Method for producing phosphoric acid

Abstract

Provided is a novel method for producing phosphoric acid using sludge, human waste, or a processed product thereof as a raw material. A production method according to the present disclosure comprises: a step S11 for bringing a raw material into contact, in a solution, with a substance containing an anion capable of dissolving a sparingly soluble phosphate and forming a sparingly soluble metal salt; and a step S12 for removing the sparingly soluble metal salt formed in step S11. The sparingly soluble phosphate in step S11 contains a metal cation contained in the sparingly soluble metal salt in step S12.

Description

Method for Producing Phosphoric Acid

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

[0002] A method for producing phosphoric acid in which phosphoric acid is recovered from a raw material containing a poorly soluble phosphate is known in the prior art. For example, Patent Document 1 discloses a method for producing phosphoric acid using bone tissue as a raw material.

[0003] International Publication No. 2023 / 167167

[0004] It is known that sludge also contains phosphoric acid in the form of poorly soluble phosphate. However, Patent Document 1 does not disclose a method for producing phosphoric acid using sludge as a raw material.

[0005] An object of one aspect of the present invention is to provide a novel method for producing phosphoric acid, which uses sludge, human waste or processed products thereof as a raw material.

[0006] The present invention includes the following aspects: <1> A method for producing phosphoric acid from sludge, human waste, or processed products thereof, comprising the following steps: Step S11: A step of contacting the above raw material with a substance containing anion that can dissolve a sparingly soluble phosphate and form a sparingly soluble metal salt in a solution; Step S12: A step of removing the sparingly soluble metal salt formed in Step S11; Here, the sparingly soluble phosphate in Step S11 contains a metal cation contained in the sparingly soluble metal salt in Step S12. <2> A method for producing phosphoric acid using sludge, human waste, or processed products thereof as raw materials, comprising the following steps: Step S21: A step of contacting the raw materials with a solution of acid or a salt thereof; Step S22: A step of removing the insoluble substance generated in Step S21; Step S23: A step of contacting the solution obtained in Step S22 with a substance that can form a sparingly soluble phosphate; Step S24: A step of removing the liquid phase generated in Step S23; Step S25: A step of contacting the sparingly soluble phosphate obtained in Step S24 with a substance containing anion that can dissolve the sparingly soluble phosphate and form a sparingly soluble metal salt in a solution; Step S26: A step of removing the sparingly soluble metal salt formed in Step S25; Here, the sparingly soluble phosphate in Step S25 contains the metal cation contained in the sparingly soluble metal salt in Step S26. <3> The manufacturing method according to <1> or <2>, wherein the substance containing anion that can dissolve the above-mentioned sparingly soluble phosphate and form a sparingly soluble metal salt is sulfuric acid, sulfate, tartaric acid, tartrate, citric acid, citrate, maleic acid, maleate, malic acid, malate, or any combination thereof. <4> The manufacturing method according to <2>, wherein the substance that can form the above-mentioned sparingly soluble phosphate is (i) and / or (ii) below: (i) a substance containing one or more selected from the group consisting of calcium, magnesium, aluminum and ammonium; (ii) a base. <5> The manufacturing method according to any one of <1> to <4>, wherein the above-mentioned sparingly soluble metal salt is one or more selected from the group consisting of sparingly soluble calcium salt, sparingly soluble magnesium salt and sparingly soluble aluminum salt.

[0007] According to one aspect of the present invention, a novel method for producing phosphoric acid is provided, using sludge, human waste, or processed products thereof as raw materials.

[0008] This is a flowchart relating to Embodiment 1 of the present invention. This is a flowchart relating to Embodiment 2 of the present invention. This is a diagram showing the results of Example 4. This shows the appearance of frilly lettuce after the seedling stage. This is a diagram showing the results of Example 4. This shows the appearance of frilly lettuce after the 60-hole cultivation period. This is a diagram showing the results of Example 4. This shows the weight of the frilly lettuce after the 60-hole cultivation period.

[0009] One embodiment of the present invention is described below. However, the present invention is not limited to the configurations described below. The present invention can be modified in various ways within the scope of the claims. The technical scope of the present invention also extends to embodiments or examples obtained by appropriately combining the multiple technical means disclosed herein. In this case, the multiple technical means may be disclosed across multiple embodiments or examples.

[0010] Unless otherwise specified in this specification, "A to B" representing a numerical range means "greater than or equal to A and less than or equal to B".

