slag mentioned above as raw material, the case where a commercially available fertilizer using as steelmaking slag, which was produced in a converter with a clearance coefficient expressed as (bucket free height / bucket internal height) equal to 0.4, as well as the case when fertilizer is used The present steelmaking slag as the raw material has not been applied.

[0174] The results of an analysis of a commercially available fertilizer using steelmaking slag as a raw material that was produced in a converter with a clearance coefficient expressed as (bucket free height / bucket internal height) of 0.4 are shown in Table 4 below. method of analysis of a commercially available fertilizer was similar to that in Example 1. The following Table 4, the units of measurement of all parameters, except basicity or density, are wt.%, and the values of soluble P ₂ O ₅ is soluble in citric sour e MnO and soluble in citric acid are shown boron, based on their total content. Alkalinity was measured in the same manner as for Table 1.

[0175] From Table 4 it is seen that in the steelmaking slag produced in the converter with a clearance factor of 0.4, the soluble P ₂ O ₅ mass fraction is 44%, the mass fraction of MnO soluble in citric acid is 53%, and the soluble Boric citric acid is 80%. For steelmaking slag produced in the converter with a clearance factor of 0.4, the total content of CaO, P ₂ O ₅ , SiO ₂ , MgO, Al ₂ O ₃ , total iron, MnO, boron and sulfur was 84.105 wt.%, And the rest impurities.

[0176] In addition, for a commercially available fertilizer, it was found that the sizes of all particles were less than 5 mm, and the mass fraction of particles with sizes less than 600 μm was greater than or equal to 60%.

[0177] [Table 4]

Table 4. The results of the analysis of commercially available fertilizers

CaO P ₂ O ₅ Soluble P ₂ O ₅ SiO ₂ MgO Al ₂ O ₃ Total iron MnO MnO Citric Acid Soluble Alkalinity Boron Boron Soluble in Citric Acid Sulfur Basicity Density 41 1.8 0.8 thirteen 3.9 4.2 17 3 1,6 43 0.005 0.004 0.2 3,1 2,4

[0178] In a fertilizer using steelmaking slag as a raw material, the analysis results of which are shown in Table 4, the ratio of SiO ₂ to CaO is low, and therefore the basicity is high, and the contents of P ₂ O ₅ and soluble P ₂ O ₅ are low compared to fertilizers using pieces of steelmaking slag of the present invention as raw materials. In addition, the content of MnO soluble in citric acid is slightly low relative to the large amount of total iron compared to fertilizers using two types of slag as raw materials, the composition of which is shown in Table 1.

[0179] Substances forming the crystalline phase of the steelmaking slag, which serves as a raw material for a commercially available fertilizer, such as the one mentioned above, were examined by X-ray diffraction and EPMA in accordance with the method described above; the results obtained are shown in Table 5 below. The notation in Table 5 is similar to that in Table 2. As shown in Table 5, neither a 2CaO⋅SiO ₂ -3CaO⋅P ₂ O ₅ solid solution nor a FeO-MnO solid solution were observed -CaO-SiO ₂ .

[0180] [Table 5]

Table 5. Solid solutions contained in steelmaking slag, which serves as raw material for commercially available fertilizers

Solid solution
2CaO⋅SiO ₂ -3CaO⋅P ₂ O ₅ Solid solution based on FeO-MnO-CaO-SiO ₂ Steelmaking slag, a raw material for commercially available fertilizer Not visible Not visible

[0181] Nitrogen and potassium were introduced as 60 kg / ha of urea and 60 kg / ha of potassium chloride, respectively, as the main fertilizer in the rice field soil before planting rice plants. Nine frames 0.6 × 0.5 m in size were placed on the rice field; 15 g of fertilizer using rapidly chilled steelmaking slag as raw materials, and 15 g of fertilizer using slowly chilled steelmaking slag as raw materials, the analysis results of which are shown in Table 1 and Table 2, and 15 g of commercially available fertilizer using as raw material steelmaking slag prepared in a converter with a clearance coefficient of 0.4, the analysis results of which are shown in Table 4 and Table 5 (in each of these fertilizers the sizes of all particles were less than 5 mm, and the mass fraction of particles with size less than 600 μm was greater than or equal to 60%), was introduced individually in three of nine areas limited by the framework (which is equivalent to the applied amount of 0.5 t / ha).

[0182] Each of these fertilizers was well mixed with soil to a depth of 10 cm; then, in each frame, 6 root groups were planted with 4 seedlings of paddy rice (Koshihikari varieties) in one root group and grown before the harvest season. As a control, the test was tested under similar conditions, also for three frames in which materials were not added. Therefore, the test was performed with three repetitions.

