JP7147734B2 - Method for producing slag containing two liquid phases and method for producing artificial phosphate rock - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing slag containing two liquid phases and a method for producing artificial phosphate ore, and particularly to effectively obtain artificial phosphate ore by recycling steelmaking slag.

Phosphorus is used in a wide variety of applications, including agriculture, food, electronic parts, medicine, and the automobile industry. However, Japan is totally dependent on imports for phosphate rock, which is the raw material for phosphorus products.
The reserves of phosphate ore are limited in the countries, and the phosphate ore that will be used in the future will increase in the content of heavy metal elements, and the quality will continue to decline. Therefore, many efforts are being made to recover phosphorus from industrial by-products such as steelmaking slag containing phosphorus.

The following proposals have been made as methods for concentrating and separating phosphorus contained in steelmaking slag.
Patent Literature 1 proposes a method for producing artificial phosphate rock from industrial by-products. That is, into a melting furnace having a carbonaceous material packed layer, an iron material is charged and melted together with a phosphorus material, a silicon material, and a carbonaceous material, which are industrial by-products containing phosphorus such as dephosphorization slag. According to this method, since phosphorus contained in the dephosphorization slag is reduced and concentrated into molten iron, the molten iron with phosphorus is recovered and used as artificial phosphate ore.

The artificial phosphate rock obtained by the two-liquid separation of iron and slag in Patent Document 1 has a C concentration of about 2% by mass, a P concentration of about 10% by mass, and the balance being iron and impurities. However, this composition has the problem that the P concentration is low compared to the composition of phosphate rock, where P ₂ O ₅ >30% by mass and iron oxide (calculated as FeO)<4% by mass. In addition, although Patent Document 1 does not have a detailed description of the iron content, it is presumed that the iron content is high compared to the composition of phosphate rock because the remaining 88% by mass is iron and impurities.

In general, phosphate rock is often used as a raw material for phosphate, but when phosphate rock is decomposed with sulfuric acid, in the presence of iron, iron phosphate complexes, which are impurities, are formed and the viscosity increases, which is not preferable in terms of the manufacturing process. . Therefore, there remains a problem in using artificial phosphate rock, which is molten iron with a high iron content, as a substitute for phosphate rock in Patent Document 1. In addition, the technique of Patent Document 1 requires the use of a reducing agent for iron and phosphorus, such as a silicon raw material and a carbonaceous material, which also poses a problem of high cost.

Further, in Patent Document 2, phosphorus in hot metal is concentrated in slag by hot metal dephosphorization, and by controlling the cooling conditions, Ca ₃ (PO ₄ ) ₂ (hereinafter referred to as “C3P”) phase is added. A method of recovering slag with a high C3P phase content by solid-liquid separation into slag with a high ratio and slag mainly composed of an iron oxide phase, cooling and solidifying, and slag with a high content ratio of the C3P phase due to the difference in hardness of the slag having these two phases. is suggesting. However, the iron oxide concentration in the slag obtained by solid-liquid separation, cooling, and crushing recovery of the slag is 28% by mass, and Patent Document 2 has a problem that the iron oxide concentration is extremely high compared to phosphate rock. . Furthermore, in this method, a solid phase solidified from the liquid phase is mixed around the recovered solid phase, and solid-liquid separation down to the level of phosphate rock is difficult.

As described above, both Patent Document 1 and Patent Document 2 are methods of concentrating phosphorus in a compound before treatment into iron or slag, but the concentration of P ₂ O ₅ is lower than that of phosphate ore, The problem is that the iron oxide concentration is high.

Therefore, as shown in Patent Document 3, the inventors found that the P ₂ O ₅ content in CaO—FeO—P ₂ O ₅ —MgO or CaO—FeO—P ₂ O ₅ —SiO ₂ in the presence of hot metal is Utilizing the property that a phase with a high iron oxide content (high phosphorus content) and a phase with a low P ₂ O ₅ content and a high iron oxide content (high iron oxide phase) exhibit a two-liquid phase, artificial We have developed a technology that can recover a high-phosphorus-low-iron phase equivalent to phosphate rock. This technique is, for example, a technique for recovering a high phosphorus phase by reducing pretreated slag or dephosphorization slag, dephosphorizing the produced hot metal, heat-treating it, and separating it into two liquid phases.