[0011] In this specification, a substance containing anions that can dissolve sparingly soluble phosphates and form sparingly soluble metal salts (such as sparingly soluble calcium salts) is sometimes abbreviated as "metal removal substance."

[0012] In one embodiment, "slowly soluble metal salt" refers to a metal salt (such as a calcium salt) whose solubility in 100 mL of water at 25°C is 1.0 g or less, 0.5 g or less, 0.4 g or less, or 0.3 g or less.

[0013] [Embodiment 1] A method for producing phosphoric acid according to Embodiment 1 will be described with reference to the illustrative Figure 1. In general terms, the production method according to Embodiment 1 separates phosphoric acid by eluting phosphate ions through cation exchange and leaving unwanted metal cations as sparingly soluble metal salts. The production method according to Embodiment 1 has the advantage of being simple and requiring few steps. Each step shown in Figure 1 will be described in detail below.

[0014] [Step S11] In step S11, the raw material and the metal removal substance are brought into contact in a solution. As a result, the sparingly soluble phosphate (generally sparingly soluble metal phosphate salt) contained in the raw material is separated into sparingly soluble metal salt and free phosphate ions by cation exchange. Therefore, the sparingly soluble phosphate contained in the raw material and the sparingly soluble metal salt produced contain the same type of metal cation.

[0015] In step S11, the raw material is sludge, human waste, or processed products thereof. Examples of sludge include sewage sludge, human waste sludge, and factory sludge (such as sludge from food processing plants). In one embodiment, the sludge is organic sludge. In one embodiment, the sludge is sewage sludge. Examples of processed products of sludge include fermented sludge, sludge with a coagulant added, dried sludge, burned sludge, and concentrated or separated sparingly soluble phosphates (such as calcium phosphate and magnesium ammonium phosphate) contained in sludge or its processed products (such as sludge fermentation liquid). An example of human waste is animal feces. Examples of processed products of human waste include fermented feces, feces with a coagulant added, dried feces, burned feces, and concentrated or separated sparingly soluble phosphates (such as calcium phosphate and magnesium ammonium phosphate) contained in feces or its processed products (such as human waste fermentation liquid).

[0016] In step S11, examples of solvents for the solution include water, lower alcohols, glycerol, propane-1,2-diol, and 1,3-propanediol. A mixed solvent, obtained by mixing two or more solvents in an appropriate ratio, may also be used.

[0017] The metal removal substance contains anions that can form sparingly soluble metal salts. Examples of anions that can form sparingly soluble metal salts include sulfate ions, tartrate ions, citrate ions, maleate ions, and malate ions. Therefore, examples of the metal removal substance in step S11 include acids or salts containing these anions. Examples of acids include sulfuric acid, tartaric acid, citric acid, maleic acid, and malic acid. Examples of salts include sulfates, tartrates, citrates, maleates, and malates. These salts may be sodium salts, potassium salts, magnesium salts, ferric salts, ammonium salts, etc. Tartaric acid, tartrates, malic acid, and malates may be D-forms, L-forms, or mixtures thereof.

[0018] In one embodiment, the metal removal substance is one or more selected from the group consisting of sulfuric acid, sulfates, tartaric acid, tartrates, citric acid, citrates, maleic acid, and maleates. Examples of sulfates include sodium sulfate, sodium bisulfate, potassium sulfate, potassium bisulfate, sodium potassium sulfate, ammonium sulfate, ammonium bisulfate, and magnesium sulfate. Examples of tartrates include sodium tartrate, sodium bisulfate, potassium tartrate, potassium bisulfate, sodium potassium tartrate, ammonium tartrate, and magnesium tartrate. Examples of citrates include trilithium citrate, dilithium hydrogen citrate, lithium dihydrogen citrate, trisodium citrate, disodium hydrogen citrate, dipotassium citrate, dipotassium hydrogen citrate, dipotassium citrate, triammonium citrate, diammonium hydrogen citrate, ammonium dihydrogen citrate, and ammonium iron citrate. An example of a maleate is disodium maleate. Examples of malate salts include sodium malate, disodium malate, potassium malate, dipotassium malate, and ammonium hydrogen malate. In one embodiment, the metal removal substance is one or more selected from the group consisting of tartaric acid, citric acid, maleic acid, potassium bisulfate, and malic acid.

