Comprehensive hydrolysis process for high-concentration and low-concentration titaniferous solution

Abstract

The invention provides a comprehensive hydrolysis process for high-concentration and low-concentration titaniferous liquid, and relates to the technical field of titaniferous liquid hydrolysis. The hydrolysis process comprises the following steps: an initial stage: adding a high-concentration titanium solution into an alkali solution to form a primary seed crystal; a primary boiling stage: adding the primary seed crystal into the high-concentration titanium solution, heating to boil, carrying out microwave treatment, and stopping stirring and heating when an ash point is reached; a primary boiling keeping stage: adding a low-concentration titanium solution at the temperature 1-5 DEG C lower than the boiling temperature; a secondary boiling raising stage: continuously raising the temperature until boiling, and supplementing the low-concentration titanium liquid; a first adjusting agent and a second adjusting agent are added in the initial stage and the first boiling keeping stage respectively, the first adjusting agent is sodium salt, and the second adjusting agent is citric acid, ammonium persulfate and sodium hexametaphosphate. The process can reduce the use amount of the high-concentration titanium solution, reduce energy consumption and cost, improve the quality of the seed crystal and improve the hydrolysis rate.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of titanium liquid hydrolysis, in particular to a high and low concentration titanium liquid comprehensive hydrolysis process. BACKGROUND

[0002] As an important inorganic pigment, the hydrolysis process in the production process of titanium dioxide directly affects the particle size distribution, optical properties and energy efficiency of the product. The traditional sulfuric acid method for producing titanium dioxide adopts autogenous seed hydrolysis method, but has the following problems: (1) high concentration titanium liquid dependence: the existing autogenous seed process requires high concentration of titanium liquid, which needs to be concentrated to increase the concentration, resulting in increased steam energy consumption (1.2-2.0 tons of steam are consumed per ton of titanium dioxide). (2) Limited application of low concentration titanium liquid: when low concentration titanium liquid is directly hydrolyzed, the generation of crystal seeds is insufficient, which easily leads to low hydrolysis rate (<90%) and uneven distribution of metatitanic acid particle size, affecting the color reduction power (<120) and brightness (<94.5%) of titanium dioxide.

[0003] To solve the above problems, the existing technology attempts to improve the bottom water formula (such as replacing pure water with hot alkali solution) or optimize the feeding rate, but it is still difficult to balance the crystal seed efficiency and energy consumption of low concentration titanium liquid. Therefore, an innovative process is needed that can integrate the advantages of high and low concentration titanium liquid, reduce the concentration energy consumption and improve the crystal seed quality. SUMMARY

[0004] The purpose of the present application is to provide a high and low concentration titanium liquid comprehensive hydrolysis process, which can reduce the use amount of high concentration titanium liquid, reduce energy consumption and cost, and also improve the crystal seed quality and increase the hydrolysis rate.

[0005] The present application is realized by the following technical solutions:

[0006] A high and low concentration titanium liquid comprehensive hydrolysis process, comprising the following steps:

[0007] Initial stage: adding high concentration titanium liquid to alkali solution to form primary crystal seeds;

[0008] First boiling stage: adding primary crystal seeds to high concentration titanium liquid, heating to boiling, microwave treatment, stopping stirring and heating when reaching the gray point;

[0009] Boiling stage: adding low concentration titanium liquid at 1-5℃ lower than the boiling temperature;

[0010] Second boiling stage: continuing to heat to boiling and adding low concentration titanium liquid;

[0011] It also includes adding a first adjusting agent and a second adjusting agent in the initial stage and the boiling stage, respectively, the first adjusting agent is a sodium salt, and the second adjusting agent is citric acid, ammonium persulfate and sodium hexametaphosphate.

