Preparation method of zinc-doped metatitanic acid and production method of titanium dioxide using sulfuric acid process

Abstract

The present invention discloses a method for preparing zinc-doped metatitanic acid and a method for producing titanium dioxide using a sulfuric acid process. The method comprises the following steps: S1, mixing or dissolving a zinc-containing compound with a sodium hydroxide solution having a concentration of not less than 1 mol / L, removing impurities and diluting the solution to obtain a diluted zinc-containing alkali solution having a sodium hydroxide concentration of 0.1 to 0.5 mol / L; S2, adding industrial titanium solution to the diluted zinc-containing alkali solution so that the pH value of the system is 4.7 to 5.3 and the system temperature is 30 to 40°C after the addition is completed, thereby obtaining a zinc hydroxide suspension; S3, heating the zinc hydroxide suspension to 70 to 90°C, then transferring the solution to preheated industrial titanium solution and stirring and mixing the solution to obtain a mixed solution; S4, heating the mixed solution to boiling and hydrolyzing the solution to obtain zinc-doped metatitanic acid. The present invention is advantageous for effectively regulating the calcination temperature and rutile grains, and does not require salt treatment of the zinc-doped metatitanic acid. The conversion to rutile titanium dioxide can be completed by direct calcination at a relatively low temperature.

Description

Technical Field

[0001] The invention relates to the technical field of titanium dioxide production, and in particular to a method for preparing zinc-doped metatitanic acid and a method for producing titanium dioxide using a sulfuric acid process. Background Art

[0002] The production of rutile titanium dioxide is primarily based on the sulfuric acid process. This process first uses a titanyl sulfate solution (industrial titanium solution) as the raw material to produce metatitanic acid through thermal hydrolysis. Rutile titanium dioxide is then obtained through calcination and post-processing. Metatitanic acid calcination is a key step in the sulfuric acid titanium dioxide production process and one of its core technologies. The quality of calcination directly affects the crystal morphology, particle size, and particle size distribution of rutile TiO2, and plays a decisive role in the pigmentary properties of the final titanium dioxide product. Promoting the transformation of anatase TiO2 to rutile TiO2 at a lower calcination intensity (low temperature, short time) is key to improving the quality of rutile titanium dioxide produced by the sulfuric acid process and is also an important way to save energy and reduce consumption in the sulfuric acid process.

[0003] Current research results show that zinc salt treatment can reduce the calcination temperature to a certain extent, but the control over the calcination temperature and rutile particles is relatively limited. Further increasing the doping amount will further reduce the calcination temperature, but the rutile sintering will be more serious and the final titanium dioxide product will be reddish, reducing the pigment performance; in addition, the doped inorganic salts will cause the rutile TiO2 dispersion viscosity to be too high, which is not conducive to subsequent surface treatment and affects the application performance of rutile titanium dioxide products. Summary of the Invention

[0004] The main purpose of the present invention is to provide a method for preparing zinc-doped metatitanic acid and a method for producing titanium dioxide by the sulfuric acid process, so as to solve the problem that zinc salt treatment has limited control over calcination temperature and rutile particles and may affect the performance of titanium dioxide products.

[0005] According to one aspect of the present invention, a method for preparing zinc-doped metatitanic acid is provided, comprising the following steps:

[0006] S1, mixing or dissolving a zinc-containing compound with a sodium hydroxide solution having a concentration of not less than 1 mol / L, then removing impurities and diluting to obtain a diluted zinc-containing alkali solution having a sodium hydroxide concentration of 0.1 to 0.5 mol / L;

[0007] S2, adding industrial titanium solution to the diluted zinc-containing alkali solution under stirring conditions, so that after the addition, the pH value of the system is 4.7-5.3 and the system temperature is 30-40° C., to obtain a zinc hydroxide suspension;

[0008] S3, heating the zinc hydroxide suspension to 70-90° C., then transferring the mixture to industrial titanium liquid preheated to 70-90° C. and stirring to obtain a mixed solution;

[0009] S4, heating the mixed solution to boiling and hydrolyzing it to obtain zinc-doped metatitanic acid.