[0019] Examples of metals removed by the metal removal substance include calcium, magnesium, aluminum, iron, cadmium, and arsenic. In one embodiment, calcium is removed by the metal removal substance. In this case, the raw material contains calcium phosphate, and the resulting sparingly soluble metal salt is a sparingly soluble calcium salt. In another embodiment, magnesium is removed by the metal removal substance. In this case, the raw material contains magnesium phosphate, and the resulting sparingly soluble metal salt is a sparingly soluble magnesium salt. In another embodiment, aluminum is removed by the metal removal substance. In this case, the raw material contains aluminum phosphate, and the resulting sparingly soluble metal salt is a sparingly soluble aluminum salt.

[0020] Here, the term "calcium phosphate" includes salts containing ions other than phosphate and calcium ions. For example, calcium hydrogen phosphate is included in the term "calcium phosphate." Similarly, the term "magnesium phosphate" includes salts containing ions other than phosphate and magnesium ions. For example, magnesium ammonium phosphate is included in the term "magnesium phosphate."

[0021] In step S11, the concentration of the metal removal substance may be appropriately selected by a person skilled in the art. The lower limit of the concentration of the metal removal substance may be 0.01 mol / L or more, 0.05 mol / L or more, 0.1 mol / L or more, 0.2 mol / L or more, 0.3 mol / L or more, 0.4 mol / L or more, 0.5 mol / L or more, 0.6 mol / L or more, 0.7 mol / L or more, 0.8 mol / L or more, 0.9 mol / L or more, 1.0 mol / L or more, 1.5 mol / L or more, or 2.0 mol / L or more. The upper limit of the concentration of the metal removal substance may be 5.0 mol / L or less, 4.5 mol / L or less, 4.0 mol / L or less, 3.5 mol / L or less, 3.0 mol / L or less, 2.5 mol / L or less, 2.0 mol / L or less, 1.5 mol / L or less, 1.0 mol / L or less, 0.9 mol / L or less, 0.8 mol / L or less, 0.7 mol / L or less, 0.6 mol / L or less, 0.5 mol / L or less, 0.4 mol / L or less, 0.3 mol / L or less, 0.2 mol / L or less, or 0.1 mol / L or less.

[0022] In step S11, the contact time may be appropriately selected by a person skilled in the art. The lower limit of the contact time may be 1 minute or more, 5 minutes or more, 10 minutes or more, 30 minutes or more, 1 hour or more, 2 hours or more, 3 hours or more, 4 hours or more, 5 hours or more, 6 hours or more, 7 hours or more, 8 hours or more, 9 hours or more, 10 hours or more, 11 hours or more, 12 hours or more, 18 hours or more, 24 hours or more, 36 hours or more, or 48 hours or more. The upper limit of the contact time may be 7 days or less, 6 days or less, 5 days or less, 4 days or less, 3 days or less, 2.5 days or less, 2 days or less, 1.5 days or less, 1 day or less, 18 hours or less, 12 hours or less, 11 hours or less, 10 hours or less, 9 hours or less, 8 hours or less, 7 hours or less, 6 hours or less, 5 hours or less, 4 hours or less, 3 hours or less, 2 hours or less, or 1 hour or less.

[0023] [Step S12] In step S12, the sparingly soluble metal salt formed in step S11 is removed. Since the phosphate ions produced by cation exchange in step S11 dissolve in the solvent, and the sparingly soluble metal salt does not dissolve in the solvent, the two can be separated. In one embodiment, the sparingly soluble metal salt forms a precipitate. The sparingly soluble metal salt can be removed by centrifugation, filtration, or compression.

[0024] The phosphoric acid obtained in step S12 may be further purified as needed. For example, if anions other than phosphate ions or cations other than hydrogen ions remain in the supernatant, these may be removed using an ion exchange resin.

[0025] [Embodiment 2] The method for producing phosphoric acid according to Embodiment 2 will be described with reference to the exemplary Figure 2. In general terms, the production method according to Embodiment 2 involves converting the eluted phosphoric acid into a specific sparingly soluble phosphate, then eluting the phosphate ions by cation exchange, and separating the phosphoric acid by leaving the unwanted metal cations as sparingly soluble metal salts. Therefore, the latter half of the production method according to Embodiment 2 is the same as the production method according to Embodiment 1. The production method according to Embodiment 2 has the advantage of producing phosphoric acid with high purity. The steps shown in Figure 2 will be described in detail below.

[0026] [Step S21] In step S21, the raw material is brought into contact with a solution of the acid or its salt. This causes phosphate ions to leach into the solution from the sparingly soluble phosphate (generally sparingly soluble metal phosphate salt) contained in the raw material. In one embodiment, the solution of the acid or its salt is an acidic solution.

