JP2016074940A - Manufacturing method of dephosphorized slag and phosphate fertilizer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a dephosphorized slag suitable for manufacturing a phosphate fertilizer raw material high in phosphate concentration and fertilizer effect even containing iron oxide rationally at low cost and making a phosphate fertilizer raw material from the dephosphorized slag preferably.SOLUTION: A dephosphorization treatment is conducted by blowing oxygen into a molten iron having phosphorus concentration of 0.5 to 4 mass% with using flux having basic degree of 0.8 to 1.5 and t.Fe concentration of 10 mass% or more at a temperature after processing end in a range of 1200°C to 1450°C. After the phosphorus concentration in the slag becomes 5 mass% or more during processing, an auxiliary material is further added and basic degree of a final slag α is adjusted to 1.5 to 3.0 to make the phosphorus concentration in the slag at 8 to (-4α+23α-4) mass% and t.Fe concentration at 5 to 25 mass%. Then the slag is cooled at cooling rate of 10°C/min or more to 600°C.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a method for producing dephosphorized slag suitable for use as a raw material for phosphate fertilizer by dephosphorizing hot metal having a high phosphorus concentration in the hot metal, and by appropriately cooling the slag and The present invention relates to a method for producing a raw material.

  Since Japan has a large amount of precipitation, minerals flow out of the soil and the soil is easily acidified. Therefore, basic phosphate fertilizers that increase not only the phosphate concentration in soil but also soil pH are widely used as phosphate fertilizers used when growing plants. At present, as a basic phosphate fertilizer, dissolved phosphorus fertilizer containing a large amount of alkali is used.

  As shown in Non-Patent Document 1, in the past, Thomaslin fertilizer manufactured as a by-product in the Thomas steelmaking method, which is one of steelmaking methods, has been used as a basic phosphate fertilizer. However, because of the decline of the Thomas steelmaking method, Thomaslin fertilizer is not used at present.

  Currently, the hot metal discharged from the blast furnace contains about 0.1% phosphorus as an impurity. Phosphorus is oxidized and removed by adding flux and blowing oxygen in the steelmaking process and discharged as steelmaking slag. ing.

As shown in Patent Document 1, the steelmaking slag has a phosphoric acid concentration of about 1 to 4% by mass, which is not a sufficient concentration as a phosphate fertilizer, but the steelmaking slag is oxidized from the CaO content derived from the flux and the hot metal. Since the removed SiO _{2 component} is contained in a large amount, it is used as a silicate phosphate fertilizer.

  However, in Japan, which still depends on imports for the total amount of phosphate ore that is a raw material for phosphate fertilizer, the phosphoric acid content in steelmaking slag is considered as a useful phosphate fertilizer resource. As shown in Fig. 2, attempts have been made to produce phosphoric acid fertilizer from steelmaking slag by concentrating the phosphoric acid content in steelmaking slag to produce high phosphoric acid slag.

  By the way, in order to enhance the fertilizer effect when using the phosphate fertilizer as a fertilizer, it is necessary to control not only the phosphoric acid concentration but also the crystal state and mineral phase of phosphorus. For example, the above-mentioned melted phosphorus fertilizer is a fertilizer manufactured by melting and mixing phosphate ore and magnesium oxide and quenching with a jet water stream, and the phosphorus-containing mineral phase is made amorphous, that is, glass. , Enhance the fertilizer effect.

  The phosphorus-containing mineral phase in the present invention refers to a phase in which phosphorus is concentrated in each mineral phase in the fertilizer.

As shown in Non-Patent Document 1, Thomas phosphorus fertilizer is mainly composed of CaO, P ₂ O ₅ and SiO ₂ , so that the phosphorus-containing mineral phase is Ca ₃ (PO ₄ ) ₂ —Ca ₂ SiO _4. It is a solid solution phase, 5CaO · SiO ₂ · P ₂ O ₅ phase, or 7CaO · 2SiO ₂ · P ₂ O ₅ phase (hereinafter sometimes referred to as "solid solution phase"). The solid solution phase is a mineral phase with a high fertilizer effect.

In Non-Patent Document 1, high P hot metal (P: 1.7-2.1%, C: 3.5-3.8%, Si: 0.2-0.4%) is charged into the converter. Then, refining is performed by adding lime and blowing air, and the basicity of the slag is 4 to 6, the P ₂ O ₅ concentration is about 15 to 20%, and the molten steel (P: 0.08% or less, C: 0.10% or less) is described.

  In this method, the temperature in the furnace is increased by utilizing the oxidation reaction of carbon and phosphorus in the hot metal. After the refining, the generated slag is used as a phosphate fertilizer (Thomaslin fertilizer) with a high fertilizer effect.

Moreover, in patent document 2, with respect to the high P hot metal (P: 0.5-3%, C: around 4.5%, Si: around 0.05%) melted by reducing steelmaking slag. In the converter, a flux having a basicity of 2 to 8 is added, an iron oxide source is added, or gaseous oxygen is blown in to remove phosphorus (temperature after treatment: 1550 ° C. or higher), and molten steel (C: 1% or less, P: 0.1 to 0.2%) and slag (basicity: 5~6, P ₂ O ₅ concentration: describes a method of producing a 10-30%).

In this method, since the Si concentration in the hot metal to be processed is reduced as compared with the aforementioned Thomas steelmaking method, the concentration of P ₂ O ₅ in the slag is increased by reducing the amount of generated slag. ing. In this method, slag with good hatchability can be obtained without using fluorite by utilizing the effect that the melting point of slag is lowered by increasing the P ₂ O ₅ concentration in the slag.

