Process for improving hydrolysis rate of titanium dioxide by sulfuric acid method

Abstract

The invention provides a process for improving the hydrolysis rate of titanium dioxide by a sulfuric acid method, and relates to the technical field of titanium dioxide hydrolysis. A process for improving the hydrolysis rate of titanium dioxide by a sulfuric acid method comprises the following steps: seed crystal preparation: respectively preheating a titaniferous solution with the concentration of 160-250g / L and an alkali solution with the mass concentration of 10-25%, then dispersing the titaniferous solution in the alkali solution according to the alkali-titanium ratio of 0.20-0.38, and curing to obtain hydrolyzed seed crystals; hydrolysis: preheating a hydrolysis titanium solution with the concentration of 160-190 g / L, adding hydrolysis seed crystals accounting for 2.5-5% of the mass of TiO2 in the hydrolysis titanium solution to form a hydrolysis system, heating to boiling, keeping slight boiling, after the hydrolysis titanium solution is whitened, adding a composite treatment agent for induction, continuing heating and keeping slight boiling after induction is finished, then adding dilution water, keeping the system slightly boiling, and finishing hydrolysis. According to the process, different seed crystal alkali-titanium ratios are obtained through different seed crystal alkali concentrations, and finally optimization of the seed crystal number is achieved so as to improve the hydrolysis rate.

Description

Technical Field

[0001] The present invention relates to the technical field of titanium dioxide hydrolysis, and in particular to a process for improving the hydrolysis rate of titanium dioxide produced by a sulfuric acid process. Background Art

[0002] The hydrolysis process is a critical step in the production of titanium dioxide produced by the sulfuric acid method. It directly determines the quality of titanic acid and ultimately the quality of titanium dioxide products. Most manufacturers use an external seed hydrolysis process to prepare hydrolysis seeds by reacting alkali and titanium liquid.

[0003] Currently, the specifications for the hydrolyzed titanium solution used in the sulfuric acid process for pigment-grade titanium dioxide production vary considerably among manufacturers. Most manufacturers use the same titanium solution for both the seed and solution, with a concentration of 185-200 g / L, an iron-titanium ratio of 0.28-0.38, and an F value of 1.80-1.95. However, to achieve higher hydrolysis rates, the F value is generally controlled to a lower limit of 1.80-1.90, with an iron-titanium ratio of 0.28-0.32. Furthermore, the concentration is generally kept to a minimum of around 190 g / L to account for concentration costs. Therefore, the alkali-titanium ratio for high-concentration seed crystals should be kept to a minimum, as this will rapidly degrade the seed stability and hinder the preheating time of the solution. Therefore, it is generally controlled below 0.18, resulting in a hydrolysis rate limit of 96-96.2%, with no room for further improvement. For a domestic sulfuric acid titanium dioxide manufacturer with an annual output of 100,000 tons, every 1 percentage point increase in hydrolysis rate is equivalent to a 0.9 percentage point increase in TiO2 yield throughout the entire process, representing a 700-ton increase in annual output and a 10 million yuan increase in net revenue. Because the TiO2 yield in the titanium dioxide production process significantly impacts cost control and profits, and increasing the hydrolysis rate in the hydrolysis step can significantly improve the TiO2 yield throughout the entire process, there is a need in this field for technologies and methods to increase the hydrolysis rate.

[0004] After preliminary exploratory tests, it was found that simply increasing the amount of seed crystals to increase the hydrolysis rate is feasible to a certain extent, but the cost will also increase. The most important thing is that the volume of the seed crystal preparation tank does not meet the needs; in addition, when the alkali-titanium ratio of the hydrolysis seed crystal is low, the alkali-titanium ratio can be increased to increase the hydrolysis rate. However, after the alkali-titanium ratio reaches 0.18, the stability of the seed crystal decreases rapidly, which does not match the preheating time of the hydrolysis titanium liquid; and increasing the alkali-titanium ratio of the seed crystal and increasing the amount of seed crystals do not improve the hydrolysis rate much, and the benefits are not obvious. Summary of the Invention

[0005] The purpose of the present invention is to provide a process for improving the hydrolysis rate of titanium dioxide produced by the sulfuric acid process, which obtains different seed alkali-titanium ratios by varying the concentration of seed titanium liquid, and ultimately optimizes the number of seed crystals to improve the hydrolysis rate.

