A method for removing soluble chloride ions from a titania sol using a membrane device

Abstract

The application provides a method for removing soluble chlorine ions in titanium dioxide sol by using a membrane device, wherein the method comprises the following steps: firstly, concentrating titanium dioxide sol slurry by using a rotary ceramic membrane filtration device to obtain concentrated slurry; then, diluting the concentrated slurry by adding desalination water, and then filtering the slurry to make the soluble chlorine ions be discharged with the filtrate; repeating the dilution and filtration operations until the conductivity detection result of the discharged filtrate reaches a required target value; and finally, adjusting the TiO2 concentration of the filtered slurry to obtain the required titanium dioxide sol. The method can effectively remove the soluble chlorine ions in the titanium dioxide sol, greatly reduces the corrosion of the titanium dioxide sol to the pipeline, saves the amount of calcined seeds, and reduces the production cost of rutile titanium dioxide; the method is simple in operation, high in economic benefit and strong in practicability.

Description

Technical Field

[0001] This invention belongs to the field of inorganic material preparation technology and relates to a method for removing soluble chloride ions. Background Technology

[0002] In the sulfuric acid process for producing rutile titanium dioxide, rutile seed crystals need to be added to promote the calcination of metatitanic acid and ultimately obtain titanium dioxide with a higher rutile content. Currently, rutile calcination seed crystals are generally used to promote the conversion of metatitanic acid from anatase to rutile during the calcination process.

[0003] Rutile-type calcined seed crystals are actually a type of titanium dioxide sol. The basic production process is as follows: First, the metatitanic acid after two washes is boiled with sodium hydroxide alkaline solution; then, the alkaline-boiled metatitanic acid is washed with water through a filter press; next, the pH of the metatitanic acid is adjusted to 2.5-3.5 with concentrated hydrochloric acid; then, concentrated hydrochloric acid (HCl:TiO2 = 0.26) is added to heat and keep it at the temperature to sol-gel, and then demineralized water is added to cool and dilute to a TiO2 concentration of 100 g / L.

[0004] Because the prepared titanium dioxide sol contains a large amount of hydrogen and chloride ions, it is highly corrosive to metal pipelines during transportation. The titanium dioxide sol needs to be mixed with metatitanic acid before being applied to the preparation of rutile titanium dioxide. This results in high concentrations of chloride ions in the secondary washing wastewater after the bleaching process. To reduce water consumption, this secondary washing wastewater is reused in the primary washing process. The volume of this secondary washing wastewater is enormous, and direct reuse leads to chloride ion enrichment, corrosion of production equipment, and reduced lifespan. Laser particle size analysis shows that the particle size distribution of the titanium dioxide sol ranges from 10 nm to 100 μm, exhibiting a sub-nanometer scale and a very wide particle size distribution. Macroscopically, it has high viscosity, causing severe filtration of small particles using traditional filter cloths, while large particles are difficult to filter due to their gel-like consistency. For the washing and dechlorination of titanium dioxide sol seeds, current methods employ chemical approaches to alter the particle size distribution of the sol seeds: by adding sodium hydroxide or sodium carbonate to the sol seeds, the acidity is adjusted to a neutral pH of 6-8, causing partial aggregation of colloidal particles and improving filterability before filtration and washing. However, the suspension and dispersibility of the neutralized titanium dioxide sol seeds decrease, leading to uneven mixing of the sol seeds with metatitanic acid during use. This results in uneven rutile transformation of the metatitanic acid after calcination, thus reducing the activity of the rutile seeds and indirectly increasing raw material costs. Summary of the Invention

[0005] To address the problem of high chloride ion content and difficulty in removing it from titanium dioxide sol as described in the background art, this invention provides a method for removing soluble chloride ions from titanium dioxide sol using a membrane device.

