AU2018282388A1

AU2018282388A1 - Steelmaking slag for fertilizer raw material, method for producing steelmaking slag for fertilizer raw material, method for producing fertilizer, and fertilizer application method

Info

Publication number: AU2018282388A1
Application number: AU2018282388A
Authority: AU
Inventors: Kimio Ito
Original assignee: Nippon Steel and Sumitomo Metal Corp
Current assignee: Nippon Steel Corp
Priority date: 2017-06-28
Filing date: 2018-06-28
Publication date: 2019-01-17
Anticipated expiration: 2038-06-28
Also published as: TWI675814B; TW201904917A; AU2018282388B2; PH12019500324A1; KR20190022720A; WO2019004339A1; MY190802A; JPWO2019004339A1; CR20190159A; CN109563005A; RU2707811C1; KR102189122B1; JP6497492B1

Abstract

PCTJP2018024529 There is provided steelmaking slag for fertilizer raw material, containing, in mass%, P2 0 5 : more than or equal to 2% and less than or equal to 8%, MnO: more than or equal to 3% and less than or equal to 10%, boron: more than or equal to 5 0.005% and less than 0.05%, the total iron: more than or equal to 7 % and less than 15%, CaO: more than or equal to 38% and less than or equal to 48%, SiO 2 : more than or equal to 22% and less than or equal to 30%, sulfur: more than or equal to 0. 1% and less than or equal to 0.6%, MgO: more than or equal to 1% and less than or equal to 8%, and A120 3 : more than or equal to 0. 5 % and less than or equal to 3%. A 10 ratio of soluble P2 05 in the P2 05 is more than or equal to 50%, a ratio of citric acid soluble MnO in the MnO is more than or equal to 80%, a slag basicity is more than 1.5 and less than or equal to 2.2, and a bulk specific gravity is more than or equal to 1.9 and less than or equal to 2.8.

Description

STEELMAKING SLAG FOR FERTILIZER RAW MATERIAL, METHOD FOR PRODUCING STEELMAKING SLAG FOR FERTILIZER RAW MATERIAL, METHOD FOR PRODUCING FERTILIZER, AND FERTILIZER APPLICATION METHOD

CROSS REFERENCE TO RELATED APPLICATION(S)

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

BACKGROUND [0001]

The present invention relates to steelmaking slag for fertilizer raw material, a method for producing steelmaking slag for fertilizer raw material, a method for producing a fertilizer, and a fertilizer application method.

[0002]

As elements essential to the growth of plants, there are known 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 elements mentioned above, nitrogen (N), phosphorus (P), and potassium (K) are called three elements of fertilizer, and are known to be elements needed by plants in large amounts. Further, calcium (Ca), magnesium (Mg), and sulfur (S) are called secondary elements, and are said to be the elements most needed by plants after the three elements mentioned above. Further, iron (Fe), manganese (Mn), boron (B), zinc (Zn), molybdenum (Mo), copper (Cu), and chlorine (Cl) are needed by plants in minute amounts, and are therefore called trace elements.

[0004]

Further, these days it is becoming clear that, among the elements mentioned above, boron (B) is an element necessary for the formation of the cell wall of the cell

PCTJP2018024529

2/69 of the roots of plants. Further, staple food crops of the world's population, such as rice, wheat, and corn, are siliceous crops that need large amounts of silicon (Si) as well as the elements mentioned above.

[0005]

As a method for supplying plants with the elements of Ca, P, Si, Mg, Fe, Mn, B, and S, there is foliar application. In the foliar application, the following substances are used for the respective elements, for example.

Ca: calcium chloride

P: potassium primary 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 application is a method in which the work takes effort, and hence a method capable of causing elements such as those mentioned above to be absorbed from roots, without using foliar application, is demanded.

[0007]

On the other hand, steelmaking slag obtained in molten iron preliminary treatment and decarburization treatment of the ironmaking industry contains various minerals as constituent components thereof, and is hence used as fertilizers and soil improvement materials, as disclosed in JP 5105322B (Patent Literature 1), JP 6040064B (Patent Literature 2), JP 5881286B (Patent Literature 3), JP 5983900B (Patent Literature 4), JP 2016-29206A (Patent Literature 5), JP 4246782B (Patent Literature 6), JP 4040542B (Patent Literature 7), JP 6119361B (Patent Literature 8), and JP 6011556B (Patent Literature 9).

[0008]

For example, Patent Literature 1 reports a raw material for silicophosphatic

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3/69 fertilizer that is collected in dephosphorization treatment during molten iron preliminary treatment of blast furnace molten iron in the ironmaking process, and a method for producing the raw material for silicophosphatic fertilizer.

[0009]

Patent Literature 2 reports a method that produces a slag phosphatic fertilizer using, as a raw material, steelmaking slag obtained from a molten iron preliminary treatment process of the ironmaking process.

[0010]

Patent Literature 3 reports that slag particles made of steelmaking slag of the ironmaking process have the effect of increasing the yield of paddy rice, and have also the effect of suppressing greenhouse effect gases.

[0011]

Patent Literature 4 and Patent Literature 5 report a molten iron preliminary treatment method that sequentially performs desiliconization treatment and dephosphorization treatment using one converter-type smelting furnace, and Patent Literature 6 reports a method that produces a siliceous fertilizer in a molten iron preliminary treatment process of the ironmaking process.

[0012]

Patent Literature 7 reports a siliceous fertilizer in which the dissolving-out of silicic acid is enabled by mixing coal ash containing only undissolvable silicic acid with slag of stainless steel in a molten state.

[0013]

Patent Literature 8 reports a method for producing phosphoric acidcontaining slag for fertilizer, and Patent Literature 9 reports a method for producing a phosphatic fertilizer raw material obtained from the ironmaking process.

SUMMARY [0014]

It takes cost and effort to apply many kinds of substances containing elements such as P, Fe, Mn, Zn, Si, Ca, Mg, B, and S at a ratio at which the fertilizer effect of each element can be expected. Further, in the case where a substance

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4/69 containing each element is applied to soil, since the specific gravity varies with substances, a substance with a small specific gravity may run off in soils of regions where the amount of rainfall is large or regions where river flooding occurs frequently. As a result, it is feared that, in the period of one cropping in which plants are cultivated, the plants will be forced to be cultivated under conditions where balance between elements is lost.

[0015]

In particular, in acidic soil, elements such as Fe, Mn, and B may run off and become lacking. Further, in an acidic soil with a high aluminum content, it is feared that aluminum will be ionized and bind to phosphoric acid to form aluminum phosphate, and the phosphoric acid absorption by the roots of plants will be inhibited. [0016]

It is very important that siliceous plants such as rice, wheat, and com be able to be stably cultivated in acidic soils of regions where the amount of rainfall is large and regions where river flooding occurs frequently, particularly in an acidic soil with a high aluminum content, also from the viewpoint of stable supply of food. [0017]

Therefore, in acidic soils of regions where the amount of rainfall is large and regions where river flooding occurs frequently, particularly in an acidic soil with a high aluminum content, it is presumed that P will be lacking among the three elements of fertilizer, and Fe, Μη, B, etc. will be lacking among the trace elements. [0018]

Among the secondary elements, Ca and Mg are elements necessary for the growth of roots and the photosynthesis of plants. Further, Ca and Mg exhibit alkalinity as lime and magnesia, and are also main constituent elements of alkali components measured by a fertilizer analysis method or the like and elements having the effect of increasing the pH of acidic soil to improve the soil to a pH suitable for the cultivation of plants.

[0019]

Further, among the secondary elements, S is an element essential to the biosynthesis of sulfur-containing amino acids, and is an element particularly

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5/69 necessary for the cultivation of plants of the amaryllis family or the lily family, such as garlic, onion, and Welsh onion. However, S is an element that, after being added to soil, may be oxidized into sulfuric acid and acidify the soil, or may be reduced by the action of sulfate-reducing bacteria into hydrogen sulfide and become a cause of root rot.

[0020]

Si is an element necessary to stably cultivate siliceous plants such as rice, wheat, and corn, and is very important from the viewpoint of stable supply of food. [0021]

Thus, the current situation is that it is desired to develop a fertilizer and a fertilizer application method that can supply many kinds of elements of P, Fe, Mn, Si, Ca, Mg, S, and B as fertilizer of plants easily at low cost even to acidic soils of regions where the amount of rainfall is large and regions where river flooding occurs frequently, without runoff due to a water current.

[0022]

Thus, the present invention has been made in view of the problem mentioned above, and an object of the present invention is to provide steelmaking slag for fertilizer raw material, a method for producing steelmaking slag for fertilizer raw material, a method for producing a fertilizer, and a fertilizer application method that can supply many kinds of elements as fertilizer of plants easily at low cost even to acidic soils of regions where the amount of rainfall is large and regions where river flooding occurs frequently, without runoff due to a water current.

[0023]

The present inventors conducted extensive studies in view of the issue mentioned above; consequently, in order to supply many kinds of elements of P, Fe, Mn, Si, Ca, Mg, B, and S, have developed steelmaking slag specialized for fertilizer raw material and a method for producing the same, and a method for producing a fertilizer and a fertilizer application method capable of supplying these elements; thus, have completed the present invention.

Main points of the present invention are as follows.

[0024]

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6/69 [1]

Steelmaking slag for fertilizer raw material, containing, in mass%, P2O5: more than or equal to 2% and less than or equal to 8%, MnO: more than or equal to 3% and less than or equal to 10%, boron: more than or equal to 0.005% and less than 0.05%, the total iron: more than or equal to 7% and less than 15%, CaO: more than or equal to 38% and less than or equal to 48%, S1O2: more than or equal to 22% and less than or equal to 30%, sulfur: more than or equal to 0.1% and less than or equal to 0.6%, MgO: more than or equal to 1% and less than or equal to 8%, and AI2O3: more than or equal to 0.5% and less than or equal to 3%, in which a ratio of soluble P2O5 in the P2O5 is more than or equal to 50%, a ratio of citric acid-soluble MnO in the MnO is more than or equal to 80%, a slag basicity expressed by (a CaO content/a S1O2 content) is more than 1.5 and less than or equal to 2.2, and a bulk specific gravity is more than or equal to 1.9 and less than or equal to 2.8.

[2]

The steelmaking slag for fertilizer raw material according to [1], containing a 2CaO-SiO2-3CaO-P2O5 solid solution and an FeO-MnO-CaO-SiO2-based solid solution.

[3]

The steelmaking slag for fertilizer raw material according to [1] or [2], in which a ratio of citric acid-soluble boron in the boron is more than or equal to 95%.

[4]

The steelmaking slag for fertilizer raw material according to any one of [1] to [3], in which a particle size is less than 5 mm as a whole, and a mass ratio of particles with particle sizes of less than 600 pm is more than or equal to 60% relative to a total mass.

[5]

A method for producing steelmaking slag for fertilizer raw material that produces the steelmaking slag for fertilizer raw material according to any one of [1] to [4], the method including: pouring blast furnace molten iron into a converter-type pot in such a manner that a gap ratio expressed by (a freeboard corresponding to a length from a throat to a liquid surface of molten iron/a furnace inner height

PCTJP2018024529

7/69 corresponding to a length from the throat to an inner bottom of a furnace) is more 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 the blast furnace molten iron in the converter-type pot; blowing quick lime and/or calcium carbonate with an average particle size of less than or equal to 1 mm and oxygen into the blast furnace molten iron from a lance inserted in the blast furnace molten iron; foaming slag at more than or equal to 1300°C and less than or equal to 1400°C to perform dephosphorization treatment; and producing slag in such a manner that a slag basicity expressed by (a CaO content/a S1O2 content) is more than 1.5 and less than or equal to 2.2 and a MnO content in the slag is more than or equal to 3 mass% and less than or equal to 10 mass%.

[6]

The method for producing steelmaking slag for fertilizer raw material according to [5], in which molten slag after the dephosphorization treatment is poured into a dish-like heat-resistant container and is rapidly cooled to be solidified.

[7]

The method for producing steelmaking slag for fertilizer raw material according to [6], in which molten slag after the dephosphorization treatment is rapidly cooled by performing water sprinkling.

[8]

The method for producing steelmaking slag for fertilizer raw material according to any one of [5] to [7], in which the converter-type pot is tilted to pour molten slag after the dephosphorization treatment into a slag pot in a tilting manner, and then the molten slag in the slag pot is poured into a tiltable first heat-resistant container in a tilting manner, water sprinkling is performed in the first heat-resistant container to rapidly cool and solidify the molten slag, and then the solidified slag is fragmented, and the first heat-resistant container is tilted to slide the solidified slag down into a second heat-resistant container, and thereby the solidified slag is fragmented.

[9]

The method for producing steelmaking slag for fertilizer raw material

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8/69 according to any one of [5] to [8], in which a 2CaOSiO2-3CaOP2Os solid solution and an FeO-MnO-CaO-SiCk-based solid solution are formed by rapid cooling.

[10]

The method for producing steelmaking slag for fertilizer raw material according to any one of [5] to [9], in which slag is pulverized such that a particle size is less than 5 mm as a whole and a mass ratio of particles with particle sizes of less than 600 pm is more than or equal to 60% relative to a total mass.

[Π]

A method for producing a fertilizer, including: powdering the steelmaking slag for fertilizer raw material according to any one of [1] to [4] or steelmaking slag for fertilizer raw material produced by the method for producing steelmaking slag for fertilizer raw material according to any one of [5] to [10].

[12]

The method for producing a fertilizer according to [11], in which a prescribed binder is added to the steelmaking slag for fertilizer raw material after powdering, and then granulation is performed.

[13]

The method for producing a fertilizer according to [11] or [12], in which an organic substance is further mixed with an obtained fertilizer.

[14]

The method for producing a fertilizer according to [13], in which the organic substance is at least one of livestock manure, a plant residue, and compost obtained from a fishery product.

