Method for producing phosphate

Abstract

To provide a method for producing a phosphate capable of easily producing a target phosphate. This method for producing a phosphate comprises: an acid leaching step (S1) for obtaining a phosphorus-containing liquid by leaching a component contained in a phosphorus-containing starting material into an acid; and a precipitation generation step (S2) for adding an alkali to the phosphorus-containing liquid to obtain a precipitate containing a phosphate. In the precipitation generation step (S2), the pH of the phosphorus-containing liquid is adjusted according to the temperature of the phosphorus-containing liquid.

Description

Phosphate manufacturing method

[0001] The present invention relates to a method for producing phosphates.

[0002] While phosphorus is used in a wide range of fields, including agriculture, food, medicine, and industry, it is a resource that is unevenly distributed around the world, with producing countries limited to China, the United States, Morocco, etc. The phosphorus resources distributed in Japan are phosphorus products such as yellow phosphorus and crude phosphoric acid, as well as phosphate rock, which is the raw material for these products, and the country is entirely dependent on imports.

[0003] The phosphorus concentration of molten pig iron tapped from a blast furnace is about 0.1 mass %. The phosphorus concentration in steelmaking slag produced by subjecting this molten pig iron to conventional treatments (dephosphorization treatment, decarburization refining) is about 0.1 mass %. ２ O ５ The phosphorus content in steelmaking slag is low, at most about 5% by mass, calculated as a percentage of the total phosphorus content. For this reason, steelmaking slag has been used as a civil engineering material such as a roadbed material, and the phosphorus in steelmaking slag has not been recovered. However, in recent years, the price of phosphorus resources has risen sharply due to the depletion of phosphate rock and the monopolization of phosphate rock by China, the United States, and other countries. Therefore, the phosphorus in steelmaking slag generated during steel smelting is being reconsidered as a valuable phosphorus resource.

[0004] Patent Document 1 discloses a method for recovering phosphorus in the form of phosphate from dephosphorization slag, which is a type of steelmaking slag (i.e., producing phosphate).

[0005] Japanese Patent Application Laid-Open No. 2022-150640

[0006] The method described in Patent Document 1 is a very complicated method consisting of many steps, and it may take a long time to obtain the target phosphate. Furthermore, Patent Document 1 essentially describes only a method for producing calcium phosphate.

[0007] The present invention has been made in view of the above points, and an object of the present invention is to provide a method for producing a phosphate, which can easily produce a target phosphate.

[0008] As a result of extensive research, the present inventors have found that the above object can be achieved by employing the following configuration, and have completed the present invention. That is, the present invention provides the following [1] to [6]. [1] A method for producing a phosphate, comprising: an acid leaching step of leaching components contained in a phosphorus-containing starting material in acid to obtain a phosphorus-containing liquid; and a precipitation step of adding an alkali to the phosphorus-containing liquid to obtain a precipitate containing a phosphate, wherein the precipitation step adjusts the pH of the phosphorus-containing liquid depending on the temperature of the phosphorus-containing liquid. [2] A method for producing a phosphate according to [1] above, wherein the phosphate is at least one selected from the group consisting of iron phosphate and aluminum phosphate. [3] The starting material contains at least CaO, P ２ O ５ , Al ２ O ３ and Fe ｔ [1] A method for producing a phosphate according to [1] or [2] above, wherein the starting material is steelmaking slag. [4] A method for producing a phosphate according to any of [1] to [3] above, wherein the starting material is steelmaking slag. [5] A method for producing a phosphate according to any of [1] to [4] above, wherein the acid leaching step uses at least one acid selected from the group consisting of nitric acid, hydrochloric acid, sulfuric acid, phosphoric acid, and an organic acid. [6] A method for producing a phosphate according to any of [1] to [5] above, wherein the precipitation step includes adding an additional raw material to the phosphorus-containing liquid.

[0009] According to the present invention, the desired phosphate can be produced simply and easily.

[0010] 1 is a flowchart showing the flow of a method for producing a phosphate according to the present embodiment; 2 is a graph showing the relationship between the pH of a phosphorus-containing liquid and the amount of iron phosphate produced for each temperature of the phosphorus-containing liquid; 3 is a graph showing the relationship between the pH of a phosphorus-containing liquid and the amount of aluminum phosphate produced for each temperature of the phosphorus-containing liquid; and 4 is an XRD pattern of the precipitate of Example 1.

