Method for producing titanium phosphate powder

Abstract

To provide means for reducing debris in titanium phosphate powder.SOLUTION: A method for producing titanium phosphate powder includes bringing a raw titanium sulfate solution into contact with activated carbon, filtering the resulting titanium sulfate solution through a filter, and mixing the filtered titanium sulfate solution with a phosphoric acid solution to prepare a mixed solution.SELECTED DRAWING: None

Description

[Technical field]

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

[0002] It is known that titanium phosphate can be formed into crystalline particles with the chemical formula Ti(HPO4)2·nH2O (n is an integer).

[0003] Patent Document 1 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. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2018 / 180797 Summary of the Invention [Problem to be solved by the invention]

[0005] In Patent Document 1, a mixture of titanium sulfate and phosphoric acid is used 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 components using a flocculant. The titanium sulfate solution contains dissolved organic carbon derived from the flocculant. The dissolved organic carbon is not separated even after a washing (water washing) step in the production of titanium phosphate powder, and remains as a foreign matter in the titanium phosphate powder. Therefore, it is desired to further reduce the foreign matter in the titanium phosphate powder in the production of titanium phosphate powder.

[0006] Therefore, the present invention has been made in consideration of the above circumstances, and an object of the present invention is to provide a means capable of removing foreign matter from titanium phosphate powder. [Means for solving the problem]

[0007] The present inventors have conducted extensive research to solve the above problems, and have found that the above problems can be solved by a method for producing titanium phosphate powder, which includes contacting a raw titanium sulfate solution with activated carbon, filtering the resulting titanium sulfate solution with a filter, and mixing the resulting titanium sulfate solution with a phosphoric acid solution to prepare a mixed solution, thereby completing the present invention. Effect of the Invention

[0008] According to the present invention, a means is provided that can reduce the amount of foreign matter in titanium phosphate powder. [Brief description of the drawings]

[0009] [Figure 1] 1 is a graph showing the results of XRD measurement of raw titanium sulfate solution 1. [Diagram 2] 1 is a graph showing the evaluation results of the transmittance of raw titanium sulfate solution 1. [Diagram 3] 1 is a graph showing the results of measuring the transmission spectrum of raw titanium sulfate solution 1. [Figure 4] 1 is a graph showing the evaluation results of the transmittance of raw titanium sulfate solution 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, an embodiment according to one aspect of the present invention will be described. The present invention is not limited to the following embodiment, and can be modified in various ways within the scope of the claims. The embodiments described in this specification can be combined in any manner to form other embodiments.

[0011] In this specification, the range "X to Y" means "X or more and Y or less." Furthermore, unless otherwise specified, the operations and measurements of physical properties are performed under conditions of room temperature (20 to 25°C) and relative humidity of 40 to 50% RH.

[0012] One aspect of the present invention relates to a method for producing titanium phosphate powder, which comprises contacting a raw titanium sulfate solution with activated carbon, filtering the resulting titanium sulfate solution with a filter, and mixing the resulting solution with a phosphoric acid solution to prepare a mixed solution. According to the present invention, it is possible to reduce foreign matter (especially organic matter) in the titanium phosphate powder.

[0013] In this specification, titanium phosphate is represented by the chemical formula Ti(HPO4)2·nH2O (0≦n≦1).

[0014] In this specification, the titanium phosphate powder refers to titanium phosphate particles or a composition containing the same. The titanium phosphate powder may contain impurities (particularly organic matter) derived from the manufacturing process (e.g., flocculant) as foreign matter. In this specification, the powder includes not only a powdery (dry) substance, but also a substance that exists in a dispersed state in a dispersion medium and can be obtained in powder form when the dispersion medium is evaporated.

[0015] The method for producing titanium phosphate powder according to the present embodiment includes 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.

[0016] The titanium sulfate solution according to this embodiment is obtained by contacting the raw titanium sulfate solution with activated carbon and then filtering it with a filter. The method for contacting the raw titanium sulfate solution with activated carbon is not particularly limited, and may be a method of mixing the raw titanium sulfate solution with activated carbon, or a method of passing the raw titanium sulfate solution through a column packed with activated carbon.

