Method for producing calcium phosphate

Abstract

To provide a production method for calcium phosphate which can produce calcium phosphate having a low aluminum content from sewage sludge incinerated ash containing phosphorus and aluminum.SOLUTION: The method for producing calcium phosphate from sewage sludge incinerated ash containing phosphorus and aluminum includes the steps (1) to (10) described herein, wherein the phosphorus content in the separated liquid 1 is 0.5 to 20 wt% in terms of P2O5.SELECTED DRAWING: None

Description

【Technical Field】 【0001】 The present invention relates to a method for producing calcium phosphate. 【Background Art】 【0002】 Phosphorus resources represented by phosphate rock are useful raw materials used in various fields because they can be used as raw materials for industrial or fertilizer use. However, in recent years, there have been problems such as soaring prices of phosphate rock due to changes in the global situation, and new means to stably obtain high-purity phosphorus resources other than phosphate rock are being sought. In addition, in recent years, attention has been increasing on the Sustainable Development Goals (SDGs), and the way society should be is being questioned. Among new economic systems aimed at achieving the SDGs, circular economy has attracted attention from the perspectives of environmental and economic goals. 【0003】 Phosphorus resources are considered to be recyclable and recoverable from sewage sludge incineration ash, steelmaking slag, industrial wastewater, etc., and various studies have been conducted. For example, Patent Document 1 discloses a dissolution step of adding a solution containing an acid to incineration ash and / or incineration fly ash containing phosphate radicals to make the pH 1.6 or less, thereby dissolving the phosphate radicals in the ash in the solution containing the acid, a residue separation step of separating insoluble residues in the solution containing the acid, and an alkali component input step of adding an alkali component to the solution from which the insoluble residues have been separated and adjusting the pH to be within the range of 1.8 to 2.2, and having an iron compound input step of inputting an iron compound in any step before the alkali component input step, and further having a recovery step of recovering iron phosphate after the alkali component input step, and it is described that phosphorus can be recovered and reused at low cost. 【Prior Art Documents】 【Patent Documents】 【0004】 【Patent Document 1】 Japanese Patent Application Laid-Open No. 2001-130903 [Overview of the Initiative] [Problems that the invention aims to solve] 【0005】 Although Patent Document 1 states that the iron phosphate obtained by the phosphate recovery method described therein contains almost no aluminum, the obtained iron phosphate contains about 10% (by mass) of Al2O3 relative to phosphoric acid (P2O5) (Table 3 in Patent Document 1), and its aluminum content was not sufficiently low. 【0006】 A high aluminum content in phosphorus resources negatively impacts plant productivity when processing phosphorus resources into various raw materials. Examples of these negative impacts include the deposition of aluminum phosphate on the inner wall of the concentration tank during the heating and concentration of phosphoric acid solution, leading to reduced heat transfer efficiency, and the precipitation of some phosphorus as aluminum phosphate during the phosphoric acid purification process, resulting in decreased productivity and a reduced extraction rate of purified phosphoric acid. 【0007】 The inventors focused on calcium phosphate, one of the phosphorus resources. The object of this invention is to provide a method for producing calcium phosphate with a low aluminum content from sewage sludge incineration ash containing phosphorus and aluminum. [Means for solving the problem] 【0008】 The inventors diligently studied to solve the aforementioned problems. As a result, they found that the aforementioned problems can be solved by having the following configuration, and thus completed the present invention. The present invention relates, for example, to the following [1] to [5]. [1] A method for producing calcium phosphate from sewage sludge incineration ash containing phosphorus and aluminum, comprising the following steps (1) to (10): A method for producing calcium phosphate, wherein the phosphorus content in the separated liquid 1 below is 0.5 to 20 wt% in terms of P2O5. (1) A step of mixing the incinerated ash and the acid solution to obtain a slurry 1 with a pH of less than 0.5. (2) Step of separating the slurry 1 into solid and liquid to obtain the separated liquid 1. (3) A step of adding an iron compound to the separated liquid 1 to obtain an iron-added separated liquid 1. (4) Adding alkali metal hydroxide to the iron-added separation liquid 1 to adjust the pH to a range of 0.5 to 2.0 to obtain a pH-adjusted separation liquid 1. (5) A step of heating the pH-adjusted separation liquid 1 at 50°C or higher and stirring to obtain slurry 2. (6) Steps to separate the slurry 2 into solid and liquid to obtain the cake 2. (7) A step of mixing the cake 2 with the alkali metal hydroxide solution to obtain a slurry 3 with a pH of 12 or higher. (8) Step of separating the slurry 3 into solid and liquid to obtain the separated liquid 3. (9) A step of mixing the separated liquid 3 with calcium hydroxide to obtain a slurry 4. (10) Steps to separate the slurry 4 into solid and liquid to obtain calcium phosphate. [2] The method for producing calcium phosphate according to [1], wherein in step (4), the pH is adjusted to within the range of 0.8 to 1.5. [3] The method for producing calcium phosphate according to [1] or [2], wherein the amount of the iron compound is such that the molar ratio of iron to phosphorus (Fe / P) in the iron-added separation liquid 1 is 1.1 to 1.5. [4] A method for producing calcium phosphate according to any one of [1] to [3], wherein the stirring time in step (5) is 0.5 to 10 hours. [5] The method for producing calcium phosphate according to any one of [1] to [4], wherein the amount of calcium hydroxide is such that the molar ratio of calcium to phosphorus (Ca / P) in the slurry 4 is 1.5 to 2.5. [Effects of the Invention] 【0009】 According to the present invention, calcium phosphate with a low aluminum content can be produced from sewage sludge incineration ash containing phosphorus and aluminum. Further, according to the production method of the present invention, iron hydroxide can be easily separated from solid and liquid in the middle process, and calcium phosphate can be produced in a shorter time. 