JP5793842B2 - Method for separating phosphorus - Google Patents

Description

  The present invention relates to a method for separating phosphorus from a specific composite oxide and a method for separating phosphorus from steelmaking slag.

  Phosphorus is a rare resource that is used as a raw material for chemical products and fertilizers, but the entire amount of phosphorus ore used as a raw material depends on imports from overseas. Phosphorus resources are soaring due to the problem of depletion of phosphate ore and the inclusion of phosphate ore in China and the United States. By-products that are currently attracting attention as valuable phosphorus resources include sewage sludge incineration ash and steelmaking slag generated in the steel refining process.

  As a method for producing phosphoric acid which is a raw material for phosphate fertilizer from phosphate ore, a wet method is generally used in which phosphate ore is decomposed with a mixed acid of sulfuric acid or phosphoric acid. A method of extracting phosphoric acid from a hydrochloric acid decomposition solution of ore with a solvent has been practiced in part, but phosphoric acid by this method is used for chemicals because of its high purity and cost.

  As a method of separating phosphorus from sewage sludge incinerated ash as phosphoric acid, a method of adding a strong acidic solution or a strong alkaline solution and dissolving it can be considered. For example, the following reports can be given.

In Patent Documents 1 and 2, a strong acid solution or a strong alkaline solution is added to sewage sludge incinerated ash to dissolve phosphorus, and after removing an insoluble component by solid-liquid separation to recover a phosphorus extract, A technique is disclosed in which a chemical that reacts with phosphorus to form an insoluble compound is added to precipitate the phosphorus compound, and then the liquid is separated by solid-liquid separation.
Patent Documents 3 to 8 disclose a technique for extracting phosphorus by adding an acid to sewage sludge incineration ash, removing insoluble components by solid-liquid separation, and separating the phosphorus extract.
Patent Documents 9 to 11 disclose a technique in which an alkaline liquid is added to sewage sludge incineration ash to extract phosphorus, an insoluble component is removed by solid-liquid separation, and the phosphorus extract is separated.

  The hot metal melted in the blast furnace contains phosphorus (P) resulting from iron ore components. Since phosphorus is a harmful component for steel products, conventionally, phosphorus removal treatment is performed in the steel making process in order to improve the material properties of steel products. In general, dephosphorization is performed by oxidizing phosphorus in hot metal or molten steel with an oxygen source (oxygen gas or iron oxide). When phosphorus in hot metal or molten steel is oxidized by an oxygen source, iron is also oxidized, and iron is also contained in the slag in the form of iron oxide. The phosphorus content in the steelmaking slag containing phosphorus generated in the steelmaking smelting process is about 1 to 2%, and the phosphorus concentration is insufficient although it is used as fertilizer or separated as phosphoric acid. For this reason, steelmaking slag has been conventionally used as a civil engineering material such as roadbed material, and phosphorus in the slag has not been separated.

JP 2010-036107 A JP 2009-207982 A JP 2001-130903 A Japanese Patent Laid-Open No. 11-278814 Japanese Patent Laid-Open No. 11-092122 JP-A-10-101332 Japanese Patent Application Laid-Open No. 09-075506 Japanese Patent Application Laid-Open No. 07-251141 JP 2008-230940 A JP 2007-261878 A JP 2006007194 A

If phosphorus in the phosphorus-containing steel slag is reduced with carbon, silicon, aluminum, hydrocarbons, etc. in a high temperature environment, P ₂ O ₅ in the phosphorus-containing steel slag is easily reduced. At the same time, FexO in the steelmaking slag is reduced to become molten metallic iron, and phosphorus-containing molten iron is generated. When the phosphorus-containing molten iron is dephosphorized using a CaO-based flux, CaO enriched with phosphorus is generated. It was investigated whether phosphorus could be separated from complex oxides such as CaO-based fluxes enriched with phosphorus.

  However, in the case of sodium hydroxide solution, potassium hydroxide solution or calcium hydroxide solution of about 4%, which is an alkali treatment chemical used in the sewage sludge incineration ash as a phosphorus separation and recovery technology, a specific composite oxide containing phosphorus Phosphorus contained in (for example, a specific composite oxide derived from a slag component) cannot be dissolved. This is presumably because the phosphorus constituent compound of the composite oxide is different from the phosphorus constituent compound of the sewage sludge incineration ash.

