Method for producing titanium phosphate powder

Abstract

Provided is a means capable of reducing impurities in titanium phosphate powder. This method for producing titanium phosphate powder comprises bringing a crude titanium sulfate solution and activated carbon into contact, filtering the product with a filter, and mixing the resulting titanium sulfate solution with a phosphoric acid solution to prepare a mixed solution.

Description

Titanium phosphate powder manufacturing method

[0001] The present invention relates to a method for producing titanium phosphate powder.

[0002] Titanium phosphate has the chemical formula Ti(HPO ４ ) ２ ・nH ２ It is known that the crystal grains can be expressed as O (n is an integer).

[0003] WO 2018 / 180797 discloses a method for producing titanium phosphate powder consisting of plate-like crystal particles of titanium phosphate by reacting raw materials containing titanium and phosphorus by hydrothermal synthesis, in which a mixture of titanium sulfate and phosphoric acid is used as the raw material.

[0004] WO 2018 / 180797 uses a mixture of titanium sulfate and phosphoric acid as a raw material containing titanium and phosphorus. Titanium sulfate can be obtained as a titanium sulfate solution by dissolving titanium-containing ore in sulfuric acid and removing impurities such as iron using a flocculant. The titanium sulfate solution contains dissolved organic carbon derived from the flocculant. The dissolved organic carbon is not separated even after the washing (water washing) process in the production of titanium phosphate powder, and remains as foreign matter in the titanium phosphate powder. Therefore, it is desirable to further reduce the foreign matter in titanium phosphate powder during the production of titanium phosphate powder.

[0005] Therefore, the present invention has been made in view of the above circumstances, and an object of the present invention is to provide a means for removing foreign matter from titanium phosphate powder.

[0006] The present inventors have conducted extensive research to solve the above-mentioned problems, and as a result have found that the above-mentioned problems can be solved by a method for producing titanium phosphate powder, which includes contacting a raw material titanium sulfate solution with activated carbon, filtering the resulting titanium sulfate solution through a filter, and mixing this with a phosphoric acid solution to prepare a mixed solution, thereby completing the present invention.

[0007] 1 is a graph showing the results of XRD measurement of raw titanium sulfate solution 1. FIG. 2 is a graph showing the results of evaluation of the transmittance of raw titanium sulfate solution 1. FIG. 3 is a graph showing the results of measurement of the transmission spectrum of raw titanium sulfate solution 1. FIG. 4 is a graph showing the results of evaluation of the transmittance of raw titanium sulfate solution 1.

[0008] An embodiment of the present invention will be described below. The present invention is not limited to the following embodiment, and various modifications can be made within the scope of the claims. The embodiments described in this specification can be combined in any manner to form other embodiments.

[0009] In this specification, the range "X to Y" means "X or more and Y or less." Unless otherwise specified, operations and measurements of physical properties are performed under conditions of room temperature (20 to 25°C) and a relative humidity of 40 to 50% RH.

[0010] One aspect of the present invention relates to a method for producing titanium phosphate powder, which includes contacting a raw titanium sulfate solution with activated carbon, filtering the resulting titanium sulfate solution, and mixing the resulting titanium sulfate solution with a phosphoric acid solution to prepare a mixed solution. According to the present invention, foreign matter (especially organic matter) in the titanium phosphate powder can be reduced.

[0011] As used herein, titanium phosphate has the chemical formula Ti(HPO ４ ) ２ ・nH ２ O (0≦n≦1).

[0012] In this specification, titanium phosphate powder refers to titanium phosphate particles or a composition containing the same. Titanium phosphate powder may contain impurities (especially organic substances) derived from the manufacturing process (e.g., flocculant) as foreign matter. In this specification, powder includes not only powdery (dry) substances but also substances that exist in a dispersed state in a dispersion medium and can be obtained as a powder by volatilizing the dispersion medium.

[0013] The method for producing titanium phosphate powder according to this embodiment includes contacting a raw material titanium sulfate solution with activated carbon, filtering the resulting titanium sulfate solution, and mixing the resulting titanium sulfate solution with a phosphoric acid solution to prepare a mixed solution.

[0014] The titanium sulfate solution according to this embodiment is obtained by contacting the raw titanium sulfate solution with activated carbon and then filtering the resultant solution. The method for contacting the raw titanium sulfate solution with activated carbon is not particularly limited, and may involve mixing the raw titanium sulfate solution with activated carbon, or passing the raw titanium sulfate solution through a column packed with activated carbon.

[0015] The raw titanium sulfate solution to be contacted with activated carbon contains titanium sulfate (Ti(SO )) as a titanium-containing substance. ４ ) ２ In this specification, titanium sulfate refers to titanium dioxide that contains sulfate ions (SO ) in water. ４ ２－ ) and titanium ions (Ti ４＋ ) means a solution containing

[0016] The raw titanium sulfate solution is not particularly limited, and can be produced, for example, by a sulfuric acid method or by dissolving titanyl sulfate in water. In the sulfuric acid method, a titanium-containing ore (e.g., ilmenite ore) is dissolved in sulfuric acid and iron is removed to obtain the raw titanium sulfate solution.