[0010] According to one embodiment of the present invention, the mass of the zinc-containing compound added in step S1 in terms of zinc oxide and the mass of the sodium hydroxide in the sodium hydroxide solution added are 0.1% to 1% and 0.5% to 2% of the mass of titanium dioxide in the industrial titanium solution in step S3, respectively.

[0011] According to one embodiment of the present invention, in step S1, the zinc-containing compound includes one or more of the following: zinc sulfate, zinc chloride, zinc hydroxide, and zinc oxide.

[0012] According to one embodiment of the present invention, in step S2, industrial titanium liquid is first slowly added, and when the pH value of the system drops to 10.7-11.3, industrial titanium liquid is rapidly added within 10 seconds to adjust the pH value of the system to 4.7-5.3.

[0013] According to one embodiment of the present invention, in step S3, the zinc hydroxide suspension is heated to 70-90° C. within 2 minutes and transferred to industrial titanium liquid that has been preheated to 70-90° C. within 30 seconds.

[0014] According to one embodiment of the present invention, in step S3, the stirring and mixing time is 3 to 10 minutes.

[0015] According to one embodiment of the present invention, in step S4, the mixed solution is first heated to boiling for hydrolysis. When the hydrolysis rate reaches 30% to 50%, heating and stirring are stopped for 20 to 40 minutes, and then the temperature is raised to boiling again and kept boiling for 3 to 5 hours to terminate the hydrolysis.

[0016] According to another aspect of the present invention, a method for producing titanium dioxide using a sulfuric acid process is provided, comprising: calcining zinc-doped metatitanic acid prepared by the method described in any one of the above embodiments to obtain rutile titanium dioxide.

[0017] Through the technical solution of the present invention, zinc-doped titanic acid can be prepared to promote the rutile conversion during the calcination process, thereby achieving precise control of the rutile crystal structure, grain size, particle size and distribution. The zinc-doped titanic acid does not need to be subsequently treated with salt and can be directly calcined at a relatively low temperature to complete the conversion to rutile TiO2. DETAILED DESCRIPTION

[0018] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the embodiments of the present invention are further described in detail below in conjunction with specific embodiments.

[0019] It should be noted that all expressions using "first" and "second" in the embodiments of the present invention are for distinguishing two non-identical entities with the same name or non-identical parameters. It can be seen that "first" and "second" are only for the convenience of expression and should not be understood as limitations on the embodiments of the present invention. Subsequent embodiments will not explain this one by one.

[0020] The present invention provides a method for preparing zinc-doped metatitanic acid, comprising the following steps:

[0021] S1, mixing or dissolving a zinc-containing compound with a sodium hydroxide solution having a concentration of not less than 1 mol / L to obtain a zinc-containing alkali solution, then removing impurities (for example, removing any insoluble matter that may be mixed by filtration, centrifugation, etc.) and diluting (for example, diluting the zinc-containing alkali solution after impurities removal by adding pure water, and slowly diluting under sufficient stirring, ensuring that no white turbidity appears during the dilution process) to obtain a diluted zinc-containing alkali solution having a sodium hydroxide concentration of 0.1 to 0.5 mol / L;

[0022] S2, adding industrial titanium solution (i.e., titanyl sulfate solution, referred to as primary titanium solution) to the diluted zinc-containing alkaline solution under stirring, so that after the addition, the system pH value is 4.7-5.3 and the system temperature is 30-40° C., to obtain a nano-sized zinc hydroxide suspension;

[0023] S3, heating the zinc hydroxide suspension to 70-90° C., then transferring it to an industrial titanium solution (referred to as secondary titanium solution, having the same composition as the primary titanium solution in step S2) that has been preheated to 70-90° C. and stirring to obtain a mixed solution;

[0024] S4, heating the mixed solution to boiling and hydrolyzing it to obtain zinc-doped metatitanic acid.

