Titanium dioxide calcination seed crystal preparation method and titanium dioxide calcination process thereof

Abstract

The invention relates to a titanium dioxide calcining seed crystal preparation method and a titanium dioxide calcining process thereof, belongs to the technical field of titanium dioxide production, and solves the technical problems that the cost is too high or the seed crystal and subsequently calcined titanium dioxide are unstable due to selection of liquid caustic soda in the existing titanium dioxide seed crystal preparation process. The seed crystal preparation method comprises the following steps of alkali dissolution, alkali dissolution filter pressing and acid dissolution, in the alkali dissolution step, a 48% NaOH solution and a 32% NaOH solution are mixed, and the volume ratio of the 48% NaOH solution to the 32% NaOH solution is 1: 0.5-1: 0.8; the titanium dioxide production process comprises the following steps: bleaching, wherein the calcined seed crystal is added in the bleaching process; s2, washing for the second time; s3, salt treatment; s4, carrying out pre-kiln filter pressing; and S5, calcining. The method has the advantages that the prepared calcined seed crystal and titanium dioxide are good in quality, low in cost and the like.

Description

Technical Field

[0001] This invention relates to the field of titanium dioxide preparation technology, specifically to a method for preparing titanium dioxide calcined seed crystals and its calcination process. Background Technology

[0002] In the preparation of titanium dioxide, seed crystals are often prepared to promote subsequent sintering. Liquid alkali is used in the seed crystal preparation process. The selection of liquid alkali needs to consider the process requirements of seed crystal preparation, its impact on the quality of the sintered titanium dioxide, and cost.

[0003] Current research on liquid alkali faces several challenges: either using high-concentration NaOH solutions leads to excessively high costs, or using too low a concentration results in unstable seed crystals and subsequent calcined titanium dioxide.

[0004] Obtaining low-cost and stable-quality seed crystals is a technical problem that urgently needs to be solved in this field and has important practical significance. Summary of the Invention

[0005] The technical problem to be solved by this invention is that the selection of liquid alkali in the existing titanium dioxide seed preparation process either leads to excessively high costs or instability of the seed crystals and the titanium dioxide after subsequent calcination. Therefore, a method for preparing titanium dioxide calcination seed crystals and its titanium dioxide calcination process are proposed.

[0006] This invention is achieved through the following technical solution:

[0007] A method for preparing titanium dioxide calcined seed crystals includes the following steps: alkali dissolution, alkali dissolution pressure filtration and acid dissolution, wherein the alkali dissolution is performed by mixing 48% NaOH solution and 32% NaOH solution.

[0008] The present invention preferably provides a method for preparing titanium dioxide calcined seed crystals, wherein the volume ratio of the 48% NaOH solution to the 32% NaOH solution is 1:0.5-1:0.8, preferably 1:0.6.

[0009] The concentrated alkali used for calcination seed preparation requires a concentration ≥550g / L. Using 32% liquid alkali alone cannot meet this concentration requirement, while using 48% liquid alkali alone is not only costly, but its concentration also fluctuates between 600g / L and 750g / L, which may cause the material to dry out and affect the quality of the calcined seed. In order to reduce costs while ensuring seed quality, it is considered to use a mixture of 48% liquid alkali and 32% liquid alkali to prepare a dilute alkali for calcination seed preparation. The dilute alkali prepared by mixing 48% liquid alkali with 32% liquid alkali has a stable concentration, which is stable at around 600g / L, resulting in more stable quality of the prepared calcined seed.

[0010] This invention preferably provides a method for preparing titanium dioxide calcined seed crystals, wherein the alkali dissolution includes the following steps:

[0011] Step 1.1: Add liquid alkali to the liquid alkali preheating tank for heating;

[0012] Step 1.2: Add metatitanic acid to the heated liquid alkali;

[0013] Step 1.3: Carry out the alkali dissolution reaction under stirring and heating conditions. After the maturation is completed, the alkali-soluble slurry is obtained and cooled for later use. Preferably, the temperature is cooled to 55-60℃.

[0014] Preferably, the heating temperature is 109–111°C;

[0015] Preferably, the mass ratio of titanium dioxide in the alkaline solution to the titanate washing slurry is 1.0-2.0, and more preferably 1.45.