[0183] A yield study was performed four months after rice planting. All 6 root groups in each frame were cut off and the weight of small brown (paddy) rice and the weight of a thousand grains were examined. The results obtained are shown in Table 6 below.

[0184] [Table 6]

Table 6. The results of the study of productivity

The weight of small brown rice (g / m ² ) Weight of a thousand grains (g) Fertilizer used using rapidly chilled steelmaking slag as a raw material 536 21.5 A fertilizer was used that used slowly cooled steelmaking slag as a raw material. 515 21.0 A commercially available fertilizer was used using steelmaking slag as a raw material. 451 20.8 Control (fertilizer using steelmaking slag as a raw material was not used) 407 19.0

[0185] As can be seen from Table 6, when applying fertilizer using rapidly chilled steelmaking slag as a raw material, the yield (weight of fine brown rice) increased by approximately 31% compared to the control zone. In addition, in the case where slowly cooled steelmaking slag was used, the yield (weight of small brown rice) increased by approximately 26% compared to the control zone. On the other hand, when applying the same amount of commercially available fertilizer using existing steelmaking slag as raw material, the yield (weight of small brown rice) increased by about 10% compared to the control zone.

[0186] In addition, for the weight of a thousand grains, the highest value was obtained when a fertilizer using fast-cooled steelmaking slag was used as a raw material, the second highest value was obtained when a fertilizer was used using a slowly cooled steelmaking slag as a raw material, the third largest value was obtained when fertilizer was used using steelmaking slag as a raw material, and the lowest value was obtained when not imenyalos fertilizer using steelmaking slag as raw material.

[0187] Based on these results, it was found that even for pieces of steelmaking slag as a raw material for fertilizer with the same chemical components, rapidly cooled steelmaking slag containing both of a 2CaO⋅SiO ₂ -3CaO⋅P ₂ O ₅ solid solution and a solid solution based on FeO-MnO-CaO-SiO ₂ has a higher fertilizer effect than slowly cooled steel slag containing 2CaO⋅SiO ₂ -3CaO⋅P ₂ O ₅ solid solution but not containing FeO-MnO-CaO solid solution SiO ₂ .

[0188] As described above, it has been found that rice yields can be increased by using fertilizer using steelmaking slag as a raw material for the fertilizer of the present invention.

(Example 3)

[0189] A paddy rice cultivation test was performed in soil, the analysis of which is shown in Table 7, using a fertilizer using rapidly chilled steelmaking slag as raw material, a fertilizer using slowly chilled steelmaking slag as a raw material, and commercially available fertilizer using steelmaking slag as raw materials, which are described above in Example 2. It should be noted that the method of soil analysis is similar to Example 2.

[0190] [Table 7]

Table 7. Soil analysis results

pH
(H ₂ O) pH
(KCl) Available phosphoric acid
(mg / 100 g dry soil) 6.5 5.8 fifteen

[0191] Nitrogen and potassium were added as 60 kg / ha of urea and 60 kg / ha of potassium chloride, respectively, as the main fertilizer in the rice field soil before planting rice plants. Nine frames 0.6 × 0.5 m in size were placed on the rice field; 15 g of fertilizer using rapidly chilled steelmaking slag as raw materials, and 15 g of fertilizer using slowly chilled steelmaking slag as raw materials, the analysis results of which are shown in Table 1 and Table 2, and 15 g of commercially available fertilizer using as raw material steelmaking slag, the analysis results of which are shown in Table 4 and Table 5 (in each of these fertilizers the sizes of all particles were less than 5 mm, and the mass fraction of particles with sizes less than 600 microns was greater than or equal to 60%), ind vidual on three of the nine sections bounded frames (equivalent to the insertion amount of 0.5 t / ha).

[0192] Each of these fertilizers was well mixed with the soil to a depth of 10 cm; then, in each frame, 6 root groups were planted with 4 seedlings of paddy rice (Koshihikari varieties) in one root group and grown before the harvest season. As a control, a test was carried out under similar conditions, also for three frames in which materials were not added. Therefore, the test was performed with three repetitions.

[0193] A yield study was performed four months after rice planting. All 6 root groups in each frame were cut off and the weight of small brown (paddy) rice and the weight of a thousand grains were examined. The results obtained are shown in Table 8 below.

