A water-saving method for the water washing process of titanium dioxide by sulfuric acid process

Abstract

The present invention belongs to the technical field of water washing of titanium dioxide by sulfuric acid process. Specifically, it relates to a water-saving method for the water washing process of preparing titanium dioxide by sulfuric acid process, including steps such as cooling, stratification, separation, bleaching, and secondary washing. Compared with the prior art, the beneficial effects of this application are as follows: Through stratification and separation, the concentration of the waste acid obtained can reach about 30%, which can save the cost of waste acid concentration; the primary washing process is omitted, reducing the investment in filter press equipment and the floor area occupied by the filter press, saving about 1 times the water washing amount, reducing the cost of wastewater treatment and reducing the loss of titanium in the primary washing process, thereby improving the titanium recovery rate and reducing the labor intensity of workers; it can efficiently recover ferrous sulfate heptahydrate, which helps to realize the recovery and utilization of iron resources.

Description

Technical Field

[0001] The invention belongs to the technical field of sulfuric acid process titanium dioxide water washing, and specifically relates to a water-saving method for the water washing process of preparing sulfuric acid process titanium dioxide. Background Art

[0002] After the titanic acid is washed once, it is difficult to wash the impurity ions contained in the titanic acid to a very low concentration. In addition, during the washing process, some metal ions in the titanic acid, especially Fe 2+ In the later stage of water washing, due to the decrease in acidity, it may be oxidized to generate Fe 3+ , and form a part of Fe(OH)3 precipitation, which is then mixed in the filter cake and cannot be removed, affecting the iron content in the filter cake, and ultimately affecting the product quality. Therefore, in the prior art, a bleaching process is usually configured after the first wash, that is, after the first washed metatitanic acid is pulped, concentrated sulfuric acid and a reducing agent are added to dissolve the metal precipitate formed in the first wash process into an ionic state, so that the high-valent oxides (mainly iron) are reduced to low-valent oxides, and then these low-valent oxides are removed by the second wash to achieve the purpose of further purifying the metatitanic acid. The diaphragm filter press used for water washing needs to replace the filter plate frequently, and each plate needs to be manually unloaded. The labor intensity is high and the water washing time is long, which affects the output. In addition, the amount of washing water used for the first and second washes per ton of titanium dioxide in the traditional process is 20 to 30 m 3 , water resources consumption is huge, and the washing time is long, which affects the output.

[0003] Therefore, there is an urgent need to improve the existing sulfuric acid method titanium dioxide washing process. Summary of the invention

[0004] The purpose of the present invention is to solve the above technical problems by simplifying the first washing step in the original process through cooling, standing, stratification and separation, thereby saving water, reducing the labor intensity of operators and improving the recovery rate of resources.

[0005] To achieve the above object, the present invention proposes a water-saving method for the sulfuric acid process titanium dioxide washing process, comprising the following steps:

[0006] S1. Cooling: cooling the hydrolyzed metatitanic acid slurry to room temperature;

[0007] S2. Layering: After cooling to room temperature, the titanate slurry is allowed to stand for a period of time, so that a stable black waste acid layer appears on the top, a stable white titanate layer appears in the middle, and a stable green block crystal layer appears on the bottom.

[0008] S3, separation: after the stratification is completed, the upper black waste acid is directly extracted, and the extraction is stopped when the white slurry is extracted, and then the remaining slurry is filtered to separate most of the green block crystals to obtain the initially purified metatitanic acid;

[0009] S4, Bleaching, Second Washing: Treat the preliminarily purified metatitanic acid through conventional bleaching and second washing processes to obtain purified metatitanic acid.

[0010] Preferably, in step S1, the temperature of the hydrolyzed metatitanic acid slurry is greater than 90 °C, usually about 100 °C, the concentration of TiO2 is 160 - 180 g / L, the concentration of H2SO4 is 22% - 30%, and the concentration of FeSO4·7H2O is 200 - 250 g / L. Under these conditions, the metatitanic acid slurry is suitable for water-saving water washing using this process.

[0011] Preferably, in step S1, the cooling method is natural cooling or forced cooling in a low-temperature environment. After normal hydrolysis, the temperature of the metatitanic acid slurry is about 100 °C. After cooling to room temperature, almost all of the ferrous sulfate heptahydrate in the slurry can crystallize out. Due to the adsorption characteristics between metatitanic acids, the metatitanic acid slurry will stratify into a black waste acid layer on the top, a white metatitanic acid layer in the middle, and a green blocky crystal layer at the bottom, i.e., the ferrous sulfate heptahydrate layer after standing.

[0012] Preferably, in step S2, the standing time ≥ 24 h, which helps the metatitanic acid slurry after cooling to room temperature to achieve sufficient stratification and ensure the stratification effect.

