Method for producing phosphoric acid

Abstract

Provided is a new method for producing phosphoric acid. A method for producing phosphoric acid according to the present disclosure comprises the following steps. Step S20: A step for treating, with an acid, a raw material containing calcium phosphate to obtain an acid extracted solution. Step S30: A step for mixing the obtained acid extracted solution with a base to obtain a calcium phosphate precipitate. Step S40: A step for mixing the obtained calcium phosphate precipitate with an acid and / or a salt thereof and forming a hardly soluble calcium salt.

Description

Phosphoric acid manufacturing method

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

[0002] Phosphoric acid is a material widely used in agriculture and industry. Phosphoric acid is generally produced using phosphate rock as a raw material, but technologies for recovering phosphoric acid from waste materials have also been developed. For example, Patent Document 1 discloses a method for recovering phosphoric acid from human waste and septic tank sludge. Patent Document 2 discloses a method for recovering phosphoric acid from steelmaking slag.

[0003] Japanese Patent Application Publication No. 2017-196619 Japanese Patent Application Publication No. 2011-213558

[0004] Phosphoric acid is a very important substance in industries such as agriculture and manufacturing. Currently, most phosphoric acid is produced from phosphate rock, and Japan relies on imports to meet its entire demand for phosphate rock. Meanwhile, phosphoric acid is also found in bone tissues and other tissues in the form of calcium phosphate (for example, bone tissue is said to contain approximately 33% phosphoric acid by weight before drying). Therefore, if phosphoric acid could be recovered from calcium phosphate-containing raw materials such as bone tissue, a huge source of phosphoric acid would be created in Japan, similar to waste bones generated at slaughterhouses and other facilities. Given these circumstances, there is a need to develop a method for recovering phosphoric acid from calcium phosphate-containing raw materials such as bone tissue.

[0005] An object of one aspect of the present invention is to provide a novel method for producing phosphoric acid.

[0006] In order to solve the above-mentioned problems, a method for producing phosphoric acid according to one embodiment of the present invention comprises the following steps: Step S20: treating a raw material containing calcium phosphate with an acid to obtain an acid extract; Step S30: mixing the obtained acid extract with a base to obtain a calcium phosphate precipitate; Step S40: mixing the obtained calcium phosphate precipitate with an acid and / or a salt thereof to form a poorly soluble calcium salt.

[0007] According to one aspect of the present invention, a novel method for producing phosphoric acid is provided.

[0008] 1 is a flowchart showing an overview of a method for producing phosphoric acid according to one embodiment of the present invention; FIG. 2 is a partial flowchart showing a first embodiment of step S40; FIG. 3 is a partial flowchart showing a second embodiment of step S40; FIG. 4 is a diagram showing the effect of pretreatment of raw materials on the amount of phosphoric acid contained in an acid extract; and FIG. 5 is a diagram showing the effect of pH on the efficiency of separating phosphoric acid and calcium salts from calcium phosphate precipitates.

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

[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] As used herein, "calcium phosphate" refers to a substance that may contain phosphate ions, calcium ions, and optionally other ions. The specific composition of calcium phosphate is not particularly limited. Examples of calcium phosphate include calcium monohydrogen phosphate, calcium dihydrogen phosphate, tricalcium phosphate, β-tricalcium phosphate, octacalcium phosphate, hydroxyapatite, fluoroapatite, 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, incineration ash, sewage sludge, dried sludge, and dephosphorized slag (usually composed primarily of fluoroapatite). In one embodiment, the raw material containing calcium phosphate is bone tissue.

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

[0013] In conventional technology, most phosphoric acid is produced by refining phosphate rock. Because mining phosphate rock requires enormous amounts of energy and the refining process releases huge amounts of carbon dioxide, the production of phosphoric acid from phosphate rock involves global environmental destruction. Therefore, from the perspective of a sustainable industry, conventional methods for producing phosphoric acid have technical problems. Furthermore, if a carbon credit system is introduced in the future, phosphoric acid obtained from phosphate rock will incur additional costs.

[0014] Furthermore, phosphate prices are soaring worldwide as phosphate-producing countries such as the United States and China reduce their mining output and increase imports. Japan imports more than 400,000 tons of phosphate annually, relying entirely on imports. In light of this situation, phosphate was designated a specific substance of priority (December 2022) from the perspective of economic security. In this regard, the benefits of producing phosphate domestically in Japan are immeasurable. Phosphate is essential for fertilizer and semiconductor manufacturing, and a shortage would have a significant impact on industry. In particular, a shortage of phosphate used as fertilizer could easily lead to a sharp decline in domestic production of agricultural products such as grains, vegetables, root vegetables, and fruits. This would further reduce Japan's food self-sufficiency rate and make healthy diets unreliable.

[0015] As shown in Patent Documents 1 and 2, techniques for extracting phosphoric acid from waste materials have been investigated, but these techniques often involve problems with impurities and heterogeneity. In contrast, raw materials containing calcium phosphate (especially bone tissue) are highly homogeneous in composition. In particular, because the rearing conditions of livestock or farmed fish are nearly the same regardless of their origin, waste bones are highly homogeneous raw materials. Furthermore, if livestock or farmed fish are raised on normal feed, it is unlikely that heavy metals or radioactive elements will be present in the bone tissue. For example, in the case of livestock raised for meat production, the period from birth to slaughter is short, so even if there is a possibility of absorbing heavy metals or radioactive elements from the environment, that period is extremely short. Therefore, bone tissue contains almost no components such as aluminum, arsenic, lead, nickel, chromium, or manganese. Thus, a method for producing phosphoric acid according to one embodiment of the present invention can solve the problems of impurities and heterogeneity. However, solving this problem is not essential to the present invention. In one embodiment of the present invention, it is also anticipated that the raw material may be bone tissue of natural animals or fish, or a substance containing calcium phosphate other than bone tissue.