[15]

A fertilizer application method including: applying a fertilizer that contains the steelmaking slag for fertilizer raw material according to any one of [1] to [4], steelmaking slag for fertilizer raw material produced by the method for producing steelmaking slag for fertilizer raw material according to any one of [5] to [10], or a fertilizer produced by the method for producing a fertilizer according to any one of [11] to [14] to a soil in which pH/tkO) is more than or equal to 4 and less than or equal to 6, a value expressed by (pH/HzO) - pH(KCl)) is more than or equal to 1, and

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9/69 an amount of available phosphoric acid is less than or equal to 5 mg/100 g of dry soil. [16]

The fertilizer application method according to [15], in which an application amount of the fertilizer is more than or equal to 0.05 t/ha and less than or equal to 2 t/ha as the steelmaking slag for fertilizer raw material.

[17]

The fertilizer application method according to [15] or [16], in which the fertilizer is scattered on a surface of a plow layer or is mixed with the plow layer before sowing or seedling planting.

[18]

The fertilizer application method according to [15] or [16], in which the fertilizer is scattered on a surface of a plow layer in a neighborhood of a plant body to be cultivated or is mixed into the plow layer.

[0025]

As described above, according to the present invention, many kinds of elements can be supplied as fertilizer of plants easily at low cost even to acidic soils of regions where the amount of rainfall is large and regions where river flooding occurs frequently, without runoff due to a water current.

DETAILED DESCRIPTION OF THE EMBODIMENT(S) [0026]

Hereinbelow, preferred embodiments of the present invention are described in detail.

[0027] (With regard to content of investigations performed by present inventors)

Before describing embodiments of the present invention, the results of investigations performed by the present inventors regarding demands on fertilizers and fertilizer application methods like those described above are described in detail. [0028] < Investigations on technology disclosed in Patent Literature 1>

With regard to demands like those described above, the raw material for

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10/69 silicophosphatic fertilizer disclosed in Patent Literature 1 above has a relatively low basicity in which the basicity expressed by (the CaO content/the S1O2 content) is more than or equal to 1.0 and less than or equal to 1.4, and is therefore less likely to exhibit effect for acidic soil. Further, the raw material for silicophosphatic fertilizer disclosed in Patent Literature 1 above has a contained amount of soluble CaO of as low as less than or equal to 30 mass% and has a weak basicity, and is therefore less likely to exhibit effect for acidic soil, after all.

[0029]

Moreover, in Patent Literature 1 above, it is stated that the AI2O3 content is less than or equal to 10 mass%; Examples show that the AI2O3 content is more than or equal to 4.84 mass% and less than or equal to 6.33 mass%, which are high values exceeding 4 mass%. Al is a substance that is likely to bind to phosphate ions and is a cause of the hindrance of phosphorus absorption by plants; hence, a lower AI2O3 content is desired.

[0030]

Further, in Patent Literature 1 above, neither a description on the containing of boron nor a description on the fertilizer effect of boron exists.

[0031] investigations on technology disclosed in Patent Literature 2>

In Patent Literature 2 above, a method that produces a slag phosphatic fertilizer using, as a raw material, steelmaking slag obtained from a molten iron preliminary treatment process of the ironmaking process is disclosed; however, a description on a method for producing the steelmaking slag serving as a raw material of the slag phosphatic fertilizer does not exist. Further, from Examples of Patent Literature 2 above, the citric acid-soluble phosphoric acid content of the steelmaking slag serving as a raw material is more than or equal to 2.56 mass% and less than or equal to 2.62 mass%, and it can be seen that the condition serving as a standard of the slag phosphatic fertilizer that the citric acid-soluble phosphoric acid content be more than or equal to 3 mass% is not satisfied. Further, in Patent Literature 2 above, neither a description on the containing of boron or manganese nor a description on the fertilizer effect of boron or manganese exists.

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11/69 [0032] <Investigations on technology disclosed in Patent Literature 3>

In Patent Literature 3 above, it is stated that the contained amount of phosphoric acid is more than or equal to 1.5 mass% and less than or equal to 5 mass%; however, a description does not exist for what ratio of the amount is soluble phosphoric acid (phosphoric acid that is dissolved out with Petermann's ammonium citrate solution), which can act on plants effectively.

[0033]

In Patent Literature 3, it is stated that the contained amount of CaO is more than or equal to 20 mass% and less than or equal to 50 mass%. As a reason for this contained amount, it is shown that steelmaking slag with a CaO content of less than 20 mass% or more than 50 mass% is hardly generated in the ironmaking process. [0034]

Further, in Patent Literature 3, it is stated that slag particles made of steelmaking slag contain more than or equal to 10 mass% and less than or equal to 30 mass% of SiO2. In Patent Literature 3, as a reason for this, it is shown that, in the case where the amount of S1O2 is less than 10 mass%, the amount of available silicic acid dissolved out is small, and hence the effect of promoting the growth of diatoms, which have the function of generating oxygen by photosynthesis on the soil surface of a paddy field covered with water, cannot be expected. Further, in Patent Literature 3, it is shown that steelmaking slag containing more than 30 mass% of S1O2 is hardly generated in the ironmaking process, and is therefore difficult to obtain.

[0035]

In Patent Literature 3 above, a description on the basicity of slag (= CaO/SiCk) does not exist; hence, a contained amount of CaO of more than or equal to 20 mass% and less than or equal to 50 mass% and a contained amount of S1O2 of more than or equal to 10 mass% and less than or equal to 30 mass% are possible as mentioned above, and the basicity of slag can take values in a very wide range from 0.67 (CaO: 20 mass%, S1O2: 30 mass%) to 5 (CaO: 50 mass%, S1O2: 10 mass%). The basicity of slag strongly relates to the dissolving-out of fertilizer effective

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12/69 components such as phosphorus, iron, and manganese, and therefore it is presumably necessary to set a basicity suitable for the dissolving-out of these fertilizer effective elements.

[0036]

Further, in Patent Literature 3, it is stated that slag particles made of steelmaking slag contain more than or equal to 3.5 mass% and less than or equal to 10 mass% of MnO. In Patent Literature 3, as a reason for this, it is shown that, in the case where the contained amount of MnO is less than 3.5 mass%, the dissolvingout of sufficient polyvalent manganese to raise the oxidation-reduction potential of paddy field soil may not occur. Here, the application amount described in Patent Literature 3 is more than or equal to 0.5 t/ha to 5 t/ha, and the literature envisages that the dissolving-out of sufficient polyvalent manganese to raise the oxidationreduction potential of paddy field soil will occur with application amounts in this range. In the case where the application amount is smaller than the range mentioned above, it is presumably necessary to investigate conditions where manganese dissolves out more efficiently.

[0037]

In Patent Literature 3, since a description on the basicity of slag does not exist as mentioned above, a basicity suitable for efficient dissolving-out of phosphorus and manganese in the basicity range of 0.67 to 5, which is envisaged from the CaO content and the S1O2 content of Patent Literature 3, is not investigated at all.

[0038]

Further, in Patent Literature 3, a description on boron does not exist, and a description on what kind of structure of slag phosphorus, calcium, silicon, manganese, etc. dissolve out from does not exist, either. In addition, the application amount is set to more than or equal to 0.5 t/ha to 5 t/ha and a relatively large application amount is needed; hence, some cost for fertilizer and some cost regarding labor for scattering are involved, and this is disadvantageous.

[0039] investigations on technologies disclosed in Patent Literature 4 and Patent Literature

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13/69

5>

In the molten iron preliminary treatment method disclosed in Patent Literature 4 and Patent Literature 5, desiliconization treatment and dephosphorization treatment are sequentially performed using one converter-type smelting furnace; thereby, slag containing silicic acid effective for fertilizer and slag containing phosphoric acid are collected separately. However, as fertilizer, it is preferable that both silicic acid and phosphoric acid be contained. Further, separately performing desiliconization treatment and dephosphorization treatment takes effort and cost from the viewpoint of obtaining slag serving as a raw material of fertilizer. Further, in Patent Literature 4 and Patent Literature 5, the composition of produced dephosphorization slag is not disclosed at all, and a description on fertilizer does not exist, either. Therefore, it is impossible to assess whether the slag disclosed in Patent Literature 4 and Patent Literature 5 above is suitable for fertilizer or not.

[0040]

The present inventors think that, in order to control the composition of produced slag appropriately, the freeboard in a converter-type pot (that is, the length from the throat to the liquid surface of molten iron) is an important condition, as described in detail below. However, in Patent Literature 4, the freeboard when desiliconization treatment and dephosphorization treatment are sequentially performed using one converter-type smelting furnace is not disclosed at all. Further, in Patent Literature 5, a description of the ratio of the freeboard exists only for desiliconization treatment, and a description on the freeboard does not exist for dephosphorization treatment.

[0041] <Investigations on technology disclosed in Patent Literature 6>

In Patent Literature 6, a method that produces a siliceous fertilizer in a molten iron preliminary treatment process of the ironmaking process is disclosed, and it is stated that citric acid-soluble phosphoric acid is added to converter slag produced by the molten iron preliminary treatment to achieve more than or equal to 5 mass% of citric acid-soluble phosphoric acid. Further, in Patent Literature 6, it is

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14/69 stated that the phosphoric acid content of the original slag is more than or equal to 1 mass% and less than or equal to 4 mass%. In Patent Literature 6, there is no description on the containing of boron nor on the fertilizer effect of boron at all. Further, in Patent Literature 6, there is no description on the freeboard at the time of slag production, and there is no description on a method for collecting the slag by slag discharge nor on a method for cooling the slag, either.

[0042] investigations on technology disclosed in Patent Literature 7>

Patent Literature 7 discloses a siliceous fertilizer in which the dissolving-out of silicic acid is enabled by mixing coal ash containing only undissolvable silicic acid with slag of stainless steel in a molten state. However, the siliceous fertilizer is slag of stainless steel, and therefore contains a large amount of chromium. Hence, if a large amount of a fertilizer using the slag as a raw material is applied or the fertilizer is applied for a long period of time, it is feared that the chromium content of the soil will be increased. Further, it is necessary to mix coal ash, and this is a factor in cost increase because of the increase in the number of operations.

[0043] investigations on technology disclosed in Patent Literature 8>

In Patent Literature 8, a method for producing phosphoric acid-containing slag for fertilizer is disclosed, and the phosphoric acid content of the phosphoric acid-containing slag for fertilizer is set to more than or equal to 18.32 mass%. However, this phosphoric acid content is greatly deviated from the phosphoric acid content of steelmaking slag that can be produced by molten iron preliminary treatment or decarburization treatment of a normal ironmaking process, and the above phosphoric acid-containing slag for fertilizer cannot be produced by molten iron preliminary treatment or decarburization treatment of a normal ironmaking process. Hence, a special process is needed to produce such slag, and this is a factor in cost increase.

[0044] investigations on technology disclosed in Patent Literature 9>

Also in Patent Literature 9, a method for producing a phosphatic fertilizer

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15/69 raw material obtained from the ironmaking process is disclosed, and the phosphoric acid content of slag serving as the phosphatic fertilizer raw material is set to more than or equal to 15 mass%. However, this phosphoric acid content is greatly deviated from the phosphoric acid content of steelmaking slag that can be produced by molten iron preliminary treatment or decarburization treatment of a normal ironmaking process, and the above slag serving as the phosphatic fertilizer raw material cannot be produced by molten iron preliminary treatment or decarburization treatment of a normal ironmaking process. Hence, a special process is needed to produce such slag, and this is a factor in cost increase.

[0045]

As described in detail hereinabove, various problems to be solved exist in the case where steelmaking slag of the ironmaking process is produced as a fertilizer raw material or steelmaking slag of the ironmaking process is used as a fertilizer raw material capable of supplying various minerals.

[0046]

The present inventors conducted extensive studies on the problems mentioned above; consequently, in order to supply many kinds of elements of P, Fe, Mn, Si, Ca, Mg, B, and S, have developed steelmaking slag specialized for fertilizer raw material and a method for producing the same, and a method for producing a fertilizer and a fertilizer application method capable of supplying these elements; and have successfully obtained steelmaking slag for fertilizer raw material that can supply many kinds of elements as fertilizer of plants more easily at lower cost. Embodiments of the present invention will now be described in detail.

[0047] (Embodiments) <With regard to common steelmaking slag>

Before describing in detail steelmaking slag for fertilizer raw material according to an embodiment of the present invention, common steelmaking slag is briefly described for comparison.

[0048]

Examples of steelmaking slag commonly used for fertilizer include

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16/69 dephosphorization slag, which is a kind of steelmaking slag produced as a by-product in a molten iron preliminary treatment process of a steel production process. Dephosphorization slag is slag containing phosphorus that is produced as a byproduct by adding lime, iron oxide, or the like as a dephosphorizing agent to molten iron and blowing a gas such as oxygen into the material in order to remove phosphorus contained in the molten iron, and is a kind of steelmaking slag.

[0049]

The composition of typical steelmaking slag (converter slag) is opened to the public by Nippon Slag Association (http://www.slg.jp/character.html), and the typical composition is as follows.

CaO: 45.8, SiCh: 11.0, the total iron: 17.4, MgO: 6.5,

AI2O3: 1.9, S: 0.06, P2O5: 1.7, MnO: 5.3 (each in mass%) [0050]

Steelmaking slag for fertilizer raw material according to an embodiment of the present invention described in detail below is a kind of dephosphorization slag, and is distinctive in that the contained amounts of P2O5 and S1O2 are high and the contained amount of the total iron is low as compared to the composition of typical steelmaking slag like that mentioned above, as described in detail below. Further, the steelmaking slag for fertilizer raw material according to the present embodiment is distinctive in that also the contained amount of citric acid-soluble boron is high as compared to the composition of typical steelmaking slag like that mentioned above. [0051] <With regard to steelmaking slag for fertilizer raw material>

Steelmaking slag for fertilizer raw material according to the present embodiment will now be described in detail.

The steelmaking slag for fertilizer raw material according to the present embodiment is steelmaking slag that contains prescribed amounts of components and is obtained by performing dephosphorization treatment on blast furnace molten iron, and contains prescribed amounts of various elements such as Ca, P, Si, Mg, Fe, Mn, B, S, and Al.