[0025] The inventors of the present application recognize that the species that plays the main doping role in the calcination process of metatitanic acid treated with zinc salts is the doped Zn ion. In theory, the use of Zn ions to in-situ dope metatitanic acid can improve the problems existing in the current calcination process. Based on this understanding, the present invention proposes the technical solution as described above, in which Zn ions are introduced in situ during the hydrolysis of titanyl sulfate to prepare Zn-doped metatitanic acid, thereby promoting the conversion of TiO2 to rutile crystal form during the calcination process. Subsequently, salt treatment is no longer performed, and the conversion of rutile TiO2 can be directly calcined at a relatively low temperature to complete the conversion. Through the technical solution of the present invention, the calcination temperature and rutile grains can be effectively regulated, and the full conversion of rutile TiO2 can be achieved under low-temperature (e.g., 850°C) calcination conditions, and the impact on the performance of titanium dioxide products can be reduced.

[0026] In step S1, the initial alkalinity is high (not less than 1mol / L), which ensures the full dissolution of the zinc-containing compound and the precipitation of zinc ions. Otherwise, filtration will cause zinc to be separated in the form of a solid, and the low preparation efficiency of the zinc-containing alkali solution will affect the rate of generating zinc hydroxide later. In step S1, by diluting, the zinc ion concentration can be adjusted to a suitable level while ensuring that zinc will not precipitate, so as to prepare for the rapid precipitation of zinc after adding titanium liquid in the next step. If directly prepared into "a zinc-containing alkali solution with a sodium hydroxide concentration of 0.1 to 0.5mol / L", the preparation efficiency is low and the stability deviation of the solution is easily caused by the influence of system temperature, stirring, etc., so the present invention first prepares a higher concentration of zinc-containing alkali solution, and then dilutes and adjusts it before use.

[0027] In step S2, the system temperature is controlled at 30-40°C, mainly to ensure the generation rate and solubility of zinc hydroxide precipitate. The generated zinc hydroxide will dissolve as the temperature rises. If the temperature is too low, the generated zinc hydroxide will be coarse, which is not conducive to becoming the crystal nucleus for the subsequent hydrolysis of titanyl sulfate; if the temperature is too high, the generated zinc hydroxide will partially dissolve, resulting in an insufficient number of crystal nuclei. The pH value of 4.7-5.3 is to control zinc hydroxide from generating sodium zincate. Below this pH value, zinc hydroxide will react with hydrogen ions to generate soluble zincate ions, which will also result in an insufficient number of crystal nuclei for subsequent induced hydrolysis.

[0028] In step S3, the temperature is increased before mixing with the titanium liquid to ensure that the temperature of the mixed solution is not significantly lower than that of the titanium liquid. The mixed solution is at the critical temperature condition for hydrolysis at a temperature of 70 to 90°C, which is conducive to subsequent heating to boiling for rapid hydrolysis reaction.

[0029] In some embodiments, the mass of the zinc-containing compound added in step S1, calculated as zinc oxide, and the mass of the sodium hydroxide in the sodium hydroxide solution added are 0.1% to 1% and 0.5% to 2% of the mass of titanium dioxide in the industrial titanium solution in step S3, respectively. The amount of zinc oxide added is intended to control the number of zinc hydroxide precipitates generated as subsequent induced hydrolysis nuclei and the efficiency of metatitanic acid generation to promote rutile conversion. Too little addition will result in low hydrolysis efficiency and rutile conversion efficiency; too much addition will be wasteful and unnecessary. The amount of sodium hydroxide added is intended to ensure sufficient dissolution of the added zinc-containing compound while avoiding the need to add too much titanium solution at one time.

[0030] In some embodiments, in step S1, the zinc-containing compound includes one or more of the following: zinc sulfate, zinc chloride, zinc hydroxide, and zinc oxide.

[0031] In some embodiments, in step S2, industrial titanium liquid is first slowly added, and the changes in the pH value of the system are monitored during the addition process. When the pH value of the system drops to 10.7-11.3, the addition rate of the titanium liquid is adjusted, and the remaining industrial titanium liquid is quickly added within 10 seconds to make the pH value of the system 4.7-5.3. The slow addition is to avoid dropping the pH value below the target range (10.7-11.3) at once, at which time zinc hydroxide will precipitate. Zinc hydroxide precipitates generally precipitate between pH values ​​of 5 and 10. The rapid addition in this process is to control the reaction rate and ensure that the generated zinc hydroxide precipitate is relatively fine.