[0017] As the raw titanium sulfate solution to be contacted with activated carbon, the raw titanium sulfate solution obtained by the sulfuric acid method may be used as is, or a further purified version of the raw titanium sulfate solution obtained by the sulfuric acid method may be used, or a solution obtained by dissolving titanyl sulfate in water may be used, or a commercially available product may be used.From the viewpoint of simplifying the production process, it is preferable to use the raw titanium sulfate solution obtained by the sulfuric acid method or a commercially available product as is as the raw titanium sulfate solution to be contacted with activated carbon.

[0018] The sulfuric acid concentration in the raw titanium sulfate solution is not particularly limited and is, for example, 10 g / L to 700 g / L, preferably 30 g / L to 600 g / L. If the sulfuric acid concentration is less than 10 g / L, the titanium component does not dissolve sufficiently, resulting in the precipitation of titanium hydroxide, titanium oxide, etc., making it impossible to stably synthesize titanium phosphate. If the sulfuric acid concentration is more than 700 g / L, the synthesis of titanium phosphate is inhibited, making it difficult to obtain titanium phosphate with a desired particle size. The sulfuric acid concentration can be measured, for example, by turbidimetry.

[0019] The titanium concentration in the raw titanium sulfate solution is not particularly limited and is, for example, 10 g / L to 300 g / L, preferably 25 g / L to 200 g / L, calculated as titanium dioxide. If the titanium concentration is less than 10 g / L, the amount of titanium phosphate obtained by synthesis will be low, posing a problem in production volume. If the titanium concentration exceeds 300 g / L, titanium hydroxide, titanium oxide, etc. will precipitate, making it impossible to synthesize titanium phosphate stably. The titanium concentration can be measured as the titanium dioxide content by the method described in JIS K 5116:2004.

[0020] The lower limit of the total organic carbon content of the raw titanium sulfate solution is not particularly limited, and may be, for example, more than 3 mg / L, 4 mg / L or more, 5 mg / L or more, 6 mg / L or more, or 7 mg / L or more. The upper limit of the total organic carbon content of the raw titanium sulfate solution is not particularly limited, and may be, for example, 15 mg / L. The total organic carbon content in the raw titanium sulfate solution can be measured as the TOC content using a TOC meter, and details of the measurement method will be described in the Examples.

[0021] The form of the activated carbon to be brought into contact with the raw titanium solution is not particularly limited, and examples thereof include powder, granules, fibers, blocks, etc. The activated carbon is preferably in the form of powder or granules. As the activated carbon, activated carbons of the same form may be used, or activated carbons of two or more forms may be used in combination.

[0022] When the activated carbon is in the form of powder or particles, the particle size of the activated carbon is, for example, 0.50 mm or more and 1.70 mm or less. The particle size of the activated carbon can be measured by the method described in JIS K 1474:2014.

[0023] The activated carbon may be a commercially available product or may be produced by a known method.

[0024] In one embodiment, the method of contacting the raw titanium sulfate solution with activated carbon comprises mixing the raw titanium sulfate solution with activated carbon.

[0025] In the method of mixing a raw titanium sulfate solution with activated carbon, the raw titanium sulfate solution is mixed with activated carbon to prepare a liquid containing titanium sulfate and activated carbon. The method of producing titanium phosphate powder according to this embodiment can include mixing the raw titanium sulfate solution with activated carbon to prepare a liquid containing titanium sulfate and activated carbon.

[0026] In the method of mixing the raw titanium sulfate solution with activated carbon, the mass ratio of activated carbon to titanium (equivalent to titanium dioxide) is preferably 0.003 or more, more preferably 0.005 or more, from the viewpoint of better exerting the effects of the present invention. The upper limit of the mass ratio of activated carbon to titanium (equivalent to titanium dioxide) is not particularly limited, but from the viewpoint of productivity, it is preferably 0.03 or less, more preferably 0.02 or less. The mass ratio of activated carbon to titanium (equivalent to titanium dioxide) is preferably 0.003 or more and 0.03 or less, more preferably 0.005 or more and 0.02 or less.

[0027] The method for mixing the raw titanium sulfate solution with activated carbon is not particularly limited, and activated carbon may be added to the raw titanium sulfate solution, or the raw titanium sulfate solution may be added to activated carbon.

[0028] The temperature at which the raw titanium sulfate solution and activated carbon are mixed is not particularly limited, and is, for example, 10°C or higher and 40°C or lower.

[0029] In the liquid containing titanium sulfate and activated carbon obtained in this manner, adsorption by the activated carbon begins. The adsorption time is not particularly limited and is, for example, from 3 hours to 24 hours, preferably from 4 hours to 12 hours. The adsorption by the activated carbon may be carried out while the liquid containing titanium sulfate and activated carbon is left to stand or while being stirred.