[0006] The present invention is achieved through the following technical solutions:

[0007] A process for increasing the hydrolysis rate of titanium dioxide produced by the sulfuric acid process, comprising the following steps:

[0008] Seed crystal preparation: Preheat titanium liquid with a concentration of 160-250g / L and alkali solution with a mass concentration of 10-25%, respectively, then disperse the titanium liquid in the alkali solution with an alkali-titanium ratio of 0.20-0.38, and obtain hydrolysis seed crystals after aging;

[0009] Hydrolysis: Preheat the hydrolysis titanium liquid with a concentration of 160-190g / L, add hydrolysis seeds of 2.5-5% of the mass of TiO2 in the hydrolysis titanium liquid to form a hydrolysis system, heat to boiling, keep it slightly boiling, wait until the hydrolysis titanium liquid turns white, add a composite treatment agent for induction, continue to heat after the induction, keep it slightly boiling, then add dilution water and maintain the system slightly boiling, and the hydrolysis is completed.

[0010] Since the number of hydrolysis seed crystals is affected by the alkali-titanium ratio, the number of seed crystals can be increased by appropriately increasing the alkali-titanium ratio, thereby improving the hydrolysis rate. Currently, when increasing the alkali-titanium ratio, it is usually achieved by increasing the amount of alkali solution. However, when the amount of alkali solution is too much, the high pH value may accelerate the hydrolysis reaction, resulting in coarse and unevenly distributed metatitanic acid particles, reducing the uniformity of the product; excessive OH - It may cause excessive hydroxylation on the surface of the seed crystal or form colloidal Ti(OH)4, resulting in reduced seed crystal activity and inability to effectively induce subsequent uniform hydrolysis of the titanium liquid; excessive alkali solution may cause part of the seed crystal to dissolve (generating titanate ions), and then re-precipitate into irregular particles when the pH fluctuates, destroying the uniformity of the seed crystal.

[0011] Based on this, the inventors changed the alkali-titanium ratio by increasing the alkali solution concentration, and used high-concentration alkali solution to react with high-F value, high-concentration concentrated titanium solution to prepare hydrolysis seeds. Without increasing the amount of alkali solution, a large amount of hydrolysis seed precursor - orthotitanic acid can be generated, thereby increasing the number of seeds. The surface of the seeds is rich in hydroxyl groups (-OH), which are highly active and can effectively induce the directional hydrolysis of titanium liquid. When the hydrolysis seeds are used to participate in the hydrolysis of titanium liquid, due to the small seed particle size and large number, under the condition of the same seed dosage, it has a higher hydrolysis rate, reduces the seed cost, and improves production efficiency.

[0012] Preferably, the F value of the titanium solution prepared by the seed crystal is 1.95-2.25. Using high-concentration, high-F value titanium solution and high-concentration alkali solution to prepare hydrolysis seed crystals helps to increase the number of seed crystals, ensure the stability of the seed crystal system, and match the preheating time of the hydrolysis titanium solution.

[0013] Preferably, during the seed crystal preparation, the preheating temperature is 70-95° C., the aging temperature is 80-102° C., and the aging time is 5-50 min.

[0014] Preferably, during the seed crystal preparation, the titanium liquid is dispersed into the alkaline solution within 5-10 minutes, and the stirring speed is 300-350 r / min during the dispersion process. The alkaline solution is a sodium hydroxide solution.

[0015] Preferably, the F value of the hydrolyzed titanium solution is 1.80-1.95.

[0016] Preferably, the mass ratio of the composite treatment agent to TiO2 in the hydrolyzed titanium solution is 0.5-1.0%.