[0012] Preferably, the concentration of the high-concentration titanium solution is 160-250 g / L, the concentration of the alkali solution is 100-200 g / L, the alkali-to-titanium ratio of the high-concentration titanium solution to the alkali solution is 0.20-0.38, and the high-concentration titanium solution and the alkali solution are each preheated to 70-96°C before mixing. During the pretreatment process, the stirring speed is 5-10 r / min to reduce turbulent shear forces and prevent premature agglomeration of the seed crystals.

[0013] Preferably, during microwave treatment, the power is 300-500 W, the frequency is 2.45 GHz, and the time is 10-15 min.

[0014] Preferably, the concentration of the low-concentration titanium liquid is 120-150 g / L, and the low-concentration titanium liquid is preheated to 60-85° C. before being added.

[0015] Preferably, the amount of primary seed crystals added is 2-4% of the total mass of hydrolyzed titanium, the total amount of low-concentration titanium liquid added is 10-30% of the total mass of hydrolyzed titanium, and the mass ratio of the low-concentration titanium liquid in the first boiling stage and the second boiling stage is 1:0.4-0.8.

[0016] Preferably, the heating rate in the first boiling stage is 0.5°C / min; the heating rate in the second boiling stage is 1°C / min, and the micro-boiling treatment is maintained for 60-80 minutes.

[0017] Preferably, during the boiling stage, a 365nm ultraviolet light source is simultaneously introduced to irradiate the hydrolysis system and maintained at this temperature for 30-60 minutes. The ultraviolet light source can stimulate the formation of hydroxyl radicals on the surface of the titanium particles, which then form complexes with organic acids in the solution, forming a dynamic dispersion interface and improving the dispersibility of the titanium solution.

[0018] Preferably, during the second boiling stage, after adding low-concentration titanium solution, the sulfuric acid concentration in the system is adjusted to 0.6±0.02 mol / L. By adjusting the sulfuric acid concentration, uniform growth of seed crystals can be induced, and non-uniform nucleation caused by local over-alkalinity can be prevented.

[0019] Preferably, the mass ratio of the first adjusting agent to the high-concentration titanium liquid is 1:8-12, and the sodium salt is sodium sulfate, sodium chloride or sodium sulfonate.

[0020] Preferably, the mass ratio of the second adjusting agent to the low-concentration titanium liquid is 1:18-22, and the mass ratio of the citric acid, ammonium persulfate and sodium hexametaphosphate is 1-3:1:1.

[0021] The technical solution of the present invention has at least the following advantages and beneficial effects:

[0022] In the initial stage, the high concentration titanium liquid is mixed with alkali solution to form primary seeds, which provide growth points for subsequent hydrolysis. However, the high concentration titanium liquid has high supersaturation, and the crystal nucleus generates rapidly. Titanium oxy groups (such as [Ti(OH)2] 2+ ) are prone to form agglomerates due to van der Waals forces or hydrogen bonding during nucleation. To avoid premature agglomeration of the seeds, a first adjusting agent is used for treatment. Sodium salt can increase the ion concentration in the solution, compress the double electric layer around the colloidal particles, reduce the electrostatic repulsion between particles, thereby inhibiting excessive agglomeration, and also inhibiting local supersaturation, reducing non-uniform nucleation, and promoting directional generation of crystal nuclei.

[0023] The first boiling, the second boiling and the third boiling are transition stages. By adding low concentration titanium liquid to gradually reduce the concentration of the system, the concentration gradient of the titanium liquid during hydrolysis is reasonably controlled, the amount of high concentration titanium liquid is reduced, and the concentration gradient is used to induce the growth of the seeds in stages. This can not only reduce the initial concentration requirement, but also improve the uniformity of the seeds to improve the quality of the seeds. However, the stability of the seeds may decrease when the concentration gradient changes, so a second adjusting agent is used for treatment. Ammonium persulfate decomposes in acidic titanium liquid to generate sulfate radicals, which oxidize Ti 3+ to Ti 4+ , and generate active Ti 3+ sites, enhancing the hydrolysis activity of the titanium liquid. The presence of Ti 3+ / Ti 4+ redox pairs can adjust the hydrolysis equilibrium of titanium oxy groups, reduce the nucleation energy barrier, and promote the effective hydrolysis of low concentration titanium liquid. Citric acid can chelate Ti 4+ , delay the hydrolysis rate, avoid rapid growth of particles, improve particle uniformity, and reduce secondary agglomeration. Sodium hexametaphosphate can prevent the agglomeration of hydrolysis products, optimize particle distribution, improve seed activity, and increase hydrolysis rate.