[0030] In one embodiment, the method for contacting the raw titanium sulfate solution with activated carbon includes a method of passing the raw titanium sulfate solution through a column packed with activated carbon.

[0031] In the method of passing a raw titanium sulfate solution through a column packed with activated carbon, the raw titanium sulfate solution is passed through a column packed with activated carbon to prepare a raw titanium sulfate solution that has been treated with activated carbon.

[0032] As the column packed with activated carbon, a conventionally known column can be used.

[0033] When the raw titanium sulfate solution is passed through a column packed with activated carbon, the contact temperature, contact time, and passage rate are not particularly limited. The contact temperature is, for example, 10° C. or higher and 40° C. or lower. The contact time is, for example, 3 hours or longer.

[0034] The titanium sulfate solution is obtained by contacting the raw titanium sulfate solution with activated carbon and then filtering the resultant mixture.

[0035] The material of the filter to be used is not particularly limited, and examples thereof include resins such as cellulose mixed esters, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-tetrafluoroethylene copolymer, polycarbonate, polyethersulfone, cellulose acetate, nitrocellulose, regenerated cellulose, polyamide, triacetyl cellulose, polypropylene, polyvinyl chloride (PVC), nylon, nylon 66, polysulfone, polyester, polypropylene / polyethylene, acrylic copolymer, polycarbonate, polylactic acid, polycaprolactone, polyglycolic acid, polydioxanone, polyhydroxybutyrate, polybutadiene, polyurethane, polystyrene (PS), polymethyl methacrylate, and polycarbonate, as well as glass and metal.

[0036] The structure of the filter to be used is not particularly limited, and examples thereof include a depth structure, a pleated structure, and a membrane structure.

[0037] The filtration accuracy of the filter used can be appropriately selected depending on the activated carbon used. The lower limit of the filtration accuracy of the filter is, for example, 0.1 μm or more, 0.6 μm or more, or 1.2 μm or more. The upper limit of the filtration accuracy of the filter is, for example, 2.5 μm or less, 2.0 μm or less, 1.5 μm or less, or 1.0 μm or less. The filtration accuracy of the filter is, for example, 0.1 μm or more and 2.5 μm or less, preferably 0.6 μm or more and 2.0 μm or less, and more preferably 1.2 μm or more and 1.5 μm or less. The filtration accuracy of the filter may be 1.2 μm or more and 2.5 μm or less, 0.6 μm or more and 2.0 μm or less, or 0.1 μm or more and 1.0 μm or less.

[0038] The filter used may be a commercially available product.

[0039] The filtration method is not particularly limited, and may be any of natural filtration under normal pressure, suction filtration, pressure filtration, and centrifugal filtration.

[0040] Filtration through a filter may be carried out two or more times.

[0041] By filtering a liquid containing titanium sulfate and activated carbon or a raw titanium sulfate solution that has been treated with activated carbon, impurities derived from the activated carbon and impurities (especially organic substances) in the raw titanium sulfate solution can be sufficiently removed.

[0042] As described above, a coagulant is used in the raw titanium sulfate solution to remove impurities such as iron derived from titanium-containing ore, and the raw titanium sulfate solution contains dissolved organic carbon derived from the coagulant as total organic carbon (TOC). This organic carbon remains as a component even after a washing (water washing) step is performed after the titanium phosphate powder is synthesized, and may appear as black and gray foreign matter in the titanium phosphate powder after the drying step or may cause a decrease in the whiteness of the titanium phosphate powder.

[0043] The total organic carbon content in the titanium sulfate solution according to this embodiment is 3 mg / L or less, preferably 1 mg / L to 3 mg / L. The total organic carbon content in the titanium sulfate solution may be 1 mg / L to 2 mg / L. Reducing the total organic carbon content in the titanium sulfate solution to less than 1 mg / L requires a large amount of activated carbon and a long adsorption time, which is undesirable from the viewpoint of productivity. If the total organic carbon content in the titanium sulfate solution exceeds 3 mg / L, the whiteness of the titanium phosphate powder decreases (whiteness index: less than 95), or a large amount of colored foreign matter, such as black or gray, is found on the surface of the titanium phosphate powder slurry. Therefore, when evaluating the formation of a coating film containing titanium phosphate powder, the appearance may be poor due to changes in the color of transmitted light and the presence of foreign matter in the coating film.

[0044] The total organic carbon content in the titanium sulfate solution is a value measured immediately after production (within 24 hours after preparation). The total organic carbon content in the titanium sulfate solution can be measured using a total organic carbon meter, and details of the measurement method are described in the Examples.

[0045] The light transmittance at a wavelength of 550 nm of the titanium sulfate solution according to this embodiment is measured immediately after production (within 24 hours after preparation) and is the transmittance value when the light transmittance at a wavelength of 550 nm of pure water is set to 100%. The light transmittance at a wavelength of 550 nm of the titanium sulfate solution can be measured using a spectrophotometer, and details of the measurement method are described in the Examples.