[0017] The raw titanium sulfate solution to be contacted with activated carbon contains titanium sulfate (Ti(SO4)2) as a titanium-containing substance. In this specification, titanium sulfate refers to a titanium-containing substance that contains sulfate ions (SO4 2- ) and titanium ions (Ti 4+ ) means a solution containing

[0018] The raw titanium sulfate solution is not particularly limited, and can be produced, for example, by using 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 a raw titanium sulfate solution.

[0019] 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 it is, or a further purified 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. As the raw titanium sulfate solution to be contacted with activated carbon, from the viewpoint of simplifying the manufacturing process, it is preferable to use the raw titanium sulfate solution obtained by the sulfuric acid method or a commercially available product as it is.

[0020] 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, titanium components do not dissolve sufficiently, and titanium hydroxide, titanium oxide, etc. are precipitated, making it impossible to synthesize titanium phosphate stably. 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.

[0021] 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 is low, which causes a problem in production volume. If the titanium concentration is more than 300 g / L, titanium hydroxide, titanium oxide, etc. are precipitated, 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.

[0022] 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 the details of the measurement method will be described in the Examples.

[0023] The shape of the activated carbon to be contacted with the raw titanium solution is not particularly limited, and examples thereof include powder, granule, fiber, block, etc. The activated carbon is preferably in the form of powder or granule. As the activated carbon, activated carbon of the same shape may be used, or activated carbon of two or more shapes may be used in combination.

[0024] When the activated carbon is in the form of a 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 K1474.

[0025] The activated carbon may be a commercially available product or may be produced by a known method.

[0026] 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.

[0027] In the method of mixing the 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.

[0028] In the method of mixing the raw titanium sulfate solution with activated carbon, the mass ratio of activated carbon to titanium (converted into titanium dioxide) is preferably 0.003 or more, more preferably 0.005 or more, from the viewpoint of being able to more effectively exert the effects of the present invention. The upper limit of the mass ratio of activated carbon to titanium (converted into 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 (converted into titanium dioxide) is preferably 0.003 or more and 0.03 or less, more preferably 0.005 or more and 0.02 or less.

[0029] 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 the activated carbon.

[0030] The temperature at which the raw titanium sulfate solution and the activated carbon are mixed is not particularly limited and is, for example, 10°C or higher and 40°C or lower.

[0031] 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, 3 hours or more and 24 hours or less, and preferably 4 hours or more and 12 hours or less. The adsorption by the activated carbon may be performed while the liquid containing titanium sulfate and activated carbon is left to stand or while being stirred.

[0032] 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.

[0033] 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.

[0034] As the column packed with activated carbon, a conventionally known column can be used.

[0035] When the raw titanium sulfate solution is passed through a column packed with activated carbon, the contact temperature, contact time, and passing speed 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.

[0036] The titanium sulfate solution is obtained by contacting the raw titanium sulfate solution with activated carbon and then filtering the resultant solution through a filter.

[0037] The material of the filter used is not particularly limited, and examples 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, glass, metal, and the like.

[0038] 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.

[0039] 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 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.

[0040] The filter used may be a commercially available product.

[0041] The filtration method is not particularly limited, and may be any of natural filtration performed at normal pressure, suction filtration, pressure filtration, and centrifugal filtration.

[0042] Filtration through a filter may be carried out two or more times.

[0043] 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 matter) in the raw titanium sulfate solution can be sufficiently removed.

[0044] As mentioned above, in the raw titanium sulfate solution, a coagulant is used to remove impurities such as iron components 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) process 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 process, or may cause a decrease in the whiteness of the titanium phosphate powder.

[0045] The total organic carbon content in the titanium sulfate solution according to this embodiment is 3 mg / L or less, preferably 1 mg / L or more and 3 mg / L or less. The total organic carbon content in the titanium sulfate solution may be 1 mg / L or more and 2 mg / L or less. In order to make the total organic carbon content in the titanium sulfate solution less than 1 mg / L, a large amount of activated carbon and a long adsorption time are required, which is not preferable 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: 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, in the evaluation of the formation of a coating film containing titanium phosphate powder, the appearance becomes poor due to the occurrence of color changes in transmitted light and the presence of foreign matter in the coating film.

[0046] The total organic carbon content in the titanium sulfate solution is the 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 the details of the measurement method are described in the Examples.

[0047] 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 taken as 100%. The light transmittance at a wavelength of 550 nm of the titanium sulfate solution can be measured using a spectrophotometer, and the details of the measurement method are described in the Examples.