[0024] The first boiling stage initiates the hydrolysis reaction to promote seed growth, providing growth points for subsequent hydrolysis. In the second boiling stage, the seeds are allowed to grow fully and stabilize, avoiding rapid hydrolysis leading to uneven particles. In the third boiling stage, the hydrolysis reaction is accelerated to promote complete hydrolysis of titanate to generate hydrated titanium dioxide, while the product particle size and crystal form are controlled. During the hydrolysis process, the ion system composed of the second adjusting agent can maintain the pH of the hydrolysis system in the range of 2.5-3.5, avoiding excessive local acidity leading to corrosion of the seeds. At the same time, the reaction of the second adjusting agent with Ti 3+ / Ti 4+ can expose the active sites of titanium oxy groups ([Ti(OH)] + ), reducing the activation energy of the hydrolysis of low concentration titanium liquid from 85 kJ / mol in traditional processes to 72 kJ / mol. The pre-dispersed seeds act as a heterogeneous nucleation template, reducing the nucleation energy barrier of low concentration titanium liquid, and inducing it to deposit on the surface of the seeds in an "epitaxial growth" mode rather than generating new crystal nuclei.

[0025] The dielectric heating with microwave selectively acts on polar molecules (such as H2O and titanium oxygen groups), increases the local reaction temperature, and promotes the activation energy reduction of the hydrolysis reaction. The microwave treatment can also promote the directional arrangement of the titanium liquid molecules through physical action, shorten the crystal nucleus formation time, and inhibit the crystal seed agglomeration. The later high-temperature micro-boiling state accelerates the hydrolysis reaction kinetics, while the titanium liquid supersaturation degree is reduced at low concentration, inhibiting the generation of new crystal nuclei and promoting the directional growth of the existing crystal seeds, to form metatitanic acid particles with uniform particle size. DETAILED DESCRIPTION

[0026] The application will be further described below in conjunction with the specific embodiments, but the embodiments do not limit the application in any form. Unless otherwise specified, the raw materials and reagents used in the embodiments of the application are commercially available.

[0027] Example 1

[0028] A high and low concentration titanium liquid comprehensive hydrolysis process, comprising the following steps:

[0029] Initial stage: the high concentration titanium liquid with a concentration of 250 g / L and the lye with a concentration of 200 g / L are preheated to 96℃ respectively, then the high concentration titanium liquid is added to the lye, the lye-titanium ratio is 0.38, the stirring speed is 10 r / min, the sodium sulfate is added while stirring, the mass ratio of the first adjusting agent to the high concentration titanium liquid is 1:12, and the primary crystal seeds are formed;

[0030] Boiling stage: the primary crystal seeds are added to the hydrolysis kettle according to 4% of the total titanium mass for hydrolysis, then added to the high concentration titanium liquid with a concentration of 200 g / L preheated to 80℃, and heated to boiling, the heating rate is 0.5℃ / min, treated by microwave with a power of 500W and a frequency of 2.45GHz for 15min, and then the stirring and heating are stopped when the gray point is reached;

[0031] Boiling stage: the low concentration titanium liquid with a concentration of 120 g / L is added at 5℃ lower than the boiling temperature, and the second adjusting agent is added, the mass ratio of the second adjusting agent to the low concentration titanium liquid is 1:22, the second adjusting agent includes citric acid, ammonium persulfate and sodium hexametaphosphate with a mass ratio of 1:1:1, the temperature is maintained for 60min, and the ultraviolet light source with a wavelength of 365nm is introduced to irradiate the hydrolysis system at the same time;

[0032] Boiling stage: continue to heat to boiling, the heating rate is 1℃ / min, supplement the low concentration titanium liquid, adjust the sulfuric acid concentration of the system to 0.6±0.02mol / L, add water, and maintain micro-boiling for 80min.