  On the other hand, in the acid treatment method, a specific composite oxide containing phosphorus (for example, a specific composite oxide derived from a slag component) coexists with iron and manganese together with phosphorus. Since iron and manganese are mixed in a high concentration and phosphorus is easily insolubilized by iron and manganese, it is necessary to separate phosphorus from iron and manganese. An example of the composition of the specific composite oxide containing phosphorus and the phosphate rock is shown in Table 1. It can be seen that the specific composite oxide containing phosphorus contains more total Fe and MnO derived from converter slag and the like than phosphate ore. Since these iron and manganese make phosphorus insoluble, it is necessary to suppress the mixing into the phosphoric acid solution as much as possible.

  Techniques for removing iron and manganese from a phosphoric acid solution in which iron and manganese coexist include (a) precipitation / removal technique as sulfide, (b) ion exchange resin, or liquid ion exchange method (for example, 06-016403), (c) Solvent extraction method, (d) Membrane technology, etc., but the technology (a) uses hydrogen sulfide and has restrictions on equipment / workplace, chemicals (acid / alkali ) It is necessary to solve problems such as high costs. On the other hand, the techniques (b), (c), and (d) also have a problem that the apparatus and the maintenance cost are high.

  Accordingly, an object of the present invention is to provide a method capable of efficiently and economically separating phosphorus from a specific composite oxide containing phosphorus, such as a specific composite oxide derived from a slag component. It is in.

  As a result of intensive studies to solve the above problems, the inventors have determined that a complex oxide in which phosphorus, iron, and calcium derived from a slag component coexist at a high concentration are mixed with a specific organic acid or an organic acid salt. It was found that phosphorus and phosphorus can be extracted by bringing them into contact with iron and manganese once dissolved in an organic acid or an organic acid salt as a complex with the organic acid or organic acid salt, and precipitated and separated.

  The present invention is a further study of the above findings, and the gist thereof is as follows.

In the first invention, a composite oxide containing, by mass%, CaO content of 10% or more, total Fe of 5% or more, and P ₂ O ₅ min of 10% or more is brought into contact with an organic acid solution or an organic acid salt solution. The phosphorus separation method is characterized in that phosphorus in the composite oxide is extracted into a solution, and dissolved iron or manganese is precipitated and separated as a complex with an organic acid or an organic acid salt.

In a second invention, iron in steelmaking slag is obtained by subjecting steelmaking slag containing phosphorus to high-temperature reduction treatment using a reducing agent containing one or more selected from carbon, silicon, aluminum, and hydrocarbons. Step (A) of reducing oxide and phosphorus oxide to produce phosphorus-containing molten iron, and step (B) of dephosphorizing the phosphorus-containing molten iron produced in step (A) using a CaO-based flux If, generated in said step (B), CaO content of 10 mass% or more, the total Fe is 5 wt% or _more, the dephosphorization slag P 2 _{O 5} minutes that contain more than 10 wt%, the organic acid solution or an organic acid Contacting with a salt solution, extracting phosphorus in dephosphorized slag into an aqueous solution, and precipitating and separating dissolved iron or manganese as a complex with an organic acid or an organic acid salt (C) This is a method for separating phosphorus.

  According to the first phosphorus separation method of the present invention, a complex oxide in which phosphorus, iron, and calcium coexist at high concentrations (for example, a specific complex oxide derived from a slag component) is converted into a specific organic acid solution or By contacting with an organic acid salt solution, phosphorus can be separated into a recyclable form that does not contain iron or manganese. Thereby, the separated phosphoric acid can be effectively used as a raw material for phosphoric acid fertilizer.

Further, according to the second method for separating phosphorus according to the present invention, phosphorus can be separated into a resource-recyclable form by adding a series of treatments to the steel-containing slag containing phosphorus and the product containing the components.

It is an X-ray diffraction pattern of the residue after leaching of 2% by volume oxalic acid.

  First, among the phosphorus separation methods according to the present invention, a phosphorus separation method using a steel-making slag containing phosphorus as a raw material (the second phosphorus separation method according to the present invention described earlier in “Effects of the Invention”) will be described.

  Examples of the slag containing phosphorus to be treated in the present invention include slag generated in hot metal pretreatment (hot metal pretreatment slag), converter slag generated in converter decarburization and refining. As hot metal pretreatment slag, dephosphorization slag is the main target, but is not limited to this. In the present invention, one or more of these steelmaking slags can be treated.