[0046] The titanium sulfate solution according to this embodiment has a light transmittance at a wavelength of 550 nm of, for example, 70% to 100%, preferably 90% to 100%, and more preferably 95% to 100%. If the light transmittance at a wavelength of 550 nm of the titanium sulfate solution is less than 70%, the presence of particles in the titanium sulfate solution can cause impurities and variations in the shape of the synthesized product during the synthesis of titanium phosphate powder.

[0047] The titanium sulfate solution according to this embodiment can suppress a decrease in light transmittance at a wavelength of 550 nm even when stored for a long period of time. The higher the storage ambient temperature, the more particle precipitation is promoted, resulting in a decrease in the light transmittance of the titanium sulfate solution at a wavelength of 550 nm. When stored at 43°C for three weeks, the light transmittance of the titanium sulfate solution at a wavelength of 550 nm is, for example, 70% or more, preferably 90% or more, more preferably 95% or more, and even more preferably 97% or more (upper limit: 100%). Even when stored at 43°C for four weeks or more (e.g., nine weeks), the light transmittance of the titanium sulfate solution at a wavelength of 550 nm is preferably 90% or more, more preferably 95% or more.

[0048] The titanium sulfate solution according to this embodiment has sufficient impurities (especially organic matter) removed, thereby suppressing changes in transmittance over time (decrease in transmittance). Therefore, one aspect of the present invention relates to a titanium sulfate solution having a total organic carbon content of 3 mg / L or less. The titanium sulfate solution according to this embodiment preferably has a light transmittance of 95% or more at a wavelength of 550 nm. Another aspect of the present invention relates to a method for purifying a titanium sulfate solution, which includes contacting the raw titanium sulfate solution with activated carbon and then filtering the solution. The method for purifying a titanium sulfate solution according to this embodiment may further include mixing the raw titanium sulfate solution with activated carbon to prepare a liquid containing titanium sulfate and activated carbon, or passing the raw titanium sulfate solution through a column packed with activated carbon to prepare an activated carbon-treated raw titanium sulfate solution. When the method for purifying a titanium sulfate solution according to this embodiment includes mixing the raw titanium sulfate solution with activated carbon to prepare a liquid containing titanium sulfate and activated carbon, the mass ratio of the activated carbon to titanium (equivalent to titanium dioxide) in the raw titanium sulfate solution is preferably 0.005 or more.

[0049] The method for producing titanium phosphate powder according to this embodiment includes mixing the titanium sulfate solution obtained above with a phosphoric acid solution to prepare a mixed solution.

[0050] The phosphoric acid solution contains phosphoric acid as the phosphorus-containing substance.

[0051] The concentration of phosphoric acid in the phosphoric acid solution is, for example, 50% by mass or more and less than 100% by mass, and preferably 80% by mass or more and less than 100% by mass.

[0052] The phosphoric acid solution may further contain a phosphate. The type of salt is not particularly limited, and examples include metal salts (e.g., alkali metal salts, Group II element salts, etc.), amine salts, etc. The type of salt may be used alone or in combination of two or more. The phosphate may be used alone or in combination of two or more. When the phosphoric acid solution contains a phosphate, the concentration of the phosphate is, for example, 50% by mass or more and less than 100% by mass, preferably 80% by mass or more and less than 100% by mass. In one embodiment, the phosphoric acid solution preferably does not contain a phosphate.

[0053] The phosphoric acid solution contains water. The concentration of water in the phosphoric acid solution is, for example, more than 0 mass% and not more than 50 mass%, preferably more than 0 mass% and not more than 20 mass%. In one embodiment, the phosphoric acid solution consists of phosphoric acid and water.

[0054] The mixed solution according to this embodiment is prepared by mixing a titanium sulfate solution, a phosphoric acid solution, and, if necessary, other components.

[0055] The method for mixing the titanium sulfate solution, the phosphoric acid solution, and, if necessary, other components is not particularly limited. The mixing method, mixing order, mixing conditions, etc. may be appropriately selected from known methods.

[0056] The concentration of phosphoric acid in the mixed solution is, for example, 20% by mass or more and 40% by mass or less, and preferably 21% by mass or more and 35% by mass or less, relative to the total mass of the mixed solution.

[0057] The concentration of sulfuric acid in the mixed solution is, for example, 2 mass % or more and 15 mass % or less, and preferably 3 mass % or more and 12 mass % or less, relative to the total mass of the mixed solution.

[0058] The concentration of titanium in the mixed solution is, for example, 1% by mass or more and 10% by mass or less, and preferably 2% by mass or more and 5% by mass or less, calculated as titanium dioxide relative to the total mass of the mixed solution.