[0032] In some embodiments, in step S3, the zinc hydroxide suspension is heated to 70-90° C. within 2 minutes and transferred to an industrial titanium solution preheated to 70-90° C. within 30 seconds. If the zinc hydroxide is heated too slowly or left for too long after heating, some of the precipitate will dissolve, resulting in an insufficient number of crystal nuclei. Therefore, the zinc hydroxide is quickly heated and then transferred to the titanium solution.

[0033] In some embodiments, in step S3, the stirring and mixing time is 3 to 10 minutes. The stirring and mixing is to achieve full dispersion of zinc hydroxide in the titanium liquid.

[0034] In some embodiments, in step S4, the mixed solution is first heated to boiling for hydrolysis, and when the hydrolysis rate reaches 30% to 50%, the heating and stirring are stopped for 20 to 40 minutes, and then the temperature is again raised to boiling, and the boiling is maintained for 3 to 5 hours to terminate the hydrolysis. "When the hydrolysis rate reaches 30% to 50%, the heating and stirring are stopped for 20 to 40 minutes" is to regulate the generation and growth rate of particles in the early stage of hydrolysis, which is conducive to obtaining titanic acid with more uniform particle size. Uniform particle size means high subsequent washing efficiency. "Heating to boiling again and maintaining boiling for 3 to 5 hours" is to ensure that the hydrolysis yield of the titanium liquid is at least above 90%. If the time is too short, the yield of titanium in the titanium liquid will be low. If the time is too long, the hydrolysis has reached equilibrium, which has little significance for improving the hydrolysis yield.

[0035] The present invention also provides a method for producing titanium dioxide using a sulfuric acid process, comprising calcining zinc-doped metatitanic acid prepared according to any of the methods described in the preceding embodiments to obtain rutile titanium dioxide. The zinc-doped metatitanic acid does not require salt treatment, and the calcination temperature is relatively low (e.g., 850°C).

[0036] The following describes the specific embodiments.

[0037] Example 1

[0038] (1) Preheating of the hydrolyzed titanium solution: Preheat 1000 mL of the hydrolyzed titanium solution (the secondary titanium solution described above, with a titanium dioxide concentration of 192 g / L) to 70°C for later use.

[0039] (2) Preparation, impurity removal and dilution of an alkaline solution containing zinc ions: Weigh 0.32 g of analytically pure zinc chloride (the mass as zinc oxide is 0.19 g, and the mass of zinc oxide is 0.1% of the mass of titanium dioxide in the hydrolyzed titanium solution) and prepare 24 mL of a 1 mol / L sodium hydroxide solution (the mass of sodium hydroxide is 0.5% of the mass of titanium dioxide in the hydrolyzed titanium solution). Mix the two and filter to obtain a clear solution. Dilute the solution to a sodium hydroxide concentration of 0.1 mol / L, and the volume of the diluted solution is 240 mL.

[0040] (3) Preparation of zinc hydroxide suspension: titanium liquid at room temperature (the primary titanium liquid described above is exactly the same as the secondary titanium liquid, and the titanium dioxide concentration of the titanium liquid is 192 g / L) is slowly added to the diluted alkaline solution containing zinc ions. Stirring is started during the addition process and the pH value is monitored. When the pH value drops to 10.7, the titanium liquid is continued to be added. After 8 seconds, the pH value of the system drops to 5.3 and the system temperature is 31°C. At this point, a zinc hydroxide suspension is obtained.

[0041] (4) Premixing: Heat the zinc hydroxide suspension to 90°C for 72 seconds; then add it to the hydrolyzed titanium solution preheated to 70°C for 15 seconds; and stir and mix for 3 minutes.

[0042] (5) Hydrolysis: After mixing, heat to boiling for hydrolysis. When the hydrolysis rate reaches 40%, stop heating and stirring for 30 minutes, then heat to boiling again and keep boiling for 5 hours to complete the hydrolysis, thus obtaining zinc-doped titanic acid; wash the titanic acid clean.

