Phosphoric acid salt production 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

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 calcium phosphate from dephosphorized slag, which is a type of steelmaking slag (i.e., producing calcium phosphate).

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

[0006] The calcium phosphate produced by the method described in Patent Document 1 may contain a large amount of impurities such as Si. Furthermore, phosphorus (phosphate) 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 a target phosphate can be obtained with few impurities.

[0008] As a result of extensive research, the present inventors have found that the above object can be achieved by adopting 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 the precipitation step varies the composition of the precipitate 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 addition step after the dissolution step, in which an additional raw material depending on the type of phosphate is added to the phosphoric acid liquid to obtain the phosphate. [3] The method for producing a phosphate according to [2] above, further comprising: a cation exchange step after the dissolution step and before the addition step, in which the phosphoric acid liquid is treated with a cation exchange resin. [4] The method for producing a phosphate according to any one of [1] to [3] above, wherein the dissolving step uses a strong acid having a concentration of 10 M or more as the acid. [5] The method for producing a phosphate according to any one of [1] to [4] above, wherein the dissolving 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] 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 a phosphorus-containing starting material are leached in the acid to obtain the phosphorus-containing liquid. [7] The method for producing a phosphate according to [6] above, wherein the dissolving step varies the time from obtaining the phosphorus-containing liquid to adding the alkali. [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 [1] to [8] above, wherein the phosphorus-containing liquid contains at least calcium, phosphorus, aluminum, and iron.

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

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

[0011] [Method for Producing Phosphate] The method for producing phosphate according to this embodiment will be described with reference to FIGS. 1 to 4. FIG. 1 is a flowchart showing the flow of the method for producing phosphate according to this embodiment. The method for producing phosphate according to 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 according to this embodiment may include an addition step (S4) after the dissolution 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 1.5 M, more preferably 0.3 to 0.8 M.

[0014] Examples of the starting material include steelmaking slag such as dephosphorization slag and decarburization slag. The starting material is a phosphorus-containing compound, and contains at least CaO, P ２O ５ , Al ２ O ３ and Fe ｔ It is preferred that O is contained.

[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, 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.

[0016] 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.

[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 results in a precipitate (II) and a filtrate (B). The precipitate (II) is the precipitate.

[0018] The phosphorus-containing liquid may be, for example, the leachate (A) obtained in the acid leaching step (S0), but may also be a liquid obtained in another step. The phosphorus-containing liquid preferably contains at least 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] The alkali used in the precipitation step (S1) may be, for example, sodium hydroxide, potassium hydroxide, calcium hydroxide, or aqueous ammonia (NH ４ OH). Of these, ammonia water is preferred because it does not contain unnecessary cations. The concentration of ammonia water is not particularly limited, but is preferably 20 to 40% by mass, more preferably 25 to 35% by mass.

[0020] <<Timing of Addition of 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, in the case where the target phosphate is calcium phosphate, these 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 solution (see Figure 2). In this case, ammonia water (concentration: 28% by mass) was used as the alkali.

[0022] 2 is a graph showing the relationship between the timing of adding an alkali to the phosphorus-containing solution and the precipitation rate of each element. Here, the timing of adding an 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) to 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 an alkali to the content in the phosphorus-containing liquid before adding the alkali. For example, when the precipitation ratio for element M is 100%, it means that all of element M in the phosphorus-containing liquid has migrated to the precipitate. On the other hand, when the precipitation ratio is 0%, it means that none of element M in the phosphorus-containing liquid has migrated to the precipitate.

[0024] 2, it can be seen that when the alkali is added early (e.g., 1 hour or less), the concentrations of Fe and Si in the precipitate are low, whereas when the alkali is added late (e.g., 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 solution 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 alkali to the solution is changed.

[0026] For example, when the target phosphate is iron phosphate, the timing of adding the alkali is delayed so that the necessary element Fe is sufficiently contained in the precipitate. 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 dissolution step (S2) described below.

[0027] Furthermore, for example, when the target phosphate is calcium phosphate, the timing of adding the alkali is advanced 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 also contains 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, Si may also be removed in the dissolving step (S2) described below.

