JP2015140473A - Phosphoric acid fertilizer raw material, phosphoric acid fertilizer and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing phosphoric acid fertilizer raw material having high fertilizer effect from a steel making slag.SOLUTION: A phosphorous-containing steel making slag generated in a steel making refining process is applied to a reduction treatment with carbon or the like as a reductant, further dephosphorization process is conducted on the resulting phosphorus-containing hot pig iron and the resulting dephosphorized slag is used as a phosphoric acid fertilizer raw material. In the dephosphorization treatment, the amount of CaO-based dephosphorizing agent injected together with oxygen gas is adjusted so that the slag has basicity of 1.5 or more. This stably provides a slag having a composition containing PO:15% by mass% based on the total amount. Further a silicon source is top added during middle to terminal stage of blowing of the dephosphorization process to adjust so that the produced slag has a composition containing SiO:10% or more in a ternary system of CaO, POand SiO. With such composition, slag where a mineral phase having high phosphoric acid solubility and high fertilizer effect can be manufactured and used as phosphoric acid fertilizer raw material having high fertilizer effect.

Description

  The present invention relates to the effective reuse of steelmaking slag generated in the steelmaking process, in particular, recovering and concentrating phosphorus from steelmaking slag, and making it a high-level phosphate fertilizer raw material that can be stably used as phosphate fertilizer, The present invention relates to a phosphate fertilizer raw material that can be used as a phosphate fertilizer and a method for producing the same.

In recent years, phosphorus resources have soared due to the depletion of phosphate ore and the inclusion of phosphate ore by China and the United States. Therefore, phosphorus in steel slag (hereinafter also referred to as steelmaking slag) generated in the steel process has been reviewed as a valuable phosphorus resource.
However, since the phosphorus concentration in the hot metal discharged from the blast furnace is about 0.1% by mass, phosphoric acid (P in the steelmaking slag produced by conventional general hot metal preliminary dephosphorization treatment and hot metal decarburization refining) ₂ O ₅ ) Concentration remains as low as 5% by mass at most. Here, the “preliminary dephosphorization process” refers to a process for removing phosphorus in the hot metal in advance before decarburizing and refining the hot metal in a converter or the like. As it is, there is little prospect that steelmaking slag can be used as a phosphate resource, for example, a phosphate fertilizer raw material. Therefore, these steelmaking slags are currently used as civil engineering materials such as roadbed materials, and phosphorus in the slag is not effectively used.

  Recently, from the viewpoint of environmental measures and resource saving, it is an urgent task to reduce the amount of steelmaking slag, including recycling and using steelmaking slag. For example, there is an attempt to recycle steelmaking slag and use it in the iron ore sintering process as a lime source for a slagging agent. However, this method has a problem that phosphorus in the steelmaking slag is reduced in the blast furnace and the phosphorus concentration in the hot metal discharged from the blast furnace increases.

  Conventionally, Thomas phosphate fertilizer is widely known as a phosphate fertilizer made from steelmaking slag. This Thomas Phosphorus fertilizer is a slag produced by refining Thomas hot metal (usually [P]: about 1.8-2.0% by mass) produced from high phosphate iron ore using a Thomas converter. The phosphoric acid concentration is as high as 16 to 22% by mass. However, this technology has limitations such as the need to use a Thomas converter, the need to use high phosphate iron ore, the high P concentration of hot metal after dephosphorization, and the amount of slag produced. There are many problems, such as many, and it is hardly implemented at present.

  For example, Patent Document 1 discloses a method for refining clean steel with respect to such a problem. In the technique described in Patent Document 1, a hot metal pre-removal process is performed between the blast furnace refining process and the converter refining process, and the P content is 0.17 in the first pre-removal process. Pre-dephosphorization of ~ 0.50 wt% high-phosphorus hot metal to produce useful slag with high P content and discharge it, and the dephosphorization obtained at this time is removed again in the second pre-furnace pre-dephosphorization process. This is a clean steel refining method in which phosphorus is reduced to low phosphorus and the resulting low phosphorus is refined in a converter to become low phosphorus steel.

  In the technique described in Patent Document 1, the phosphorus-containing slag generated in the second pre-furnace preliminary dephosphorization process is charged into the blast furnace as part of the blast furnace charging raw material, and P in the hot metal discharged from the blast furnace is added. The content is maintained at 0.17 to 0.50% by weight. In addition, slag with a high P content discharged in the first out-of-core preliminary dephosphorization process is recovered as a phosphoric acid resource and can be used as a raw material for phosphoric acid and fertilizer. Moreover, according to the technique described in patent document 1, it is supposed that the quantity of slag discharged | emitted by a steelmaking process can be reduced significantly.