However, in Patent Document 3, the melting temperature must be 1550 ° C. or higher to achieve two-liquid phase separation, and further heating is required after dephosphorization refining. It was an expensive method.

JP 2014-24695 A JP 2009-132544 A JP 2018-123047 A

In the conventional method of phosphorus concentration and separation by solid-liquid separation of steelmaking slag, the high iron phase adheres to the periphery of the finely dispersed solid phosphorus-rich phase (high phosphorus phase). In addition to the problem that the concentration is low and the iron oxide concentration is high, there is a problem that a high temperature equal to or higher than the dephosphorization refining temperature is required.

The present invention utilizes a technology for effectively separating steelmaking slag into multiple phases, including at least two liquid phases, even at relatively low temperatures, by specifying target slag components and process conditions, and the separation technology. It is an object of the present invention to provide a technology capable of advantageously recovering a high-phosphorus-low-iron phase equivalent to artificial phosphate rock.

By separating the phosphorus-enriched slag into multiple phases containing at least two liquid phases, the present inventors have increased the P ₂ O ₅ concentration to a value equivalent to phosphate ore in the component composition of the slag after melting, Also, a method for reducing the iron oxide concentration was investigated.
As a result, by controlling the properties of the steelmaking slag to be melted, specifically the component composition of the phosphorus-enriched slag, within a specific range and controlling the atmosphere during melting to a specific reducing atmosphere, a high P ₂ O ₅ concentration can be obtained. In addition, the inventors have found that the separation of a liquid phase with a low iron oxide concentration can be effectively achieved even at a relatively low temperature.
The present invention has been made based on the above findings, and the gist thereof is as follows.

1. 1. A method of separating the slag into multiple phases comprising at least two liquid phases in the molten state using a phosphorus-enriched slag, comprising:
As the phosphorus-enriched slag, steelmaking slag is reduced to obtain high-phosphorus hot metal, and then the high-phosphorus hot metal is dephosphorized with lime, and the component composition is at least CaO, P ₂ O ₅ , SiO ₂ , and iron oxide. and metallic iron, and P ₂ O ₅ > ₇ % by mass, SiO ₂ < ₁₀ % by mass (including ₀ % by mass), iron oxide ( FeO + Fe ₂ O ₃ : FeO conversion) and metallic iron (M. Fe: FeO conversion) using slag satisfying the sum > 15% by mass,
By holding the phosphorus-enriched slag at a temperature of 1400° C. or higher for 10 minutes or longer in an atmosphere having an oxygen partial pressure P _O2 of 10 ^−10.6 atm or lower,
In the molten state, in the upper layer, a high phosphorus phase of P ₂ O ₅ >25% by mass, the sum of iron oxide (FeO + Fe ₂ O ₃ : FeO conversion) and metallic iron (M.Fe: FeO conversion) ≦ 15% by mass, In the lower layer, a two-liquid phase of P ₂ O ₅ <20% by mass and a high iron phase with a sum of iron oxide (FeO+Fe ₂ O ₃ : FeO conversion) and metallic iron (M.Fe: FeO conversion) >15% by mass. A method for producing a slag comprising two liquid phases to form.

In the present invention, when the phosphorus-enriched slag is held at a temperature of 1400° C. or higher for 10 minutes or more, for example, when the preceding dephosphorization treatment is completed at a temperature of 1400° C. or higher, the phosphorus-enriched slag is The predetermined temperature can be maintained for the predetermined time without performing heat treatment again. Alternatively, when the preceding dephosphorization treatment is completed at a temperature of less than 1400° C., the phosphorus-enriched slag can be heat-treated again to the predetermined temperature and then held for the predetermined time.

2. The component composition includes MgO and manganese oxide, MgO < 16% by mass, and 15% by mass < iron oxide (FeO + Fe ₂ O ₃ : FeO conversion) and metallic iron (M.Fe: FeO conversion) and manganese oxide (MnO + MnO) ₂ : The method for producing a slag containing two liquid phases according to 1 above, further satisfying the condition that the sum of <80% by mass of MnO).

3. 3. The method for producing slag containing two liquid phases according to 1 or 2 above, wherein the temperature is less than 1540°C.

4. 4. The method for producing slag containing two liquid phases according to any one of 1 to 3 above, wherein the temperature is 1450° C. or less.