[0194] [Table 8]

Table 8. The results of the study of productivity

The weight of small brown rice (g / m ² ) Weight of a thousand grains (g) Fertilizer was used using rapidly chilled steelmaking slag as a raw material. 535 21.3 A fertilizer was used that used slowly cooled steelmaking slag as a raw material. 517 20.8 A commercially available fertilizer was used using steelmaking slag as a raw material. 492 20.1 Control (fertilizer using steelmaking slag as a raw material was not used) 478 19.1

[0195] As can be seen from the above Table 8, when applying fertilizer using rapidly chilled steelmaking slag as a raw material, the yield (weight of small brown rice) increased by approximately 12% compared to the control zone. In addition, when using slowly chilled steelmaking slag, the yield (weight of small brown rice) increased by approximately 8% compared to the control zone. On the other hand, when using the same amount of commercially available fertilizer using existing steelmaking slag as a raw material, yield (weight of small brown rice) increased by about 3% compared to the control zone.

[0196] In addition, for the weight of a thousand grains, the highest value was obtained when a fertilizer using fast-cooled steelmaking slag was used as raw material, the second highest value was obtained when a fertilizer was used using a slowly cooled steelmaking slag as a raw material, the third highest value was obtained when fertilizer was used using steelmaking slag as raw material, and the lowest value was obtained when fertilizer e, using steelmaking slag as a raw material, was not used.

[0197] As described above, it was found that rice yields can be increased even in soil with a pH (H ₂ O) of 6.5 by using fertilizer using steelmaking slag as a raw material for the fertilizer of the present invention.

[0198] However, compared with the results of Example 2, while in the soil with the analysis results shown in Table 3, the yield when using fertilizer using pieces of steelmaking slag as raw material for fertilizer of the present invention increased by about 30% compared with the yield of the control zone where fertilizer from steelmaking slag was not applied, in the soil with the analysis results shown in Table 7, the yield in the case of fertilizer using pieces of steelmaking slag in the quality of the fertilizer feed of the present invention increased by about 12% compared with the yield of the control zone, where fertilizer from steelmaking slag was not used, and the growth rate decreased. The reason for this is that the yield of the control zone, where fertilizer from steelmaking slag was not applied, was higher than in Example 2. The possible reason is that the pH value (H ₂ O) of the soil with the analysis results shown in the Table 7 was in the range 5.5-6.5, which is suitable for rice paddy growth, and in addition, the amount of available phosphoric acid was 15 mg / 100 g of dry soil, which is within the range of recommended values of available phosphoric acid in soils farmland provided go by the Ministry of Agriculture, Forestry and Fisheries of Japan (10-75 mg / 100 g of dry soil); thus, phosphoric acid successfully entered plants from the soil, even when fertilizer using steelmaking slag as a raw material was not used.

[0199] Therefore, it was found that although fertilizers using pieces of steelmaking slag as raw materials for fertilizing in accordance with the present invention have some effect in the soil of Table 7, they have a more significant effect in the soil of Table 3.

[0200] Preferred embodiments of the present invention have been described above with reference to the attached drawings, but the present invention is not limited to the above examples. A person skilled in the art will be able to find various changes and modifications within the scope of protection of the appended claims, and it should be understood that they will naturally fall within the technical scope of the present invention.

Claims (42)