Japanese Patent No. 5105322 JP-A-11-158526 JP 2009-132544 A JP 2011-208277 A

Japan Soil Fertilizer Journal, Vol. 13, p93

  In Japan, where phosphorus ore, the raw material for phosphate fertilizer, is imported from overseas, phosphorus in hot metal is a very attractive resource. It is desirable to manufacture phosphate fertilizer using phosphorus in hot metal and phosphoric acid in steelmaking slag as raw materials. However, in this case, it is inevitable that iron oxide is mixed into phosphate fertilizer. Therefore, it is desired to develop a phosphate fertilizer having a high phosphate concentration and a high fertilizer effect.

  However, it is of course desirable that phosphate fertilizer is inexpensive, and in order to reduce the cost, it is necessary to develop a method for stably producing dephosphorized slag as a raw material at low cost. Furthermore, it is also necessary to develop a method for appropriately treating the slag to make a phosphate fertilizer having a high fertilizer effect.

For example, the above-mentioned Thomaslin fertilizer is in a very high composition region where the basicity expressed by the weight ratio of CaO and SiO ₂ is 4 or more, and the steelmaking slag is often less than 4 as a raw material. However, the solid solution phase does not always precipitate, and the fertilizer effect is unknown.

  Furthermore, in recent years, as the steelmaking method, the top-bottom blow converter method currently generally performed is advantageous in terms of cost and energy, and it is possible to obtain molten steel with a lower impurity concentration. The Thomas steelmaking process has ceased. In the Thomas steelmaking method, the initial impurity concentration of the hot metal to be refined is high, and as a result, the impurity concentration of the molten steel after refining also becomes high.

In order to obtain the slag having a high P ₂ O ₅ concentration desired this time, when the Thomas steel making method is used for hot metal having a high P concentration, a converter and an exhaust gas treatment facility for that purpose are required. Since a large amount of CO gas is generated due to the oxidation reaction of C in the hot metal, a converter with a large furnace volume is necessary so that forming and slopping of the generated slag is not a problem. Since equipment is also required, an increase in equipment costs cannot be avoided.

  Patent Document 1 discloses that slag recovered in the hot metal pretreatment process is used as a silicate phosphate fertilizer, but there is no step of intentionally concentrating the phosphoric acid concentration. The phosphate concentration is as low as 5% or less, and the fertilizer effect as a phosphate fertilizer is low.

Using the technique disclosed in Patent Document 2, it is possible to produce high phosphate slag, but the cooling rate is not clearly shown, and the phosphate-containing mineral phase is intentionally controlled. The fertilizer effect is unknown. Furthermore, when this technology is used to obtain the desired slag with a high P ₂ O ₅ concentration, there are problems such as converters and exhaust gas facilities similar to the case of using the above-mentioned Thomas steelmaking method. To do.

  Therefore, in view of the above situation, the present invention does not presuppose the use of converter equipment for dephosphorization slag suitable for dephosphorizing hot metal having a high phosphorus concentration in the hot metal and using it as a raw material for phosphate fertilizer. It is an object of the present invention to provide a method for producing a phosphate fertilizer raw material with a high fertilizer effect by cooling the slag appropriately and at a low cost.

  In order to achieve the above-mentioned object, the present inventors have repeatedly studied phosphoric acid fertilizer raw materials having a high fertilizer effect in terms of the component composition and production conditions, and arranging the phosphorus-containing mineral phases in terms of the fertilizer effect has a hierarchy. I found. Then, dephosphorization slag suitable as a raw material for such phosphate fertilizer is refined under appropriate conditions without assuming the use of converter facilities for hot metal with high phosphorus concentration in hot metal. Has found that it can be manufactured at a reasonable and low cost. Furthermore, by appropriately cooling the dephosphorized slag thus produced, the precipitation of a mineral phase with a high fertilizer effect is promoted, the precipitation of a mineral phase with a low fertilizer effect is suppressed, and iron oxide is contained. However, the present inventors have found a method for stably producing a phosphate fertilizer having a high fertilizer effect.

  The present invention has been made based on the above findings, and the gist thereof is as follows.

(1) The hot metal having a phosphorus concentration in the hot metal of 0.5 to 4% by mass, the basicity as an index indicating the mass ratio of CaO and SiO ₂ is 0.8 to 1.5, and the iron oxide concentration Is t. A flux containing 10% by mass or more in Fe concentration is added and oxygen is blown to perform a dephosphorization treatment at a temperature at the end of the treatment in a range of 1200 ° C. or higher and 1450 ° C. or lower,
After the phosphoric acid concentration in the slag reaches 5% by mass or more during the dephosphorization treatment, by adding a secondary material, the basicity α which is the mass ratio of CaO and SiO _{2 in} the final slag is obtained. The phosphoric acid concentration in the slag is adjusted to 8 to (-4α ² + 23α-4) mass%, and the iron oxide (Fe conversion) concentration is adjusted to 5 to 25 mass%. The manufacturing method of the dephosphorization slag characterized by the above-mentioned.