[0027] The raw materials, sludge, human waste, or processed products thereof, have been described in relation to Embodiment 1, so a further explanation will be omitted.

[0028] In step S21, the acid brought into contact with the raw material is not particularly limited. Examples of acids include hydrochloric acid, nitric acid, formic acid, sulfuric acid, and trichloroacetic acid. These acids may be diluted with a solvent. Examples of solvents for the solution include water, lower alcohols, glycerol, propane-1,2-diol, and 1,3-propanediol. A mixed solvent, obtained by mixing two or more solvents in an appropriate ratio, may also be used.

[0029] In step S21, the acid or its salt brought into contact with the raw material may be a metal removal substance. As explained above, the metal removal substance is omitted here. Bringing the raw material into contact with the metal removal substance in step S21 can remove large amounts of metal components from the raw material, which can be efficient.

[0030] In step S21, the concentration of the acid may be appropriately selected by a person skilled in the art. The lower limit of the acid concentration may be 0.01 mol / L or more, 0.05 mol / L or more, 0.1 mol / L or more, 0.2 mol / L or more, 0.3 mol / L or more, 0.4 mol / L or more, 0.5 mol / L or more, 0.6 mol / L or more, 0.7 mol / L or more, 0.8 mol / L or more, 0.9 mol / L or more, 1.0 mol / L or more, 1.5 mol / L or more, or 2.0 mol / L or more. The upper limit of the acid concentration may be 5.0 mol / L or less, 4.5 mol / L or less, 4.0 mol / L or less, 3.5 mol / L or less, 3.0 mol / L or less, 2.5 mol / L or less, 2.0 mol / L or less, 1.5 mol / L or less, 1.0 mol / L or less, 0.9 mol / L or less, 0.8 mol / L or less, 0.7 mol / L or less, 0.6 mol / L or less, 0.5 mol / L or less, 0.4 mol / L or less, 0.3 mol / L or less, 0.2 mol / L or less, or 0.1 mol / L or less.

[0031] In step S21, the contact time may be appropriately selected by a person skilled in the art. The lower limit of the contact time may be 1 minute or more, 5 minutes or more, 10 minutes or more, 30 minutes or more, 1 hour or more, 2 hours or more, 3 hours or more, 4 hours or more, 5 hours or more, 6 hours or more, 7 hours or more, 8 hours or more, 9 hours or more, 10 hours or more, 11 hours or more, 12 hours or more, 18 hours or more, 24 hours or more, 36 hours or more, or 48 hours or more. The upper limit of the contact time may be 7 days or less, 6 days or less, 5 days or less, 4 days or less, 3 days or less, 2.5 days or less, 2 days or less, 1.5 days or less, 1 day or less, 18 hours or less, 12 hours or less, 11 hours or less, 10 hours or less, 9 hours or less, 8 hours or less, 7 hours or less, 6 hours or less, 5 hours or less, 4 hours or less, 3 hours or less, 2 hours or less, or 1 hour or less.

[0032] [Step S22] In step S22, insoluble substances are removed. Since phosphate ions dissolve into the solution in step S21, the residual insoluble substances are poor in phosphoric acid. Therefore, by removing the insoluble substances, the concentration of phosphoric acid can be increased. In one embodiment, the insoluble substances form a precipitate. The insoluble substances can be removed by centrifugation, filtration, or compression.

[0033] [Step S23] In step S23, the solution obtained in step S22 is brought into contact with a substance capable of forming sparingly soluble phosphate. In step S23, sparingly soluble phosphate is formed from phosphate ions in the solution and separated from the solution. Only one type of substance capable of forming sparingly soluble phosphate may be used, or two or more types may be used in combination.

[0034] Examples of substances that can form sparingly soluble phosphates include substances containing cations that can form sparingly soluble phosphates (or substances that generate cations). Certain types of cations have a low solubility product with phosphate ions and form sparingly soluble phosphates. Examples of such cations include calcium ions, magnesium ions, aluminum ions, and ammonium ions. Therefore, examples of substances containing cations that can form sparingly soluble phosphates include substances containing one or more selected from the group consisting of calcium, magnesium, aluminum, and ammonium. Specific examples include calcium salts, magnesium salts, aluminum salts, ammonium salts, calcium hydroxide, magnesium hydroxide, and aluminum hydroxide. It is preferable that the anions contained in these substances remain in the solution and do not precipitate. From this viewpoint, chloride salts and hydroxides are preferred.