[0052]

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17/69

More specifically, the steelmaking slag for fertilizer raw material according to the present embodiment contains, in mass%, P2O5: more than or equal to 2% and less than or equal to 8%, MnO: more than or equal to 3% and less than or equal to 10%, boron: more than or equal to 0.005% and less than 0.05%, the total iron: more than or equal to 7% and less than 15%, CaO: more than or equal to 38% and less than or equal to 48%, S1O2: more than or equal to 22% and less than or equal to 30%, sulfur: more than or equal to 0.1% and less than or equal to 0.6%, MgO: more than or equal to 1% and less than or equal to 8%, and AI2O3: more than or equal to 0.5% and less than or equal to 3%. Further, the steelmaking slag for fertilizer raw material according to the present embodiment may contain various impurities as well as the components mentioned above.

Each component contained in the steelmaking slag for fertilizer raw material according to the present embodiment will now be described in detail.

[0053] [CaO: more than or equal to 38 mass% and less than or equal to 48 mass%]

First, Ca is described.

Ca is a fertilizer element essential to plants. In a fertilizer or steelmaking slag, when the contained amount of Ca is written, the contained amount is written on the basis of an oxide of CaO; thus, hereinafter the contained amount of Ca is shown as CaO.

[0054]

CaO is a compound exhibiting alkalinity, and has effect for the improvement of acidic soil. In the case where the contained amount of CaO in the steelmaking slag is less than 38 mass%, the alkalinity is weak; hence, in an acidic soil in which iron excess has occurred, it is feared that the improvement of the acidic soil will be insufficient, and Fe contained in the steelmaking slag will cause iron excess to become worse. On the other hand, in the case where the CaO content in the steelmaking slag is more than 48 mass%, the CaO content is too high; hence, the contained amount of any of P2O5, MnO, boron, the total iron, sulfur, S1O2, MgO, and AI2O3, which are other components contained in the steelmaking slag for fertilizer raw material according to the present embodiment, needs to be set smaller than a

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18/69 desired value in order to make the total contained amount including the contained amounts of these other components less than or equal to 100%; thus, this is not preferable. Further, it is preferable that the steelmaking slag used in the present embodiment be able to be stably supplied in a large amount and be able to be produced in a normal ironmaking process. Also from this point of view, the contained amount of CaO of the steelmaking slag for fertilizer raw material according to the present embodiment is set to more than or equal to 38 mass% and less than or equal to 48 mass%. The contained amount of CaO is preferably more than or equal to 39 mass% and less than or equal to 47 mass%, and more preferably more than or equal to 40 mass% and less than or equal to 46 mass%.

[0055]

The contained amount of CaO can be measured by, for example, the X-ray fluorescence analysis method.

Specifically, a plurality of measurement samples of which the contained amount of CaO is known are prepared, with the contained amount varied, and X-ray fluorescence intensity derived from Ca of the prepared measurement samples is measured by an X-ray fluorescence analysis apparatus. By using the obtained Xray fluorescence intensity derived from Ca and the contained amount of CaO, a calibration curve indicating the relationship between the contained amount of CaO and the X-ray fluorescence intensity is created in advance. Then, in regard to a focused-on sample of which the contained amount of CaO is unknown, X-ray fluorescence intensity derived from Ca is measured by the X-ray fluorescence analysis apparatus, and the contained amount of CaO can be specified by using the obtained X-ray fluorescence intensity and the calibration curve.

[0056]

Here, a sample is taken as described below, then the focused-on sample is prepared in the following steps, and X-ray fluorescence intensity is measured under the following measurement conditions.

That is, an analysis sample is set in a vibrating mill (T-100 manufactured by Kawasaki Heavy Industries, Ltd.), and the analysis sample is pulverized into powder (apparatus conditions: pulverizing time of 30 seconds, 1000 rpm). The pulverized

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19/69 sample is subjected to classification using a sieve with an aperture of 212 pm. Next, 6 g of lithium tetraborate (a flux), 0.3g of the sample that has passed through the sieve with the above aperture (212 pm), and approximately two ear pick spoons of lithium iodide (a parting agent) are introduced into a platinum dish, and fusion of l,150°C x 10 minutes x 3 to 4 times is performed by a bead sampler to prepare glass beads. Similarly, a reference material is also processed into glass beads. A calibration curve is created by an X-ray fluorescence analysis apparatus (ZSX PrimusII manufactured by Rigaku Corporation), and the sample that has passed through the sieve with the above aperture (212 pm) is quantified and subjected to confirmatory analysis using the reference material. This analysis method conforms to JIS standard “JIS M 8205”.

[0057] [SiCh: more than or equal to 22 mass% and less than or equal to 30 mass%]

Next, Si is described.

Si is not an essential element of plants, but is a very important element to siliceous plants of the grass family such as rice, wheat, and com. Silicic acid (S1O2) accounts for approximately 5% of the dry mass of a plant body of rice. In a fertilizer and steelmaking slag, when the contained amount of Si is written, the contained amount is written on the basis of an oxide of S1O2; thus, hereinafter the contained amount of Si is shown as S1O2.

[0058]

The steelmaking slag for fertilizer raw material according to the present embodiment contains a large amount of S1O2 as compared to the composition of typical steelmaking slag, as mentioned above. The steelmaking slag for fertilizer raw material according to the present embodiment contains a large amount of available silicic acid effective to plants, and is therefore effective to supply Si to gramineous plants and the like.

[0059]

In the case where the contained amount of S1O2 of the steelmaking slag for fertilizer raw material according to the present embodiment is less than 22 mass%, the possibility that Si cannot be sufficiently supplied to plants is increased; thus, this

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20/69 is not preferable. On the other hand, in the case where the contained amount of S1O2 is more than 30 mass%, also the CaO content is high from a restriction regarding the basicity described later; hence, the contained amount of any of MnO, boron, the total iron, sulfur, S1O2, MgO, and AI2O3, which are other components contained in the steelmaking slag for fertilizer raw material according to the present embodiment, needs to be set smaller than a desired value in order to make the total contained amount including the contained amounts of these other components less than or equal to 100%; thus, this is not preferable. Therefore, in the steelmaking slag for fertilizer raw material according to the present embodiment, the contained amount of S1O2 is set to more than or equal to 22 mass% and less than or equal to 30 mass%. The contained amount of S1O2 is preferably more than or equal to 23 mass% and less than or equal to 29 mass%, and more preferably more than or equal to 24 mass% and less than or equal to 28 mass%.

[0060]

The contained amount of S1O2 can be measured by, for example, the X-ray fluorescence analysis method.

Specifically, a plurality of measurement samples of which the contained amount of S1O2 is known are prepared, with the contained amount varied, and X-ray fluorescence intensity derived from Si of the prepared measurement samples is measured by an X-ray fluorescence analysis apparatus. By using the obtained Xray fluorescence intensity derived from Si and the contained amount of S1O2, a calibration curve indicating the relationship between the contained amount of S1O2 and the X-ray fluorescence intensity is created in advance. Then, in regard to a focused-on sample of which the contained amount of S1O2 is unknown, X-ray fluorescence intensity derived from Si is measured by the X-ray fluorescence analysis apparatus, and the contained amount of S1O2 can be specified by using the obtained X-ray fluorescence intensity and the calibration curve.

[0061]

Here, a method for preparing the focused-on sample and measurement conditions of X-ray fluorescence intensity are similar to those for CaO.

[0062]

PCTJP2018024529

21/69 [Basicity (CaO content/SiO2 content): more than 1.5 and less than or equal to 2.2]

In the steelmaking slag for fertilizer raw material according to the present embodiment, conditions regarding both the CaO content and the S1O2 content like those mentioned above are satisfied, and furthermore the basicity expressed by (the CaO content/the S1O2 content) is more than 1.5 and less than or equal to 2.2.

[0063]

In the steelmaking slag for fertilizer raw material according to the present embodiment, the contained amount of CaO is more than or equal to 38 mass% and less than or equal to 48 mass%; thus, the contained amount of S1O2 is prescribed as follows when the basicity is grasped with 0.1 intervals.

In the case where the basicity is less than or equal to 27 mass%

In the case where the basicity is less than or equal to 28 mass%

In the case where the basicity is less than or equal to 30 mass%

In the case where the basicity is less than or equal to 32 mass%

In the case where the basicity is less than or equal to 34 mass% [0064]

1.8: more than or equal to 21 mass% and

1.7: more than or equal to 22 mass% and

1.6: more than or equal to 24 mass% and

1.5: more than or equal to 25 mass% and

1.4: more than or equal to 27 mass% and

As mentioned above, it is in the case where the basicity is in the range of 1.6 to 1.7 that the contained amount of S1O2 is in the range of the contained amount of S1O2 prescribed in the steelmaking slag for fertilizer raw material according to the present embodiment (more than or equal to 22 mass% and less than or equal to 30 mass%).

[0065]

On the other hand, in the steelmaking slag for fertilizer raw material according to the present embodiment, the contained amount of S1O2 is more than or equal to 22 mass% and less than or equal to 30 mass%; thus, the CaO content is as follows when the basicity is grasped with 0.1 intervals.

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22/69

In the case where the basicity is 2.1: more than or equal to 46 mass% and less than or equal to 63 mass%

In the case where the basicity is 2.2: more than or equal to 48 mass% and less than or equal to 66 mass%

In the case where the basicity is 2.3: more than or equal to 51 mass% and less than or equal to 69 mass% [0066]

It is in the case where the basicity is in the range of 2.1 to 2.2 that the result mentioned above is in the range of the contained amount of CaO prescribed in the steelmaking slag for fertilizer raw material according to the present embodiment (more than or equal to 38 mass% and less than or equal to 48 mass%).

[0067]

Therefore, it can be said that the basicities of more than 1.5 and less than or equal to 2.2 are basicities that can satisfy the conditions regarding the CaO content and the S1O2 content in the steelmaking slag for fertilizer raw material according to the present embodiment.

[0068]

The reasons why attention is focused on basicities around 1.4 to 1.8 and basicities around 2.1 to 2.3 in the above description are as follows.

[0069]

The feature most characterizing the properties of slag is basicity. CaO is a component serving as a main factor of the basicity of slag. In the actual ironmaking process, most basicities of steelmaking slag obtained in dephosphorization treatment of molten iron preliminary treatment are approximately 1.5 to 1.8, and are easy to obtain. The present inventors have found by test studies that a basicity of slag at which the dissolving-out of fertilizer effective components such as silicic acid, phosphoric acid, manganese, and boron can be achieved with better balance exists around 1.5 to 1.8. Thus, attention is focused on basicities around 1.4 to 1.8 in the above description.

[0070]

On the other hand, as mentioned above, most basicities of steelmaking slag

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23/69 obtained in dephosphorization treatment of molten iron preliminary treatment are approximately 1.5 to 1.8 in the actual ironmaking process; hence, in order to produce steelmaking slag with a basicity of more than or equal to 2, an operation for increasing the contained amount of CaO is performed, or an operation for reducing the contained amount of S1O2 is performed. Here, in the operation for increasing the contained amount of CaO, the addition amount of lime added as a CaO source is increased, and this involves some cost. Hence, an operation of making the contained amount of S1O2 relatively low may be performed, and thereby steelmaking slag like that mentioned above can be obtained while an increase in cost is suppressed. By using steelmaking slag with a basicity of more than or equal to 2 as a fertilizer raw material, a larger amount of CaO can be incorporated in the steelmaking slag for fertilizer raw material. CaO is alkaline, and exhibits effect for the improvement of an acidic soil with a low pH; thus, even if an operation different from a normal ironmaking process is performed, there is a reason for achieving a basicity like that mentioned above. Hence, attention is focused on basicities around 2.1 to 2.3 in the above description.

[0071]

In the steelmaking slag for fertilizer raw material according to the present embodiment, in the case where the basicity is less than or equal to 1.5, the contained amount of CaO is relatively low in terms of use for fertilizer raw material, and hence the effect of improving acidic soil is weak; thus, this is not preferable. On the other hand, in the steelmaking slag for fertilizer raw material according to the present embodiment, in the case where the basicity is more than 2.2, there is a possibility that, in terms of use for fertilizer raw material, a larger amount of CaO than the amount of CaO necessary for the improvement of acidic soil will be applied, and this is a cause of a cost increase of lime added as a CaO source; thus, this is not preferable. Therefore, in the steelmaking slag for fertilizer raw material according to the present embodiment, the basicity is set to more than 1.5 and less than or equal to 2.2. By setting the basicity to more than 1.5 and less than or equal to 2.2, the cost of lime that is, in terms of use for fertilizer raw material, added to obtain an effect of moderate improvement of acidic soil and to increase the CaO content can be suppressed. The

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24/69 basicity is preferably more than or equal to 1.6 and less than or equal to 2.1, and more preferably more than or equal to 1.6 and less than or equal to 2.0.

[0072]

Furthermore, by adjusting the basicity to more than 1.5 and less than or equal to 2.2, both a 2CaOSiO2-3CaOP2Os solid solution and an FeO-MnO-CaOSiC>2-based solid solution are formed easily in the produced steelmaking slag. Furthermore, as described in detail below, rapid cooling may be performed when solidifying slag in the production process of steelmaking slag, and thereby two kinds of solid solutions like those mentioned above are formed more easily. As described in detail below, these solid solutions promote the dissolving-out of not only silicic acid but also phosphoric acid, manganese, and boron; thus, for steelmaking slag for fertilizer raw material, both these solid solutions are preferably contained.

[0073] [P2O5: more than or equal to 2 mass% and less than or equal to 8 mass%; ratio of soluble P2O5: more than or equal to 50%]

Next, P is described.

P is an essential element of plants, along with N and K. P is an element necessary for energy metabolism substances such as DNA and RNA, which are genes, and ATP, constituent substances of the cell membrane, etc. Further, P is an element that acts on the growing point of roots and has effect for the growth of roots. If P is lacking, the growth of roots is suppressed.