[0016] 1. Overview of the Method for Producing Phosphoric Acid An overview of the method for producing phosphoric acid according to one embodiment of the present invention is illustrated in the flowchart of FIG. 1. A raw material containing calcium phosphate (particularly bone tissue) contains inorganic components such as calcium and organic components such as collagen in addition to phosphoric acid. In the method illustrated in FIG. 1, phosphoric acid is dissolved in steps S10 and S20, and components other than phosphoric acid and calcium are removed in step S30. Thereafter, calcium is removed in step 40. Each step is described in detail below.

[0017] [1.1. Step S10] In step S10, a raw material containing calcium phosphate is pretreated. Step S10 is an optional step and may not be performed. Pretreating the raw material can increase the amount of phosphoric acid contained in the acid extract (see Example 7).

[0018] The raw material to be subjected to step S10 may be of any type. When the raw material contains bone tissue, the bone tissue may be derived from any organism. Examples of organisms include mammals, birds, amphibians, and fish. For mass production, it is preferable that the raw material be available in large quantities, and for example, bone tissue from livestock (such as cattle, pigs, sheep, and chickens) or whales or farmed fish is preferably used. The raw material may be shredded or crushed before or after step S10. This may allow the raw material to be decomposed more efficiently, thereby shortening the production time.

[0019] In one embodiment, in step S10, the raw material is heated. The heating temperature at this time may be 30° C. or higher or 40° C. or higher; or 100° C. or lower or 80° C. or lower. The raw material may be heated while immersed in acid.

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

[0021] In one embodiment, in step S10, the raw material is irradiated with microwaves. Heating, heating under pressure, and microwave irradiation may be performed in any combination. Among these, microwave irradiation is more preferable as step S10 because it can achieve its effect in a short time. The microwave irradiation time can be appropriately determined depending on the volume of the raw material. For example, when the volume of the raw material is 1 cm ３ When the microwave irradiation time is about 5 seconds or more, 10 seconds or more, or 15 seconds or more; or 10 minutes or less, 7 minutes or less, or 5 minutes or less. Of course, when the volume of the raw material is large, the irradiation time may be longer. When the microwave irradiation time is within an appropriate range, inorganic components including phosphoric acid can be efficiently extracted from the raw material.

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

[0023] The acid used to treat 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. An acidic decalcifying solution such as Planck-Lycros solution may also be used. From the viewpoint of availability, one or more acids selected from the group consisting of nitric acid, hydrochloric acid, formic acid, and sulfuric acid are preferred. From the viewpoint of phosphoric acid recovery efficiency, one or more acids selected from the group consisting of hydrochloric acid, sulfuric acid, and nitric acid are preferred, and one or more acids selected from the group consisting of hydrochloric acid and nitric acid are more preferred. Two or more acids may be mixed in an appropriate ratio and used.

[0024] In step S20, the raw material may be acid-treated with a solution prepared by diluting an acid in a solvent. Examples of the solvent include water, lower alcohols, glycerol, propane-1,2-diol, and 1,3-propanediol. Two or more types of solutions may be mixed in an appropriate ratio.

[0025] The acid concentration can be appropriately determined depending on the volume of the raw material to be acid-treated. When the volume of the raw material is small, it can be treated with a low-concentration acid. When the volume of the raw material is large, it is preferable to use a high-concentration acid. When performing acid treatment with a low-concentration acid, it is preferable to treat a finely powdered raw material. However, even when the volume of the raw material is large, inorganic components can be sufficiently extracted by increasing the acid concentration and immersing for a long period of time. For example, when the volume of the raw material is several cm ３ When the following crushed bone material is used as the raw material, the lower limit of the acid concentration in step S20 may be 0.6 mol / L or more, 0.7 mol / L or more, 0.8 mol / L or more, or 0.9 mol / L or more. The upper limit of the acid concentration in step S20 may be 2.0 mol / L or less, 1.5 mol / L or less, 1.0 mol / L or less, or 0.9 mol / L or less. When the acid concentration is within the above range, inorganic components including phosphoric acid can be efficiently extracted, and the cost of neutralizing the acid extract can be reduced because the acid concentration is not too high.

[0026] Examples of suitable acid concentrations when treating the pulverized raw material with an acid are as follows: 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 .... 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 concentrations are examples of suitable concentrations when the raw material is pulverized, and the acid concentration may be higher when the raw material has a larger volume.

[0027] For example, a volume of several cm ３ When the following crushed bone material is used as the 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, inorganic components including phosphate contained in the raw material can be sufficiently extracted.

[0028] For example, a volume of several cm ３ When using crushed bone material as the raw material, the temperature of the acid treatment in step S20 is preferably 5 to 60°C. Carrying out the acid treatment within the above temperature range can reduce the generation of unpleasant odors associated with the acid treatment. This also mitigates the location requirements for the manufacturing plant. Furthermore, adjusting the temperature to 60°C or below does not require expensive special equipment; a constant temperature can be maintained using a water bath or incubator.

[0029] In step S20, a chelating agent capable of capturing calcium ions may be added in addition to the acid. Alternatively, in step S20, the raw material may be treated with a chelating agent before or after the acid treatment (the solutions may or may not be exchanged between the acid treatment and the chelating agent treatment). Examples of chelating agents include ethylenediaminetetraacetic acid (EDTA, CAS Registry Number: 60-00-4), glycol ether diaminetetraacetic acid (EGTA, CAS Registry Number: 67-42-5), and ethylenediamine-N,N'-disuccinic acid (EDDS, CAS Registry Number: 20846-91-7). In step S20, the pH of the solution containing the chelating agent is preferably 6.0 to 8.0. For example, when the volume of the solution is several cm ３ When the following crushed bone material is used as the raw material, the lower limit of the chelating agent concentration in step S20 may 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, and the upper limit of the chelating agent concentration in step S20 may 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 and a base are mixed. In step S30, the phosphate ions contained in the acid extract are precipitated as calcium phosphate, and other components (such as components derived from bone impurities) are contained in the supernatant. Therefore, phosphoric acid can be purified by recovering the precipitate. Examples of bases that can be used include sodium hydroxide and potassium hydroxide.