[0016] This invention preferably provides a method for preparing titanium dioxide calcined seed crystals, wherein the alkali dissolution and pressure filtration includes the following steps:

[0017] Step 2.1: Pump the cooled alkali-soluble slurry into a filter press for filtration;

[0018] Step 2.2: Wash with demineralized water;

[0019] Step 2.3: Add the washed filter cake to the pulping tank for later use.

[0020] Preferably, the washing process combines a center wash and a side wash, specifically a center wash of 20 minutes and a side wash of 150-180 minutes.

[0021] This invention preferably provides a method for preparing titanium dioxide calcined seed crystals, wherein the acid dissolution includes the following steps:

[0022] Step 3.1: Add the slurry from the pulping tank to the acid dissolving tank, and add hydrochloric acid to heat and neutralize;

[0023] Step 3.2: After the pH value reaches 2.7~3.0, perform a second heating;

[0024] Step 3.3: Add hydrochloric acid after the second heating to perform gelation.

[0025] Preferably, in step 3.1, the temperature rise and neutralization specifically involves raising the temperature to 60°C at a rate of 1°C / min, and in step 3.2, raising the temperature a second time to 101±2°C.

[0026] Preferably, during the acid dissolution process, the HCl concentration is controlled at 15–30 g / L.

[0027] The present invention preferably provides a method for preparing calcined titanium dioxide seed crystals, wherein the method further includes: diluting the solution according to the concentration after the gelation is completed to obtain calcined seed crystals.

[0028] A titanium dioxide calcination process includes the following steps:

[0029] S1: Bleaching, wherein the above-mentioned calcined seed crystals are added during the bleaching process;

[0030] S2: Filter and wash the metatitanic acid slurry after adding calcined seed crystals and bleaching in S1;

[0031] S3: Salt treatment

[0032] The metatitanic acid after the second washing in S2 was pulped, and then potassium hydroxide, phosphoric acid and aluminum sulfate were added and matured.

[0033] S4: The metatitanic acid slurry that has been salt-treated in S3 is filtered before the kiln to obtain filter cake.

[0034] S5: Calcine the filter cake obtained from the pre-kiln pressure filtration in S4.

[0035] The present invention preferably describes a titanium dioxide calcination process, wherein in step S1, the amount of seed crystals added is 2-5% of the metatitanic acid slurry.

[0036] The present invention preferably describes a titanium dioxide calcination process, wherein in step S4, the P2O5 content of the filter cake from the pre-kiln pressure filter is 0.18-0.22%, the Al2O3 content is 0.23-0.29%, and the K2O content is 0.23-0.27%.

[0037] The present invention has the following advantages and beneficial effects:

[0038] 1. This invention uses a mixture of 48% liquid alkali and 32% liquid alkali to prepare a dilute alkali for use in the preparation of calcined seed crystals. The concentration of the mixed liquid alkali is stable at over 550 g / L. The dilute alkali prepared by mixing 48% liquid alkali with 32% liquid alkali has a stable concentration, resulting in more stable quality of the prepared calcined seed crystals.

[0039] 2. When the calcined seed crystals prepared by this invention are used in the titanium dioxide calcination process, the use of 48% liquid alkali and 32% liquid alkali to prepare dilute alkali reduces the occurrence of dry pot materials and improves product quality. Furthermore, the 32% liquid alkali is cheaper, reducing the cost of seed crystal production. This can improve the quality of finished products while reducing the cost of finished products, thus achieving cost reduction and efficiency improvement. Attached Figure Description

[0040] The accompanying drawings, which are included to provide a further understanding of embodiments of the invention and form part of this application, do not constitute a limitation thereof. In the drawings:

[0041] Figure 1 This is a flowchart illustrating the preparation process of the calcined seed crystals of this invention. Detailed Implementation

[0042] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings. The illustrative embodiments and descriptions of the present invention are only used to explain the present invention and are not intended to limit the present invention.