  Patent Document 2 describes a steelmaking method. In the technique described in Patent Document 2, an out-of-core preliminary dephosphorization step of hot metal is provided between the blast furnace refining step and the converter refining step, and the P content is 0.17 to 0.50% by weight in this out-of-core preliminary dephosphorization step. Preliminarily dephosphorizing the high phosphorus content hot metal to produce useful slag with a high P content and discharging it. The preliminary dephosphorized iron obtained at this time is refined into a converter to form a low phosphorus steel. Phosphorus-containing slag produced by furnace refining is charged into the blast furnace as part of the blast furnace charge, and the P content in the hot metal discharged from the blast furnace is maintained at 0.17 to 0.50% by weight, and the amount of waste slag This is a steelmaking method that enables reduction. According to the technique described in Patent Document 2, slag having a high P content discharged in the hot metal pre-furnace preliminary dephosphorization process is recovered as a phosphoric acid resource and can be used as a raw material for phosphoric acid and fertilizer. Moreover, according to the technique described in patent document 2, it is supposed that the quantity of slag discharged | emitted by a steelmaking process can be reduced significantly.

  Patent Document 3 describes a method for producing high P slag. In the technique described in Patent Document 3, phosphorus-containing slag obtained by dephosphorizing hot metal having a P concentration of 0.15% by mass or less is introduced into a hot metal bath, and a carbon material and iron oxide or / and oxygen are supplied. After reducing and extracting P in the slag into the hot metal bath to produce hot metal with a P concentration of 0.5 to 3% by mass, and discharging the slag produced in the first step, Add the flux so that the slag basicity becomes 2-8, and then add the iron oxide source and / or blow in oxygen gas to reduce the carbon concentration in the hot metal to 1% or less. This is a method for obtaining a high P slag having a phosphoric acid concentration of 10 to 35%. The slag obtained by this method contains a high concentration of phosphoric acid and can be used directly as a fertilizer.

Patent Document 4 describes a method for recycling steelmaking slag. The technique described in Patent Document 4 is based on the basicity (mass) after mixing decarburization refining slag generated in hot metal decarburization refining in a converter and predephosphorization slag generated in pretreatment of hot metal. % CaO / mass% SiO ₂ ) is mixed to 1.5 to 2.8, and the mixture is oxidized with iron in the slag using a reducing agent containing at least one of carbon, silicon, and aluminum. This is a method for recycling steelmaking slag by performing a reduction treatment for reducing substances, using metallic iron obtained by the reduction treatment as an iron source, and using slag after the reduction treatment as a raw material for phosphate fertilizer.

JP 08-3612 A Japanese Patent Laid-Open No. 08-3613 JP-A-11-158526 JP 2012-7190

  However, in the techniques described in Patent Documents 1 and 2, it is necessary to provide a special process called hot metal out-of-core preliminary dephosphorization process, and there is a problem that the dephosphorization cost and the slag recovery cost are increased. For example, in the technique described in Patent Document 1, since the hot metal out-of-furnace preliminary dephosphorization step is performed in two steps, it is necessary to provide two dephosphorization processing apparatuses, which increases the dephosphorization cost. Further, with one group, the amount of dephosphorization treatment is halved, and productivity is lowered.

  Moreover, according to the technique described in patent documents 1-3, the slag containing a high concentration phosphoric acid can be obtained. However, Patent Documents 1 to 3 do not refer to soluble phosphoric acid and soluble phosphoric acid, and it is unclear whether the obtained slag retains an effective fertilizer effect as a phosphate fertilizer. As used herein, “soluble phosphoric acid” refers to phosphoric acid dissolved in 2% citric acid (pH 2.0), and “soluble phosphoric acid” refers to phosphoric acid dissolved in diammonium citrate solution (pH 7). . It is said that the higher the concentration of “soluble phosphate” or “soluble phosphate” is, the more effective as a fertilizer. In order for the obtained slag to be effective as a phosphate fertilizer, the soluble phosphate or soluble phosphate is used. Many need to be included. However, in the inventions described in Patent Documents 1 to 3, no consideration is given to measures for increasing the concentration of “soluble phosphoric acid” and “soluble phosphoric acid” in slag, and it has a high level of fertilizer effect. It is hard to say that slag is obtained.

  Further, Patent Document 4 has a description of the content of “soluble phosphoric acid” in the slag, but there is no description of “soluble phosphoric acid”, and the technique described in Patent Document 4 has a high level of fertilizer effect. It is not always possible to obtain a slag having In addition, the fertilizer effect is often evaluated by “soluble phosphoric acid” or “soluble phosphoric acid” indicating the solubility of phosphoric acid (phosphoric acid solubility). It is said that the correlation with crop growth promotion is stronger than the evaluation by

  The present invention advantageously solves such problems of the prior art, collects steelmaking slag generated in the steelmaking process, makes a slag containing a component having a high phosphoric acid content and a high fertilizer effect, and can be used as a phosphate fertilizer An object of the present invention is to provide a stable method for producing a phosphate fertilizer raw material, which is a phosphate fertilizer raw material.

