A method for improving the zeta potential of grinding slurry and the grinding effect

Abstract

This invention discloses a method for improving the Zeta potential of a sand-milling slurry, comprising the following steps: S1, placing deionized water in a beaker, stirring, slowly adding coarse titanium dioxide powder, and then adding more deionized water to obtain a titanium dioxide slurry with a weight percentage concentration of 21.16-30.85%; S2, slowly heating and maturing the titanium dioxide slurry obtained in step S1, filtering to obtain a filter cake, washing with water, and pressing off excess water from the filter cake with a spatula; S3, adding water to the filter cake pressed off in step S2 to make a high-concentration sand-milling slurry, adding sodium hydroxide solution dropwise to control the pH value of the sand-milling slurry at 6-9, and placing the sand-milling slurry in a polyurethane sand-milling jar for sand milling. This invention, through hot beating and washing of the titanium dioxide slurry, removes all impurity ions, resulting in a high Zeta potential for the high-concentration sand-milling slurry, improving the dispersibility of the titanium dioxide slurry; the sand-milling slurry has a uniform particle size and good sand-milling effect.

Description

Technical Field

[0001] This invention relates to the field of titanium dioxide, and in particular to a method for improving the zeta potential of grinding slurry and the grinding effect. Background Technology

[0002] In the production process of rutile titanium dioxide by the sulfuric acid process, the coarse titanium dioxide powder needs to be sand-milled before the titanium dioxide can be coated. The reason is: (1) The primary particles grown during the calcination process are very small, have a high specific surface energy, are extremely unstable, and quickly agglomerate at high temperature. After preliminary crushing, the particle surface has uneven defects, but after sand milling, the particles are spherical, without edges and corners, and the particle size distribution is relatively concentrated.

[0003] (2) Even after Raymond milling, a certain number of coarse particles or aggregates of 1-10 micrometers remain after calcination of titanium dioxide. Larger energy is required to separate them. Sand milling can crush aggregates and agglomerates in calcined products.

[0004] (3) The ideal state of titanium dioxide coating is to coat each individual particle with the coating agent. Only in this way can each particle be guaranteed to have a coating layer during air jet pulverization after coating, thereby achieving the purpose of surface treatment coating. If TiO2 is not ground and dispersed before coating, it is possible to coat aggregated or flocculated particles. After air jet pulverization, the coating layer is broken, presenting an incomplete coating state, which does not achieve the expected purpose of coating. Therefore, sand milling must be performed before coating to ensure that the final product has pigment properties.

[0005] Coarsely ground titanium dioxide needs to be pulped before sand milling. The pulped slurry should be in a dispersed state. Good slurry dispersion leads to good sand milling effect, while poor dispersion leads to poor sand milling effect. The dispersion effect of the slurry is measured by its Zeta potential. A high Zeta potential (an absolute value exceeding 70mV indicates a high Zeta potential) indicates good dispersion and sand milling effect; a low Zeta potential indicates poor dispersion and sand milling effect, resulting in uneven coating on the particle surface, or even some particles not being coated, thus affecting the application performance of the product. Therefore, studying the factors affecting the Zeta potential of the slurry is of great significance.

[0006] The value of the zeta potential is related to the dispersibility of the system; the higher the absolute value of the zeta potential, the more stable the system. The lower the absolute value of the zeta potential, the more the system tends to aggregate, meaning that the attractive force outweighs the repulsive force. The factors affecting the zeta potential are as follows:

[0007] (1) pH of slurry

[0008] If the particles in the slurry are negatively charged, adding alkali makes it even harder for them to become positively charged. Adding acid initially neutralizes the charge, and further acid addition gradually increases the positive charge. In the correlation curve between zeta potential and pH, the potential is positive at low pH points and negative at high pH points. The curve passes through the zeta zero potential; this point is called the isoelectric point. Slurry at the isoelectric point exhibits poor dispersibility, is thickened, and has poor milling performance.