[0006] The method of the present invention includes the following steps:

[0007] Step 1: Pump the titanium dioxide sol slurry from the raw material tank into the filter tank of the rotary ceramic membrane filter using a diaphragm pump. Turn on the membrane rotation motor and maintain a certain speed to disperse the titanium dioxide sol slurry on the membrane surface.

[0008] Step 2: Control the flow rate of slurry return by pumping pressure, maintain the pressure difference on the membrane surface for filtration, make the pressure high first and then low to maintain the discharge of clear liquid and collect and store it, and concentrate the titanium dioxide sol slurry to obtain concentrated slurry.

[0009] Step 3: After returning the concentrated slurry to the raw material tank, add demineralized water of the same volume as the discharged clear liquid to obtain diluted slurry. Stir it evenly and then pass it into the filter tank of the rotary ceramic membrane filter. Maintain the membrane pressure difference for filtration for a period of time and backflushing. Collect and process the discharged filtrate to obtain filtered slurry.

[0010] Step 4: After returning the filtered slurry to the raw material tank, repeat Step 3 until the conductivity test result of the discharged filtrate reaches the required target value. Add demineralized water to the filtered slurry until the TiO2 concentration is 100±5g / L to obtain the required titanium dioxide sol.

[0011] Furthermore, in step one, the temperature of the cooled titanium dioxide sol slurry is 50±5℃; the rotation speed of the membrane rotary motor is 450-550 r / min; and the dispersion time of the titanium dioxide sol slurry on the membrane surface is 3-5 min.

[0012] Furthermore, in step one, the membrane used in the rotating ceramic membrane filtration device is a disc-shaped rotatable ceramic membrane, made of alumina or silicon carbide, with a membrane pore diameter of 30, 40 or 80 nm.

[0013] Furthermore, in step two, the membrane pressure difference is maintained at 0.05-0.25 MPa, the initial pressure is 0.15-0.25 MPa, the pressure after stabilizing the filtrate is 0.05-0.15 MPa, the concentration filtration time is 20-40 min, and the concentration ratio of the titanium dioxide sol slurry is 1.5-2.5 times.

[0014] Furthermore, the purified liquid from step two, after being recovered and stored, is used in the neutralization process for preparing calcined seed crystals in the production of rutile titanium dioxide.

[0015] Furthermore, in step three, the membrane pressure difference is maintained at 0.1-0.2 MPa, the filtration time for each filtration process is 30 min, and the backflushing time after each filtration is 20 s.

[0016] Furthermore, in step three, the chloride ion concentration of the demineralized water is less than 100 mg / L.

[0017] Furthermore, in step three, if the chloride ion concentration of the filtrate discharged in the early stage of filtration is ≥3000mg / L, it is collected and sent to the sewage treatment plant for neutralization treatment. If the chloride ion concentration of the filtrate discharged in the later stage of filtration is <3000mg / L, it is collected and diluted as demineralized water for the next batch of concentrated slurry.

