JP4913023B2 - Slag manufacturing method - Google Patents

Description

The present invention has a high content ratio of 3CaO · P ₂ O ₅ phase and / or 4CaO · P ₂ O ₅ phase (hereinafter sometimes collectively referred to as “CP phase”) for use as a phosphorus resource. The present invention relates to a method for producing slag.

  Usually, hot metal produced from a blast furnace contains about 0.1% by mass of phosphorus. Therefore, among steelmaking slag generated in the hot metal refining process, the converter slag and the hot metal dephosphorization slag contain 1 to 3 mass% of phosphoric acid. Phosphoric acid is mainly used for fertilizers, etc., but in Japan it depends on imports and is an important strategic resource. Therefore, in the past, efforts have been made to make phosphoric acid resources from steelmaking slag.

  As a conventional method of recovering phosphoric acid from steelmaking slag, the separation and recovery method of useful components utilizing the property that the converter slag separates into a phase with a high phosphorus content and a phase with a low phosphorus content during the cooling and solidification process ( For example, refer to Patent Document 1), and a method of separating the phosphorus content in the separated liquid by the difference in specific gravity after pulverizing the converter slag (for example, refer to Patent Document 2) has been proposed.

  In addition, as a method of obtaining slag with high phosphorus concentration, a reducing agent is added to the molten steel slag on the molten metal to reduce it, and phosphorus and iron are transferred to the molten metal side, and then phosphorus is transferred into the slag. A method for taking out high phosphorus slag is proposed (for example, see Patent Document 3).

JP-A-53-54196 Japanese Patent Laid-Open No. 55-10092 JP 52-33897 A

  However, in the methods described in Patent Document 1 and Patent Document 2, it is difficult to recover phosphoric acid because phosphoric acid is strongly dissolved in the main phase.

  On the other hand, in the method described in Patent Document 3, a slag containing a large amount of other components such as FeO in addition to high concentration phosphoric acid having a phosphoric acid concentration exceeding 20% by mass is obtained and pulverized to be used for a phosphorous fertilizer. It is disclosed. However, a method for separating and recovering components such as FeO in slag has not been presented, and FeO or the like cannot be effectively utilized industrially.

  Therefore, in the present invention, the CP phase and the FeO phase are phase-separated in the slag, and the slag having a high content ratio of the CP phase is separated and recovered, and the slag mainly composed of the remaining FeO phase is separated and recovered as an iron source. It aims to provide a way to do.

  As a result of intensive research to solve the above problems, the present inventors obtained slag having a high phosphoric acid concentration by hot metal dephosphorization, then solidified the slag at an appropriate cooling rate, and pulverized and separated it. Thus, the slag having a high CP phase content and the slag having the FeO phase as a main component can be separated, whereby the slag having a high CP phase content can be recovered as a phosphorus fertilizer or a chemical raw material, and the FeO phase as a main component. The present inventors have found that slag to be recovered can be recovered as an iron source, and have completed the present invention based on this finding.

The gist of the present invention is as follows.
(1) a first step of concentration ratio of CaO and _P 2 _{O 5} to obtain a slag CaO _/ P 2 _{O 5} ≦ 5 and dephosphorization of molten pig iron, from the temperature at which the slag starts to solidify, the entire slag the range up to the solidification temperature, allowed to cool and solidify the average cooling rate is not more than 5 ° C. / min, crystallization of the 3CaO _· P 2 _{O 5} phase and / or 4CaO _· P 2 _{O 5} phase in said slag after solidification a second step of issued after grinding the slag after the second step, slag composed mainly of slag and FeO mainly composed of 3CaO _· P 2 _{O 5} phase and / or 4CaO _· P 2 _{O 5} phase And a third step of recovering slag mainly composed of 3CaO · P ₂ O ₅ phase and / or 4CaO · P ₂ O ₅ phase.
(2) The slag obtained in the first step is characterized in that the concentration ratio of SiO ₂ and P ₂ O ₅ is SiO ₂ / P ₂ O ₅ ≦ 1.5. Manufacturing method.
(3) The method for producing slag according to (1) or (2), wherein the hot metal dephosphorization slag generated by the dephosphorization treatment is reused when the hot metal is dephosphorized in the first step. .
(4) Before the first step, a reduction treatment step is performed in which a reduction carbon source is added to a reaction vessel charged with steelmaking slag and molten iron to reduce the slag after the reduction treatment. Further including
In the first step, the hot metal obtained in the reduction treatment step is dephosphorized, wherein the slag manufacturing method according to (1) or (2) is characterized.
(5) The method for producing slag according to (1) or (2), wherein in the first step, hot metal obtained by charging a substance containing phosphorus into a blast furnace is dephosphorized.
(6) Before the second step, after solidifying the slag obtained in the first step, the method further includes a step of reheating and melting the slag, (1) to (5) ) The manufacturing method of the slag in any one of.
(7) In the third step, as a method for separating and recovering the pulverized slag, at least one of sieving, magnetic ore flotation, and flotation is performed, and the 3CaO · P ₂ O ₅ phase and / or The method for producing slag according to any one of (1) to (6), wherein the slag is separated into slag mainly composed of 4CaO · P ₂ O ₅ phase and slag mainly composed of FeO.