【Brief Description of Drawings】 【0010】 [Figure 1] FIG. 1 is a SEM image of an iron hydroxide cake obtained by filtering an iron hydroxide slurry in Example 1. 【Embodiments for Carrying Out the Invention】 【0011】 Next, the present invention will be specifically described. The description of "A to B" regarding the numerical range means A or more and B or less unless otherwise specified. Further, % means mass %. 【0012】 A method for producing calcium phosphate from sewage sludge incineration ash containing phosphorus and aluminum, comprising the following steps (1) to (10), and the phosphorus content in the following separation liquid 1 is 0.5 to 20 wt% in terms of P2O5. This method is also referred to as the production method (X) hereinafter. (1) A step of mixing the incineration ash and an acid solution to obtain slurry 1 with a pH of less than 0.5 (2) A step of separating the solid and liquid of the slurry 1 to obtain separation liquid 1 (3) A step of adding an iron compound to the separation liquid 1 to obtain an iron-added separation liquid 1 (4) A step of adding an alkali metal hydroxide to the iron-added separation liquid 1 to adjust the pH within the range of 0.5 to 2.0 to obtain a pH-adjusted separation liquid 1 (5) A step of heating and stirring the pH-adjusted separation liquid 1 at 50 °C or higher to obtain slurry 2 (6) A step of separating the solid and liquid of the slurry 2 to obtain cake 2 (7) A step of mixing the cake 2 and an alkali metal hydroxide solution to obtain slurry 3 with a pH of 12 or higher (8) A step of separating the solid and liquid of the slurry 3 to obtain separation liquid 3 (9) Mixing the separation liquid 3 and calcium hydroxide to obtain a slurry 4 (10) Separating the solid and liquid of the slurry 4 to obtain calcium phosphate 【0013】 The production method (X) can be rephrased as a method for producing high-purity calcium phosphate, a method for purifying calcium phosphate, or a method for recovering calcium phosphate. 【0014】 In steps (1) to (10), the mixing method is not limited, and known methods such as stirring and mixing, pump circulation mixing, and pipeline mixing can be used, but stirring and mixing are preferred. 【0015】 In steps (1) to (10), the equipment used for stirring is not limited, and known equipment can be used. Examples of the equipment used for stirring include a stirrer, a propeller, a turbine, and a paddle. 【0016】 In steps (1) to (10), the method of solid-liquid separation is not limited, and known methods such as filtration with a filter medium, decantation, and centrifugation can be used. When performing solid-liquid separation by filtration, known filter media such as filter paper, membrane filter, and fiber filter can be used, and preferably filter paper is used. The filtration can be any of natural filtration, vacuum filtration, pressure filtration, and centrifugal filtration, but preferably vacuum filtration. The temperature for performing solid-liquid separation is not limited, but normal temperature (for example, 10 to 30 °C) is preferred. 【0017】 In steps (1) to (10), the pH is the value measured at 25 to 30 °C and is measured by the method described in the examples below. 【0018】 <Sewage sludge incineration ash> The sewage sludge incineration ash used in the present invention contains phosphorus and aluminum. Sewage sludge incineration ash is the residue obtained by incinerating activated sludge generated in sewage treatment, and its form and composition are not particularly limited as long as it contains phosphorus and aluminum. For example, sewage sludge incineration ash can be used, as well as sewage sludge incineration ash from sewage treatment facilities and various wastewater treatment equipment. 【0019】 In sewage treatment, coagulants such as ferric polysulfate and aluminum sulfate, and coagulation / sedimentation / dewatering aids such as slaked lime (Ca(OH)2) are added to the sewage for the purpose of coagulation, sedimentation separation, and dewatering of activated sludge containing phosphorus. Therefore, in sewage sludge incineration ash, phosphorus mainly exists as phosphates represented by iron phosphate (FePO4, Fe3(PO4)2, etc.), aluminum phosphate (AlPO4, etc.), and calcium phosphate (Ca3(PO4)2, Ca5(PO4)3OH, etc.). 【0020】 <Process (1)> Step (1) is a step of mixing the incinerated ash and the acid solution to obtain a slurry 1 with a pH of less than 0.5. In step (1), phosphates contained in the incinerated ash, mainly iron phosphate (FePO4, Fe3(PO4)2, etc.), aluminum phosphate (AlPO4, etc.), and calcium phosphate (Ca3(PO4)2, Ca5(PO4)3OH, etc.), are eluted with acid. The solubility of phosphates varies greatly with pH, ​​but iron phosphate, aluminum phosphate, and calcium phosphate have sufficiently high solubility at pH less than 0.5, and are eluted from the incinerated ash at pH less than 0.5 and dissolved in slurry 1. The slurry 1 in step (1) is preferably at a pH of less than 0.3, and more preferably at a pH of less than 0.1. 【0021】 SiO2, Fe2O3, CaSO4, etc., contained in incinerated ash have low solubility at pH levels below 0.5 and become insoluble in slurry 1. 【0022】 The acid used in the acid solution is not particularly limited, and known acids such as sulfuric acid, nitric acid, and acetic acid can be used. One or more acids may be used. If the calcium phosphate obtained in step (10) contains a large amount of chlorine, it may corrode the metal equipment used when manufacturing other products using calcium phosphate as a raw material. Therefore, the acid solution is a chlorine-free acid solution, and more preferably a sulfuric acid solution. 【0023】 The concentration of the acid in the acid solution varies depending on the type of acid and the composition of the incinerated ash, but it should be used at a concentration such that the pH of slurry 1 obtained by mixing with the incinerated ash is less than 0.5. If the acid solution is a sulfuric acid solution, the concentration of sulfuric acid is preferably 0.3 to 3 mol / L, more preferably 0.5 to 2 mol / L, and even more preferably 0.8 to 1.2 mol / L. 