[0017] Preferably, the composite treatment agent comprises, by weight, 5-15 parts of ammonium carbonate, 5-10 parts of aluminum sulfate, 5-10 parts of potassium sulfate and 10-20 parts of polyoxyethylene ether phosphate.

[0018] When titanium liquid undergoes hydrolysis, the dispersibility of the hydrolysis system and the quality of the seed crystals are key factors in determining the quality of the metatitanic acid, ultimately affecting the quality of the pigment titanium dioxide product. The present invention, by adding a composite treatment agent, can, on the one hand, improve the dispersibility of the material in the hydrolysis system, thereby enabling the seed crystals to induce more uniform and sufficient hydrolysis of the titanium liquid. On the other hand, it can enhance the stability of the seed crystals, ensure the activity of the seed crystals and the nucleation sites, promote the uniformity of the hydrolysis reaction, thereby increasing the hydrolysis rate of the titanium liquid and improving the washing efficiency of the hydrolyzed metatitanic acid.

[0019] Ammonium carbonate, as a weak alkaline salt, can slowly release NH 4+ and CO3 2- ions, CO3 2- With H in solution + The reaction produces HCO 3- or CO2, stabilize the pH value, avoid hydrolysis side reactions caused by local over-acidity or over-alkalinity, and avoid drastic fluctuations in the pH value of the titanium liquid; NH 4+ Combined with titanium complex anions, it reduces their solubility and promotes directional crystallization. In the titanium liquid system, ammonium carbonate neutralizes free acids (such as H + ), maintain pH in a suitable range (usually weakly acidic to neutral), prevent Ti 4+ Premature hydrolysis of metal ions or formation of oxygen-containing precipitates. 4+It can be adsorbed on the surface of the seed crystal to form a double electric layer structure, enhance the electrostatic repulsion between colloidal particles, affect the surface charge state of the seed crystal, improve the colloid dispersion through adsorption or complexation, reduce particle agglomeration, and thus enhance the catalytic activity and uniformity of the seed crystal. Aluminum sulfate and potassium sulfate can regulate the hydrolysis kinetics, optimize the hydrolysis balance, and delay hydrolysis to enhance the activity of the seed crystal. Aluminum sulfate can also enhance high temperature stability and reduce side reactions. The molecular structure of polyoxyethylene ether phosphate contains hydrophilic phosphate groups and hydrophobic polyoxyethylene ether chains, which can inhibit the agglomeration of seed crystal particles through electrostatic repulsion and steric hindrance effects, ensuring uniform distribution of seed crystal particle size. Specifically: phosphate group (-PO4 3- ) is ionized and adsorbed on the surface of the seed particles, forming a double electric layer structure, which prevents the particles from approaching each other through Coulomb repulsion; the hydrophobic polyoxyethylene ether chain extends into the solution, forming a physical barrier, hindering direct contact between particles. This effect is more significant in low-concentration titanium liquid and can reduce secondary agglomeration during seed growth. The ionization of the phosphate group gives the surface of the seed particles a negative charge, enhancing the stability of the colloidal system. This charge regulation effect can prevent non-uniform nucleation caused by local supersaturation. The phosphate group and the titanium ion (Ti 4+ ) undergoes a weak complexation, slowing the hydrolysis rate, thereby controlling the balance between seed nucleation and growth and enhancing seed activity. As a surfactant, polyoxyethylene ether phosphate reduces the surface tension of the solution, promoting uniform nucleation of titanate colloids. It also synergizes with aluminum sulfate and potassium sulfate to improve the kinetics of the hydrolysis reaction.

[0020] The composite treatment agent overcomes the shortcomings of traditional inorganic salt dispersants that are easy to introduce impurities, sensitive to acidity, and easy to decompose, and high molecular polymer dispersants that are difficult to remove and affect the quality of titanium dioxide. It can simultaneously improve the dispersion and stability of hydrolysis seeds to promote the hydrolysis of titanium liquid and increase the hydrolysis rate.

[0021] Preferably, the composite treatment agent is prepared by mixing ammonium carbonate, aluminum sulfate and potassium sulfate, adding the mixture to polyoxyethylene ether phosphate, and ultrasonically treating the mixture for 5-10 minutes.

