Method for producing phosphoric acid

Abstract

The present disclosure provides a novel method for producing phosphoric acid. A method for producing phosphoric acid according to the present disclosure includes the following steps. And step S20, carrying out acid treatment on the raw material containing calcium phosphate to obtain an acid extracting solution. And S30, mixing the obtained acid extracting solution with alkali to obtain calcium phosphate precipitate. And S40, mixing the obtained calcium phosphate precipitate with acid and / or salt thereof, and forming insoluble calcium salt.

Description

Technical Field

[0001] This invention relates to a method for manufacturing phosphoric acid. Background Technology

[0002] Phosphoric acid is a widely used material in agricultural production and industry. It is typically manufactured from phosphate rock, but technologies for recovering phosphoric acid from waste have also been developed. For example, Patent Document 1 discloses a method for recovering phosphoric acid from feces and sludge from septic tanks. Patent Document 2 discloses a method for recovering phosphoric acid from steelmaking slag. Existing technical documents Patent documents

[0003] Patent Document 1: Japanese Patent Application Publication No. 2017-196619 Patent Document 2: Japanese Patent Application Publication No. 2011-213558 Summary of the Invention The technical problem that the invention aims to solve

[0004] Phosphoric acid is a crucial substance in agriculture, industry, and other sectors. Currently, most phosphoric acid is produced from phosphate rock, and Japan relies on imports to meet all its phosphate rock needs. On the other hand, phosphoric acid is also present in bone tissue and other materials in the form of calcium phosphate (for example, it is claimed that bone tissue, by weight before drying, contains approximately 33% phosphoric acid). Therefore, if phosphoric acid could be recovered from calcium phosphate-containing raw materials such as bone tissue, Japan would gain a significant source of phosphoric acid, including waste bones from slaughterhouses. Based on the above, there is a need to develop a method for recovering phosphoric acid from calcium phosphate-containing raw materials such as bone tissue.

[0005] One objective of this invention is to provide a novel method for manufacturing phosphoric acid. Technical means for solving problems

[0006] To solve the above problems, one technical solution of the present invention relates to a method for manufacturing phosphoric acid, which includes the following steps: Step S20: Acid treatment is performed on the raw material containing calcium phosphate to obtain an acid extract; Step S30: Mix the obtained acid extract with alkali to obtain calcium phosphate precipitate; Step S40: The obtained calcium phosphate precipitate is mixed with an acid and / or its salt to form an insoluble calcium salt. Invention Effects

[0007] According to one technical solution of the present invention, a novel method for manufacturing phosphoric acid is provided. Attached Figure Description

[0008] Figure 1This is a flowchart illustrating a method for manufacturing phosphoric acid according to one of the technical solutions of the present invention. Figure 2 This is a partial flowchart illustrating the first implementation of step S40. Figure 3 This is a partial flowchart illustrating the second implementation scheme of step S40. Figure 4 A graph illustrating the effect of raw material pretreatment on the amount of phosphoric acid contained in the acid extract. Figure 5 A graph illustrating the effect of pH on the efficiency of separating phosphate and calcium salts from calcium phosphate precipitate. Detailed Implementation

[0009] Hereinafter, an example of an embodiment of the present invention will be described in detail, but the present invention is not limited thereto.

[0010] In this instruction manual, unless otherwise specified, "AB" indicating a numerical range means "above A and below B".

[0011] In this specification, "calcium phosphate" refers to a substance that may contain phosphate ions, calcium ions, and any other ions. The specific composition of calcium phosphate is not particularly limited. Examples of calcium phosphate include monocalcium phosphate, dicalcium phosphate, tricalcium phosphate, β-tricalcium phosphate, octacalcium phosphate, hydroxyapatite, fluorapatite, chloroapatite, and carbonate apatite. Specific examples of raw materials containing calcium phosphate include bone tissue (usually composed primarily of carbonate apatite), apatite (usually composed primarily of chloroapatite), chicken manure ash, incinerator ash, sewage sludge, dried sludge, and dephosphorization furnace slag (usually composed primarily of fluorapatite). In one embodiment, the raw material containing calcium phosphate is bone tissue.

[0012] In this specification, solids that dissolve to produce an acidic solution are also generally referred to as "acids". Examples of such acids include some organic acids, specifically tartaric acid and citric acid.

[0013] In current technologies, most phosphoric acid is produced by purifying phosphate rock. Mining phosphate rock consumes enormous amounts of energy, and the purification process releases large quantities of carbon dioxide, thus leading to global environmental damage in the production of phosphoric acid from phosphate rock. Therefore, from a sustainable industry perspective, current methods of phosphoric acid production present technical problems. Furthermore, the introduction of a carbon credit system in the future would incur additional costs associated with obtaining phosphoric acid from phosphate rock.

[0014] Furthermore, phosphate rock producing countries such as the United States and China are reducing their mining output and increasing imports, leading to a surge in phosphoric acid prices globally. Japan imports over 400,000 tons of phosphoric acid annually, relying entirely on imports. Based on this situation, from the perspective of economic security, phosphoric acid was designated as a substance of particular importance (December 2022). In this regard, the benefits of domestic phosphoric acid production in Japan are immeasurable. Phosphoric acid is indispensable in fertilizers, semiconductor manufacturing, and other industries, and its shortage would have a significant impact on these industries. In particular, a shortage of phosphoric acid used as fertilizer would likely lead to a sharp decline in the domestic production of agricultural products such as grains, vegetables, root vegetables, and fruits. As a result, Japan's food self-sufficiency rate would further decrease, making it impossible to guarantee a healthy diet.

[0015] As shown in Patent Documents 1 and 2, techniques for extracting phosphoric acid from waste have been studied to date, but most of these techniques suffer from impurities and heterogeneity. In contrast, raw materials containing calcium phosphate (especially bone tissue) are tissues with extremely high homogeneity. In particular, livestock or farmed fish are raised under largely similar conditions, regardless of their origin, so their waste bones are very homogeneous raw materials. Furthermore, it is difficult to imagine that bone tissue from livestock or farmed fish fed with ordinary feed would contain heavy metals or radioactive elements. For example, for livestock raised for meat, the time from birth to slaughter is relatively short, so even if there is a possibility of absorbing heavy metals or radioactive elements from the environment, the time is extremely short. Therefore, bone tissue contains almost no aluminum, arsenic, lead, nickel, chromium, manganese, or other components. Thus, the method for manufacturing phosphoric acid according to one technical solution of the present invention can solve the problem of impurities and heterogeneity. However, solving this problem is not a necessary requirement of the present invention. Furthermore, in one embodiment of the present invention, it is also contemplated that natural animal or fish bone tissue, or substances containing calcium phosphate other than bone tissue, be used as raw materials.