  According to the present invention, slag having a high CP phase content can be obtained separately, and phosphoric acid can be separated and recovered effectively, and can be recovered as a phosphorus resource with high added value. Moreover, the slag which has a FeO phase as a main component can also be collect | recovered as an iron source.

  Exemplary embodiments of the present invention will be described below in detail with reference to the accompanying drawings. The present inventors examined a method for suitably separating and recovering slag having a high CP phase content and slag mainly composed of FeO phase from steelmaking slag.

  Specifically, paying attention to the difference in hardness between the CP phase and the FeO phase, the CP phase is pulverized more than the FeO phase by appropriately adjusting the crushing strength of the slag in which the CP phase and the FeO phase are grain-grown. Later particle size can be made relatively small, and by utilizing this difference in particle size, slag having a high CP phase content (CP phase is the main component) and slag having the FeO phase as the main component And found that it can be separated and recovered suitably. For this purpose, the slag composition should be in an appropriate range so that each of the CP phase and the FeO phase is generated, and an appropriate cooling rate should be set so that each of the CP phase and the FeO phase can be suitably grown. It turned out to be important.

  The present invention comprises the following three steps.

  First, the first step is a process of increasing the phosphoric acid concentration of the entire slag by recovering phosphorus in the hot metal as phosphoric acid in the slag by hot metal dephosphorization. Incidentally, hot metal dephosphorization means a process of dephosphorizing hot metal containing phosphorus.

From the experimental results described in the examples to be described later, the slag component obtained in the first step may be described as the mass concentration ratio CaO / P ₂ O ₅ (hereinafter referred to as “C / P”) of CaO and P ₂ O _5. It was found that the ratio of the CP phase contained in the entire slag increases significantly when the cooling rate is appropriately controlled in the second step described later. Here, the smaller the C / P, the more the proportion of the CP phase contained in the entire slag in the slag after cooling, so C / P ≦ 2, more preferably C / P ≦ 1.2. is there. However, since hot metal dephosphorization is impossible at C / P = 0, the lower limit value of C / P is set to more than zero.

  In addition, as a condition for satisfying C / P ≦ 5, for example, dephosphorization slag obtained when dephosphorizing ordinary blast furnace hot metal is reused in the dephosphorization process to increase the phosphoric acid concentration in the slag. / P ≦ 5 can be achieved. In order to achieve C / P ≦ 5, usually, the dephosphorization step can be carried out twice or more with the same slag. Further, as will be described in detail later, C / P ≦ 5 can be achieved by using a high phosphorus hot metal.

On the other hand, when C / P> 5, according to the test results of the present inventors, the CP phase contained in the entire slag in the slag even if the cooling rate is appropriately controlled in the second step described later. reduced the proportion of rapidly, it is hardly concentrated P ₂ O ₅ in the slag.

  Next, in the second step, the slag obtained in the first step is cooled and solidified at a suitable average cooling rate, and a CP phase and an FeO phase are grown in the slag.

  Here, it is important that the average cooling rate from the liquidus temperature to the solidus temperature is 5 ° C./min or less.

  In the cooling process, the slag is separated into a CP phase and an FeO phase, and each crystallizes. At this time, when the average cooling rate from the liquidus temperature to the solidus temperature is set to 5 ° C./min or less from the experimental results described in the examples described later, the slag is crushed in the third process described later. Furthermore, it has been found that the particle size of each phase can be grown to such an extent that a difference in particle size occurs between the CP phase and the FeO phase so as to be industrially separable. Thereby, it becomes possible to separate and recover the slag having a high CP phase content and the slag mainly composed of the FeO phase in the third step described later.

  The lower the average cooling rate, the better. However, 0 ° C./min means that cooling cannot be performed, and therefore 0 ° C./min is not included as the lower limit. On the other hand, as will be described in detail later, when it is rapidly cooled beyond 5 ° C./min, the grain growth of each phase becomes insufficient, and there is a difference in particle size between the CP phase and the FeO phase when pulverized in the third step described later. Since it is small, it is difficult to separate industrially.

  Since the liquidus temperature and the solidus temperature vary depending on the composition of the slag, it is desirable to investigate by conducting a heating / cooling test of the molten slag in advance.

  The liquidus temperature and solidus temperature are differential heats for examining changes in sample temperature over time during heating and cooling at a constant rate after heating and melting a certain amount of slag in an argon atmosphere. It can be examined by analysis.

  Control of the average cooling rate can be achieved by a method of suppressing heat dissipation from the slag with a holding container lined with a refractory having a heat insulating function, a method of controlling the cooling rate by heating the slag with a burner or the like.

  The slag gradually cooled in the second step is phase-separated in a state where the CP phase and the FeO phase are grown. Specific examples will be described later in Examples, but it has been confirmed that the CP phase and the FeO phase have different hardness, and the CP phase is more easily pulverized.