[0033] The total amount of the low concentration titanium liquid is 30% of the total titanium mass for hydrolysis, and the mass ratio of the low concentration titanium liquid in the first holding and boiling stage and the second boiling stage is 1:0.4. The low concentration titanium liquid in each stage is added within 20 minutes.

[0034] Example 2

[0035] A high and low concentration titanium liquid comprehensive hydrolysis process, comprising the following steps:

[0036] The initial stage: the high concentration titanium liquid with a concentration of 200 g / L and the alkali liquid with a concentration of 150 g / L are preheated to 85℃ respectively, then the high concentration titanium liquid is added to the alkali liquid for pretreatment, the alkali-titanium ratio is 0.25, the stirring speed is 5 r / min, sodium chloride is added while stirring, the mass ratio of the first adjusting agent to the high concentration titanium liquid is 1:8, and the primary crystal seeds are formed;

[0037] The first boiling stage: the primary crystal seeds are added to the hydrolysis kettle according to 2% of the total titanium mass for hydrolysis, then added to the high concentration titanium liquid with a concentration of 180 g / L preheated to 70℃, and heated to boiling with a heating rate of 0.5℃ / min, treated by microwave with a power of 300 W and a frequency of 2.45 GHz for 10 minutes, and then the stirring and heating are stopped when the gray point is reached;

[0038] The first holding and boiling stage: the low concentration titanium liquid with a concentration of 130 g / L is added 1℃ below the boiling temperature, and the second adjusting agent is added, the mass ratio of the second adjusting agent to the low concentration titanium liquid is 1:18, the second adjusting agent includes citric acid, ammonium persulfate and sodium hexametaphosphate with a mass ratio of 2:1:1, the temperature is maintained for 30 minutes, and the ultraviolet light source with a wavelength of 365 nm is introduced to irradiate the hydrolysis system at the same time;

[0039] The second boiling stage: the temperature is continuously increased to boiling with a heating rate of 1℃ / min, the low concentration titanium liquid is supplemented, the sulfuric acid concentration of the system is adjusted to 0.6±0.02 mol / L, water is added, and the system is maintained at a slight boiling state for 60 minutes.

[0040] The total amount of the low concentration titanium liquid is 10% of the total titanium mass for hydrolysis, and the mass ratio of the low concentration titanium liquid in the first holding and boiling stage and the second boiling stage is 1:0.6. The low concentration titanium liquid in each stage is added within 20 minutes.

[0041] Example 3

[0042] A high and low concentration titanium liquid comprehensive hydrolysis process, comprising the following steps:

[0043] Initial stage: high concentration titanium solution with a concentration of 160 g / L and alkali solution with a concentration of 100 g / L are preheated to 70℃ respectively, then the high concentration titanium solution is added to the alkali solution for pretreatment, the alkali-titanium ratio is 0.20, the stirring speed is 8 r / min, sodium sulfonate is added while stirring, the mass ratio of the first adjusting agent to the high concentration titanium solution is 1:10, and the primary crystal seeds are formed;

[0044] Boiling stage: the primary crystal seeds are added to the hydrolysis kettle according to 3% of the total titanium mass, then added to the high concentration titanium solution with a concentration of 190 g / L preheated to 96℃, and then heated to boiling, the heating rate is 0.5℃ / min, treated by microwave with a power of 400W and a frequency of 2.45GHz for 12min, and then the stirring and heating are stopped when the gray point is reached;