[0031] [1.4. Step S40] In step S40, calcium phosphate is mixed with an acid and / or a salt thereof, and a poorly soluble calcium salt is further formed. In a first embodiment, calcium phosphate is mixed with an acid and / or a salt thereof that forms a poorly soluble calcium salt. Thereafter, a base is added, if necessary, 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. Thereafter, another acid or its salt is added to form a poorly soluble calcium salt. By removing the poorly soluble calcium salt formed in step S40, phosphoric acid can be concentrated. A step of recollecting phosphoric acid remaining in the poorly soluble calcium salt obtained in step S40 may be provided.

[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 derived from upstream steps. High-purity phosphoric acid can be obtained by adsorbing these ions, for example, on 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 is a partial flowchart showing a first embodiment of step S40. Step S40 of the first embodiment includes step S42 and optional step S44. Each step will be 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 poorly soluble calcium salt. In step S42, the pH of the system is lowered by adding the acid, thereby dissolving the calcium phosphate precipitate. At the same time (or after step S44), anions contained in the acid and calcium ions form a poorly soluble calcium salt. By removing the poorly soluble calcium salt, phosphoric acid is concentrated in the liquid phase.

[0035] Examples of acids and / or salts thereof to be mixed in step S42 include condensed phosphoric acid, tartaric acid, oxalic acid, sulfuric acid, and salts thereof. These acids and / or salts are strong enough to dissolve calcium phosphate and contain anions that form sparingly soluble calcium salts. Examples of salts to be mixed in step S42 will be described later in Section [3.2].

[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, since the condensed phosphate anions are converted to phosphoric acid by hydrolysis, the influence of the remaining anions is substantially eliminated. In this specification, condensed phosphoric acid refers to an acid in which two or more phosphoric acids are condensed via a phosphate ester bond. 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 ability, it is preferable to mix one or more selected from the group consisting of tartaric acid, oxalic acid, and salts thereof in step S42. This is because the solubilities of calcium tartrate and calcium oxalate are particularly low (solubility in 100 mL of water at 25°C: calcium tartrate: 0.0023 g, calcium oxalate: 0.00067 g). Therefore, these calcium salts precipitate as precipitates preferentially over calcium phosphate.

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

[0039] [2.2. Step S44] In step S44, a base is added to lower the pH of the system. Step S44 is an optional step and may not be performed. Depending on the type of acid added in step S42, a poorly soluble calcium salt may be formed through step S44. For example, when pyrophosphoric acid is added in step S42, it is preferable to include step S44.

[0040] P.O. ４ ３－ and Ca ２＋ Ca, which is a salt of ３ (P.O. ４ ) ２ The solubility product of calcium phosphate at 25°C is 2.0 x 10 －２９ mol / L, and HPO ４ ２－ and Ca ２＋ CaHPO ４ The solubility product of calcium hydrogen phosphate at 25°C is 2.6 x 10 －７mol / L, and P ２ O ７ ４－ and Ca ２＋ Ca, which is a salt of ２ P ２ O ７ The solubility product of calcium pyrophosphate at 25°C is 2.0 x 10 －１９ mol / L. Based on this difference in solubility, ４ ３－ If calcium pyrophosphate is formed in an environment where there is almost no P, calcium can be successfully removed from a solution of phosphate ions and calcium ions. Here, the acid dissociation constants of phosphoric acid are pK1 = 2.12, pK2 = 7.21, and pK3 = 12.67, and the acid dissociation constants of pyrophosphate are pK1 = 0.2, pK2 = 0.9, pK3 = 6.76, and pK4 = 8.95. Therefore, at a pH of about 10, the P in pyrophosphate is ２ O ７ ４－ 90% of the phosphoric acid is in the PO ４ ３－ Therefore, when pyrophosphoric acid is mixed in step S42, calcium pyrophosphate can be preferentially precipitated by adjusting the pH of the solution to about 10 in step S44.

[0041] 3 is a partial flowchart showing a second aspect of step S40. Step S40 of the second aspect includes steps S46 and S48. Each step will be described in detail below.

[0042] [3.1. Step S46] In step S46, the calcium phosphate precipitate is mixed with an acid. This redissolves the calcium phosphate that was precipitated. Examples of acids that can be used include hydrochloric acid, nitric acid, formic acid, and phosphoric acid. In step S46, it is preferable to mix phosphoric acid. In this way, the anion added to the system is a phosphate ion, and therefore the purity of the phosphoric acid obtained via step S40 is not affected.

[0043] In the second embodiment, steps S30 and S46 may be repeated. Repeating these steps increases the purity of the phosphoric acid. Steps S30 and S46 may be repeated, for example, two or more times, three or more times, four or more times, or five or more times. From an economical standpoint, steps S30 and S46 may be repeated, for example, ten or fewer times. After repeating steps S30 and S46, a washing treatment may be performed as many times as necessary to wash away unnecessary components contained in the calcium phosphate precipitate with pure water before proceeding to step S15.

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

[0045] In one embodiment, the solubility of the poorly soluble calcium salt at 25°C (maximum amount dissolved per 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 still more preferably 0.01 g or less.

[0046] Specific examples of poorly soluble calcium salts include calcium sulfate, calcium sulfite, calcium carbonate, calcium tartrate, calcium oxalate, calcium citrate, calcium silicate, and calcium salts of condensed phosphates (e.g., calcium pyrophosphate). Therefore, examples of acids to be mixed with the phosphate ion and calcium ion solution in step S48 include sulfuric acid, sulfite, carbonic acid, tartaric acid, oxalic acid, citric acid, silicic acid, and condensed phosphates (e.g., pyrophosphoric acid). Examples of salts to be mixed with the phosphate ion and calcium ion solution in step S48 include sulfate, sulfite, carbonate, bicarbonate, tartrate, oxalate, citrate, silicate, and salts of condensed phosphates (e.g., pyrophosphate). These salts may be sodium salts, potassium salts, magnesium salts, ferric salts, ammonium salts, and the like. Tartaric acid and tartrate salts may be in the D- or L-form, or a mixture thereof. Silicic acid is a general term for acids whose main components are silicon, oxygen, and hydrogen, and includes orthosilicic acid, metasilicic acid, etc.