  Next, in the third step, the average cooling rate in the second step is set to 5 ° C./min or less, and the slag obtained by grain growth of the CP phase and the FeO phase is crushed with an appropriate load. Since the particle size is relatively larger than the phase, it can be separated and recovered into slag having a high CP phase content and slag mainly composed of FeO phase by a general separation method.

  Here, in the present invention, as a separation method for separating and recovering the pulverized slag, at least any one method of sieving, magnetic ore flotation, and flotation can be performed.

  In addition, slag with a high CP phase content ratio is a level in which components other than the CP phase are mixed at most about 30% by mass, that is, a slag having a CP phase content rate of approximately 70% by mass or more. As a phosphorus resource, it can be used without problems. Moreover, the slag which has a FeO phase as a main component is a slag whose FeO content is generally 70% by mass or more.

  Through the above process, a slag having a high CP phase content that can be used as a phosphorus resource can be obtained.

  In addition, slag having a high CP phase content can be used as phosphorous fertilizer, and phosphoric acid can be produced by decomposing it by adding an inorganic acid. Examples of inorganic acids include sulfuric acid and hydrochloric acid.

In this case, it is preferable that the SiO ₂ in the slag is as small as possible. When SiO ₂ is present, a 2CaO · SiO ₂ phase (hereinafter sometimes referred to as “CS phase”) is formed, and the CP phase and the CS phase form a solid solution. Since it is hardly soluble, it is difficult to produce phosphoric acid. According to the test results of the inventors that shown in Examples described later, the mass concentration ratio of SiO ₂ and _{P 2 O 5 SiO 2 / P} 2 O 5 ( hereinafter, may be referred to as "S / P".) In the case of S / P> 1.5, it was found that the elution of phosphoric acid by acid is low, and long-time elution is required to realize resource recycling as phosphoric acid.

  Therefore, it is desirable that S / P ≦ 1.5. Further, the lower the S / P, the better the elution of phosphoric acid, so S / P ≦ 1.2, more preferably S / P ≦ 0.9, and even more preferably S / P ≦ 0.5. It is. As described above, S / P is preferably as low as possible, and therefore 0 is included as the lower limit value.

  Incidentally, crude phosphoric acid produced by decomposition with an inorganic acid can be concentrated by vacuum filtration.

  In order to obtain a higher concentration of phosphoric acid, it is sent to an extraction step using an organic solvent, impurities are removed, and then the organic solvent containing phosphoric acid is brought into contact with water to concentrate the phosphoric acid transferred to the water. Thus, a high concentration of phosphoric acid can be obtained.

  Incidentally, as described above, it is important to obtain slag having a high phosphoric acid concentration in the first step. However, the phosphoric acid concentration in the slag obtained by ordinary hot metal dephosphorization is as low as about 1 to 3% by mass.

  Therefore, the present inventors have reused the hot metal dephosphorization slag used in the hot metal dephosphorization process to increase the phosphoric acid concentration in the slag and recover the phosphoric acid-containing phase. It has been found that possible slag can be produced. Here, “reuse” indicates that a plurality of dephosphorization processes are performed using the same slag. The hot metal dephosphorization slag refers to slag containing phosphoric acid, such as dephosphorization slag in the hot metal pretreatment or slag by ordinary hot metal blowing.

  A method for reusing the hot metal dephosphorization slag in the dephosphorization step will be specifically described.

  First, normal blast furnace hot metal is charged into a converter and dephosphorization is performed. And hot metal is discharged | emitted from a steel outlet hole, leaving the slag produced by the dephosphorization process in a converter furnace. Next, new hot metal is charged into the converter that left the slag, and an appropriate amount of auxiliary material is added to perform dephosphorization. After completion of the dephosphorization treatment, the hot metal is discharged from the steel outlet hole while leaving the slag in the furnace.

  By repeating the above method, dephosphorization treatment can be performed a plurality of times using the same slag.

  Incidentally, about the hot metal to be used for the second and subsequent dephosphorization treatment, it is preferable to perform a desiliconization reaction in advance and discharge the slag generated at that time. This is because, in the first dephosphorization treatment, it is necessary to hatch the quick lime introduced by silicon dioxide produced by the desiliconization reaction. This is because the amount of quicklime input increases and the phosphoric acid concentration in the finally obtained slag decreases.

The silicon concentration in the hot metal after pre-silicon removal is 0.1% by mass or less, preferably 0.05% by mass or less. This is because by reducing the silicon concentration in the hot metal, it is easy to produce slag with C / P ≦ 5 from the balance between the amount of quicklime input and the amount of phosphoric acid produced by dephosphorization. In addition, by reducing the silicon concentration in the hot metal, the amount of SiO ₂ produced during the dephosphorization process is sufficiently reduced, and it is easy to satisfy S / P ≦ 1.5.

  Moreover, the dephosphorization ability of slag decreases as the number of repetitions increases. Therefore, it is also possible to charge an appropriate amount of auxiliary raw materials including quick lime within a range where the phosphoric acid concentration in the slag is not lowered.