[0009] (2) The influence of impurity ions

[0010] According to the double-layer theory, the double layer of negatively charged particles will be compressed by anions or cations in the system, leading to a decrease in slurry potential and consequently a decrease in the dispersibility of the titanium dioxide slurry. A large number of impurity ions, such as SO42-, are introduced during the production of rutile titanium dioxide. 2- K + Plasma is used, so it is necessary to remove these impurities before sand milling to bring the zeta of the slurry to a high potential.

[0011] To achieve optimal performance in sand milling, the slurry concentration and dispersibility entering the mill must be high. However, increasing the titanium dioxide slurry concentration lowers the zeta potential, resulting in poor slurry dispersibility. How to increase slurry concentration without reducing dispersibility has always been a technical challenge in the industry. Currently, many titanium dioxide manufacturers use optimized pulping processes to improve the dispersibility of titanium dioxide slurry, such as adding appropriate amounts of dispersants, sodium hexametaphosphate, sodium silicate, and polycarboxylate salts. However, the addition of these chemical reagents will inevitably have adverse environmental impacts.

[0012] In the method for reducing the viscosity of titanium dioxide slurry in patent CN105921212A, the raw titanium dioxide is ground and then classified through a standard sieve. The material undersized is pulped and dispersed, while the material oversized is retold. The fineness of the raw titanium dioxide is controlled by a roller mill, and the concentration of the titanium dioxide slurry is increased by changing the fineness of the pulped material. This method uses a roller mill, which is energy-intensive, and the process of classifying and retoldting to control the fineness increases the cost. Summary of the Invention

[0013] The technical problem to be solved by the present invention is to provide a method for improving the Zeta potential and grinding effect of the grinding slurry, which addresses the shortcomings of the existing technology. The method removes titanium dioxide impurity ions by hot slurry washing and adjusts the pH value of the titanium dioxide slurry to increase the zeta potential of the slurry. The grinding effect is characterized by the particle size parameter of the grinding slurry. The narrower the particle size distribution of the grinding slurry, the more uniform the particle size of the grinding slurry.

[0014] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a method for improving the Zeta potential of sand milling slurry, specifically including the following steps:

[0015] S1: Place deionized water in a beaker, stir, slowly add pre-crushed titanium dioxide powder, and then add deionized water to obtain a titanium dioxide slurry with a weight percentage concentration of 21.16-30.85%.

[0016] S2: Slowly heat the titanium dioxide slurry obtained in step S1, mature it, filter it to obtain a filter cake, wash it with water, and press off the excess water from the filter cake with a cutting knife.

[0017] S3: Add water to the filter cake that was pressed out of water in step S2 and slurry it to make a sand milling slurry with a weight percentage concentration of 51.77-59.92%. Add sodium hydroxide solution dropwise to control the pH value of the sand milling slurry at 6-9. Place the sand milling slurry in a polyurethane sand milling tank for sand milling.

[0018] In a preferred embodiment of the present invention, the weight percentage concentration of the titanium dioxide slurry in step S1 is 21.16-30.85%, preferably 23.25-27.8%. If the concentration of the titanium dioxide slurry is too low, the efficiency during pulping and washing will be low; if the concentration of the titanium dioxide slurry is too high, the viscosity will be too high, and the material will not be stirred evenly.

[0019] In a preferred embodiment of the present invention, the titanium dioxide slurry in step S2 is slowly heated to 50-80°C, preferably 55-65°C, at a rate of 1-2°C / minute. In this invention, the heating rate of the titanium dioxide slurry should not be too fast or too slow. A slow heating rate results in low efficiency, while a fast heating rate causes localized high material temperatures, leading to material sticking to the wall. When the temperature of the titanium dioxide slurry after heating is below 50°C, impurity ions adhering to the TiO2 surface cannot completely diffuse into the titanium dioxide slurry, affecting working efficiency. When the temperature of the titanium dioxide slurry after heating is above 80°C, the titanium dioxide slurry sticks to the wall, wasting heat energy. Impurity ions in the sticky titanium dioxide slurry cannot diffuse into the slurry, and these impurity ions cannot be effectively removed.