[0035] Other examples of substances that can form sparingly soluble phosphates include bases. By increasing the pH of a solution, the solubility product between phosphate ions and certain cations in the solution decreases, leading to the formation of sparingly soluble phosphates. Examples of bases include sodium hydroxide, potassium hydroxide, and aqueous ammonia.

[0036] By using a substance containing a cation capable of forming a sparingly soluble phosphate, the type of sparingly soluble phosphate produced can be controlled. For example, the type of anion contained in the resulting sparingly soluble phosphate can be limited to almost one type. This is preferable because it eliminates unstable elements in subsequent processes.

[0037] In step S23, the concentration of the substance that can form sparingly soluble phosphates may be appropriately selected by a person skilled in the art. The lower limit of the concentration of the substance that can form sparingly soluble phosphates may be 0.01 mol / L or more, 0.05 mol / L or more, 0.1 mol / L or more, 0.2 mol / L or more, 0.3 mol / L or more, 0.4 mol / L or more, 0.5 mol / L or more, 0.6 mol / L or more, 0.7 mol / L or more, 0.8 mol / L or more, 0.9 mol / L or more, 1.0 mol / L or more, 1.5 mol / L or more, or 2.0 mol / L or more. The upper limit of the concentration of substances that can form poorly soluble phosphates may be 5.0 mol / L or less, 4.5 mol / L or less, 4.0 mol / L or less, 3.5 mol / L or less, 3.0 mol / L or less, 2.5 mol / L or less, 2.0 mol / L or less, 1.5 mol / L or less, 1.0 mol / L or less, 0.9 mol / L or less, 0.8 mol / L or less, 0.7 mol / L or less, 0.6 mol / L or less, 0.5 mol / L or less, 0.4 mol / L or less, 0.3 mol / L or less, 0.2 mol / L or less, or 0.1 mol / L or less.

[0038] In step S23, the contact time may be appropriately selected by a person skilled in the art. The lower limit of the contact time may be 1 minute or more, 5 minutes or more, 10 minutes or more, 30 minutes or more, 1 hour or more, 2 hours or more, 3 hours or more, 4 hours or more, 5 hours or more, 6 hours or more, 7 hours or more, 8 hours or more, 9 hours or more, 10 hours or more, 11 hours or more, 12 hours or more, 18 hours or more, 24 hours or more, 36 hours or more, or 48 hours or more. The upper limit of the contact time may be 7 days or less, 6 days or less, 5 days or less, 4 days or less, 3 days or less, 2.5 days or less, 2 days or less, 1.5 days or less, 1 day or less, 18 hours or less, 12 hours or less, 11 hours or less, 10 hours or less, 9 hours or less, 8 hours or less, 7 hours or less, 6 hours or less, 5 hours or less, 4 hours or less, 3 hours or less, 2 hours or less, or 1 hour or less.

[0039] [Step S24] In step S24, the liquid phase is removed from the solution. In step S23, phosphate ions precipitate as a poorly soluble phosphate, so the remaining liquid phase is poor in phosphoric acid. Therefore, the concentration of phosphoric acid can be increased by removing the liquid phase. In one embodiment, the poorly soluble phosphate forms a precipitate, and the liquid phase forms a supernatant. The liquid phase can be removed by centrifugation, filtration, pressing, or the like.

[0040] [Step S25] In step S25, the poorly soluble phosphate obtained in step S24 is brought into contact with a metal removing substance in a solution. In step S25, the poorly soluble phosphate (generally a poorly soluble metal phosphate) is separated into a poorly soluble metal salt and free phosphate ions through cation exchange. Therefore, the poorly soluble phosphate in step S25 and the poorly soluble metal salt generated in step S25 contain the same type of metal cation. The metal removing substance may be the same substance as that used in step S21, or may be a different substance.

[0041] Step S25 is the same step as step S11 of Embodiment 1. Therefore, unless there is a contradiction, the description regarding step S11 is incorporated herein by reference for the description of step S25. For example, examples of the metal removing substance that can be used in step S25 include the metal removing substances exemplified in relation to step S11.

[0042] It should be noted that whereas in step S11 a raw material containing a poorly soluble phosphate is brought into contact with the metal removing substance, in step S25 a poorly soluble phosphate that has been purified to a certain extent is brought into contact with the metal removing substance. Therefore, from the viewpoint of obtaining high-purity phosphoric acid, the production method of Embodiment 2 including step S25 is more preferable.

[0043] [Step S26] In step S26, the poorly soluble metal salt formed in step S25 is removed. Step S26 is the same step as step S12 of Embodiment 1. Therefore, unless there is a contradiction, the description regarding step S12 is incorporated herein by reference for the description of step S26.