(2) The temperature drop during the dephosphorization slag produced by the method described in the above item (1) from 1200 to 1450 ° C., which is the temperature at the end of the dephosphorization treatment, to 600 ° C. until reaching 600 ° C. Cooling at a cooling rate of 10 ° C./min or more by dividing the amount by the time until reaching 600 ° C.
Total of existing concentrations of one or more of Ca ₃ (PO ₄ ) ₂ -Ca ₂ SiO ₄ solid solution phase, 5CaO · SiO ₂ · P ₂ O ₅ phase, and 7CaO · 2SiO ₂ · P ₂ O ₅ phase The manufacturing method of the phosphate fertilizer raw material whose is 28 mass% or more.

  According to the present invention, dephosphorization slag containing iron oxide but having a high phosphoric acid concentration and suitable for producing a fertilizer raw material having a high fertilizer effect can be produced reasonably and at low cost. it can. Furthermore, by appropriately cooling the dephosphorization slag, a phosphate fertilizer raw material having a high fertilizer effect can be obtained.

It is a figure which shows an example of the process of manufacturing phosphoric acid containing slag in a steelmaking process. It is a figure which shows the relationship between phosphoric acid concentration and basicity, and a phosphorus containing mineral phase. Crystallinity and t. It is a figure which shows the relationship of Fe density | concentration. The concentration of the solid solution phase and t. Relationship between Fe concentration, C ₃ P phase existing concentration and t. It is a figure which shows the relationship of Fe density | concentration. Is a diagram showing the relationship between existence concentration and the cooling rate of the solid solution phase or C ₃ P phase.

In the method for producing the dephosphorized slag of the present invention, the basicity, which is an index indicating the mass ratio of CaO and SiO ₂ , of hot metal having a phosphorus concentration in the hot metal of 0.5 to 4% by mass is 0.8 to 1.5. And the iron oxide concentration is t. A dephosphorization process is performed in which a flux containing 10% by mass or more in Fe concentration is used and oxygen is blown so that the temperature at the end of the process is in the range of 1200 ° C. to 1450 ° C.

In the dephosphorization treatment, after determining that the phosphoric acid concentration in the slag has reached 5% by mass or more in the middle of the dephosphorization treatment, it is the mass ratio of CaO and SiO _{2 in} the final slag by further adding a secondary material. The basicity α is adjusted to 1.5 or more and 3.0 or less, and the phosphoric acid concentration in the slag is 8 to (−4α ² + 23α-4) mass%, and t. Fe concentration is 5 to 25 mass%.

Furthermore, the method of producing phosphoric acid fertilizer raw materials of the present invention, by using the dephosphorization slag manufactured by the manufacturing method of dephosphorization slag according to the present invention, the basicity to be displayed in the mass concentration ratio of CaO and SiO ₂ alpha is 1. 5 or 3.0 or less, P ₂ O ₅ to 8% by mass or more (-4α ² + 23α-4)% by mass or less, containing iron oxide than 25 wt% 5 wt% or more in terms of Fe, 1200-1450 By cooling the molten slag at 0 ° C. by controlling the amount of temperature drop until reaching 600 ° C. by the time until reaching 600 ° C. so that it becomes 10 ° C./min or more, The basicity α expressed by the mass concentration ratio of CaO and SiO ₂ is 1.5 or more and 3.0 or less, P ₂ O ₅ is 8 mass% or more (−4α ² + 23α-4) mass%, iron oxide is Contains 5% to 25% by mass in terms of Fe A phosphate fertilizer material, further, the phosphate fertilizer raw _{material, Ca 3 (PO 4) 2} -Ca 2 SiO 4 solid solution _{phase, 5CaO · SiO 2 · P 2} O 5 phase, and, 7CaO · 2SiO ₂ · A raw material for phosphate fertilizer in which the total concentration of one or more P ₂ O ₅ phases is 28% by mass or more is produced.

  First, the manufacturing method of the dephosphorization slag (phosphoric acid containing slag) suitable for making it the raw material (phosphate fertilizer raw material) of the phosphate fertilizer for plant growth is demonstrated. FIG. 1 shows an example of a process for producing phosphoric acid-containing slag in the steel making process.

  As shown in FIG. 1, in the steelmaking process, the hot metal produced in a blast furnace, usually containing 0.08 to 0.15% by mass of phosphorus, is transferred to a converter and slag is formed on the hot metal. The hot metal dephosphorization treatment S01 is performed by the reaction of the hot metal and slag by blowing an oxygen source.

  The converter dephosphorization slag 41 generated by the dephosphorization process S01 is discharged from the converter, and then slag is formed again on the molten iron in the converter, and an oxygen source is blown to perform a decarburization process S02. After subjecting the molten steel obtained in the decarburization treatment S02 to secondary refining S03, a steel slab is produced in continuous casting S04.

  After the dephosphorization treatment S01, the converter dephosphorization slag 41 discharged from the converter contains a large amount of iron together with phosphoric acid obtained by oxidizing phosphorus in the hot metal. Therefore, in order to recover valuable elements such as iron and phosphorus from the converter dephosphorization slag 41, the converter dephosphorization slag 41 is subjected to reduction / reforming treatment S11.

In the reduction / reformation treatment S11, the converter dephosphorization slag 41 is melted, pulverized coal, an Al ₂ O ₃ source, and an SiO ₂ source are added as a reducing agent and a modifying agent, and phosphorus is added in an amount of 0.5-4. A high phosphorus hot metal 42 containing a large amount of mass% is produced.

Then, a flux made from quick lime, SiO ₂ or the like is added to the high phosphorus hot metal 42 and subjected to dephosphorization treatment S13 in which oxygen is blown, and used as a raw material for phosphate fertilizer for plant growth (phosphate fertilizer raw material) A possible phosphoric acid-containing slag 50 is produced.