  In order to achieve the above-described object, the present inventors have earnestly studied about a policy that can make a recovered steelmaking slag as a raw material into a slag having an effective composition as a phosphate fertilizer. As a result, first, it was confirmed that the hot metal obtained by reducing the recovered phosphorus-containing steelmaking slag was a high-phosphorus hot metal containing 0.5% by mass or more of phosphorus. Therefore, if dephosphorization treatment is performed using the high-phosphorus hot metal as a starting material, the hot metal becomes low-phosphorus, and phosphorus is concentrated in the slag to be produced to form high-phosphorus-containing slag (also referred to as dephosphorized slag). I came to think that it would be possible to use it as a fertilizer raw material. However, conventionally, in order to use the produced slag as a phosphate fertilizer raw material, it has been required that the slag contains a large amount of phosphoric acid having a fertilizer effect.

Therefore, further studies were conducted on measures for increasing the phosphoric acid concentration in the slag to be produced. As a result, oxygen gas is applied so that the slag (dephosphorization slag) to be generated when the dephosphorization treatment is performed on the high phosphorus hot metal has a basicity ((mass% CaO) / (mass% SiO ₂ )): 1.5 or more. I came to think of adjusting the amount of CaO source to be projected. By adjusting the basicity of the dephosphorized slag to be 1.5 or more, as shown in FIG. 1, the phosphoric acid content in the slag can be stably increased to 15% or more by mass% with respect to the total amount of slag. I found out that I can do it. When the basicity of the slag is less than 1.5, the desired phosphoric acid content in the slag cannot be ensured due to insufficient dephosphorization ability. Incidentally, phosphoric acid content expressed as P ₂ O ₅ content.

However, slag with various phosphoric acid concentrations (P ₂ O ₅ content) was fertilized as a phosphate fertilizer on pak choi, paddy rice, etc., and a cultivation test (also called a growth test) was conducted to confirm the fertilizer effect. It has been found that even if the phosphoric acid concentration is high, a sufficient fertilizer effect is not always exhibited. Even if the phosphoric acid concentration is as high as 15% by mass or more, when the total amount of CaO, P ₂ O ₅ and SiO ₂ is less than 50% by mass with respect to the total amount of slag, FeO, MnO, MgO, etc. It is thought that the fertilizer effect became insufficient due to too much component.

On the other hand, even when phosphoric acid P ₂ O ₅ is as high as 15% or more by mass% with respect to the total amount of slag, and even when the total amount of CaO, SiO ₂ and P ₂ O ₅ is as high as 50% or more by mass% with respect to the total amount of slag It was found that the fertilizer effect may not be sufficient as a quality fertilizer.
Therefore, the relationship between the slag composition and the fertilizer effect was evaluated for various slags as phosphate fertilizers in a cultivation test using chingensai.

The cultivation test was as follows.
Chingensai was planted in a glass greenhouse in 1 / 5000a Wagner pot charged with 1kg of polyhumic black soil corrected to pH (H20) 6.5 with calcium carbonate and magnesium oxide and 0.5g of slag as a phosphate fertilizer raw material. And cultivated for a predetermined period (60 days) and observed the growth. Note that potassium nitrate and potassium chloride were applied to all the pots so that the nitrogen (N) was 0.5 g / pot and the potassium (K20) was 0.5 g / pot. As for the growth situation of Chingensai, compared with the growth situation in the pot where the superphosphate lime, which is a control fertilizer, is applied as a phosphate fertilizer, if it is equal or superior, it is marked with `` ○ '', otherwise it is marked with `` X '' evaluated. The obtained results are shown in Table 1.

  Table 1 shows the amount of phosphoric acid (soluble phosphoric acid) dissolved in the diammonium citrate solution (pH: 7.0) defined in the official fertilizer standard for the used phosphate fertilizer raw material (slag). The ratio of the amount of soluble phosphoric acid to the total amount of phosphoric acid in the fertilizer raw material (slag) and the result of calculating the phosphoric acid solubility (%) are also shown. Table 1 also shows the results of identifying the mineral phase contained in the phosphate fertilizer raw material (slag) by X-ray diffraction. The identified mineral phase is indicated by a circle.