5. Only the upper layer is recovered in a molten state from the slag containing two liquid phases (hereinafter sometimes referred to as "two liquid phase slag") produced by the method according to any one of 1 to 4 above, and then the above A method for producing artificial phosphate rock, in which the recovered upper layer is cooled.

6. Slag containing two solid phases by cooling and solidifying the two-liquid-phase slag produced by the method according to any one of the above 1 to 4 while at least the upper layer and the lower layer are phase-separated (hereinafter referred to as " A method for producing artificial phosphate ore, which comprises obtaining the two-layered slag, mechanically breaking the two-layered slag, and then recovering only the solidified and broken upper layer.

According to the present invention, the composition of the phosphorus-enriched slag is controlled within a specific range, and the partial pressure of oxygen in the atmosphere during melting is controlled to a specific value or less. , a slag comprising at least two liquid phases, separated into an upper P ₂ O ₅ -rich and iron oxide-poor layer and a lower P ₂ O ₅ -rich and iron oxide-rich lower layer, can advantageously be obtained.
Further, according to the present invention, by separating and recovering only the upper phosphorus-rich phase from the slag containing at least two liquid phases, artificial phosphate rock having a composition comparable to that of natural phosphate rock can be obtained. Therefore, the artificial phosphate rock obtained by the present invention can be effectively used as a substitute material for natural phosphate rock, which is a phosphorus-containing substance for phosphoric acid raw materials, fertilizer raw materials, and chemical raw materials.
Furthermore, the lower layer of the phosphorus-enriched slag separated in the present invention is a high-iron phase, which is mainly composed of iron oxide. Therefore, there is also the effect that this lower layer can be separated and recovered and recycled as an iron source.

3 is a ternary phase diagram of CaO—FeO _n —P ₂ O ₅ at 1600° C. FIG. In the figure, the black □Δ indicates the phosphorus-enriched slag, the white □ indicates the inventive example of the present invention, and the white Δ indicates the comparative example. 1 is a flow chart illustrating a method for producing a slag containing two liquid phases according to the present invention; Fig. 2 is an SEM image showing a cross section of a phosphorus enriched slag separated into two liquid phases according to the invention and a cross section of a phosphorus enriched slag not separated into two liquid phases according to the invention;

Preferred embodiments of the present invention will be described in detail below.
The present inventors have studied a method of separating steelmaking slag into multiple phases including at least two liquid phases, namely, slag with a high P ₂ O ₅ content and slag mainly composed of iron oxide.
As a result, first of all, the slag to be used is phosphorus-enriched slag, and its component composition contains at least CaO, P ₂ O ₅ , SiO ₂ , iron oxide and metallic iron, and P ₂ O ₅ , SiO ₂ , iron oxide and metallic iron are respectively P ₂ O ₅ >7% by mass, SiO ₂ <10% by mass (including 0% by mass), iron oxide (FeO + Fe ₂ O ₃ : FeO conversion) and metallic iron (M.Fe: It has been found that a slag satisfying the sum of >15% by mass of FeO conversion) is effective.
It has been found that when the phosphorus-enriched slag contains SiO ₂ , it is more advantageous to set the basicity of the slag, represented by CaO/SiO ₂ , to 5 or more.

In addition, the inventors of the present invention separated the phosphorus-enriched slag having the above-mentioned predetermined composition into two-liquid-phase slag, by controlling the oxygen partial pressure in the atmosphere to 10 ^-10.6 atm or less. A novel melting condition was found that allows separation into the desired two liquid phases even at a relatively low temperature of 1400°C. This is because the morphology of the oxides in the slag changed when the oxygen partial pressure in the atmosphere during melting was reduced to 10 ^-10.6 atm or less, and the melting point and viscosity of the slag decreased. This is thought to be caused by As an example of the change in the form of oxides in the slag in an atmosphere with a low oxygen partial pressure as described above, the reaction "Fe ₂ O ₃ →2FeO+O" progresses and Fe ₂ O ₃ in the slag decreases. A change in which FeO is increased is included. Since the temperature of 1400° C. is within the temperature range for the dephosphorization treatment, if the slag is appropriately kept warm, reheating after the dephosphorization treatment may be unnecessary.

In addition, as the phosphorus-enriched slag, MgO is combined with manganese oxide so that MgO < 16 mass% and 15 mass% < iron oxide (FeO + Fe ₂ O ₃ : FeO conversion) and metallic iron (M.Fe: FeO conversion) and manganese oxide (MnO+MnO ₂ : converted to MnO) in a range of <80% by mass, which is more suitable.