[0048] The light transmittance of the titanium sulfate solution according to this embodiment at a wavelength of 550 nm is, for example, 70% to 100%, preferably 90% to 100%, and more preferably 95% to 100%. If the light transmittance of the titanium sulfate solution at a wavelength of 550 nm 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.

[0049] The light transmittance of the titanium sulfate solution according to this embodiment at a wavelength of 550 nm can be suppressed from decreasing even when stored for a long period of time. The higher the storage temperature, the more the precipitation of particles is promoted, and therefore the transmittance of the titanium sulfate solution decreases. When stored at 43° C. for 3 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%). When stored at 43° C. for 4 weeks or more (for example, 9 weeks), the light transmittance of the titanium sulfate solution at a wavelength of 550 nm is preferably 90% or more, and more preferably 95% or more.

[0050] The titanium sulfate solution according to this embodiment has impurities (particularly organic matter) sufficiently removed, and the change in transmittance over time (decrease in transmittance) can be suppressed. Thus, one embodiment 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. One embodiment 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 with a filter. 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 filled with activated carbon to prepare a raw titanium sulfate solution that has been treated with activated carbon. 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, it is preferable that the mass ratio of the activated carbon to titanium (in terms of titanium dioxide) in the raw titanium sulfate solution is 0.005 or more.

[0051] 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.

[0052] The phosphoric acid solution contains phosphoric acid as a phosphorus-containing substance.

[0053] 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.

[0054] The phosphoric acid solution may further contain a phosphate. The type of salt is not particularly limited, and examples thereof 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 100% by mass or less, and preferably 80% by mass or more and 100% by mass or less. In one embodiment, it is preferable that the phosphoric acid solution does not contain a phosphate.

[0055] 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 %, and preferably more than 0 mass % and not more than 20 mass %.

[0056] The mixed solution according to this embodiment is prepared by mixing a titanium sulfate solution, a phosphoric acid solution, and, if necessary, other components.

[0057] The method for mixing the titanium sulfate solution, the phosphoric acid solution, and other components as necessary is not particularly limited. The mixing method, mixing order, mixing conditions, etc. may be appropriately selected from known methods.

[0058] The concentration of phosphoric acid in the mixed liquid is, for example, 20 mass % or more and 40 mass % or less, and preferably 21 mass % or more and 35 mass % or less, relative to the total mass of the mixed liquid.

[0059] The concentration of sulfuric acid in the mixed liquid is, for example, from 2 mass % to 15 mass %, and preferably from 3 mass % to 12 mass %, relative to the total mass of the mixed liquid.

[0060] The concentration of titanium in the mixed liquid is, for example, 1 mass % or more and 10 mass % or less, and preferably 2 mass % or more and 5 mass % or less, calculated as titanium dioxide relative to the total mass of the mixed liquid.

[0061] Other components include acids that do not contain phosphorus and do not contain titanium. The acids that do not contain phosphorus and do not contain titanium are not particularly limited, and include known organic acids and known inorganic acids. Examples of the acids that do not contain phosphorus and do not contain titanium include hydrochloric acid, sulfuric acid, nitric acid, carbonic acid, acetic acid, citric acid, and formic acid. The acids that do not contain phosphorus and do not contain titanium may be used alone or in combination of two or more. The acids that do not contain phosphorus and do not contain titanium 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 acids that do not contain phosphorus and do not contain titanium (the total content when two or more 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).

[0062] Titanium phosphate can be produced by reacting the mixed solution obtained above by a hydrothermal synthesis method. The method for producing titanium phosphate powder according to this embodiment can include reacting the mixed solution obtained above by a hydrothermal synthesis method to prepare a liquid containing titanium phosphate powder.

[0063] 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, from 50° C. to 140° C., and preferably from 80° C. to 130° C. The reaction time is, for example, from 1 hour to 100 hours, and preferably from 3 hours to 72 hours.

[0064] The method for producing the titanium phosphate powder according to the present embodiment can include washing (preferably washing with pure water) and / or drying the liquid containing the titanium phosphate powder obtained above. The washing method and drying method are not particularly limited, and conventionally known methods can be appropriately adopted.

[0065] Powder X-ray diffraction confirmed that the powder obtained was titanium phosphate powder, which exhibits the crystallinity of titanium phosphate represented by the chemical formula Ti(HPO4)2·nH2O (0≦n≦1).