[0011] [Method for Producing Phosphate] The method for producing a phosphate according to this embodiment will be described with reference to Figures 1 to 3. Figure 1 is a flowchart showing the flow of the method for producing a phosphate according to this embodiment. The method for producing a phosphate according to this embodiment is a method for recovering phosphorus from a starting material in the form of a target phosphate (e.g., at least one selected from the group consisting of iron phosphate and aluminum phosphate), and includes an acid leaching step (S1) and a precipitation step (S2) in this order.

[0012] <Acid Leaching Step (S1)> In the acid leaching step (S1), components contained in the starting material are leached with acid to obtain a phosphorus-containing liquid. Specifically, for example, acid is added to the starting material, followed by stirring and filtration. This yields a residue (I) and a leachate (A). The leachate (A) is the phosphorus-containing liquid.

[0013] The acid used in the acid leaching step (S1) may be at least one selected from the group consisting of nitric acid, hydrochloric acid, sulfuric acid, phosphoric acid, and organic acids (e.g., citric acid), with nitric acid or hydrochloric acid being preferred, and nitric acid being more preferred. The concentration of the acid is not particularly limited, but is preferably 0.1 to 1.5 M, more preferably 0.3 to 0.8 M.

[0014] The starting material is, for example, a steelmaking slag such as dephosphorization slag or decarburization slag. The starting material is a phosphorus-containing compound (including a mixture of a phosphorus-containing compound with other compounds), and contains at least CaO, P ２ O ５ , Al ２ O ３ and Fe ｔ It is preferred that O is contained.

[0015] The particle size of the starting material is not particularly limited. However, the smaller the particle size of the starting material (e.g., steelmaking slag), the better, since this increases the phosphorus leaching rate (the ratio of the phosphorus content in the resulting phosphorus-containing liquid to the phosphorus content in the starting material). Specifically, the particle size of the starting material is preferably 355 μm or less, since this increases the phosphorus leaching rate to 80% at most. Note that "a particle size of 355 μm or less" means "passing through a JIS test sieve with a mesh size of 355 μm."

[0016] When the starting material is steelmaking slag, the pH of the acid used in the acid leaching step (S1) is preferably 4.0 or less, more preferably 1.0 or less, and even more preferably 0.5 or less. For example, when the pH of the acid is within this range, a higher ratio of the starting material to the acid increases the amount of eluted Si, which may cause the resulting phosphorus-containing solution to gel. Therefore, it is preferable to determine the ratio of the starting material to the acid while carefully considering the conditions of each step described below.

[0017] The pH is measured in accordance with JIS Z8802:2011 "pH measurement method" (hereinafter the same). The temperature when measuring the pH is 25°C unless otherwise specified.

[0018] The inventors obtained a phosphorus-containing solution by adding 1.00 g of steelmaking slag having a particle size of 355 μm or less to 100 mL of nitric acid (concentration: 0.5 M) and stirring the mixture. The leaching time (stirring time) was varied appropriately within the range of 0.1 to 2.0 hours. The relationship between the composition (content of each element) of the obtained phosphorus-containing solution and the leaching time is shown in Table 1 below.

[0019]

[0020] For example, consider the case of obtaining iron phosphate or aluminum phosphate. In this case, Table 1 shows that a leaching time of 0.4 to 0.5 hours is preferable because the contents of P, Fe, and Al in the resulting phosphorus-containing solution are high to a certain extent and the contents of other elements (such as Mg) are not too high. This tendency remains the same even when the process is scaled up.

[0021] <Precipitation Step (S2)> In the precipitation step (S2), an alkali is added to the phosphorus-containing solution obtained in the acid leaching step (S1) to obtain a precipitate containing phosphate. Specifically, for example, an alkali is added to the phosphorus-containing solution, and then the solution is filtered. This yields a precipitate (II) and a filtrate (B). The precipitate (II) is the precipitate.

[0022] The alkali used in the precipitation step (S2) may be, for example, sodium hydroxide, potassium hydroxide, calcium hydroxide, or aqueous ammonia (NH ４ OH). Of these, aqueous ammonia is preferred because it does not contain unnecessary cations. The concentration of aqueous ammonia is not particularly limited, but is preferably 20 to 40% by mass, and more preferably 25 to 35% by mass.