[0020] In a preferred embodiment of the present invention, the curing time in step S2 is 0.5 to 2 hours, preferably 1 hour. If the curing time is less than 0.5 hours, the impurity ions on the TiO2 surface do not completely diffuse into the titanium dioxide slurry. Those skilled in the art have detected that when the curing time of the titanium dioxide slurry is 10 minutes, 95% of the impurity ions on the TiO2 surface have essentially diffused into the slurry; and when the curing time of the titanium dioxide slurry is 30 minutes, 99.5% of the impurity ions on the TiO2 surface have essentially diffused into the slurry.

[0021] In a preferred embodiment of the present invention, deionized water is used for washing in step S2. During washing, the weight ratio of titanium dioxide slurry (based on TiO2) to deionized water is 1:1 to 5, preferably 1:2 to 3. If the amount of deionized water during washing is too small, impurity ions on the surface of titanium dioxide will not be completely removed. When the weight ratio of titanium dioxide slurry (based on TiO2) to deionized water during washing is 1:1 to 5, preferably 1:2 to 3, all soluble impurity ions can diffuse into the titanium dioxide slurry. If the amount of water used during washing is too large, it will result in resource waste.

[0022] The titanium dioxide slurry of this invention undergoes hot beating and washing treatment, which allows impurity ions adhering to the TiO2 surface to diffuse almost completely into the titanium dioxide slurry, removing titanium dioxide impurity ions. This results in good dispersibility of the titanium dioxide slurry. In step S3, the weight percentage concentration of the sand-milling slurry is 51.77–59.92%, achieving excellent sand-milling results with no dispersant or only 0.01–0.03% dispersant. In contrast, the titanium dioxide slurry without hot beating and washing treatment has many impurity ions adhering to the TiO2 surface, leading to poor dispersibility. It requires the addition of 0.2–0.5% dispersants such as sodium hexametaphosphate, sodium silicate, and polycarboxylate to control the weight percentage concentration of the sand-milling slurry at 36.41–43.67%. A low concentration of the sand-milling slurry results in poor sand-milling performance.

[0023] In a preferred embodiment of the present invention, the Zeta potential of the grinding slurry in S3 is -70 to -85 mV, at which point the Zeta potential of the grinding slurry is high.

[0024] To achieve optimal sand milling, the slurry entering the mill must have a high concentration and good dispersibility. However, increasing the concentration of titanium dioxide slurry lowers the Zeta potential, resulting in poor dispersibility. High titanium dioxide slurry concentration and good dispersibility are contradictory. Therefore, this invention removes all impurity ions by hot-beating and washing the titanium dioxide slurry, ensuring that the high-concentration sand milling slurry has a high Zeta potential, thereby improving the dispersibility of the titanium dioxide slurry.

[0025] This invention uses a polyurethane grinding jar for sanding because the aforementioned grinding jar has good wear resistance.

[0026] In a preferred embodiment of the present invention, the milling speed in step S3 is 3500-4500 rpm, and the milling time is 50-80 min. If the milling speed is too low, there will be fewer opportunities for collision between titanium dioxide and zirconium beads and titanium dioxide particles, thus failing to achieve the desired milling effect, resulting in a coarse particle size in the milled slurry. If the milling speed is too high, a large amount of heat will be generated, causing a large number of zirconium beads to be ground and pulverized, mixing into the slurry, affecting product quality and increasing production costs.