  Further, as another form in the first step, after steelmaking slag and hot metal are charged into a reaction vessel, a reduction carbon source is added to the reaction vessel to perform a reduction treatment, and the slag after the reduction treatment is discharged A method for dephosphorizing the obtained hot metal will be specifically described.

  When a reducing carbon source is added to steelmaking slag, oxides such as iron oxide and phosphoric acid contained in the steelmaking slag are reduced, and iron, phosphorus, and the like are generated. Therefore, when a reducing carbon source is added to the steelmaking slag in the refining vessel in which the hot metal is held, since phosphorus moves from the steelmaking slag into the hot metal, a high phosphorus hot metal, which is a hot metal having an increased phosphorus concentration, is obtained. Here, the high phosphorus hot metal indicates a hot metal having a higher phosphorus concentration than ordinary hot metal obtained by reducing iron ore in a blast furnace.

  A slag having a high concentration of phosphoric acid can be produced by adding a suitable amount of an auxiliary material to the high-phosphorus molten iron to cause a dephosphorization reaction. Then, dephosphorization slag with high phosphoric acid concentration can be obtained by discharging slag from the refining vessel. In order to satisfy C / P ≦ 5 for the slag obtained by the high phosphorus hot metal, the phosphorus concentration in the high phosphorus hot metal is 0.2% by mass or more, so that the range of dephosphorization conditions in a normal steelmaking process is reached. This is desirable because Moreover, it is preferable that the amount of CaO input per phosphorus concentration of 0.1% by mass in the high phosphorus hot metal is 11.5 kg / t or less.

  Here, as a reducing condition for setting the phosphorus concentration in the hot metal to 0.2 mass% or more, by reducing the steelmaking slag of 80 kg or more per 1 ton of hot metal, the phosphorus concentration in the hot metal after the treatment is 0.2. It can be exemplified that a mass% or more is obtained. Steelmaking slag is steelmaking slag obtained when dephosphorizing ordinary blast furnace hot metal, and the phosphoric acid concentration in the steelmaking slag is usually about 1 to 3% by mass. Moreover, coke, waste plastics, etc. can be used as a carbon source for reduction. Although the amount of the carbon source for reduction varies depending on the slag composition, the amount of carbon source for reduction of 100 kg to 200 kg per 1 ton of slag is a standard. Furthermore, since the reduction of phosphoric acid proceeds at higher temperatures, the hot metal temperature during the reduction treatment is desirably 1500 ° C. or higher.

  Further, in order to obtain a slag having a lower S / P, it is preferable to desiliconize the hot metal to be used for the production of high phosphorus hot metal in advance and discharge the generated slag by the method as described above. .

  Further, as still another form in the first step, a method for charging a molten iron obtained by charging a substance containing phosphorus into a blast furnace will be specifically described.

  Usually, the hot metal obtained by reducing iron ore in a blast furnace has a phosphorus concentration of about 0.1% by mass. On the other hand, if a substance containing phosphorus is charged into the blast furnace, the phosphorus concentration in the hot metal can be increased. At this time, in order for the slag obtained when the obtained hot metal is dephosphorized to satisfy C / P ≦ 5, the phosphorus concentration in the hot metal is desirably 0.2% by mass or more as described above. Moreover, it is preferable that the amount of CaO input per phosphorus concentration of 0.1% by mass in the high phosphorus hot metal is 11.5 kg / t or less.

  As the substance containing phosphorus, for example, steelmaking slag and sewage sludge can be used. Here, the sewage sludge contains 1 to 5% by mass of phosphorus per sludge dry mass.

  A slag with a high phosphoric acid concentration can be obtained by adding an appropriate amount of an auxiliary material to dephosphorylate the high phosphorus hot metal having a high phosphorus concentration.

  In the second step, the slag obtained in the first step may be solidified once, reheated to melt the slag, and then cooled and solidified. That is, once the slag obtained in the first step is solidified, it is reheated until the slag is totally melted, and then cooled and solidified again at an average cooling rate (for example, 5 ° C./min). The particle size of the CP phase and the FeO phase can also be grown by controlling to the following.

  In addition, in order to melt the whole slag at the time of reheating, it is important to sufficiently heat the slag to be equal to or higher than the solidification start temperature. Further, as a reheating method, burner heating, arc heating, induction heating, or the like can be selected.

  In the third step, when the pulverized slag is separated and recovered, it is preferable to perform sieving to separate and recover the slag having a predetermined particle size or less as the slag mainly composed of the CP phase.

  As described above, the CP phase and the FeO phase have different hardnesses, and the CP phase is more easily pulverized. Therefore, the slag obtained in the second step is pulverized with an appropriate load, so as to correspond to the pulverization load. Since the slag having a particle size of less than or equal to the particle size is mainly the CP phase and the slag exceeding the predetermined particle size is mainly the FeO phase, it can be sieved. That is, by sieving, it is possible to separate and collect slag having a high CP phase content as the sieving and slag mainly composed of the FeO phase as the sieving.

  The predetermined particle size at the time of sieving is appropriately determined according to the particle size distribution of the CP phase and the FeO phase after pulverization corresponding to the pulverization load.