[0023] The present inventors adjusted the pH of a phosphorus-containing liquid by adding aqueous ammonia (concentration: 28% by mass) as an alkali to the phosphorus-containing liquid at a temperature of 25°C or 50°C, and confirmed the amount of precipitate produced (amount of precipitate produced). Specifically, the amounts of iron phosphate and aluminum phosphate produced in the precipitate were confirmed. The results are shown in Figures 2 and 3.

[0024] Fig. 2 is a graph showing the relationship between the pH of the phosphorus-containing liquid and the amount of iron phosphate produced for each temperature of the phosphorus-containing liquid. Fig. 3 is a graph showing the relationship between the pH of the phosphorus-containing liquid and the amount of aluminum phosphate produced for each temperature of the phosphorus-containing liquid. Findings obtained from Figs. 2 and 3 will be explained below.

[0025] First, please refer to the graph when the temperature of the phosphorus-containing liquid is 25°C. As shown in Figure 2, at pH 3, iron phosphate (FePO ４ ・2H ２ However, as the pH increases, the amount of iron phosphate produced decreases and, instead, the amount of iron hydroxide (not shown in FIG. 2) produced increases. On the other hand, as shown in FIG. 3, aluminum phosphate (AlPO ４ ・2H ２The amount of aluminum phosphate produced gradually increases as the pH increases, reaching a maximum at a pH of 4 to 5. However, at pH levels above 5, the amount of aluminum phosphate produced decreases, and instead, the amount of aluminum hydroxide produced (not shown in Figure 3) increases.

[0026] Next, please refer to the graph when the temperature of the phosphorus-containing liquid is 50°C. In this case, the pH range in which iron phosphate is produced increases (see Figure 2), while the pH range in which aluminum phosphate is produced decreases (see Figure 3). In other words, iron phosphate is produced regardless of the pH, and aluminum phosphate is not produced regardless of the pH.

[0027] Based on this knowledge, in the present embodiment, the pH of the phosphorus-containing liquid is adjusted depending on the temperature of the phosphorus-containing liquid in the precipitation step (S2), thereby allowing the target phosphate to be easily obtained.

[0028] For example, when the target phosphate is aluminum phosphate, an alkali is added to a phosphorus-containing liquid at 25°C to adjust the pH to 4 to 5. This results in aluminum phosphate being obtained as the phosphate (although the resulting precipitate contains iron hydroxide, which is a compound other than phosphate).

[0029] Furthermore, for example, when the target phosphate is iron phosphate, the temperature of the phosphorus-containing liquid is raised to 50°C, and then an alkali is added to adjust the pH to 4. This results in iron phosphate being obtained as the phosphate (however, the resulting precipitate contains aluminum hydroxide, which is a compound other than phosphate).

[0030] The temperature of the phosphorus-containing liquid is preferably 15 to 80° C., more preferably 20 to 70° C. The pH of the phosphorus-containing liquid after the addition of alkali is preferably 1 to 8, more preferably 3 to 6.

[0031] When the temperature of the phosphorus-containing liquid is 25°C, it is difficult to obtain iron phosphate if the pH is 4 or higher. However, when the temperature of the phosphorus-containing liquid is 50°C, iron phosphate can be obtained even if the pH is 4 or higher. That is, at least when iron phosphate is to be obtained, the higher the temperature of the phosphorus-containing liquid, the higher the upper limit of pH. On the other hand, when the temperature of the phosphorus-containing liquid is 50°C, it is difficult to obtain aluminum phosphate. However, when the temperature of the phosphorus-containing liquid is 25°C, aluminum phosphate can be obtained at a pH of 3.1 or higher. That is, at least when aluminum phosphate is to be obtained, the lower the temperature of the phosphorus-containing liquid, the wider the pH range.

[0032] Furthermore, in the precipitation step (S2), an additional raw material may be added to the phosphorus-containing liquid as needed. The additional raw material is preferably selected depending on the target phosphate and the content of each element (element constituting the target phosphate) in the phosphorus-containing liquid. For example, iron phosphate (FePO ４ When the phosphorus-containing solution contains less P than Fe, a phosphoric acid solution whose concentration has been adjusted so that the molar ratio of Fe to P in the phosphorus-containing solution is 1:1 is added as an additional raw material. This allows Fe and P to react with each other without excess, thereby increasing the purity of the iron phosphate contained in the precipitate.