First, it was found that if phosphorus-containing steelmaking slag is subjected to high temperature reduction treatment using carbon, silicon, aluminum, hydrocarbons, etc., P ₂ O ₅ in the phosphorus-containing steelmaking slag is easily reduced. At the same time, phosphorus-containing steelmaking slag contains iron as an oxide in the form of FeO or Fe ₂ O ₃ (hereinafter collectively referred to as FexO), and these iron oxides have an affinity for oxygen. Since it is equivalent to phosphorus, when steelmaking slag containing phosphorus is subjected to high temperature reduction treatment using one or more of carbon, silicon, aluminum, hydrocarbons, etc., FexO in the steelmaking slag may be reduced to become metallic iron. all right. Since phosphorus has a relatively low concentration, it is possible to efficiently separate phosphorus and slag by using high-concentration iron and simultaneously separating phosphorus from slag in a state where phosphorus is dissolved in iron. In order to efficiently separate the phosphorus, iron, and slag, it is desirable to reduce at a high temperature so that the iron produced by the reduction is in a molten state.

  Therefore, in the step (A) (first step) of the present invention, the steelmaking slag containing phosphorus is reduced at high temperature using a reducing agent containing one or more selected from carbon, silicon, aluminum and hydrocarbons. By processing, iron oxide and phosphorous oxide in steelmaking slag are reduced to produce phosphorus-containing molten iron (a). That is, in this step (A), the steelmaking slag is separated into molten iron containing reduced phosphorus (phosphorus-containing molten iron) and slag from which the phosphorus and iron have been removed. This high-temperature reduction treatment needs to be performed while heating the steelmaking slag and the reducing agent, and is performed using, for example, an arc furnace or a cupola.

  Here, the higher the fluidity of the produced phosphorus-containing molten iron (a), the more the separation of phosphorus-containing molten iron and slag is promoted. In this step (A), (i) the produced phosphorus-containing Although it is desirable to perform the treatment under the condition that the melting point of the molten iron (a) is lowered or (ii) the treatment is performed at a high temperature, in any case, the reduction treatment is preferably performed at 1300 ° C. or higher.

  In the case of the above (i), it is preferable to dissolve the carbon in the phosphorus-containing molten iron (a) to form molten iron. Specifically, when the carbon concentration is 3% by mass or more, the liquidus temperature is 1300 ° C. or less. Therefore, the carbon concentration of molten iron (molten metal) is preferably 3% by mass or more. In order to dissolve carbon in the produced molten iron, it is preferable to use carbon as a reducing agent. By increasing the carbon concentration of the molten iron (hot metal) and lowering the melting point in this way, the fluidity of the molten iron is usually sufficiently secured at a processing temperature slightly exceeding 1300 ° C., and the phosphorus-containing molten iron and slag Separation is promoted.

  In the case of (ii), the reduction treatment is performed at 1300 ° C. or higher, more preferably 1400 ° C. or higher. However, when the carbon content is low and the melting point is high, the load on the equipment for performing the reduction treatment becomes large, so it is preferable to set the upper limit of the treatment temperature at about 1550 ° C.

  Examples of the reducing agent used in this step (A), that is, a reducing agent containing one or more selected from carbon, silicon, aluminum, and hydrocarbon include coke, ferrosilicon, ferroaluminum, charcoal, One or more types of anthracite, lignite, tar pitch, carbon black, aluminum scrap, waste plastic (hydrocarbon source), methane, propane, and the like can be used.

  The phosphorus concentration of the phosphorus-containing molten iron (a) produced in the step (A) is considerably higher than that of ordinary blast furnace hot metal. Usually, since the mass ratio (P / Fe) of phosphorus and iron in the phosphorus-containing steelmaking slag is about 0.005 to 0.075, the phosphorus concentration of the phosphorus-containing molten iron (a) is 0.5 to 7.5. It becomes about mass%. On the other hand, the phosphorus concentration of the blast furnace hot metal discharged from the blast furnace is about 0.1% by mass. Therefore, the application of the phosphorus-containing molten iron (a) is limited unless the phosphorus concentration of the phosphorus-containing molten iron (a) produced in the step (A) is dephosphorized to a blast furnace hot metal level of about 0.1% by mass. In some cases, it may not be used as an iron source.

  Therefore, in the step (B) (second step) of the present invention, the phosphorus-containing molten iron (a) produced in the step (A) is dephosphorized using a CaO-based flux, and the phosphorus-containing molten iron (a ) To produce dephosphorization slag (b) enriched in phosphorus. Here, quick lime or the like is usually used as the CaO-based flux, but a CaO-based flux that does not contain a fluorine source such as fluorite is preferable. The phosphorus-containing molten iron (a) is dephosphorized using a hot metal dephosphorization facility or the like and is usually performed by adding an oxygen source (oxygen gas or the like) together with a CaO-based flux.