[0022] The technical solution of the present invention has at least the following advantages and beneficial effects:

[0023] 1. A separate concentrated titanium liquid is used to prepare the seed crystals, which overcomes the shortcomings of existing high-concentration externally added hydrolysis seed crystals, such as the inability to control the stability due to factors such as low concentration and low F value, the inability to adjust the hydrolysis seed crystal process, and the inability to change the size and number of the hydrolysis seed crystals, thereby failing to improve the hydrolysis rate. By increasing the alkali solution concentration, the alkali-titanium ratio is increased while ensuring the amount of alkali solution added, and the hydrolysis seed crystal preparation tank does not need to be increased, the hydrolysis rate can be increased by about 0.64% when the same amount of seed titanium liquid is added, and the brightness and whiteness are both improved, resulting in a very small increase in seed crystal cost, simple operation, and the ability to stabilize the hydrolysis quality of low-concentration titanium liquid.

[0024] 2. By adding a composite treatment agent to the hydrolysis system, on the one hand, the dispersion of the material in the hydrolysis system can be improved, so that the seed crystals can induce the titanium liquid to undergo more uniform and sufficient hydrolysis. On the other hand, the stability of the seed crystals can be enhanced, the activity of the seed crystals and the nucleation sites can be ensured, and the uniformity of the hydrolysis reaction can be promoted, thereby increasing the hydrolysis rate of the titanium liquid and improving the washing efficiency of the hydrolyzed metatitanic acid. DETAILED DESCRIPTION

[0025] The present invention will be further described below in conjunction with specific embodiments, but the examples do not limit the present invention in any form. Unless otherwise stated, the raw materials and reagents used in the examples of the present invention are conventionally purchased raw materials and reagents.

[0026] Example 1

[0027] A process for increasing the hydrolysis rate of titanium dioxide produced by the sulfuric acid process, comprising the following steps:

[0028] S1. Seed crystal preparation: Preheat a titanium solution with a concentration of 250 g / L and an F value of 2.1 and a sodium hydroxide solution with a mass concentration of 16% to 70° C., then disperse the titanium solution into the sodium hydroxide solution within 5 minutes, stirring at a speed of 350 r / min during the dispersion process, with an alkali-titanium ratio of 0.38, and mature at 102° C. for 5 minutes to obtain hydrolysis seed crystals;

[0029] S2. Hydrolysis: Preheat the hydrolysis titanium liquid with a concentration of 160g / L and an F value of 1.90 to 98°C, add hydrolysis seeds that are 3.5% of the mass of TiO2 in the hydrolysis titanium liquid to form a hydrolysis system, raise the temperature to boiling, and keep it slightly boiling. When the hydrolysis titanium liquid turns white, add a composite treatment agent for induction. The mass ratio of the composite treatment agent to TiO2 in the hydrolysis titanium liquid is 0.8%. After the induction is completed, continue to heat up and keep it slightly boiling for 2 hours, then add dilution water and maintain the system slightly boiling for 30 minutes, and the hydrolysis is completed.

[0030] Preparation of the composite treatment agent: 5 parts of ammonium carbonate, 5 parts of aluminum sulfate, and 5 parts of potassium sulfate were mixed and added to 10 parts of polyoxyethylene ether phosphate, and ultrasonically treated for 5 minutes.

[0031] Example 2

[0032] A process for increasing the hydrolysis rate of titanium dioxide produced by the sulfuric acid process, comprising the following steps:

[0033] S1. Seed crystal preparation: Preheat a titanium solution with a concentration of 200 g / L and an F value of 1.95 and a sodium hydroxide solution with a mass concentration of 10% to 80° C., then disperse the titanium solution into the sodium hydroxide solution within 6 minutes, stirring at a speed of 300 r / min during the dispersion process, with an alkali-titanium ratio of 0.26, and mature at 95° C. for 20 minutes to obtain hydrolysis seed crystals;

[0034] S2. Hydrolysis: Preheat the hydrolysis titanium liquid with a concentration of 180g / L and an F value of 1.88 to 95°C, add hydrolysis seeds that are 5% of the mass of TiO2 in the hydrolysis titanium liquid to form a hydrolysis system, raise the temperature to boiling, and keep it slightly boiling. When the hydrolysis titanium liquid turns white, add a composite treatment agent for induction. The mass ratio of the composite treatment agent to TiO2 in the hydrolysis titanium liquid is 0.5%. After the induction is completed, continue to heat up and keep it slightly boiling for 2 hours, then add dilution water and maintain the system slightly boiling for 30 minutes, and the hydrolysis is completed.