[0059] Other components include phosphorus-free, titanium-free acids. The phosphorus-free, titanium-free acids are not particularly limited and include known organic acids and known inorganic acids. Examples of phosphorus-free, titanium-free acids include hydrochloric acid, sulfuric acid, nitric acid, carbonic acid, acetic acid, citric acid, and formic acid. The phosphorus-free, titanium-free acids may be used alone or in combination of two or more. The phosphorus-free, titanium-free acids preferably contain at least one acid selected from the group consisting of hydrochloric acid, sulfuric acid, nitric acid, carbonic acid, acetic acid, citric acid, and formic acid, and more preferably contain sulfuric acid. The content of these acids (preferably sulfuric acid) relative to the total mass of the phosphorus-free, titanium-free acids (the total content when two or more acids are included) is preferably 50% by mass or more, more preferably 90% by mass or more, and even more preferably 100% by mass (upper limit 100% by mass).

[0060] Titanium phosphate can be produced by reacting the mixed solution obtained above by hydrothermal synthesis. The method for producing titanium phosphate powder according to this embodiment can include reacting the mixed solution obtained above by hydrothermal synthesis to prepare a liquid containing titanium phosphate powder.

[0061] The conditions for the hydrothermal synthesis method are not particularly limited, and conventionally known conditions can be appropriately adopted. The reaction temperature is, for example, 50° C. to 140° C., preferably 80° C. to 130° C. The reaction time is, for example, 1 hour to 100 hours, preferably 3 hours to 72 hours.

[0062] The method for producing titanium phosphate powder according to this embodiment can include washing (preferably with pure water) and / or drying the liquid containing the titanium phosphate powder obtained above. The washing and drying methods are not particularly limited, and conventionally known methods can be used as appropriate.

[0063] The resulting powder has the chemical formula Ti(HPO ４ ) ２ ・nH ２ It can be confirmed by powder X-ray diffraction that the titanium phosphate powder exhibits the crystallinity of titanium phosphate represented by O (0≦n≦1).

[0064] The method for producing titanium phosphate powder according to this embodiment can reduce foreign matter (especially organic matter) other than titanium phosphate. Therefore, one embodiment of the present invention relates to a titanium phosphate powder having a carbon content per unit mass of 0.005% by mass or less. The lower limit of the carbon content per unit mass of the titanium phosphate powder is not particularly limited, and may be, for example, 0.001% by mass or more. The carbon content per unit mass of the titanium phosphate powder is preferably 0.001% by mass or more and 0.005% by mass or less, and may be 0.002% by mass or more and 0.004% by mass or less, or 0.003% by mass or more and 0.004% by mass or less. The carbon content per unit mass of the titanium phosphate powder can be measured using a carbon / sulfur measuring device; details of the measurement method are described in the Examples.

[0065] The use of the obtained titanium phosphate powder is not particularly limited, and it can be used in a variety of applications. Examples of uses of titanium phosphate powder include inorganic particles for light scattering, specifically inorganic particles or materials for light scattering used in light diffusion films, light diffusion plates, cosmetics, etc.; white pigments, functional fillers, lubricants, etc. The shape of the titanium phosphate particles contained in the titanium phosphate powder is preferably thin and plate-like, from the viewpoint of improving the sliding properties between particles. The shape of the titanium phosphate particles contained in the titanium phosphate powder is preferably thin and plate-like, from the viewpoint of ensuring good particle-to-particle sliding properties, etc., in a coating film obtained by applying a slurry (e.g., an ink containing titanium phosphate powder or a paint containing titanium phosphate powder) obtained by dispersing or suspending titanium phosphate powder in a solvent and drying the solvent, whereby the surface direction of the particles is parallel to the substrate to which the coating is applied, making it easy to obtain a uniform thickness, and providing high dispersibility and reducing the likelihood of aggregation.

[0066] Furthermore, the refractive index of titanium phosphate is 1.79, which is higher than that of commonly used inorganic particles such as silica particles and polymer particles such as acrylic beads, but lower than that of titanium oxide, which is used as a white pigment. For this reason, coating films containing titanium phosphate powder and a polymer binder have good light scattering transmittance, and can therefore be used as inorganic light-scattering particles to be contained in light diffusion films, light diffusion plates, etc.

[0067] The inorganic light-scattering particles preferably have a high degree of whiteness so as not to change the color of the scattered transmitted light, and preferably do not contain impurities of colored substances other than white, such as black or gray.

[0068] The present invention encompasses the following aspects and configurations. [1] A method for producing titanium phosphate powder, comprising contacting a raw titanium sulfate solution with activated carbon, filtering the resulting titanium sulfate solution, and mixing the resulting titanium sulfate solution with a phosphoric acid solution to prepare a mixed solution. [2] A method for purifying a titanium sulfate solution, comprising contacting the raw titanium sulfate solution with activated carbon and filtering the resulting titanium sulfate solution with a filter. [3] The method for purifying a titanium sulfate solution according to [2], wherein the mass ratio of the activated carbon to the titanium (equivalent to titanium dioxide) in the raw titanium sulfate solution is 0.005 or more. [4] Titanium phosphate powder having a carbon content per unit mass of 0.005 mass% or less. [5] A titanium sulfate solution having a total organic carbon content of 3 mg / L or less. [6] The titanium sulfate solution according to [5], having a light transmittance at a wavelength of 550 nm of 95% or more.