Phosphoric fertilizer raw materials (slag) that have been evaluated as “○” in the cultivation test are all mass% of the total amount of slag, and the total amount of CaO, SiO ₂ , P ₂ O ₅ is 50% or more, phosphoric acid (P ₂ O ₅ ) is a slag containing 15% or more and 10% or more of SiO ₂ by mass% in a ternary system of CaO, SiO ₂ and P ₂ O ₅ .
From this, in order to find out that the amount of SiO ₂ greatly affects the fertilizer effect in addition to the phosphoric acid content in the phosphate fertilizer raw material, to become a phosphate fertilizer raw material (slag) with a high fertilizer effect, The composition of slag is the mass% of the total amount of slag, the total amount of CaO, SiO ₂ , P ₂ O ₅ is 50% or more, P ₂ O ₅ is 15% or more, and CaO, SiO ₂ , P ₂ O ₅ It has been found that it is necessary to obtain a slag having a composition containing 10% or more of SiO _{2 by} mass% in the ternary system.

The slag having a composition containing 10% or more of SiO ₂ by mass% in the ternary system of CaO, SiO ₂ and P ₂ O ₅ described above is soluble as a mineral phase (CaO—P ₂ O ₅ system crystal). It has been found that it contains a mineral phase having a crystalline structure of silicocarnotite (Ca ₅ (PO ₄ ) ₂ SiO ₄ ), which has a high phosphoric acid content and a high phosphoric acid solubility and exhibits a high fertilizer effect. Here, silicocarnotite (Ca ₅ (PO ₄ ) ₂ SiO ₄ ) is a Ca ₃ (PO ₄ ) ₂ —Ca ₂ SiO ₄ solid solution, and is usually expressed as Ca ₅ (PO ₄ ) ₂ SiO _4. .

This is also evident from a comparison of the phosphate solubility measured for each mineral phase purified as a reagent. That is, phosphoric acid solubility of Ca ₅ (PO ₄ ) ₂ SiO ₂ is 85%, whereas 39% for β-Ca ₃ (PO ₄ ) _{2 and} 56% for Ca ₁₉ Mn ₂ (PO ₄ ) _14. Ca ₉ Fe (PO ₄ ) ₇ is as low as 15%, and the presence of silicocarnotite (Ca ₅ (PO ₄ ) ₂ SiO ₂ ) is considered to greatly improve the fertilizer effect.

In addition, the inventors of the present invention have made it possible to achieve a SiO ₂ content of 10% or more in the ternary system of CaO, SiO ₂ , and P ₂ O _{5 in} the dephosphorization slag. It has also been found that it is easier to achieve by supplying a silicon source together with a dephosphorizing agent from the middle to the last stage of blowing, especially by supplying a silicon source to a fire point.
The present invention has been completed based on such findings and further studies. That is, the gist of the present invention is as follows.
(1) The phosphorus-containing molten iron obtained by subjecting the steel-making slag containing phosphorus generated in the steel refining process to reduction treatment is further subjected to dephosphorization treatment, and the resulting dephosphorization slag is used as a phosphate fertilizer raw material. In the dephosphorization treatment, the dephosphorization slag obtained has a basicity defined by the ratio of CaO content and SiO ₂ content, [mass% CaO] / [mass% SiO ₂ ] of 1.5 or more, and CaO, SiO ₂ In addition, the amount of CaO source projected with oxygen gas is adjusted so that it has a composition in which SiO ₂ is 10% or more by mass% in the ternary system of P ₂ O ₅ and further a silicon source is supplied. A method for producing a phosphate fertilizer raw material.
(2) The method for producing a phosphate fertilizer raw material according to (1), wherein the reduction treatment is a treatment performed using a reducing agent containing one or more of carbon, silicon, and aluminum.
(3) The method for producing a phosphate fertilizer raw material according to (1) or (2), wherein the CaO source is a powder having a particle diameter of 1 mm or less.
(4) The method for producing a phosphate fertilizer raw material according to any one of (1) to (3), wherein the silicon source is supplied to a fire point.
(5) The phosphoric acid according to any one of (1) to (4), wherein the obtained dephosphorized slag has a composition in which P ₂ O ₅ is 15% or more by mass% with respect to the total amount of slag. Manufacturing method of fertilizer raw material.
(6) In any one of (1) to (5), the dephosphorized slag obtained is a composition in which the total content of CaO, P ₂ O ₅ and SiO ₂ is 50% or more by mass% with respect to the total amount of slag. A process for producing a phosphate fertilizer raw material characterized by comprising:
(7) A phosphate fertilizer, part or all of which comprises a phosphate fertilizer raw material produced by the production method according to any one of (1) to (6).
(8) The phosphate fertilizer according to (7), wherein the phosphate fertilizer includes a CaO—P ₂ O ₅ crystal having a silicocarnotite crystal structure.
(9) Dephosphorization slag obtained by treating steelmaking slag is used as a raw material, and contains at least CaO, P ₂ O ₅ and SiO ₂ , and the total content of CaO, P ₂ O ₅ and SiO ₂ is 50% by mass. Phosphoric acid characterized by having a composition containing SiO ₂ : 10% or more by mass% in a ternary system of CaO, P ₂ O ₅ and SiO ₂ with P ₂ O ₅ of 15% or more Fertilizer raw material.
(10) The phosphate fertilizer material according to (9), wherein the phosphate material includes a CaO—P ₂ O ₅ crystal having a silicocarnotite crystal structure.
(11) A phosphate fertilizer comprising the phosphate fertilizer raw material according to (9) or (10).