[0018] Compared with the prior art, the present invention first concentrates the titanium dioxide sol slurry using a rotary ceramic membrane filtration device to obtain a concentrated slurry. Then, the concentrated slurry is diluted with demineralized water and filtered again, so that soluble chloride ions are discharged with the filtrate. The filtrate is continuously diluted and filtered repeatedly until the conductivity of the discharged filtrate reaches the required target value. After adjusting the TiO2 concentration of the filtrate, the desired titanium dioxide sol is obtained. The beneficial effects of this invention are as follows: 1. Using a rotating ceramic membrane to treat titanium dioxide sol and remove soluble chloride ions is not only simple to operate, but also provides better filtration than traditional filter cloth filtration. When the membrane pore size is less than 80 nm, metatitanic acid in the titanium dioxide sol will not permeate through the filter. 2. The concentration treatment increases the solid content of the titanium dioxide sol, reduces the absolute chloride ion content in the slurry, reduces the time for subsequent dilution and washing, and the filtrate with a chloride ion concentration <3000 mg / L discharged in the later stage of filtration can be collected and diluted as demineralized water for the next batch of concentrated slurry, maximizing water conservation. 3. Repeated concentration and dilution filtration operations allow the chloride ion removal process to run continuously in a cycle, thereby achieving a balance between the demineralized water and the soluble chloride ions in the titanium dioxide sol. The invention achieves a thorough mixing reaction, significantly reducing the amount of demineralized water used compared to conventional chemical methods; fourth, the membrane device used in this invention has low electrical load and a small footprint; fifth, experiments have shown that the titanium dioxide sol obtained by this invention, after the removal of soluble chloride ions, still maintains high rutile conversion activity; sixth, compared with traditional titanium dioxide sol without dechlorination, the titanium dioxide sol obtained by this invention purifies a large amount of secondary washing wastewater after the bleaching process during the preparation of rutile titanium dioxide, resulting in lower chloride ion content in the wastewater returned to the primary washing process. This allows the primary washing wastewater to be reused through membrane treatment, recovers iron from the primary washing wastewater, and indirectly reduces the production of titanium gypsum. Simultaneously, the reduced chloride ion content significantly reduces the corrosion of pipelines caused by the primary and secondary washing wastewater. In summary, the method of this invention can effectively remove soluble chloride ions from titanium dioxide sol, greatly reducing pipeline corrosion during the titanium dioxide sol transportation process and the production of rutile titanium dioxide. It can effectively solve the problem of utilizing acidic wastewater in titanium dioxide production, allowing for large-scale reuse of acidic wastewater and further reducing the generation of titanium gypsum. By directly adding titanium dioxide sol seed crystals after chloride ion removal through salt treatment, the amount of calcined seed crystals is saved, reducing the production cost of rutile titanium dioxide. It has high economic benefits and strong practicality. Attached Figure Description

[0019] Figure 1 This is a flowchart of the method of the present invention.

[0020] Figure 2 This is a flow chart of the calcination process for rutile titanium dioxide. Detailed Implementation

[0021] To make the technical problems, technical solutions, and beneficial effects to be solved by this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and are not intended to limit the scope of this application.

[0022] This invention provides a method for removing soluble chloride ions from titanium dioxide sol using a membrane device, the flowchart of which is shown below. Figure 1 As shown, the details are as follows.

[0023] Step 1: Pump the titanium dioxide sol slurry from the raw material tank into the filter tank of the rotary ceramic membrane filter using a diaphragm pump. Turn on the membrane rotation motor and maintain a certain speed to disperse the titanium dioxide sol slurry on the membrane surface.

[0024] Specifically, in step one, the temperature of the cooled titanium dioxide sol slurry is 50±5℃; the rotation speed of the membrane rotary motor is 450-550 r / min; and the dispersion time of the titanium dioxide sol slurry on the membrane surface is 3-5 min.

[0025] More specifically, the membranes used in the rotating ceramic membrane filtration equipment are disc-shaped rotatable ceramic membranes, made of alumina or silicon carbide, with a membrane pore diameter of 30, 40 or 80 nm.

[0026] Step 2: Control the flow rate of slurry return by pumping pressure, maintain the pressure difference on the membrane surface for filtration, make the pressure high first and then low to maintain the discharge of clear liquid and collect and store it, and concentrate the titanium dioxide sol slurry to obtain concentrated slurry.

[0027] Specifically, the membrane pressure difference is maintained at 0.05-0.25 MPa, the initial pressure is 0.15-0.25 MPa, the pressure after stabilizing the filtrate is 0.05-0.15 MPa, the concentration filtration time is 20-40 min, and the concentration ratio of the titanium dioxide sol slurry is 1.5-2.5 times.

[0028] More specifically, the clear liquid from step two, after being recovered and stored, is used in the neutralization process for preparing calcined seed crystals in the production of rutile titanium dioxide.