  In addition, since the hot metal 51 dephosphorized to a phosphorus content concentration of 0.1 to 0.3% by mass by the dephosphorization treatment S13 is supplied to the converter together with the hot metal generated in the blast furnace, the hot metal is produced wastefully. It is a reasonable process with no loss.

  Here, the manufacturing method of the molten slag (raw material slag of this invention fertilizer raw material) cooled with this invention manufacturing method is further demonstrated.

The high P hot metal containing 0.5 to 4% by mass of phosphorus is subjected to Cr removal treatment as necessary, and then the basicity displayed by the mass concentration ratio of CaO and SiO ₂ is 0.8 to 1.5, In addition, a flux containing 10 mass% or more of iron oxide in terms of Fe is used and oxygen is blown, and dephosphorization is performed at a temperature after the completion of the processing at 1200 to 1450 ° C., and the phosphoric acid concentration in the slag is 5 mass%. After the above, the secondary material is further added and manufactured.

  The phosphorus concentration of the high P hot metal is 0.5 to 4% by mass. When the phosphorus concentration of the high P hot metal is less than 0.5% by mass, the phosphoric acid concentration in the slag after the treatment does not reach 8% by mass or more, and the hot metal having a normal phosphorus concentration of 0.15% by mass or less is dephosphorized. Since the phosphoric acid concentration of the dephosphorized slag produced at the time is less than 5% by mass, the phosphorus concentration of the high P molten iron is suitably 0.5% by mass or more. Preferably it is 1 mass% or more.

On the other hand, if the phosphorus concentration of the high P hot metal exceeds 4% by mass, the phosphoric acid concentration in the slag exceeds (-4α ² + 23α-4)% by mass, and only phosphate slag with a low fertilizer effect can be obtained. The phosphorus concentration of the high P hot metal is 4% by mass or less.

The basicity of the flux (the mass concentration ratio of CaO and SiO ₂ ) is 0.8 to 1.5. When the basicity of the flux is less than 0.8, dephosphorization cannot be performed even in high phosphorus hot metal, and the phosphoric acid concentration in the slag does not reach 8% by mass, so the basicity of the flux is 0. .8 or more.

On the other hand, if the basicity of the flux exceeds 1.5, the phosphoric acid concentration of the slag is still low (P ₂ O ₅ <5% by mass) at the initial stage of the dephosphorization treatment. The chemical properties become worse. Therefore, if the temperature of the slag is increased in order to improve hatchability, the dephosphorization ability of the slag is lowered, so the basicity of the flux needs to be 1.5 or less.

The concentration of iron oxide in the flux is 10% by mass or more in terms of Fe. When the iron oxide in the flux is less than 10% by mass in terms of Fe, when the phosphoric acid concentration of the slag is low (P ₂ O ₅ <5% by mass), it is not possible to obtain a slag with good hatchability, Since dephosphorization does not proceed because the oxygen potential is low, the iron oxide in the flux needs to be 10% by mass or more in terms of Fe. More preferably, it is 14 mass% or more.

  Dephosphorization is performed in the range of 1200 to 1450 ° C. at the temperature at the end of the treatment. If the temperature at the end of the treatment is less than 1200 ° C., it is difficult for the added flux to melt and not sufficiently melt, so that the temperature at the end of the dephosphorization treatment needs to be 1200 ° C. or higher. Preferably it is 1250 degreeC or more.

  On the other hand, if the temperature at the end of the dephosphorization process exceeds 1450 ° C., the transfer of P to the slag decreases due to the equilibrium of the dephosphorization reaction, and the melting loss of the inner wall refractory of the processing container also increases. The temperature at the end of the treatment needs to be 1450 ° C. or lower. Preferably it is 1400 degrees C or less.

  The temperature during the dephosphorization treatment is not limited to when the dephosphorization treatment is completed, and is preferably performed in the range of 1200 to 1450 ° C. for the reason described above. This temperature can be adjusted by blowing oxygen into the hot metal, but supply of a heat source may be used in combination as appropriate.

When the phosphoric acid concentration in the slag reaches 5% by mass or more during the dephosphorization process, the secondary material (CaO-containing substances such as quick lime and slag produced by the dephosphorization S01 and decarburization S02) To adjust the basicity of the slag to 1.5 or more and 3.0 or less, and finally, “basicity α expressed by weight concentration ratio of CaO and SiO ₂ is 1.5 or more and 3.0 or less. And dephosphorization slag containing P ₂ O ₅ in an amount of 8% by mass or more (−4α ² + 23α-4)% by mass and iron oxide in an amount of 5% by mass to 25% by mass in terms of Fe.

  The determination of the phosphoric acid concentration in the slag and the addition of the secondary material can be performed as follows, for example. However, if the component of the hot metal to be dephosphorized and the composition and amount of the flux to be added are known, it can be easily judged with reference to the reaction progress in the past dephosphorization, It does not necessarily require hot metal or slag sampling during the process.

  (a) The hot metal is sampled and analyzed rapidly once in the middle, and the mass balance is calculated from the hot metal concentration and the flux addition amount to calculate the phosphoric acid concentration. If the phosphoric acid concentration is 5% by mass or more, a secondary material (lime) is added. If the phosphoric acid concentration is less than 5% by mass, dephosphorization is continued, and the hot metal is sampled again to calculate the phosphoric acid concentration.