The temperature at which the phosphorus-enriched slag is held is good for separation into the desired two liquid phases even at 1400° C., but the higher the temperature, the better the separation tends to be. This is because the higher the temperature, the less suspended and mixed the high iron phase in the high phosphorus phase, the higher the phosphorus concentration in the separated and collected high phosphorus phase, and the lower the iron concentration. However, when the holding temperature is in the range of 1540° C. or higher, even if the temperature is further increased, the further progress of separation is small. Therefore, from the viewpoint of cost, the temperature to be held is preferably 1400°C or higher and lower than 1540°C.
In addition, although the maximum temperature of the dephosphorization treatment is usually about 1450° C., if the holding temperature is also about 1450° C., as described above, there is an advantage that the heating after the dephosphorization treatment is unnecessary.

First, a method for producing phosphorus-enriched slag will be described.
FIG. 2 is a flow chart illustrating one example of a process for separating a phosphorus-enriched slag into multiple phases, including at least two liquid phases, in accordance with the present invention.
The phosphorus-enriched slag used in the present invention includes, for example, dephosphorization slag (not shown in FIG. 2) generated during hot metal preliminary dephosphorization treatment as a starting material, or converter slag generated during decarburization refining in a converter ( (not shown in FIG. 2) can be used.

Next, the iron oxides and phosphorus oxides in the steelmaking slag are reduced in a rotary kiln by supplying a reducing agent containing one or more of carbon, silicon, and aluminum to reduce the phosphorus concentration to 0.5 mass. % or more of high phosphorus hot metal is recovered. In addition to the rotary kiln, the treatment vessel used in the reduction treatment step may be an arc furnace, a ladle or a torpedo car holding molten iron as a heat source and a seed bath.

Next, a CaO-based solvent is sprayed on the obtained high-phosphorus hot metal together with oxygen gas, and the phosphorus in the high-phosphorus hot metal is transferred as a phosphorus oxide to the slag generated by the dephosphorization treatment to perform a dephosphorization treatment. The P ₂ O ₅ concentration in the slag is concentrated to over 7% by mass, and the resulting slag is recovered as phosphorus-enriched slag. In addition, in order to control not only the P ₂ O ₅ concentration in the phosphorus-enriched slag, but also the SiO ₂ concentration and, if necessary, the manganese oxide concentration, before performing the dephosphorization treatment, desiliconization treatment and/or demanganization treatment You may

Next, a method for producing slag containing two liquid phases will be described.
The phosphorus-enriched slag obtained as described above is transferred to a container such as a slag pot or an electric furnace, and melted by heating from the periphery, top, or bottom of the container. Here, in order to obtain a two-liquid phase slag by separating the phosphorus-enriched slag into multiple phases containing the desired two liquid phases, the oxygen partial pressure P _O2 in the atmosphere should be 10 ^−10.6 atm or less during melting. And, it is important to set the temperature to 1400° C. or higher and maintain the temperature for 10 minutes or longer. As a method for adjusting the oxygen partial pressure in the atmosphere, for example, CO gas or hydrogen gas can be flowed into or lance blown into the furnace atmosphere. Moreover, after keeping the slag at a temperature of 1400° C. or higher for a predetermined period of time, the slag may be reheated as necessary. Although the heating means is not particularly limited, direct heating such as burner heating, arc heating and plasma heating, and indirect heating such as induction heating can be used.

The resulting _{two -} liquid _- phase slag is separated into at _least an upper layer and a lower layer due to the difference in specific gravity. : in terms of FeO) becomes a high phosphorus phase containing ≤ 15% by mass. It is more advantageous that the high phosphorus phase has a CaO/P ₂ O ₅ mass ratio in the range of 1.0 to 1.4, and a CaO+P ₂ O ₅ >70 mass % range.
On the other hand, the lower layer becomes a high-iron phase containing P ₂ O ₅ <20% by weight and the sum of iron oxide (FeO+Fe ₂ O ₃ : as FeO) and metallic iron (M. Fe: as FeO) >15% by weight. .