[0016] [1. Overview of phosphoric acid manufacturing methods] A summary example of a method for producing phosphoric acid according to one technical solution of the present invention is shown below. Figure 1 The flowchart. Raw materials containing calcium phosphate (especially bone tissue) contain, in addition to phosphoric acid, inorganic components such as calcium and organic components such as collagen. Figure 1 In the illustrated method, phosphoric acid is dissolved in steps S10 and S20, and components other than phosphoric acid and calcium are removed in step S30. Then, calcium is removed in step 40. Each step is described in detail below.

[0017] [1.1. Step S10] In step S10, the raw material containing calcium phosphate is pretreated. Step S10 is optional and may be omitted. By pretreating the raw material, the amount of phosphoric acid contained in the acid extract can be increased (see Example 7).

[0018] The raw materials used in step S10 can be of any kind. When the raw materials contain bone tissue, the bone tissue can come from any organism. Examples of organisms include mammals, birds, amphibians, and fish. For large-scale production, raw materials that are readily available are preferred; for example, bone tissue from livestock (cattle, pigs, sheep, chickens, etc.) or whales or farmed fish is preferred. The raw materials can be chopped or pulverized before or after step S10. This allows for more efficient decomposition of the raw materials and may thus shorten manufacturing time.

[0019] In one embodiment, in step S10, the raw material is heated. The heating temperature can be above 30°C or 40°C, below 100°C or 80°C. Heating can also be performed while the raw material is immersed in acid.

[0020] In one embodiment, in step S10, the raw material is heated under pressure. The pressure can be 200 kPa or more, 1 MPa or more, 500 MPa or less, or 800 MPa or less. The heating temperature can be 10°C or more, 50°C or more, 120°C or less, or 200°C or less. Heating under pressure can also be performed while the raw material is immersed in acid.

[0021] In one embodiment, in step S10, the raw material is irradiated with microwaves. Heating, pressurized heating, and microwave irradiation can also be implemented in any combination. Microwave irradiation is preferred because it provides results quickly. The irradiation time can be appropriately determined based on the volume of the raw material. For example, the volume of the raw material is 1 cm³. 3 The irradiation time can be 5 seconds or more, 10 seconds or more, or 15 seconds or more, and less than 10 minutes, 7 minutes or less, or less than 5 minutes. Of course, when the volume of the raw material is large, the irradiation time can be further extended. If the microwave irradiation time is within an appropriate range, inorganic components containing phosphoric acid can be extracted from the raw material efficiently.

[0022] [1.2. Step S20] In step S20, the raw material containing calcium phosphate is subjected to acid treatment to obtain an acid extract. In step S20, the inorganic components containing phosphoric acid are separated from the raw material and dissolved into the acid extract.

[0023] The acid used to process the raw material in step S20 is not particularly limited. Examples of acids include hydrochloric acid, nitric acid, formic acid, sulfuric acid, and trichloroacetic acid. Acidic decalcification solutions such as Plank-Rychlo solution can also be used. From the viewpoint of easy availability, it is preferable to select one or more acids from the group consisting of nitric acid, hydrochloric acid, formic acid, and sulfuric acid. From the viewpoint of phosphoric acid recovery efficiency, it is preferable to select one or more acids from the group consisting of hydrochloric acid, sulfuric acid, and nitric acid, and more preferably one or more acids from the group consisting of hydrochloric acid and nitric acid. Two or more acids can also be mixed in an appropriate ratio.

[0024] In step S20, the raw material can be acid-treated using a solution obtained by diluting the acid in a solvent. Examples of solvents include water, lower alcohols, glycerol, propane-1,2-diol, and 1,3-propanediol. Two or more solutions can also be mixed in appropriate ratios.

[0025] The acid concentration can be appropriately determined based on the volume of the raw material to be acid-treated. When the volume of the raw material is small, a low-concentration acid can be used. When the volume of the raw material is large, a higher concentration acid is preferred. When using a low-concentration acid for acid treatment, it is preferable to treat the micronized raw material. However, even when the volume of the raw material is large, by increasing the acid concentration and allowing for prolonged impregnation, inorganic components can be sufficiently extracted. For example, when the volume of the raw material is several cm³... 3 When using bone powder as raw material, the lower limit of the acid concentration in step S20 can be 0.6 mol / L or higher, 0.7 mol / L or higher, 0.8 mol / L or higher, or 0.9 mol / L or higher. The upper limit of the acid concentration in step S20 can be 2.0 mol / L or lower, 1.5 mol / L or lower, 1.0 mol / L or lower, or 0.9 mol / L or lower. If the acid concentration is within the above range, inorganic components containing phosphoric acid can be extracted efficiently, and the acid concentration will not be too high, thus reducing the cost of neutralizing the acid extract.

[0026] Examples of preferred acid concentrations for acid treatment of micronized raw materials are shown below. When the acid is nitric acid, the lower limit of the nitric acid concentration is preferably 0.6 mol / L or more, more preferably 0.7 mol / L or more. The upper limit of the nitric acid concentration is preferably 1.0 mol / L or less, more preferably 0.9 mol / L or less. When the acid is hydrochloric acid, the lower limit of the hydrochloric acid concentration is preferably 0.8 mol / L or more, more preferably 0.9 mol / L or more. The upper limit of the hydrochloric acid concentration is preferably 1.2 mol / L or less, more preferably 1.1 mol / L or less. When the acid is formic acid, the lower limit of the formic acid concentration is preferably 0.8 mol / L or more, more preferably 0.9 mol / L or more. The upper limit of the formic acid concentration is preferably 1.2 mol / L or less, more preferably 1.1 mol / L or less. When the acid is sulfuric acid, the lower limit of the sulfuric acid concentration is preferably 0.8 mol / L or more, more preferably 0.9 mol / L or more. The upper limit of the sulfuric acid concentration is preferably 1.2 mol / L or less, more preferably 1.1 mol / L or less. However, the above concentration is an example of a preferred concentration when the raw material has been micronized, and the acid concentration can be further increased when the volume of the raw material is larger.

[0027] For example, when the volume is several cm 3 When using bone powder as raw material, the lower limit of the extraction time in step S20 is preferably 6 hours or more, more preferably 8 hours or more, and even more preferably 10 hours or more. The upper limit of the extraction time in step S20 is preferably 48 hours or less, more preferably 24 hours or less, and even more preferably 14 hours or less. If the extraction time is within the above range, the inorganic components containing phosphoric acid contained in the raw material can be sufficiently extracted.

[0028] For example, when the volume is several cm 3 When using bone powder as raw material, the acid treatment temperature in step S20 is preferably 5-60°C. Acid treatment within this temperature range reduces the unpleasant odor associated with acid treatment. Therefore, the location requirements for the manufacturing plant become less stringent. Furthermore, to maintain a temperature below 60°C, expensive specialized equipment is not required; the temperature can be kept constant using a water bath or incubator.