[0074]

In a fertilizer and steelmaking slag, when the contained amount of P is written, the contained amount is written on the basis of an oxide of P2O5; thus, hereinafter the contained amount of P is shown as P2O5.

[0075]

In a soil in acidic conditions where Al and Fe are likely to be ionized and dissolved out, there is a possibility that P will be insolubilized as aluminum phosphate (AIPO4) or iron phosphate (FePCF), and the roots of plants cannot absorb phosphate ions (PO4³') containing P. Since the steelmaking slag for fertilizer raw material according to the present embodiment contains CaO and MgO and is alkaline,

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25/69 the steelmaking slag for fertilizer raw material can improve the acidic soil to prevent Al and Fe from being ionized and dissolved out from the soil, and at the same time can gradually dissolve out P as phosphate ions (PO4³').

[0076]

In the steelmaking slag for fertilizer raw material according to the present embodiment, P exists mainly as a substance having the composition of Ca2SiO4Ca3(PO4)2. In soil, P is gradually dissolved out as PO4³' from a fertilizer containing the steelmaking slag for fertilizer raw material according to the present embodiment, along with Ca and Si. Therefore, P can be gradually supplied to plants without being insolubilized by Al or Fe, for a long period of time of a several-month level equivalent to one cropping of crops such as rice.

[0077]

In the steelmaking slag for fertilizer raw material according to the present embodiment, in the case where the contained amount of P2O5 is less than 2 mass%, effects like those mentioned above cannot be obtained reliably. Hence, in the steelmaking slag for fertilizer raw material according to the present embodiment, the contained amount of P2O5 is set to more than or equal to 2 mass%.

[0078]

On the other hand, in the steelmaking slag for fertilizer raw material according to the present embodiment, in the case where the contained amount of P2O5 is more than 8 mass%, there is a possibility that, in terms of use for fertilizer raw material, P2O5 will be excessively supplied to soil while balance with nitrogen and potassium, which are others of the three major fertilizer elements, is lost; thus, this is not preferable. Therefore, in the steelmaking slag for fertilizer raw material according to the present embodiment, the contained amount of P2O5 is set to less than or equal to 8 mass%.

[0079]

In the steelmaking slag for fertilizer raw material according to the present embodiment, the contained amount of P2O5 is preferably more than or equal to 3 mass% and less than or equal to 8 mass%, and more preferably more than or equal to 3 mass% and less than or equal to 6 mass%.

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26/69 [0080]

In the Fertilizer Control Faw of Japan, the contained amount of citric acidsoluble P2O5 is prescribed to be more than or equal to 3 mass%, for a slag phosphatic fertilizer. The steelmaking slag for fertilizer raw material according to the present embodiment does not necessarily satisfy the standard of a slag phosphatic fertilizer, but promises the fertilizer effect of P for the reason mentioned above. In the steelmaking slag for fertilizer raw material according to the present embodiment, since the contained amount of P2O5 is more than or equal to 2 mass%, the contained amount of citric acid-soluble P2O5 is approximately more than or equal to 1.0 mass%. [0081]

On the other hand, in regard to P2O5 that plants can actually absorb from roots, it is known that soluble P2O5, which is dissolved out with a neutral ammonium citrate aqueous solution (Petermann's ammonium citrate solution), provides a more suitable value than citric acid-soluble P2O5, which is dissolved out with a 2% citric acid aqueous solution. The steelmaking slag for fertilizer raw material according to the present embodiment has succeeded in increasing the ratio of soluble P2O5 in the P2O5 contained in the slag to more than or equal to 50%, by means of the composition of slag and structure control. That is, the mass ratio of soluble P2O5 in the P2O5 contained in the slag can be made more than or equal to 50% by producing steelmaking slag for fertilizer raw material in accordance with a method for producing steelmaking slag for fertilizer raw material like that described in detail below. The upper limit value of the mass ratio of soluble P2O5 in the P2O5 contained in the slag is not particularly prescribed, and is preferably as high as possible; but the mass ratio cannot be made 100% in view of results obtained by actually preparing and analyzing a large number of steelmaking slag samples, and the upper limit value is approximately 85%. The mass ratio of soluble P2O5 in the P2O5 contained in the slag is preferably more than or equal to 60%, and more preferably more than or equal to 70%.

[0082]

The contained amount of P2O5 can be measured by, for example, the X-ray fluorescence analysis method.

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27/69

Specifically, a plurality of measurement samples of which the contained amount of P is known are prepared, with the contained amount varied, and X-ray fluorescence intensity derived from P of the prepared measurement samples is measured by an X-ray fluorescence analysis apparatus. By using the obtained Xray fluorescence intensity derived from P and an amount on a P2O5 basis calculated from the contained amount of P, a calibration curve indicating the relationship between the amount on a P2O5 basis and the X-ray fluorescence intensity is created in advance. Then, in regard to a focused-on sample of which the contained amount of P is unknown, X-ray fluorescence intensity derived from P is measured by the Xray fluorescence analysis apparatus, and the contained amount of P2O5 can be specified by using the obtained X-ray fluorescence intensity and the calibration curve. [0083]

[0084]

The contained amount of soluble P2O5 can be measured by using the ammonium vanadomolybdate absorption spectroscopy method using Petermann's ammonium citrate solution. The mass ratio of soluble P2O5 in the P2O5 can be calculated by using the contained amount of P2O5 and the contained amount of soluble P2O5 measured.

[0085] [MgO: more than or equal to 1 mass% and less than or equal to 8 mass%]

Next, Mg is described.

Mg is an element necessary for plants, and is regarded as a secondary element.

[0086]

In general, the MgO content of steelmaking slag is a value well below the CaO content. Mg contained in steelmaking slag is derived mainly from Mg added in a sintering process or dissolved out from firebricks of the furnace wall of a converter. In a fertilizer and steelmaking slag, when the contained amount of Mg is written, the contained amount is written on the basis of an oxide of MgO; thus,

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28/69 hereinafter the contained amount of Mg is shown as MgO.

[0087]

MgO is alkaline, and has effect for the improvement of acidic soil, along with CaO. In the steelmaking slag for fertilizer raw material according to the present embodiment, in the case where the contained amount of MgO is less than 1 mass%, the effect of improving acidic soil like that mentioned above cannot be exhibited. On the other hand, an ideal lime/magnesia ratio is considered to be approximately 2.5 to 6 in terms of use for fertilizer raw material. In the steelmaking slag for fertilizer raw material according to the present embodiment, the CaO content is as high as 38% to 48%; hence, in order to satisfy the lime/magnesia ratio mentioned above, the magnesia content is, for example, 6.3% to 8% even when the lime/magnesia ratio is at the maximum of 6. However, unless a MgO source is additionally added in the actual ironmaking process, it is difficult to make the MgO content more than 8 mass%. Therefore, in the steelmaking slag for fertilizer raw material according to the present embodiment, the MgO content is set to more than or equal to 1 mass% and less than or equal to 8 mass%. The contained amount of MgO is preferably more than or equal to 2 mass% and less than or equal to 8 mass%, and more preferably more than or equal to 3 mass% and less than or equal to 8 mass%.

[0088]

The contained amount of MgO can be measured by, for example, the X-ray fluorescence analysis method.

Specifically, a plurality of measurement samples of which the contained amount of Mg is known are prepared, with the contained amount varied, and X-ray fluorescence intensity derived from Mg of the prepared measurement samples is measured by an X-ray fluorescence analysis apparatus. By using the obtained Xray fluorescence intensity derived from Mg and an amount on a MgO basis calculated from the contained amount of Mg, a calibration curve indicating the relationship between the amount on a MgO basis and the X-ray fluorescence intensity is created in advance. Then, in regard to a focused-on sample of which the contained amount of Mg is unknown, X-ray fluorescence intensity derived from Mg

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29/69 is measured by the X-ray fluorescence analysis apparatus, and the contained amount of MgO can be specified by using the obtained X-ray fluorescence intensity and the calibration curve.

[0089]

[0090] [Total iron: more than or equal to 7 mass% and less than 15 mass%]

Next, Fe is described.

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

[0091]

The steelmaking slag for fertilizer raw material according to the present embodiment contains CaO at more than or equal to 38 mass% and less than or equal to 48 mass% and contains MgO at more than or equal to 1 mass% and less than or equal to 8 mass%, and is therefore alkaline; further, as described later, suppresses the total iron to a relatively low contained amount of more than or equal to 7 mass% and less than 15 mass%; thus, can supply Fe as a trace element to plants even in a soil in which there is a concern of iron excess in acidic soil.

[0092]

As a feature of a fertilizer containing the steelmaking slag for fertilizer raw material according to the present embodiment, there is a feature of having a large bulk specific gravity and hence not running off due to rainwater but remaining behind to allow each element having a fertilizer effect to be dissolved out for a long period of time. Fe is an important element also in terms of increasing the bulk specific gravity of a fertilizer containing the steelmaking slag for fertilizer raw material according to the present embodiment.

[0093]

Fe is an element unavoidably contained in various kinds of steelmaking slag. In the steelmaking slag for fertilizer raw material according to the present

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30/69 embodiment, in the case where the contained amount of the total iron is less than 7 mass%, the bulk specific gravity is small, and the possibility that a fertilizer containing the steelmaking slag for fertilizer raw material according to the present embodiment will run off due to rainwater is increased. On the other hand, if the contained amount of the total iron is more than or equal to 15 mass%, the possibility that iron excess will be caused to plants in acidic soil is increased; thus, this is not preferable. Therefore, the contained amount of the total iron of the steelmaking slag for fertilizer raw material according to the present embodiment is set to more than or equal to 7 mass% and less than 15 mass%. The contained amount of the total iron is preferably more than or equal to 8 mass% and less than or equal to 14 mass%, and more preferably more than or equal to 9 mass% and less than or equal to 13 mass%.

[0094]

When the steelmaking slag for fertilizer raw material according to the present embodiment is analyzed with an X-ray diffraction apparatus, a peak of a mineral belonging to an FeO-CaO-SiCfi system is observed. On the other hand, when the steelmaking slag for fertilizer raw material according to the present embodiment is immersed in water for a long period of time and then the structure is observed with an electron probe microanalyzer (ΕΡΜΑ), a trace of concentration reduction is seen in a portion where Fe and Mn exist to overlap. From this fact, it is presumed that, when an FeO-MnO-CaO-SiO2-based solid solution in which MnO and FeO are dissolved together as a solid solution is formed, the dissolving-out of Mn, together with Fe, into soil is promoted more. Such an oxidization state of Fe is obtained by producing steelmaking slag for fertilizer raw material in accordance with a method for producing steelmaking slag for fertilizer raw material like that described in detail below. The term of the solid solution in the present embodiment describes main chemical components specifically, and can include, in terms of its properties, also components not specifically described. For example, the FeOMnO-CaO-SiCb-based solid solution includes one in which MgO is dissolved as a solid solution.

[0095]

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31/69

By producing steelmaking slag for fertilizer raw material in accordance with a method for producing steelmaking slag for fertilizer raw material like that described in detail below, in the produced steelmaking slag for fertilizer raw material, the contained amount of the total iron is made lower than that of steelmaking slag produced by a common converter process, and a range of the contained amount like that mentioned above is achieved and an oxidization state of Fe like that mentioned above is obtained.

[0096]

The contained amount of the total iron can be measured by, for example, the X-ray fluorescence analysis method.

Specifically, a plurality of measurement samples of which the contained amount of the total iron is known are prepared, with the contained amount varied, and X-ray fluorescence intensity derived from Fe of the prepared measurement samples is measured by an X-ray fluorescence analysis apparatus. By using the obtained X-ray fluorescence intensity derived from Fe and the contained amount of the total iron, a calibration curve indicating the relationship between the contained amount of the total iron and the X-ray fluorescence intensity is created in advance. Then, in regard to a focused-on sample of which the contained amount of the total iron is unknown, X-ray fluorescence intensity derived from Fe is measured by the Xray fluorescence analysis apparatus, and the contained amount of the total iron can be specified by using the obtained X-ray fluorescence intensity and the calibration curve. [0097]

[0098] [MnO: more than or equal to 3 mass% and less than or equal to 10 mass%; ratio of citric acid-soluble manganese: more than or equal to 80%]

Next, Mn is described.

Also Mn is an element having a fertilizer effect for plants as a trace element. In a fertilizer and steelmaking slag, when the contained amount of Mn is written, the contained amount is written on the basis of an oxide of MnO; thus, hereinafter the

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32/69 contained amount of Μη is shown as MnO.

[0099]

In the steelmaking slag for fertilizer raw material according to the present embodiment, in the case where the contained amount of MnO is less than 3 mass%, the contained amount of MnO is small; hence, the dissolving-out of Mn from a fertilizer containing the steelmaking slag for fertilizer raw material according to the present embodiment is not sufficient, and the fertilizer effect of Mn cannot be exhibited. On the other hand, in the case where the contained amount of MnO is more than 10 mass%, manganese excess is caused to plants particularly in acidic soil; thus, this is not preferable. Therefore, in the steelmaking slag for fertilizer raw material according to the present embodiment, the contained amount of MnO is set to more than or equal to 3 mass% and less than or equal to 10 mass%. The contained amount of MnO is preferably more than or equal to 4 mass% and less than or equal to 9 mass%, and more preferably more than or equal to 5 mass% and less than or equal to 8 mass%.

[0100]

By forming both of a 2CaOSiO2-3CaOP2Os solid solution and an FeOMnO-CaO-SiO2-based solid solution in the steelmaking slag for fertilizer raw material according to the present embodiment, the dissolving-out of Mn like that mentioned above is promoted more, and furthermore the dissolving-out of silicic acid, phosphoric acid, and boron can be promoted.