【0024】 There are no particular restrictions on the ratio of incinerated ash to acid solution to be mixed; the incinerated ash and acid solution can be mixed in any ratio. The incinerated ash and acid solution are preferably mixed at a solid-liquid ratio (L / S, Liquid / Solid) of 5 to 20 L / kg, more preferably 7 to 15 L / kg, and even more preferably 8 to 12 L / kg. Mixing at a solid-liquid ratio within the above range allows for efficient elution of phosphates. 【0025】 It is preferable to further stir and / or heat slurry 1 in order to facilitate the efficient elution of phosphates. The stirring time is preferably 1 minute to 10 hours, more preferably 10 minutes to 5 hours, even more preferably 30 minutes to 4 hours, and particularly preferably 1 hour to 3 hours. When the stirring time is within the above range, phosphates are more easily and efficiently eluted. The heating temperature is preferably 50°C to 100°C, more preferably 60°C to 95°C, and even more preferably 70°C to 90°C. When the heating temperature is within the above range, the phosphate is more efficiently eluted. 【0026】 <Process (2)> Step (2) is a step in which slurry 1 is separated into solid and liquid to obtain separated liquid 1. Through solid-liquid separation, slurry 1 is separated into a solid (cake 1) and a liquid (separated liquid 1). Since SiO2, Fe2O3, CaSO4, etc. are separated from the solid (cake 1), a liquid (separated liquid 1) is obtained with low content of these substances and high content of phosphates. 【0027】 The phosphorus content in separated liquid 1 is 0.5 to 20 wt% in terms of P2O5. The phosphorus content in the separated liquid 1 is preferably 1 to 10 wt% in terms of P2O5, and more preferably 1 to 5 wt% in terms of P2O5. When the phosphorus content is 1 to 5 wt% in terms of P2O5, the reaction efficiency of phosphorus and iron compounds in step (3) tends to improve, and the iron phosphate obtained in step (6) has excellent filterability, so that iron phosphate with fewer impurities can be obtained as cake 2. 【0028】 The manufacturing method (X) may include a step of washing cake 1 with water to obtain washing solution 1. The cake produced in this step will be referred to as post-washed cake 1. 【0029】 The manufacturing method (X) may include the following steps (2a) to (2c) between steps (2) and (3). (2a) A step of adding sulfuric acid solution to the separated liquid 1 to adjust the pH to 0.1 or less to obtain sulfuric acid-added separated liquid 1. (2b) A step of mixing the sulfuric acid-added separation liquid 1 with fresh sewage sludge incineration ash containing phosphorus and aluminum to obtain slurry 1-1. (2c) Steps to obtain separated liquid 1-2 by solid-liquid separation of the slurry 1-1. 【0030】 Steps (2a) to (2c) may be repeated two or more times, with separation liquid 1-2 used instead of separation liquid 1 in step (2a). By performing acid extraction of the incinerated ash multiple times, the phosphate content of separation liquid 1-2 increases, so it can be preferably used instead of separation liquid 1 in the next step (3). 【0031】 <Process (3)> Step (3) is the step of adding an iron compound to the separation liquid 1 to obtain an iron-added separation liquid 1. By adding an iron compound to the separated liquid 1, even if the amount of iron compound in the incinerated ash is trace, the phosphate ions (PO4) in the separated liquid 1 can be reduced. 3- ) can all be converted to iron phosphate. 【0032】 The iron compound is not limited to any known iron compound, but trivalent iron ions (Fe 3+ ) is a phosphate ion (PO4 3- Since it readily reacts with ferric iron to form iron phosphate (FePO4), the iron compound is preferably an iron compound containing trivalent iron. Examples of iron compounds containing trivalent iron include ferric sulfate (Fe2(SO4)3), iron hydroxide (Fe(OH)3 (amorphous)), and iron nitrate (Fe(NO3)3). If the calcium phosphate obtained in step (10) contains a large amount of chlorine, the metal equipment used when manufacturing other products using calcium phosphate as a raw material may corrode. Therefore, the iron compound is preferably an iron compound that does not contain chlorine atoms, and more preferably ferric sulfate (Fe2(SO4)3). 【0033】 The iron compound may also be the cake 3 produced in step (8) described later. 【0034】 The amount of iron compound added to the separation solution 1 is not limited, but preferably, it is an amount such that the molar ratio of iron to phosphorus (Fe / P) in the iron-added separation solution 1 is 1.1 to 1.5. This allows the phosphate ions in the separation solution 1 to be efficiently converted to iron phosphate, making it easier for iron phosphate to precipitate in step (5). 【0035】 The manufacturing method (X) preferably includes a step between step (2) and step (3) to measure the iron content and phosphorus content of the separated liquid 1. This process allows for the determination of the amount of iron compound to be added so that the molar ratio of iron to phosphorus (Fe / P) in the iron-added separation solution 1 becomes a specific value. The method for measuring iron and phosphorus content is not limited, and known methods can be used, such as colorimetric methods, atomic absorption spectrophotometric methods, and inductively coupled plasma emission spectrometry. 【0036】 The manufacturing method (X) preferably includes a step of adding washing solution 1 to separation solution 1 before step (3). This can increase the recovery rate of phosphate. 【0037】 <Process (4)> Step (4) is the step of adding an alkali metal hydroxide to the iron-added separation liquid 1 to adjust the pH to a range of 0.5 to 2.0 in order to obtain a pH-adjusted separation liquid 1. By adjusting the pH to within the range of 0.5 to 2.0, the solubility of iron phosphate in the iron-added separation solution 1 decreases. In step (4), almost no iron phosphate precipitates, and by adjusting the pH to within the range of 0.5 to 2.0, the filterability of the iron phosphate obtained in step (6) improves, and a cake 2 with higher purity iron phosphate can be obtained. 【0038】 In step (4), the pH is preferably adjusted to a range of 0.8 to 1.5, more preferably 1.0 to 1.5, and even more preferably 1.1 to 1.3. Adjusting the pH to the above range further reduces the solubility of iron phosphate to a degree where it does not immediately precipitate, making it easier for iron phosphate to precipitate in step (5). 