[0027] This invention also discloses a method for improving the grinding effect by increasing the Zeta potential of the grinding slurry. The grinding effect is characterized by the particle size parameter of the grinding slurry, mainly through D... 50 The parameters are used to characterize, in D 50 When the value reaches a certain requirement, the diameter-to-spacing ratio parameter is used as a characterization index for the D of the sand-milled slurry. 50 With a diameter of 0.3–0.4 μm and a diameter-to-gap ratio of 1.2–1.5, the particle size of the sand-milled slurry is more uniform.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0029] This invention removes all impurity ions by hot beating and washing titanium dioxide slurry, resulting in a high zeta potential in the high-concentration milled slurry and improving the dispersibility of the titanium dioxide slurry.

[0030] This invention also provides a method for improving the grinding effect by increasing the Zeta potential of the grinding slurry. The grinding effect is characterized by the particle size parameter of the grinding slurry, wherein the particle size ratio of the grinding slurry is 1.2–1.5. 50 The diameter is 0.3–0.4 μm, D 50 The diameter represents the particle size at which the cumulative particle distribution is 50%. The diameter-to-spacing ratio indicates the width of the particle size distribution in the sand-milled slurry. The smaller the diameter-to-spacing ratio, the narrower the particle size distribution and the more uniform the particle size of the sand-milled slurry. Attached Figure Description

[0031] Figure 1 The particle size parameters of the sand-milling slurry in Example 1 of this invention;

[0032] Figure 2 The particle size parameters of the sand-milling slurry in Example 2 of this invention;

[0033] Figure 3 The particle size parameters of the sand-milling slurry in Example 3 of this invention;

[0034] Figure 4 The particle size parameters of the sand grinding slurry in Comparative Example 1 of this invention;

[0035] Figure 5 The particle size parameters of the sand grinding slurry in Comparative Example 2 of this invention;

[0036] Figure 6 The particle size parameters of the sand grinding slurry in Comparative Example 3 of this invention;

[0037] Figure 7 Photographs of high Zeta potentials in Examples 1-3. Detailed Implementation

[0038] The slurry zeta potential was detected using a high-concentration zeta potential analyzer (model Zetaprobe) from colloidal dynamics, USA.

[0039] For ease of testing and accurate measurement, the testing process was conducted by weighing. The slurry concentration in the examples is expressed as a weight percentage.

[0040] The inventors, through numerous experiments, determined that the percentage concentration corresponds to the slurry concentration in g / l.

[0041] The fitting formula is Y Where x represents the titanium dioxide slurry in g / l, and Y represents the weight percentage concentration.

[0042] Example 1

[0043] (1) Take 1000ml of deionized water and put it in a glass beaker. Turn on the stirrer and slowly add 350g of titanium dioxide coarse powder sample. Then add 200ml of water to prepare a titanium dioxide slurry with a weight percentage concentration of 22.58%. Adjust the pH of the titanium dioxide slurry to 8.5 and use a colloidal dynamics high-concentration Zeta potential analyzer to measure that the Zeta of the titanium dioxide slurry is -35.3mV.

[0044] (2) Slowly heat the titanium dioxide slurry to 60°C and mature it for 60 minutes. Filter the titanium dioxide slurry using a Buchner funnel to obtain a filter cake. Add 800ml of deionized water to wash the filter cake and press out the excess water with a knife.

[0045] (3) The filter cake with water removed was mixed with water to make a sand milling slurry with a weight percentage concentration of 56.9%. Sodium hydroxide solution was added dropwise to adjust the pH of the sand milling slurry to 8.5. The Zeta of the sand milling slurry was measured to be -80.5mV using a colloidal dynamics high-concentration Zeta potential analyzer.

[0046] (4) Place the sand-milled slurry in a sand mill jar and mill at a speed of 4000 rpm for 1 hour. Use a Bettersize 3000 particle size analyzer to measure the particle size of the sand-milled slurry; the particle size ratio is 1.29, D. 10 : 0.182μm, D 50 : 0.360μm, D 90 : 0.647μm (e.g.) Figure 1 (As shown).