[0045] Boiling stage: the low concentration titanium solution with a concentration of 150 g / L is added at 3℃ lower than the boiling temperature, then the second adjusting agent is added, the mass ratio of the second adjusting agent to the low concentration titanium solution is 1:20, the second adjusting agent includes citric acid, ammonium persulfate and sodium hexametaphosphate with a mass ratio of 3:1:1, the temperature is maintained for 40min, and the ultraviolet light source with a wavelength of 365nm is introduced to irradiate the hydrolysis system at the same time;

[0046] Boiling stage: the low concentration titanium solution is continuously added to adjust the sulfuric acid concentration of the system to 0.6±0.02 mol / L, water is added, and the system is maintained at a low boiling state for 70min.

[0047] The total amount of the low concentration titanium solution is 20% of the total titanium mass, the mass ratio of the low concentration titanium solution in the boiling stage and the second boiling stage is 1:0.8, and the low concentration titanium solution in each stage is added within 20min.

[0048] Comparative Example 1

[0049] The difference between this comparative example and Example 1 is that the low concentration titanium solution is added completely in the boiling stage.

[0050] Comparative Examples 2-3

[0051] The amount of the primary crystal seeds is 1% and 10% of the total titanium mass respectively, and the rest is the same as Example 1.

[0052] Comparative Examples 4-5

[0053] The total amount of the low concentration titanium solution is 5% and 40% of the total titanium mass respectively, and the rest is the same as Example 1.

[0054] Comparative Example 6

[0055] The difference between this comparative example and Example 1 is that no microwave treatment is performed.

[0056] Comparative Example 7

[0057] The difference between the present comparative example and Example 1 is that the hydrolysis system is not irradiated by the ultraviolet light source.

[0058] Comparative Example 8

[0059] The difference between the present comparative example and Example 1 is that the first adjusting agent is not added.

[0060] Comparative Example 9

[0061] The difference between the present comparative example and Example 1 is that the second adjusting agent is not added.

[0062] Comparative Example 10

[0063] The difference between the present comparative example and Example 1 is that the second adjusting agent only includes citric acid.

[0064] Comparative Example 11

[0065] The difference between the present comparative example and Example 1 is that the second adjusting agent only includes ammonium persulfate.

[0066] The test data of the examples and comparative examples are recorded, and the results are as follows:

[0067] Table 1 Test results

[0068] Group Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Hydrolysis rate% 96 95.9 95.7 94.68 94.75 94.81 94.98 D10(μm) 1.879 1.948 1.891 1.109 1.039 1.309 1.349 D50(μm) 3.133 3.39 3.453 3.642 3.715 2.712 2.851 D90(μm) 5.333 5.172 5.701 5.882 5.918 4.382 4.458 Pitch (μm) 1.162 0.951 1.103 1.264 1.218 1.294 1.285 Blue light whiteness 92.9 91.9 92.4 90.7 90.7 90.7 91.7 brightness 95.2 95.0 95.1 92.6 92.1 91.7 92.5 Tinting power ≥130 ≥130 ≥130 ≥120 ≥120 ≥120 ≥120 Group Comparative Example 5 Comparative Example 6 Comparative Example 7 Comparative Example 8 Comparative Example 9 Comparative Example 10 Comparative Example 11 Hydrolysis rate% 94.5 95.0 95.3 94.12 94.35 94.51 94.68 D10(μm) 1.579 1.436 1.299 1.266 1.325 1.471 1.352 D50(μm) 4.133 3.179 2.961 2.888 3.025 3.289 3.173 D90(μm) 5.933 5.566 5.097 4.896 5.118 5.677 5.487 Pitch (μm) 1.195 1.299 1.283 1.257 1.254 1.279 1.303 Blue light whiteness 90.9 92.5 92.4 89.7 90.1 91.2 91.5 brightness 93.2 94.5 95.1 91.6 90.7 92.2 92.8 Tinting power ≥120 ≥120 ≥120 ≤120 ≤120 ≤120 ≤120

[0069] According to Table 1, compared with the comparative examples, the hydrolysis rate, blue light whiteness, brightness and color reduction of Examples 1-3 are higher, the crystal seed particle size distribution is narrow, and the product uniformity is high.