【0039】 The alkali metal hydroxide is not limited and any known alkali metal hydroxide can be used. Examples of alkali metal hydroxides include sodium hydroxide and potassium hydroxide, but sodium hydroxide is preferred. Alkali metal hydroxides may be added as a solid or dissolved in water and added as an aqueous solution, but it is preferable to add them as an aqueous solution. Because alkali metal hydroxides are strong bases, less solution is needed for pH adjustment compared to when using ammonia, and the phosphorus concentration in the reaction solution does not become excessively low. Also, unlike ammonia, alkali metal hydroxides are non-volatile, so their concentration in the solution does not decrease even when heated, resulting in a small change in pH. 【0040】 The amount of alkali metal hydroxide to be added will vary depending on the type of alkali metal hydroxide and the pH of the iron-added separation solution 1, but an amount should be used so that the pH of the pH-adjusted separation solution 1 is within the range of 0.5 to 2.0. 【0041】 <Process (5)> Step (5) is a step in which the pH-adjusted separation liquid 1 is heated to 50°C or higher and stirred to obtain slurry 2. By heating pH-adjusted separation solution 1 to over 50°C and stirring, the solubility of iron phosphate decreases further, causing it to precipitate and form a slurry. 【0042】 Although little iron phosphate precipitates in step (4), it precipitates in step (5) by heating and stirring at over 50°C. By performing step (5), the iron phosphate contained in cake 2 obtained in step (6) becomes uniform in particle size and the particle size distribution becomes sharper. As a result, the iron hydroxide contained in cake 3 obtained in step (8) is nearly spherical and relatively dispersible, and the filterability of cake 3 obtained in step (8) is improved, shortening the time required for solid-liquid separation in step (8). In addition, the improved filterability increases the recovery efficiency of the separated liquid 3, resulting in a higher total phosphorus yield of calcium phosphate obtained in step (10). 【0043】 The heating temperature in step (5) is not limited as long as it is 50°C or higher, but is preferably 50°C to 100°C, more preferably 60°C to 100°C, even more preferably 70°C to 100°C, and particularly preferably 80°C to 95°C. When the heating temperature is within the aforementioned range, iron phosphate precipitates more easily, and the particle size of iron phosphate tends to become more uniform. 【0044】 The stirring time in step (5) is not limited, but is preferably 0.5 to 10 hours, more preferably 0.5 to 5 hours, and even more preferably 0.5 to 4 hours. If the stirring time is within the aforementioned range, iron phosphate is more likely to precipitate, and the particle size of iron phosphate tends to become more uniform. 【0045】 <Process (6)> Step (6) is the step of separating the slurry 2 into solid and liquid to obtain the cake 2. Through solid-liquid separation, slurry 2 is separated into a solid (cake 2) and a liquid (separated liquid 2). Since heavy metals and other substances derived from sewage sludge incineration ash are separated into the liquid (separated liquid 2), iron phosphate with a low content of heavy metals and other substances can be obtained as a solid (cake 2). 【0046】 The manufacturing method (X) preferably includes a step between step (6) and step (7) to wash the cake 2 with water and obtain the cake 2 after washing. This makes it possible to further reduce heavy metals and other substances contained in the cake 2. The cleaning solution produced in this process is referred to as cleaning solution 2. After washing, cake 2 may be dried before proceeding to the next step. 【0047】 The manufacturing method (X) preferably involves, between step (6) and step (7), (6a) Add alkali metal hydroxide to the separated liquid 2 to readjust the pH to within the range of 0.5 to 2.0 to obtain pH-adjusted separated liquid 2. (6b) A step of heating the pH-adjusted separation liquid 2 to 50°C or higher and stirring to obtain slurry 2-1. (6c) A step of separating the slurry 2-1 into solid and liquid to obtain cake 2-1, and (6d) Adding cake 2-1 to cake 2 It also includes. 【0048】 Since the phosphate ions remaining in the separated liquid 2 are reprecipitated as iron phosphate to obtain a solid (cake 2-1), cake 2 to which cake 2-1 has been added has a higher phosphorus yield while maintaining a low aluminum content. 【0049】 Steps (6a) to (6d) are preferably repeated two or more times. This further increases the phosphorus yield of cake 2 to which cake 2-1 has been added. 【0050】 <Process (7)> Step (7) is a step of mixing the cake 2 with an alkali metal hydroxide solution to obtain a slurry 3 with a pH of 12 or higher. In step (7), the iron phosphate contained in cake 2 dissolves, and the resulting iron ions precipitate as iron hydroxide. 【0051】 The pH in step (7) is preferably 13 or higher, more preferably 14 or higher. When the pH is within the above range, iron phosphate dissolves more easily, and therefore iron hydroxide precipitates more readily. 【0052】 The alkali metal hydroxide is not limited and any known alkali metal hydroxide can be used. Examples of alkali metal hydroxides include sodium hydroxide and potassium hydroxide, but sodium hydroxide is preferred. Alkali metal hydroxides are strong bases and do not volatilize easily, so compared to using ammonia for pH adjustment, less is needed, thus not lowering the phosphorus concentration in the solution, and the pH change due to heating is small. Also, even in a saturated solution, ammonia has a pH of around 12-13, and when mixed with cake 2 and neutralized with iron phosphate, it is difficult to raise the pH of slurry 3 above 12, making it unsuitable for use in step (7). On the other hand, with alkali metal hydroxides, a small amount is sufficient to raise the pH of slurry 3 above 12. 【0053】 The amount of alkali metal hydroxide used will vary depending on the type of alkali metal hydroxide and the amount of cake 2, but an amount that results in a pH of 12 or higher in slurry 3 should be used. 【0054】 The ratio of cake 2 to alkali metal hydroxide solution to be mixed is not particularly limited; cake 2 and alkali metal hydroxide solution can be mixed in any ratio. Cake 2 and the alkali metal hydroxide solution are preferably mixed in a solid-liquid ratio (L / S) of 13 to 27 L / kg, more preferably 15 to 25 L / kg, and even more preferably 17 to 23 L / kg. Mixing within the above range of solid-liquid ratios results in a faster precipitation rate of iron hydroxide in step (7), a faster precipitation rate of calcium phosphate in step (9), and a higher yield of calcium phosphate obtained in step (10). 