[0047] D 10 D represents the particle size at which the cumulative particle distribution is 10%. 50 D represents the particle size at which the cumulative particle distribution is 50%. 90 This indicates the particle size at which 90% of the particles are cumulatively distributed; the diameter-to-size ratio = (D90 -D 10 ) / D 50 The value of the particle size distribution is denoted by , which indicates the width of the particle size distribution. The smaller the value of the diameter-to-spacing ratio, the narrower the particle size distribution of the sand-milled slurry, and the more uniform the particle size of the sand-milled slurry.

[0048] Example 2

[0049] Steps (1) to (2) are the same as in Example 1.

[0050] (3) The filter cake with water removed was mixed with water to make a sand milling slurry with a weight percentage concentration of 56.9%. Sodium hydroxide solution was added dropwise to adjust the pH of the sand milling slurry to 9.0. The Zeta of the sand milling slurry was measured to be -81.2mV using a colloidal dynamics high-concentration Zeta potential analyzer.

[0051] (4) Place the sand-milled slurry in a sand mill jar and mill at a speed of 4000 rpm for 1 hour. Use a Bettersize 3000 particle size analyzer to measure the particle size of the sand-milled slurry; the particle size ratio is 1.50, D. 10 : 0.205μm, D 50 : 0.394μm, D 90 : 0.796μm (e.g.) Figure 2 (As shown).

[0052] Example 3

[0053] Steps (1) to (2) are the same as in Example 1.

[0054] (3) The filter cake with water removed was mixed with water to make a sand milling slurry with a weight percentage concentration of 56.9%. Sodium hydroxide solution was added dropwise to make the pH of the sand milling slurry 7.5. The Zeta of the sand milling slurry was measured to be -75.5mV using a colloidal dynamics high-concentration Zeta potential analyzer.

[0055] (4) Place the sand-milled slurry in a sand mill jar and mill at a speed of 4000 rpm for 1 hour. Use a Bettersize 3000 particle size analyzer to measure the particle size of the sand-milled slurry; the particle size ratio is 1.421, D. 10 : 0.203μm, D 50 : 0.387μm, D 90 : 0.753μm (e.g.) Figure 3 (As shown).

[0056] Comparative Example 1

[0057] (1) Take 265ml of deionized water and put it in a glass beaker. Turn on the stirring and slowly add 350g of titanium dioxide coarse powder sample to prepare a titanium dioxide slurry with a weight percentage concentration of 56.9%. Adjust the pH of the titanium dioxide slurry to 8.5 and measure the zeta of the titanium dioxide slurry to be -25.3mV using a colloidaldynamics high-concentration zeta potential analyzer.

[0058] (2) The titanium dioxide slurry was placed in a sand mill and milled at 4000 rpm for 1 hour. The titanium dioxide slurry without hot slurry washing treatment had many impurity ions adhering to the TiO2 surface, resulting in a low Zeta potential value, poor dispersibility, and poor particle size reduction during sand milling, leading to coarse particles. The particle size was measured using a Bettersize 3000 particle size analyzer, and the particle size ratio was 1.975. 10 : 0.799μm, D 50 : 1.419μm, D 90 3.602μm (e.g.) Figure 4 (As shown).

[0059] In the comparative example, the titanium dioxide slurry had a low Zeta potential, poor dispersibility, and poor milling effect. 50 The value is high. When the D50 value exceeds 0.5 μm, the particle size of the sand-milled slurry is very coarse. At this time, using the diameter-to-gap ratio as a characterization index is meaningless.

[0060] Comparative Example 2

[0061] (1) Take 265ml of deionized water and put it in a glass beaker. Turn on the stirrer and slowly add 350g of titanium dioxide coarse powder sample to prepare a titanium dioxide slurry with a weight percentage concentration of 56.9%. Then add 0.3% dispersant sodium hexametaphosphate and stir for 30 minutes. Adjust the pH of the titanium dioxide slurry to 8.5 and measure the zeta of the titanium dioxide slurry to be -35.3mV using a colloidal dynamics high-concentration zeta potential analyzer.

