Method for producing phosphorus compound

Abstract

To provide a method for producing a phosphorus compound capable of obtaining a target phosphorus compound from a phosphorus-containing liquid.SOLUTION: In preparation step (S1), a phosphorus-containing liquid containing at least P and Fe is prepared by leaching a component contained in a steel refining slag as a starting material into an acid. In precipitation generation step (S2), alkali is added to the phosphorus-containing liquid to obtain a precipitate. The precipitate is a precursor of the target phosphorus compound. The pH of the phosphorus-containing liquid for obtaining the precipitate and the molar ratio of Fe to P (Fe / P) are adjusted according to the type of the target phosphorus compound.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for producing a phosphorus compound. [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 a limited number of countries, including China, the United States, and Morocco. 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 supply is imported.

[0003] Incidentally, the price of phosphorus resources has been rising sharply in recent years. For example, lithium iron phosphate has recently been used as a positive electrode material for batteries mounted on electric vehicles, and demand for it is expected to further expand in the future.

[0004] For this reason, methods for recovering used phosphorus in a desired form have been studied. For example, methods for producing a target phosphorus compound from a phosphorus-containing liquid have been studied, and Patent Document 1 discloses a method for producing iron phosphate, a raw material for lithium iron phosphate, by contacting a "mixed aqueous solution" containing phosphorus and iron with a "buffer solution." [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2012 / 023439 Summary of the Invention [Problem to be solved by the invention]

[0006] The present inventors have investigated conventional methods (such as the method disclosed in Patent Document 1) and found that there are cases in which the desired phosphorus compound cannot be obtained. More specifically, it has been difficult to obtain iron phosphate with a high ratio of ferric phosphate (FePO4) from a phosphorus-containing liquid using conventional methods.

[0007] The present invention has been made in consideration of the above points, and an object of the present invention is to provide a method for producing a phosphorus compound, which allows a target phosphorus compound to be obtained from a phosphorus-containing liquid. [Means for solving the problem]

[0008] As a result of extensive investigations, 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 [5]. [1] A method for producing a phosphorus compound, which produces a target phosphorus compound, comprising: a preparation step of preparing a phosphorus-containing liquid containing at least P and Fe by leaching components contained in steel refining slag as a starting material in an acid; and a precipitation step of obtaining a precipitate by adding an alkali to the phosphorus-containing liquid, wherein the precipitate is a precursor of the phosphorus compound, and the pH of the phosphorus-containing liquid and the molar ratio of Fe to P (Fe / P) when obtaining the precipitate are adjusted according to the type of the phosphorus compound. [2] The method for producing a phosphorus compound according to [1] above, wherein the phosphorus compound is a single-phase iron phosphate having a ferric phosphate content of 80 mass% or more. [3] The method for producing a phosphorus compound according to the above item [2], wherein the pH of the phosphorus-containing liquid having the molar ratio (Fe / P) in the range of more than 0.5 and less than 2.0 is adjusted to 2.0 or more and less than 4.0, thereby obtaining a precursor of the single-phase iron phosphate as the precipitate. [4] The method for producing a phosphorus compound according to any one of [1] to [3] above, further comprising a calcination step of calcining the precipitate after the precipitation step. [5] The method for producing a phosphorus compound according to any one of the above [1] to [4], wherein the steel refining slag is at least one of blast furnace slag, steelmaking slag, and reduced iron slag. Effect of the Invention

[0009] According to the present invention, the target phosphorus compound can be obtained from the phosphorus-containing liquid. [Brief description of the drawings]

[0010] [Figure 1] 1 is a flowchart showing the flow of a method for producing a phosphorus compound according to an embodiment of the present invention. [Diagram 2] 1 is an XRD pattern of a phosphorus compound obtained by calcining the precipitate. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] [Method of producing phosphorus compounds] The method for producing a phosphorus compound according to the present embodiment will be described with reference to FIGS. FIG. 1 is a flow chart showing the flow of the method for producing a phosphorus compound according to this embodiment. The method for producing a phosphorus compound according to the present embodiment is a method for producing a target phosphorus compound, and includes a preparation step (S1) and a precipitation step (S2) in this order. After the precipitation step (S2), a calcination step (S3) may be further included.

[0012] The phosphorus compound is a compound containing at least the elements phosphorus (P), iron (Fe) and oxygen (O). P, Fe and O may be bonded to each other. The phosphorus compound includes, for example, iron phosphate such as ferric phosphate (FePO4).