【0055】 Since slurry 3 is more prone to iron hydroxide precipitation, it is preferable to further stir and / or heat it. The stirring time is preferably 1 minute to 5 hours, more preferably 10 minutes to 4 hours, and even more preferably 30 minutes to 2 hours. When the stirring time is within the above range, iron hydroxide precipitates more easily. The heating temperature is preferably 40°C to 80°C, more preferably 50°C to 70°C, and even more preferably 55°C to 65°C. When the heating temperature is within the above range, iron hydroxide precipitates more easily, and the fluidity of slurry 3 increases, improving filterability and thus improving the phosphorus yield. 【0056】 <Process (8)> Step (8) is a step of separating the slurry 3 into solid and liquid to obtain the separated liquid 3. Through solid-liquid separation, the slurry 3 is separated into a solid (cake 3) and a liquid (separated liquid 3). Since iron hydroxide is mainly separated from the solid (cake 3), a liquid (separated liquid 3) with a low iron content and a high phosphate ion content is obtained. 【0057】 Since cake 3 mainly contains iron hydroxide, it can be used as an iron compound in step (3). At the same time, since cake 3 contains alkali metal hydroxide, and iron hydroxide is basic, it can also be used as an alkali metal hydroxide for pH adjustment in step (4). Furthermore, if the pH becomes too high when using cake 3 for pH adjustment in step (4), the pH can be adjusted using an acid (such as sulfuric acid). 【0058】 <Process (9)> Step (9) is a step of mixing the separation liquid 3 with calcium hydroxide to obtain a slurry 4. In step (9), calcium phosphate is precipitated from the phosphate ions contained in the separation liquid 3 and the calcium ions of calcium hydroxide. 【0059】 Calcium hydroxide (Ca(OH)2) is also known as slaked lime or lime. While the purity and grade of calcium hydroxide are not restricted, it is preferable to use calcium hydroxide with low levels of impurities such as chlorine and aluminum. Calcium hydroxide may be mixed with the separation liquid 3 in any form: powder, aqueous solution (also called limewater), or suspension (also called lime milk), but it is preferably mixed in powder form. This makes it easier to obtain calcium phosphate with a low aluminum content and tends to increase the phosphorus yield. Furthermore, mixing in powder form tends to result in better filterability of the calcium phosphate obtained in step (10) compared to mixing in suspension form. 【0060】 It is preferable to further stir slurry 4, as this makes calcium phosphate more likely to precipitate. The stirring time is preferably 1 to 10 hours, more preferably 1 to 7 hours, and even more preferably 4 to 6 hours. When the stirring time is within the above range, calcium phosphate precipitates more easily. 【0061】 The amount of calcium hydroxide mixed with the separation liquid 3 is not limited, but preferably it is an amount that results in a calcium-to-phosphorus molar ratio (Ca / P) of 1.5 to 2.5 in the slurry 4, more preferably 1.67 to 2.3, and even more preferably 1.8 to 2.2. When the calcium-to-phosphorus molar ratio is within the above range, it is easier to obtain calcium phosphate with a low aluminum content, and the phosphorus yield tends to be high. 【0062】 The manufacturing method (X) preferably includes a step of measuring the phosphorus content of the separated liquid 3 between step (8) and step (9). This process allows for the determination of the amount of calcium hydroxide so that the molar ratio (Ca / P) of calcium to phosphorus in slurry 4 reaches a specific value. The method for measuring phosphorus content is not limited, and known methods can be used, such as colorimetric methods, atomic absorption spectrophotometric methods, and inductively coupled plasma emission spectrometry. 【0063】 <Process (10)> Step (10) is a step of separating the slurry 4 into solid and liquid to obtain calcium phosphate. Through solid-liquid separation, the slurry 4 is separated into a solid (cake 4) and a liquid (separated liquid 4). Since sodium hydroxide and other substances are separated into the liquid (separated liquid 4), high-purity calcium phosphate is obtained as a solid (cake 4). 【0064】 The manufacturing method (X) preferably includes a step after step (10) to wash the cake 4 with water to obtain the cake 4 after washing. This makes it possible to further reduce the content of sodium hydroxide and the like in the cake 4. The cleaning solution produced in this process is referred to as cleaning solution 4. After washing, it is preferable to dry the cake 4. [Examples] 【0065】 The present invention will now be described in more detail with reference to examples, but the present invention is not limited thereto. 【0066】 <Raw materials and reagents> Incineration ash: Sewage sludge incineration ash (transferred from the Tokyo Metropolitan Government Bureau of Sewerage) with the composition ratios listed in Table 1 was used. The method for measuring the composition of incineration ash 1 and 2 will be described later. 【0067】 [Table 1] 【0068】 Sulfuric acid: In Production Example 1 and Comparative Example 1, (1+1) sulfuric acid (65%) (manufactured by Kanto Chemical Co., Ltd.) was used, while in Production Examples 2-5, 98% sulfuric acid (manufactured by Taiki Pharmaceutical Co., Ltd.) was used. 【0069】 Sodium hydroxide: In Production Example 1 and Comparative Example 1, 40% NaOH (special grade) (manufactured by Kanto Chemical Co., Ltd.) was used, while in Production Examples 2-5, 48% NaOH (first grade) (manufactured by Kanto Chemical Co., Ltd.) was used. 【0070】 Iron(III) sulfate:Fe2(SO4)3·n hydrate (grade 1) (manufactured by Kanto Chemical Co., Ltd.) was used. 【0071】 <Measurement of the composition ratio of the sample> (moisture) After accurately weighing a 50mmφ flat weighing bottle to obtain the accurate weighing value (A), 5.0g of the sample was quickly placed into the 50mmφ flat weighing bottle, the lid was closed, and it was accurately weighed to obtain the accurate weighing value (B). The lid was removed, and it was dried at 105°C (forced-air dryer) for 5 hours. The lid was closed, and it was cooled in a silica gel desiccator for 30 minutes, and then accurately weighed to obtain the accurate weighing value (C). This sample will be referred to as the dried sample below. Using the precision values ​​(A) to (C), the moisture content (by weight) was calculated from the following formula (I). Moisture (weight %)=(BC)×100 / (BA)...Formula (I) 【0072】 (Pre-processing) Approximately 2.3 g of the dried sample was accurately weighed into a 200 mL PYREX® conical beaker and lightly moistened with water. After adding 10 mL of nitric acid and 30 mL of hydrochloric acid, the conical beaker was placed on the heating element of a preheated electric heater and gently boiled for at least 30 minutes. After cooling, the sample was rinsed with pure water and transferred to a 500 mL volumetric flask. The sample was filtered using quantitative filter paper No. 6, and at least 150 mL of filtrate was collected. The obtained filtrate was used as the test solution. 