[0044] Steps S23 to S26 may be repeated two or more times. By repeating these steps, the purity of the resulting phosphoric acid can be further improved.

[0045] [Example 1] Phosphoric acid was produced from a processed product of sludge by the method according to Embodiment 1.

[0046] [Example 1-1] Phosphoric acid was produced using a bacterial cell phosphate fertilizer made from incinerated ash of sewage sludge as a raw material. Specific procedures are as follows. 1. 0.10 g of the bacterial cell phosphate fertilizer was weighed and immersed in the solution (1 mL) described in Table 1. The immersion time was 48 hours, and the immersion temperature was room temperature. 2. Precipitates of poorly soluble metal salts (mainly calcium salts) were removed, and the supernatant was collected. 3. The collected supernatant was diluted 4000-fold with distilled water. Using this sample, the concentration of phosphate ions was quantified by ion chromatography.

[0047] (Results) The results are shown in Table 1.

[0048] As can be seen from Table 1, phosphoric acid could not be recovered from the bacterial cell phosphate fertilizer treated with water containing no metal-removing substance. On the other hand, phosphoric acid could be recovered from the bacterial cell phosphate fertilizer treated with a solution containing a metal-removing substance.

[0049] [Example 1-2] Phosphoric acid was produced using incinerated ash A of sewage sludge as a raw material. Specific procedures are as follows. 1. 0.10 g of the incinerated ash A was weighed and immersed in the solution (1 mL) described in Table 2. The immersion time was 48 hours, and the immersion temperature was room temperature. 2. Precipitates of poorly soluble metal salts (mainly calcium salts) were removed, and the supernatant was collected. 3. The collected supernatant was diluted 10,000-fold with distilled water. Using this sample, the concentration of phosphate ions was quantified using a phosphoric acid measurement kit.

[0050] (Results) The results are shown in Table 2.

[0051] As can be seen from Table 2, phosphoric acid could not be recovered from incinerated ash A of sewage sludge treated with water containing no metal-removing substance. On the other hand, phosphoric acid could be recovered from incinerated ash A of sewage sludge treated with a solution containing a metal-removing substance.

[0052] [Examples 1-3] Phosphate was produced using magnesium ammonium phosphate derived from sewage sludge as a raw material. The specific procedure is as follows: 1. 0.10 g of magnesium ammonium phosphate was weighed and immersed in the solution (1 mL) described in Table 3. The immersion time was 48 hours and the immersion temperature was room temperature. 2. The precipitate of sparingly soluble metal salts (mainly magnesium salts) was removed and the supernatant was collected. 3. The concentration of phosphate ions in the collected supernatant was quantified.

[0053] (Results) The results are shown in Table 3.

[0054] As can be seen from Table 3, phosphoric acid could not be recovered from magnesium ammonium phosphate treated with water that did not contain a metal removal agent. On the other hand, phosphoric acid could be recovered from magnesium ammonium phosphate treated with a solution containing a metal removal agent.

[0055] [Examples 1-4] Phosphate was produced using calcium phosphate (hydroxyapatite) derived from sewage sludge as a raw material. The specific procedure is as follows: 1. 0.10 g of calcium phosphate derived from sewage sludge was weighed and immersed in the solution (1 mL) described in Table 4. The immersion time was 48 hours and the immersion temperature was room temperature. 2. The precipitate of sparingly soluble metal salts (mainly calcium salts) was removed and the supernatant was collected. 3. The concentration of phosphate ions in the collected supernatant was quantified.

[0056] (Results) The results are shown in Table 4.

[0057] As can be seen from Table 4, phosphoric acid could not be recovered from calcium phosphate treated with water that did not contain a metal-removing agent. On the other hand, phosphoric acid could be recovered from calcium phosphate treated with a solution containing a metal-removing agent.

[0058] [Examples 1-5] Phosphate was produced using incinerated ash B (obtained from a sewage treatment plant) derived from sewage sludge as a raw material. The specific procedure was as follows: 1. 5.0 g of incinerated ash B was weighed and immersed in 50 mL of a 1 mol / L malic acid aqueous solution. The immersion time was 24 hours and the immersion temperature was room temperature. 2. The precipitate of sparingly soluble metal salts (mainly calcium salts) was removed and the supernatant was collected. 3. The concentration of phosphate ions in the collected supernatant was quantified.

[0059] (Results) The results are shown in Table 5.

