Phosphate manufacturing method

Abstract

Provided is a phosphoric acid salt production method by which a desired phosphoric acid salt can be obtained in the state where fewer impurities are contained. This phosphoric acid salt production method is for producing a desired phosphoric acid salt, and comprises: a precipitate generation step (S1) in which an alkali is added to a phosphorus-containing liquid so as to obtain a precipitate; and a dissolution step (S2) in which the precipitate is dissolved with an acid so as to obtain a phosphoric acid solution. In the precipitate generation step (S1), the composition of the precipitate is changed by changing the timing to add the alkali depending on the type of the phosphoric acid salt.

Description

[Technical Field]

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

[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, and is only produced in China, the United States, Morocco, and other countries. The phosphorus resources circulating in Japan are phosphorus products such as yellow phosphorus and crude phosphoric acid, and the raw material for these, phosphate rock, and the entire amount is imported.

[0003] The phosphorus concentration of molten pig iron tapped from a blast furnace is about 0.1% by mass. The phosphorus concentration in steelmaking slag produced by subjecting this molten pig iron to conventional treatments (dephosphorization and decarburization refining) is as low as about 5% by mass at most, calculated as P2O5. For this reason, steelmaking slag has been used as a civil engineering material such as roadbed material, and the phosphorus in the steelmaking slag has not been recovered. However, in recent years, the price of phosphorus resources has been rising sharply due to factors such as the depletion of phosphate rock and the monopolization of phosphate rock by China, the United States, and other countries. As a result, 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 calcium phosphate (that is, producing calcium phosphate) from dephosphorized slag, which is a type of steelmaking slag. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2022-150640 Summary of the Invention [Problem to be solved by the invention]

[0006] Calcium phosphate produced by the method described in Patent Document 1 may contain a large amount of impurities such as Si. In addition, phosphorus (phosphate salt) cannot be recovered in a form other than 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 by which the target phosphate can be obtained with few impurities. [Means for solving the problem]

[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 [9]. [1] A method for producing a target phosphate, comprising: a precipitation step of adding an alkali to a phosphorus-containing liquid to obtain a precipitate; and a dissolution step of dissolving the precipitate with an acid to obtain a phosphoric acid liquid, wherein in the precipitation step, the composition of the precipitate is changed by changing the timing of adding the alkali depending on the type of phosphate. [2] The method for producing a phosphate according to [1] above, further comprising an adding step after the dissolving step, in which an additional raw material according to the type of phosphate is added to the phosphoric acid solution in the adding step to obtain the phosphate. [3] The method for producing phosphate according to [2] above, further comprising a cation exchange step after the dissolving step and before the adding step, in which the phosphoric acid solution is treated with a cation exchange resin. [4] The method for producing a phosphate according to any one of [1] to [3] above, wherein in the dissolving step, a strong acid having a concentration of 10 M or more is used as the acid. [5] The method for producing a phosphate according to any one of [1] to [4] above, wherein the acid used in the dissolving step is at least one selected from the group consisting of nitric acid, hydrochloric acid, sulfuric acid, phosphoric acid, and organic acids. [6] The method for producing a phosphate according to any one of [1] to [5] above, further comprising an acid leaching step before the precipitation step, in which components contained in the phosphorus-containing starting material are leached with acid to obtain the phosphorus-containing liquid. [7] The method for producing a phosphate according to [6] above, wherein in the dissolving step, the time from obtaining the phosphorus-containing liquid to adding the alkali is changed. [8] The method for producing a phosphate according to [6] or [7] above, wherein the starting material is steelmaking slag. [9] The method for producing a phosphate according to any one of the above [1] to [8], wherein the phosphorus-containing liquid contains at least calcium, phosphorus, aluminum and iron elements. [Effects of the Invention]

[0009] According to the present invention, the target phosphate can be obtained with few impurities. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a flowchart showing the flow of a method for producing a phosphate according to the present embodiment. [Figure 2] 1 is a graph showing the relationship between the timing of adding alkali to a phosphorus-containing liquid and the precipitation rate of each element. [Figure 3] 1 is a graph showing the content (unit: mmol / 100 mL) of each element in phosphoric acid solution for each concentration of acid used (0.5 M and 13.5 M). [Figure 4] 1 shows the X-ray diffraction pattern of the residue (III) obtained when a 13.5M acid (nitric acid) was used. DETAILED DESCRIPTION OF THE INVENTION

[0011] [Phosphate manufacturing method] The method for producing a phosphate salt according to this embodiment will be described with reference to FIGS. FIG. 1 is a flowchart showing the flow of the method for producing a phosphate salt according to this embodiment. The method for producing phosphate of this embodiment is a method for recovering phosphorus from a starting material in the form of a target phosphate (calcium phosphate, iron phosphate, etc.), and includes an acid leaching step (S0), a precipitation step (S1), a dissolution step (S2), and a cation exchange step (S3) in this order. The acid leaching step (S0) and the cation exchange step (S3) are optional steps and may be omitted. The method for producing phosphate of this embodiment may include an addition step (S4) after the dissolving step (S2) or the cation exchange step (S3).