[0035] Preparation of the composite treatment agent: 8 parts of ammonium carbonate, 7 parts of aluminum sulfate, and 8 parts of potassium sulfate were mixed and added to 15 parts of polyoxyethylene ether phosphate, and ultrasonically treated for 8 minutes.

[0036] Example 3

[0037] A process for increasing the hydrolysis rate of titanium dioxide produced by the sulfuric acid process, comprising the following steps:

[0038] S1. Seed crystal preparation: Preheat a titanium solution with a concentration of 160 g / L and an F value of 2.25 and a sodium hydroxide solution with a mass concentration of 25% to 95° C., then disperse the titanium solution into the sodium hydroxide solution within 10 minutes, stirring at a speed of 350 r / min during the dispersion process, with an alkali-titanium ratio of 0.20, and mature at 102° C. for 50 minutes to obtain hydrolysis seed crystals;

[0039] S2. Hydrolysis: Preheat the hydrolysis titanium liquid with a concentration of 190g / L and an F value of 1.80 to 98°C, add hydrolysis seeds that are 2.5% of the mass of TiO2 in the hydrolysis titanium liquid to form a hydrolysis system, raise the temperature to boiling, and keep it slightly boiling. When the hydrolysis titanium liquid turns white, add a composite treatment agent for induction. The mass ratio of the composite treatment agent to TiO2 in the hydrolysis titanium liquid is 1%. After the induction is completed, continue to heat up and keep it slightly boiling for 2 hours, then add dilution water and maintain the system slightly boiling for 30 minutes, and the hydrolysis is completed.

[0040] Preparation of the composite treatment agent: 15 parts of ammonium carbonate, 10 parts of aluminum sulfate, and 10 parts of potassium sulfate were mixed and added to 20 parts of polyoxyethylene ether phosphate, and ultrasonically treated for 10 minutes.

[0041] Test Examples 1-5

[0042] The alkali concentration was the same as that in Example 1, the alkali-titanium ratios were 0.18, 0.25, 0.31, 0.38, and 0.41, respectively, and the rest of the treatment process was the same as that in Example 1.

[0043] Table 1 Test indicators

[0044] Alkali-Titanium ratio 0.18 0.25 0.31 0.38 0.41 Hydrolysis rate% 96.2 96.8 96.7 96.9 96.1 D 50 / μm 2.736 2.928 2.925 2.930 2.768

[0045] Test Examples 8-9

[0046] The alkali-titanium ratio is the same as that in Example 1, and the alkali concentrations are 10%, 15%, 18%, and 20%, respectively. The rest of the treatment process is the same as that in Example 1.

[0047] Table 2 Test indicators

[0048] Alkali concentration% 10 15 18 20 Hydrolysis rate% 96.1 96.9 96.8 95.8 <![CDATA[D 50 / μm]]> 2.828 3.023 3.014 2.856

[0049] Test Examples 10-13

[0050] The alkali concentration and alkali-titanium ratio were the same as those in Example 1. The amount of hydrolysis seed crystals added was 2.2%, 3%, 4%, and 10%. The rest of the treatment process was the same as that in Example 1.

[0051] Table 3 Test indicators

[0052] Seed addition % 2.2 3 4 10 Hydrolysis rate% 95.8 97 96.9 95.7 <![CDATA[D 50 / μm]]> 2.996 3.018 3.104 2.916

[0053] Test Example 14

[0054] The difference between this test example and Example 1 is that the composite treatment agent does not contain polyoxyethylene ether phosphate.