[0029] In step S20, in addition to the acid, a chelating agent capable of capturing calcium ions may be added. Alternatively, in step S20, the raw material may be treated with a chelating agent before and after the acid treatment (the solution may or may not be changed during the acid treatment and chelating agent treatment). Examples of chelating agents include ethylenediaminetetraacetic acid (EDTA, CAS Registry No.: 60-00-4), ethylene glycol ether diaminetetraacetic acid (EGTA, CAS Registry No.: 67-42-5), and ethylenediamine-N,N'-disuccinic acid (EDDS, CAS Registry No.: 20846-91-7). In step S20, the pH of the solution containing the chelating agent is preferably 6.0-8.0. For example, when the volume is several cm³... 3 When the following bone fragments are used as raw materials, the lower limit of the concentration of the chelating agent in step S20 can be 0.1 mol / L or more, 0.2 mol / L or more, 0.3 mol / L or more, or 0.4 mol / L or more. The upper limit of the concentration of the chelating agent in step S20 can be 0.9 mol / L or less, 0.8 mol / L or less, 0.7 mol / L or less, or 0.6 mol / L or less.

[0030] [1.3. Step S30] In step S30, the acid extract is mixed with an alkali. Through step S30, the phosphate ions contained in the acid extract precipitate as calcium phosphate, while other components (such as those derived from bone fragments) remain in the supernatant. Therefore, by recovering the precipitate, phosphoric acid can be purified. Examples of usable alkalis include sodium hydroxide and potassium hydroxide.

[0031] [1.4. Step S40] In step S40, calcium phosphate is mixed with an acid and / or its salt to further form a sparingly soluble calcium salt. In a first embodiment, calcium phosphate is mixed with an acid and / or its salt that forms a sparingly soluble calcium salt. Then, an alkali is mixed in as needed to lower the pH of the system. In a second embodiment, calcium phosphate is mixed with an acid to obtain a solution of phosphate ions and calcium ions. Then, other acids or their salts are mixed in to form a sparingly soluble calcium salt. By removing the sparingly soluble calcium salt formed in step S40, phosphoric acid can be concentrated. A step may also be included to recover residual phosphoric acid from the sparingly soluble calcium salt obtained in step S40.

[0032] [1.5. Step S50] In step S50, the supernatant after calcium removal is purified. The supernatant may contain anions and cations other than phosphate ions from the upstream step. High-purity phosphoric acid can be obtained by adsorbing these ions onto, for example, an ion exchange resin. In step S50, only anions other than phosphate ions may be removed, only cations may be removed, or both may be removed.

[0033] [2. First implementation scheme of step S40] Figure 2 This is a partial flowchart illustrating a first embodiment of step S40. Step S40 of the first embodiment includes step S42 and step S44 as an optional step. The steps are described in detail below.

[0034] [2.1. Step S42] In step S42, calcium phosphate is mixed with an acid and / or its salt that forms a sparingly soluble calcium salt. In step S42, the pH of the system is lowered by mixing the acid, thus dissolving the calcium phosphate precipitate. Simultaneously (or, after step S44), the anions contained in the acid react with the calcium ions to form a sparingly soluble calcium salt. By removing the sparingly soluble calcium salt, the phosphoric acid is concentrated in the liquid phase.

[0035] Examples of acids and / or their salts mixed in step S42 include condensed phosphoric acid, tartaric acid, oxalic acid, sulfuric acid, and their salts. These acids and / or their salts have sufficient strength to dissolve calcium phosphate and contain anions that form insoluble calcium salts. Examples of salts mixed in step S42 will be described in Section [3.2] below.

[0036] From the viewpoint of avoiding impurities, it is preferable to mix condensed phosphoric acid and / or its salt in step S42. In step S42, due to the solubility product, some of the anions contained in the acid will remain in the liquid phase. However, the condensed phosphoric acid anion is converted to phosphoric acid through hydrolysis, and therefore is essentially unaffected by the residual anions. In this specification, condensed phosphoric acid refers to an acid formed by the condensation of two or more phosphoric acids via phosphate ester bonds. Examples of condensed phosphoric acid include pyrophosphoric acid, tripolyphosphoric acid, and tetrapolyphosphoric acid. In one embodiment, the condensed phosphoric acid is pyrophosphoric acid.

[0037] From the viewpoint of calcium removal capacity, it is preferable to mix one or more of the group consisting of tartaric acid, oxalic acid, and their salts in step S42. This is because calcium tartrate and calcium oxalate have particularly low solubility (solubility in 100 mL of water at 25°C: calcium tartrate: 0.0023 g, calcium oxalate: 0.00067 g). Therefore, these calcium salts preferentially precipitate out as precipitates compared to calcium phosphate.

[0038] In step S42, the lower limit of the pH of the system after mixing the acid and / or its salt that forms the insoluble calcium salt can be 1.0 or higher, 1.1 or higher, 1.2 or higher, 1.3 or higher, 1.4 or higher, 1.5 or higher, 1.6 or higher, 1.7 or higher, 1.8 or higher, 1.9 or higher, 2.0 or higher, 2.1 or higher, 2.2 or higher, 2.3 or higher, 2.4 or higher, 2.5 or higher, 2.6 or higher, 2.7 or higher, 2.8 or higher, 2.9 or higher, 3.0 or higher, 3.1 or higher, 3.2 or higher, 3.3 or higher, 3.4 or higher, 3.5 or higher, 3.6 or higher, 3.7 or higher, 3.8 or higher, 3.9 or higher, or 4.0 or higher. In step S42, the upper limit of the pH of the system after mixing the acid and / or its salt that forms the sparingly soluble calcium salt can be below 6.0, 5.9, 5.8, 5.7, 5.6, 5.5, 5.4, 5.3, 5.2, 5.1, 5.0, 4.9, 4.8, 4.7, 4.6, 4.5, 4.4, 4.3, 4.2, 4.1, 4.0, 3.9, 3.8, 3.7, 3.6, 3.5, 3.4, 3.3, 3.2, 3.1, 3.0, 2.9, 2.8, 2.7, 2.6, or 2.5.

[0039] [2.2. Step S44] In step S44, a base is mixed to lower the pH of the system. Step S44 is optional and may be omitted. Depending on the type of acid mixed in step S42, a poorly soluble calcium salt will be formed after step S44. For example, if pyrophosphate is mixed in step S42, step S44 is preferred.

[0040] As PO4 3- With Ca 2+ The solubility product of the salt Ca3(PO4)2 (calcium phosphate) at 25°C is 2.0 × 10⁻⁶. -29 mol / L, as HPO4 2- With Ca 2+ The solubility product of the salt CaHPO4 (calcium hydrogen phosphate) at 25°C is 2.6 × 10⁻⁶. -7 mol / L, as P2O7 4- With Ca 2+ The solubility product of the salt Ca2P2O7 (calcium pyrophosphate) at 25°C is 2.0 × 10⁻⁶. -19 mol / L. Based on this difference in solubility, if PO4 is almost non-existent in the system... 3-Calcium pyrophosphate is formed in a suitable environment, allowing for the efficient removal of calcium from solutions containing phosphate and calcium ions. The acid dissociation constants for phosphate are pK1 = 2.12, pK2 = 7.21, and pK3 = 12.67, while those for pyrophosphate are pK1 = 0.2, pK2 = 0.9, pK3 = 6.76, and pK4 = 8.95. Therefore, at approximately pH 10, pyrophosphate is in the P2O7 phase. 4- Pyrophosphate in the PO4 state accounts for 90%, while phosphoric acid in the PO4 state accounts for 20%. 3- The phosphoric acid in this state is only 1%. Therefore, when pyrophosphate is mixed in step S42, calcium pyrophosphate can be preferentially precipitated by setting the pH of the solution to around 10 in step S44.