[0047] Anion A produced when a solution of phosphate ions and calcium ions is mixed with an acid (HA) or a salt (MA) ｎ－ For the anion, it is preferable that the solubility product of the calcium salt is small and the acid dissociation constant pKa is far from the third acid dissociation constant of phosphoric acid (12.67). By selecting such an anion, it is possible to form a poorly soluble calcium salt while minimizing the occurrence of calcium phosphate precipitation by appropriately adjusting the pH of the system. For reference, the acid dissociation constants of representative acids and the solubilities of calcium salts (at 25°C, per 100 mL of water) are listed below. For some calcium salts, the solubility product (at 25°C) is also listed. Sulfuric acid (H ２ SO ４ ) ・pK1=-5 ・pK2=1.99 ・CaSO ４ Solubility product: 6.1 × 10 －５ mol / L ・CaSO ４ Solubility: 0.25g Sulfurous acid (H ２ SO ３ ) ・pK1=1.85 ・pK2=7.19 ・CaSO ３Solubility: 0.0043 g Carbonic acid (H ２ CO ３ ) ・pK1=6.35 ・pK2=10.33 ・CaCO ３ Solubility product: 4.7 × 10 －９ mol / L ・CaCO ３ Solubility of tartaric acid (C ４ O ４ (OH) ２ ) ・pK1=2.93 ・pK2=4.20 ・CaC ４ O ４ (OH) ２ Solubility: 0.01 g Pyrophosphate (H ４ P ２ O ７ ) ・pK1=0.2 ・pK2=0.9 ・pK3=6.76 ・pK4=8.95 ・Ca ２ P ２ O ７ Solubility product: 2.0 × 10 －１９ mol / L Ca ２ P ２ O ７ Solubility: Less than 0.01 g Oxalic acid (H ２ C ２ O ４ ) ・pK1=1.27 ・pK2=4.27 ・CaC ２ O ４ Solubility product: 2.0 × 10 －８ mol / L CaC ２ O ４ Solubility: 0.00067g Citric acid (C(OH)(CH ２ COOH) ２ COOH) ・pK1=3.1 ・pK2=4.8 ・pK3=6.4 ・Ca ３ (C(OH)(CH ２ COOH) ２ COOH) 2.4H ２ Solubility of O: 0.085 g Metasilicic acid (H ２ SiO ３ ) CaSiO ３ Solubility: 9.5 x 10 －３ g Orthosilicic acid (H ４ SiO ４ ) Ca ２ SiO ４Solubility: 0.01 g Phosphoric acid (H ３ P.O. ４ (Reference) ・pK1 = 2.12 ・pK2 = 7.21 ・pK3 = 12.67 ・CaHPO ４ Solubility product: 2.6 × 10 －７ mol / L ・CaHPO ４ Solubility: 0.02 g Ca ３ (P.O. ４ ) ２ Solubility product: 2.0 × 10 －２９ mol / L Ca ３ (P.O. ４ ) ２ Solubility: 0.002g

[0048] Considering the balance of solubility and pKa, it is preferable that the compound mixed in step S48 be one or more selected from the group consisting of tartaric acid, tartrates, sulfurous acid, sulfites, oxalic acid, oxalates, citric acid, citrates, silicic acid, silicates, condensed phosphoric acids (such as pyrophosphoric acid), and condensed phosphates (such as pyrophosphates). Examples of tartrates include sodium tartrate, sodium hydrogen tartrate, potassium tartrate, potassium hydrogen tartrate, potassium sodium potassium tartrate, and ammonium tartrate. Examples of sulfites include sodium sulfite, sodium hydrogen sulfite, potassium sulfite, ammonium sulfite, and sodium potassium sulfite. Examples of oxalates include sodium oxalate and ammonium oxalate. Examples of citrates include monosodium citrate, disodium citrate, trisodium citrate, potassium citrate, and ammonium ferric citrate. Examples of silicates include sodium metasilicate. Examples of pyrophosphates include sodium pyrophosphate, potassium pyrophosphate, and ferric pyrophosphate. Salts of calcium ions with anions constituting these acids or salts have lower solubility than calcium sulfate and are therefore considered to have a higher calcium removal capacity.

[0049] The amount of acid and / or its salt to be mixed in step S48 can be appropriately determined by those skilled in the art. The amount of acid and / or its salt to be added may be, for example, an amount that results in a concentration of the acid and / or its salt in the mixed system of 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. The larger the amount of acid and / or its salt to be added, the less residual calcium there will be. The upper limit of the amount of acid and / or its salt to be added may be, for example, an amount that results in a sulfate concentration in the mixed system of 3.0 M or less, 2.0 M or less, or 1.0 M. The smaller the amount to be added, the less anions other than phosphate ions and cations other than hydrogen ions there will be in the system.

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

[0051] [4. Characteristics of Obtained Phosphoric Acid] The isotopic composition of phosphoric acid obtained by the production method according to one embodiment of the present invention reflects the isotopic composition of elements in the raw materials. Therefore, the isotopic composition of phosphoric acid can be strong evidence for estimating the origin of the phosphoric acid. There are three types of stable isotopes in the oxygen atoms that make up phosphoric acid. On Earth, the stable isotope ratio of oxygen atoms is as follows: １６ O is 99.759%, １７ O is 0.037%, １８ However, in the water molecules present in the water system, １８ The stable isotope ratio of O is lower than that in the atmosphere, at 0.1981% in freshwater and 0.1995% in seawater. Generally, the P-O bond of phosphate preserves stable isotope information unless it is metabolized by an organism. In other words, the oxygen atoms of phosphate derived from minerals that do not come into contact with water are stable and are not replaced by other oxygen atoms. On the other hand, a temperature-dependent isotope exchange equilibrium reaction of oxygen atoms is universally observed in the living world, and this reaction is mediated by pyrophosphatase. In other words, phosphate derived from living organisms is in contact with water molecules, and the oxygen of phosphate molecules is replaced by the oxygen of water molecules at a certain ratio through an equilibrium reaction. Therefore, the oxygen stable isotope ratio of phosphate (δ １８ O ｐBy analyzing the phosphates, it is possible to distinguish between biologically derived phosphates and mineral-derived phosphates. The stable oxygen isotope ratio is analyzed using a pyrolysis elemental analyzer and a stable isotope ratio mass spectrometer (TC / EA-IRMS).