  ADVANTAGE OF THE INVENTION According to this invention, the dephosphorization slag used as the phosphate fertilizer raw material with the fertilizer effect stably stabilized from the steel-making slag which cannot be reused conventionally can be manufactured, and there is a remarkable industrial effect. Moreover, according to the present invention, steelmaking slag can be used effectively, and there is an effect that the amount of slag discharged from the steelworks can be reduced.

It is a graph showing the effect of the slag basicity on the phosphoric acid content of dephosphorization slag (wt% CaO) / (wt% SiO _2). The composition range of the present invention phosphate fertilizer material (dephosphorization slag), CaO, is an explanatory diagram showing a three-component phase diagram of P ₂ O _5, SiO _2. It is explanatory drawing which shows typically an example of the dephosphorization processing equipment which can be utilized for this invention dephosphorization process.

In the present invention, steelmaking slag containing phosphorus generated in a steelmaking refining process (hereinafter referred to as “phosphorus-containing steelmaking”) such as slag generated during preliminary dephosphorization of hot metal and slag generated by decarburization refining of hot metal in a converter. First, a reduction process is performed on the slag.
Phosphorus-containing steelmaking slag contains CaO and SiO ₂ as main components, phosphorus is contained as an oxide of P ₂ O ₅ , and iron is contained as an oxide in the form of FeO, Fe ₂ O ₃ or the like. Such phosphorus-containing steel slag is subjected to a reduction treatment using a reducing agent. The reducing agent used is preferably one or more of carbon, silicon, and aluminum.

Phosphorus and iron have a weaker affinity for oxygen than Ca and Si, and P ₂ O ₅ and iron oxide in slag are easily reduced. The reduction treatment can be performed using equipment such as a rotary kiln equipped with a heating means such as a burner, an arc furnace, etc., but preferably at a high temperature of 1000 ° C. or higher so that the iron produced by the reduction is in a molten state. It is preferable to carry out by heating. Thereby, the iron produced by reduction (molten iron) can be easily separated from the slag, and further, the phosphorus produced by the reduction is dissolved in the molten iron to form high phosphorus-containing molten iron.

  The lower the melting point of the produced molten iron, the more the separation of the molten iron and slag is promoted. Therefore, it is preferable to dissolve the carbon in the produced molten iron to form molten iron. In order to dissolve carbon in molten iron, it is preferable to use carbon as a reducing agent. In addition, when silicon or aluminum is used as the reducing agent, it is preferable that the molten iron produced by the reduction is carburized to coexist with carbon and steelmaking slag to obtain a high phosphorus content hot metal.

In addition, the slag after the reduction treatment has a low phosphoric acid content and can be used as a refining agent in the iron making process or the steel making process. Even if the slag after the reduction treatment is used as a substitute for the refining agent (lime), the phosphorus content in the hot metal is not increased and can be reused.
Next, in the present invention, the obtained high phosphorus-containing hot metal is subjected to a dephosphorization treatment. Note that the obtained high phosphorus-containing hot metal may be mixed with the hot metal discharged from the blast furnace to adjust to an appropriate phosphorus concentration.

Any ordinary dephosphorization processing equipment can be used for the dephosphorization processing of the hot metal of the present invention.
As the dephosphorization processing equipment, for example, as shown in FIG. 3, equipment provided with a reaction vessel (converter type) 1 with an upper blowing lance 2, an injection lance 3, a hopper 11, storage tanks 5, 6 and the like can be exemplified. .
In the dephosphorization treatment, the obtained high phosphorus content hot metal is charged into the reaction vessel 1 and oxygen gas is blown from the top blowing lance 2 and at the same time, the oxygen gas is used as a carrier gas to store CaO stored in the storage tank 6. Spray source 4. As the CaO source, quick lime can be exemplified, and it is preferable to use a CaO-based refining agent (dephosphorizing agent) in which no fluorine compound is mixed. From the viewpoint of promoting the reaction, the CaO-based refining agent is preferably in the form of powder and powder having a particle size of 1 mm under (less than 1 mm). In addition, spraying powder such as a CaO-based refining agent on the hot metal from the top blowing lance 2 is also referred to as “projection”. Further, by using the injection lance 3, a CaO-based refining agent (dephosphorizing agent) stored in the storage tank 5 using nitrogen gas as a carrier gas may be blown into the hot metal.