【0073】 (Analysis of P2O5 (colorimetric method)) 1. Preparation of the color-developing solution 1.12 g of ammonium metavanadate (NH4VO3) was dissolved in 200-300 mL of pure water, and 250 mL of nitric acid was added. While stirring this solution, ammonium molybdate ((NH4)6Mo7O) dissolved in water was added. 24 27g of (4H2O) was added, and then pure water was added to make a total volume of 1L. The mixture was then stored in a colored bottle. Before use, it was filtered. 【0074】 2. Preparation of P2O5 standard solution 19.17 g of KH2PO4 was dissolved in pure water, and 10 mL of nitric acid was added to make exactly 1 L to obtain a P2O5 standard stock solution (10 mg / mL). This was diluted to prepare P2O5 standard solutions (0.2 mg / mL) and P2O5 standard solution (0.3 mg / mL). 【0075】 3 Quantitative P2O5 standard sample solutions of different concentrations were prepared using a P2O5 standard solution. The test solution was diluted appropriately with pure water. A color developer was added to the P2O5 standard sample solution and the test solution and mixed. After standing at room temperature for 30 minutes, the absorbance at 420 nm was measured. The P2O5 concentration (weight %) of the test solution was calculated from the obtained absorbance using a colorimetric method. 【0076】 (SO3 analysis (BaSO4 gravimetric method)) 5.0 g of the dried sample was weighed into a weighing bottle and then transferred to a 500 mL PYLEX beaker using water. 30 mL of hydrochloric acid and 10 mL of perchloric acid were added. After cooling, the solution was made up to 100 mL with pure water, and 10 mL of hydrochloric acid was added. The solution was heated and dissolved, and filtered using quantitative filter paper No. 6. 20 mL of hydroxylamine hydrochloride solution was added to the filtrate and heated for 5 minutes to decompose it. 10 mL of 10% barium chloride solution was added, the solution was made up to 300 mL with pure water, boiled, and heated and aged for 3 hours or more. The solution was filtered using quantitative filter paper No. 6 and washed with hot water. The obtained precipitate and the filter paper used were dried in an electric furnace and a silica gel desiccator, then weighed to obtain weighed value (D). The precipitate was removed from the filter paper with a brush and weighed to obtain weighed value (E). 【0077】 Using the weighed values ​​(D) and (E), SO3 (weight %) was calculated from the following formula (II). SO3 (wt%) = (D - E) × 0.343 × 100 / dried sample (g) ··· Equation (II) 【0078】 (Analysis of SiO2 (atomic absorption spectrometry)) After precisely weighing 5.0 g of the dried sample into a nickel crucible, approximately 1 - 2 mL of pure water and 10 g of potassium hydroxide were added and mixed well. The crucible was heated to dissolve the potassium hydroxide and completely remove the moisture. After cooling, it was transferred to a 50 mL beaker, water was added to dissolve the melt. After adding 1 drop of phenolphthalein solution, (1 + 2) hydrochloric acid was added little by little to the beaker to neutralize the solution, and then (1 + 2) hydrochloric acid was added in excess. After cooling, it was diluted with water to obtain a SiO2 measurement solution. The SiO2 measurement solution was subjected to measurement using an atomic absorption spectrometer (ZA-3300, manufactured by Hitachi, Ltd.). The measurement conditions are shown in Table 2 below. 【0079】 SiO2 (wt%) was calculated from the following Equation (III). SiO2 (wt%) = (atomic absorption (Si) × 2.1393 × 100) / (dried sample (g) × 1 / 500 × 1000000) ··· Equation (III) 【0080】 (Analysis of CaO, Fe2O3, Al2O3, MgO, Na2O (atomic absorption spectrometry)) The test solution was appropriately diluted with pure water and subjected to measurement using an atomic absorption spectrometer (ZA-3300, manufactured by Hitachi, Ltd.) to measure the concentrations of Ca, Fe, Al, Mg, and Na. The concentrations of Ca, Fe, Al, Mg, and Na were measured as the concentrations (wt%) of CaO, Fe2O3, Al2O3, MgO, and Na2O, respectively. The measurement conditions are shown in Table 2 below. Note that the measurement of the Na concentration was carried out under the conditions of "Na" when the concentration was 0 - 1 ppm and "Na (fluorescence)" when the concentration was between 1 - 30 ppm. 【0081】 【Table 2】 【0082】 (Measurement of pH) pH measurements were performed at 25-30°C using a HORIBA LAQUA benchtop pH meter F-72S and a combined electrode: HORIBA LAQUA long ToupH electrode (9680S-10D). 【0083】 <Measurement of particle size> The particle size of the sample was measured using a particle size analyzer (Microtrac, Leeds & Northrup, Microtrac9320-X100). The 10%, 50%, and 90% diameters of the cumulative distribution were defined as D10, D50 (median diameter), and D90, respectively. 【0084】 <Observation using a scanning electron microscope (SEM)> The sample was observed using a scanning electron microscope (JSM-6010LA, manufactured by JEOL Ltd.). 【0085】 <Evaluation of filtration performance> The filterability during vacuum filtration was evaluated according to the following criteria. A: Good filtration performance (The filtration process takes 5 minutes or less.) B: Poor filtration performance (The filtration process took more than 30 minutes.) 【0086】 [Experiment 1] Recovery of iron phosphate from incinerator ash [Manufacturing Example 1] A 1 mol / L sulfuric acid solution was added to reaction vessel 1 and heated to 80°C. While stirring the sulfuric acid solution at 80°C, incinerated ash 1, as described in Table 1, was added to reaction vessel 1 so that the solid-liquid ratio L / S was 10 L / kg, and slurry 1 was obtained. The pH of slurry 1 was approximately 0 to 0.3. The mixture was heated for 2 hours while maintaining the temperature at 80°C. Subsequently, slurry 1 was filtered by suction using filter paper (ADVANTEC, quantitative filter paper No. 5C) to recover separated liquid 1 (incinerator ash extract) and filter cake 1 (incinerator ash extract residue). Filter cake 1 was then filtered and washed with water to recover washing liquid 1. 