[0013] Preparation Step (S1) In the preparation step (S1), a phosphorus-containing liquid is prepared. The phosphorus-containing liquid contains at least P and Fe. The phosphorus-containing liquid may further contain calcium (Ca) and aluminum (Al) elements. However, from the viewpoint of obtaining iron phosphate as the target phosphorus compound, it is preferable that the content of metal elements (Ca, Al, etc.) other than Fe in the phosphorus-containing liquid subjected to the precipitation generation step (S2) described later is low.

[0014] In the preparation step (S1), a phosphorus-containing liquid is obtained by leaching components contained in the starting material with an acid. Specifically, for example, an acid is added to the starting material, followed by stirring and then filtering. As a result, a residue (I) and a leachate (A) are obtained. The leachate (A) is the phosphorus-containing liquid.

[0015] The starting material is iron and steel refining slag. Examples of the iron and steel refining slag include at least one of blast furnace slag, steelmaking slag, and reduced iron slag.

[0016] The acid used may be, for example, at least one selected from the group consisting of nitric acid, hydrochloric acid, sulfuric acid, phosphoric acid, and citric acid, with nitric acid or hydrochloric acid being preferred, and nitric acid being more preferred.

[0017] The pH of the phosphorus-containing liquid obtained in such a preparation step (S1) is usually 1.0 or less, and preferably less than 1.0.

[0018] <Precipitation Step (S2)> In the precipitation step (S2), an alkali is added to the phosphorus-containing liquid obtained in the preparation step (S1) 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. The precipitate is a precursor of the final product, the phosphorus compound.

[0019] Examples of the alkali used in the precipitation step (S2) include sodium hydroxide, calcium hydroxide, and aqueous ammonia (NH4OH), among which aqueous ammonia is preferred because it does not contain unnecessary cations. The concentration of aqueous ammonia is preferably 20 to 40% by mass, more preferably 25 to 35% by mass.

[0020] <Baking step (S3)> The method for producing a phosphorus compound of the present embodiment preferably further includes a calcination step (S3) after the precipitation step (S2). As described above, the precipitate obtained in the precipitation step (S2) is a precursor of the final product, the phosphorus compound. The phosphorus compound is obtained by calcining this precipitate (the precursor of the phosphorus compound). From the viewpoint of crystallizing the resulting phosphorus compound, the firing temperature is preferably 500° C. or higher, more preferably 570° C. or higher, and even more preferably 650° C. or higher. On the other hand, the firing temperature is preferably 900° C. or lower, more preferably 830° C. or lower, and even more preferably 750° C. or lower.

[0021] <pH and molar ratio (Fe / P) of phosphorus-containing liquid> In this embodiment, the pH of the phosphorus-containing liquid (hereinafter, also simply referred to as "phosphorus-containing liquid") when obtaining a precipitate (a precursor of the phosphorus compound) is adjusted depending on the type of phosphorus compound. In this embodiment, the molar ratio (Fe / P) of Fe to P in the phosphorus-containing liquid is adjusted according to the type of phosphorus compound. That is, a phosphorus-containing liquid with an adjusted molar ratio (Fe / P) is prepared.

[0022] For convenience, a phosphorus compound having an iron phosphate (FePO4) content of 80% by mass or more is called "single-phase iron phosphate," and a phosphorus compound having an iron phosphate content of less than 80% by mass is called "mixed-phase iron phosphate."

[0023] The ferric phosphate content is determined by Rietveld analysis. More specifically, an X-ray diffraction (XRD) pattern of the phosphorus compound is obtained under the following conditions. Next, the obtained XRD pattern is subjected to Rietveld analysis and pattern fitting using RIETAN-FP (profile: extended pseudo-Voigt function). In this way, the content of ferric phosphate (FePO4) in the phosphorus compound is determined. XRD equipment: SmartLab (Rigaku) ·Incoming X-ray: CuKα ray Diffraction angle 2θ: 5°~60° Scan speed: 24° / min Step width: 0.02° / min IS:2 / 3deg RS1: 20.0 min RS2: 20.1 min Tube voltage: 45kV ·Tube current: 100mA

[0024] The present inventors have investigated the conditions for obtaining single-phase iron phosphate as the desired phosphorus compound. Specifically, first, without adjusting the pH and molar ratio (Fe / P) of the phosphorus-containing liquid, an alkali was added to the phosphorus-containing liquid to obtain a precipitate (a precursor of the phosphorus compound), and the obtained precipitate was calcined at 700°C. As a result, mixed-phase iron phosphate was obtained as the phosphorus compound.