[0041] [3. Second implementation scheme for step S40] Figure 3 This is a partial flowchart illustrating step S40 in the second embodiment. Step S40 in the second embodiment includes steps S46 and S48. Each step is described in detail below.

[0042] [3.1. Step S46] In step S46, the calcium phosphate precipitate is mixed with an acid. This causes the precipitated calcium phosphate to dissolve again. Examples of usable acids include hydrochloric acid, nitric acid, formic acid, and phosphoric acid. In step S46, it is preferable to mix with phosphoric acid. This ensures that the anion added to the system is a phosphate ion, thus not affecting the purity of the phosphoric acid obtained in step S40.

[0043] In the second embodiment, steps S30 and S46 can also be repeated. By repeating these steps, the purity of phosphoric acid increases. The number of times steps S30 and S46 are repeated can be, for example, two or more, three or more, four or more, or five or more. From an economic point of view, the number of times steps S30 and S46 are repeated can be, for example, less than 10 times. After repeating steps S30 and S46, before proceeding to step S15, a necessary number of washing processes can also be performed, which involves rinsing the calcium phosphate precipitate with pure water to remove unwanted components.

[0044] [3.2. Step S48] In step S48, the solution of phosphate ions and calcium ions is mixed with an acid and / or its salt that forms a sparingly soluble calcium salt. As a result, the calcium ions in the solution precipitate as a sparingly soluble calcium salt. The precipitated sparingly soluble calcium salt is removed by centrifugation, filtration, or the like. Furthermore, the anions contained in the acid and / or salt in step S48 are different from the anions contained in the acid in step S46.

[0045] In one embodiment, the solubility of the sparingly soluble calcium salt at 25°C (maximum amount dissolved in 100 mL of water) is preferably 0.3 g or less, more preferably 0.1 g or less, even more preferably 0.05 g or less, and even more preferably 0.01 g or less.

[0046] Specific examples of sparingly soluble calcium salts include calcium sulfate, calcium sulfite, calcium carbonate, calcium tartrate, calcium oxalate, calcium citrate, calcium silicate, and calcium salts of condensed phosphoric acid (such as calcium pyrophosphate). Similarly, examples of acids that mix with the solution of phosphate and calcium ions in step S48 include sulfuric acid, sulfurous acid, carbonic acid, tartaric acid, oxalic acid, citric acid, silicic acid, and condensed phosphoric acid (such as pyrophosphate). Furthermore, examples of salts that mix with the solution of phosphate and calcium ions in step S48 include sulfates, sulfites, carbonates, bicarbonates, tartrates, oxalates, citrates, silicates, and salts of condensed phosphoric acid (such as pyrophosphate). These salts can be sodium, potassium, magnesium, iron, or ammonium salts. Tartaric acid and tartrates can be of the D-type, L-type, or mixtures thereof. Silicic acid is a general term for acids whose main components are silicon, oxygen, and hydrogen, including orthosilicic acid and metasilicic acid.

[0047] When an acid (HA) or salt (MA) is mixed in a solution of phosphate ions and calcium ions, the resulting anion A... n- For this purpose, it is preferable that the calcium salt has a small solubility product and an acid dissociation constant pKa far from the third-order acid dissociation constant of phosphate (12.67). If such anion is chosen, by appropriately adjusting the pH of the system, it is possible to form a sparingly soluble calcium salt while minimizing the precipitation of calcium phosphate. For reference, the acid dissociation constants of representative acids and the solubility of calcium salts (25°C, per 100 mL of water) are illustrated below. The solubility product (25°C) is also illustrated for some calcium salts. ● Sulfuric acid (H2SO4) pK1 = -5 pK2 = 1.99 • Solubility product of CaSO4: 6.1 × 10⁻⁶ -5 mol / L • Solubility of CaSO4: 0.25 g ● Sulfurous acid (H2SO3) pK1 = 1.85 pK2 = 7.19 • Solubility of CaSO3: 0.0043 g ● Carbonic acid (H2CO3) pK1 = 6.35 pK2 = 10.33 • Solubility product of CaCO3: 4.7 × 10⁻⁶ -9 mol / L • Solubility of CaCO3: 0.0013 g ● Tartaric acid (C4O4(OH)2) pK1 = 2.93 pK2 = 4.20 • Solubility of CaC4O4(OH)2: 0.01 g ● Pyrophosphate (H4P2O7) pK1 = 0.2 pK2 = 0.9 pK3 = 6.76 pK4 = 8.95 • Solubility product of Ca2P2O7: 2.0 × 10⁻⁶ -19 mol / L • Solubility of Ca2P2O7: less than 0.01 g ● Oxalic acid (H2C2O4) pK1 = 1.27 pK2 = 4.27 • Solubility product of CaC₂O₄: 2.0 × 10⁻⁶ -8 mol / L • Solubility of CaC₂O₄: 0.00067 g ● Citric acid (C(OH)(CH2COOH)2COOH) pK1 = 3.1 pK2 = 4.8 pK3 = 6.4 The solubility of Ca3(C(OH)(CH2COOH)2COOH)2·4H2O is 0.085 g. ● Metasilicic acid (H2SiO3) • Solubility of CaSiO3: 9.5 × 10⁻⁶ -3 g ● Orthosilicic acid (H4SiO4) • Solubility of Ca2SiO4: 0.01 g ● Phosphoric acid (H3PO4: reference) pK1 = 2.12 pK2 = 7.21 pK3 = 12.67 • Solubility product of CaHPO4: 2.6 × 10⁻⁶ -7 mol / L • Solubility of CaHPO4: 0.02 g • Solubility product of Ca3(PO4)2: 2.0 × 10 -29 mol / L • Solubility of Ca3(PO4)2: 0.002 g

[0048] Considering the balance between solubility and pKa, the substances mixed in step S48 are preferably selected from one or more of the group consisting of tartaric acid, tartrates, sulfurous acid, sulfites, oxalic acid, oxalates, citric acid, citrates, silicates, silicates, condensed phosphoric acid (such as pyrophosphate), and condensed phosphates (such as pyrophosphate). Examples of tartrates include sodium tartrate, sodium bitartrate, potassium tartrate, potassium hydrogen tartrate, potassium sodium tartrate, and ammonium tartrate. Examples of sulfites include sodium sulfite, sodium bisulfite, potassium sulfite, ammonium sulfite, and potassium sodium sulfite. Examples of oxalates include sodium oxalate and ammonium oxalate. Examples of citrates include monosodium citrate, disodium citrate, trisodium citrate, potassium citrate, and ferric ammonium citrate. Examples of silicates include sodium metasilicate. Examples of pyrophosphates include sodium pyrophosphate, potassium pyrophosphate, and ferric pyrophosphate. The anions that make up these acids or salts have lower solubility than calcium ions in their salts than calcium sulfate, so it can be said that they have a higher calcium removal capacity.