In the dephosphorization slag (b) produced in this step (B), phosphorus, iron and calcium coexist at a high concentration. Usually, the CaO content is 10 mass% or more, and the total Fe is 5 mass% or more (generally 10 mass). % Or more), and P ₂ O ₅ min is a composite oxide containing 10% by mass or more. Further, as will be described later, this composite oxide has calcium phosphate in which Fe is dissolved as a main mineral.

  An example of the composition of this dephosphorization slag (b) is shown in Table 1 together with an example of the composition of the mineral of phosphate rock. It can be seen that this dephosphorization slag (b) has a high phosphorus concentration almost equal to that of the phosphate ore, but the high total Fe and MnO are greatly different from the phosphate ore.

Step dephosphorization slag generated in (B) (b) _is, P 2 _{O 5} to 10% by mass or more, usually are contained more than 20 wt%, equivalent to 3CaO _· P 2 _{O 5} having a composition of phosphate ore Because of its level, it can be used as a phosphorus resource. However, as described above, the dephosphorization slag (b) contains 5% by mass or more (generally 10% by mass or more) of total Fe and 1% by mass or more of manganese, depending on the use as a phosphorus resource. Therefore, it was found that there are cases where it is difficult to use the raw material mineral as it is.

Therefore, a method for separating phosphorus and iron by wet-treating the dephosphorization slag (b) was examined. 2 vol% sulfuric acid and 2% by volume of sodium hydroxide was charged dephosphorization slag (b) was in the aqueous solution added, the case of 2 hours stirring treatment at room temperature, examined de P ratio k _P and de Fe ratio k _Fe An example of the results is shown in Table 2 described later. In the treatment with 2% by volume sulfuric acid, there was a tendency that iron and manganese were also dissolved under the condition that phosphorus was dissolved. On the other hand, the treatment with 2% by volume sodium hydroxide hardly dissolved phosphorus or iron.

  The mineral phase of the dephosphorization slag (b) was investigated. An example of the XRD chart is similarly shown in FIG. 1 to be described later, and it has been found that this mineral has solid iron partly dissolved in calcium phosphate. For example, in strong alkaline extraction at low concentrations such as sewage sludge, phosphorus element exists in a different mineral phase from the target to be separated, whereas dephosphorized slag (b) has the same mineral phase in which iron and phosphorus to be separated are separated. Because of the coexistence, it was estimated that separation of phosphorus would not proceed under conditions such as acid or low-concentration alkali. Therefore, when the type of acid was changed to an organic acid and investigated, and the reaction state was observed in detail, it was found that once oxalic acid was dissolved, iron and manganese once dissolved were insolubilized with iron oxalate and manganese oxalate. It was.

  Therefore, in the step (C) (third step) of the present invention, the dephosphorization slag (b) produced in the step (B) is brought into contact with (1) an organic acid solution or an organic acid salt solution, and (2) Phosphorus, iron and manganese in dephosphorization slag (b) are leached into the solution, (3) an organic acid complex or an organic acid salt complex of iron and manganese is precipitated, and (4) an iron complex by solid-liquid separation, The manganese complex is removed and only phosphorus is separated.

  The dephosphorization slag (b) is brought into contact with the organic acid solution in a state where the dephosphorization slag (b) is filled or slurried in a vessel such as a treatment tank, a tank or a column, or the dephosphorization slag (b) is used. It can be stacked to form a heap.

  Further, it is preferable that the dephosphorization slag (b) has a small particle diameter and a large surface area in contact with the treatment liquid. Although a particle diameter is not specifically limited, 0.1 mm-10 cm are preferable, 0.1 mm-5 cm are more preferable, 0.1 mm-3 cm are further more preferable. Within this range, the treatment liquid can easily flow through the voids between the particles, and the contact surface area can be secured.

When the particle diameter exceeds 10 cm, the specific surface area becomes small and the contact surface area decreases,
Leaching speed / efficiency decreases. On the other hand, when the particle diameter is less than 0.1 mm, the treatment liquid becomes difficult to flow, so that the leaching speed and the leaching efficiency are lowered.

  As a method of reducing the particle diameter, a method of crushing using a jaw crusher, a rolling mill or the like can be used. When the particle diameter of a sample or the like is within the above range, it may not be further crushed.

  As the organic acid, oxalic acid, citric acid and tartaric acid are used, and as the organic acid salt, oxalate, citrate and tartrate, or a solution obtained by adjusting the pH of an organic acid solution is used. As long as it is equivalent to an acid, it is not limited thereto. Oxalic acid is preferred.