  However, the particle size distribution of the CP phase and the FeO phase after pulverization is affected by the slag composition in the first step and the cooling conditions in the second step. For this reason, it is desirable to select an appropriate sieve size at the time of sieving by confirming it beforehand by an offline test. Incidentally, in order to carry out sieving at an industrially feasible speed, it is recommended that the operating conditions be such that the particle size of the FeO phase is more than 0.212 mm.

  In addition, if an excessively large load is applied during slag crushing, the CP phase and the FeO phase are pulverized to the same particle size, making it difficult to separate the CP phase and the FeO phase. Also, it is desirable to confirm by offline testing.

  As a pulverization method, pulverization with a ball mill, a hammer mill, or a jaw crusher is possible.

  Preferably, after the sieving, it is easier to recover the non-magnetized product as a CP phase-containing phase by performing magnetic separation. As a method of magnetic separation, dry and wet drum type magnetic separators can be used.

  Moreover, it becomes easier to collect the suspended matter as a CP phase-containing phase by performing flotation after sieving.

(Example 1: C / P setting basis)
First, the grounds for setting C / P ≦ 5 will be described.

  As a result of hot metal dephosphorization under various conditions, slag having a composition as shown in Table 1 was obtained. For these slags, the temperature at which the slag begins to solidify (hereinafter sometimes referred to as “liquidus temperature”) and the temperature at which the whole solidifies (hereinafter referred to as “solidus temperature”). ) Was measured by differential thermal analysis. The results are also shown in Table 1.

  As an index of the ratio of the CP phase, a suitable C / P range was examined by using the ratio of the area of the CP phase contained in the entire slag after cooling these slags. Specifically, these slags are cooled at an average cooling rate from the liquidus temperature to the solidus temperature of 3 ° C./min, and the area of the CP phase contained in the entire slag is measured by EPMA (Electron Probe Micro Analyzer). The ratio (hereinafter sometimes referred to as “CP phase area ratio”) was analyzed. The average cooling rate was adjusted with a Tamman furnace.

  The results are shown in FIG. In the slag satisfying C / P ≦ 5, the CP phase area ratio is 30% or more, whereas in the slag satisfying C / P> 5, the CP phase area ratio is remarkably lowered. Therefore, it was found that C / P ≦ 5 must be satisfied in order to efficiently generate the CP phase.

(Example 2: Composition and hardness of CP phase and FeO phase)
Next, the result confirmed about the composition and hardness of CP phase and FeO phase is demonstrated. FIG. 2 shows a schematic diagram of the structure when observed with EPMA using the slag of Invention Example 1 in Table 1 where C / P ≦ 5 as a representative sample. When the composition of each phase was analyzed in FIG. 2, it was confirmed that the white portion was the FeO phase and the shaded portion was the CP phase.

  The hardness of each phase of this slag was measured with a micro Vickers hardness tester in accordance with JIS Z 2244. The results are shown in FIG. 3, and it was confirmed that the CP phase and the FeO phase had different hardness, and the CP phase was more easily pulverized. Similarly, it is confirmed that there is a difference in hardness between the CP phase and the FeO phase in Invention Examples 2 to 5 in Table 1.

(Example 3: Setting basis of cooling rate)
Next, the grounds for setting the cooling rate of 5 ° C./min or less will be described.

  For the slag of Invention Example 1 in Table 1 where C / P ≦ 5, the slag was solidified at an average cooling rate from the liquidus temperature to the solidus temperature of 3 to 20 ° C./min. The average cooling rate was adjusted by heating the slag with a burner. Next, these slags were pulverized with a ball mill, and as a separation method, they were sieved with a sieve having an interval of 0.212 mm.

  The mass% of the CP phase in the slag under the sieve is defined as the CP phase content ratio. FIG. 4 shows the results of examining the CP phase content by conducting an EPMA analysis and a fluorescent X-ray analysis on each slag under the sieve.

  As shown in FIG. 4, when the average cooling rate was 5 ° C./min or less, a CP phase content of 70% or more was obtained. On the other hand, it was found that when the average cooling rate exceeds 5 ° C./min, the CP phase content is significantly reduced. Moreover, also about the invention examples 2-5 of Table 1, when the average cooling rate exceeds 5 degrees C / min similarly to the above, it has also confirmed that the CP phase content rate after a grinding | pulverization falls notably.

(Example 4: S / P setting basis)
Next, the basis for setting S / P ≦ 1.5 will be described.

  As a result of hot metal dephosphorization under various conditions, slag having a composition as shown in Table 2 was obtained. These slags were measured by differential thermal analysis for liquidus temperature and solidus temperature. The results are also shown in Table 2.

  The slag shown in Table 2 was cooled at an average cooling rate from the liquidus temperature to the solidus temperature of 3 ° C./min. The average cooling rate was adjusted by heating the slag with a burner. Next, these slags were pulverized with a ball mill, and as a separation method, they were sieved with a sieve having an interval of 0.212 mm.