[0049] The amount of acid and / or its salt mixed in step S48 can be appropriately set by those skilled in the art. For example, the amount of acid and / or its salt added can be such that the concentration of acid and / or its salt in the mixed system is 0.2 M or more, 0.4 M or more, 0.6 M or more, 0.8 M or more, or 1.0 M or more. A higher amount of acid and / or its salt added can reduce residual calcium. The upper limit of the amount of acid and / or its salt added can be such that the concentration of sulfate in the mixed system is 3.0 M or less, 2.0 M or less, or 1.0 M. A lower amount added results in a lower amount of anions other than phosphate ions and cations other than hydrogen ions in the system.

[0050] In step S48, the upper and lower limits of the pH of the system after mixing the acid and / or its salt that forms the sparingly soluble calcium salt can be the values ​​exemplified in section [2.1].

[0051] [4. Characteristics of the obtained phosphoric acid] The isotopic composition of phosphoric acid obtained by the manufacturing method according to one of the technical solutions of this invention reflects the isotopic composition of the elements in the raw materials. Therefore, the isotopic composition of phosphoric acid can serve as strong evidence for inferring the origin of the phosphoric acid. The oxygen atom constituting phosphoric acid has three stable isotopes. On Earth, the stable isotopes of the oxygen atom are as follows: 16 O was 99.759%. 17 O was 0.037%. 18 O is 0.204%. However, among the water molecules present in aquatic systems, 18 The stable isotope ratio of oxygen (O) is lower than that in the atmosphere, at 0.1981% in freshwater and 0.1995% in seawater. Generally, as long as it is not metabolized by organisms, the stable isotope information of the PO bond in phosphate is preserved. That is, the oxygen atom in phosphate from minerals that are not in contact with water is stable and will not be replaced by other oxygen atoms. On the other hand, temperature-dependent isotope exchange equilibrium reactions of oxygen atoms are common in the biological world, mediated by pyrophosphatase. That is, when phosphate from organisms comes into contact with water molecules, the oxygen in the phosphate molecule and the oxygen in the water molecule are replaced by an equilibrium reaction at a certain ratio. Therefore, if the stable isotope ratio of oxygen in phosphate (δ¹⁸O) is analyzed... 18 O p This allows for the differentiation between phosphate derived from biological sources and phosphate derived from minerals. Oxygen stable isotope ratios were analyzed using a thermal decomposition-type elemental analysis apparatus and a stable isotope ratio mass spectrometer (TC / EA-IRMS).

[0052] Typically, the amount of oxygen in bone tissue is less than that in phosphate rock. 18 The proportion of O is even lower. Therefore, it can be strongly inferred that... 18 Phosphoric acid with a lower oxygen content than usual is phosphoric acid produced from bone tissue. In one embodiment, the phosphoric acid obtained by a technical solution of the present invention contains oxygen atoms in... 18 The proportion of O can be 0.1981% or higher. Similarly, in the phosphoric acid obtained through one technical solution of the present invention, the oxygen atoms contained in the phosphoric acid are... 18 The proportion of O can be less than 0.204.

[0053] [5. Summary] <1> A method for producing phosphoric acid includes the following steps: Step S20: Acid treatment is performed on the raw material containing calcium phosphate to obtain an acid extract; Step S30: Mix the obtained acid extract with alkali to obtain calcium phosphate precipitate; Step S40: The obtained calcium phosphate precipitate is mixed with an acid and / or its salt to form an insoluble calcium salt. <2> according to <1> The manufacturing method, wherein step S40 includes the following step S42: Step S42: Mix the obtained calcium phosphate precipitate with an acid and / or its salt that forms an insoluble calcium salt. <3> according to <2> In the manufacturing method described above, the acid and / or its salt that forms the insoluble calcium salt in step S42 is selected from one or more of the group consisting of condensed phosphoric acid, tartaric acid, oxalic acid, sulfuric acid and their salts. <4> according to <1> - <3> The manufacturing method described in any one of the following statements, wherein step S40 includes the following steps S46 and S48: Step S46: Mix the obtained calcium phosphate precipitate with acid to obtain a solution of phosphate ions and calcium ions; Step S48: Mix the resulting solution of phosphate ions and calcium ions with an acid and / or its salt that forms a sparingly soluble calcium salt to remove the precipitated calcium. The acid in step S46 is different from the acid in step S48. <5> according to <4> In the manufacturing method described above, the acid in step S46 is selected from one or more of the group consisting of hydrochloric acid, nitric acid, formic acid, and phosphoric acid. <6> according to <4> or <5> In the manufacturing method described above, the acid or its salt in step S48 is selected from one or more of the group consisting of tartaric acid, sulfurous acid, oxalic acid, citric acid, silicic acid, condensed phosphoric acid and their salts. <7> according to <4> - <6> The manufacturing method according to any one of the following methods, wherein step S30 and step S46 are repeated more than twice. <8> according to <1> - <7> The manufacturing method described in any one of the above, wherein, after step S40, it further includes the following step S50: Step S50: Remove anions other than cations and / or phosphate ions. <9> according to <1> - <8> The manufacturing method described in any one of the following methods, wherein, prior to step S20, it further includes step S10: Step S11: Pre-treat the raw materials. The pretreatment is selected from one or more of the group consisting of heating the raw material, heating the raw material under pressure, and irradiating the raw material with microwaves. <10> according to <1> - <9> The manufacturing method according to any one of the following, wherein in step S20, the raw material is acid-treated with one or more selected from the group consisting of nitric acid, hydrochloric acid, formic acid and sulfuric acid. <11> according to <1> - <10> The manufacturing method according to any one of the following methods, wherein the raw material containing calcium phosphate comprises one or more selected from the group consisting of bone tissue, apatite, dicalcium phosphate, calcium dihydrogen phosphate, tricalcium phosphate, and β-tricalcium phosphate. Example

[0054] [Example 1: Removal of calcium ions using pyrophosphate] Phosphoric acid is extracted and purified from bone tissue through the following steps. 1. Crush the raw pork bones into small pieces of 1-3 mm. 2. Soak 1.0 g of pork bone in 10 mL of nitric acid aqueous solution (1N) and shake at 25°C for 48 hours. 3. Centrifuge at 12000×g, 25°C for 5 minutes, and recover the supernatant. This is the acid extract. Bone inclusions are removed as precipitate. 4. Add 2 mL of sodium hydroxide aqueous solution (5N) to 10 mL of acid extract and mix. 5. Remove the supernatant to obtain calcium phosphate precipitate. 6. Wash the calcium phosphate precipitate three times with pure water, removing the supernatant each time. 7. Add 2.6 mL of pyrophosphate aqueous solution (1M) to the calcium phosphate precipitate to dissolve it. 8. Add the specified amount of sodium hydroxide aqueous solution (1N) and mix overnight at 4°C. This will produce a sparingly soluble calcium pyrophosphate precipitate. 9. Pass the supernatant after removing the precipitate through a cation exchange gel to remove sodium ions from sodium hydroxide. This yields high-purity phosphoric acid.