[0043] Example 1

[0044] A method for preparing titanium dioxide calcined seed crystals includes the following steps:

[0045] Step 1: Alkali dissolution

[0046] The qualified metatitanic acid second washing slurry is pumped to the metatitanic acid high-level tank, while the liquid alkali is pumped to the liquid alkali preheating tank. First, the calculated amount of liquid alkali is put into the alkali dissolving tank for heating, and then metatitanic acid is added. The alkali dissolution reaction is carried out under stirring and heating conditions. After the maturation is completed, the alkali-dissolved slurry is transferred to the alkali-dissolved slurry cooling tank to cool down to 55-60℃ for later use. The alkali-dissolved slurry is the sodium titanate slurry.

[0047] The liquid alkali was a mixture of 32% NaOH solution and 48% NaOH solution, with a volume ratio of 0.6:1. The mass ratio of the alkali solution to titanium dioxide in the secondary titanate washing slurry was 1.45. The stirring speed was 65 rpm, and the heating temperature was 109–111 °C. The Fe content in the secondary titanate washing slurry was less than 30 ppm, and the total titanium concentration was 340–370 g / L. The aging time was 90 min.

[0048] Step 2: Alkali dissolution and pressure filtration

[0049] After the slurry in the alkali-soluble slurry cooling tank is cooled, it is pumped into the alkali-soluble filter press for washing. The filtrate is sent to the titanium recovery section. After the feed is completed, demineralized water is added for washing. The wash water is sent to the calcination tail gas treatment section. The washing adopts a combination of central washing and side washing, specifically 20 minutes for central washing and 150-180 minutes for side washing. After washing, the filter cake is placed in the pulping tank for later use.

[0050] Step 3: Acid dissolution

[0051] Sodium titanate slurry in the alkali dissolution slurry tank is pumped to the sodium titanate high-level tank, and then a certain amount of sodium titanate slurry is put into the acid dissolution tank. Calculated hydrochloric acid is added and the temperature is raised to 60°C at a rate of 1°C / min for neutralization, wherein the acid-to-titanium mass ratio is 0.15–0.17.

[0052] Once the pH reaches 2.7-3.0, the temperature is raised again to 101±2℃, and hydrochloric acid is added for gelation. The mass ratio of gelation acid to titanium is 0.20-0.25. After gelation, a sample is taken to measure the concentration, and dilution water is added to obtain calcined seed crystals. After seed crystal preparation is complete, qualified seed crystals are placed in a seed crystal storage tank for later use.

[0053] Example 2

[0054] The difference between this embodiment and Embodiment 1 is that the volume ratio of the 32% NaOH solution to the 48% NaOH solution is 0.5:1.

[0055] Example 3

[0056] The difference between this embodiment and Embodiment 1 is that the volume ratio of the 32% NaOH solution to the 48% NaOH solution is 0.8:1.

[0057] Comparative Example 1

[0058] The difference between this comparative example and Example 1 is that the volume ratio of the 32% NaOH solution and the 48% NaOH solution in the liquid alkali is different, specifically 0.3:1.

[0059] Comparative Example 2

[0060] The difference between this comparative example and Example 1 is that the volume ratio of the 32% NaOH solution and the 48% NaOH solution in the liquid alkali is different, specifically 1:1.

[0061] Comparative Example 3

[0062] The difference between this comparative example and Example 1 is that the volume ratio of the 32% NaOH solution and the 48% NaOH solution in the liquid alkali is different, specifically 2:1.

[0063] Comparative Example 4

[0064] The difference between Comparative Example 4 and Example 1 is that only 48% NaOH is used in the liquid alkali.

[0065] The test results of calcined seed crystals in different embodiments and comparative examples are shown in Table 1 below.

[0066] Table 1

[0067]

[0068] As can be seen from Table 1 above:

[0069] When 32% NaOH and 48% NaOH are mixed in a suitable ratio, as shown in Examples 1 and 2, not only can the activity of the seed crystals be improved, but the phenomenon of material drying out can also be prevented.

[0070] When the concentration of alkali solution is too high, such as in Comparative Example 4 where only 48% NaOH is used, the filtration efficiency will be reduced and the amount of alkali residue after washing will be large. When the concentration of alkali solution is too low, such as in Comparative Examples 2 and 3, the filter cake will be loose and the washing effect will be poor, which will increase the subsequent neutralization consumption. At the same time, too high a concentration of alkali solution will also cause the material to dry out.

[0071] When the 32% NaOH ratio is too high, as shown in Comparative Examples 2 and 3, it will cause a significant reduction in the activity of the seed crystals.