  The concentration of the organic acid or organic acid salt is not particularly limited, but is preferably 1% by volume to 5% by volume. If the concentration is lower than 1% by volume, the leaching rate and leaching efficiency of phosphorus will decrease. If the concentration is higher than 5% by volume, the effect of the concentration of organic acid will be reduced. It is because it cannot be obtained.

  The treatment temperature is not particularly limited, but is preferably from room temperature to 75 ° C. This is because when the temperature is increased, the leaching rate and leaching efficiency of phosphorus are increased, but at the same time, the processing cost is also increased.

  As a method of solid-liquid separation, precipitation separation, membrane separation, and other known methods can be used.

  According to the method of the present invention described above, steel-making slag containing phosphorus (dephosphorization slag generated by dephosphorization of hot metal, generated when decarburizing and refining of dephosphorized hot metal, which is usually not enough or dephosphorized) In the converter slag, etc., first, in step (A), iron oxide and phosphorus oxide are reduced and recovered as phosphorus-containing molten iron (a), and then the phosphorus-containing molten iron (a) is converted into step (B). In the dephosphorization slag (b) produced in this step (B), phosphorus is concentrated to a degree sufficient to separate it as a phosphorus resource, and this phosphorus was dissolved in the step (C). Phosphorus does not coexist with iron and manganese, which are easily insolubilized, so it is easy to effectively use it as a phosphorus resource, and it can be used as a raw material substitute for processes using phosphoric acid raw materials, phosphorus fertilizer raw materials, and other phosphate rocks it can.

  Next, among the methods for separating phosphorus according to the present invention, a method for separating phosphorus from a complex oxide in which phosphorus, iron and calcium coexist at high concentrations (the first method according to the present invention described in “Effects of the Invention”). A method for separating phosphorus will be described.

This method is a wet separation method of iron and phosphorus corresponding to the above step (C), but the CaO content is 10 mass% or more, the total Fe is 5 mass% or more (generally 10 mass% or more), P ₂ O A composite oxide containing 10% by mass or more of ₅ minutes is brought into contact with an organic acid solution or an organic acid salt solution, and phosphorus in the composite oxide is extracted into an aqueous solution. A typical example of the composite oxide is, but not limited to, the dephosphorization slag (b) generated in the step (B).

As described above, as a general method for separating phosphorus from phosphate ore in a wet manner, a method of treating with phosphoric acid is known, but when a complex oxide in which phosphorus and iron coexist is treated with sulfuric acid, Since phosphorus and iron generate FePO ₄ and coprecipitate, phosphorus cannot be separated from iron. Here, when the composite oxide contains 5% by mass of Fe, about 6% by mass of phosphorus in terms of P ₂ O ₅ generates FePO _4. For example, the dephosphorization slag generated in the step (B) above. In the case of (b), _1/4 to 1/6 of phosphorus and iron generate FePO ₄ and coprecipitate.

In general, the composite oxide often includes 10 mass% or more of Fe. For example, if the dephosphorization slag (b) generated in the step (B) includes 10 mass% or more of Fe, at least 1/2 of phosphorus. When a large amount of iron is contained depending on the operating conditions, almost the entire amount of iron is generated by coprecipitation with iron and FePO ₄ . For this reason, in this separation method, the complex oxide containing iron in a relatively high concentration (total Fe: 5% by mass or more, particularly 10% by mass or more) together with phosphorus to be separated is treated.

  As described above, complex oxides in which iron, phosphorus, and calcium coexist in high concentrations, especially complex oxides that contain calcium phosphate with a solid solution of Fe as the main mineral, are separated from phosphorus and iron when treated with acid as described above. In addition, in the treatment with a low concentration alkali metal hydroxide aqueous solution, there is almost no solubility of phosphorus and iron, but when treated with an organic acid solution or an organic acid salt solution, iron or manganese dissolved simultaneously with phosphorus However, it becomes possible to isolate | separate both by insolubilizing as an organic acid complex or organic acid salt complex of iron and manganese. As a result, phosphorous becomes a high-concentration phosphoric acid solution and does not coexist with iron and manganese that are easily insolubilized, making it easy to effectively use it as a phosphorous resource. Phosphoric acid raw material, phosphorus fertilizer raw material, and other phosphate rocks It can be used as a raw material substitute for the process.