[0012] <Acid leaching step (S0)> In the acid leaching step (S0), components contained in the starting material are leached in acid to obtain a phosphorus-containing liquid. Specifically, for example, the starting material is added to acid, stirred, and then filtered. 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 (S0) 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 1.5M, more preferably 0.3 to 0.8M.

[0014] Examples of starting materials include steelmaking slag such as dephosphorization slag and decarburization slag. The starting materials are phosphorus-containing compounds, and include at least CaO, P2O5, Al2O3, and Fe. t It is preferred that it contains O.

[0015] When the starting material is steelmaking slag, the pH of the acid used in the acid leaching step (S0) 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, if the ratio of the starting material to the acid is high, the amount of Si eluted increases accordingly, and the resulting phosphorus-containing solution may gel. Therefore, it is preferable to determine the ratio of the starting material to the acid by carefully considering the conditions of each step described below.

[0016] pH is measured in accordance with JIS Z8802:2011 "pH measurement method" (hereinafter the same). The temperature when measuring pH is 25°C unless otherwise specified.

[0017] <Precipitation step (S1)> In the precipitation step (S1), an alkali is added to the phosphorus-containing liquid to obtain a precipitate. Specifically, for example, an alkali is added to the phosphorus-containing liquid, and then the liquid is filtered. This yields a precipitate (II) and a filtrate (B). The precipitate (II) is the precipitate.

[0018] As the phosphorus-containing liquid, for example, the leachate (A) obtained in the acid leaching step (S0) is used, but a liquid obtained in another step may also be used. The phosphorus-containing liquid preferably contains at least the elements calcium (Ca), phosphorus (P), aluminum (Al) and iron (Fe). The phosphorus-containing liquid may further contain elements such as silicon (Si), magnesium (Mg), and manganese (Mn).

[0019] Examples of the alkali used in the precipitation step (S1) include sodium hydroxide, potassium hydroxide, calcium hydroxide, and aqueous ammonia (NH4OH). Of these, aqueous ammonia is preferred because it does not contain unnecessary cations. The concentration of the aqueous ammonia is not particularly limited, but is preferably 20 to 40% by mass, more preferably 25 to 35% by mass.

[0020] <Timing for adding alkali> The present inventors have investigated suitable conditions for the precipitation step (S1) from the viewpoint of selectively producing the target phosphate and reducing the amount of impurities. Note that "impurities" are elements other than those constituting the target phosphate; for example, if the target phosphate is calcium phosphate, they are elements (Fe, Si, Al, etc.) other than calcium (Ca), phosphorus (P), and oxygen (O).

[0021] As a result of the investigation, it was found that the composition of the resulting precipitate changes depending on the timing of adding alkali to the phosphorus-containing liquid (see Figure 2). Here, ammonia water (concentration: 28% by mass) was used as the alkali.

[0022] FIG. 2 is a graph showing the relationship between the timing of adding alkali to the phosphorus-containing solution and the precipitation rate of each element. Here, the timing of adding the alkali to the phosphorus-containing solution specifically means, for example, the time from when the phosphorus-containing solution is obtained in the acid leaching step (S0) until when the alkali is added to the phosphorus-containing solution.

[0023] The vertical axis in FIG. 2 represents the ratio (precipitation ratio) of the content of each element in the precipitate obtained by adding the alkali to the content in the phosphorus-containing liquid before adding the alkali. For example, when the precipitation rate for element M is 100%, it means that all of element M in the phosphorus-containing liquid has been transferred to the precipitate, whereas when the precipitation rate is 0%, it means that none of element M in the phosphorus-containing liquid has been transferred to the precipitate.

[0024] Referring to FIG. 2, it can be seen that when the timing of adding alkali is early (for example, 1 hour or less), the concentrations of Fe and Si in the precipitate are low. On the other hand, when the timing of adding alkali is late (for example, 4 hours or more), the concentrations of Fe and Si in the precipitate are high.

[0025] Therefore, in this embodiment, in the precipitation step (S1), the timing of adding alkali to the phosphorus-containing liquid is changed depending on the type of target phosphate, thereby changing the composition of the resulting precipitate. Specifically, for example, the time from obtaining the phosphorus-containing solution in the acid leaching step (S0) to adding the alkali thereto is changed.

[0026] For example, when the target phosphate is iron phosphate, the timing of adding the alkali is delayed so that the precipitate contains a sufficient amount of the necessary element Fe. Specifically, the time from obtaining the phosphorus-containing solution to adding the alkali is preferably 4 hours or more. In this case, since the precipitate also contains a large amount of Si as an impurity, it is preferable to remove Si in the dissolving step (S2) described below.