[0055] [result] The amount of sodium hydroxide added in step 8, and the amount and percentage of residual calcium in the phosphoric acid obtained in step 9 are shown in Table 1. A small calcium ion meter, LAQUAtwin, was used for the determination of calcium. <ca-11>(Horiba Manufacturing Co., Ltd.).

[0056] [Table 1]

[0057] As shown in Table 1, the more sodium hydroxide is added, the lower the calcium residue rate becomes, and eventually the calcium can be removed to below the detection limit.

[0058] In the steps of Example 1, a very small amount of pyrophosphoric acid may be mixed into the final product. However, pyrophosphoric acid can be converted to phosphoric acid by hydrolysis, so it will not have a substantial impact on the purity of the resulting phosphoric acid.

[0059] [Example 2: Removal of calcium ions using tartaric acid] Phosphoric acid is extracted and purified from bone tissue through the following steps. 1. Crush the raw pork bones into small pieces of 1-3 mm. 2. Soak 1.0 g of pork bone in 10 mL of nitric acid aqueous solution (1N) and shake at 25°C for 48 hours. 3. Centrifuge at 12000×g and 25°C for 5 minutes, recovering the supernatant each time. This is the acid extract. Bone inclusions are removed as precipitates. 4. Add 2 mL of sodium hydroxide aqueous solution (5N) to 10 mL of acid extract and mix. 5. Remove the supernatant to obtain calcium phosphate precipitate. 6. Wash the calcium phosphate precipitate three times with pure water and remove the supernatant. 7. Add 6 mL of tartaric acid aqueous solution (specified concentration, pH 1.3) to the calcium phosphate precipitate to dissolve it. Mix the solution overnight at 4°C. This will produce a sparingly soluble calcium tartrate precipitate. 8. The supernatant after removing the precipitate is recovered to obtain high-purity phosphoric acid.

[0060] [result] The concentration of tartaric acid added in step 7, the amount and residual rate of calcium remaining in the phosphoric acid obtained in step 8, and the amount and recovery rate of phosphoric acid recovered in step 8 are shown in Table 2.

[0061] [Table 2]

[0062] As shown in Table 2, the higher the concentration of tartaric acid, the lower the residual calcium rate, ultimately removing calcium below the detection limit. Furthermore, the lowest recovery rate of phosphoric acid is approximately 88%. If the phosphoric acid contained in the calcium tartrate precipitate is recovered through washing steps or by scaling up the phosphoric acid recovery equipment, a recovery rate of over 95% can be expected.

[0063] [Example 3: Removal of calcium ions using sulfites] Phosphoric acid is extracted and purified from bone tissue through the following steps. 1. Crush the raw pork bones into small pieces of 1-3 mm. 2. Soak 1.0 g of pork bone in 10 mL of nitric acid aqueous solution (1N) and shake at 25°C for 48 hours. 3. Centrifuge at 12000×g, 25°C for 5 minutes, and recover the supernatant. This is the acid extract. Bone inclusions are removed as precipitate. 4. Add 2 mL of sodium hydroxide aqueous solution (5N) to 10 mL of acid extract and mix. 5. Remove the supernatant to obtain calcium phosphate precipitate. 6. Wash the calcium phosphate precipitate three times with pure water, removing the supernatant each time. 7. Add 10 mL of phosphoric acid to the calcium phosphate precipitate to dissolve it. 8. Add 2 mL of potassium sulfite aqueous solution (specified concentration) and mix overnight at 4°C. This produces a sparingly soluble calcium sulfite precipitate. This step was performed in three systems with different calcium ion concentrations. 9. Pass the supernatant after removing the precipitate through a cation exchange gel to remove potassium ions from potassium sulfite. This yields high-purity phosphoric acid.

[0064] [result] The concentration of potassium sulfite added in step 8 and the amount of residual calcium in the phosphoric acid obtained in step 9 are shown in Table 3. A small calcium ion meter, LAQUAtwin, was used for the determination of calcium. <ca-11>(HORIBA, Ltd.).

[0065] [Table 3]

[0066] As shown in Table 3, in any system where the initial concentration of calcium ions is different, the higher the concentration of potassium sulfite, the lower the residual rate of calcium, and ultimately the calcium can be removed to below the detection limit.

[0067] [Example 4: Purification of phosphoric acid by adding sulfuric acid or a sulfate salt] Phosphoric acid was extracted from bone tissue using sulfuric acid or a sulfate salt by the following procedure. 1. Pig bones obtained from a slaughterhouse were finely pulverized using a pulverizer (IKA TUBE MILL 100, IKA JAPAN Co., Ltd.). 2. The pulverized pig bones were immersed in a 1N aqueous nitric acid solution or a 1N aqueous hydrochloric acid solution for 48 hours. 3. The supernatant was recovered to obtain an acid extract. Bone inclusions were removed as a precipitate. 4. To 0.5 mL of the acid extract, 100 μL of a 5N aqueous sodium hydroxide solution was added, and left to stand at room temperature for 1 hour. 5. The calcium phosphate precipitate was recovered by centrifugal separation. 6. 0.5 mL of a 1N aqueous hydrochloric acid solution was added to redissolve the calcium phosphate. 7. Sulfuric acid or a sulfate salt (sodium sulfate, potassium sulfate, ammonium sulfate, or magnesium sulfate) was added. The amount of sulfuric acid or a sulfate salt added was an amount such that the final concentration was 0.4M, 0.6M, 0.8M, or 1.0M. 8. The generated calcium sulfate precipitate was removed by centrifugal separation. 9. The weight of the phosphoric acid contained in the supernatant was measured. In the measurement, a Malachite Green Phosphate Assay Kit (BioAssay Systems) was used. Furthermore, based on the phosphoric acid content in the calcium phosphate precipitate obtained in step 5, the phosphoric acid recovery rate was calculated.

[0068] [Table 4]

[0069] [Results] The results are shown in Table 4. As shown by the results, if the concentration is appropriate, the same degree of phosphoric acid recovery rate can be achieved with either sulfuric acid or a sulfate salt. In the acid treatment, there is a tendency for the recovery rate of phosphoric acid to be higher when using hydrochloric acid than when using nitric acid. Among the sulfate salts, potassium sulfate and ammonium sulfate have a tendency to enable the smooth recovery of phosphoric acid even at low concentrations.