[0013] Preferably, in step S3, the concentration of the extracted waste acid is greater than 29% and can be concentrated and reused. In the traditional process, the concentration of the waste acid in the filtrate after the first washing and pressure filtration is about 20%. The concentration of the waste acid obtained after stratification in this application can be increased to about 30%, which helps to save the concentration cost of the waste acid.

[0014] Preferably, in step S3, the green blocky crystals obtained by filtration are ferrous sulfate heptahydrate and can be used to prepare polyferric. This process not only efficiently and conveniently removes most of the Fe in the metatitanic acid slurry 2+ , and the ferrous sulfate heptahydrate obtained by filtration is used to prepare polyferric, thereby improving the recovery rate and utilization rate of iron resources.

[0015] Preferably, in step S3, a filter cloth or other filter is set at the pipe head for extracting the waste acid to reduce the filtration of metatitanic acid. After the extracted waste acid is settled, the part containing metatitanic acid at the bottom can be returned to the hydrolyzed metatitanic acid tank for recycling, thereby further improving the recovery rate of titanium resources.

[0016] Preferably, in step S3, the filtration treatment method is pressure filtration by a filter press, which can efficiently separate and recover the green blocky crystals after stratification. More preferably, the filter cake can be rinsed during the pressure filtration process to further improve the titanium recovery rate.

[0017] Preferably, in step S3, in the preliminarily purified metatitanic acid, the content of TiO2 is greater than 60%, the content of iron is less than 550 PPM, and the concentration of H2SO4 is less than 8%.

[0018] The present invention also includes other steps that can enable its normal implementation, all of which adopt conventional means in the art. In addition, for the steps not defined in the present invention, the existing technologies in the art are also adopted, and those skilled in the art can make selections according to actual needs.

[0019] The working principle of the present invention is as follows: The metatitanic acid slurry with a temperature of about 100 °C after hydrolysis is cooled to room temperature by natural cooling or heat exchange. Thus, almost all of the ferrous sulfate heptahydrate is crystallized out by utilizing the adsorption between metatitanic acids and the characteristic that ferrous ions will crystallize after cooling. After the metatitanic acid slurry stands still, it is stratified into the upper black waste acid layer, the middle white metatitanic acid layer, and the bottom green ferrous sulfate heptahydrate crystal layer. Then, the upper black waste acid is directly pumped out and stopped when the white slurry is pumped out. The pumped waste acid can be concentrated and reused, and then filtered to separate most of the green massive crystals. The preliminarily purified metatitanic acid can be directly bleached, thus omitting the first washing process in the existing water washing process and simplifying the bleaching process. Moreover, the iron content in the metatitanic acid slurry after the first washing in the traditional method is generally above 1000 ppm, while the iron content in this application can be reduced to below 550 ppm. It can also save the water consumption of the second washing and the dosage of the bleaching agent, thereby greatly saving the water consumption for water washing and overcoming the technical defects of the long water washing time, large manual labor intensity, long time consumption, and limited output of the traditional filter press.

[0020] Compared with the prior art, the present application has the following beneficial effects:

[0021] (1) Omitting the first washing process reduces the investment in filter press equipment and the floor area occupied by the filter press, saves about 1 time of water washing amount, reduces the cost of wastewater treatment and the loss of titanium in the first washing process, thereby improving the titanium recovery rate and reducing the manual labor intensity.

[0022] (2) Through layering and separation, the concentration of the obtained waste acid reaches about 30%, which can save the cost of waste acid concentration.

[0023] (3) It can efficiently recover ferrous sulfate heptahydrate, which helps to realize the recovery and utilization of iron resources. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic process flow diagram of the present invention in the embodiment.

[0025] Figure 2 It is a schematic process flow diagram of the prior art in the comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0026] The technical solution of the present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0027] Embodiment:

[0028] As Figure 1 shown, this embodiment proposes a water-saving method for the water washing process of titanium dioxide by sulfuric acid method, including the following steps:

[0029] S1. Cooling: The hydrolyzed metatitanic acid slurry is cooled to room temperature by natural cooling; the temperature of the hydrolyzed metatitanic acid slurry is about 100 °C, and the concentration of TiO2 is 160-180 g / L, the concentration of H2SO4 is 22%-30%, and the concentration of FeSO4·7H2O is 200-250 g / L.

[0030] S2. Laminating: The metatitanic acid slurry cooled to room temperature is allowed to stand for 24 hours, so that a stable black waste acid layer appears on the top layer, a stable white metatitanic acid layer appears in the middle, and a stable green massive crystal layer appears at the bottom.

[0031] S3. Separating: After laminating, the upper black waste acid is directly pumped out, and the pumping is stopped when the white slurry is pumped out. Then, the remaining slurry is filtered by a filter press to separate most of the green massive crystals, and the preliminarily purified metatitanic acid is obtained.