[0025] Therefore, the inventors have investigated the conditions for obtaining a precipitate and found that a precursor of single-phase iron phosphate can be obtained as a precipitate by adjusting the pH and molar ratio (Fe / P) of the phosphorus-containing liquid.

[0026] 《pH》 If the pH of the phosphorus-containing liquid is too high when obtaining the precipitate, the proportion of ferric phosphate decreases, and therefore, from the viewpoint of obtaining single-phase iron phosphate, the pH of the phosphorus-containing liquid is preferably less than 4.0, more preferably 3.5 or less, and even more preferably 3.0 or less. When the target phosphorus compound is not single-phase iron phosphate but mixed-phase iron phosphate or a compound other than iron phosphate, it is preferable to adjust the pH of the phosphorus-containing liquid to 4.0 or higher.

[0027] On the other hand, if the pH of the phosphorus-containing liquid is too low when obtaining the precipitate, single-phase iron phosphate is obtained, but the amount of precipitate produced is reduced due to the small amount of alkali added, resulting in a low yield. Therefore, from the viewpoint of obtaining a sufficient yield, the pH of the phosphorus-containing liquid is preferably 2.0 or higher, more preferably 2.3 or higher, and even more preferably 2.4 or higher.

[0028] In addition, when the phosphorus-containing liquid is added to an alkali (e.g., ammonia water), the pH of the phosphorus-containing liquid increases significantly and rapidly, which means that it is difficult to control the pH of the phosphorus-containing liquid, and the pH of the phosphorus-containing liquid cannot be adjusted to a desired value. For this reason, in the precipitation step (S2) of this embodiment, the phosphorus-containing liquid is not added to the alkali, but the alkali is added to the phosphorus-containing liquid.

[0029] Molar ratio (Fe / P) If the molar ratio (Fe / P) of the phosphorus-containing liquid is too large, the crystallinity of the obtained iron phosphate decreases, and the proportion of ferric phosphate decreases. Therefore, from the viewpoint of obtaining single-phase iron phosphate, the molar ratio (Fe / P) of the phosphorus-containing liquid is preferably close to 1.0, specifically, preferably less than 2.0, more preferably 1.6 or less, and even more preferably 1.2 or less. When the target phosphorus compound is not single-phase iron phosphate but mixed-phase iron phosphate or a compound other than iron phosphate, it is preferable to adjust the molar ratio (Fe / P) of the phosphorus-containing liquid to 2.0 or more.

[0030] On the other hand, if the molar ratio (Fe / P) of the phosphorus-containing liquid is too small, the pH range in which single-phase iron phosphate can be obtained may decrease, and the amount of alkali added will decrease, resulting in a decrease in the amount of precipitate produced and a decrease in yield. Therefore, from the viewpoint of obtaining a sufficient yield, the molar ratio (Fe / P) of the phosphorus-containing liquid is preferably more than 0.5, more preferably 0.7 or more, and even more preferably 0.9 or more.

[0031] The method for adjusting the molar ratio (Fe / P) of the phosphorus-containing liquid is not particularly limited, and examples thereof include a method of mixing two or more phosphorus-containing liquids having different molar ratios (Fe / P).

[0032] The present inventors added aqueous ammonia (concentration: 28 mass%) as an alkali to a phosphorus-containing liquid having a molar ratio (Fe / P) of 1.0 to adjust the pH and obtain a precipitate. The obtained precipitate was then fired at 700°C to obtain a crystallized phosphorus compound. The XRD pattern of the obtained phosphorus compound is shown in FIG. 2.

[0033] FIG. 2 shows the XRD pattern of the phosphorus compound obtained by calcining the precipitate, together with the pH value of the phosphorus-containing liquid when the precipitate was obtained. As shown in Figure 2, when the pH of the phosphorus-containing solution is between 7.8 and 4.0, the height of the peak near 2θ=29° (the peak indicating Fe3(PO4)O3) is relatively large. In this case, it can be said that the obtained phosphorus compound is not single-phase iron phosphate (it is mixed-phase iron phosphate). On the other hand, when the pH of the phosphorus-containing liquid is lower than 4.0, the height of this peak decreases, indicating that iron phosphate (single-phase iron phosphate) containing a large amount of ferric phosphate (FePO4) as the phosphorus compound was obtained. EXAMPLES

[0034] The present invention will be specifically described below with reference to examples, although the present invention is not limited to the examples described below.