In the present invention, in the dephosphorization treatment, the dephosphorization slag obtained has a basicity defined by the ratio of CaO content to SiO ₂ content, [mass% CaO] / [mass% SiO ₂ ] of 1.5 or more. The amount of CaO source to be projected is adjusted so as to have a composition to be Thereby, the phosphoric acid (P ₂ O ₅ ) content of the dephosphorized slag obtained can be stably increased to a desired value or more.
When the basicity of the obtained slag is less than 1.5, as shown in FIG. 1, the phosphoric acid content cannot be stably increased to a desired value or more. The “desired value” here is mass% with respect to the total amount of slag, and is P ₂ O ₅ : 15% or more. If the content of P ₂ O ₅ in the slag can be secured at 15% or more, a desired fertilizer effect can be expected as a phosphate fertilizer.

Furthermore, in the dephosphorization treatment of the present invention, since the obtained slag (dephosphorization slag) has a higher fertilizer effect, the above-described CaO-based refining agent (dephosphorization agent) is used from the middle stage of blowing to the end stage of blowing. In addition to the projection, the silicon source is supplied.
In the dephosphorization process, a CaO-based refining agent (dephosphorizing agent) is added to the molten iron for phosphorus concentration in the slag, and a silicon source is supplied to obtain a slag having a higher fertilizer effect.

  The supply of the silicon source is preferably performed by adding the silicon source from a hopper. Note that it is preferable to supply the silicon source to a fire point. Thereby, the additive thrown in at the last stage of blowing can be taken in in slag without remaining undissolved. Examples of the silicon source include SiC and silica stone. Further, the “fire point” here is a high temperature region where the iron bath and the oxygen supply source interfere with each other.

Here, “a composition having a higher fertilizer effect” means mass% with respect to the total amount of dephosphorized slag obtained, and the total amount of CaO, P ₂ O ₅ and SiO ₂ is 50% or more, and P ₂ O ₅ is 15%. % Or more, CaO 1.5% (SiO ₂ )% or more, and also a composition containing 10% or more of SiO ₂ in terms of mass% in the ternary system of CaO, P ₂ O ₅ and SiO ₂ . Preferably, the mass% in the ternary system of CaO, P ₂ O ₅ and SiO ₂ is 30% or more for P ₂ O _{5 and} 40% or more for CaO.

By making the dephosphorization slag composition as described above, a mineral phase with a crystalline structure of silicocarnotite (Ca ₅ (PO ₄ ) ₂ SiO ₄ ) that has a high phosphate solubility and a high fertilizer effect is formed. As a result, the amount of phosphoric acid and the phosphoric acid solubility of the dephosphorized slag are increased, and a phosphate fertilizer raw material having an excellent fertilizer effect can be obtained. From the viewpoint of fertilizer effect, the amount of soluble phosphoric acid in the dephosphorized slag is preferably 15% by mass or more based on the total amount of slag.

Note that the introduction of a CaO source (CaO-based refining agent (dephosphorization agent)) for the purpose of phosphorus concentration in the slag decreases the fluidity of the slag. This, Si in the molten iron, because they are oxidized in preference to P, SiO ₂ is unevenly distributed in the early formed phosphate enriched slag, SiO ₂ phosphate concentrated in the slag formed in the blow end This is because the concentration decreases. In order to prevent such fluidity deterioration of slag, in the present invention, preferably from the middle to the end of blowing, a silicon source is supplied together with a dephosphorizing agent, preferably supplied to a hot spot, and the components in the slag are unevenly distributed. To improve the quality of phosphate fertilizer.

When the silicon source is introduced, the Si concentration [% Si] in the molten iron is expressed by the following formula (1) [% Si] ≤ 1/2 [% Si] _input (1)
[% Si] _input : Charged Si concentration (mass%)
It is preferable that the Si concentration in the hot metal satisfying the above is the time when the Si concentration [% Si] at the time of charging is reduced to half or less of the _input . The concentration of Si in the hot metal t seconds after the start of blowing is expressed by the following formula: [% Si] = [% Si] _input exp (−k _Si · Input O ₂ ) (1a)
[% Si] _input : charged Si concentration (mass%), k _Si : constant determined by processing equipment,
Input O ₂ : Amount of oxygen (Nm ³ / t) supplied from the start of blowing to t seconds later
It can be calculated by In addition, the amount Q _SiO2 (ton) of the silicon source at that time is expressed by the following formula (2): Q _SiO2 ≦ (0.6 / 0.85) × (W _CaO + W _P205 + (W _SiO2 ) ^input ) (2)
It is preferable to adjust so as to satisfy the above.