[0060] As can be seen from Table 5, phosphoric acid could not be recovered from incinerated ash B of sewage sludge treated with water that did not contain metal removal substances. On the other hand, phosphoric acid could be recovered from incinerated ash B of sewage sludge treated with a solution containing metal removal substances.

[0061] [Example 2] Phosphate was produced using calcium phosphate extracted from sewage sludge as a raw material by the method according to Embodiment 2. The specific procedure is as follows: 1. 0.10 g of calcium phosphate extracted from sewage sludge was weighed and immersed in the solution (1 mL) described in Table 6. The immersion time was 48 hours and the immersion temperature was room temperature. This allowed phosphate ions to be eluted into the supernatant. 2. The supernatant was collected by centrifugation at 10,000 × g at room temperature for 5 minutes. This removed some of the calcium and insoluble impurities. 3. A small amount of calcium hydroxide powder (equivalent to an equimolar amount by weight to the phosphoric acid) was added to the collected supernatant and allowed to stand at room temperature for 24 hours. This allowed calcium phosphate to precipitate. 4. The precipitate was collected by centrifugation at 10,000 × g at room temperature for 5 minutes. 5. The recovered precipitate was immersed in 1 mL each of 1.0 mol / L sulfuric acid, 0.6 mol / L tartaric acid, or 1.0 mol / L potassium bisulfate. The immersion time was 24 hours, and the immersion temperature was room temperature. This allowed phosphate ions to be eluted into the supernatant, and unwanted calcium was converted into sparingly soluble salts. 6. Each solution was centrifuged at 10,000 × g at room temperature for 5 minutes, and the supernatant was collected. 7. The concentration of phosphate ions in the collected supernatant was quantified.

[0062] (Results) The results are shown in Table 6.

[0063] As can be seen from Table 6, phosphoric acid was successfully recovered from calcium phosphate using the manufacturing method according to Embodiment 2.

[0064] [Example 3] The impurities contained in the phosphoric acid obtained by the manufacturing method according to Embodiment 1 were compared with the impurities contained in the phosphoric acid obtained by the manufacturing method according to Embodiment 2. Incinerator ash B derived from sewage sludge was used as the raw material. The specific procedure was as follows: 1. Incinerator ash B derived from sewage sludge was immersed in 1N hydrochloric acid. The immersion time was 48 hours, and the immersion temperature was room temperature. The content of various ions contained in the extract was quantified by ion chromatography. 2. Phosphoric acid was produced by the manufacturing method according to Embodiment 1. For the specific procedure, please refer to Example 1. The metal removal substances used are as shown in Table 7. The content of various ions contained in the supernatant obtained in step S12 was quantified by ion chromatography. In addition, the removal rate was calculated based on the ion content quantified in step 1. The calculation formula is as follows: (Ion content quantified in step 1 - Ion content quantified in step 2) ÷ Ion content quantified in step 1 × 100 3. Phosphoric acid was produced by the manufacturing method according to Embodiment 2. For specific procedures, please refer to Example 2. The metal removal materials used are as shown in Table 7. The content of various ions in the supernatant obtained in step S26 was quantified by ion chromatography. The removal rate was calculated based on the ion content quantified in step 1. The calculation formula is as follows: (Ion content quantified in step 1 - Ion content quantified in step 3) ÷ Ion content quantified in step 1 × 100

[0065] (Results) The results are shown in Table 7.

[0066] As shown in Table 7, the manufacturing method according to Embodiment 2 yielded phosphoric acid of much higher purity than the manufacturing method according to Embodiment 1. The amount of impurities in the phosphoric acid obtained by the manufacturing method according to Embodiment 2 was 10% by weight or less, which corresponds to technical grade.

[0067] [Example 4] The practicality of phosphoric acid obtained by a manufacturing method according to one embodiment of the present invention was investigated. Specifically, phosphoric acid was used as an agricultural fertilizer, and its effects were compared with those of commercially available phosphoric acid fertilizers.

[0068] (Production of phosphoric acid) Using the incinerated sewage sludge ash A used in Examples 1-2 as a raw material, phosphoric acid was produced in the same manner as in those examples. Tartaric acid at a concentration of 1.0 mol / L was used as the metal removal agent.