  (b) The slag is sampled once in the middle, and the slag composition is quickly analyzed by XRF or the like. If the phosphoric acid concentration is 5% by mass or more, a secondary material (lime) is added. If the phosphoric acid concentration is less than 5% by mass, dephosphorization is subsequently performed, slag is sampled again, and the phosphoric acid concentration is calculated.

  The addition of this secondary material may be performed after the time point when the phosphoric acid concentration has been determined to be 5% by mass or more, but considering the ease of melt hatching of this secondary material and the stability of the dephosphorization treatment, It is preferable to finish the addition by 3 minutes before finishing the dephosphorization treatment.

Having described a method for manufacturing the molten slag (raw slag of the present invention the fertilizer raw materials) for cooling in the present invention production process, in the production method, performed operations in low basicity, further liquid by P ₂ O ₅ Since the effect of lowering the phase line temperature (melting point) is used, it is possible to obtain a slag with good hatchability at a temperature (1200 to 1450 ° C.) lower than that of the Thomas Steelmaking method (non-patent document 1 (processing temperature 1550 ° C. or higher)). is there.

  In the method of the present invention, slag suitable for fertilizer having a high phosphoric acid concentration and hot metal having a P concentration that does not hinder normal steel product production are produced from the hot P concentration hot metal, and therefore the method of the present invention is wasteful in processing contents. This is a rational process.

  Moreover, since hot metal is produced from high phosphorus hot metal instead of molten steel, decarburization reaction hardly occurs. As a result, it is possible to operate with a simple dephosphorization facility such as a pot without the need for a converter or exhaust gas facility. Therefore, the slag used as the raw material for the fertilizer raw material according to the present invention can be manufactured at a low cost.

  After producing the dephosphorization slag by performing the dephosphorization treatment S13 as described above, in order to produce a phosphate fertilizer raw material with a high fertilizer effect from the slag, when discharging the slag after the dephosphorization treatment from the processing furnace In addition, it is necessary to control the cooling rate of the slag to increase the amount of soluble phosphoric acid in the phosphate fertilizer raw material.

As a result of the dephosphorization treatment described above, the phosphate fertilizer raw material produced according to the present invention has a basicity α expressed by a weight ratio of CaO to SiO ₂ of 1.5 to 3.0 and P ₂ O ₅ of 8 Mass% or more (-4α ² + 23α-4) mass% or less, iron oxide is 5 mass% or more and 25 mass% or less in terms of Fe, and this slag is appropriately cooled from the temperature after dephosphorization to solidify Ca ₃ (PO ₄ ) ₂ —Ca ₂ SiO ₄ solid solution phase, 5CaO · SiO ₂ · P ₂ O ₅ phase, and 7CaO · 2SiO ₂ · P ₂ O ₅ phase (hereinafter referred to as three mineral phases). (Sometimes collectively referred to as “solid solution phase.”), The total concentration of one or more of them is 28% by mass or more.

When performing the dephosphorization treatment S13 (see FIG. 1), the basicity α of the molten slag in the treatment container at the end of the dephosphorization treatment S13 is 1.5 or more and 3.0 or less, and P ₂ O ₅ is 8 One of the reasons why the dephosphorization conditions were adjusted so that the iron oxide was 5% by mass or more and 25% by mass or less in terms of Fe was not less than 4% by mass (−4α ² + 23α-4)% by mass. This is because it is suitable for manufacturing under the phosphorus treatment conditions.

  However, the molten slag whose composition and temperature are adjusted in this way is divided by the time until the temperature reaches 600 ° C. until the temperature reaches 600 ° C. from 1200 to 1450 which is the temperature at the end of the treatment. When it is controlled to be 10 ° C./min or more, preferably 30 ° C./min or more, and cooled by the numerical value obtained (hereinafter sometimes referred to as “cooling rate to 600 ° C.”), The present inventors have found that a phosphate fertilizer raw material having a high fertilizer effect can be obtained as described below, together with the method for adjusting the dephosphorization treatment conditions described above.

  Therefore, it is another reason why the conditions for performing the dephosphorization treatment S13 are determined as described above, aiming for consistency with this finding.

Hereinafter, from the viewpoint of making a phosphate fertilizer raw material with a high fertilizer effect, precipitation of a solid solution phase is promoted from the phosphorus-containing mineral phase of the phosphoric acid-containing slag, and the Ca ₃ (PO ₄ ) ₂ phase (hereinafter referred to as “C ₃ P phase”). )), The reason why the component composition is limited, the reason why the basicity, the P ₂ O ₅ concentration and the iron oxide concentration are limited, and the phosphoric acid after dephosphorization treatment. The reason for limiting the cooling rate from the molten slag when producing the containing slag will be described.

First, the reason for promoting the precipitation of the solid solution phase and suppressing the precipitation of the C ₃ P phase will be described.

  The slag raw material having the composition shown in Table 1 is produced by dephosphorization treatment S13 (see FIG. 1). The slag generated by the dephosphorization treatment S13 is cooled by controlling the cooling rate from 1200 to 1450 ° C. to 600 ° C., which is the slag temperature at the end of the treatment, to 10 ° C./min or more. After the temperature reached room temperature of about 25 ° C., the phosphorus-containing mineral phase in the sample was confirmed by XRD, SEM or the like.

In some slag samples, a glass phase was confirmed in addition to the crystalline phase. The glass phase was confirmed to contain phosphorus. On the other hand, the crystal phase could be classified into three mineral phases: phosphate phase, silicate phase, and FeO phase. There were two types of phosphate phases: C ₃ P phase and solid solution phase. The results are summarized in Table 1.