[0052] Normally, the oxygen in bone tissue is higher than that in phosphate rock. １８ The percentage of O is low. １８ It is strongly believed that phosphoric acid having a low O content is phosphoric acid produced from bone tissue. １８ The proportion of O may be 0.1981% or more. １８ The proportion of O may be less than 0.204.

[0053] [5. Summary] <1> A method for producing phosphoric acid, comprising the following steps: Step S20: treating a raw material containing calcium phosphate with an acid to obtain an acid extract; Step S30: mixing the obtained acid extract with a base to obtain a calcium phosphate precipitate; Step S40: mixing the obtained calcium phosphate precipitate with an acid and / or a salt thereof, and forming a poorly soluble calcium salt. <2> The method according to <1>, wherein Step S40 further comprises Step S42: mixing the obtained calcium phosphate precipitate with an acid and / or a salt thereof that forms a poorly soluble calcium salt. <3> The method according to <2>, wherein the acid and / or a salt thereof that forms a poorly soluble calcium salt in Step S42 is one or more selected from the group consisting of condensed phosphoric acid, tartaric acid, oxalic acid, sulfuric acid, and salts thereof. <4> The method according to any one of <1> to <3>, wherein step S40 includes the following steps S46 and S48: step S46: mixing the obtained calcium phosphate precipitate with an acid to obtain a solution of phosphate ions and calcium ions; step S48: mixing the obtained solution of phosphate ions and calcium ions with an acid that forms a poorly soluble calcium salt and / or a salt thereof to remove the precipitated calcium; wherein the acid in step S46 is different from the acid in step S48. <5> The method according to <4>, wherein the acid in step S46 is one or more selected from the group consisting of hydrochloric acid, nitric acid, formic acid, and phosphoric acid. <6> The method according to <4> or <5>, wherein the acid or a salt thereof in step S48 is one or more selected from the group consisting of tartaric acid, sulfurous acid, oxalic acid, citric acid, silicic acid, condensed phosphoric acid, and salts thereof. <7> The manufacturing method according to any one of <4> to <6>, wherein the steps S30 and S46 are repeated two or more times. <8> The manufacturing method according to any one of <1> to <7>, further comprising the following step S50 after the step S40: Step S50: A step of removing cations and / or anions other than phosphate ions.<9> The manufacturing method according to any one of <1> to <8>, further comprising the following step S10 prior to step S20: S11: pretreating the raw material, the pretreatment being one or more selected from 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 <1> to <9>, wherein in step S20, the raw material is acid-treated with one or more acids selected from the group consisting of nitric acid, hydrochloric acid, formic acid, and sulfuric acid. <11> The manufacturing method according to any one of <1> to <10>, wherein the calcium phosphate-containing raw material includes one or more acids selected from the group consisting of bone tissue, apatite, calcium monohydrogen phosphate, calcium dihydrogen phosphate, tricalcium phosphate, and β-tricalcium phosphate.

[0054] Example 1: Removal of calcium ions using pyrophosphate Phosphate was extracted and purified from bone tissue using the following procedure. 1. Raw pork bones were crushed into small pieces of 1-3 mm. 2. 1.0 g of pork bones were immersed in 10 mL of nitric acid aqueous solution (1N) and shaken at 25°C for 48 hours. 3. The mixture was centrifuged at 12,000 xg and 25°C for 5 minutes, and the supernatant was collected. This is the acid extract. Bone impurities were removed as a precipitate. 4. 2 mL of sodium hydroxide aqueous solution (5N) was added to 10 mL of the acid extract and mixed. 5. The supernatant was removed to obtain a calcium phosphate precipitate. 6. The calcium phosphate precipitate was washed three times with pure water, and the supernatant was removed each time. 7. 2.6 mL of pyrophosphate aqueous solution (1M) was added to the calcium phosphate precipitate to dissolve it. 8. A predetermined amount of aqueous sodium hydroxide (1N) was added and mixed overnight at 4°C. This resulted in the formation of a poorly soluble calcium pyrophosphate precipitate. 9. The supernatant from which the precipitate was removed was passed through a cation exchange gel to remove sodium ions derived from the sodium hydroxide. In this way, highly pure phosphoric acid was obtained.

[0055] [Results] The amount of sodium hydroxide added in step 8 and the amount and percentage of calcium remaining in the phosphoric acid obtained in step 9 are shown in Table 1. Calcium was measured using a compact calcium ion meter, LAQUAtwin. <ca-11>(Horiba Ltd.) was used.

[0056]

[0057] As can be seen from Table 1, the residual calcium rate decreased as the amount of sodium hydroxide added increased, and calcium was finally removed to below the detection limit.

[0058] In the procedure of Example 1, a small amount of pyrophosphate may be mixed into the final product, but this does not substantially affect the purity of the resulting phosphoric acid, since the pyrophosphate is converted to phosphoric acid by hydrolysis.