Here, W _CaO is the amount of CaO input at the time of dephosphorization (ton), W _P205 , (W _SiO2 ) ^input is the amount of P ₂ O ₅ (ton) and SiO ₂ due to the molten iron in the slag ( ton). Note that W _P205 and (W _SiO2 ) ^input are defined by the following equations (3) and (4), respectively.
_{W P205 = ([% P]} input - [% P] output) / 100 × (M P205 / M P) × W m ‥‥ (3)
(W _SiO2 ) ^input = ([% Si] _input − [% Si] _output ) / 100 × (M _SiO2 / M _Si ) × W _m (4)
Here, [% P] _input is the P concentration (mass%) in the molten iron, [% P] _output is the P concentration (mass%) in the molten iron at the end of dephosphorization (at the end point), [% Si ] _{input the} Si concentration in the loading hot metal (mass%), a [% Si] _output is Si concentration in the hot metal dephosphorization treatment end (at the end point) (wt%), W _m is charged hot metal It is a quantity (ton). M _P205 and M _SiO2 are the molecular weights of the respective compounds, and M _P and M _Si are the atomic weights of the respective elements.

W _SiO2 is the amount of SiO ₂ contained in the slag, and W _total is the _total amount of CaO, P ₂ O ₅ and SiO ₂ contained in the slag, and can be defined by the following equation.
W _SiO2 = (W _SiO2 ) ^input + Q _SiO2 (5)
W _total = W _CaO + W _P205 + W _SiO2 (6)
And the conditions of the obtained slag (dephosphorization slag) that the above-mentioned formulas (3) to (6), slag basicity: 1.5 or more, and phosphoric acid content: 15 mass% or more W _CaO / W _SiO2 ≧ 1.5 (7)
W _P205 / W _total ≧ 0.15 (8)
From the above, the above equation (2) can be derived.

In the present invention, it is preferable that the amount of silicic acid source Q _SiO2 is adjusted so as to satisfy the above-described formula (2), and the slag is charged into a portion where SiO ₂ is insufficient. Thereby, the fluidity | liquidity of slag improves, Moreover, the homogeneous slag (dephosphorization slag) which has a desired composition can be manufactured stably, and it can be set as the siliceous fertilizer raw material with a high fertilizer effect.

  50 tons of phosphorus-containing steelmaking slag generated in the steelmaking process was charged into a rotary kiln furnace together with carbon as a reducing agent. And the reduction process which heats the steel-making slag with which it charged with a reducing agent to 1000 degreeC or more with the heating burner attached to the rotary kiln furnace was performed, and high phosphorus reduced iron 10ton was obtained. In addition, it confirmed that the slag produced | generated at the time of this reduction process has low phosphoric acid concentration, and can be used as a substitute (refining agent) of the lime of a ironmaking process and a steelmaking process.

The phosphorus content of the high phosphorus reduced iron obtained by the above reduction treatment was 1.0 to 4.0% by mass. Therefore, the obtained high phosphorus reduced iron was put into the hot metal discharged from the blast furnace, and the phosphorus content was adjusted to a value within the range of 0.5 to 3.0% by mass, respectively, so that the high phosphorus hot metal was 200 tons. Table 2 shows the hot metal components before dephosphorization.
Next, 200 tons of these high phosphorus hot metal was charged into a converter reactor and subjected to dephosphorization treatment.

In the dephosphorization treatment, oxygen gas was blown from the top blowing lance and a powdered CaO-based dephosphorization agent (flux) was blown as a CaO source. The CaO-based dephosphorizing agent was only powdered quicklime having a particle size of 1 mm or less (CaO pure content: about 95% by mass) and did not contain a fluorine compound such as fluorite. The basic unit of the slag ([CaO] / [SiO ₂ ]) was changed by adjusting the basic unit of the CaO-based dephosphorizing agent to be added. In some cases, the silicon source was added from the hopper at the basic unit shown in Table 2 with respect to the fire point. The silicon source was introduced when the Si concentration [% Si] in the hot metal defined by the above formula (1a) became 1/2 or less of the charged Si concentration [% Si] _input . Further, the amount of silicon source input was determined so as to satisfy the above-described equation (2). In addition, by adding the silicon source to a high-temperature fire point, the additive added at the end of the blowing process could be taken into the slag without remaining undissolved.

After dephosphorization treatment, the composition of the obtained hot metal was measured and shown in Table 2. After the dephosphorization treatment, the hot metal was discharged out of the reaction vessel, and the slag was allowed to cool in the reaction vessel.
Moreover, the slag produced | generated in the last stage of blowing was extract | collected, and the composition was analyzed using the glass bead analysis method. Moreover, it measured using the X-ray diffraction about the mineral phase contained in slag. Further, the amount of phosphoric acid (soluble phosphoric acid) dissolved in the diammonium citrate solution (pH 7) was measured in accordance with the official fertilizer standard. From the obtained value, the ratio of the soluble phosphoric acid to the total phosphoric acid contained in the slag (phosphoric acid solubility) was calculated.