  The slag under the sieve was subjected to a phosphoric acid elution test. Sulfuric acid having a concentration of 35% by mass was used as the acid, and the phosphoric acid concentration in the aqueous solution was analyzed after being kept at 80 ° C. for 2 hours. Further, assuming that the dissolution property of phosphoric acid was very good, a phosphate dissolution test from phosphate rock was performed under the same conditions as described above.

  The ratio of the phosphate concentration eluted from the slag under the sieve to the phosphate concentration eluted from the phosphate rock is defined as P-Index. As shown in FIG. 5, when S / P ≦ 1.5, the test result was able to approach a phosphoric acid concentration of 50% or more compared to the case of phosphate rock. On the other hand, in the case of S / P> 1.5, P-Index is remarkably low, and it can be seen that phosphoric acid has poor elution.

  As described above, when S / P ≦ 1.5, phosphoric acid extraction with an inorganic acid can be performed satisfactorily. Therefore, in order to further elute phosphoric acid from slag having a high CP phase content, S / P It is desirable that P ≦ 1.5.

(Example 5: Verification of influence of C / P and average cooling rate)
In this example, the effects of C / P and average cooling rate were verified. First, as a result of hot metal dephosphorization under various conditions, slag having a composition as shown in Table 3 was obtained. These slags were measured by differential thermal analysis for liquidus temperature and solidus temperature. All slags were heated to 1600 ° C. and then lowered to 800 ° C. When the temperature was lowered, the cooling rate was adjusted by heating with a burner. Each slag was analyzed by EPMA in order to examine the CP phase area ratio, which is the ratio of the CP phase contained in the entire slag before pulverization after cooling.

  These results are shown in Table 3. In the slag satisfying C / P ≦ 5, the proportion of the CP phase was 30% or more.

  Therefore, crushing and sieving were performed on the slags of Invention Examples 13 to 14 and Comparative Examples 3 to 4 in Table 3 that satisfy C / P ≦ 5. Each slag was pulverized with a ball mill and sieved with a sieve having an interval of 0.212 mm. Further, the sieving obtained by sieving was analyzed by EPMA and fluorescent X-ray analysis as slag having a high CP phase content.

  As a result, as shown in Table 3, in the slags of Invention Examples 13 to 14 where C / P ≦ 5 and the average cooling rate is 5 ° C./min or less, the CP phase is contained under 70% by mass under the sieve. It was possible to recover the slag with a high CP phase content. In Invention Examples 13 and 14 where C / P ≦ 5 and the average cooling rate is 5 ° C./min or less, the slag on the sieve contains 95.4 mass% and 97.2 mass% of the FeO phase, respectively. As a result, slag mainly composed of FeO phase could be recovered.

(Example 6: Verification of influence of S / P)
Next, in this example, in order to verify the influence of S / P, a phosphoric acid elution test from slag was performed.

  In Example 5, the slag of Invention Examples 13 to 14 in Table 3 in which the CP phase in the slag under sieving was 70% by mass or more was pulverized with a ball mill and sieved with 0.212 mm intervals. It was. The slag under the sieve obtained by sieving was subjected to a phosphoric acid elution test. Sulfuric acid having a concentration of 35% by mass was used as the acid, and the phosphoric acid concentration in the aqueous solution was analyzed after being kept at 80 ° C. for 2 hours. For comparison, a phosphoric acid elution test from phosphate rock was performed under the same conditions as described above.

  The concentration of phosphoric acid eluted from the phosphate rock and the concentration of phosphoric acid from the CP phase-containing phase were measured. The latter ratio with respect to the former is defined as P-Index. The results of this test are shown in Table 3. Inventive Example 13 where S / P ≦ 1.5 has a higher P-Index than Inventive Example 14, and was able to obtain a phosphoric acid concentration of 50% or higher compared to the case of phosphate rock.

(Example 7: Verification of the effect of cooling once solidified and then remelted)

  In this example, the following test was performed in order to verify the effect of cooling once solidified and then remelted. First, the slag of Invention Example 13 of Example 5 was rapidly cooled to room temperature and solidified. Then, the slag was solidified by again melting by burner heating and adjusting the burner output so that the average cooling rate from the liquidus temperature to the solidus temperature was 3 ° C./min.

  The slag after solidification was crushed with a ball mill and sieved with a sieve having an interval of 0.212 mm. As a result, the slag under the sieve contained 81.9% by mass of the CP phase. It was recovered as high slag. Further, the slag on the sieve contained 96.8% by mass of the FeO phase, and the slag mainly composed of the FeO phase could be recovered.

(Example 8: Verification of the effect when the hot metal dephosphorization slag is reused in the dephosphorization process)
In this example, the following test was performed in order to verify the influence when the hot metal dephosphorization slag is reused in the dephosphorization process. First, each time, the generated slag was repeatedly used for 340 tons of hot metal without discharging, and the dephosphorization reaction was performed three times in total.

  First, hot metal produced in a blast furnace with a phosphorus concentration of 0.11% by mass and a silicon concentration of 0.32% by mass (hereinafter referred to as “blast furnace hot metal”) was charged into the converter and subjected to dephosphorization treatment. It was.