Here, the reason for limiting the temperature for separating into at least two liquid phases to a predetermined value or higher will be explained as follows. That is, the dephosphorization treatment is generally preferably performed at a lower temperature, and is carried out at about 1300 to 1450°C. However, in such a low temperature range, almost no liquid phase is generated in the slag in the atmosphere. Therefore, the phosphorus-enriched slag cannot be separated into two liquid phases and a phosphorus-rich and low-iron phase cannot be obtained simply by dephosphorizing the high-phosphorus hot metal again. Surprisingly, however, by holding the phosphorus-enriched slag in a predetermined reducing atmosphere for a predetermined period of time, the liquid phase ratio of the slag was reduced to 70 mass even at a relatively low melting temperature of 1400 ° C. or higher. % or more and can be separated into two liquid phases. From the viewpoints of slag heating cost and container melt damage, the melting temperature is preferably 1680°C or less, more preferably less than 1540°C. Further, the melting temperature is more preferably 1450° C. or less, including 1450° C., which is the maximum temperature at which the dephosphorization process ends.

In order to obtain the desired two-liquid phase slag, it is necessary to control the oxygen partial pressure P _O2 in the atmosphere during melting to 10 ^−10.6 atm or less, that is, to create a predetermined reducing atmosphere. Also, the oxygen partial pressure P _O2 is preferably 10 ^−11.6 atm or less. This oxygen partial pressure condition can be achieved by supplying, for example, CO gas, hydrogen gas, or hydrocarbon-based gas. More specifically, for example, when adjusting by supplying CO gas, the CO ₂ /CO ratio in the atmosphere is 10 ⁻¹ or less, and when adjusting by supplying hydrogen gas, H ₂ in the atmosphere is adjusted to 10 −1 or less. The O/H ₂ ratio should be controlled to 10 ^−0.5 or less.
Moreover, the holding time is set to 10 minutes or longer from the viewpoint of sufficiently melting the phosphorus-enriched slag. The upper limit of the retention time is not particularly limited, but about 120 minutes is sufficient, and 20 minutes or less is preferable from the viewpoint of cost.

Next, reasons for limiting the composition of the phosphorus-enriched slag of the present invention will be explained.
The present inventors have confirmed the separation of the two liquid phases of the phosphorus-enriched slag within the composition range indicated by A in FIG. However, when a phosphorus-enriched slag having a P ₂ O ₅ concentration of 7% by mass or less is used, when the two-liquid-phase slag separated into multiple phases containing two liquid phases is recovered, the phosphorus concentration is satisfactorily high. Phosphorus phase cannot be obtained.
Therefore, the P ₂ O ₅ concentration in the phosphorus-enriched slag should be greater than 7% by mass. The P ₂ O ₅ concentration in the phosphorus-enriched slag is preferably 10% by mass or more, more preferably 25% by mass or more.

Also, SiO ₂ may be mixed in the phosphorus-enriched slag. If the SiO ₂ concentration is 10% by mass or more, the phosphorus-enriched slag will not separate into two liquid phases, and a phosphorus-rich phase will not be obtained, or the iron oxide concentration in the phosphorus-rich phase will increase. Therefore, the SiO ₂ concentration in the phosphorus-enriched slag is set to less than 10% by mass. A more desirable SiO ₂ concentration is 5% by mass or less, and may be 0% by mass.

In addition, in a phosphorus-enriched slag having a composition in which the sum of iron oxide (FeO + Fe ₂ O ₃ : FeO conversion) and metallic iron (M.Fe: FeO conversion) is 15% by mass or less, a high iron phase (high Fe phase) and a high phosphorus phase (high P phase) is not confirmed, and a two-liquid phase slag is not obtained. Therefore, the sum of iron oxide (FeO+Fe ₂ O ₃ : FeO conversion) and metallic iron (M.Fe: FeO conversion) in the phosphorus-enriched slag should be more than 15% by mass. Although there is no particular upper limit for the sum of iron oxide and metallic iron, 80% by mass is practical.

Next, the reasons for limiting the slag compositions of the upper and lower layers separated into multiple phases including two liquid phases will be explained.
If the P ₂ O ₅ concentration in the upper layer is 25% by mass or less, the separated and recovered upper layer cannot be used to obtain an artificial phosphate rock containing a satisfactory phosphorus concentration. Therefore, the P ₂ O ₅ concentration in the upper layer was made over 25% by mass. The P ₂ O ₅ concentration in the upper layer is preferably 30 mass % or more. Although the upper limit of the P ₂ O ₅ concentration is not particularly limited, 45% by mass is practical.