[0069] The present invention will be described in more detail using the following examples and comparative examples. However, the technical scope of the present invention is not limited to the following examples. Unless otherwise specified, "%" and "parts" mean "% by mass" and "parts by mass", respectively. In the following examples, unless otherwise specified, the operations were carried out at room temperature (25°C).

[0070] <Production of Titanium Sulfate Solution> [Production of Titanium Sulfate Solution 1] Raw titanium sulfate solution 1 (a titanium sulfate aqueous solution containing 118 g / L of titanium, calculated as titanium dioxide, and 500 g / L of sulfuric acid, with a total organic carbon content of 4 mg / L) and activated carbon (particle size: 1.70 mm to 0.50 mm, GW10 / 32 manufactured by Kuraray Co., Ltd.) were mixed so that the mass ratio of activated carbon to titanium (in terms of titanium dioxide) was 0.01, to prepare a solution containing titanium sulfate and activated carbon 1. After allowing to stand for 12 hours, the solution was filtered using a filter (filtration accuracy 0.65 μm, CES-006 manufactured by Roki Techno Co., Ltd.), to produce titanium sulfate solution 1.

[0071] [Production of Titanium Sulfate Solution 2] Raw material titanium sulfate solution 2 (a titanium sulfate aqueous solution containing 190 g / L of titanium, calculated as titanium dioxide, and 290 g / L of sulfuric acid, with a total organic carbon content of 7 mg / L) and activated carbon (particle size: 1.70 mm to 0.50 mm, GW10 / 32 manufactured by Kuraray Co., Ltd.) were mixed so that the mass ratio of activated carbon to titanium (calculated as titanium dioxide) was 0.01, to prepare a solution containing titanium sulfate and activated carbon 2. After allowing to stand for 12 hours, the solution was filtered using a filter (filtration accuracy 0.65 μm, CES-006 manufactured by Roki Techno Co., Ltd.), to produce titanium sulfate solution 2.

[0072] <Evaluation> [Long-term Storage Test 1 (XRD Measurement)] Raw titanium sulfate solution 1 was filtered using a filter (pore size: 0.6 μm, Whatman Nuclepore Membrane Filter) within 14 days after production and after 4 weeks of storage at 43°C to recover the solid content. XRD measurement of each solid content was performed using X-ray diffraction. The results are shown in Figure 1. The upper panel of Figure 1 shows the measurement results for raw titanium sulfate solution 1 within 14 days after production, and the lower panel of Figure 1 shows the measurement results for raw titanium sulfate solution 1 after 4 weeks of storage at 43°C.

[0073] Details of the XRD measurement are as follows: Measurement equipment: Rigaku Corporation, horizontal sample type multipurpose X-ray diffractometer Ultima IV X-Ray: 20 kV / 10 mA Divergence slit: 1° Divergence vertical limiting slit: 10 mm Scattering slit: 2° Receiving slit: 0.05 mm kβ filter Start: 10 Stop: 70 Step: 0.01 Standard card: 01-075-2544 or 00-014-053.

[0074] As shown in FIG. 1, titanium oxide was already contained in the raw titanium sulfate solution 1 within 14 days after production, and titanyl sulfate was precipitated in the raw titanium sulfate solution 1 after storage at 43° C. for 4 weeks.

[0075] [Long-term Storage Test 2 (Transmittance Evaluation)] The measurement samples used were raw titanium sulfate solution 1 stored within 14 days after production, after storage at 20°C (7 days, 14 days, 21 days, 28 days, 42 days, and 43 days), and after storage at 43°C (7 days, 14 days, and 21 days).

[0076] The transmittance of light at a wavelength of 550 nm of the measurement sample was measured using an ultraviolet-visible spectrophotometer (UV-2450, manufactured by Shimadzu Corporation), and the transmittance of the measurement sample was evaluated when the transmittance of light at a wavelength of 550 nm of pure water was set to 100%.

[0077] The results are shown in Figure 2. As shown in Figure 2, it can be seen that the raw material titanium sulfate solution 1 has low stability and its transmittance deteriorates during storage.

[0078] [Long-term Storage Test 3 (Measurement of Transmission Spectrum and Evaluation of Transmittance)] Titanium sulfate solution 1 immediately after production (within 24 hours after preparation) and after storage at 43°C for 1 to 9 weeks (every week except for the 4th week) were used as measurement samples.

[0079] The transmission spectrum of the measurement sample was measured using an ultraviolet-visible spectrophotometer (UV-2450, manufactured by Shimadzu Corporation) (baseline (Tt=100%): pure water). The results are shown in FIG.

[0080] The transmittance of the measurement sample at a wavelength of 550 nm was measured using an ultraviolet-visible spectrophotometer (UV-2450, manufactured by Shimadzu Corporation), and the transmittance of the measurement sample was evaluated when the transmittance of pure water at a wavelength of 550 nm was set to 100%. The results are shown in Figure 4.