It was found that the mineral phase in which phosphorus, which is an important part as a phosphate fertilizer, is present (hereinafter sometimes referred to as “phosphorus-containing mineral phase”) is a glass phase, a C ₃ P phase, and a solid solution phase. ○ in Table 1 indicates that it is a major mineral phase, and Δ means a minor mineral phase or a minor mineral phase. The C ₃ P phase and the solid solution phase which are crystal phases are not precipitated at the same time, and when the C ₃ P phase or the solid solution phase is precipitated, the glass phase may be precipitated at the same time.

From the results of separate investigation, (a) the soluble phosphoric acid ratio of the C ₃ P phase, glass phase, and solid solution phase has an order, and (b) the soluble phosphorus in the order of C ₃ P phase << glass phase <solid solution phase. It is known that the acid ratio increases, (c) the solid solution phase is the phase having the highest soluble phosphoric acid ratio, and the C ₃ P phase is the phase having the lowest soluble phosphoric acid ratio.

Therefore, in order to increase the fertilizer effect in slag, that is, the concentration of soluble phosphoric acid, it was necessary to suppress the precipitation of the C ₃ P phase as much as possible and to actively precipitate the solid solution phase.

That is, the present inventors make dephosphorization slag (phosphoric acid fertilizer raw material) with a high soluble phosphoric acid concentration by suppressing the precipitation of the C ₃ P phase and promoting the precipitation of the solid solution phase in the phosphorus-containing mineral phase. He knew that he could do it.

The phosphate fertilizer raw material contains CaO, SiO ₂ , P ₂ O ₅ , and iron oxide as main components, and the total of each component is preferably 60% by mass or more. If the total amount of each component is less than 60% by mass, components other than the above components and phosphoric acid may form a compound, and the generation of the phosphoric acid-containing mineral phase may not be controlled. It is suitable that the total is 60 mass% or more. Preferably it is 70 mass% or more.

  However, the concentration of iron oxide is expressed as the Fe concentration in the sample, and hereinafter referred to as “t.Fe concentration”.

The present inventors examined the conditions under which the solid solution phase is most stably precipitated. In FIG. The Fe concentration is 10% by mass, the MnO concentration is 5% by mass, the MgO concentration is 5% by mass, the Al ₂ O ₃ concentration is 3% by mass, and the molten slag is 1200 to 1450 which is the temperature after the dephosphorization treatment S13. The relationship between the phosphoric acid concentration and the basicity and the phosphorus-containing mineral phase when the cooling rate from 10 ° C. to 600 ° C. is controlled to be 10 ° C./min or higher is shown.

That is, FIG. 2 shows the basicity dependence and the P ₂ O ₅ concentration dependence of the phosphorus-containing mineral phase. ○ indicates a case where a solid solution phase is precipitated, and × indicates a case where a C ₃ P phase is precipitated. When the basicity α (= CaO / SiO ₂ ) is 1.5 or more and 3.0 or less, a solid solution phase is precipitated. Therefore, in order to enhance the fertilizer effect, the basicity α needs to be 1.5 or more and 3.0 or less.

Basicity α is 1.5 or less, or, if greater than 3.0, the fertilizer effect decreases in precipitation C ₃ P phase. Therefore, during the dephosphorization treatment, the amount of flux such as quick lime and SiO _{2 to be} added is adjusted, and the basicity α of the slag is adjusted to 1.5 or more and 3.0 or less.

  When the abundance ratio of the solid solution phase in the slag having a basicity α of 1.5 or more and 3.0 or less with respect to the total slag mass is measured by SEM, the phosphoric acid concentration is 8 mass% or more and the solid solution phase is 28 mass% or more. Was confirmed.

Next, the reason why the upper limit of the phosphoric acid concentration is limited by a secondary expression of basicity α will be described. As shown in FIG. 2, even when the basicity α is in the range of 1.5 to 3.0, when the phosphoric acid concentration is increased to a certain extent, the C ₃ P phase starts to precipitate. Since it was experimentally confirmed that the phosphate concentration at which the C ₃ P phase begins to precipitate increases with a quadratic curve when the basicity α increases, the phosphate concentration that increases with a quadratic curve is set to (−4α ² + 23α-4).

That is, when the basicity is kept constant and the phosphoric acid concentration is increased from 0% by mass, a solid solution phase is precipitated from the condition of 8% by mass, and the phosphoric acid concentration becomes (−4α ² + 23α-4). In the region of mass% or less, the phosphorus-containing mineral phase is a solid solution phase, but when it exceeds (−4α ² + 23α-4) mass%, the phosphorus-containing mineral phase becomes a C ₃ P phase.

Therefore, if the phosphorus-containing mineral phase of the phosphate fertilizer raw material is a C ₃ P phase, the fertilizer effect is reduced, so the phosphoric acid concentration is 8 mass% or more (−4α ² + 23α-4) mass% or less. Therefore, it is necessary to adjust the amount of flux added to the slag during the dephosphorization treatment so that the phosphoric acid concentration is 8 mass% or more (−4α ² + 23α-4) mass% or less.