In the case where the two-liquid-phase slag is separated into three or more phases, the "upper layer" is a high-phosphorus phase containing the above-mentioned predetermined components and is formed vertically above the "lower layer". The “lower layer” is a layer that is a “high iron phase” containing the predetermined components and is formed vertically below the “upper layer”. That is, in this specification, "upper layer" and "lower layer" are designations that indicate relative positions.

Further, when the sum of iron oxide (FeO + Fe ₂ O ₃ : FeO conversion) and metallic iron (M.Fe: FeO conversion) in the upper layer exceeds 15% by mass, when using the obtained artificial phosphate rock as a phosphoric acid raw material In addition, iron phosphate impurities are generated, and the adverse effects are increased. Therefore, the sum of iron oxide and metallic iron in the upper layer is set to 15% by mass or less, and may be 0% by mass.

Next, if the P ₂ O ₅ concentration in the lower layer is 20% by mass or more, the P ₂ O ₅ recovery efficiency from the upper layer is lowered, which is not preferable. Therefore, the P ₂ O ₅ concentration in the lower layer was set to less than 20% by mass. The P ₂ O ₅ concentration in the lower layer is preferably 10 mass % or less.

Also, if the sum of iron oxide (FeO+Fe ₂ O ₃ : FeO conversion) and metal iron (M.Fe: FeO conversion) in the lower layer is 15% by mass or less, the Fe content in the upper layer becomes high, which is undesirable. Therefore, the sum of iron oxide (FeO+Fe ₂ O ₃ : FeO conversion) and metallic iron (M.Fe: FeO conversion) in the lower layer was set to more than 15% by mass. The sum of iron oxide and metallic iron in the lower layer is preferably 50% by mass or more. The upper limit of the sum of iron oxide and metal iron is not particularly limited, but 80% by mass is practical.

Furthermore, in the present invention, MgO is added to the phosphorus-enriched slag together with manganese oxide so that MgO < 16% by mass and < 15% by mass < iron oxide (FeO + Fe ₂ O ₃ : FeO conversion) and metallic iron (M.Fe : in terms of FeO) and manganese oxide (MnO+MnO ₂ : in terms of MnO) of <80% by mass.

Here, if the MgO concentration in the phosphorus-enriched slag is 16% by mass or more, the replacement ratio of MgO with respect to the C3P phase, which is the main phase of the phosphorus-rich phase after cooling, increases, which is not preferable. In general, phosphate rock is mainly used as a raw material for phosphoric acid, but when phosphate rock is decomposed with sulfuric acid, in the presence of a large amount of MgO, a large amount of magnesium ammonium phosphate (MAP), which is an impurity, is produced. . Therefore, in order to prevent the generation of such MAP, the MgO concentration in the phosphorus-enriched slag is preferably less than 16% by mass, more preferably 10% by mass or less.

Also, if the sum of the concentrations of iron oxide, metallic iron and manganese oxide in the phosphorus-enriched slag is 15% by mass or less, it is not preferable because two-liquid phase separation is unlikely to occur and the phase tends to be substantially uniform. On the other hand, when the sum of the concentrations of iron oxide, metallic iron and manganese oxide is 80% by mass or more, the amount of the high phosphorus phase produced is small, and the amount of recovered material produced relative to the reheating cost becomes small, which is not preferable. The sum of the concentrations of iron oxide, metallic iron and manganese oxide is more preferably 25% by mass or more and 55% by mass or less. More preferably, it is in the range of 40% by mass or more and 55% by mass or less. The sum of the concentrations of iron oxide, metallic iron and manganese oxide is more preferably 25% by mass or more, still more preferably 40% by mass or more, and more preferably 55% by mass or less.

The phosphorus-enriched slag may contain, for example, about 5% by mass or less of Al ₂ O ₃ as another component composition.

Next, a method for producing artificial phosphate rock will be described.
In the method for producing artificial phosphate ore of the present invention, artificial phosphate ore is produced from the upper layer of the slag containing two liquid phases obtained as described above. Here, as a method of obtaining artificial phosphate ore from the upper layer, only the upper layer is recovered in a molten state, and then the recovered upper layer is cooled (Method A). A method (Method B) of obtaining a two-layered slag by solidifying it with a pressure, mechanically destroying the two-layered slag, and then recovering only the solidified and destroyed upper layer (Method B).