[0070] Example 5: Purification of phosphoric acid by adding carbonate Phosphoric acid was extracted from bone tissue using carbonate by the following procedure. 1. Pig bones obtained from a slaughterhouse were finely pulverized using a pulverizer (IKA TUBE MILL 100, IKA JAPAN Co., Ltd.). 2. The pulverized pig bones were immersed in a 1N aqueous nitric acid solution or a 1N aqueous hydrochloric acid solution for 48 hours. 3. The supernatant was recovered to obtain an acid extract. Bone inclusions were removed as a precipitate. 4. To 0.5 mL of the acid extract, 100 μL of a 5N aqueous sodium hydroxide solution was added, and left to stand at room temperature for 1 hour. 5. The calcium phosphate precipitate was recovered by centrifugal separation. 6. 0.5 mL of a 1N aqueous hydrochloric acid solution was added to redissolve the calcium phosphate. 7. A carbonate (solid sodium bicarbonate or sodium carbonate) was added. The amount of sodium bicarbonate added was an amount to make the final concentration 0.4M. The amount of sodium carbonate added was an amount to make the final concentration 0.6M. 8. The generated calcium carbonate precipitate was removed by centrifugal separation. 9. The concentration (ppm) of phosphate ions contained in the supernatant was measured. The measurement of phosphate ions can be performed by a high-performance ion chromatograph IC-8100 EX (Tosoh Corporation) connected with TSKgel Super IC-Anion HS (4.6 mm I.D. x 10 cm) under precision measurement conditions. A mixture of 7.5 mmol / L sodium bicarbonate and 0.8 mmol / L sodium carbonate was used as an eluent. The measurement temperature was 40°C, the flow rate was 1.5 mL / minute, and the injection amount was 30 μL. The conductivity (μS) was measured, and a regression formula was obtained from the area of a standard substance, whereby the concentration of phosphate ions was measured. The content of phosphate ions per sample (30 μL) was obtained from the concentration of phosphate ions.

[0071] [Table 5]

[0072] [Results] The results are shown in Table 5. By adding a carbonate, calcium ions became calcium carbonate and precipitated, and phosphate ions remained in the supernatant. For example, in the system in which sodium bicarbonate was added to the acid extract using hydrochloric acid, the supernatant contained 9000 ppm or more of phosphoric acid. The carbonate ions remaining in the supernatant are converted into carbon dioxide upon heating, and thus can be easily removed.

[0073] Example 6: Removal of cations contained in a sulfate [Example 6-1: Removal of sodium or potassium ions] The following steps remove cations (sodium or potassium ions) contained in the sulfate added to remove calcium ions. Specifically, a strong cation exchange gel is used to adsorb sodium or potassium ions. 1. Decant TSKgel SP-TOYOPEARL 650M gel (Tosoh Corporation) with pure water and pack it into a microcentrifuge column (GE Healthcare). 2. Add an appropriate amount of the supernatant after removing calcium sulfate by adding sulfate to the upper layer of the gel. 3. Centrifuge using a benchtop centrifuge to pass the supernatant through the gel. Collect the flow-through liquid that has passed through the gel. 4. Determine the sodium or potassium ion content (mg) in the flow-through solution. For sodium ion determination, LAQUAtwin-Na-11 (Horiba Advanced Technology Co., Ltd.) is used. For potassium ion determination, LAQUAtwin-K-11 (Horiba Advanced Technology Co., Ltd.) is used.

[0074] [Table 6]

[0075] [result] The results are shown in Table 6. The supernatant after calcium sulfate precipitation by adding sodium sulfate or potassium sulfate contained sodium or potassium ions. These ions could be removed by passing through a strong cation exchange gel. Specifically, 83% of sodium ions and 86% of potassium ions were removed. Repeated flow through the strong cation exchange gel removed even more cations.

[0076] [Example 6-2: Removal of magnesium or ammonium ions] The following steps remove cations (magnesium or ammonium ions) contained in the sulfate added to remove calcium ions. Specifically, a strong cation exchange gel is used to adsorb magnesium or ammonium ions. 1. Decant the TSKgel SP-TOYOPEARL 650M gel (Tosoh Corporation) with pure water and pack it into a microcentrifuge column (GE Healthcare). 2. Add an appropriate amount of the supernatant after removing calcium sulfate by adding sulfate to the upper layer of the gel. 3. Centrifuge using a benchtop centrifuge to pass the supernatant through the gel. Collect the flow-through liquid that has passed through the gel. 4. Determine the content (μg) of magnesium, ammonium, or calcium ions in the flow-through solution. Ion concentration determination can be performed under precise measurement conditions using a high-performance ion chromatograph IC-8100 EX (Tosoh Corporation) connected to a TSKgel SuperIC-Cation HSII (4.6 mm ID × 10 cm). A mixture of 3.0 mmol / L methanesulfonic acid and 2.7 mmol / L 18-crown ether-6 was used as the dissolution solution. The measurement temperature was 40°C, the flow rate was 1.0 mL / min, and the injection volume was 30 μL. The conductivity (μS) was measured, and a regression equation was derived based on the area of ​​the standard substance to determine the calcium ion concentration. The ion content of each sample (30 μL) was calculated from the ion concentration.

[0077] [Table 7]

[0078] [result] The results are shown in Table 7. The results indicate that magnesium, ammonium, and calcium ions can also be removed from the supernatant by contact with a strong cation exchange gel. Repeated flow into the strong cation exchange gel removes even more cations, including calcium ions. This suggests that the purity of phosphoric acid can be improved.

[0079] [Example 7: Improving Phosphoric Acid Recovery Rate Through Pretreatment] It has been confirmed that pretreatment of the raw materials increases the amount of phosphoric acid in the acid extract. Specifically, the acid extract is prepared by the following steps, and the amount of phosphoric acid contained therein is quantified. 1. The pig bones obtained from the slaughterhouse are shredded using a shredder (IKA TUBE MILL 100, IKA JAPAN Co., Ltd.). 2. Pretreatment of 5 g of crushed pig bone by any one of the following (1)-(5). (1) Unprocessed (2) Soak in 30 mL of nitric acid (1 mol / L) at 50°C for one day. (3) Irradiate with 500W microwave for 30 seconds. (4) Irradiate with 500W microwave for 60 seconds. (5) Irradiate with 500W microwave for 120 seconds. 3. Add 30 mL of nitric acid (1 mol / L) to the pig bones (1) and (3)-(5). Immerse the pig bones (1)-(5) in 30 mL of nitric acid at 20°C with shaking (100 rpm) for 48 hours. This decalcifies the bone tissue. 4. Recover the supernatant as an acid extract. 5. Determine the phosphoric acid concentration using the Malachite Green Phosphate Assay Kit (BioAssay Systems). Follow the instructions in the accompanying manual. Dilute the supernatant with distilled water before testing.

[0080] [result] The results are shown in Figure 4 From bone tissue (2) pretreated by heating at 50°C, 1.18 times more phosphoric acid was extracted compared to bone tissue (1) that was not pretreated. Furthermore, from bone tissue (3)-(5) pretreated by microwave irradiation, up to 1.26 times more phosphoric acid was extracted compared to bone tissue (1) that was not pretreated. These results indicate that phosphoric acid can be recovered more effectively from calcium phosphate-containing raw materials such as bone tissue using a pretreated acid extract.