【0087】 The concentrations of P2O5, Al2O3, and Fe2O3 in separated liquid 1 were measured. Separated liquid 1 was pretreated as a test solution using the method described above before measurement. Next, the separated liquid 1 was placed in a separate reaction tank 2, and washing liquid 1 was added to achieve a phosphoric acid concentration equivalent to 1.87 wt% as P2O5. The mixture was then stirred and mixed to obtain the mixed solution. In the mixture, iron(III) sulfate was added to reaction vessel 2 so that the molar ratio of iron to phosphorus (Fe / P, mol / mol) was 1.1, and the mixture was stirred until it was completely dissolved. Sodium hydroxide was added to the liquid in reaction vessel 2 (iron-added separation solution 1) while measuring the pH with a pH meter, and the pH was adjusted to 1.2 to obtain pH-adjusted separation solution 1. The mixture was then heated at 80°C for 1 hour and stirred to obtain slurry 2. The obtained slurry 2 was filtered under reduced pressure, and the separated liquid 2 and filter cake 2 were recovered. The filter cake 2 was washed with water and dried to obtain iron phosphate precipitate 1. 【0088】 The filterability of slurry 2 was evaluated during vacuum filtration. The results are shown in Table 3. The recovered iron phosphate precipitate 1 was used as a sample, and its composition was analyzed using the method described above. The results are shown in Table 3. 【0089】 [Manufacturing Example 2] Except for replacing incinerated ash 1 with incinerated ash 2 in Production Example 1, and setting the target phosphoric acid concentration of the mixed solution in reaction vessel 2 to 1.5 wt%, iron phosphate precipitate 1 was recovered from the incinerated ash using the same method as in Production Example 1, and its composition was analyzed. The results are shown in Table 3. 【0090】 [Manufacturing Example 3] Except for replacing incinerated ash 1 with incinerated ash 2 in Production Example 1, and further adjusting the phosphoric acid concentration of the mixed solution in reaction vessel 2 to 1.5 wt%, and changing the stirring conditions after adding sodium hydroxide solution to 80°C for 2 hours, iron phosphate precipitate 1 was recovered from the incinerated ash using the same method as in Production Example 1, and its composition was analyzed. The results are shown in Table 3. 【0091】 [Manufacturing Example 4] Except for replacing incinerated ash 1 with incinerated ash 2 in Production Example 1, and further adjusting the phosphoric acid concentration of the mixed solution in reaction vessel 2 to 1.5% wt, and changing the stirring conditions after adding sodium hydroxide solution to 95°C for 2 hours, iron phosphate precipitate 1 was recovered from the incinerated ash using the same method as in Production Example 1, and its composition was analyzed. The results are shown in Table 3. In addition, the particle size of iron phosphate precipitate 1 was also measured for Production Example 4. 【0092】 [Manufacturing Example 5] Except for replacing incinerated ash 1 with incinerated ash 2 in Production Example 1, and further adjusting the phosphoric acid concentration of the mixed solution in reaction vessel 2 to 1.54 wt%, and changing the stirring conditions after adding sodium hydroxide solution to 95°C for 4 hours, iron phosphate precipitate 1 was recovered from the incinerated ash using the same method as in Production Example 1, and its composition was analyzed. The results are shown in Table 3. 【0093】 [Comparative Manufacturing Example 1] In the same method as in Production Example 1, comparative iron phosphate precipitate 1 was recovered from incinerated ash, except that the phosphoric acid concentration of the mixture in reaction vessel 2 of Production Example 1 was set to 1.6 wt%, sodium hydroxide solution was added to adjust the pH to 2.5, and the stirring conditions after the addition of sodium hydroxide solution were set to 40°C for 1 hour. The composition was analyzed and the particle size was measured. The results are shown in Table 3. 【0094】 [Table 3] 【0095】 In production examples 1-5, iron phosphate with a lower aluminum content was obtained compared to comparative production example 1 (Table 3). Furthermore, in production examples 1-5, slurry 2 exhibited superior filterability compared to comparative production example 1. Furthermore, compared to the one obtained in comparative production example 1, iron phosphate precipitate 1 showed a smaller difference between D10 and D90, a more uniform particle size, and a sharper particle size distribution. 【0096】 [Experiment 2] Reprecipitation of iron phosphate [Manufacturing Example 6] The separation liquid 2 obtained in Production Example 1 was stirred, and while measuring the pH, NaOH was added to adjust the pH to 1.2, obtaining pH-adjusted separation liquid 2-1. Then, it was further heated to 80°C and stirred for 1 hour to obtain slurry 2-1. Slurry 2-1 was filtered under reduced pressure to recover separation liquid 2-1 and filter cake 2-1. Filter cake 2-1 was washed and dried to obtain iron phosphate precipitate 2. The composition of iron phosphate precipitate 2 was analyzed. 【0097】 Separation liquid 2-1 was stirred, and while measuring the pH, NaOH was added to adjust the pH to 1.5, obtaining pH-adjusted separation liquid 2-2. Then, it was further heated to 80°C and stirred for 1 hour to obtain slurry 2-2. Slurry 2-2 was filtered (vacuum filtration) to recover separation liquid 2-2 and filter cake 2-2. Filter cake 2-2 was washed and dried to obtain iron phosphate precipitate 3. The composition of iron phosphate precipitate 3 was analyzed. 【0098】 Iron phosphate precipitate 2, iron phosphate precipitate 3, and iron phosphate precipitate 1 obtained in Production Example 1 were combined to form one sample (iron phosphate precipitate 4). The composition of iron phosphate precipitate 4 was calculated by summing the analytical values ​​of iron phosphate precipitate 2, iron phosphate precipitate 3, and iron phosphate precipitate 1 obtained in Production Example 1. The yields of phosphorus, iron, and aluminum in iron-added separation solution 1 were calculated, with the phosphorus, iron, and aluminum content of iron-added separation solution 1 set to 100%. The results are shown in Table 4. 