  250 tons of steelmaking slag (converter slag, or slag in which converter slag and hot metal dephosphorization slag are mixed at a mass ratio of 1: 1), 50 tons of blast furnace hot metal, and coke as a reducing agent are charged into an arc furnace. The steelmaking slag and coke were heated by generating an arc to reduce the steelmaking slag. The blast furnace hot metal heats steelmaking slag by pre-existing molten metal in the furnace, thereby promoting the reduction of steelmaking slag and quickly taking in the phosphorus-containing molten iron produced by the reduction of the mixed slag. It is inserted for the purpose of promoting the separation of molten iron and steelmaking slag. About 100 tons of high phosphorus hot metal (phosphorus-containing molten iron (a)) was obtained by the reduction treatment for 30 minutes together with the previously charged blast furnace hot metal.

  The obtained high phosphorus hot metal was discharged from an arc furnace into a hot metal ladle, and then about 200 tons of steelmaking slag remaining in the furnace was discharged into a slag pot. In the present invention example 1, the chemical components of the obtained high phosphorus hot metal were: carbon: 4.3% by mass, silicon: 0.01% by mass, manganese: 2.2% by mass, phosphorus: 3.0% by mass, sulfur : 0.05% by mass.

  The high phosphorus hot metal was dephosphorized using a dephosphorization equipment. It was confirmed that the phosphorus concentration of the high phosphorus hot metal was reduced to 0.1% by mass by this dephosphorization treatment.

The chemical components of the dephosphorization slag generated by the dephosphorization treatment were P ₂ O ₅ : 32% by mass, CaO: 36% by mass, total Fe: 16% by mass, and MnO: 4% by mass.

  In order to treat the dephosphorization slag with an organic acid, the dephosphorization slag was brought into contact with a 1 to 5% by volume oxalic acid solution in a treatment tank. The ratio of dephosphorization slag and oxalic acid solution was 1:10. As a comparative example, 2% by volume sulfuric acid and 2% by volume sodium hydroxide were used. The mixture was stirred at room temperature for 2 hours, allowed to stand, and then subjected to solid-liquid separation in a separation tank. Phosphorus, iron, and manganese in the treatment solution were analyzed. As for the residue, a dissolved residue component and a new product component were identified by X-ray diffraction.

  Table 2 shows the ratio of phosphorus, iron, and manganese leached from the dephosphorized slag by oxalic acid treatment. Although phosphorus was extracted from the treatment solution, it was confirmed that the leaching rate of iron and manganese was low. This is because iron or manganese dissolved in oxalic acid is precipitated as a complex with oxalic acid and remains in the residue. The X-ray diffraction pattern of the residue is shown in FIG. The upper side of FIG. 1 shows the X-ray diffraction result of dephosphorization slag before leaching with oxalic acid, and the lower side shows the X-ray diffraction result of the residue after leaching with 2% by volume oxalic acid. It can be seen that iron and manganese are detected as oxalic acid complexes in the residue.

On the other hand, in the sulfuric acid treatment as a comparative example, iron and manganese were extracted into the solution simultaneously with phosphorus, and phosphorus could not be separated. Moreover, phosphorus was not extracted by the low concentration sodium hydroxide treatment.
The phosphorus-containing solution after the treatment of the present invention example can be used as a raw material substitute for a process using a phosphoric acid raw material, a phosphorus fertilizer raw material, or other phosphate rock as a main raw material.

Claims (2)

By mass%, the CaO content of 10% or more, a total Fe 5% or _more, a composite oxide containing P 2 _{O 5} minutes more than 10%, is contacted with oxalic San溶solution, a solution of phosphorus in the composite oxide A method for separating phosphorus, characterized in that the extracted iron and manganese are precipitated and separated as a complex with oxalic acid . Steelmaking slag containing phosphorus is subjected to a high-temperature reduction treatment using a reducing agent containing one or more selected from carbon, silicon, aluminum, and hydrocarbons, whereby iron oxide and phosphorous oxide in the steelmaking slag are reduced. Step (A) of reducing to produce phosphorus-containing molten iron, step (B) of dephosphorizing the phosphorus-containing molten iron produced in step (A) using a CaO-based flux, and step (B) produced in), CaO content of 10 mass% or more, the total Fe is 5 wt% or _more, the dephosphorization slag P 2 _{O 5} minutes that contain more than 10 wt%, it is contacted with oxalic San溶liquid, dephosphorization slag A method for separating phosphorus, comprising the step (C) of extracting phosphorus in an aqueous solution and precipitating and separating dissolved iron or manganese as a complex with oxalic acid .

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