[0066] In the method for producing titanium phosphate powder according to this embodiment, foreign matter (particularly organic matter) other than titanium phosphate can be reduced. Thus, one embodiment of the present invention relates to 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 titanium phosphate powder is not particularly limited, and is, for example, 0.001% by mass or more. The carbon content per unit mass of 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 titanium phosphate powder can be measured using a carbon / sulfur measuring device, and the details of the measurement method will be described in the Examples.

[0067] The use of the obtained titanium phosphate powder is not particularly limited, and it is used in various applications. Examples of the use 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 a thin plate shape from the viewpoint of good slippage between particles. The shape of the titanium phosphate particles contained in the titanium phosphate powder is preferably a thin plate shape from the viewpoint of coating a coating film obtained by applying a slurry (e.g., an ink containing titanium phosphate powder, a paint containing titanium phosphate powder) obtained by dispersing or suspending titanium phosphate powder in a solvent and drying the solvent, in which the surface direction of the particles and the substrate to which the particles are applied are parallel, making it easy to obtain a uniform thickness, and the dispersibility is high and aggregation is unlikely to occur.

[0068] In addition, the refractive index of titanium phosphate is 1.79, which is higher than that of silica particles, which are generally used inorganic particles, and acrylic beads, which are polymer particles, and is lower than that of titanium oxide, which is used as a white pigment. For this reason, a coating film containing titanium phosphate powder and a polymer binder has good light scattering and transmittance, and can be used as inorganic particles for light scattering contained in light diffusion films, light diffusion plates, etc.

[0069] 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 matter other than white, such as black or gray.

[0070] 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 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 a raw titanium sulfate solution with activated carbon and then filtering the solution through a filter. [3] The method for purifying a titanium sulfate solution according to [2], wherein a mass ratio of the activated carbon to 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 [5], having a light transmittance of 95% or more at a wavelength of 550 nm. EXAMPLES

[0071] 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 performed under room temperature (25°C).

[0072] <Production of titanium sulfate solution> [Preparation of titanium sulfate solution 1] A raw titanium sulfate solution 1 (a titanium sulfate aqueous solution containing 118 g / L of titanium and 500 g / L of sulfuric acid in terms of titanium dioxide, 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 liquid 1 containing titanium sulfate and activated carbon. After leaving it to stand for 12 hours, it was filtered using a filter (filtration accuracy 0.65 μm, CES-006 manufactured by Roki Techno Co., Ltd.) to produce a titanium sulfate solution 1.

[0073] [Production of titanium sulfate solution 2] A titanium sulfate solution 2 (a titanium sulfate aqueous solution containing 190 g / L of titanium and 290 g / L of sulfuric acid in terms of titanium dioxide, with 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 liquid 2 containing titanium sulfate and activated carbon. After leaving the mixture to stand for 12 hours, the mixture was filtered using a filter (filtration accuracy 0.65 μm, CES-006 manufactured by Roki Techno Co., Ltd.) to produce a titanium sulfate solution 2.

[0074] <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 solids. XRD measurements of each solid were performed using X-ray diffraction. The results are shown in Figure 1. The upper part of Figure 1 shows the measurement results of raw titanium sulfate solution 1 within 14 days after production, and the lower part of Figure 1 shows the measurement results of raw titanium sulfate solution 1 after 4 weeks of storage at 43°C.

[0075] The details of the XRD measurements are given below: Measurement equipment: Rigaku Corporation, sample horizontal type multipurpose X-ray diffraction equipment Ultima IV X-Ray: 20kV / 10mA Divergence slit: 1° Divergence vertical limit slit: 10mm 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.

[0076] As shown in FIG. 1, titanium oxide was already contained in raw titanium sulfate solution 1 within 14 days after production, and titanyl sulfate was precipitated in raw titanium sulfate solution 1 after storage at 43°C for 4 weeks.

[0077] [Long-term storage test 2 (evaluation of transmittance)] The measurement samples used were raw titanium sulfate solution 1 taken 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).

[0078] The light 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 light transmittance of pure water at a wavelength of 550 nm was set at 100%.

[0079] 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.

[0080] [Long-term storage test 3 (measurement of transmission spectrum and evaluation of transmittance)] The measurement samples used were 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 the 4th week).