[0081] As shown in FIGS. 3 and 4, it can be seen that the storage stability of titanium sulfate solution 1 is improved compared to raw titanium sulfate solution 1 (FIG. 2) by performing activated carbon treatment and filtration.

[0082] [Long-term Storage Test 4 (Evaluation of Transmittance)] The measurement samples used were Liquid 1 containing titanium sulfate and activated carbon immediately after production (after adsorption by activated carbon), Titanium Sulfate Solution 1 and Titanium Sulfate Solution 2 immediately after production (within 24 hours after preparation) and after storage at 43°C for 3 weeks, and Raw Titanium Sulfate Solution 1 and Raw Titanium Sulfate Solution 2 within 14 days after production and after storage at 43°C for 3 weeks.

[0083] The transmittance of light at a wavelength of 550 nm of the measurement sample was measured using an ultraviolet-visible spectrophotometer (UV-2450, manufactured by Shimadzu Corporation), and the transmittance of the measurement sample was evaluated when the transmittance of light at a wavelength of 550 nm of pure water was set to 100%.

[0084] The results are shown in "Transmittance (λ=550 nm)" in Table 1. In Table 1, "Before storage" indicates the evaluation results of the measurement samples immediately after production and within 14 days after production, and "After storage at 43°C for 3 weeks" indicates the evaluation results of the measurement samples after storage at 43°C for 3 weeks.

[0085] [Measurement of Total Organic Carbon Amount] The total organic carbon amounts of titanium sulfate solution 1, titanium sulfate solution 2, raw titanium sulfate solution 1, and raw titanium sulfate solution 2 were measured using a total organic carbon meter (TOC-L, manufactured by Shimadzu Corporation).

[0086] The measurement samples used were titanium sulfate solution 1 and titanium sulfate solution 2 immediately after production, and raw titanium sulfate solution 1 and raw titanium sulfate solution 2 produced within 14 days.

[0087] The results are shown in Table 1 under "TOC amount (mg / L) of titanium sulfate solution."

[0088] <Production of Titanium Phosphate Powder 1> [Production of Titanium Phosphate Powder 1] Titanium sulfate solution 1 and pure water were added to an 85% by mass aqueous phosphoric acid solution with stirring to obtain a mixed solution. The mixed solution was filled into an autoclave (sealed container) and heated to 130°C for hydrothermal treatment. The hydrothermal treatment was carried out for 5 hours under natural pressure. After the hydrothermal treatment, the mixture was washed with pure water (water washing treatment) and dried in a crucible at 105°C for 24 hours (drying treatment) to obtain titanium phosphate powder 1. The titanium phosphate powder 1 had a white appearance, and no gray or black impurities were visually observed.

[0089] [Production of Titanium Phosphate Powder 2] Titanium phosphate powder 2 was obtained in the same manner as in the production of titanium phosphate powder 1, except that titanium sulfate solution 2 was used instead of titanium sulfate solution 1. Titanium phosphate powder 2 had a white appearance, and no gray or black impurities were visually observed.

[0090] [Production of Titanium Phosphate Powder 3] Titanium phosphate powder 3 was obtained in the same manner as in the production of titanium phosphate powder 1, except that starting titanium sulfate solution 1 was used instead of titanium sulfate solution 1. Titanium phosphate powder 3 had a white appearance, but gray or black impurities were visually confirmed.

[0091] [Production of Titanium Phosphate Powder 4] Titanium phosphate powder 4 was obtained in the same manner as in the production of titanium phosphate powder 1, except that starting titanium sulfate solution 2 was used instead of titanium sulfate solution 1. Titanium phosphate powder 4 had a white appearance, but gray or black impurities were visually confirmed.

[0092] <Evaluation> [Measurement of Carbon Amount] The carbon amount per unit mass in titanium phosphate powders 1 to 4 was measured using a carbon / sulfur measuring device (manufactured by Horiba Ltd., EMIA-320V2 model).

[0093] If the carbon content per unit mass was 0.005 mass% or less, it was judged to be good, and if the carbon content per unit mass was more than 0.005 mass%, it was judged to be poor.

[0094] The results are shown in Table 2.

[0095] [Evaluation of foreign matter in titanium phosphate powder] Slurries were prepared by adding water to 50 g of each of titanium phosphate powders 1 to 4 so that the titanium phosphate powder concentration was 10 mass %. After hand shaking the slurries, the presence of foreign matter on the liquid surface was visually confirmed.

[0096] The case where there were 5 or less foreign matters was marked as "good", and the case where there were 6 or more foreign matters was marked as "poor".

[0097] The results are shown in Table 2.

[0098]

[0099]

[0100] As shown in Table 1, the titanium sulfate solution of the example was prepared by treating the raw titanium sulfate solution with activated carbon and filtering it, and the transmittance immediately after production (before storage) was 100%, demonstrating a higher transmittance than the raw titanium sulfate solution. Furthermore, the titanium sulfate solution of the example had a transmittance of 100% after storage at 43°C for 3 weeks, demonstrating no decrease in transmittance due to storage and high storage stability. Furthermore, the total organic carbon content of the titanium sulfate solution of the example was 3 mg / L or less, demonstrating a reduced amount of impurities.