[0101]

It is known that plants secrete an organic acid from roots, and regarding citric acid-soluble manganese, which is manganese that is dissolved out with a 2% citric acid aqueous solution, as manganese usable by plants serves as an index. The steelmaking slag for fertilizer raw material according to the present embodiment has succeeded in allowing citric acid-soluble MnO to account for more than or equal to 80% of the MnO contained in the steelmaking slag, by means of the composition and structure control. That is, the mass ratio of citric acid-soluble MnO in the MnO contained in the slag can be made more than or equal to 80% by producing steelmaking slag for fertilizer raw material in accordance with a method for

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33/69 producing steelmaking slag for fertilizer raw material like that described in detail below. The upper limit value of the mass ratio of citric acid-soluble MnO in the MnO contained in the slag is not particularly prescribed, and is preferably as high as possible; but the mass ratio cannot be made 100% in view of results obtained by actually preparing and analyzing a large number of steelmaking slag samples, and the upper limit value is approximately 95%. The mass ratio of citric acid-soluble MnO in the MnO contained in the slag is preferably more than or equal to 85%, and more preferably more than or equal to 90%.

[0102]

The contained amount of MnO can be measured by, for example, the X-ray fluorescence analysis method.

Specifically, a plurality of measurement samples of which the contained amount of Mn is known are prepared, with the contained amount varied, and X-ray fluorescence intensity derived from Mn of the prepared measurement samples is measured by an X-ray fluorescence analysis apparatus. By using the obtained Xray fluorescence intensity derived from Mn and an amount on a MnO basis calculated from the contained amount of Mn, a calibration curve indicating the relationship between the amount on a MnO basis and the X-ray fluorescence intensity is created in advance. Then, in regard to a focused-on sample of which the contained amount of Mn is unknown, X-ray fluorescence intensity derived from Mn is measured by the X-ray fluorescence analysis apparatus, and the contained amount of MnO can be specified by using the obtained X-ray fluorescence intensity and the calibration curve.

[0103]

[0104]

The contained amount of citric acid-soluble MnO can be measured by using a method described in Testing Methods for Fertilizers (2016) of leaching using a 2% citric acid aqueous solution and the flame atomic absorption spectroscopy method prescribed by Food and Agricultural Materials Inspection Center (FAMIC). The

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34/69 mass ratio of citric acid-soluble MnO in the MnO can be calculated by using the contained amount of MnO and the contained amount of citric acid-soluble MnO measured.

[0105] [Boron: more than or equal to 0.005 mass% and less than 0.05 mass%; the ratio of citric acid-soluble boron: more than or equal to 95 %]

Next, boron is described.

Boron is a trace element necessary for plants; it is known that, if boron is lacking, boron deficiency occurs in plants. Boron is an element necessary for the synthesis of the cell wall of plants.

[0106]

On the other hand, it is known that, in the case where the boron content of soil is more than 5 mg/kg, boron excess may occur in plants. The boron content of 5 mg/kg is a very low value. Examples of commercially available fertilizer containing boron include a borate fertilizer (citric acid-soluble boron: more than or equal to 35%), a fused boron fertilizer (citric acid-soluble boron: approximately 24%), and a fused trace element composite fertilizer (FTE) (citric acid-soluble boron: 5 to 9%); however, all of these contain large amounts of boron, and hence it is feared that boron excess will occur due to excessive use of these fertilizers. When these commercially available fertilizers are applied to soil, it is not easy to make the boron content of the soil less than or equal to 5 mg/kg.

[0107]

For example, in the case where a fertilizer with a boron content of 5% is applied to 1 kg of soil, assuming that boron is not contained in the soil, an attempt to make the boron content of the soil less than or equal to 5 mg/kg requires that a small amount of less than or equal to 100 mg of the fertilizer be applied by being mixed with the soil uniformly. Hence, a common application amount has a great concern that boron will be applied excessively. To apply small amounts of these fertilizers containing large amounts of boron uniformly, it may be possible to dissolve or disperse the fertilizers in water and apply them; but it is presumed that conventional fertilizers are likely to run off due to rainwater etc. Therefore, it is presumed that,

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35/69 in terms of supplying boron to soil optimally, a fertilizer with a low boron content and of a type of being free from runoff is preferable.

[0108]

In the steelmaking slag for fertilizer raw material according to the present embodiment, in the case where the contained amount of boron is less than 0.005 mass% (= 50 mg/kg), even when a fertilizer containing the steelmaking slag for fertilizer raw material according to the present embodiment is applied to soil, the fertilizer effect of boron for plants cannot be exhibited because the amount of boron supplied is small. On the other hand, steelmaking slag in which the contained amount of boron is more than or equal to 0.05 mass% is obtained in a normal ironmaking process; and taking the trouble to additionally add a boron source such as borax in order to increase the boron content is a factor in cost increase and hence is not preferable. The steelmaking slag for fertilizer raw material according to the present embodiment has a much higher ratio of citric acid-soluble boron in the contained boron than conventional boron-based fertilizers, and therefore has a boron supply capacity approximately equal to that of conventional boron-based fertilizers even when the boron content is less than 0.05 mass%. Therefore, in the steelmaking slag for fertilizer raw material according to the present embodiment, the contained amount of boron is set to more than or equal to 0.005 mass% and less than 0.05 mass%. The contained amount of boron is preferably more than or equal to 0.01 mass% and less than or equal to 0.05 mass%, and more preferably more than or equal to 0.02 mass% and less than or equal to 0.05 mass%.

[0109]

It is known that plants secrete an organic acid from roots as mentioned above, and regarding citric acid-soluble boron, which is boron that is dissolved out with a 2% citric acid aqueous solution, as boron usable by plants serves as an index. The steelmaking slag for fertilizer raw material according to the present embodiment has succeeded in incorporating boron in a form of being easily dissolved in soil and has been able to allow citric acid-soluble boron to account for more than or equal to 95% of the boron contained in the steelmaking slag, by performing structure control by setting the basicity, which is the ratio between the contained amounts of CaO and

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36/69

S1O2, to more than 1.5 and less than or equal to 2.2 and appropriately setting the temperature at the time of molten slag production and the cooling method at the time of slag solidification, and thereby producing boron as, for example, a compound in which a part of S1O2 in the compound of S1O2 is replaced with B2O3, or the like. That is, the mass ratio of citric acid-soluble boron in the boron contained in the slag can be made more than or equal to 95% by producing steelmaking slag for fertilizer raw material in accordance with a method for producing steelmaking slag for fertilizer raw material like that described in detail below. By increasing the ratio of citric acid-soluble boron, a high fertilization effect can be obtained in spite of the fact that the amount of boron contained in the steelmaking slag for fertilizer raw material is low.

[0110]

The contained amount of boron can be measured by, for example, the ICP atomic emission spectroscopy method.

Specifically, 0.5 g of a sample and a reagent (2 g of sodium carbonate and 3 g of sodium peroxide) are put into a Ni crucible, and alkali fusion (burner heating) is performed. The Ni crucible after the alkali fusion is put into a beaker, water and hydrochloric acid (1:9) are put in, the Ni crucible is taken out after the contents of the Ni crucible are dissolved, and the beaker is heated; thus, the sample is dissolved. The obtained dissolved sample is introduced into inductively coupled plasma (apparatus: SPS3100 manufactured by Hitachi High-Tech Science Corporation), light emission due to boron is measured at a wavelength of 249.753 nm; thus, boron is quantified. This analysis method conforms to Appendix A of JIS A 5011 -3.

[0111]

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

[0112]

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37/69 [Sulfur: 0.1 mass% to 0.6 mass%]

Next, sulfur is described.

Sulfur is an element necessary for the biosynthesis of sulfur-containing amino acids such as cysteine and methionine and further the biosynthesis of proteins, and is an element essential to the growth of Welsh onion, onion, garlic, etc.

[0113]

In the case where the sulfur content of the steelmaking slag for fertilizer raw material according to the present embodiment is less than 0.1 mass%, even when a fertilizer using the steelmaking slag for fertilizer raw material according to the present embodiment is applied to soil, there is a possibility that the fertilizer effect of sulfur for plants cannot be exhibited, because the amount of sulfur supplied is small. On the other hand, in the case where the sulfur content of the steelmaking slag for fertilizer raw material according to the present embodiment is more than 0.6 mass%, a problem that sulfur supplied from the fertilizer generates hydrogen sulfide in soil and lets roots rot, and like problems may occur. Therefore, the sulfur content of the steelmaking slag for fertilizer raw material according to the present embodiment is set to more than or equal to 0.1 mass% and less than or equal to 0.6 mass%. The contained amount of sulfur is preferably more than or equal to 0.2 mass% and less than or equal to 0.6 mass%, and more preferably more than or equal to 0.3 mass% and less than or equal to 0.6 mass%.

[0114]

The contained amount of sulfur can be measured by, for example, alkali fusion and the ICP atomic emission spectroscopy method.

Specifically, 0.5 g of a sample and a reagent (2 g of sodium carbonate and 3 g of sodium peroxide) are put into a Ni crucible, and alkali fusion (burner heating) is performed. The Ni crucible after the alkali fusion is put into a beaker, water and hydrochloric acid (1:9) are put in, the Ni crucible is taken out after the contents of the Ni crucible are dissolved, and the beaker is heated; thus, the sample is dissolved. The obtained dissolved sample is introduced into inductively coupled plasma (apparatus: SPS3100 manufactured by Hitachi High-Tech Science Corporation), light emission due to sulfur is measured at a wavelength of 182.036 nm; thus, sulfur is

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38/69 quantified. This analysis method conforms to Appendix A of JIS A 5011 -3.

[0115] [AI2O3: more than or equal to 0.5 mass% and less than or equal to 3 mass%]

Next, Al is described.

In a fertilizer and steelmaking slag, when the contained amount of Al is written, the contained amount is written on the basis of an oxide of AI2O3; thus, hereinafter the contained amount of Al is shown as AI2O3.

[0116]

In acidic soil, Al becomes an aluminum ion, Al³⁺, and binds to a phosphate ion, PO4³'; hence, Al has the action of suppressing the absorption of P by the roots of plants. Therefore, the contained amount of AI2O3 in the steelmaking slag for fertilizer raw material according to the present embodiment is preferably as low as possible.

[0117]

In the case where the contained amount of AI2O3 of the steelmaking slag for fertilizer raw material according to the present embodiment is more than 3 mass%, the dissolving-out of P from a fertilizer containing the steelmaking slag for fertilizer raw material according to the present embodiment is suppressed for a reason like that mentioned above. On the other hand, in the case where dephosphorization treatment is performed on blast furnace molten iron, AI2O3 unavoidably mixes in the slag, and hence it is difficult to make the contained amount of AI2O3 less than or equal to 0.5 mass%. Therefore, in the steelmaking slag for fertilizer raw material according to the present embodiment, the contained amount of AI2O3 is set to more than or equal to 0.5 mass% and less than or equal to 3 mass%. The contained amount of AI2O3 is preferably more than or equal to 0.5 mass% and less than or equal to 2.5 mass%, and more preferably more than or equal to 0.5 mass% and less than or equal to 2 mass%.

[0118]

The contained amount of AI2O3 can be measured by, for example, the X-ray fluorescence analysis method.

Specifically, a plurality of measurement samples of which the contained

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39/69 amount of Al is known are prepared, with the contained amount varied, and X-ray fluorescence intensity derived from Al of the prepared measurement samples is measured by an X-ray fluorescence analysis apparatus. By using the obtained Xray fluorescence intensity derived from Al and an amount on an AI2O3 basis calculated from the contained amount of Al, a calibration curve indicating the relationship between the amount on an AI2O3 basis and the X-ray fluorescence intensity is created in advance. Then, in regard to a focused-on sample of which the contained amount of Al is unknown, X-ray fluorescence intensity derived from Al is measured by the X-ray fluorescence analysis apparatus, and the contained amount of AI2O3 can be specified by using the obtained X-ray fluorescence intensity and the calibration curve.

[0119]

[0120] [Bulk specific gravity: more than or equal to 1.9 and less than or equal to 2.8]

By having a composition like that mentioned above, the steelmaking slag for fertilizer raw material according to the present embodiment has a bulk specific gravity (more specifically, loose bulk specific gravity) of more than or equal to 1.9 and less than or equal to 2.8. In the case where the bulk specific gravity is less than 1.9, the possibility that the fertilizer will run off due to a large amount of rainfall is increased; thus, this is not preferable. On the other hand, in the case where the bulk specific gravity is more than 2.8, the handler of the fertilizer feels weightiness, and this is not preferable. The bulk specific gravity of the steelmaking slag for fertilizer raw material according to the present embodiment is preferably more than or equal to 2.0 and less than or equal to 2.7, and more preferably more than or equal to 2.1 and less than or equal to 2.6.

[0121]

The bulk specific gravity of the steelmaking slag for fertilizer raw material can be measured by, for example, the following method. That is, bulk specific gravity (loose bulk specific gravity) can be obtained as a value that is obtained by

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40/69 dividing a mass lightly filling a certain volume by the volume. Here, the slag used for the measurement has a particle size corresponding to MS-25 prescribed in JIS A5015, and a mass per unit volume (= bulk specific gravity) is measured in conformity with JIS All04.

[0122] [With regard to structure of steelmaking slag for fertilizer raw material]

The steelmaking slag for fertilizer raw material according to the present embodiment preferably contains, as its structure, both a 2CaOSiO2-3CaOP2O5 solid solution and an FeO-MnO-CaO-SiCb-based solid solution. These solid solutions can be formed with better efficiency by, during the production of steelmaking slag for fertilizer raw material, rapidly cooling the slag when solidifying the slag in a molten state, as described below.

[0123]

In soil, in addition to calcium and silicic acid, phosphoric acid is dissolved out more efficiently from a 2CaOSiCb-3CaOP2O5 solid solution. Further, in soil, iron and manganese are dissolved out more efficiently from an FeO-MnO-CaO-SiCbbased solid solution. Therefore, by the steelmaking slag for fertilizer raw material according to the present embodiment containing both these solid solutions as its structure, elements having a fertilizer effect such as calcium, silicic acid, phosphoric acid, iron, and manganese can be dissolved out in soil more efficiently. In addition, in a steelmaking slag for fertilizer raw material produced by a production method described below, a part of S1O2 in these solid solutions is likely to be replaced with B2O3 for some uncertain reason; therefore, by containing both these solid solutions, boron can also be dissolved out.