[0081] The transmission spectrum of the measurement sample was measured using an ultraviolet-visible spectrophotometer (Shimadzu Corporation, UV-2450) (baseline (Tt=100%): pure water). The results are shown in FIG. 3.

[0082] 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%. The results are shown in Figure 4.

[0083] As shown in FIG. 3 and FIG. 4, it can be seen that the storage stability of titanium sulfate solution 1 is improved by performing activated carbon treatment and filtration treatment, compared with raw titanium sulfate solution 1 (FIG. 2).

[0084] [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.

[0085] The light 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 light transmittance of pure water at a wavelength of 550 nm was set at 100%.

[0086] The results are shown in Table 1.

[0087] [Measurement of total organic carbon] 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).

[0088] As measurement samples, 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 were used.

[0089] The results are shown in Table 1.

[0090] <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 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 solution 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.

[0091] [Production of titanium phosphate powder 2] Titanium phosphate powder 2 was obtained in the same manner as 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 confirmed.

[0092] [Production of titanium phosphate powder 3] Titanium phosphate powder 3 was obtained in the same manner as titanium phosphate powder 1, except that raw 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.

[0093] [Production of titanium phosphate powder 4] Titanium phosphate powder 4 was obtained in the same manner as titanium phosphate powder 1, except that raw 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.

[0094] <Evaluation> [Measurement of carbon content] The carbon amount per unit mass in titanium phosphate powders 1 to 4 was measured using a carbon / sulfur measuring device (Horiba, Ltd., EMIA-320V2 type).

[0095] If the amount of carbon per unit mass was 0.005% by mass or less, it was judged to be good, and if the amount of carbon per unit mass was more than 0.005% by mass, it was judged to be poor.

[0096] The results are shown in Table 2.

[0097] [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 shaking the slurries by hand, the presence of foreign matter on the liquid surface was visually confirmed.

[0098] The case where there were 5 or less foreign objects was marked as "O", and the case where there were 6 or more foreign objects was marked as "X".

[0099] The results are shown in Table 2.

[0100] [Table 1]

[0101] [Table 2]

[0102] As shown in Table 1, the titanium sulfate solution of the example is produced by treating the raw titanium sulfate solution with activated carbon and filtering it, so that the transmittance immediately after production (before storage) is 100%, indicating that the transmittance is higher than that of the raw titanium sulfate solution. Furthermore, the titanium sulfate solution of the example has a transmittance of 100% after storage at 43°C for 3 weeks, indicating that no decrease in transmittance due to storage is observed and that the storage stability is high. Furthermore, the total organic carbon content of the titanium sulfate solution of the example is 3 mg / L or less, indicating that the amount of impurities is reduced.

[0103] As shown in Table 2, the titanium phosphate powder of the example can be reduced to a carbon content of 0.005 mass% or less by using a titanium sulfate solution (see Table 1) with a total organic carbon content of 3 mg / L or less. This shows that foreign matter (organic carbon) in the slurry of the titanium phosphate powder of the example can be sufficiently removed.

[0104] <Production of titanium phosphate powder 2> [Production of titanium phosphate powder 5] A titanium sulfate solution 2 (a titanium sulfate aqueous solution containing 190 g / L of titanium and 290 g / L of sulfuric acid in terms of titanium dioxide, 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 (in terms of titanium dioxide) was 0.01 to prepare a liquid 2 containing titanium sulfate and activated carbon. After standing for 12 hours, the mixture 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.

[0105] Titanium sulfate solution 3 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 5. The titanium phosphate powder 5 had a white appearance, and no gray or black impurities were visually observed.

[0106] [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 in terms of titanium dioxide, 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 (in terms of titanium dioxide) was 0.01 to prepare a liquid 2 containing titanium sulfate and activated carbon. After standing for 12 hours, the mixture 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.

[0107] 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.

[0108] <Evaluation> [Evaluation of foreign matter] During the hydrothermal treatment and the water washing treatment, the mixed liquid was visually inspected for the presence of foreign matter on the liquid surface.

[0109] 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 cause any practical problems. In the production of titanium phosphate powder 6, no foreign matter derived from activated carbon was observed.

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 a raw titanium sulfate solution with activated carbon and then filtering the resultant solution through a filter.

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

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

Images