In method A, for example, only the upper layer in the molten liquid phase state can be recovered by scraping it out with a natural slag or a slag remover or the like, and then cooled. While recovering the upper liquid phase with a relatively high phosphorus concentration, the slag in the furnace is visually determined by the difference in emissivity, determined by infrared image processing, determined by laser light, etc. It is desirable to stop the recovery when the lower layer having a relatively low phosphorus concentration has flowed out. Alternatively, the weight of the upper layer separated into the two liquid phases may be calculated in advance from the composition and weight of the phosphorus-enriched slag, and collection may be stopped when the calculated weight is reached. Even if the lower layer is partly mixed in the recovered upper layer, the sum of the concentrations of iron oxide and metallic iron in the entire recovered material should be 15% by mass or less.

In method B, for example, the slag containing two liquid phases is solidified in a container as it is to obtain a two-layer slag, and then the upper high-phosphorus phase and the lower high-iron phase in the two-layer slag are mechanically separated. Only the upper layer can be recovered by In this separation method, after removing the entire solidified two-layer slag from the container, the boundary between the upper layer side and the lower layer side is visually judged by color, and the components are measured using a portable XRF device. It is possible to adopt a method of determining by Even if a part of the lower layer is mixed in the collected upper layer, the sum of the concentrations of iron oxide and metallic iron in the entire collected material should be 15% by mass or less.

Further, in method B, for example, after mechanically destroying the two-layer slag obtained by solidifying the slag containing the two liquid phases in the container as it is, the upper high phosphorus phase and the lower high iron phase are formed. can be mechanically separated to recover only the upper layer. In this separation method, the solidified two-layer slag is crushed to a particle size of, for example, 40 mm or less, and then the color of the high phosphorus phase is visually lighter than the color of the high iron phase. A method of gravity separation utilizing the fact that the specific gravity of the phosphorus phase is smaller than that of the high-iron phase can be used. Even if a part of the lower layer is mixed in the collected upper layer, the sum of the concentrations of iron oxide and metallic iron in the entire collected material should be 15% by mass or less.

Examples of the present invention will be described below.
(Example 1)
In the practice of the present invention, various phosphorus-enriched slags produced by reducing dephosphorization slag in a rotary kiln and subjecting the resulting high-phosphorus hot metal to dephosphorization treatment again were used.
Table 1 shows the component composition of the phosphorus-enriched slag used.

The phosphorus-enriched slag 1 shown in Table 1 was placed in an electric furnace, held at a temperature of 1400° C. for 1 hour to melt, and then cooled to room temperature. Gas was introduced into the melting atmosphere at a CO ₂ /CO ratio of 10 ^−1.5 (oxygen partial pressure P ₀₂ : 10 ^−11.6 atm).
Tables 2 and 3 show the results of investigating the composition of the slag melted and cooled as described above. Here, invention examples 1 to 3 are examples in which phosphorus-enriched slags 1 to 3 are melted and cooled, and comparative examples 1 to 6 are examples in which phosphorus-enriched slags 4 to 9 are melted and cooled.

As shown in Table 2, in Examples 1 to 3 using phosphorus-enriched slags 1 to 3, a high phosphorus phase and a high iron phase having a predetermined composition are separated vertically as the upper and lower layers, respectively. confirmed. On the other hand, as shown in Table 3, in Comparative Examples 1 to 6 using phosphorus-enriched slags 4 to 9, the solid phase of the high phosphorus phase was dispersed and precipitated in the liquid phase of the high iron phase, and the liquid phase was separated vertically. was not confirmed.