Quick lime was added at a rate of 12 kg / ton per hot metal, the oxygen flow rate was 27500 Nm ³ / h, and the acid delivery time was 15 minutes. The hot metal temperature was 1300-1450 ° C. After completion of the dephosphorization treatment, only the molten iron was discharged from the outlet hole, and the dephosphorization slag was left in the converter furnace.

Next, a desiliconization hot metal having a phosphorus concentration of 0.11 mass% and a silicon concentration of 0.07 mass% was charged into the converter, and a second dephosphorization process was performed using the dephosphorization slag. . Quick lime was added at 2 kg / ton per hot metal, the oxygen flow rate was 27500 Nm ³ / h, and the acid delivery time was 15 minutes. The hot metal temperature was 1300-1400 ° C. After completion of the dephosphorization treatment, only the molten iron was discharged from the outlet hole.

Finally, a new desiliconization hot metal having a phosphorus concentration of 0.10 mass% and a silicon concentration of 0.06 mass% is charged into the converter, and a third dephosphorization process is performed using the dephosphorization slag. It was. Quick lime was added at 2 kg / ton per hot metal, the oxygen flow rate was 27500 Nm ³ / h, and the acid delivery time was 15 minutes. The hot metal temperature was 1300-1400 ° C. After completion of the dephosphorization treatment, only the molten iron was discharged from the outlet hole. The converter was tilted and dephosphorization slag was discharged into the waste pan.

  As shown in Table 4, the dephosphorization slag obtained by the above dephosphorization treatment was C / P = 3.8 and S / P = 0.9. Further, the liquidus temperature and the solidus temperature of this dephosphorization slag were examined by the method described in Example 5. The results are shown in Table 4, and were 1370 ° C. and 1180 ° C., respectively.

  This dephosphorization slag was subjected to burner heating, and the burner output was adjusted so that the average cooling rate from the liquidus temperature to the solidus temperature was 3 ° C./min.

  In order to examine the ratio of the CP phase contained in the whole slag before pulverization after cooling, analysis by EPMA was performed. The results are shown in Table 4. The CP phase area ratio was 34.1%.

  Further, the dephosphorized slag after solidification was pulverized with a ball mill and sieved with a sieve having an interval of 0.212 mm. The slag under the sieving obtained by sieving was analyzed by EPMA and fluorescent X-ray analysis. The results are shown in Table 4. The CP phase in the slag under the sieve was 80.2% by mass, and a slag having a high CP phase content was obtained. The slag on the sieve contained 97.4% by mass of FeO phase.

  When the slag with a high CP phase content obtained in this way was used as phosphorous fertilizer, it was found that it could be used without problems. Moreover, the slag which has a FeO phase as a main component could be used without a problem as an iron source.

  Phosphoric acid was extracted from the slag having a high CP phase content by the method described in Example 6. The results are shown in Table 4. The concentration of phosphoric acid in the extract was 66% compared to the case where phosphoric acid was extracted from the phosphate ore in Example 6, and the phosphoric acid extraction from the CP phase-containing phase was carried out industrially. It was possible.

(Example 9: Verification of influence in the case of performing reduction treatment before dephosphorization)
In this example, the following test was performed in order to verify the effect of performing the reduction treatment before dephosphorization. First, 340 tons of blast furnace hot metal having a phosphorus concentration of 0.11% by mass was dephosphorized and decarburized in a converter, and as a result, a steelmaking slag having a phosphoric acid concentration of 3.1% by mass was obtained. .

Further, 2 tons of blast furnace hot metal was charged into the refining furnace, and desiliconization treatment was performed at an acid feed rate of 180 Nm ³ / h. As a result, desiliconized hot metal having a Si concentration of 0.09 mass% was obtained. The hot metal temperature was 1250 to 1350 ° C. The desiliconized slag generated at this time was discharged from the furnace port of the refining furnace. Next, 2 tons of steelmaking slag in a molten state was charged into a refining furnace containing 2 tons of desiliconized molten iron, and 120 kg of carbon powder was added to reduce oxides in the slag. After completion of the reduction treatment, the smelting furnace was tilted to discharge the slag after the reduction treatment from the furnace port, leaving only the hot metal in the smelting furnace. As a result of the above reduction treatment, a high phosphorus hot metal having a phosphorus concentration of 1.2% by mass was obtained.

To this high phosphorus hot metal, 15 kg / ton of quick lime was added per hot metal to cause a dephosphorization reaction. Here, in order to promote hatching of quicklime, quicklime was added in three times. The oxygen flow rate was 150 Nm ³ / h, and the acid delivery time was 35 minutes. The hot metal temperature was 1300-1450 ° C. After completion of the dephosphorization treatment, the smelting furnace was tilted, and the dephosphorization slag was discharged into the waste pan. As a result, as shown in Table 5, dephosphorization slag having C / P = 1.2 and S / P = 0.15 was obtained.

  The liquidus temperature and solidus temperature of this dephosphorization slag were examined by the method described in Example 1. The results are shown in Table 5 and were 1210 ° C. and 970 ° C., respectively.

  This dephosphorization slag was subjected to burner heating, and the burner output was adjusted so that the average cooling rate from the liquidus temperature to the solidus temperature was 3 ° C./min.