[0033] The present invention will be specifically described below with reference to examples, but the present invention is not limited to the examples described below.

[0034] Example 1: First, in the acid leaching step (S1), steelmaking slag with a particle size of 355 μm or less was added to nitric acid (concentration: 0.5 M) and stirred for 0.4 h to obtain a phosphorus-containing solution. Next, in the precipitation step (S2), ammonia water (concentration: 28% by mass) was added to the phosphorus-containing solution, which was maintained at 25°C, while stirring at 200 rpm to adjust the pH to 4, thereby forming a precipitate. More specifically, the pH of the phosphorus-containing solution was increased by adding ammonia water, and once the pH became constant, the solution was stirred for 0.5 h and then allowed to stand for 0.5 h. After standing, the solution was filtered to obtain a filtrate and a precipitate. The obtained precipitate was calcined at 700°C to crystallize it. XRD patterns were obtained for the precipitate before and after calcination using an X-ray diffraction (XRD) device. Figure 4 shows the XRD patterns of the precipitate in Example 1. From the XRD pattern shown in FIG. 4, it is clear that the phosphate contained in the precipitate is aluminum phosphate (AlPO ４ ) was found to be obtained.

[0035] Example 2 In the precipitation step (S2), the pH of the phosphorus-containing liquid at 25°C was adjusted to 3. Except for this, a precipitate was generated in the same manner as in Example 1. As a result, iron phosphate (FePO) was found to be present as the phosphate salt contained in the precipitate. ４ ) was found to be obtained.

[0036] Example 3 In the precipitation step (S2), the pH of the phosphorus-containing liquid at 50°C was adjusted to 3. Except for this, a precipitate was generated in the same manner as in Example 1. As a result, iron phosphate (FePO) was found to be present as the phosphate salt in the precipitate. ４ ) was obtained. The precipitate also contained iron hydroxide and aluminum hydroxide.

[0037] Example 4 In the precipitation step (S2), the pH of the phosphorus-containing liquid at 25°C was adjusted to 3.5. Except for this, a precipitate was generated in the same manner as in Example 1. As a result, aluminum phosphate (AlPO) was found to be present as the phosphate salt in the precipitate. ４ ) and iron phosphate (FePO ４ ) was obtained in a molar ratio of 3:1.

[0038] Example 5 In the precipitation step (S2), the pH of the phosphorus-containing solution at 25°C was adjusted to 3. Prior to this, a phosphoric acid solution with an adjusted concentration was added as an additional raw material so that the molar ratio of Fe to P contained in the phosphorus-containing solution was 1:1. Except for this, a precipitate was generated in the same manner as in Example 1. As a result, the phosphate contained in the precipitate was iron phosphate (FePO ４ ) was obtained. Analysis of the filtrate revealed that the content of Fe and P was zero. In other words, the purity of the iron phosphate contained in the precipitate was increased.

Claims

1. an acid leaching step in which a component contained in the phosphorus-containing starting material is leached with an acid to obtain a phosphorus-containing liquid; and a precipitation step of adding an alkali to the phosphorus-containing liquid to obtain a precipitate containing phosphate, A method for producing a phosphate, comprising adjusting a pH of the phosphorus-containing liquid depending on a temperature of the phosphorus-containing liquid in the precipitation step.

2. The method for producing a phosphate according to claim 1, wherein the phosphate is at least one selected from the group consisting of iron phosphate and aluminum phosphate.

3. The starting material contains at least CaO, P ２ O ５ , Al ２ O ３ and Fe ｔ The method for producing a phosphate according to claim 1 or 2, wherein the phosphate contains O.

4. The method for producing phosphate according to claim 1 or 2, wherein the starting material is steelmaking slag.

5. 3. The method for producing a phosphate according to claim 1 or 2, wherein the acid leaching step uses as the acid at least one selected from the group consisting of nitric acid, hydrochloric acid, sulfuric acid, phosphoric acid and an organic acid.

6. The method for producing a phosphate according to claim 1 or 2, wherein in the precipitation step, an additional raw material is added to the phosphorus-containing liquid.