[0043] The obtained metatitanic acid and the metatitanic acid (after washing) hydrolyzed by titanyl sulfate and seed crystals from conventional industrial titanium liquid were calcined under the same calcination intensity (heating from room temperature to 850°C, heating time 6h, and keeping at 850°C for 1h). The content of rutile crystal titanium dioxide was detected. The sample prepared by the present invention had a rutile crystal content of 56%, while the comparative sample had a rutile crystal content of 0.

[0044] Example 2

[0045] (1) Preheating of the hydrolyzed titanium solution: Preheat 1000 mL of the hydrolyzed titanium solution (the secondary titanium solution described above, with a titanium dioxide concentration of 187 g / L) to 80°C for later use.

[0046] (2) Preparation, impurity removal and dilution of alkaline solution containing zinc ions: Weigh 1.57 g of analytically pure zinc chloride (the mass as zinc oxide is 0.93 g, and the mass of zinc oxide is 0.5% of the mass of titanium dioxide in the hydrolyzed titanium solution), prepare 67.3 mL of 1.2 mol / L sodium hydroxide solution (the mass of sodium hydroxide is 1.2% of the mass of titanium dioxide in the hydrolyzed titanium solution), mix the two and filter to obtain a clear solution, and dilute the solution to a sodium hydroxide concentration of 0.3 mol / L. The volume of the diluted solution is 270 mL.

[0047] (3) Preparation of zinc hydroxide suspension: titanium liquid at room temperature (the primary titanium liquid described above is exactly the same as the secondary titanium liquid, and the titanium dioxide concentration of the titanium liquid is 187 g / L) is slowly added to the diluted alkaline solution containing zinc ions. Stirring is started during the addition process and the pH value is monitored. When the pH value drops to 11.2, the titanium liquid is continued to be added. After 2 seconds, the pH value of the system drops to 5.1 and the system temperature is 36°C. At this point, a zinc hydroxide suspension is obtained.

[0048] (4) Premixing: Heat the zinc hydroxide suspension to 70°C for 50 seconds; then add it to the hydrolyzed titanium solution preheated to 80°C for 11 seconds; stir and mix for 7 minutes.

[0049] (5) Hydrolysis: After mixing, heat to boiling for hydrolysis. When the hydrolysis rate reaches 50%, stop heating and stirring for 20 minutes, then heat to boiling again and keep boiling for 3 hours to complete the hydrolysis, thus obtaining zinc-doped titanic acid; wash the titanic acid clean.

[0050] The obtained metatitanic acid and the metatitanic acid (after washing) hydrolyzed by titanyl sulfate and seed crystals from conventional industrial titanium liquid were calcined under the same calcination intensity (heating from room temperature to 850°C, heating time 6h, and keeping at 850°C for 1h). The content of rutile crystal titanium dioxide was detected. The sample prepared by the present invention had a rutile crystal content of 88%, while the comparative sample had a rutile crystal content of 0.

[0051] Example 3

[0052] (1) Preheating of the hydrolyzed titanium solution: Preheat 1000 mL of the hydrolyzed titanium solution (the secondary titanium solution described above, with a titanium dioxide concentration of 200 g / L) to 90°C for later use.

[0053] (2) Preparation, impurity removal and dilution of an alkaline solution containing zinc ions: Weigh 3.36 g of analytically pure zinc chloride (2 g in terms of zinc oxide, where the mass of zinc oxide is 1% of the mass of titanium dioxide in the hydrolyzed titanium solution) and prepare 140 mL of a 1.4 mol / L sodium hydroxide solution (where the mass of sodium hydroxide is 2% of the mass of titanium dioxide in the hydrolyzed titanium solution). Mix the two and filter to obtain a clear solution, which is then diluted to a sodium hydroxide concentration of 0.5 mol / L. The volume of the diluted solution is 392 mL.

[0054] (3) Preparation of zinc hydroxide suspension: titanium liquid at room temperature (the primary titanium liquid described above is exactly the same as the secondary titanium liquid, and the titanium dioxide concentration of the titanium liquid is 200 g / L) is slowly added to the diluted alkaline solution containing zinc ions. Stirring is started during the addition process and the pH value is monitored. When the pH value drops to 11.0, the titanium liquid is continued to be added. After 5 seconds, the pH value of the system drops to 4.8 and the system temperature is 39°C. At this point, a zinc hydroxide suspension is obtained.