[0059] Example 2: Removal of calcium ions using tartaric acid Phosphate was extracted and purified from bone tissue using the following procedure. 1. Raw pork bones were crushed into 1-3 mm pieces. 2. 1.0 g of pork bones were immersed in 10 mL of 1N nitric acid solution and shaken at 25°C for 48 hours. 3. The mixture was centrifuged at 12,000 x g at 25°C for 5 minutes, and the supernatant was collected each time. This was the acid extract. Bone impurities were removed as a precipitate. 4. 2 mL of 5N sodium hydroxide solution was added to 10 mL of the acid extract and mixed. 5. The supernatant was removed to obtain a calcium phosphate precipitate. 6. The calcium phosphate precipitate was washed three times with pure water, and the supernatant was removed. 7. 6 mL of tartaric acid solution (predetermined concentration, pH 1.3) was added to the calcium phosphate precipitate to dissolve it. This solution was mixed overnight at 4°C. This resulted in the formation of a poorly soluble calcium tartrate precipitate. 8. The precipitate was removed and the supernatant was collected to obtain highly purified phosphoric acid.

[0060] [Results] Table 2 shows 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.

[0061]

[0062] As can be seen from Table 2, the higher the concentration of tartaric acid, the lower the residual calcium rate, and ultimately calcium was removed to below the detection limit. Furthermore, the phosphate recovery rate reached a minimum of approximately 88%. By re-recovering the phosphate contained in the calcium tartrate precipitate through a washing process or by scaling up the phosphate recovery equipment, it is expected that the phosphate recovery rate can be increased to 95% or more.

[0063] Example 3: Removal of calcium ions using sulfite Phosphate was extracted and purified from bone tissue using the following procedure. 1. Raw pork bones were crushed into 1-3 mm pieces. 2. 1.0 g of pork bones were immersed in 10 mL of 1N nitric acid solution and shaken at 25°C for 48 hours. 3. The mixture was centrifuged at 12,000 x g and 25°C for 5 minutes, and the supernatant was collected. This is the acid extract. Bone impurities were removed as a precipitate. 4. 2 mL of 5N sodium hydroxide solution was added to 10 mL of the acid extract and mixed. 5. The supernatant was removed to obtain a calcium phosphate precipitate. 6. The calcium phosphate precipitate was washed three times with pure water, and the supernatant was removed each time. 7. 10 mL of phosphoric acid was added to the calcium phosphate precipitate to dissolve it. 8. 2 mL of potassium sulfite solution (predetermined concentration) was added, and the mixture was mixed overnight at 4°C. This resulted in the formation of a poorly soluble calcium sulfite precipitate. This process was carried out in three systems with different calcium ion concentrations. 9. The supernatant from which the precipitate was removed was passed through a cation exchange gel to remove potassium ions derived from potassium sulfite. In this way, high-purity phosphoric acid was obtained.

[0064] [Results] The concentration of potassium sulfite added in step 8 and the amount of calcium remaining in the phosphoric acid obtained in step 9 are shown in Table 3. Calcium was measured using a compact calcium ion meter, LAQUAtwin. <ca-11>(Horiba Ltd.) was used.

[0065]

[0066] As can be seen from Table 3, in all systems with different initial concentrations of calcium ions, the residual calcium rate decreased as the potassium sulfite concentration increased, and calcium was ultimately removed to below the detection limit.

[0067] Example 4: Purification of Phosphoric Acid by Addition of Sulfuric Acid or Sulfate Phosphoric acid was extracted from bone tissue using sulfuric acid or sulfate according to the following procedure. 1. Pork bones obtained from a slaughterhouse were finely ground using a mill (IKA TUBE MILL 100, IKA JAPAN Co., Ltd.). 2. The ground pork bones were immersed in 1N aqueous nitric acid or 1N aqueous hydrochloric acid for 48 hours. 3. The supernatant was collected to obtain an acid extract. Bone impurities were removed as a precipitate. 4. 100 μL of 5N aqueous sodium hydroxide was added to 0.5 mL of the acid extract and allowed to stand at room temperature for 1 hour. 5. The calcium phosphate precipitate was collected by centrifugation. 6. 0.5 mL of 1N aqueous hydrochloric acid was added to redissolve the calcium phosphate. 7. Sulfuric acid or sulfate (sodium sulfate, potassium sulfate, ammonium sulfate, or magnesium sulfate) was added. The amount of sulfuric acid or sulfate added was adjusted to a final concentration of 0.4 M, 0.6 M, 0.8 M, or 1.0 M. 8. The resulting calcium sulfate precipitate was removed by centrifugation. 9. The weight of phosphate contained in the supernatant was measured. For the measurement, a Malachite Green Phosphate Assay Kit (BioAssay Systems) was used. The phosphate recovery rate was calculated based on the phosphate content in the calcium phosphate precipitate obtained in step 5.

[0068]

[0069] [Results] The results are shown in Table 4. It was found that, at appropriate concentrations, similar phosphoric acid recovery rates can be achieved with sulfuric acid and sulfate salts. In the acid treatment, the use of hydrochloric acid tended to result in higher phosphoric acid recovery rates than nitric acid. Among sulfate salts, potassium sulfate and ammonium sulfate tended to be able to successfully recover phosphoric acid even at low concentrations.

[0070] Example 5: Purification of Phosphoric Acid by Addition of Carbonate Phosphoric acid was extracted from bone tissue using carbonate according to the following procedure. 1. Pork bones obtained from a slaughterhouse were finely ground using a mill (IKA TUBE MILL 100, IKA JAPAN Co., Ltd.). 2. The ground pork bones were immersed in 1N aqueous nitric acid or 1N aqueous hydrochloric acid for 48 hours. 3. The supernatant was collected to obtain an acid extract. Bone impurities were removed as a precipitate. 4. 100 μL of 5N aqueous sodium hydroxide was added to 0.5 mL of the acid extract and allowed to stand at room temperature for 1 hour. 5. The calcium phosphate precipitate was collected by centrifugation. 6. 0.5 mL of 1N aqueous hydrochloric acid was added to redissolve the calcium phosphate. 7. Carbonate (solid sodium bicarbonate or sodium carbonate) was added. The amount of sodium bicarbonate added was such that the final concentration was 0.4 M. The amount of sodium carbonate added was adjusted to a final concentration of 0.6 M. 8. The resulting calcium carbonate precipitate was removed by centrifugation. 9. The phosphate ion concentration (ppm) in the supernatant was measured. Phosphate ion measurement was performed under precise measurement conditions using a high-performance ion chromatograph (IC-8100EX, Tosoh Corporation) connected to a TSKgel SuperIC-Anion HS (4.6 mm I.D. x 10 cm). A mixture of 7.5 mmol / L sodium bicarbonate and 0.8 mmol / L sodium carbonate was used as the eluent. The measurement temperature was 40°C, the flow rate was 1.5 mL / min, and the injection volume was 30 μL. The electrical conductivity (μS) was measured, and the phosphate ion concentration was determined by calculating a regression equation from the area of ​​the standard substance. The phosphate ion content per sample (30 μL) was calculated from the phosphate ion concentration.