[0062] (2) The titanium dioxide slurry was placed in a sand mill and sand-milled at a speed of 4000 rpm for 1 hour. In Comparative Example 2, a dispersant was added, and the Zeta potential of the titanium dioxide slurry was higher than that of Comparative Example 1. However, compared to Examples 1-3, the titanium dioxide slurry was not subjected to hot slurrying and washing treatment. The titanium dioxide slurry without hot slurrying and washing treatment had many impurity ions attached to the TiO2 surface, resulting in a very low Zeta potential value. This led to poor dispersibility of the titanium dioxide slurry, poor particle size reduction during sand milling, and very coarse particle size. The particle size of the slurry was measured using a Bettersize 3000 particle size analyzer, and its diameter-to-size ratio was 3.17. 10 : 0.502μm, D 50: 0.971μm, D 90 3.582μm (e.g.) Figure 5 (As shown).

[0063] Comparative Example 3

[0064] (1) Take 550ml of deionized water and put it in a glass beaker. Turn on the stirrer and slowly add 350g of titanium dioxide coarse powder to prepare a titanium dioxide slurry with a weight percentage concentration of 38.9%. Then add 0.3% sodium silicate and stir for 30 minutes.

[0065] (2) The pH of the titanium dioxide slurry was adjusted to 8.5, and the Zeta of the titanium dioxide slurry was measured to be -50.5mV using a colloidal dynamics high-concentration Zeta potential analyzer.

[0066] (3) The titanium dioxide slurry was placed in a sand mill and milled at a speed of 4000 rpm for 1 hour. The particle size of the slurry was measured using a Bettersize 3000 particle size analyzer, and the particle size ratio was 2.0. 10 : 0.181μm, D 50 : 0.570μm, D 90 1.321μm (e.g.) Figure 6 (As shown).

Claims

1. A method for improving the Zeta potential of sand milling slurry and the sand milling effect, characterized in that, It includes the following steps: S1: Place deionized water in a beaker, stir, slowly add coarse titanium dioxide powder, and then add deionized water to obtain a titanium dioxide slurry with a weight percentage concentration of 21.16-30.85%. S2: The titanium dioxide slurry obtained in step S1 is slowly heated to 50-80°C at a rate of 1-2°C / min, and the maturation time is 0.5-2 hours. The slurry is then filtered to obtain a filter cake, washed with water, and excess water is removed from the filter cake by pressing it with a cutting knife. S3: The filter cake from step S2, after pressing out the water, is mixed with water to form a slurry with a weight percentage concentration of 51.77–59.92%. Sodium hydroxide solution is added dropwise to control the pH of the slurry at 6–9, resulting in a zeta potential of -70–-85 mV. The slurry is then placed in a polyurethane milling jar for milling to obtain a diameter-to-gap ratio of 1.2–1.5, D. 50 It is a sand grinding slurry with a particle size of 0.3 to 0.4 μm.

2. The method for improving the Zeta potential of grinding slurry and the grinding effect as described in claim 1, characterized in that, In step S2, the titanium dioxide slurry is slowly heated to 55-65°C.

3. The method for improving the Zeta potential of grinding slurry and the grinding effect as described in claim 1, characterized in that, The maturation time in step S2 is 1 hour.

4. The method for improving the Zeta potential of grinding slurry and the grinding effect as described in claim 1, characterized in that, In step S2, deionized water is used for washing. During washing, the weight ratio of titanium dioxide to deionized water in the titanium dioxide slurry is 1:1 to 5.

5. The method for improving the Zeta potential of grinding slurry and the grinding effect as described in claim 1, characterized in that, In step S3, the grinding speed is 3500-4500 rpm, and the grinding time is 50-80 min.

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