[0070] The above only is the preferred embodiment of the present application, and is not used to limit the present application, for the person skilled in the art, the present application can have various changes and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. A comprehensive hydrolysis process for high and low concentration titanium liquids, characterized by: The following steps are involved: Initial stage: adding high concentration titanium liquid into alkaline solution to form primary crystal seeds; First boiling stage: add primary seed crystals to high-concentration titanium liquid, heat to boiling, and microwave treatment until the gray point is reached, then stop stirring and heating; Maintaining the boiling stage: adding low-concentration titanium liquid at 1-5℃ below the boiling temperature; Second boiling stage: continue to heat up to boiling and add low-concentration titanium liquid; The method further includes adding a first adjusting agent and a second adjusting agent in the initial stage and the first boiling maintaining stage respectively, wherein the first adjusting agent is sodium salt and the second adjusting agent is citric acid, ammonium persulfate and sodium hexametaphosphate.

2. The comprehensive hydrolysis process of high and low concentration titanium liquid according to claim 1, characterized in that: The concentration of the high-concentration titanium liquid is 160-250 g / L, the concentration of the alkali liquid is 100-200 g / L, the alkali-titanium ratio of the high-concentration titanium liquid and the alkali liquid is 0.20-0.38, and the high-concentration titanium liquid and the alkali liquid are preheated to 70-96° C. before mixing.

3. The comprehensive hydrolysis process of high and low concentration titanium liquid according to claim 1, characterized in that: During microwave treatment, the power is 300-500 W, the frequency is 2.45 GHz, and the time is 10-15 minutes.

4. The comprehensive hydrolysis process of high and low concentration titanium liquid according to claim 1, characterized in that: The concentration of the low-concentration titanium liquid is 120-150 g / L, and the low-concentration titanium liquid is preheated to 60-85°C before being added.

5. The comprehensive hydrolysis process of high and low concentration titanium liquid according to claim 4, characterized in that: The amount of primary seed added is 2-4% of the total mass of hydrolyzed titanium, the total amount of low-concentration titanium liquid added is 10-30% of the total mass of hydrolyzed titanium, and the mass ratio of low-concentration titanium liquid in the first boiling stage and the second boiling stage is 1:0.4-0.

8.

6. The comprehensive hydrolysis process of high and low concentration titanium liquid according to claim 5, characterized in that: The heating rate in the first boiling stage is 0.5°C / min; the heating rate in the second boiling stage is 1°C / min, and the micro-boiling treatment is maintained for 60-80 minutes.

7. The comprehensive hydrolysis process of high and low concentration titanium liquid according to claim 6, characterized in that: During the boiling-maintaining stage, a UV light source with a wavelength of 365 nm is simultaneously introduced to irradiate the hydrolysis system, and the temperature is maintained for 30-60 minutes.

8. The comprehensive hydrolysis process of high and low concentration titanium liquid according to claim 1, characterized in that: During the second boiling stage, after adding low-concentration titanium liquid, the sulfuric acid concentration in the system was adjusted to 0.6±0.02mol / L.

9. The comprehensive hydrolysis process of high and low concentration titanium liquid according to claim 1, characterized in that: The mass ratio of the first adjusting agent to the high-concentration titanium liquid is 1:8-12, and the sodium salt is sodium sulfate, sodium chloride or sodium sulfonate.

10. The comprehensive hydrolysis process of high and low concentration titanium liquids according to claim 1, characterized in that: The mass ratio of the second adjusting agent to the low-concentration titanium liquid is 1:18-22, and the mass ratio of the citric acid, ammonium persulfate and sodium hexametaphosphate is 1-3:1:1.