When the phosphoric acid concentration is less than 8% by mass, the phosphoric acid concentration is low and the phosphorus-containing mineral phase is not a solid solution phase but a C ₃ P phase. As a result, the amount of phosphoric acid fertilizer used becomes large, and the commercial value as a fertilizer decreases.

  t. Fe concentration shall be 5 mass% or more and 25 mass%. Among the samples shown in Table 1, the degree of crystallinity and t. In a sample having a basicity α of 1.5 or more and 3.0 or less and a phosphoric acid concentration of 12% by mass or more and 20% by mass or less. The relationship of Fe concentration is shown in FIG.

  t. When the Fe concentration is less than 5% by mass, a glass phase is present in the slag. When the Fe concentration is 5% by mass or more, the crystallinity is 100% and the crystal phase is present. Iron oxide is considered to exist as FeO and is a basic oxide and a component that promotes crystallization of slag. Therefore, it can be understood that 5% by mass or more of iron oxide is necessary to precipitate the solid solution phase which is a crystalline phase.

FIG. 4 shows the concentration of the solid solution phase in the sample and t. Relationship between Fe concentration, C ₃ P phase existing concentration and t. The relationship of Fe concentration is shown. t. When the Fe concentration is in the range of 5% by mass or more and 25% by mass or less, a solid solution phase is precipitated, and t. When the Fe concentration exceeded 25% by mass, a C ₃ P phase was precipitated.

  From this result, in order to precipitate the solid solution phase, the amount of oxygen blown during the dephosphorization treatment is adjusted, and t. It can be seen that the Fe concentration needs to be 5 mass% or more and 25 mass% or less.

  When manufacturing a phosphate fertilizer raw material, it is necessary to control and cool the 1200 to 1450 degreeC molten slag adjusted to the said composition so that the cooling rate to 600 degreeC may be 10 degreeC / min or more. If the temperature of the molten slag is less than 1200 ° C., the slag may not be completely melted, and in that case, the fertilizer effect as a phosphate fertilizer does not appear.

  When the temperature of the molten slag exceeds 1450 ° C., a little time elapses until the temperature at which the molten slag begins to solidify. Therefore, the cooling rate control for adjusting the precipitation phase is performed for such time as the molten slag. Inclusion in the period is inappropriate.

Molten slag basicity, phosphoric acid concentration, t. Even when the Fe concentration is within the above-described range, it is not always possible to suppress the precipitation of the C ₃ P phase. This is because the cooling rate for cooling the molten slag is an important factor for suppressing the precipitation of the C ₃ P phase.

The inventors of the present invention have a basicity α: 1.6, Al ₂ O ₃ : 3% by mass, MgO: 9% by mass, P ₂ O ₅ : 18% by mass, t. Control of a molten slag sample having an Fe concentration of 6 mass% so that the cooling rate to 600 ° C. is 1 ° C./min, 5 ° C./min, 10 ° C./min, 30 ° C./min, and 50 ° C./min. The sample was then cooled, and the concentration of the phosphorus-containing mineral phase in the sample was examined.

  It was decided that the cooling rate between the temperature after the dephosphorization process to 600 ° C. was controlled to be equal to or higher than the predetermined cooling rate until reaching 600 ° C. This is because the phase is determined within the temperature range, and in the temperature region below 600 ° C., the mineral phase does not change. The survey results are shown in FIG.

As shown in FIG. 5, when the cooling rate is 1 ° C./min and 5 ° C./min, only the C ₃ P phase is precipitated, and when the cooling rate is 10 ° C./min, 30 ° C./min, and 50 ° C./min. Only the solid solution phase precipitated.

  From this result, in order to increase the existing concentration of the solid solution phase to 28% by mass or more, the above-mentioned numerical value until reaching 600 ° C. is used by using water cooling or a method of pouring molten slag into a steel plate and quenching. It turns out that it is necessary to control and cool so that it may become 10 degrees C / min or more. Preferably it is 30 degrees C / min or more.

  As mentioned above, although the manufacturing method and phosphoric acid containing slag of phosphoric acid containing slag were demonstrated, this invention is not limited to the said description, In the range which does not deviate from the technical idea of invention, it can change suitably.

  In addition, in the process of manufacturing the phosphoric acid containing slag shown in FIG. 1, although it demonstrated that the high phosphorus hot metal obtained from the converter dephosphorization slag was dephosphorized and manufactured phosphoric acid containing slag, manufacturing phosphoric acid containing slag was manufactured. Is not limited to this description.

For example, the hot metal produced in the blast furnace may be manufactured by dephosphorization. In addition, quick lime, SiO ₂ , P ₂ O ₅ , iron oxide and the like are mixed as starting materials so as to enter the above composition range, and then melted and cooled at the cooling rate to produce a phosphate fertilizer raw material. Also good.

  Next, examples of the present invention will be described. The conditions in the examples are one example of conditions used for confirming the feasibility and effects of the present invention, and the present invention is based on these one example conditions. It is not limited. The present invention can adopt various conditions as long as the object of the present invention is achieved without departing from the gist of the present invention.

(Example)
The basicity, which is an index indicating the mass ratio of CaO and SiO _2, of hot metal having a phosphorus concentration in the hot metal of 0.5 to 4 mass% and a C concentration of 3 to 5 mass%. And the iron oxide concentration is t. A flux containing 10% by mass or more in Fe concentration was used, and oxygen was blown to perform a dephosphorization treatment in which the temperature at the end of the treatment was in the range of 1200 ° C. to 1450 ° C.

In the dephosphorization process, a slag after a general steelmaking refining process was further added as a secondary material within 2 minutes from the time when it was determined that the phosphoric acid concentration in the slag became 5 mass% or more. By this operation, the basicity α which is the mass ratio of CaO and SiO _{2 in} the final slag is adjusted to 1.5 or more and 3.0 or less, and the phosphoric acid concentration in the slag is adjusted to 8 to (−4α ² + 23α− 4) mass%, and t. The dephosphorization slag characterized by making Fe concentration into 5-25 mass% was able to be manufactured stably.