[0029] Step 3: After returning the concentrated slurry to the raw material tank, add an equal volume of demineralized water to the discharged clear liquid to obtain a diluted slurry. Stir the diluted slurry evenly and then pass it into the filter tank of the rotary ceramic membrane filter. Maintain the membrane pressure difference for filtration for a period of time and perform backflushing. Collect and process the discharged filtrate to obtain the filtered slurry.

[0030] Specifically, the membrane pressure difference is maintained at 0.1-0.2 MPa, the filtration time for each filtration process is 30 min, and the backflushing time after each filtration is 20 s.

[0031] More specifically, the chloride ion concentration of the desalinated water is below 100 mg / L.

[0032] More specifically, if the chloride ion concentration of the filtrate discharged in the early stage of filtration is ≥3000mg / L, it is collected and sent to the wastewater treatment plant for neutralization. If the chloride ion concentration of the filtrate discharged in the later stage of filtration is <3000mg / L, it is collected and diluted as demineralized water for the next batch of concentrated slurry.

[0033] Step 4: After returning the filtered slurry to the raw material tank, repeat Step 3 until the conductivity test result of the discharged filtrate reaches the required target value. Add demineralized water to the filtered slurry until the TiO2 concentration is 100±5g / L to obtain the required titanium dioxide sol.

[0034] The present invention will be further described below with reference to specific embodiments. It should be noted that only a portion of the materials and / or operating parameters used in the preparation method are shown in the specific embodiments, and not all materials and / or operating parameters in the preparation method are listed. The specific embodiments are only used to more clearly explain the present invention and further demonstrate the beneficial effects achieved by the present invention.

[0035] In the following examples, the chloride ion concentration in the titanium dioxide sol slurry to be treated was 40-43 g / L, pH = 0.5 ± 0.1, and TiO2 concentration = 100 ± 5 g / L. The membrane used in the rotating ceramic membrane filtration device is a disc-shaped rotatable ceramic membrane made of silicon carbide.

[0036] Example 1

[0037] The titanium dioxide sol slurry in the raw material tank is pumped into the filter tank of the rotary ceramic membrane filter using a diaphragm pump. The membrane rotation motor is turned on and a certain rotation speed is maintained to disperse the titanium dioxide sol slurry on the membrane surface. The temperature of the titanium dioxide sol slurry is 50℃; the rotation speed of the membrane rotation motor is 500 r / min; the dispersion time of the titanium dioxide sol slurry on the membrane surface is 4 min; and the pore size of the membrane in the rotary ceramic membrane filter is 30 nm.

[0038] The flow rate of the slurry return is controlled by pump pressure to maintain the membrane pressure difference for filtration. The pressure is initially high and then gradually decreases to maintain the discharged clear liquid, which is then collected and stored. The titanium dioxide sol slurry is then concentrated to obtain a concentrated slurry. The initial membrane pressure difference is 0.20 MPa, and the pressure after stabilizing the filtrate is 0.10 MPa. The concentration and filtration time is 30 minutes, resulting in a concentration ratio of 2.1 times for the titanium dioxide sol slurry. The collected clear liquid is then used in the neutralization process for preparing calcined seed crystals in the production of rutile titanium dioxide.

[0039] After the concentrated slurry is returned to the raw material tank, an equal volume of demineralized water is added to supplement the diluted slurry. This diluted slurry is then stirred thoroughly and passed into the filter tank of a rotary ceramic membrane filter for filtration for a period of time, followed by backflushing. The discharged filtrate is collected and processed to obtain the filtered slurry. The membrane pressure difference is maintained at 0.15 MPa. Each filtration cycle lasts 30 minutes, with a 20-second backflushing interval after each filtration. The chloride ion concentration of the demineralized water is 80 mg / L. If the chloride ion concentration of the discharged filtrate in the early stage of filtration is ≥3000 mg / L, it is collected and sent to a wastewater treatment plant for neutralization. If the chloride ion concentration of the discharged filtrate in the later stage of filtration is <3000 mg / L, it is collected and diluted to be used as demineralized water for the next batch of concentrated slurry.