[0055] (4) Premixing: Heat the zinc hydroxide suspension to 80°C for 68 seconds; then add it to the hydrolyzed titanium solution preheated to 90°C for 27 seconds; stir and mix for 10 minutes.

[0056] (5) Hydrolysis: After mixing, the temperature is raised to boiling for hydrolysis. When the hydrolysis rate reaches 40%, the heating and stirring are stopped for 40 minutes. Then the temperature is raised to boiling again and kept boiling for 4 hours to complete the hydrolysis, thereby obtaining zinc-doped titanic acid; the titanic acid is washed clean.

[0057] The obtained metatitanic acid and the metatitanic acid (after washing) hydrolyzed by titanyl sulfate and seed crystals in conventional industrial titanium liquid were calcined under the same calcination intensity (heating from room temperature to 850°C, heating time 6h, and keeping at 850°C for 1h), and the content of rutile crystal titanium dioxide was detected. The sample prepared by the present invention had a rutile crystal content of 100%, while the comparative sample had a rutile crystal content of 0.

[0058] Those skilled in the art should understand that the discussion of any of the above embodiments is merely illustrative and is not intended to imply that the scope of the disclosure of the embodiments of the present invention (including the claims) is limited to these examples. Within the spirit of the embodiments of the present invention, the technical features of the above embodiments or different embodiments may be combined, and there are many other variations of the different aspects of the embodiments of the present invention described above, which are not provided in detail for the sake of clarity. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the embodiments of the present invention should be included within the scope of protection of the embodiments of the present invention.

Claims

1. A method for preparing zinc-doped metatitanic acid, characterized in that: The following steps are involved: S1, mixing a zinc-containing compound with a sodium hydroxide solution having a concentration of not less than 1 mol / L to ensure that the zinc-containing compound is fully dissolved, then removing impurities and diluting to obtain a diluted zinc-containing alkali solution having a sodium hydroxide concentration of 0.1 to 0.5 mol / L; S2, adding industrial titanium solution to the diluted zinc-containing alkali solution under stirring conditions, so that after the addition, the pH value of the system is 4.7-5.3 and the system temperature is 30-40° C., to obtain a zinc hydroxide suspension; S3, heating the zinc hydroxide suspension to 70-90° C., then transferring the mixture to industrial titanium liquid preheated to 70-90° C. and stirring to obtain a mixed solution; S4, heating the mixed solution to boiling and hydrolyzing it to obtain zinc-doped metatitanic acid; The mass of the zinc-containing compound added in step S1 in terms of zinc oxide and the mass of the sodium hydroxide in the sodium hydroxide solution added are 0.1% to 1% and 0.5% to 2% of the mass of the titanium dioxide in the industrial titanium solution in step S3, respectively; In step S2, industrial titanium liquid is first slowly added, and when the pH value of the system drops to 10.7-11.3, industrial titanium liquid is rapidly added within 10 seconds to adjust the pH value of the system to 4.7-5.

3.

2. The method according to claim 1, characterized in that In step S1, the zinc-containing compound includes one or more of the following: zinc sulfate, zinc chloride, zinc hydroxide, and zinc oxide.

3. The method according to claim 1, characterized in that In step S3, the zinc hydroxide suspension is heated to 70-90° C. within 2 minutes and transferred to industrial titanium liquid that has been preheated to 70-90° C. within 30 seconds.

4. The method according to claim 1, wherein In step S3, the stirring and mixing time is 3 to 10 minutes.

5. The method according to claim 1, wherein In step S4, the mixed solution is first heated to boiling for hydrolysis. When the hydrolysis rate reaches 30% to 50%, heating and stirring are stopped for 20 to 40 minutes. Then, the mixed solution is heated to boiling again and kept boiling for 3 to 5 hours to terminate the hydrolysis.

6. A method for producing titanium dioxide using the sulfuric acid process, characterized in that: include: The zinc-doped metatitanic acid prepared according to the method according to any one of claims 1 to 5 is calcined to obtain rutile titanium dioxide.