The slag contained 60% by mass or more in total of CaO, SiO ₂ , P ₂ O ₅ , and iron oxide (Fe conversion).

  At this time, the hot metal components produced at the same time had a phosphorus concentration of 0.1 to 0.3% by mass and a C concentration of 3 to 4% by mass, so they were mixed with ordinary hot metal discharged from the blast furnace. We were able to use it for the usual converter steelmaking process.

  Further, the dephosphorization slag produced by the above dephosphorization treatment is mainly cooled to 600 ° C. so that the cooling rate is 10 ° C./min, and the abundance ratio of the solid solution phase of the slag, The soluble phosphate rate and crystallinity were investigated. The results are shown in Table 2 in comparison with the examples carried out while satisfying the requirements according to the present invention and the comparative examples carried out without satisfying some of the requirements.

  The soluble phosphoric acid ratio was evaluated by evaluating the soluble phosphoric acid ratio of 0.6 or more as ◎, ○, and less than 0.5 as x.

In the slag samples of Examples 1 to 9 having a cooling rate of 10 ° C./min, the basicity is 1.5 or more and 3.0 or less, and the phosphoric acid concentration is 8 mass% or more (−4α ² + 23α-4) mass% or less. T. The Fe concentration is 5% by mass or more and 25% by mass or less, and the solid solution phase existing concentration is 28% by mass or more with respect to the total slag mass.

In the slag samples of Comparative Examples 1 to 8, since the basicity α was as low as less than 1.5 and the phosphoric acid concentration exceeded (−4α ² + 23α-4) mass%, in the slag sample of Comparative Example 9, Basicity α is as low as less than 1.5, t. Since the Fe concentration was as high as more than 25% by mass, in the slag sample of Comparative Example 10, since the basicity was higher than 3.0, the solid solution phase did not precipitate.

In the slag sample of Comparative Example 11, the phosphoric acid concentration is lower than 8% by mass, and in the slag sample of Comparative Example 12, the phosphoric acid concentration is higher than (−4α ² + 23α-4)% by mass, so that the solid solution phase does not precipitate. It was. In the slag sample of Comparative Example 13, t. When the Fe concentration is lower than 5% by mass, a glass phase is obtained. In the slag samples of Comparative Examples 14 and 15, t. Since the Fe concentration was higher than 25% by mass, no solid solution phase was precipitated.

  In the slag sample of Comparative Example 13, the cooling rate was less than 10 ° C./min, so no solid solution was precipitated.

  When Examples 6 and 10 having the same composition and different cooling rates are compared with Comparative Example 16, when the cooling rate up to 600 ° C. is set to 10 ° C./min or more, the solid solution phase is 28% by mass or more. It was confirmed that the concentration of the solid solution phase was higher when the cooling rate to 600 ° C. was increased to 30 ° C./min.

In the examples in which the requirements according to the present invention were implemented including the control of the cooling rate, the Ca ₃ (PO ₄ ) ₂ —Ca ₂ SiO ₄ solid solution phase, 5CaO. Suitable as a raw material for phosphate fertilizer, with the total concentration of one or more of the SiO ₂ · P ₂ O ₅ phase and 7CaO · 2SiO ₂ · P ₂ O ₅ phase being 28% by mass or more It was confirmed that the product was manufactured.

  As described above, according to the present invention, dephosphorization slag suitable for dephosphorizing hot metal having a high phosphorus concentration in the hot metal and using it as a raw material for phosphate fertilizer is not premised on the use of converter equipment. It is possible to provide a method for producing a phosphate fertilizer raw material by appropriately cooling the slag appropriately and at a low cost. Therefore, the present invention has high applicability in the steel industry and the plant breeding industry.

Claims (2)

The hot metal having a phosphorus concentration of 0.5 to 4% by mass in the hot metal has a basicity of 0.8 to 1.5 as an index indicating the mass ratio of CaO and SiO ₂ and an iron oxide concentration of t. A flux containing 10% by mass or more in Fe concentration is added and oxygen is blown to perform a dephosphorization treatment at a temperature at the end of the treatment in a range of 1200 ° C. or higher and 1450 ° C. or lower,
After the phosphoric acid concentration in the slag reaches 5% by mass or more during the dephosphorization treatment, by adding a secondary material, the basicity α which is the mass ratio of CaO and SiO _{2 in} the final slag is obtained. The phosphoric acid concentration in the slag is adjusted to 8 to (-4α ² + 23α-4) mass%, and the iron oxide (Fe conversion) concentration is adjusted to 5 to 25 mass%. The manufacturing method of the dephosphorization slag characterized by the above-mentioned. The dephosphorization slag produced by the method according to claim 1 is set to a temperature drop amount of 600 ° C. from 1200 to 1450 ° C., which is a temperature at the end of the dephosphorization treatment, to 600 ° C. Cooling at a cooling rate of 10 ° C / min or more by a numerical value divided by the time to reach,
Total of existing concentrations of one or more of Ca ₃ (PO ₄ ) ₂ -Ca ₂ SiO ₄ solid solution phase, 5CaO · SiO ₂ · P ₂ O ₅ phase, and 7CaO · 2SiO ₂ · P ₂ O ₅ phase The manufacturing method of the phosphate fertilizer raw material whose is 28 mass% or more.

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