[0040] The filtered slurry is returned to the raw material tank and the above dilution and filtration operations are repeated until the conductivity test result of the discharged filtrate reaches the required target value. Deionized water is added to the filtered slurry until the TiO2 concentration is 100±5g / L to obtain the required titanium dioxide sol I.

[0041] Example 2

[0042] The concentration ratio of the titanium dioxide sol slurry in this embodiment is 2.0 times.

[0043] Everything else is the same as in Example 1. The desired titanium dioxide sol II is obtained.

[0044] Example 3

[0045] The rotating ceramic membrane filtration device used in this embodiment has a membrane pore size of 80nm and a titanium dioxide sol slurry concentration ratio of 2.1 times.

[0046] Everything else is the same as in Example 1. The desired titanium dioxide sol III is obtained.

[0047] Example 4

[0048] In this embodiment, the rotating ceramic membrane filtration device uses a membrane with a pore size of 80 nm, and the concentration ratio of the titanium dioxide sol slurry is 2.0 times. The desired titanium dioxide sol IV is obtained.

[0049] Everything else is the same as in Example 1.

[0050] Comparative Example

[0051] Add 0.05 mol / L sodium hydroxide solution to the titanium dioxide sol seed crystals to neutralize to pH 6.5, stir evenly, transfer to polypropylene filter cloth, and repeatedly filter and wash with deionized water until the chloride ion concentration of the filtrate is lower than 100 mg / L to obtain the desired titanium dioxide sol V.

[0052] The titanium dioxide sols I, II, III, and IV obtained in Examples 1-4 above and the titanium dioxide sol V obtained in the comparative example were tested, and the data are shown in Table 1.

[0053] Table 1. Experimental data of titanium dioxide sol after removal of soluble chloride ions.

[0054]

[0055] As shown in Table 1, the turbidity of the filtrates from titanium dioxide sols I, II, III, and IV obtained using the method of the present invention is lower than that of the filtrate from titanium dioxide sol V obtained in the comparative example. The final chloride ion concentration in titanium dioxide sols I, II, III, and IV obtained using the method of the present invention is significantly reduced. In particular, when the membrane pore size of the rotating ceramic membrane filtration device is 30 nm, the average flux of the titanium dioxide sol treatment process using the method of the present invention is low, resulting in less loss of small sol particles. Although titanium dioxide sol V obtained in the comparative example can also significantly reduce the final chloride ion concentration, its average flux is higher, leading to more severe filtration through-filtering. In summary, the method of the present invention solves the technical problems existing in the comparative example while achieving the same treatment effect.

[0056] The calcination process flow chart of rutile titanium dioxide is shown in Figure 2. Titanium dioxide sols I, II, III, and IV from Examples 1-4 were added to the metatitanic acid slurry of the four salt-treated processes at ratios of 2.5 wt% and 4 wt%, respectively. Titanium dioxide sol V from the comparative example was added to the metatitanic acid slurry of the salt-treated process at a ratio of 6 wt%. These samples were then dehydrated and calcined to obtain small-scale calcined metatitanic acid samples. Titanium dioxide sol without dechlorination treatment was added at a ratio of 6 wt% to the metatitanic acid after one washing and pulping. The samples were then bleached, washed a second time, salt-treated, dehydrated, and calcined to obtain small-scale calcined metatitanic acid samples. The obtained small-scale calcined metatitanic acid samples were tested, and the data are shown in Table 2.

[0057] Table 2 Calcination test data

[0058]

[0059] As can be seen from the data in Table 2, the titanium dioxide sol V obtained in the comparative example has low activity as a calcination seed crystal. Compared with the comparative example and the traditional process without dechlorination treatment, the titanium dioxide sol in Examples 1-4 of the present invention, which uses the method of the present invention, can achieve a rutile conversion rate of more than 98.5% by adding a dechlorination treatment ratio of as low as 2.5 wt% to the rutile titanium dioxide production, without causing significant impact on product quality, and can significantly reduce the amount of rutile calcination seed crystal used.