[0124]

The existence of the 2CaOSiO2-3CaOP2O5 solid solution and the FeOMnO-CaO-SiCb-based solid solution mentioned above can be verified by a method like that shown below.

[0125]

For example, the steelmaking slag for fertilizer raw material according to the present embodiment is powdered, and is then subjected to X-ray diffraction with

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41/69 a common X-ray diffraction apparatus (e.g., SmartLab manufactured by Rigaku Corporation) by focusing (Θ-2Θ measurement), in which Co-Κα (λ = 1.7902 A) is used as an X-ray source, X-ray source load power (tube voltage/tube current) is 5.4 kW (40 kV/135 mA), a scintillation counter is used as a detector, and a scan speed is 1.5°/min, to observe a 2CaOSiCk crystal, an FeOCaOSiCk crystal, etc. Further, the steelmaking slag for fertilizer raw material according to the present embodiment is embedded in a known resin such as an epoxy resin, then grinding and polishing are performed to expose a smooth cross section of the steelmaking slag for fertilizer raw material, and distributions of elements of slag structures observed on the cross section at an acceleration voltage of 15 kV are mapped using a common ΕΡΜΑ apparatus (e.g., JXA-8100 manufactured by JEOF Ftd.). In a slag structure in which all of Ca, Si, O, and P are observed and a slag structure in which all of Fe, Mn, Ca, Si, and O are observed in a measurement region narrowed to a diameter of 100 pm, the count in ΕΡΜΑ of each element is analyzed and semi-quantified by a ZAF method; thereby, it can be verified that a 2CaOSiCk-3CaOP2O5 solid solution or an FeO-MnO-CaO-SiCk-based solid solution exists.

[0126] [With regard to particle size of steelmaking slag for fertilizer raw material]

In the present embodiment, steelmaking slag for fertilizer raw material like that described above can be suitably used as a raw material of a fertilizer by being adjusted to an appropriate particle size by pulverization or the like. For the pulverization of the steelmaking slag for fertilizer raw material, for example, known means such as a jaw crusher, a hammer crusher, a rod mill, a ball mill, a roll mill, and a roller mill may be used.

[0127]

By a pulverization method like that mentioned above, the steelmaking slag for fertilizer raw material is preferably adjusted to a particle size of less than 5 mm, and more preferably a particle size of less than 600 pm. These particle sizes are particle sizes based on the sieving method using a sieve prescribed in JIS Z8801. In the case where the particle size of the steelmaking slag for fertilizer raw material is more than or equal to 5 mm, the specific surface area of the steelmaking slag for

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42/69 fertilizer raw material is too small, and the efficiency of dissolving-out of each fertilizer effect element may be reduced. By the particle size of the steelmaking slag for fertilizer raw material being less than 600 pm, the specific surface area of the steelmaking slag for fertilizer raw material is increased, and the efficiency of dissolving-out of each fertilizer effect element can be enhanced.

[0128]

In the steelmaking slag for fertilizer raw material according to the present embodiment, the mass ratio of particles with particle sizes of less than 600 pm is preferably more than or equal to 60% relative to the total mass. By the mass ratio of particles with particle sizes of less than 600 pm being more than or equal to 60%, the efficiency of dissolving-out of each fertilizer effect element can be enhanced more. The mass ratio of particles with particle sizes of less than 600 pm is more preferably more than or equal to 80%.

[0129]

Hereinabove, the steelmaking slag for fertilizer raw material according to the present embodiment is described in detail.

[0130] <With regard to method for producing steelmaking slag for fertilizer raw material>

Next, a method for producing the steelmaking slag for fertilizer raw material according to the present embodiment is described in detail. The steelmaking slag for fertilizer raw material according to the present embodiment is produced by performing a specific dephosphorization treatment like that described below on blast furnace molten iron.

[0131]

Steelmaking slag for fertilizer raw material according to the present embodiment like that described above is produced by (1) pouring blast furnace molten iron into a converter-type pot in such a manner that the gap ratio expressed by (the freeboard corresponding to the length from the throat to the liquid surface of molten iron/the furnace inner height corresponding to the length from the throat to the inner bottom of the furnace) is more 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

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43/69 slag, and ferromanganese to the blast furnace molten iron in the converter-type pot, and (3) blowing quick lime and/or calcium carbonate with an average particle size of less than or equal to 1 mm and oxygen into the blast furnace molten iron from a lance inserted in the blast furnace molten iron and foaming the slag at more than or equal to 1300°C and less than or equal to 1400°C to perform dephosphorization treatment, and at this time, is produced such that the slag basicity expressed by (the CaO content/the S1O2 content) is more than 1.5 and less than or equal to 2.2 and the MnO content in the slag is more than or equal to 3 mass% and less than or equal to 10 mass%.

[0132] [1: Blast furnace molten iron pouring process]

The blast furnace molten iron pouring process shown in (1) above is a process that pours produced blast furnace molten iron into a converter-type pot. In the case where the gap ratio expressed by (the freeboard/the furnace inner height) is less than 0.5 when pouring the blast furnace molten iron into the converter-type pot, the freeboard is too small, and consequently the gap existing above the liquid surface of the molten iron is too narrow; hence, it is difficult to sufficiently foam the blast furnace molten iron, and dephosphorization reaction cannot be advanced sufficiently; thus, this is not preferable. On the other hand, in the case where the gap ratio expressed by (the freeboard/the furnace inner height) is more than 0.9, the amount of dephosphorized molten iron is small and this is inefficient; thus, this is not preferable; further, since only a small amount of blast furnace molten iron is poured into the converter-type pot, operating efficiency is reduced, and productivity is reduced. The gap ratio expressed by (the freeboard/the furnace inner height) is preferably more than or equal to 0.5 and less than or equal to 0.8, and more preferably more than or equal to 0.6 and less than or equal to 0.8.

[0133] [2: Additive material introduction process]

The additive material introduction process shown in (2) above is a process that introduces at least one of manganese ore, manganese-containing decarburization slag, and ferromanganese into the blast furnace molten iron in the converter-type pot

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44/69 so as to obtain a desired MnO content in the slag (that is, so that the MnO content in the slag is more than or equal to 3 mass% and less than or equal to 10 mass%). Here, what amount of which additive material among the additive materials mentioned above to introduce is not particularly limited, and may be determined in accordance with a desired MnO content in the slag, as appropriate.

[0134] [3: Dephosphorization treatment process]

The dephosphorization treatment process shown in (3) above is a process that blows a calcium source and oxygen into the blast furnace molten iron with an adjusted MnO content and foams the slag at a prescribed temperature to perform the dephosphorization treatment of the blast furnace molten iron.

[0135]

Here, as the calcium source used for dephosphorization treatment, at least one of quick lime and calcium carbonate with an average particle size of less than or equal to 1 mm is used. Quick lime and calcium carbonate with an average particle size of less than or equal to 1 mm can be obtained by using an industrial sieve prescribed in JIS Z8801. In the case where quick lime is used as a calcium source, when the average particle size thereof is more than 1 mm, unreacted quick lime may remain; thus, this is not preferable. In the case where the average particle size of quick lime and calcium carbonate is more than 1 mm, the lance may be damaged due to blowing-in, and the life of the lance may be shortened; thus, this is not preferable. Here, the average particle size of quick lime and calcium carbonate refers to, in a particle size distribution of particles that pass through an industrial sieve prescribed in JIS Z8801, the particle size at an integrated value in mass% of 50%. The amount of the calcium source blown in is set to such an amount that a desired basicity (that is, more than 1.5 and less than or equal to 2.2) is obtained when the dephosphorization treatment process ends.

[0136]

The temperature of the slag at the time of foaming is set to more than or equal to 1300°C and less than or equal to 1400°C. In the case where the temperature of the slag is less than 1300°C, dephosphorization reaction does not

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45/69 progress; thus, this is not preferable. On the other hand, in the case where the temperature of the slag is more than 1400°C, there is a possibility of rephosphorization in which phosphorus melts back to the molten steel; thus, this is not preferable. The temperature of the slag at the time of foaming is preferably more than or equal to 1310°C and less than or equal to 1390°C, and more preferably more than or equal to 1320°C and less than or equal to 1380°C. The temperature of the slag can be measured using a thermocouple or an optical pyrometer.

[0137]

Dephosphorization treatment like that mentioned above is performed such that the slag basicity is more than 1.5 and less than or equal to 2.2 and the MnO content in the slag is more than or equal to 3 mass% and less than or equal to 10 mass%, and the dephosphorization treatment ends at the time point when the slag basicity and the MnO content fall within ranges like those mentioned above.

[0138]

By dephosphorization treatment like above being performed, the components of the produced steelmaking slag obtain characteristics like those described above, and also the specific gravity of the produced steelmaking slag falls within the range described above.

[0139]

After the dephosphorization treatment process described above, (4) a slag solidification process and (5) a slag pulverization process like those described below are preferably performed.

[0140] [4: Slag solidification process]

The slag solidification process shown in (4) above is a process that solidifies the molten slag after dephosphorization treatment by a prescribed method.

[0141]

The slag solidification process may be, for example, a process that solidifies the molten slag after dephosphorization treatment by pouring the molten slag after dephosphorization treatment into a dish-like heat-resistant container and performing rapid cooling. At this time, in order to cool the molten slag more effectively, the

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46/69 molten slag is preferably thinly spread in the dish-like heat-resistant container, and further water sprinkling is preferably performed on the thinly spread molten slag to rapidly cool the molten slag.

[0142]

As well as the method mentioned above, a method like below may be employed as the slag solidification process.

That is, (a) the converter-type pot is tilted to pour the molten slag after dephosphorization treatment into a slag pot in a tilting manner, and then the molten slag in the slag pot is poured into a tiltable first heat-resistant container in a tilting manner, (b) water sprinkling is performed in the first heat-resistant container to rapidly cool the molten slag to, for example, approximately 600°C to solidify the molten slag, and then the solidified slag is fragmented, and (c) the first heat-resistant container is tilted to slide the solidified slag down into a second heat-resistant container and thereby fragment the solidified slag.

[0143]

In both two kinds of slag solidification processes like those mentioned above, it is preferable to perform water sprinkling or the like when solidifying the molten slag and thereby rapidly cool the molten slag. By rapidly cooling the molten slag, both of a 2CaOSiO2-3CaOP2Os solid solution and an FeO-MnO-CaO-SiChbased solid solution can be formed in the slag more reliably.

[0144] [5. Slag pulverization process]

The slag pulverization process shown in (5) above is a process that pulverizes the steelmaking slag solidified in the above manner to a desired particle size.

[0145]

In the slag pulverization process, the steelmaking slag in a solid state is fragmented and pulverized to a desired particle size using, for example, a known means such as a jaw crusher, a hammer crusher, a rod mill, a ball mill, a roll mill, or a roller mill. Here, the fragmentation and pulverization are preferably performed such that, for the particle size of the steelmaking slag, all the particle sizes are less

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47/69 than 5 mm and the mass ratio of particles with particle sizes of less than 600 pm is more than or equal to 60% relative to the total mass, as mentioned above.

[0146]

Through processes like those described above, the steelmaking slag for fertilizer raw material according to the present embodiment is produced.

[0147] <With regard to method for producing fertilized

Next, a method for producing a fertilizer using the steelmaking slag for fertilizer raw material according to the present embodiment is briefly described.

Steelmaking slag for fertilizer raw material according to the present embodiment like that described above can be used as a fertilizer as it is by adjusting the particle size to within a prescribed range (for example, all the particles sizes being approximately less than 600 pm). That is, the method for producing a fertilizer according to the present embodiment is powdering steelmaking slag for fertilizer raw material produced by a method for producing steelmaking slag for fertilizer raw material like that mentioned above by a known means.

[0148]

Although the steelmaking slag for fertilizer raw material after powdering can be used as a fertilizer as it is as mentioned above, granulation may be performed after a prescribed binder is added. Here, the binder used at the time of granulation is not particularly limited; for example, molasses, lignin, a metal lignin sulfonate, starch, polyvinyl alcohol, carboxymethyl cellulose, etc. may be used.

[0149]

An organic substance may be further mixed with the fertilizer obtained by a method like that mentioned above. Such an organic substance may be, for example, at least one of livestock manure such as cattle manure, swine manure, and poultry manure, plant residues, and compost obtained from fishery products. By further mixing such an organic substance, the fertilizer effect of the fertilizer containing the steelmaking slag for fertilizer raw material according to the present embodiment can be further improved.

[0150]

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By a fertilizer according to the present embodiment like that described above, many kinds of elements of phosphorus (P), iron (Fe), manganese (Mn), silicon (Si), calcium (Ca), magnesium (Mg), boron (B), and sulfur (S) can be supplied more effectively.

[0151] <With regard to fertilizer application method>

Next, a method for applying a fertilizer containing the steelmaking slag for fertilizer raw material according to the present embodiment is described.

A fertilizer containing steelmaking slag for fertilizer raw material like that described above can supply many kinds of elements as fertilizer of plants easily at low cost even to acidic soils of regions where the amount of rainfall is large and regions where river flooding occurs frequently, without runoff due to a water current. More specifically, by applying the fertilizer on a specific acidic soil by a method like that described below, the acidic soil can be alkalized, and many kinds of elements can be supplied as fertilizer more effectively to plants that are intended to be grown. [0152]

That is, in the fertilizer application method according to the present embodiment, a fertilizer containing steelmaking slag for fertilizer raw material or a fertilizer like that mentioned above is applied to a soil in which (i) pH/HzO) is more than or equal to 4 and less than or equal to 6, (ii) the value expressed by (pH/HzO) pH(KCl)) is more 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.