[0101] As shown in Table 2, the carbon content of the titanium phosphate powder of the Example can be reduced to 0.005% by mass or less by using a titanium sulfate solution (see Table 1) with a total organic carbon content of 3 mg / L or less, which demonstrates that foreign matter (organic carbon) in the slurry of the titanium phosphate powder of the Example can be sufficiently removed.

[0102] <Production of Titanium Phosphate Powder 2> [Production of Titanium Phosphate Powder 5] A raw titanium sulfate solution 2 (a titanium sulfate aqueous solution containing 190 g / L of titanium dioxide equivalent, 290 g / L of sulfuric acid, and a total organic carbon content of 7 mg / L) was mixed with activated carbon (particle size: 1.70 mm to 0.50 mm, GW10 / 32 manufactured by Kuraray Co., Ltd.) so that the mass ratio of activated carbon to titanium (in terms of titanium dioxide) was 0.01, to prepare a solution 2 containing titanium sulfate and activated carbon. After allowing to stand for 12 hours, the solution was filtered using a filter (filtration accuracy 1.2 μm, CES-012 manufactured by Roki Techno Co., Ltd.) to produce a titanium sulfate solution 3. The total organic carbon content of the titanium sulfate solution 3 was 1 mg / L.

[0103] Titanium sulfate solution 3 and pure water were added to an 85% by mass aqueous solution of phosphoric acid while stirring to obtain a mixed solution. The mixed solution was filled into an autoclave (sealed container) and heated to 130°C for hydrothermal treatment. The hydrothermal treatment was carried out for 5 hours under natural pressure. After the hydrothermal treatment, the mixture was washed with pure water and dried in a crucible at 105°C for 24 hours to obtain titanium phosphate powder 5. The titanium phosphate powder 5 had a white appearance, and no gray or black impurities were visually observed.

[0104] [Production of Titanium Phosphate Powder 6] A titanium sulfate solution 2 (a titanium sulfate aqueous solution containing 190 g / L of titanium and 290 g / L of sulfuric acid, calculated as titanium dioxide, and having a total organic carbon content of 7 mg / L) was mixed with activated carbon (particle size: 1.70 mm to 0.50 mm, GW10 / 32 manufactured by Kuraray Co., Ltd.) so that the mass ratio of activated carbon to titanium (calculated as titanium dioxide) was 0.01, thereby preparing a solution 2 containing titanium sulfate and activated carbon. After allowing to stand for 12 hours, the solution was filtered using a filter (filtration accuracy 0.65 μm, CES-006 manufactured by Roki Techno Co., Ltd.) to produce a titanium sulfate solution 4. The total organic carbon content of the titanium sulfate solution 4 was 1 mg / L.

[0105] Titanium sulfate solution 4 and pure water were added to an 85% by mass aqueous phosphoric acid solution while stirring to obtain a mixed solution. The mixed solution was filled into an autoclave (sealed container) and heated to 130°C for hydrothermal treatment. The hydrothermal treatment was carried out for 5 hours under natural pressure. After the hydrothermal treatment, the mixture was washed with pure water and dried in a crucible at 105°C for 24 hours to obtain titanium phosphate powder 6. The titanium phosphate powder 6 had a white appearance, and no gray or black impurities were visually observed.

[0106] <Evaluation> [Evaluation of foreign matter] The mixed liquid during the hydrothermal treatment and the water washing treatment was visually inspected for the presence of foreign matter on the liquid surface.

[0107] In the production of titanium phosphate powder 5, a small amount of foreign matter derived from activated carbon was observed, but it was determined that this would not pose a problem in practical use. In the production of titanium phosphate powder 6, no foreign matter derived from activated carbon was observed.

[0108] This application is based on Japanese Patent Application No. 2023-188363, filed on November 2, 2023, the disclosure of which is incorporated herein by reference in its entirety.

Claims

1. A method for producing titanium phosphate powder, comprising contacting a raw titanium sulfate solution with activated carbon, filtering the resulting titanium sulfate solution through a filter, and mixing the resulting titanium sulfate solution with a phosphoric acid solution to prepare a mixed solution.

2. A method for purifying a titanium sulfate solution, comprising contacting the raw titanium sulfate solution with activated carbon and then filtering the resultant solution through a filter.

3. A method for purifying a titanium sulfate solution according to claim 2, wherein the mass ratio of the activated carbon to the titanium (calculated as titanium dioxide) in the raw titanium sulfate solution is 0.005 or more.

4. Titanium phosphate powder having a carbon content per unit mass of 0.005 mass% or less.

5. A titanium sulfate solution with a total organic carbon content of 3 mg / L or less.

6. The titanium sulfate solution according to claim 5, having a light transmittance of 95% or more at a wavelength of 550 nm.

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