[0032] S4. Bleaching and secondary washing: The preliminarily purified metatitanic acid is treated by conventional bleaching and secondary washing processes to obtain the purified metatitanic acid.

[0033] In step S3, the concentration of the pumped-out waste acid is greater than 29% and can be concentrated and reused. In the traditional process, the concentration of the waste acid in the filtrate after the first washing and filtration is about 20%. The concentration of the waste acid obtained after laminating in this application can be increased to about 30%, which helps to save the concentration cost of the waste acid. The green massive crystals obtained by filtration are ferrous sulfate heptahydrate and can be used to prepare polyferric. This process not only efficiently and conveniently removes most of the Fe2+ in the metatitanic acid slurry, but also the ferrous sulfate heptahydrate obtained by filtration is used to prepare polyferric, thereby improving the recovery rate and utilization rate of iron resources. A filter cloth or other filter is set at the pipe head for pumping out the waste acid to reduce the filtration of metatitanic acid. After the pumped-out waste acid is settled, the part containing metatitanic acid at the bottom can be returned to the hydrolyzed metatitanic acid tank for recycling, thereby further improving the recovery rate of titanium resources; in the preliminarily purified metatitanic acid, the content of TiO2 is greater than 60%, the content of iron is less than 550 PPM, and the concentration of H2SO4 is less than 8%.

[0034] According to the above embodiments, three groups of parallel tests are carried out and recorded as test 1, test 2 and test 3, and the components of the waste acid and the preliminarily purified metatitanic acid obtained in test 1, test 2 and test 3 in step 3 are detected.

[0035] Comparative Example

[0036] As Figure 2 shown, this comparative example adopts the conventional process in the prior art, and the hydrolyzed metatitanic acid slurry still adopts the conditions and components defined in Example 1.

[0037] According to the above comparative example, two groups of parallel tests were carried out and recorded as Test 4 and Test 5, and the components of the waste acid and metatitanic acid obtained after the first washing were detected.

[0038] The test results in Test 1, Test 2, Test 3, Test 4 and Test 5 are statistically summarized as follows:

[0039]

[0040] It can be seen from the above test results that when the traditional method is used, the iron content in the metatitanic acid slurry after the first washing is above 1000 ppm, while after using the method of the present application, the iron content can be reduced to below 550 ppm, and the concentration of the waste acid obtained can reach about 30%, which helps to save the cost of waste acid concentration. In addition, the content of TiO2 in the preliminarily purified metatitanic acid is greater than 60%, the iron content is less than 550 PPM, and the concentration of H2SO4 is less than 8%, which is beneficial to ensuring the iron removal effect of the second washing and saving the water consumption of the second washing and bleaching processes.

[0041] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A water-saving method for the water washing process of titanium dioxide by sulfuric acid method, characterized in that, It includes the following steps: S1. Cooling: Cool the hydrolyzed metatitanic acid slurry to room temperature. The temperature of the hydrolyzed metatitanic acid slurry is greater than 90 °C, the concentration of TiO2 is 160 - 180 g / L, the concentration of H2SO4 is 22% - 30%, and the concentration of FeSO4·7H2O is 200 - 250 g / L; S2. Laminating: Let the hydrolyzed metatitanic acid slurry cooled to room temperature stand for more than 24 hours, so that a stable black waste acid layer appears on the top layer, a stable white metatitanic acid layer appears in the middle, and a stable green massive crystal layer appears at the bottom; S3. Separating: After laminating, directly pump out the upper black waste acid. The concentration of the pumped-out waste acid is greater than 29%. Stop when pumping out the white slurry. Then filter the remaining slurry through a filter press to separate most of the green massive crystals to obtain preliminarily purified metatitanic acid. The green massive crystals obtained by filtration are ferrous sulfate heptahydrate; in the preliminarily purified metatitanic acid, the content of TiO2 is greater than 60%, the content of iron is less than 550 PPM, and the concentration of H2SO4 is less than 8%; S4. Bleaching and secondary washing: Treat the preliminarily purified metatitanic acid through conventional bleaching and secondary washing processes to obtain purified metatitanic acid.

2. The water-saving method for the water washing process of titanium dioxide by sulfuric acid method according to claim 1, characterized in that: In step S1, the cooling method is natural cooling or forced cooling in a low-temperature environment.

3. The water-saving method for the water washing process of titanium dioxide by sulfuric acid method according to claim 1, characterized in that: In step S3, a filter cloth or other filter is set at the pipe head for pumping out the waste acid to reduce the filtration of metatitanic acid. After sedimentation of the pumped-out waste acid, the part containing metatitanic acid at the bottom is returned to the hydrolyzed metatitanic acid tank for recycling.

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