Subsequently, the obtained slag after cooling was used as a phosphate fertilizer raw material, and a cultivation test was conducted using Hiroshima. The cultivation test was as follows.
Hiromana was planted in a glass greenhouse with 1 / 5000a Wagner pot charged with 1kg of polyhumic black soil, adjusted to pH (H20) 6.5 with calcium carbonate and magnesium oxide, and 0.5g of slag as phosphate fertilizer. And cultivated for a predetermined period (60 days) and observed the growth. Note that potassium nitrate and potassium chloride were applied to all the pots so that the nitrogen (N) was 0.5 g / pot and the potassium (K20) was 0.5 g / pot. The growth situation of Hiroshima is compared with the growth situation in the pot applied with phosphoperphosphate as a control fertilizer as a phosphate fertilizer, `` ○ '' if it is equal or superior, `` X '' otherwise evaluated.

  The obtained results are shown in Table 2. In addition, the slag composition shown in Table 2 was plotted in the ternary diagram of FIG.

In all of the examples of the present invention, the total amount of CaO, SiO ₂ , and P ₂ O ₅ is 50% by mass or more, the amount of P ₂ O ₅ is 15% by mass or more, and CaO, SiO ₂ , The SiO ₂ content satisfies 10% by mass or more in mass% of P ₂ O ₅ ternary system, Ca ₅ (PO ₄ ) SiO ₂ is detected, and the fertilizer effect is excellent. On the other hand, a comparative example out of the scope of the present invention is a ternary system of CaO, SiO ₂ and P ₂ O ₅ , the SiO ₂ content is less than 10% by mass, and Ca ₅ (PO ₄ ) ₂ SiO ₂ is not detected. The fertilizer effect is also low.

  Note that the hot metal obtained by performing the dephosphorization treatment in the present invention has a phosphorus concentration that is reduced to 0.10% by mass or less, and at this low phosphorus concentration, steelmaking is no different from blast furnace hot metal. It can be used as an iron source.

1 Reaction vessel 2 Top blowing lance 3 Injection lance 4 CaO source 5 Storage tank 6 Storage tank 7 Hot metal
11 Hopper
12 Generated slag

Claims (11)

When the phosphorus-containing molten iron obtained by subjecting steelmaking slag containing phosphorus generated in the steelmaking refining process to reduction treatment is further subjected to dephosphorization treatment, and the resulting dephosphorized slag is used as a phosphate fertilizer raw material,
In the dephosphorization treatment, the dephosphorization slag obtained has a basicity defined by a ratio of CaO content to SiO ₂ content of [mass% CaO] / [mass% SiO ₂ ] of 1.5 or more, and CaO, P A process of adjusting the amount of CaO source projected with oxygen gas and further supplying a silicon source so that the composition is such that SiO ₂ is 10% or more by mass% in the ternary system of ₂ O ₅ and SiO ₂ A method for producing a phosphate fertilizer raw material.   The method for producing a phosphate fertilizer raw material according to claim 1, wherein the reduction treatment is a treatment performed using a reducing agent containing at least one of carbon, silicon, and aluminum.   The method for producing a phosphate fertilizer raw material according to claim 1 or 2, wherein the CaO source is a powder having a particle size of 1 mm or less.   The method for producing a phosphate fertilizer raw material according to any one of claims 1 to 3, wherein the silicon source is supplied to a fire point. 5. The production of a phosphate fertilizer raw material according to claim 1, wherein the dephosphorized slag obtained has a composition in which P ₂ O ₅ is 15% or more by mass% with respect to the total amount of slag. Method. 6. The obtained dephosphorized slag has a composition in which the total content of CaO, P ₂ O ₅ and SiO ₂ is 50% or more by mass% with respect to the total amount of slag. The manufacturing method of the phosphate fertilizer raw material of description.   A phosphate fertilizer, part or all of which comprises a phosphate fertilizer raw material produced by the production method according to any one of claims 1 to 6. The phosphate fertilizer according to claim 7, wherein the phosphate fertilizer includes a CaO-P ₂ O ₅ based crystal having a silicocarnotite crystal structure. Dephosphorization slag obtained by processing steelmaking slag as a raw material, containing at least CaO, P ₂ O ₅ and SiO ₂ , and by mass, the total content of CaO, P ₂ O ₅ and SiO ₂ is 50% or more, P ₂ O _5: 15% or more, and CaO, in percent by weight in P ₂ O _5, SiO ₂ ternary, SiO _2: phosphate fertilizer raw material and having a composition containing 10% or more . The phosphate fertilizer raw material according to claim 9, wherein the phosphate fertilizer raw material includes CaO-P ₂ O ₅ based crystals having a silicocarnotite crystal structure.   A phosphate fertilizer comprising the phosphate fertilizer raw material according to claim 9 or 10.

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