(Example 2)
The phosphorus-enriched slags 1 to 9 shown in Table 1 were subjected to heat treatment while changing the melting temperature and oxygen partial pressure P ₀₂ . The holding time was 10 minutes.
Table 4 shows the results of an investigation of the relationship between the melting temperature and oxygen partial pressure P _O2 and the presence or absence of liquid phase separation in the phosphorus-enriched slag after the melting treatment when the phosphorus-enriched slag 1 was used.
In Table 4, ◯ indicates that the high phosphorus phase and the high iron phase separated into a continuous phase of the upper layer and the lower layer, respectively, without intrusion of the solid phase, and a two-liquid phase slag was formed, and × indicates that the solid phosphorus-rich phase did not become a continuous phase but existed dispersedly in the liquid high iron phase, and a two-liquid-phase slag was not formed. Representative images of each are shown in FIG.
Since FIG. 3 is an SEM image, the color of the high phosphorus phase, which is the upper layer, is dark, and the color of the high iron phase, which is the lower layer, is light. The color of the high iron phase, which is the lower layer, is observed to be dark.
In addition, for all the two-liquid phase slags evaluated as ◯ in Table 4, the composition of the upper layer was P ₂ O ₅ >25% by mass, iron oxide (FeO + Fe ₂ O ₃ : FeO conversion) and metallic iron (M.Fe : FeO conversion) is within the range of ≤ 15 mass%, and the composition of the lower layer is P ₂ O ₅ < 20 mass%, iron oxide (FeO + Fe ₂ O ₃ : FeO conversion) and metallic iron (M.Fe:FeO conversion) > 15% by mass.

When phosphorus-enriched slags 4 to 9 were used, a solid-liquid phase was observed under all conditions, and no vertical separation into liquid phases was confirmed.
As shown in Table 4, by controlling the CO ₂ /CO ratio in an atmosphere of 10 ⁻¹ or less (oxygen partial pressure P ₀₂ : 10 ^−10.6 atm or less), phosphorus-enriched slag having a predetermined composition was melted. It was confirmed that the phosphorus-enriched slag separates into two liquid phases having a predetermined composition even when the temperature is as low as 1400°C.

It should be noted that the conditions in the examples are an example of conditions adopted for confirming the feasibility and effects of the present invention, and the present invention is not limited to this example of conditions. Various conditions can be adopted in the present invention as long as the objects of the present invention are achieved without departing from the gist of the present invention.

Claims (5)

1. A method of separating the slag into multiple phases comprising at least two liquid phases in the molten state using a phosphorus-enriched slag, comprising:
As the phosphorus-enriched slag, steelmaking slag is reduced to obtain high-phosphorus hot metal, and then the high-phosphorus hot metal is dephosphorized with lime, and the component composition is at least CaO, P ₂ O ₅ , SiO ₂ , and iron oxide. and metallic iron, wherein P ₂ O ₅ > ₇ % by mass, SiO ₂ < ₁₀ % by mass (including ₀ % by mass), iron oxide ( FeO + Fe ₂ O ₃ : FeO conversion) and metallic iron (M. Fe: FeO conversion) using slag that satisfies the sum > 15% by mass,
By holding the phosphorus-enriched slag at a temperature of 1400° C. or more and less than 1500° C. for 10 minutes or more in an atmosphere where the oxygen partial pressure PO ₂ is 10 ^−10.6 atm or less,
In the molten state, in the upper layer, a high phosphorus phase of P ₂ O ₅ > 25% by mass, the sum of iron oxide (FeO + Fe ₂ O ₃ : FeO conversion) and metallic iron (M.Fe: FeO conversion) ≤ 15 mass%, In the lower layer, a two-liquid phase of P ₂ O ₅ <20% by mass and a high iron phase with a sum of iron oxide (FeO + Fe ₂ O ₃ : FeO conversion) and metallic iron (M.Fe: FeO conversion) >15% by mass. A method for producing a slag comprising two liquid phases to form. The component composition is MgO together with manganese oxide, MgO < 16% by mass, and 15% by mass < iron oxide (FeO + Fe ₂ O ₃ : FeO conversion) and metallic iron (M.Fe: FeO conversion) and manganese oxide (MnO + MnO) ₂ : MnO conversion) < 80 mass%, the method for producing a slag containing two liquid phases according to claim 1. The method for producing slag containing two liquid phases according to claim 1 or 2, wherein said temperature is 1450°C or less. Production of artificial phosphate ore by recovering only the upper layer in a molten state from the slag containing two liquid phases produced by the method according to any one of claims 1 to 3, and then cooling the recovered upper layer. Method. The slag containing two liquid phases produced by the method according to any one of claims 1 to 3 is cooled and solidified while at least the upper layer and the lower layer are phase-separated, thereby containing two solid phases. A method for producing artificial phosphate ore, comprising obtaining slag, mechanically breaking the slag containing the two solid phases, and then recovering only the solidified and broken upper layer.

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