1. Steelmaking slag as a raw material for fertilizer, containing, wt.%, P ₂ O ₅ : greater than or equal to 2% and less than or equal to 8%, MnO: greater than or equal to 3% and less than or equal to 10%, boron: greater than or equal to 0.005% and less than 0.05%, total iron: greater than or equal to 7% and less than 15%, CaO: greater than or equal to 38% and less than or equal to 48%, SiO ₂ : greater than or equal to 22% and less than or equal to 30%, sulfur: greater than or equal to 0.1% and less than or equal to 0.6%, MgO: greater than or equal to 1% and less than or equal to 8%, and Al ₂ O ₃ : greater than or equal to 0.5% and less than or equal to 3%, moreover, the proportion of soluble P ₂ O ₅ in P ₂ O _{5 is} greater than or equal to 50%, the proportion of MnO soluble in citric acid in MnO is greater than or equal to 80%, slag basicity, expressed as (CaO content / SiO ₂ content), is greater than 1.5 and less than or equal to 2.2, and bulk density greater than or equal to 1.9 and less than or equal to 2.8. 2. Steelmaking slag as a raw material for fertilizer according to claim 1, containing a solid solution of 2CaO · SiO ₂ -3CaO · P ₂ O ₅ and a solid solution based on FeO-MnO-CaO-SiO ₂ . 3. Steelmaking slag as a raw material for fertilizer according to claim 1 or 2, in which the proportion of boron soluble in citric acid in boron is greater than or equal to 95%. 4. Steelmaking slag as a raw material for fertilizer according to any one of paragraphs. 1-3, in which the particle size is less than 5 mm in General, and the mass fraction of particles with sizes less than 600 microns is greater than or equal to 60% of the total mass. 5. A method of manufacturing steelmaking slag as a raw material for fertilizer, which produces steelmaking slag as a raw material for fertilizer according to any one of paragraphs. 1-4, containing: pouring molten cast iron into a converter bucket in such a way that the clearance coefficient expressed as (height of the free side of the bucket corresponding to the length from the mouth to the surface of the molten molten iron / internal height of the bucket corresponding to the distance from the neck to the inner bottom of the bucket) is greater than or equal to 0.5 and less than or equal to 0.9; adding at least one of manganese ore, manganese-containing decarburization slag and ferromanganese to molten cast iron in a converter-type ladle; blowing quicklime and / or calcium carbonate with an average particle size of less than or equal to 1 mm and oxygen into molten blast furnace iron from a tuyere inserted into molten blast furnace iron; foaming slag at a temperature greater than or equal to 1300 ° C and less than or equal to 1400 ° C to perform dephosphorization treatment; and obtaining slag in such a way that the slag basicity, expressed as (CaO content / SiO ₂ content), is greater than 1.5 and less than or equal to 2.2, and the MnO content in the slag is greater than or equal to 3 wt.% and less than or equal to 10 wt. .%. 6. A method of manufacturing steelmaking slag as a fertilizer feed according to claim 5, wherein the molten slag after dephosphorization is poured into a heat-resistant container and quickly cooled to solidify. 7. A method for producing steelmaking slag as a fertilizer feed according to claim 6, wherein the molten slag after dephosphorization is rapidly cooled by spraying water. 8. The method of production of steelmaking slag as a raw material for fertilizer according to any one of paragraphs. 5-7, in which the converter-type bucket is tilted to pour molten slag after dephosphorization into a slag ladle, and then molten slag in a slag ladle is poured into a tiltable first heat-resistant container by tilting, water is sprayed in a first heat-resistant container for quick cooling and solidification of the molten slag, and then the solidified slag is fragmented, and tilt the first heat-resistant container to slide the hardened slag down into the second heat-resistant container, and thereby harden the slag fragment. 9. The method of production of steelmaking slag as a raw material for fertilizer according to any one of paragraphs. 5-8, in which, by rapid cooling, a solid solution of 2CaO · SiO ₂ -3CaO · P ₂ O ₅ and a solid solution based on FeO-MnO-CaO-SiO _{2 are formed} . 10. The method of production of steelmaking slag as a raw material for fertilizer according to any one of paragraphs. 5-9, in which the slag is crushed so that the particle size is less than 5 mm in total, and the mass fraction of particles with sizes less than 600 microns is greater than or equal to 60% of the total mass. 11. A method of manufacturing a fertilizer containing: grinding into powder steelmaking slag as a raw material for fertilizer according to any one of paragraphs. 1-4 or steelmaking slag as a raw material for fertilizer produced by the method of manufacturing steelmaking slag as a raw material for fertilizer according to any one of paragraphs. 5-10. 12. The fertilizer production method according to claim 11, in which the prescribed binder is added to the steelmaking slag as a raw material for fertilizer after grinding into powder, and then granulation is performed, wherein the binder is at least one selected from the group consisting of molasses, lignin, metal ligninsulfonate, starch, polyvinyl alcohol and carboxymethyl cellulose. 13. A method of manufacturing a fertilizer according to claim 11 or 12, in which an organic substance is additionally mixed with the obtained fertilizer. 14. The fertilizer production method according to claim 13, wherein the organic matter is at least one of manure, plant residues, and compost obtained from fishery products. 15. The use of fertilizer obtained by the method according to any one of paragraphs. 11-14, by applying to the soil in which the pH (H ₂ O) is greater than or equal to 4 and less than or equal to 6, a value expressed as (pH (H ₂ O) - pH (KCl)) is greater than or equal to 1, and the amount of phosphoric acid available is less than or equal to 5 mg / 100 g of dry soil. 16. The use of fertilizer, which contains steelmaking slag as a raw material for fertilizer according to any one of paragraphs. 1-4, by applying to the soil in which the pH (H ₂ O) is greater than or equal to 4 and less than or equal to 6, a value expressed as (pH (H ₂ O) - pH (KCl)) is greater than or equal to 1, and the amount of phosphoric acid available is less than or equal to 5 mg / 100 g of dry soil. 17. The use of fertilizer under item 15 or 16, in which the applied amount of fertilizer is greater than or equal to 0.05 t / ha and less than or equal to 2 t / ha of steelmaking slag as a raw material for fertilizer. 18. The use of fertilizer according to claim 15 or 16, in which the fertilizer is spread on the surface of the arable layer or mixed with the arable layer before sowing or planting plants. 19. The use of fertilizer according to claim 15 or 16, in which the fertilizer is spread on the surface of the arable layer next to the body of the plant being grown or mixed into the arable layer.