[0153]

Here, pH(H2O) refers to the pH of a suspension obtained by adding water to the soil at a prescribed ratio, and pH(KCl) refers to the pH of a suspension obtained by adding a potassium chloride solution to the soil at a prescribed ratio. Hydrogen ions, H⁺, existing in the soil include two types, i.e., those dissolved in the soil water and those electrically adsorbed on the surfaces of soil colloidal particles (for example, clay, humus, etc.). pH(H2O) indicates the concentration of H⁺ dissolved in the soil water, and pH(KCl) indicates the total concentration of H⁺ dissolved in the soil water and H⁺ adsorbed on soil colloidal particles. It is said that pH(H2O) indicates the

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49/69 strength and weakness of soil acidity (active acidity), which directly relates to the growth of the roots of plants, and on the other hand pH(KCl) indicates the potential acidity held by the soil (potential acidity).

[0154]

The value shown in (ii) above can be used as an index of how much Al exists in the soil. The available phosphoric acid shown in (iii) indicates the amount of phosphoric acid absorbable by plants, and can be measured by a known fertilizer etc. testing method such as the Tmog method using a sulfuric acid solution with a pH of approximately 3. A soil in which the available phosphoric acid of soil is less than or equal to 5 mg/100 g of dry soil indicates that it is a soil in which the amount of phosphoric acid supplied from the soil is very small. For example, in Japan, the recommended value of available phosphoric acid of farmland soil provided by the Ministry of Agriculture, Forestry and Fisheries of Japan is 10 to 75 mg/100 g of dry soil. In an acidic soil in which the value of pH(H2O) - pH(KCl) is large and the amount of Al is large, it is feared that a phosphate ion will bind to an Al ion to be insolubilized as AIPO4, and phosphoric acid absorbable by plants will be lacking. The fertilizer according to the present embodiment can supply phosphoric acid to such a soil in which available phosphoric acid is lacking, and exhibits a fertilizer effect.

[0155]

Note that pH(H2O) and pH(KCl) mentioned above can be measured by putting 20 g of air-dry soil into a 100-ml shaking bottle, adding 50 ml of distilled water or 50 ml of a IN KC1 aqueous solution, performing shaking for 30 minutes, and then measuring pH of an aqueous solution with a pH glass electrode. In addition, the available phosphoric acid content can be measured by a Tmog method. [0156]

In high rainfall regions where each fertilizer effect element is likely to mn off and become lacking, the fertilizer according to the present embodiment exhibits an excellent fertilizer effect to a specific acidic soil like that mentioned above.

[0157]

Here, the application amount of the fertilizer according to the present

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50/69 embodiment is preferably more than or equal to 0.05 t/ha and less than or equal to 2 t/ha as the steelmaking slag for fertilizer raw material. In the case where the application amount is less than 0.05 t/ha, the application amount is too small, and there is a possibility that the effect of the fertilizer according to the present embodiment containing a plurality of fertilizer effect elements cannot be exhibited clearly. On the other hand, in the case where the application amount is more than 2 t/ha, the cost is increased because of the use of a large amount of the fertilizer according to the present embodiment. A more preferred application amount is more than or equal to 0.1 t/ha and less than or equal to 1 t/ha.

[0158]

In the fertilizer application method according to the present embodiment, a fertilizer according to the present embodiment like that mentioned above may be scattered on the surface of a plow layer or may be mixed with the plow layer before sowing or seedling planting. Further, a fertilizer according to the present embodiment like that mentioned above may be scattered on the surface of a plow layer in the neighborhood of a plant body to be cultivated or may be mixed into the plow layer.

[0159]

The target crop of a fertilizer according to the present embodiment like that mentioned above may be, for example, a plant falling under any one of gramineous plants, cyperaceous plants, cucurbitaceous plants, leguminous plants, amaryllidaceous plants, liliaceous plants, solanaceous plants, cruciferous plants, rosaceous plants, musaceous plants, palmaceous plants, vitaceous plants, araceous plants, orchidaceous plants, convolvulaceous plants, asteraceous plants, pedaliaceous plants, lamiaceous plants, papaveraceous plants, rutaceous plants, umbelliferous plants, piperaceous plants, rabiaceous plants, and urticaceous plants, and the like. The steelmaking slag for fertilizer raw material according to the present embodiment is likely to release three elements, secondary elements, and trace elements of fertilizer, and a fertilizer using the steelmaking slag for fertilizer raw material has demonstrated an effect on paddy rice, which is a typical gramineous plant, as shown in Examples below; hence, an effect is expected to be obtained for the plants

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51/69 mentioned above as well as gramineous plants. It goes without saying that the fertilizer according to the present embodiment can be used also for plants other than those mentioned above.

[0160]

Hereinabove, the fertilizer application method according to the present embodiment is briefly described.

[Examples] [0161]

In the following, the steelmaking slag for fertilizer raw material according to the present invention, and the fertilizer and the fertilizer application method using the steelmaking slag are specifically described while showing Examples and Comparative Examples. Examples shown below are only examples, and the present invention is not limited to the examples shown below.

[0162] (Example 1)

Pieces of steelmaking slag for fertilizer raw material were produced by the method shown below.

That is, manganese-containing decarburization slag was additionally introduced into common blast furnace molten iron in a converter in which the gap ratio expressed by (the freeboard/the furnace inner height) was 0.7, then quick lime with an average particle size of less than or equal to 1 mm and oxygen were blown in from a lance inserted in the molten iron, and dephosphorization treatment was performed while foaming was performed at 1350°C. After the steel was taken out, two cooling treatments were performed on the produced slag. In one cooling treatment, the converter was tilted to put the slag into a dish-like heat-resistant container, and the slag was thinly spread and water sprinkling was performed; thus, the slag was rapidly cooled. In the other cooling treatment, the converter was tilted to put the slag into a slag pot; after 30 minutes, the slag pot was tilted in a slag discharging place to discharge the slag, and the slag was allowed to stand; thus, the slag was slowly cooled to normal temperature.

[0163]

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The rapidly cooled steelmaking slag and the slowly cooled steelmaking slag obtained by the above process were pulverized, and all the particle sizes were made less than 5 mm and the mass ratio of particles with particle sizes of less than 600 pm was made more than or equal to 60%. The resulting pieces of steelmaking slag were analyzed in accordance with the method described above; the analysis results of rapidly cooled steelmaking slag are shown in Table 1 below. An X-ray fluorescence analysis apparatus used for analysis was ZSX PrimusII manufactured by Rigaku Corporation, and an ICP atomic emission spectroscopy apparatus used for analysis was ICPS-8100 manufactured by Shimadzu Corporation.

[0164]

The chemical components of the rapidly cooled steelmaking slag and the slowly cooled steelmaking slag were the same as each other. In addition, the mass ratio of soluble P2O5, the mass ratio of citric acid-soluble MnO, and the mass ratio of citric acid-soluble boron of the slowly cooled steelmaking slag were respectively 60%, 65%, and 75%.

[0165]

Here, in Table 1 below, the units of the items other than the basicity or the specific gravity are mass%, and the values of soluble P2O5, citric acid-soluble MnO, and citric acid-soluble boron are on a content basis. Further, in Table 1 below, the alkali content indicates the capacity of the relevant fertilizer to neutralize the acidity of soil, and shows a value measured by the ethylenediaminetetraacetate method described in Testing Methods for Fertilizers (2016) prescribed by Food and Agricultural Materials Inspection Center (FAMIC).

[0166]

From Table 1 below, it is found that, in the rapidly cooled pieces of steelmaking slag, the mass ratio of soluble P2O5 is 80%, the mass ratio of citric acidsoluble MnO is 83%, and the mass ratio of citric acid-soluble boron is 100%. Further, for the resulting pieces of steelmaking slag, the total contained amount of CaO, P2O5, S1O2, MgO, AI2O3, the total iron, MnO, boron, and sulfur was 97.761 mass%, and the balance was impurities.

[0167]

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53/69 [Table 1]

Table 1 Analysts results of steelmaking slag

Specific gravity	2,2
Basicity	r«·
Sulfur	0.45
ο I -2 c CO-Op	I LOO
i Boron \| 1 _1	110Ό
Alkali content	<D
Citric acidsoluble 1 MnO i	IO
MnO	co
Total iron	-
o <	co
0 to 2	4.5
Q⁴	26
3 O O Q_ CO	'd-
O □?	5.5
CaO	43

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54/69 [0168]

Further, the substances forming the crystal phase of each of the rapidly cooled steelmaking slag and the slowly cooled steelmaking slag were investigated by X-ray diffraction (an X-ray diffraction apparatus SmartLab manufactured by Rigaku

Corporation) and ΕΡΜΑ (JXA-8100 manufactured by JEOL Ltd.) in accordance with the method described above; the obtained results are shown in Table 2 below. In Table 2 shown below, observed indicates that the focused-on solid solution was observed, and not observed indicates that the focused-on solid solution was not observed. As is clear from Table 2 below, in the rapidly cooled steelmaking slag, the existence of both of a 2CaO-SiO2-3CaO-P2Os solid solution and an FeO-MnOCaO-SiC>2-based solid solution was observed; on the other hand, in the slowly cooled steelmaking slag, although the existence of a 2CaO-SiO2-3CaO-P2Os solid solution was observed, the existence of an FeO-MnO-CaO-SiCb-based solid solution was not observed.

[0169] [Table 2]

Table 2 Solid solutions contained in steelmaking slag

	2CaO-SiO2-3CaO-P2C>5 solid solution	F eO-MnO-CaO-SiO2-based solid solution
Rapidly cooled steelmaking slag	Observed	Observed
Slowly cooled steelmaking slag	Observed	Not observed

[0170] (Example 2)

Using fertilizers like those mentioned above, a cultivation test of paddy rice was performed in a soil of which the analysis results are described in Table 3 below. In this soil, pH/HzO), pH(KCl), and the available phosphoric acid content were measured by the methods described above; pH(H2O) was in the range of more than or equal to 4 and less than or equal to 6, the value of pH/HzO) - pH(KCl) was more than or equal to 1, and the available phosphoric acid content was less than or equal to

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55/69 mg/100 g of dry soil, as well. [0171] [Table 3]

Table 3 Analysis results of soil

pH (H₂O)	pH (KC1)	Available phosphoric acid (mg/100 g of dry soil)
5.3	4.1	2

[0172]

More specifically, a test of fertilizer effect for paddy rice was performed for cases where fertilizers using the rapidly cooled steelmaking slag and the slowly cooled steelmaking slag mentioned above as raw materials were applied, a case where a commercially available fertilizer using, as a raw material, steelmaking slag that had been generated in a converter with a gap ratio expressed by (the freeboard/the furnace inner height) of 0.4 was applied, and a case where a fertilizer using steelmaking slag as a raw material was not applied.

[0173]

The analysis results of the commercially available fertilizer using, as a raw material, steelmaking slag that had been generated in a converter with a gap ratio expressed by (the freeboard/the furnace inner height) of 0.4 are shown in Table 4 below. The method for analyzing the commercially available fertilizer was similar to that in Example 1. In Table 4 below, the units of the items other than the basicity or the specific gravity are mass%, and the values of soluble P2O5, citric acid-soluble MnO, and citric acid-soluble boron are on a content basis. The alkali content was measured in a similar manner to Table 1 above.

[0174]

From Table 4 below, it is found that, in the steelmaking slag generated in a converter with a gap ratio of 0.4, the mass ratio of soluble P2O5 is 44%, the mass ratio of citric acid-soluble MnO is 53%, and the mass ratio of citric acid-soluble boron is 80%. For the steelmaking slag generated in a converter with a gap ratio of 0.4, the total contained amount of CaO, P2O5, S1O2, MgO, AI2O3, the total iron, MnO,

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56/69 boron, and sulfur was 84.105 mass%, and the balance was impurities.

[0175]

Further, for the commercially available fertilizer, it was found that all the particle sizes were less than 5 mm and the mass ratio of particles with particle sizes of less than 600 pm was more than or equal to 60%.

[0176] [Table 4]

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Table 4 Analysis results of commercially available fertilizer

Specific gravity	2.4
Basicity
Sulfur	0.20
Citric acid- soluble boron	0.004
Boron	0.005
Alkali content	43
Citric acid- soluble MnO	co
O c	CO
Total iron	r-
O CM <	4.2
0 no 2	3.9
<N o ώ	C*D
φ □ o _ cv o 0, ω	80
Ιίϊ o CN 0.	OO
CaO j _1	N-

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58/69 [0177]

In the fertilizer using, as a raw material, steelmaking slag of which the analysis results are shown in Table 4, the content ratio of S1O2 to CaO is small and accordingly the basicity is high, and the contained amounts of P2O5 and soluble P2O5 are low, as compared to the fertilizers using the pieces of steelmaking slag according to the present invention as raw materials. Further, the contained amount of citric acid-soluble MnO is a little low with respect to the large amount of the total iron, as compared to the fertilizers using, as raw materials, two kinds of slag of which the composition is shown in Table 1 above.

[0178]

The substances forming the crystal phase of steelmaking slag serving as a raw material of a commercially available fertilizer like that mentioned above were investigated by X-ray diffraction and ΕΡΜΑ in accordance with the method described above; the obtained results are shown in Table 5 below. The writing system in Table 5 below is similar to that in Table 2. As shown in Table 5 below, neither the existence of a 2CaOSiO2-3CaOP2O5 solid solution nor the existence of an FeO-MnO-CaO-SiO2-based solid solution was observed.

[0179] [Table 5]

Table 5 Solid solutions contained in steelmaking slag serving as raw material of commercially available fertilizer

	2CaO-SiO2-3CaO-P2C>5 solid solution	FeO-MnO-CaO-SiO2-based solid solution
Steelmaking slag serving as a raw material of a commercially available fertilizer	Not observed	Not observed

[0180]

Nitrogen and potassium were added as 60 kg/ha of urea and 60 kg/ha of potassium chloride, respectively, as a basal fertilizer to the soil of a paddy field

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59/69 before rice planting. Nine 0.6 x 0.5-m frames were placed on the paddy field; 15 g of the fertilizer using the rapidly cooled steelmaking slag as a raw material and 15 g of the fertilizer using the slowly cooled steelmaking slag as a raw material, of which the analysis results are shown in Table 1 and Table 2, and 15 g of the commercially available fertilizer using, as a raw material, steelmaking slag prepared in a converter with a gap ratio of 0.4, of which the analysis results are shown in Table 4 and Table 5 (each of these fertilizers was one in which it had been found that all the particle sizes were less than 5 mm and the mass ratio of particles with particle sizes of less than 600 pm was more than or equal to 60%) were added individually to three of the nine partitioned places (equivalent to an application amount of 0.5 t/ha).