[0055] Test Example 15

[0056] The difference between this test example and Example 1 is that the composite treatment agent does not contain ammonium carbonate.

[0057] Test Example 16

[0058] The difference between this test example and Example 1 is that the composite treatment agent does not contain aluminum sulfate and potassium sulfate.

[0059] Table 4 Experimental indicators of Examples 1-3 and Test Examples 14-16

[0060] Group Example 1 Example 2 Example 3 Test Example 14 Test Example 15 Test Example 16 Hydrolysis rate% 97 96.9 96.9 96.1 96.3 96.2 <![CDATA[D 50 / μm]]> 2.931 2.985 3.128 2.715 2.732 2.741 brightness 95.5 95.3 95.1 94.2 94.5 94.6 Whiteness 93.8 93.5 93.5 90.3 91.2 91.5 Black pulp b value 0.17 0.19 0.18 0.28 0.31 0.30

[0061] According to Tables 1-4, by adopting the process of the present invention, the hydrolysis rate is higher than 96.5%, the brightness and whiteness are improved, the b value of the black slurry is reduced, and the hydrolysis quality of low-concentration titanium liquid can be stabilized.

[0062] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A process for increasing the hydrolysis rate of titanium dioxide produced by the sulfuric acid process, characterized in that: The following steps are involved: Seed crystal preparation: Preheat titanium liquid with a concentration of 160-250g / L and alkali solution with a mass concentration of 10-25%, respectively, then disperse the titanium liquid in the alkali solution with an alkali-titanium ratio of 0.20-0.38, and obtain hydrolysis seed crystals after aging; Hydrolysis: Preheat the hydrolysis titanium liquid with a concentration of 160-190g / L, add hydrolysis seeds of 2.5-5% of the mass of TiO2 in the hydrolysis titanium liquid to form a hydrolysis system, heat to boiling, keep it slightly boiling, wait until the hydrolysis titanium liquid turns white, add a composite treatment agent for induction, continue to heat and keep it slightly boiling after the induction, then add dilution water and maintain the system slightly boiling, and the hydrolysis is completed.

2. The process for increasing the hydrolysis rate of titanium dioxide produced by the sulfuric acid process according to claim 1, wherein: The F value of the titanium liquid prepared by the seed crystal is 1.95-2.

25.

3. The process for improving the hydrolysis rate of titanium dioxide produced by the sulfuric acid process according to claim 1, wherein: When preparing the seed crystals, the preheating temperature is 70-95°C, the aging temperature is 80-102°C, and the aging time is 5-50 minutes.

4. The process for increasing the hydrolysis rate of titanium dioxide produced by the sulfuric acid process according to claim 1, wherein: During seed crystal preparation, the titanium liquid is dispersed into the alkaline solution within 5-10 minutes, and is stirred at a speed of 300-350 r / min during the dispersion process.

5. The process for increasing the hydrolysis rate of titanium dioxide produced by the sulfuric acid process according to claim 1, wherein: The F value of the hydrolyzed titanium solution is 1.80-1.

95.

6. The process for improving the hydrolysis rate of titanium dioxide produced by the sulfuric acid process according to any one of claims 1 to 5, characterized in that: The mass ratio of the composite treatment agent to TiO2 in the hydrolyzed titanium solution is 0.5-1.0%.

7. The process for increasing the hydrolysis rate of titanium dioxide produced by the sulfuric acid process according to claim 6, wherein: The composite treatment agent comprises, by weight, 5-15 parts of ammonium carbonate, 5-10 parts of aluminum sulfate, 5-10 parts of potassium sulfate and 10-20 parts of polyoxyethylene ether phosphate.

8. The process for increasing the hydrolysis rate of titanium dioxide produced by the sulfuric acid process according to claim 7, wherein: The preparation method of the composite treatment agent is as follows: ammonium carbonate, aluminum sulfate and potassium sulfate are mixed, added into polyoxyethylene ether phosphate, and ultrasonically treated for 5-10 minutes.