[0069] (Preparation of Nutrient Solution) A nutrient solution was prepared with the following composition. First, as a base nutrient solution, OAT House No. 2, OAT House No. 3, OAT House No. 5, and OAT House No. 6 (all from OAT Agrio Co., Ltd.) were mixed according to Formula B as described in the manufacturer's instructions. Each nutrient solution was diluted according to the instructions provided by the manufacturer before use. The following components were further added to the base nutrient solution to make the nutrient solution. Nutrient solution 1: Phosphate produced by the method according to one embodiment of the present invention. Control: OAT House No. 9 (phosphate-containing nutrient solution)

[0070] The composition of the prepared nutrient solutions is shown in Table 8. As shown in the table, the concentrations of phosphoric acid and nitrate were approximately the same in nutrient solution 1 and the control.

[0071] (Hydroponic cultivation) Using the prepared nutrient solution, frilly lettuce was cultivated from seed to seedling under the following cultivation conditions. ◆Germination period: 2 days, Planting density: approximately 1666 plants / m ２ ・Light irradiation time: 0 hours / day ・Temperature: 23 to 25℃ ・Humidity: 65 to 80% RH ・Carbon dioxide concentration: 1500 ppm ◆Seedling raising period: 12 days ・Planting density: Approximately 1666 plants / m ２ ・Light irradiation time: 24 hours / day ・Temperature: 23-25℃ ・Humidity: 65-80% RH ・Carbon dioxide concentration: 1500 ppm ◆60-hole cultivation period ・Period: 14 days ・Cultivation density: Approximately 111 plants / m ２ • Light exposure time: 16 hours / day • Temperature: 23-25°C • Humidity: 65-80% RH • Carbon dioxide concentration: 1500 ppm

[0072] During the germination and seedling stages, frilly lettuce was cultivated using either cultivation solution 1 or the control solution. During the 60-cell cultivation period, the same conditions were followed using cultivation solutions containing OAT House S1 and OAT House 2 (all manufactured by OAT Agrio Co., Ltd.).

[0073] (Results) The results are shown in Figures 3 to 5. Figure 3 shows the appearance of frilly lettuce at the end of the seedling period. Figure 4 shows the above-ground and underground parts of frilly lettuce at the end of the 60-cell cultivation period. Figure 5 is a graph showing the fresh weight of the above-ground part of frilly lettuce at the end of the 60-cell cultivation period. As can be seen from these figures, the nutrient solution containing phosphoric acid obtained by the manufacturing method according to one embodiment of the present invention promoted the growth of frilly lettuce to the same extent as a commercially available nutrient solution (control) containing compound phosphoric acid.

[0074] This invention can be used for the production of phosphoric acid, among other applications.

Claims

1. A method for producing phosphoric acid using sludge, human waste, or processed products thereof as raw materials, comprising the following steps: Step S11: A step of contacting the above raw materials with a substance containing anions that can dissolve sparingly soluble phosphate and form sparingly soluble metal salts in a solution; Step S12: A step of removing the sparingly soluble metal salt formed in Step S11; Here, the sparingly soluble phosphate in Step S11 contains metal cations contained in the sparingly soluble metal salt in Step S12.

2. A method for producing phosphoric acid using sludge, human waste, or processed products thereof as raw materials, comprising the following steps: Step S21: A step of contacting the above raw materials with a solution of acid or a salt thereof; Step S22: A step of removing insoluble substances generated in Step S21; Step S23: A step of contacting the solution obtained in Step S22 with a substance that can form a sparingly soluble phosphate; Step S24: A step to remove the liquid phase generated in step S23; Step S25: A step of contacting the sparingly soluble phosphate obtained in step S24 with a substance containing anion that can dissolve the sparingly soluble phosphate and form a sparingly soluble metal salt in a solution; Step S26: A step of removing the sparingly soluble metal salt formed in step S25; Here, the sparingly soluble phosphate in step S25 contains the metal cation contained in the sparingly soluble metal salt in step S26.

3. The manufacturing method according to claim 1 or 2, wherein the substance containing anion capable of dissolving the above-mentioned sparingly soluble phosphate and forming a sparingly soluble metal salt is sulfuric acid, sulfate, tartaric acid, tartarate, citric acid, citrate, maleic acid, maleate, malic acid, malate, or any combination thereof.

4. The manufacturing method according to claim 2, wherein the substance capable of forming the above-mentioned poorly soluble phosphate is (i) and / or (ii) below: (i) a substance comprising one or more selected from the group consisting of calcium, magnesium, aluminum and ammonium; (ii) a base.

5. The manufacturing method according to claim 1 or 2, wherein the sparingly soluble metal salt is one or more selected from the group consisting of sparingly soluble calcium salts, sparingly soluble magnesium salts, and sparingly soluble aluminum salts.

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