[0081] [Example 8: pH dependence of phosphate recovery efficiency and calcium removal efficiency] Phosphoric acid is extracted and purified from bone tissue through the following steps. 1. Crush the raw pork bones into small pieces of 1-3 mm. 2. Soak 1.0 g of pork bone in 10 mL of nitric acid aqueous solution (1N) and shake at 25°C for 48 hours. 3. Centrifuge at 12000×g, 25°C for 5 minutes, and recover the supernatant. This is the acid extract. Bone inclusions are removed as precipitate. 4. Add 2 mL of sodium hydroxide aqueous solution (5N) to 10 mL of acid extract and mix. 5. Place 0.3 mL of the mixed solution into a 2 mL microtube, centrifuge at 12000×g and 25°C for 5 minutes, discard the supernatant, and obtain calcium phosphate precipitate. 6. Wash the calcium phosphate precipitate three times with pure water and remove the supernatant. 7. Dissolve the calcium phosphate precipitate by adding 0.3 mL of an acid or its salt that forms a sparingly soluble calcium salt. The acid or salt added can be a sulfate (potassium sulfate or ammonium sulfate), citric acid, or tartaric acid. Adjust the pH of the mixed solution by adding an appropriate amount of common acid or base. 8. Centrifuge at 12000×g and 25°C for 5 minutes, and collect the supernatant after removing the precipitate of insoluble calcium salts (calcium sulfate, calcium citrate or calcium tartrate). 9. The phosphate and calcium ions in the supernatant after removing the precipitate of insoluble calcium salts were quantified using the Malachite Green Phosphate Assay Kit (BioAssay Systems) and the CalciumAssay Kit, QuantiChrom (500 assays).

[0082] [result] The results are shown in Figure 5 The upper section of the figure shows the pH dependence of phosphate ion concentration (g / L), and the lower section shows the pH dependence of calcium ion concentration (g / L). As shown in the figure, if the pH of the system changes after the addition of acid or salt, the concentrations of phosphate and calcium ions in the supernatant also change. This indicates that the optimal pH for phosphate extraction varies depending on the type of acid and / or its salt added in step S42 or S48. When sulfates (potassium sulfate, ammonium sulfate, etc.) are added, the preferred pH after mixing is 1.3-2.8. When citric acid is added, the preferred pH after mixing is 3.3-4.5. When tartaric acid is added, the preferred pH after mixing is 2.5-5.2.

[0083] [Example 9: Purification of phosphoric acid from calcium phosphate compounds in non-bone tissue] The following steps confirm that phosphoric acid can be manufactured from materials other than bone tissue. 1. Prepare calcium phosphate reagent and apatite as raw materials. The calcium phosphate reagent specifically includes monocalcium phosphate (CMP, CaHPO4), dicalcium phosphate (CDP, Ca(H2PO4)2), tricalcium phosphate (TP, 10CaO·3P2O5), and β-tricalcium phosphate (β-TCP, Ca3(PO4)2). 2. The raw material was immersed in a 1N hydrochloric acid aqueous solution, and the concentrations of phosphate ions and calcium ions in the acid extract were determined. The Malachite Green Phosphate Assay Kit (BioAssay Systems) and Calcium Assay Kit, QuantiChrom (500 assays) were used in the determination.

[0084] [result] The results are shown in Table 8. [Table 8]

[0085] The acid extracts obtained from any of the raw materials contain significant amounts of phosphate and calcium ions. The recoveries of phosphate and calcium ions exceed 81% in CMP and CDP, and are nearly 100% in TP and β-TCP. In the case of apatite, the calculated recovery rate of 32% is lower due to discrepancies between the composition and purity of the calcium phosphate (fluorapatite) used in the calculations and the actual ratio of phosphate to calcium. However, it is believed that by optimizing impregnation time, etc., phosphate and calcium can be recovered from apatite with the same level of recovery as other raw materials.

[0086] Phosphoric acid can be extracted and purified from the acid extract thus obtained by the same method as in any of the above embodiments. That is, as shown in this embodiment, the acid extract obtained in step S20 contains a high concentration of phosphate ions and calcium ions. Therefore, phosphoric acid can be obtained by steps S30, S40, and optional step S50. Industrial practicality

[0087] Phosphoric acid obtained by the manufacturing method involved in one of the technical solutions of this invention can be used in fertilizers, the semiconductor industry, etc.

Claims

1. A method for producing phosphoric acid, comprising the following steps: Step S20: Acid treatment is performed on the raw material containing calcium phosphate to obtain an acid extract; Step S30: Mix the obtained acid extract with alkali to obtain calcium phosphate precipitate; Step S40: The obtained calcium phosphate precipitate is mixed with an acid and / or its salt to form an insoluble calcium salt.

2. The manufacturing method according to claim 1, wherein, Step S40 includes the following step S42: Step S42: Mix the obtained calcium phosphate precipitate with an acid and / or its salt that forms an insoluble calcium salt.

3. The manufacturing method according to claim 2, wherein, The acid and / or its salt that forms the insoluble calcium salt in step S42 is selected from one or more of the group consisting of condensed phosphoric acid, tartaric acid, oxalic acid, sulfuric acid and their salts.

4. The manufacturing method according to claim 1, wherein, Step S40 includes the following steps S46 and S48: Step S46: Mix the obtained calcium phosphate precipitate with acid to obtain a solution of phosphate ions and calcium ions; Step S48: Mix the resulting solution of phosphate ions and calcium ions with an acid and / or its salt that forms a sparingly soluble calcium salt to remove the precipitated calcium. The acid in step S46 is different from the acid in step S48.

5. The manufacturing method according to claim 4, wherein, The acid in step S46 is selected from one or more of the group consisting of hydrochloric acid, nitric acid, formic acid, and phosphoric acid.

6. The manufacturing method according to claim 4, wherein, The acid or its salt in step S48 is selected from one or more of the group consisting of tartaric acid, sulfurous acid, oxalic acid, citric acid, silicic acid, condensed phosphoric acid and their salts.

7. The manufacturing method according to claim 4, wherein, Steps S30 and S46 may be repeated more than twice.

8. The manufacturing method according to any one of claims 1-7, further comprising step S50 after step S40: Step S50: Remove anions other than cations and / or phosphate ions.

9. The manufacturing method according to any one of claims 1-7, further comprising step S10 before step S20: Step S11: Pre-treat the raw materials. The pretreatment is selected from one or more of the group consisting of heating the raw material, heating the raw material under pressure, and irradiating the raw material with microwaves.

10. The manufacturing method according to any one of claims 1-7, wherein, In step S20, the raw material is acid-treated using one or more of the group consisting of nitric acid, hydrochloric acid, formic acid and sulfuric acid.

11. The manufacturing method according to any one of claims 1-7, wherein, The calcium phosphate-containing raw material comprises one or more of the group consisting of bone tissue, apatite, monocalcium phosphate, dicalcium phosphate, tricalcium phosphate, and β-tricalcium phosphate.

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