[0072] Example 4

[0073] A process for preparing titanium dioxide, wherein the calcined seed crystals from Example 1 are used in the preparation of titanium dioxide.

[0074] Includes the following steps:

[0075] S1: Bleaching and addition of seed crystals

[0076] After testing the concentration of 60-65 cubic meters of metatitanic acid slurry, place it in a bleaching tank. The total titanium concentration of the slurry should be 280-340 g / L. Then, add 0.7-0.9 mg / L of [a specific ingredient / component]. 3 98% sulfuric acid, 3.5% calcined seed crystals from Example 1, 300-400 L Ti 3+ The solution is heated to 60°C with steam to bleach the metatitanic acid in the bleaching tank;

[0077] S2: Second wash

[0078] The metatitanic acid slurry with calcined seed crystals added to S1 and bleached was filtered and washed with demineralized water.

[0079] S3: Salt treatment

[0080] After the second washing, the metatitanic acid pulp is pumped to the salt treatment density control tank. After measuring the concentration and pre-treatment salt content, it flows to the salt treatment mixing tank, where potassium hydroxide, phosphoric acid, and aluminum sulfate are added in sequence. After stirring and maturing for 90 minutes, it is pumped to the kiln pre-filtering process. The amount of potassium hydroxide, phosphoric acid, and aluminum sulfate added is adjusted according to the salt content of the pre-filtering cake.

[0081] S4: Pre-kiln filter press

[0082] After being treated with salt, the slurry is sent to a metatitanic acid storage tank. A diaphragm filter press is then used to filter, press, and dehydrate the metatitanic acid slurry into a cake. The filtrate is sent to a filtrate buffer tank, and the filter cake is fed to a rotary kiln via a feeding screw for calcination. The filter cake from the kiln pre-press has a P2O5 content of 0.18–0.22%, an Al2O3 content of 0.23–0.29%, and a K2O content of 0.23–0.27%.

[0083] S5: Calcination

[0084] As the rotary kiln rotates, the material inside the kiln slowly moves towards the kiln head. Hot air and the material exchange heat directly inside the rotary kiln. The material undergoes four stages of dehydration, desulfurization, crystal transformation, and particle growth, controlled by the rotation speed of the rotary kiln and the temperatures at the kiln head and kiln tail, to become titanium dioxide (i.e., kiln feed).

[0085] After being cooled by the rotary kiln discharge port, the calcined titanium dioxide enters the cooling drum and then enters the intermediate crushing hopper. The hot air after the cold air enters the cooling drum and exchanges heat with the material enters the kiln head.

[0086] In this embodiment, the kiln head temperature is 900-1200℃, specifically controllable at 1000℃, the kiln tail temperature is 280-500℃, specifically controllable at 400℃, and the calcination time is 10-14 hours, specifically controllable at 12 hours.

[0087] Example 5

[0088] The difference between this comparative example and Example 4 is that the calcined seed crystals are from Example 2.

[0089] Example 6

[0090] The difference between this comparative example and Example 4 is that the calcined seed crystals are from Example 3.

[0091] Comparative Example 5

[0092] The difference between this comparative example and Example 3 is that the calcined seed crystals are from Comparative Example 1.

[0093] Comparative Example 6

[0094] The difference between this comparative example and Example 3 is that the calcined seed crystals are from Comparative Example 2.

[0095] Comparative Example 7

[0096] The difference between this comparative example and Example 3 is that the calcined seed crystals are from Comparative Example 3.

[0097] Comparative Example 8

[0098] The difference between this embodiment and Embodiment 2 is that the calcined seed crystals are derived from Comparative Example 4.

[0099] The test results of titanium dioxide from different embodiments and comparative examples are shown in Table 2 below.

[0100] Table 2

[0101]

[0102] The results in Table 2 show that:

[0103] By using an alkaline solution with an appropriate ratio of 48% NaOH and 32% NaOH, not only can the conversion rate be maintained at a similar level as when using 48% NaOH alkaline solution alone, but the particle size uniformity of the obtained titanium dioxide is also about the same. However, when the proportion of 32% NaOH increases to 50%, the conversion rate shows a significant downward trend, and the particle size uniformity of the titanium dioxide also deteriorates.