[0071]

[0072] [Results] The results are shown in Table 5. By adding carbonate, calcium ions precipitated as calcium carbonate, and phosphate ions remained in the supernatant. For example, in a system in which sodium bicarbonate was added to the acid extract with hydrochloric acid, more than 9,000 ppm of phosphate was contained in the supernatant. Carbonate ions remaining in the supernatant were converted to carbon dioxide when heated, and could be easily removed.

[0073] Example 6: Removal of Cations Contained in Sulfate Example 6-1: Removal of Sodium or Potassium Ions The cations (sodium or potassium ions) contained in sulfate added to remove calcium ions were removed using the following procedure. Specifically, sodium or potassium ions were adsorbed using a strong cation exchange gel. 1. TSKgel SP-TOYOPEARL 650M gel (Tosoh Corporation) was decanted with purified water and loaded into a microspin column (GE Healthcare). 2. An appropriate amount of the supernatant obtained after adding sulfate and removing calcium sulfate was added to the upper layer of the gel. 3. The supernatant was passed through the gel by centrifugation in a tabletop centrifuge. The flow-through fraction was collected. 4. The sodium or potassium ion content (mg) in the flow-through fraction was measured. LAQUAtwin-Na-11 (HORIBA Advanced Techno Co., Ltd.) was used to measure sodium ions. Potassium ions were measured using LAQUAtwin-K-11 (HORIBA Advanced Techno Co., Ltd.).

[0074]

[0075] [Results] The results are shown in Table 6. After calcium sulfate is precipitated by adding sodium sulfate or potassium sulfate, the supernatant contains sodium ions or potassium ions. These ions could be removed by passing the solution through a strong cation exchange gel. Specifically, 83% of the sodium ions were removed, and 86% of the potassium ions were removed. By repeatedly passing the solution through the strong cation exchange gel, even more cations could be removed.

[0076] Example 6-2: Removal of Magnesium or Ammonium Ions. The cations (magnesium or ammonium ions) contained in the sulfate added to remove calcium ions were removed using the following procedure. Specifically, magnesium or ammonium ions were adsorbed using a strong cation exchange gel. 1. TSKgel SP-TOYOPEARL 650M gel (Tosoh Corporation) was decanted with purified water and loaded into a microspin column (GE Healthcare). 2. An appropriate amount of the supernatant, after adding sulfate and removing calcium sulfate, was added to the top layer of the gel. 3. The supernatant was passed through the gel by centrifugation in a tabletop centrifuge. The flow-through fraction was collected. 4. The content (μg) of magnesium, ammonium, or calcium ions in the flow-through fraction was measured. Ion concentrations were measured using a high-performance ion chromatograph IC-8100EX (Tosoh Corporation) connected to a TSKgel SuperIC-Cation HSII (4.6 mm ID x 10 cm) under precise measurement conditions. A mixture of 3.0 mmol / L methanesulfonic acid and 2.7 mmol / L 18-crown-6 was used as the eluent. The measurement temperature was 40°C, the flow rate was 1.0 mL / min, and the injection volume was 30 μL. The calcium ion concentration was determined by measuring the electrical conductivity (μS) and calculating a regression equation from the area of ​​the standard substance. The ion content per sample (30 μL) was calculated from the ion concentration.

[0077]

[0078] [Results] The results are shown in Table 7. It was shown that magnesium ions, ammonium ions, and calcium ions could also be removed from the supernatant by contacting it with the strong cation exchange gel. By repeatedly passing it through the strong cation exchange gel, more cations, including calcium ions, could be removed. This suggests that the purity of the phosphoric acid could be increased.

[0079] Example 7: Improving Phosphate Recovery Rate by Pretreatment We confirmed that pretreating the raw material increases the amount of phosphate contained in the acid extract. Specifically, the acid extract was prepared using the following procedure, and the amount of phosphate contained therein was quantified. 1. Pork bones obtained from a slaughterhouse were crushed using a mill (IKA TUBE MILL 100, IKA JAPAN Co., Ltd.). 2. 5 g of crushed pork bones were subjected to one of the following pretreatments (1) to (5): (1) No treatment; (2) Soaking in 30 mL of nitric acid (1 mol / L) at 50°C for 1 day; (3) Irradiation with 500 W microwaves for 30 seconds; (4) Irradiation with 500 W microwaves for 60 seconds; (5) Irradiation with 500 W microwaves for 120 seconds. 3. 30 mL of nitric acid (1 mol / L) was added to the pork bones (1) and (3) to (5). The pork bones (1) to (5) were soaked in 30 mL of nitric acid for 48 hours at 20°C with shaking (100 rpm). In this way, the bone tissue was decalcified. 4. The supernatant was collected and used as the acid extract. 5. The phosphate concentration was measured using a Malachite Green Phosphate Assay Kit (BioAssay Systems). The measurement method followed the instructions provided with the product. For the measurement, the supernatant was diluted with distilled water.

[0080] [Results] 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 than from bone tissue (1) that was not pretreated. Furthermore, from bone tissues (3) to (5) pretreated by microwave irradiation, up to 1.26 times more phosphoric acid was extracted than from bone tissue (1) that was not pretreated. These results suggest that the use of pretreated acid extracts can more efficiently recover phosphoric acid from calcium phosphate-containing raw materials such as bone tissue.