[0181]

Each of the fertilizers was well mixed with a soil of a depth of 10 cm; then, 6 root clumps were planted in each frame, with 4 seedlings of paddy rice (variety: Koshihikari) as one root clump, and were cultivated up to the harvesting season. As a control, a test was performed under similar conditions also for three frames in which materials were not added. Therefore, the test was performed by three repetitions.

[0182]

Yield investigation was performed after four months after rice planting.

All the 6 root clumps in each frame were cut down, and the weight of fine brown rice and the thousand-kernel weight were investigated. The obtained results are shown in Table 6 below.

[0183] [Table 6]

Table 6 Results of yield investigation

	Weight of fine brown rice (g/m²)	Thousand-kernel weight (g)
A fertilizer using rapidly cooled steelmaking slag as a raw material was applied	536	21.5
A fertilizer using slowly cooled steelmaking slag as a raw material was applied	515	21.0

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A commercially available fertilizer using steelmaking slag as a raw material was applied	451	20.8
A control (a fertilizer using steelmaking slag as a raw material was not applied)	407	19.0

[0184]

As is clear from Table 6 above, by applying the fertilizer using the rapidly cooled steelmaking slag as a raw material, the yield (the weight of fine brown rice) was increased by approximately 31% as compared to the control zone. Further, in the case where the slowly cooled steelmaking slag was applied, the yield (the weight of fine brown rice) was increased by approximately 26% as compared to the control zone. On the other hand, in the case where the same amount of the commercially available fertilizer using existing steelmaking slag as a raw material was applied, the yield (the weight of fine brown rice) was increased by approximately 10% as compared to the control zone.

[0185]

Further, for the thousand-kernel weight, the highest value was obtained in the case where the fertilizer using the rapidly cooled steelmaking slag as a raw material was applied, the second highest value was obtained in the case where the fertilizer using the slowly cooled steelmaking slag as a raw material was applied, the third highest value was obtained in the case where the fertilizer using steelmaking slag as a raw material was applied, and the lowest value was obtained in the case where a fertilizer using steelmaking slag as a raw material was not applied.

[0186]

From these results, it has been revealed that, even for pieces of steelmaking slag for fertilizer raw material of the same chemical components, rapidly cooled steelmaking slag containing both of a 2CaOSiO2-3CaOP2O5 solid solution and an FeO-MnO-CaO-SiO2-based solid solution has a higher fertilizer effect than slowly cooled steelmaking slag containing a 2CaOSiO2-3CaOP2O5 solid solution but not containing an FeO-MnO-CaO-SiCk-based solid solution.

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61/69 [0187]

As described above, it has been revealed that the yield of rice can be increased by using a fertilizer using the steelmaking slag for fertilizer raw material according to the present invention as a raw material.

[0188] (Example 3)

A cultivation test of paddy rice was performed in a soil of which the analysis results are shown in Table 7 below, using the fertilizer using the rapidly cooled steelmaking slag as a raw material, the fertilizer using the slowly cooled steelmaking slag as a raw material, and the commercially available fertilizer using steelmaking slag as a raw material that are described in Example 2 above. Note that the method for analyzing the soil is similar to that in Example 2.

[0189] [Table 7]

Table 7 Analysis results of soil

pH (H₂O)	pH (KC1)	Available phosphoric acid (mg/100 g of dry soil)
6.5	5.8	15

[0190]

Nitrogen and potassium were added as 60 kg/ha of urea and 60 kg/ha of potassium chloride, respectively, as a basal fertilizer to the soil of a paddy field before rice planting. Nine 0.6 x 0.5-m frames were placed on the paddy field; 15 g of the fertilizer using the rapidly cooled steelmaking slag as a raw material and 15 g of the fertilizer using the slowly cooled steelmaking slag as a raw material, of which the analysis results are shown in Table 1 and Table 2, and 15 g of the commercially available fertilizer using steelmaking slag as a raw material, of which the analysis results are shown in Table 4 and Table 5 (each of these fertilizers was one in which it had been found that all the particle sizes were less than 5 mm and the mass ratio of particles with particle sizes of less than 600 pm was more than or equal to 60%) were added individually to three of the nine partitioned places (equivalent to an

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62/69 application amount of 0.5 t/ha).

[0191]

Each of the fertilizers was well mixed with a soil of a depth of 10 cm; then, 6 root clumps were planted in each frame, with 4 seedlings of paddy rice (variety:

Koshihikari) as one root clump, and were cultivated up to the harvesting season. As a control, a test was performed under similar conditions also for three frames in which materials were not added. Therefore, the test was performed by three repetitions.

[0192]

Yield investigation was performed after four months after rice planting.

All the 6 root clumps in each frame were cut down, and the weight of fine brown rice and the thousand-kernel weight were investigated. The obtained results are shown in Table 8 below.

[0193] [Table 8]

Table 8 Results of yield investigation

~—	Weight of fine brown rice (g/m²)	Thousand-kernel weight (g)
A fertilizer using rapidly cooled steelmaking slag as a raw material was applied	535	21.3
A fertilizer using slowly cooled steelmaking slag as a raw material was applied	517	20.8
A commercially available fertilizer using steelmaking slag as a raw material was applied	492	20.1
A control (a fertilizer using steelmaking slag as a raw material was not applied)	478	19.1

[0194]

As is clear from Table 8 above, by applying the fertilizer using the rapidly cooled steelmaking slag as a raw material, the yield (the weight of fine brown rice)

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63/69 was increased by approximately 12% as compared to the control zone. Further, in the case where the slowly cooled steelmaking slag was applied, the yield (the weight of fine brown rice) was increased by approximately 8% as compared to the control zone. On the other hand, in the case where the same amount of the commercially available fertilizer using existing steelmaking slag as a raw material was applied, the yield (the weight of fine brown rice) was increased by approximately 3% as compared to the control zone.

[0195]

[0196]

As described above, it has been revealed that the yield of rice can be increased even in the soil with a pH/tkO) of 6.5 by using a fertilizer using the steelmaking slag for fertilizer raw material according to the present invention as a raw material.

[0197]

However, as compared to the results of Example 2, while in the soil with the analysis results shown in Table 3 the yields in the case where the fertilizers using the pieces of steelmaking slag for fertilizer raw material according to the present invention were applied were increased by approximately 30% as compared to the yield of the control zone where a steelmaking slag fertilizer was not applied, in the soil with the analysis results shown in Table 7 the yields in the case where the fertilizers using the pieces of steelmaking slag for fertilizer raw material according to the present invention were applied were increased by approximately 12% as compared to the yield of the control zone where a steelmaking slag fertilizer was not applied, and the amount of increase was reduced. The reason for this is that the

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64/69 yield of the control zone where a steelmaking slag fertilizer was not applied was higher than in Example 2. A possible reason is that the ρΗ(Η₂Ο) of the soil with the analysis results shown in Table 7 was in the pH range of 5.5 to 6.5, which is suitable for the growth of paddy rice, and further 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 of farmland soil provided by the Ministry of Agriculture, Forestry and Fisheries of Japan (10 to 75 mg/100 g of dry soil); thus, phosphoric acid will have been successfully supplied from the soil even when a fertilizer using steelmaking slag as a raw material was not used.

[0198]

Therefore, it has been revealed that, although the fertilizers using the pieces of steelmaking slag for fertilizer raw material according to the present invention as raw materials have some effect in the soil of Table 7, they have more significant effect in the soil of Table 3.

[0199]

The preferred embodiment(s) of the present invention has/have been described above with reference to the accompanying drawings, whilst the present invention is not limited to the above examples. A person skilled in the art may find various alterations and modifications within the scope of the appended claims, and it should be understood that they will naturally come under the technical scope of the present invention.

Claims

What is claimed is:

1. Steelmaking slag for fertilizer raw material, containing, in mass%,

P2O5: more than or equal to 2% and less than or equal to 8%,

MnO: more than or equal to 3% and less than or equal to 10%, boron: more than or equal to 0.005% and less than 0.05%, the total iron: more than or equal to 7% and less than 15%,

CaO: more than or equal to 38% and less than or equal to 48%,

SiO2: more than or equal to 22% and less than or equal to 30%, sulfur: more than or equal to 0.1% and less than or equal to 0.6%,

MgO: more than or equal to 1% and less than or equal to 8%, and AI2O3: more than or equal to 0.5% and less than or equal to 3%, wherein a ratio of soluble P2O5 in the P2O5 is more than or equal to 50%, a ratio of citric acid-soluble MnO in the MnO is more than or equal to 80%, a slag basicity expressed by (a CaO content/a S1O2 content) is more than 1.5 and less than or equal to 2.2, and a bulk specific gravity is more than or equal to 1.9 and less than or equal to
2.8.

2. The steelmaking slag for fertilizer raw material according to claim 1, containing a 2CaO-SiO2-3CaO-P2O5 solid solution and an FeO-MnO-CaO-SiO2-based solid solution.
3. The steelmaking slag for fertilizer raw material according to claim 1 or 2, wherein a ratio of citric acid-soluble boron in the boron is more than or equal to 95%.
4. The steelmaking slag for fertilizer raw material according to any one of claims 1 to 3, wherein a particle size is less than 5 mm as a whole, and a mass ratio of particles with particle sizes of less than 600 pm is more than or equal to 60% relative to a total mass.

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5. A method for producing steelmaking slag for fertilizer raw material that produces the steelmaking slag for fertilizer raw material according to any one of claims 1 to 4, the method comprising:

pouring blast furnace molten iron into a converter-type pot in such a manner that a gap ratio expressed by (a freeboard corresponding to a length from a throat to a liquid surface of molten iron/a furnace inner height corresponding to a length from the throat to an inner bottom of a furnace) is more 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 the blast furnace molten iron in the converter-type pot;

blowing quick lime and/or calcium carbonate with an average particle size of less than or equal to 1 mm and oxygen into the blast furnace molten iron from a lance inserted in the blast furnace molten iron;

foaming slag at more than or equal to 1300°C and less than or equal to 1400°C to perform dephosphorization treatment; and producing slag in such a manner that a slag basicity expressed by (a CaO content/a S1O2 content) is more than 1.5 and less than or equal to 2.2 and a MnO content in the slag is more than or equal to 3 mass% and less than or equal to 10 mass%.
6. The method for producing steelmaking slag for fertilizer raw material according to claim 5, wherein molten slag after the dephosphorization treatment is poured into a dish-like heat-resistant container and is rapidly cooled to be solidified.
7. The method for producing steelmaking slag for fertilizer raw material according to claim 6, wherein molten slag after the dephosphorization treatment is rapidly cooled by performing water sprinkling.

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8. The method for producing steelmaking slag for fertilizer raw material according to any one of claims 5 to 7, wherein the converter-type pot is tilted to pour molten slag after the dephosphorization treatment into a slag pot in a tilting manner, and then the molten slag in the slag pot is poured into a tiltable first heat-resistant container in a tilting manner, water sprinkling is performed in the first heat-resistant container to rapidly cool and solidify the molten slag, and then the solidified slag is fragmented, and the first heat-resistant container is tilted to slide the solidified slag down into a second heat-resistant container, and thereby the solidified slag is fragmented.
9. The method for producing steelmaking slag for fertilizer raw material according to any one of claims 5 to 8, wherein a 2CaOSiO2-3CaOP2Os solid solution and an FeO-MnO-CaOSiC>2-based solid solution are formed by rapid cooling.
10. The method for producing steelmaking slag for fertilizer raw material according to any one of claims 5 to 9, wherein slag is pulverized such that a particle size is less than 5 mm as a whole and a mass ratio of particles with particle sizes of less than 600 pm is more than or equal to 60% relative to a total mass.
11. A method for producing a fertilizer, comprising:

powdering the steelmaking slag for fertilizer raw material according to any one of claims 1 to 4 or steelmaking slag for fertilizer raw material produced by the method for producing steelmaking slag for fertilizer raw material according to any one of claims 5 to 10.
12. The method for producing a fertilizer according to claim 11, wherein a prescribed binder is added to the steelmaking slag for fertilizer

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68/69 raw material after powdering, and then granulation is performed.
13. The method for producing a fertilizer according to claim 11 or 12, wherein an organic substance is further mixed with an obtained fertilizer.
14. The method for producing a fertilizer according to claim 13, wherein the organic substance is at least one of livestock manure, a plant residue, and compost obtained from a fishery product.
15. A fertilizer application method comprising:

applying a fertilizer that contains the steelmaking slag for fertilizer raw material according to any one of claims 1 to 4, steelmaking slag for fertilizer raw material produced by the method for producing steelmaking slag for fertilizer raw material according to any one of claims 5 to 10, or a fertilizer produced by the method for producing a fertilizer according to any one of claims 11 to 14 to a soil in which pH/HzO) is more than or equal to 4 and less than or equal to 6, a value expressed by (pH/HzO) - pH(KCl)) is more than or equal to 1, and an amount of available phosphoric acid is less than or equal to 5 mg/100 g of dry soil.
16. The fertilizer application method according to claim 15, wherein an application amount of the fertilizer is more than or equal to 0.05 t/ha and less than or equal to 2 t/ha as the steelmaking slag for fertilizer raw material.
17. The fertilizer application method according to claim 15 or 16, wherein the fertilizer is scattered on a surface of a plow layer or is mixed with the plow layer before sowing or seedling planting.
18. The fertilizer application method according to claim 15 or 16, wherein the fertilizer is scattered on a surface of a plow layer in a neighborhood of a plant body to be cultivated or is mixed into the plow layer.