[0027] Furthermore, for example, when the target phosphate is calcium phosphate, the timing of adding the alkali is made earlier in order to reduce the impurities Si and Fe from the precipitate. Specifically, the time from obtaining the phosphorus-containing solution to adding the alkali is preferably 1 hour or less. In this case, since the precipitate contains only a small amount of the necessary Ca, it is preferable to add an additional raw material (calcium nitrate) corresponding to the target phosphate (calcium phosphate) in the adding step (S4) described below. Furthermore, in this case too, Si may be removed in the dissolving step (S2) described below.

[0028] <Dissolution step (S2)> In the dissolution step (S2), the precipitate (II) obtained in the precipitation step (S1) is dissolved using an acid. This results in a phosphoric acid solution. Specifically, for example, the precipitate is added to an acid, stirred, and then filtered. This results in a residue (III) and a filtrate (C). The filtrate (C) is the phosphoric acid solution.

[0029] The acid used in the dissolving step (S2) may be at least one selected from the group consisting of nitric acid, hydrochloric acid, sulfuric acid, phosphoric acid, and organic acids (for example, citric acid), with nitric acid or hydrochloric acid being preferred, and nitric acid being more preferred.

[0030] Acid Concentration The present inventors have investigated suitable conditions for the dissolution step (S2) from the viewpoint of selectively producing the target phosphate and reducing the amount of impurities. As a result of the investigation, it was found that the composition of the resulting phosphoric acid solution changes depending on the concentration of the acid (for example, nitric acid) used in the dissolution step (S2) (see FIG. 3). Figure 3 is a graph showing the content (unit: mmol / 100 mL) of each element in the phosphoric acid solution for each concentration of acid used (0.5 M and 13.5 M). The phosphoric acid solution shown in Figure 3 is a filtrate (C) obtained by dissolving a precipitate (precipitate (II)) when the timing of adding alkali in the above-mentioned precipitation generation step (S1) was set to 4 hours or more. Referring to FIG. 3, it can be seen that when the concentration of the acid (nitric acid) used is 13.5M, the content of Si in the phosphoric acid solution is very small.

[0031] Figure 4 shows the X-ray diffraction pattern of residue (III) obtained when 13.5 M acid (nitric acid) was used. Figure 4 shows that residue (III) contains silica (SiO2), and that Si was separated as silica.

[0032] Therefore, in this embodiment, the concentration of the acid used in the dissolving step (S2) is preferably 10.0 M or more, more preferably 11.5 M or more, and even more preferably 13.0 M or more, which can reduce the Si content in the resulting phosphoric acid solution. For example, when the target phosphate is iron phosphate, calcium phosphate, or the like, Si is an impurity, so it is very beneficial to reduce the Si content in the resulting phosphoric acid solution.

[0033] Cation exchange step (S3) It is preferred to provide a cation exchange step (S3) after the dissolution step (S2). In the cation exchange step (S3), the phosphoric acid solution obtained in the dissolution step (S2) is treated with a cation exchange resin (cation exchange treatment), which removes cations from the phosphoric acid solution and increases the purity of the resulting phosphate. Examples of treatments using cation exchange resins include treatments similar to those described in paragraphs

[0022] to

[0024] of Patent Document 1.

[0034] <Addition step (S4)> It is preferable to provide an addition step (S4) after the dissolution step (S2) or the cation exchange step (S3). In the addition step (S4), additional raw materials are added to the phosphoric acid solution obtained in the dissolution step (S2) (or the phosphoric acid solution treated in the cation exchange step (S3)) depending on the type of target phosphate, thereby obtaining the target phosphate.

[0035] For example, if the target phosphate is calcium phosphate, calcium nitrate is added as an additional raw material to the phosphoric acid solution in the adding step (S4). Then, an alkali is added to the phosphoric acid solution to which calcium nitrate has been added, thereby obtaining a precipitate of calcium phosphate. Suitable examples of the alkali added here include those listed as alkalis used in the precipitation step (S1) described above. At this time, by advancing the timing of addition of the alkali in the above-mentioned precipitation forming step (S1), the content of impurities such as Si and Fe in the finally obtained phosphate (calcium phosphate) can be reduced.

[0036] Furthermore, for example, when the target phosphate is iron phosphate, in the adding step (S4), iron nitrate is added as an additional raw material to the phosphoric acid solution, thereby obtaining a precipitate of iron phosphate. In this case, by delaying the timing of adding alkali in the above-mentioned precipitation step (S1) and increasing the concentration of acid in the above-mentioned dissolution step (S2), the content of Si, an impurity, in the finally obtained phosphate (iron phosphate) can be reduced.