[0060] The above-described embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application, and should all be included within the protection scope of this application.

Claims

1. A method for removing soluble chloride ions from a titanium dioxide sol using a membrane device, characterized in that, Includes the following steps: Step 1: The titanium dioxide sol slurry in the raw material tank is pumped into the filter tank of the rotary ceramic membrane filter using a diaphragm pump. The membrane rotation motor is turned on and a certain rotation speed is maintained to disperse the titanium dioxide sol slurry on the membrane surface. The membrane used in the rotary ceramic membrane filter is a disc-shaped rotatable ceramic membrane with a pore diameter of 30, 40, or 80 nm. The titanium dioxide sol slurry has a chloride ion concentration of 40-43 g / L, a pH of 0.5±0.1, and a TiO2 concentration of 100±5 g / L. The temperature of the titanium dioxide sol slurry is 50±5℃. The rotation speed of the membrane rotation motor is 450-550 r / min, and the dispersion time of the titanium dioxide sol slurry on the membrane surface is 3-5 min. The membrane material used in the rotary ceramic membrane filter is either alumina or silicon carbide. Step 2: Control the flow rate of slurry return by pumping pressure, maintain the pressure difference on the membrane surface for filtration, make the pressure high first and then low to maintain the discharge of clear liquid and collect and store it, and concentrate the titanium dioxide sol slurry to obtain concentrated slurry. The initial pressure during filtration is 0.15-0.25 MPa, and the pressure after filtrate is stabilized is 0.05-0.15 MPa. The concentration ratio of titanium dioxide sol slurry is 1.5-2.5 times. Step 3: After returning the concentrated slurry to the raw material tank, add an equal volume of demineralized water to the discharged clear liquid to obtain diluted slurry. Stir the diluted slurry evenly and then pass it into the filter tank of the rotary ceramic membrane filter. Maintain the membrane pressure difference for filtration for a period of time and perform backflushing. Collect and process the discharged filtrate to obtain filtered slurry. Each filtration process lasts for 30 minutes, and the backflushing time after each filtration is 20 seconds. The chloride ion concentration of the demineralized water is less than 100 mg / L. If the chloride ion concentration of the discharged filtrate in the early stage of filtration is ≥3000 mg / L, it is collected and sent to the wastewater treatment plant for neutralization. If the chloride ion concentration of the discharged filtrate in the later stage of filtration is <3000 mg / L, it is collected and diluted as demineralized water for the next batch of concentrated slurry. Step 4: After returning the filtered slurry to the raw material tank, repeat Step 3 until the conductivity test result of the discharged filtrate reaches the required target value. Add demineralized water to the filtered slurry until the TiO2 concentration is 100±5g / L to obtain the required titanium dioxide sol. Add 2.5wt% of the obtained titanium dioxide sol to the metatitanic acid slurry in the salt treatment process. After calcination, the rutile conversion rate is ≥98.5%.

2. The method for removing soluble chloride ions from a titanium dioxide sol using a membrane device according to claim 1, characterized in that: In step two, the membrane pressure difference is maintained at 0.05-0.25 MPa, and the concentration and filtration time is 20-40 min.

3. The method for removing soluble chloride ions from titanium dioxide sol using a membrane device according to claim 2, characterized in that: The purified liquid from step two is recovered and stored, and then used in the neutralization process for preparing calcined seed crystals in the production of rutile titanium dioxide.

4. The method for removing soluble chloride ions from titanium dioxide sol using a membrane device according to claim 1, characterized in that: In step three, the pressure difference across the membrane surface is maintained at 0.1-0.2 MPa.

Images