【0099】 [Comparative Manufacturing Example 2] Comparative iron phosphate precipitate 5 was prepared using the same method as in Comparative Production Example 1. Similar to Production Example 6, the yields of phosphorus, iron, and aluminum in Comparative Iron Phosphate Precipitate 5 were calculated, with the phosphorus, iron, and aluminum content of iron-added separation liquid 1 set to 100%, and the results are shown in Table 4. 【0100】 [Table 4] 【0101】 By repeating the process of adding alkali metal hydroxide to the separated liquid 2 after recovering the iron phosphate precipitate obtained in Production Example 1, heating and stirring, and recovering the iron phosphate precipitate again, it was confirmed that iron phosphate could be obtained while maintaining a low aluminum content, and that the phosphorus yield was high (Table 4). 【0102】 [Experiment 3] Production of artificial phosphate rock (calcium phosphate) [Example 1] <Iron hydroxide precipitation process> A 1 mol / L NaOH solution was introduced into reaction vessel 3 and heated to 60°C. While stirring the heated NaOH solution, iron phosphate precipitate 4 obtained in production example 6 was added to the reaction vessel at a solid-liquid ratio of L / S = 20 (L / kg) to precipitate iron hydroxide and obtain slurry 3 (iron hydroxide slurry). The pH of slurry 3 was approximately 13-14. The mixture was then stirred for 1 hour while maintaining a temperature of 60°C. The iron hydroxide slurry was filtered under reduced pressure to recover the separated liquid 3 and the iron hydroxide cake 3. The iron hydroxide cake 3 was then filtered and washed with water to recover the washing solution 3. The time required for the vacuum filtration process of the iron hydroxide slurry was measured, and the filterability (filtration time) was evaluated. The results are shown in Table 5. Furthermore, the composition of the separated liquid 3 was analyzed. Iron hydroxide cake 3 was observed using a scanning electron microscope (SEM). The SEM image is shown in Figure 1. 【0103】 <Calcium phosphate precipitation process> The separated liquid 3 obtained in the above process was introduced into the reaction vessel 4, and powdered slaked lime (Ca(OH)2) (manufactured by Fujifilm Wako Pure Chemical Industries, reagent grade, product code: 034-16297) was added while stirring so that the molar ratio of calcium to phosphorus (Ca / P, mol / mol) was 2.0, causing calcium phosphate to precipitate and obtain slurry 4 (calcium phosphate slurry). After stirring at room temperature for 5 hours, the calcium phosphate slurry was filtered by suction to recover the calcium phosphate cake 4. The calcium phosphate cake 4 was washed with water and dried to obtain artificial phosphate rock (calcium phosphate). 【0104】 The composition of artificial phosphate rock (calcium phosphate) was analyzed. The results are shown in Table 5. 【0105】 [Comparative Example 1] Instead of iron phosphate precipitate 4 obtained in Production Example 6, comparative iron phosphate precipitate 1 obtained in Comparative Production Example 1 was used, and the iron hydroxide precipitation step and calcium phosphate precipitation step were carried out in the same manner as in Example 1 to obtain artificial phosphate rock (calcium phosphate), and its composition was analyzed. The results are shown in Table 5. In addition, the time required for the step of vacuum filtration of the iron hydroxide slurry was measured in the same manner as in Example 1, and the filterability (filtration time) was evaluated, and the results are shown in Table 5. 【0106】 [Table 5] 【0107】 In Example 1, artificial phosphate rock was obtained with a very low aluminum content and a high phosphorus content (Table 5). Calcium phosphate with a low aluminum content was obtained using the method of Example 1. Furthermore, the time required for filtering the iron hydroxide slurry in Example 1 was significantly shorter than in Comparative Example 1. The particles constituting the iron hydroxide cake obtained by filtering the iron hydroxide slurry in Example 1 were substantially spherical (Figure 1). Furthermore, in the calcium phosphate precipitation step of Example 1, when comparing the case where slaked lime was added in powder form and the case where it was added in suspension form, it was confirmed that the filterability was superior when it was added in powder form.

Claims

[Claim 1] A method for producing calcium phosphate from sewage sludge incineration ash containing phosphorus and aluminum, comprising the following steps (1) to (10): The phosphorus content in the separated liquid 1 below is P 2 O 5 A method for producing calcium phosphate in an amount of 0.5 to 20 wt% by conversion. (1) A step of mixing the incinerated ash and the acid solution to obtain a slurry 1 with a pH of less than 0.

5. (2) Step of separating the slurry 1 into solid and liquid to obtain the separated liquid 1. (3) A step of adding an iron compound to the separation liquid 1 to obtain an iron-added separation liquid 1. (4) Adding alkali metal hydroxide to the iron-added separation liquid 1 to adjust the pH to a range of 0.5 to 2.0 to obtain a pH-adjusted separation liquid 1. (5) A step of heating the pH-adjusted separation liquid 1 to 50°C or higher and stirring to obtain slurry 2. (6) Steps to separate the slurry 2 into solid and liquid to obtain the cake 2. (7) A step of mixing the cake 2 with an alkali metal hydroxide solution to obtain a slurry 3 with a pH of 12 or higher. (8) Steps to separate the slurry 3 into solid and liquid to obtain the separated liquid 3. (9) A step of mixing the separated liquid 3 with calcium hydroxide to obtain a slurry 4. (10) Steps to separate the slurry 4 into solid and liquid to obtain calcium phosphate. [Claim 2] The method for producing calcium phosphate according to claim 1, wherein in step (4) above, the pH is adjusted to a range of 0.8 to 1.

5. [Claim 3] The method for producing calcium phosphate according to claim 1 or 2, wherein the amount of the iron compound is such that the molar ratio of iron to phosphorus (Fe / P) in the iron-added separation liquid 1 is 1.1 to 1.

5. [Claim 4] A method for producing calcium phosphate according to claim 1 or 2, wherein the stirring time in step (5) is 0.5 to 10 hours. [Claim 5] The method for producing calcium phosphate according to claim 1 or 2, wherein the amount of calcium hydroxide is such that the molar ratio of calcium to phosphorus (Ca / P) in the slurry 4 is 1.5 to 2.5.

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