[0037] As described above, according to this embodiment, the target phosphate can be obtained with few impurities. [Example]

[0038] The present invention will be specifically described below with reference to examples, but the present invention is not limited to the examples described below.

[0039] Through the steps described above, the target phosphate salt was obtained. At this time, the timing of adding the alkali in the precipitation step (S1) and the concentration of the acid (nitric acid) in the dissolution step (S2) were changed. Ammonia water (concentration: 28% by mass) was used as the alkali.

[0040] Prior to the precipitation step (S1), in the acid leaching step (S0), components contained in slag 1 (steelmaking slag) having the composition shown in Table 1 below were leached in nitric acid (concentration: 0.5M) to obtain a phosphorus-containing liquid.

[0041] [Table 1]

[0042] Example 1 The desired phosphate was calcium phosphate. In the precipitation step (S1), the timing of adding the alkali (the time from obtaining the phosphorus-containing liquid to adding the alkali) was set to 1 hour or less to obtain a precipitate. In the dissolution step (S2), the precipitate was dissolved using nitric acid with a concentration of 13.5 M to obtain a phosphoric acid solution. In the cation exchange step (S3), the phosphoric acid solution was passed through a cation exchange resin to obtain a phosphoric acid solution having the composition shown in Table 2 below. Thereafter, in the adding step (S4), calcium nitrate was added as an additional raw material to the phosphoric acid solution to obtain single-phase calcium phosphate.

[0043] Example 2 In the precipitation step (S1), the timing of adding the alkali was changed to 4 hours. Otherwise, the same procedure as in Example 1 was carried out to obtain a phosphoric acid solution having the composition shown in Table 2 below. Thereafter, in the adding step (S4), calcium nitrate was added as an additional raw material to the phosphoric acid solution to obtain single-phase calcium phosphate. As shown in Table 2 below, the phosphoric acid solution in Example 2 had a higher content of Fe as an impurity than that in Example 1. As a result, the calcium phosphate obtained from the phosphoric acid solution had a higher content of Fe as an impurity.

[0044] [Table 2]

[0045] Example 3 The desired phosphate was iron phosphate. In the precipitation step (S1), the timing of adding the alkali (the time from obtaining the phosphorus-containing liquid to adding the alkali) was set to 4 hours to obtain a precipitate. In the dissolution step (S2), the precipitate was dissolved using nitric acid with a concentration of 13.5 M to obtain a phosphoric acid solution. In the cation exchange step (S3), the phosphoric acid solution was passed through a cation exchange resin to obtain a phosphoric acid solution having the composition shown in Table 3 below. Thereafter, in the adding step (S4), iron nitrate was added as an additional raw material to the phosphoric acid solution to obtain iron phosphate.

[0046] Example 4: In the dissolution step (S2), nitric acid with a concentration of 8.5 M was used. Except for this, the procedure was the same as in Example 3 to obtain a phosphoric acid solution having the composition shown in Table 3 below. Thereafter, in the adding step (S4), iron nitrate was added as an additional raw material to the phosphoric acid solution to obtain iron phosphate. As shown in Table 3 below, the phosphoric acid solution in Example 4 had a higher content of Si as an impurity than Example 3. As a result, the iron phosphate obtained from the phosphoric acid solution had a higher content of Si as an impurity.

[0047] [Table 3]

Claims

1. 1. A method for producing a target phosphate salt, comprising: a precipitation step of adding an alkali to the phosphorus-containing liquid to obtain a precipitate; a dissolving step of dissolving the precipitate in an acid to obtain a phosphoric acid solution, In the precipitation step, the composition of the precipitate is changed by changing the timing of adding the alkali depending on the type of the phosphate; further comprising an acid leaching step prior to the precipitation step; In the acid leaching step, components contained in the phosphorus-containing starting material are leached with acid to obtain the phosphorus-containing liquid, A method for producing a phosphate, wherein the precipitation step varies the time from obtaining the phosphorus-containing liquid to adding the alkali.

2. After the dissolving step, the method further comprises an adding step, The method for producing a phosphate according to claim 1 , wherein in the adding step, an additional raw material according to the type of the phosphate is added to the phosphoric acid solution to obtain the phosphate.

3. further comprising a cation exchange step after the dissolving step and before the adding step; The method for producing phosphate according to claim 2 , wherein the cation exchange step involves treating the phosphoric acid solution with a cation exchange resin.

4. The method for producing a phosphate according to any one of claims 1 to 3, wherein in the dissolving step, a strong acid having a concentration of 10 M or more is used as the acid.

5. The method for producing a phosphate according to any one of claims 1 to 3, wherein the dissolving 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 any one of claims 1 to 3, wherein the starting material is steelmaking slag.

7. The method for producing a phosphate according to any one of claims 1 to 3, wherein the phosphorus-containing liquid contains at least calcium, phosphorus, aluminum, and iron elements.

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