[0035] <Examples 1-14> First, in the preparation step (S1), steelmaking slag was added to nitric acid (concentration: 0.5M) and stirred for 0.4 hours to obtain a phosphorus-containing liquid. At this time, multiple types of steelmaking slag were used to obtain multiple types of phosphorus-containing liquid with different molar ratios (Fe / P). The molar ratios (Fe / P) of the phosphorus-containing liquids are shown in Table 1 below.

[0036] Next, in the precipitation step (S2), ammonia water (concentration: 28% by mass) was added to the phosphorus-containing liquid while stirring at 200 rpm, thereby adjusting the pH of the phosphorus-containing liquid to the value shown in Table 1 below, and a precipitate (a precursor of the phosphorus compound) was generated. Then, in the calcination step (S3), the precipitate was calcined at 700° C. to obtain a crystallized phosphorus compound. The obtained phosphorus compound was subjected to Rietveld analysis by the above-mentioned method to determine the content of ferric phosphate (FePO4).

[0037] Depending on the content of ferric phosphate (FePO4) in the obtained phosphorus compound, "◯", "△" or "×" is entered in the "Production Phase" column in Table 1 below. Specifically, for the obtained phosphorus compounds, if the content of ferric phosphate (FePO4) was 80 mass% or more, it was marked with "○", if the content was 50 mass% or more and less than 80 mass%, it was marked with "△", and if the content was less than 50 mass%, it was marked with "×".

[0038] [Table 1]

[0039] <Summary of evaluation results> First, among Examples 1 to 14 shown in Table 1 above, Examples 4 to 11 in which the molar ratio (Fe / P) of the phosphorus-containing liquid is 1.0 will be compared. In Examples 9 to 11 in which the pH of the phosphorus-containing liquid was adjusted to the range of 4.0 to 7.9, the resulting phosphorus compound production phase was "x". In contrast, in Examples 4 to 8 in which the pH of the phosphorus-containing liquid was adjusted to the range of 2.0 to 2.9, the resulting phosphorus compound product phase was "○" and the content of ferric phosphate (FePO4) was 80 mass% or more.

[0040] Next, Examples 1 to 3 are compared with Examples 4 to 8 and Examples 12 to 14. All of these are examples in which the pH of the phosphorus-containing liquid was adjusted to a range of 2.0 to 3.0. In both Examples 1 to 3 in which the molar ratio (Fe / P) of the phosphorus-containing liquid was 0.5 and Examples 12 to 14 in which the molar ratio (Fe / P) of the phosphorus-containing liquid was 2.0, the product phase of the obtained phosphorus compound was “Δ”. In contrast, in Examples 4 to 8, in which the molar ratio (Fe / P) of the phosphorus-containing liquid was 1.0, the resulting phosphorus compound product phase was marked "◯" and the content of ferric phosphate (FePO4) was 80 mass% or more.

Claims

1. A method for producing a phosphorus compound, comprising the steps of: A preparation step of preparing a phosphorus-containing liquid containing at least P and Fe by leaching components contained in steel refining slag as a starting material with an acid; A precipitation step of adding an alkali to the phosphorus-containing liquid to obtain a precipitate, the precipitate is a precursor of the phosphorus compound, A method for producing a phosphorus compound, comprising adjusting a pH of the phosphorus-containing liquid and a molar ratio of Fe to P (Fe / P) when obtaining the precipitate, depending on the type of the phosphorus compound.

2. The method for producing a phosphorus compound according to claim 1, wherein the phosphorus compound is a single-phase iron phosphate having an iron(III) phosphate content of 80 mass% or more.

3. 3. The method for producing a phosphorus compound according to claim 2, wherein a pH of the phosphorus-containing liquid having the molar ratio (Fe / P) in the range of more than 0.5 and less than 2.0 is adjusted to 2.0 or more and less than 4.0, thereby obtaining a precursor of the single-phase iron phosphate as the precipitate.

4. The method for producing a phosphorus compound according to any one of claims 1 to 3, further comprising a calcination step of calcining the precipitate after the precipitation step.

5. The method for producing a phosphorus compound according to any one of claims 1 to 3, wherein the steel refining slag is at least one of blast furnace slag, steelmaking slag, and reduced iron slag.

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