[0028] <Dissolving Step (S2)> In the dissolving 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, followed by stirring and then filtering. This results in a residue (III) and a filtrate (C). The filtrate (C) is the phosphoric acid solution.

[0029] The acid used in the dissolution step (S2) may be, for example, 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.

[0030] <Acid Concentration> The inventors 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 (e.g., nitric acid) used in the dissolution step (S2) (see FIG. 3). FIG. 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 FIG. 3 is the filtrate (C) obtained by dissolving the precipitate (precipitate (II)) when the alkali addition timing in the above-mentioned precipitation 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 was 13.5 M, the content of Si in the phosphoric acid solution was very low.

[0031] Fig. 4 shows the X-ray diffraction pattern of the residue (III) obtained when 13.5M acid (nitric acid) was used. From Fig. 4, it can be seen that the residue (III) is composed of silica (SiO ２ ), which indicates 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. This allows the Si content in the resulting phosphoric acid solution to be reduced. For example, when the target phosphate is iron phosphate, calcium phosphate, or the like, Si is an impurity, so reducing the Si content in the resulting phosphoric acid solution is very beneficial.

[0033] <Cation Exchange Step (S3)> It is preferable 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). This removes cations from the phosphoric acid solution, thereby increasing the purity of the phosphate salt finally obtained. Examples of treatments using a cation exchange resin include 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), an additional raw material according to the type of target phosphate is added to the phosphoric acid solution obtained in the dissolution step (S2) (or the phosphoric acid solution treated in the cation exchange step (S3)). This allows the target phosphate to be obtained.

[0035] For example, when the target phosphate is calcium phosphate, in the adding step (S4), calcium nitrate is added as an additional raw material to the phosphoric acid solution. 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 described as the alkali used in the precipitation step (S1) described above. In this case, by accelerating the timing of the alkali addition in the precipitation step (S1) described above, the content of impurities, 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. This results in a precipitate of iron phosphate. In this case, by delaying the timing of adding the alkali in the precipitation forming step (S1) and increasing the acid concentration in the dissolving 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.

[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] The target phosphate was obtained through the above-mentioned steps. The timing of adding alkali in the precipitation step (S1) and the concentration of acid (nitric acid) in the dissolution step (S2) were varied. 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: 0.5 M) to obtain a phosphorus-containing solution.

[0041]

[0042] Example 1: Calcium phosphate was used as the target phosphate. In the precipitation step (S1), the timing of alkali addition (the time from obtaining the phosphorus-containing solution 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 addition step (S4), calcium nitrate was added to the phosphoric acid solution as an additional raw material to obtain single-phase calcium phosphate.

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

[0044]

[0045] Example 3: The target phosphate was iron phosphate. In the precipitation step (S1), the timing of alkali addition (the time from obtaining the phosphorus-containing solution 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 addition step (S4), iron nitrate was added to the phosphoric acid solution as an additional raw material to obtain iron phosphate.

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

[0047]

Claims

1. 1. A method for producing a phosphate salt of interest, comprising the steps of: a precipitation step of adding an alkali to the phosphorus-containing liquid to obtain a precipitate; A dissolving step of dissolving the precipitate with an acid to obtain a phosphoric acid solution, A method for producing a phosphate, wherein in the precipitation step, a composition of the precipitate is changed by changing a timing of adding the alkali depending on a type of the phosphate.

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 a 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 in the cation exchange step, the phosphoric acid solution is treated 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 in the dissolving step, at least one acid selected from the group consisting of nitric acid, hydrochloric acid, sulfuric acid, phosphoric acid, and an organic acid is used as the acid.

6. Further comprising an acid leaching step prior to the precipitation step; The method for producing a phosphate according to any one of claims 1 to 3, wherein in the acid leaching step, a component contained in a starting material containing phosphorus is leached with an acid to obtain the phosphorus-containing liquid.

7. The method for producing a phosphate according to claim 6, wherein in the precipitation step, a time from obtaining the phosphorus-containing liquid to adding the alkali is changed.

8. The method for producing phosphate according to claim 6 or 7, wherein the starting material is steelmaking slag.

9. 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.