[0104] In terms of cost, using a mixed alkaline solution of 48% NaOH and 32% NaOH in a suitable ratio reduces costs compared to using only 48% alkali, as shown in the calculation below:

[0105] When using 48% NaOH alone, 95.66 kg of 48% NaOH is consumed to produce one ton of TiO2, and the price of 48% NaOH is 1485.31 yuan / ton.

[0106] Cost of using alkali: 95.66 / 1000*1,485.31 = 142.09 yuan / t TiO2

[0107] When using a mixture of 32% NaOH solution and 48% NaOH as alkali, with a volume ratio of 0.6:1, producing one ton of TiO2 requires 70.34 kg of 48% NaOH and 37.99 kg of 32% NaOH.

[0108] Cost of using alkali: 70.34 / 1000*1,485.31 + 37.99 / 1000*939.91 = 140.18 yuan / t TiO2

[0109] Compared with using only 48% NaOH, the cost savings of using a mixed alkaline solution of 48% NaOH and 32% NaOH is: 142.09-140.18=1.91 yuan / t TiO2.

[0110] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing titanium dioxide calcined seed crystals, characterized in that, The process includes the following steps: alkali dissolution, alkali dissolution pressure filtration, and acid dissolution, wherein the alkali dissolution uses a mixture of 48% NaOH solution and 32% NaOH solution.

2. The method for preparing titanium dioxide calcination seed crystals according to claim 1, characterized in that, The volume ratio of the 48% NaOH solution to the 32% NaOH solution is 1:0.5-1:0.

8.

3. A method for preparing titanium dioxide calcination seed crystals according to claim 1 or 2, characterized in that, The alkaline dissolution includes the following steps: Step 1.1: Add liquid alkali to the liquid alkali preheating tank for heating; Step 1.2: Add metatitanic acid to the heated liquid alkali; Step 1.3: Carry out the alkali dissolution reaction under stirring and heating conditions. After the maturation is completed, the alkali-soluble slurry is obtained and cooled for later use.

4. The method for preparing titanium dioxide calcination seed crystals according to claim 3, characterized in that, The alkaline dissolution pressure filtration includes the following steps: Step 2.1: Pump the cooled alkali-soluble slurry into a filter press for filtration; Step 2.2: Wash with demineralized water; Step 2.3: Add the washed filter cake to the pulping tank for later use.

5. The method for preparing titanium dioxide calcination seed crystals according to claim 4, characterized in that, The acid dissolution includes the following steps: Step 3.1: Add the slurry from the pulping tank to the acid dissolving tank, and add hydrochloric acid to heat and neutralize; Step 3.2: After the pH value reaches 2.7~3.0, perform a second heating. Step 3.3: Add hydrochloric acid after the second heating to perform gelation.

6. The method for preparing titanium dioxide calcination seed crystals according to claim 5, characterized in that, In step 3.1, the temperature increase and neutralization specifically involves raising the temperature to 60°C at a rate of 1°C / min. In step 3.2, the temperature is raised again to 101±2°C.

7. A method for preparing titanium dioxide calcination seed crystals according to claim 5 or 6, characterized in that, The process after the gelation step further includes: diluting the solution according to the concentration after gelation to obtain calcined seed crystals.

8. A titanium dioxide calcination process, characterized in that, Includes the following steps: S1: Bleaching, wherein calcined seed crystals as described in any one of claims 1-7 are added during the bleaching process; S2: Filter and wash the metatitanic acid slurry after adding calcined seed crystals and bleaching in S1; S3: Salt treatment The metatitanic acid after the second washing in S2 was pulped, and then potassium hydroxide, phosphoric acid and aluminum sulfate were added and matured. S4: The metatitanic acid slurry that has been salt-treated in S3 is filtered before the kiln to obtain filter cake. S5: Calcine the filter cake obtained from the pre-kiln pressure filtration in S4.

9. The titanium dioxide calcination process according to claim 8, characterized in that, In S1, the amount of seed crystal added is 2-5% of the metatitanic acid slurry.

10. A titanium dioxide calcination process according to claim 8 or 9, characterized in that, In S4, the P2O5 content of the filter cake from the pre-kiln press is 0.18-0.22%, the Al2O3 content is 0.23-0.29%, and the K2O content is 0.23-0.27%.

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