  In order to examine the proportion of the CP phase contained in the entire slag before pulverization after cooling, analysis by EPMA and fluorescent X-ray analysis were performed. The results are shown in Table 5, and the CP phase area ratio was 60.3%.

  Further, the dephosphorized slag after solidification was pulverized with a ball mill and sieved with a sieve having an interval of 0.212 mm. The slag under the sieve obtained by sieving was analyzed by EPMA. The results are shown in Table 5. The CP phase in the slag under the sieve was 83.1% by mass, and a slag having a high CP phase content was obtained. The slag on the sieve contained 96.8% by mass of FeO phase.

  When the slag with a high CP phase content obtained in this way was used as phosphorous fertilizer, it was found that it could be used without problems. Moreover, the slag which has a FeO phase as a main component could be used without a problem as an iron source.

  Phosphoric acid was extracted from the slag having a high CP phase content by the method described in Example 6. The results are shown in Table 5. The concentration of phosphoric acid in the extract is 81% as compared with the case where phosphoric acid is extracted from the phosphate ore in Example 6, and the phosphoric acid extraction from the CP phase-containing phase can be industrially performed.

(Example 10: Verification of influence by separation method of slag)
In this example, the effect of the separation method was verified. First, after the slag of Invention Example 13 was pulverized with a ball mill, it was sieved as a separation method, and magnetic ore and flotation were used alone or in combination. Further, as a reference example, the slag of Invention Example 13 was only pulverized with a ball mill and was not separated.

  For sieving, sieves with an interval of 0.212 mm were used, and the undersieving was collected. In addition, a high-gradient magnetic separator was used for magnetic separation, and wet magnetic separation was performed with a magnetic field of 0.5 T to recover non-magnetic deposits. In the flotation, dodecylamine acetate was used as a surfactant, tannic acid and starch were used as an Fe flocculant, and pine ani was used as a foaming agent. In the flotation in this example, the pH was adjusted to 9-10, and the floated material was collected.

  The final recovered material after sieving as described above was analyzed by EPMA and fluorescent X-ray analysis. The results are shown in Table 6. As shown in Table 6, it can be seen that the CP phase in the recovered product contains 70 mass% or more by performing at least one separation method.

  As mentioned above, although preferred embodiment of this invention was described referring an accompanying drawing, it cannot be overemphasized that this invention is not limited to this example. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the claims, and these are naturally within the technical scope of the present invention. Understood.

It is a figure which shows an example of the relationship between C / P and CP phase area ratio. It is a schematic diagram which shows an example of the structure | tissue of CP phase and FeO phase in slag. It is a figure which shows an example of the Vickers hardness of CP phase and FeO phase. It is a figure which shows an example of the relationship between an average cooling rate and CP phase content rate. It is a figure which shows an example of the relationship between S / P and P-Index.

Claims (7)

A first step of concentration ratio of CaO and _P 2 _{O 5} to obtain a slag CaO _/ P 2 _{O 5} ≦ 5 and dephosphorization of hot metal,
The range from the temperature at which the slag begins to solidify to the temperature at which the entire slag solidifies is cooled and solidified at an average cooling rate of 5 ° C./min or less, and 3CaO · P ₂ O is solidified in the slag after solidification. _A second step of crystallizing the ₅ phase and / or the 4CaO.P ₂ O ₅ phase;
After grinding the slag after the second step, it is separated into the slag composed mainly of slag and FeO mainly composed of 3CaO _· P 2 _{O 5} phase and / or 4CaO _· P 2 _{O 5} phase, 3CaO · A third step of recovering slag mainly composed of P ₂ O ₅ phase and / or 4CaO · P ₂ O ₅ phase;
A method for producing slag, comprising: _{2. The} method for producing slag according to claim 1, wherein the slag obtained in the first step has a concentration ratio of SiO ₂ and P ₂ O ₅ of SiO ₂ / P ₂ O ₅ ≦ 1.5. .   The method for producing slag according to claim 1 or 2, wherein the hot metal dephosphorization slag produced by the dephosphorization treatment is reused when dephosphorizing the hot metal in the first step. Before the first step, further includes a reduction treatment step of adding a reduction carbon source to a reaction vessel charged with steelmaking slag and molten iron to reduce the slag after the reduction treatment. ,
The method for producing slag according to claim 1 or 2, wherein in the first step, the hot metal obtained in the reduction treatment step is dephosphorized.   The method for producing slag according to claim 1 or 2, wherein in the first step, the hot metal obtained by charging a substance containing phosphorus into a blast furnace is dephosphorized.   6. The method according to claim 1, further comprising a step of solidifying the slag obtained in the first step before the second step and then reheating and melting the slag. The manufacturing method of slag as described. In the third step, as a method of separating and recovering the pulverized slag, at least one of sieving, magnetic ore flotation, and flotation is carried out, and the 3CaO · P ₂ O ₅ phase and / or 4CaO · P is used. and separating the slag and FeO mainly composed of ₂ O ₅ phase and slag mainly method of slag according to any one of claims 1 to 6.