[0081] Example 8: pH Dependence of Phosphate Recovery Efficiency and Calcium Removal Efficiency Phosphate was extracted and purified from bone tissue using the following procedure. 1. Raw pork bones were crushed into 1-3 mm pieces. 2. 1.0 g of pork bones was immersed in 10 mL of nitric acid aqueous solution (1N) and shaken at 25°C for 48 hours. 3. The mixture was centrifuged at 12,000 x g and 25°C for 5 minutes, and the supernatant was collected. This is the acid extract. Bone impurities were removed as a precipitate. 4. 2 mL of sodium hydroxide aqueous solution (5N) was added to 10 mL of the acid extract and mixed. 5. 0.3 mL of the mixed solution was placed in a 2 mL microtube and centrifuged at 12,000 x g and 25°C for 5 minutes. The supernatant was discarded, and a calcium phosphate precipitate was obtained. 6. The calcium phosphate precipitate was washed three times with pure water, and the supernatant was removed. 7. The calcium phosphate precipitate was dissolved by adding 0.3 mL of an acid or salt solution that forms a poorly soluble calcium salt. The added acid or salt was sulfate (potassium sulfate or ammonium sulfate), citric acid, or tartaric acid. The pH of the mixed solution was adjusted by adding a common acid or base as appropriate. 8. The mixture was centrifuged at 12,000 x g and 25°C for 5 minutes, and the supernatant was collected after removing the poorly soluble calcium salt (calcium sulfate, calcium citrate, or calcium tartrate) precipitate. 9. The phosphate ions and calcium ions contained in the supernatant after removing the poorly soluble calcium salt precipitate were quantified using the Malachite Green Phosphate Assay Kit (BioAssay Systems) and the Calcium Assay Kit, QuantiChrom (500 assays), respectively.

[0082] [Results] The results are shown in Figure 5. The upper graph shows the pH dependence of phosphate ion concentration (g / L), and the lower graph shows the pH dependence of calcium ion concentration (g / L). As can be seen from the figure, when the pH of the system changes after adding an acid or salt, the concentrations of phosphate ions and calcium ions contained in the supernatant also change. This suggests that the pH suitable for extracting phosphoric acid varies depending on the type of acid and / or its salt added in step S42 or step S48. When adding a sulfate salt (potassium sulfate, ammonium sulfate, etc.), the pH after mixing is preferably 1.3 to 2.8. When adding citric acid, the pH after mixing is preferably 3.3 to 4.5. When adding tartaric acid, the pH after mixing is preferably 2.5 to 5.2.

[0083] [Example 9: Purification of phosphoric acid from calcium phosphate compounds other than bone tissue] It was confirmed that phosphoric acid can be produced from raw materials other than bone tissue by the following procedure. 1. A calcium phosphate reagent and apatite were prepared as raw materials. The calcium phosphate reagent consisted of calcium hydrogen phosphate (CMP, CaHPO ４ ), dihydrogen calcium phosphate (CDP, Ca(H ２ P.O. ４ ) ２ ), tricalcium phosphate (TP, 10CaO·3P ２ O ５ ) and β-tricalcium phosphate (β-TCP, Ca ３ (P.O. ４ ) ２ 2. The raw material was immersed in a 1N hydrochloric acid solution, and the phosphate ion and calcium ion concentrations in the acid extract were measured. Measurements were performed using a Malachite Green Phosphate Assay Kit (BioAssay Systems) and a Calcium Assay Kit, QuantiChrom (500 assays).

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

[0085] The acid extracts obtained from both raw materials contained large amounts of phosphate and calcium ions. The recovery rates of phosphate and calcium ions were over 81% for CMP and CDP, and nearly 100% for TP and β-TCP. In the case of apatite, the calculated recovery rate was low at 32%, due to a discrepancy between the composition and purity of the calcium phosphate (fluoroapatite) used in the calculation and the actual ratio of phosphate and calcium contained. However, by optimizing the soaking time, etc., it is believed that phosphate and calcium can be recovered from apatite at rates similar to those of other raw materials.

[0086] From the acid extract thus obtained, phosphoric acid can be extracted and purified by the same method as in any of the above-mentioned Examples. That is, as shown in this Example, the acid extract obtained in step S20 contains high concentrations of phosphate ions and calcium ions. Therefore, phosphoric acid can be obtained by going through steps S30, S40, and the optional step S50.

[0087] The phosphoric acid obtained by the production method according to one embodiment of the present invention can be used in fertilizers, the semiconductor industry, and the like.

Claims

1. A method for producing phosphoric acid comprising the following steps: step S20: treating a raw material containing calcium phosphate with an acid to obtain an acid extract; step S30: mixing the obtained acid extract with a base to obtain a calcium phosphate precipitate; step S40: mixing the obtained calcium phosphate precipitate with an acid and / or a salt thereof to form a poorly soluble calcium salt.

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

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

4. The manufacturing method of claim 1, wherein step S40 includes the following steps S46 and S48: step S46: mixing the obtained calcium phosphate precipitate with an acid to obtain a solution of phosphate ions and calcium ions; step S48: mixing the obtained solution of phosphate ions and calcium ions with an acid and / or a salt thereof that forms a poorly soluble calcium salt to remove the precipitated calcium; wherein the acid in step S46 and the acid in step S48 are different.

5. The manufacturing method according to claim 4, wherein the acid in step S46 is one or more selected from 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 salt thereof in step S48 is one or more selected from the group consisting of tartaric acid, sulfurous acid, oxalic acid, citric acid, silicic acid, condensed phosphoric acid, and salts thereof.

7. The manufacturing method according to claim 4, wherein steps S30 and S46 are repeated two or more times.

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

9. The manufacturing method according to any one of claims 1 to 7, further comprising the following step S10 prior to step S20: S11: a step of pretreating the raw material; the pretreatment is one or more selected from 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 to 7, wherein in step S20, the raw material is acid-treated with one or more acids selected from the group consisting of nitric acid, hydrochloric acid, formic acid and sulfuric acid.

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

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