Continuous coating method for titanium dioxide

Abstract

The invention discloses a titanium dioxide continuous coating method which comprises the following steps: S1, acquiring titanium dioxide slurry concentration C, coating agent quantity n, coating sequence, concentration Cn of each coating agent, coating amount xn% of each coating agent, coating time tn of each coating agent, coating pH of each coating agent and concentration of each coating pH regulator; s2, determining the titanium dioxide slurry flow Q, the flow Qn of each coating agent, the flow of each coating pH regulator, the number n of coating tanks and the volume Vn of each coating tank; s3, continuously conveying the titanium dioxide slurry, the coating agent and the coating pH regulator into the corresponding coating tanks according to the corresponding flow; s4, monitoring the real-time pH of the slurry in the coating process of each coating agent; and S5, adjusting the flow of the coating pH regulator according to the real-time pH of the slurry, so that the pH of the slurry meets the target requirement. According to the continuous coating device, continuous coating of titanium dioxide is achieved, the productivity is improved, meanwhile, the coating effect is fully guaranteed, and the product quality is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of titanium dioxide production, and in particular relates to a titanium dioxide continuous coating method. Background Art

[0002] In order to improve the performance of titanium dioxide, titanium dioxide generally needs to be coated with unit or multi-element inorganic coatings such as silicon, aluminum, zirconium, and phosphorus. The traditional coating method is single-batch intermittent coating. Taking conventional aluminum coating as an example, first, the sand-milled qualified slurry is put into the coating tank, and after adjusting the concentration and temperature, a quantitative first aluminum source is added. After homogenization, a quantitative second aluminum source is added, and finally a pH regulator is added to adjust the end pH of the slurry. After the entire coating is completed, the slurry is put into the next process, and the material is re-coated for the next coating. The entire coating process takes more than 5 hours. When more multi-element coating is used, it will take longer and the production efficiency is lower. Moreover, more importantly, in order to maximize production capacity, the volume of the coating tank is generally designed to be larger, resulting in different material distributions at different positions in the coating tank, making the titanium dioxide and the coating agent unevenly mixed, affecting the uniformity of the coating, and at the same time, the differences between intermittent coating batches are also large. Summary of the invention

[0003] The purpose of the present invention is to provide a titanium dioxide continuous coating method to solve the deficiencies of the prior art.

[0004] The purpose of the present invention is achieved by the following technical solutions:

[0005] A titanium dioxide continuous coating method comprises the following steps:

[0006] S1. Obtain the titanium dioxide slurry concentration C, the number of coating agents n and the coating sequence, and the concentration C of each coating agent n 、The coating amount of each coating agent x n %, coating time t of each coating agent n , the coating pH of each coating agent and the concentration of each coating pH adjusting agent;

[0007] S2. Confirm the flow rate Q of titanium dioxide slurry and the flow rate Q of each coating agent n , the flow rate of each coating pH regulator, the number of coating tanks n and the volume V of each coating tank n ; The number of coating tanks corresponds to the number of coating agents;

[0008] S3. Continuously convey titanium dioxide slurry, the first coating agent and the first coating pH adjusting agent to the first coating tank with a volume of V1 according to the titanium dioxide slurry flow rate Q, the first coating agent flow rate Q1 and the first coating pH adjusting agent flow rate respectively; the material flows in the first coating tank, and after the flow time reaches t1, it is continuously discharged to the second coating tank with a volume of V2, and at the same time, the second coating agent and the second coating pH adjusting agent are continuously conveyed to the second coating tank according to the second coating agent flow rate Q2 and the second coating pH adjusting agent flow rate, and the above steps are followed until all n coating agents are added; the material is fully mixed and reacted during the flow of each coating tank to complete the coating;

[0009] S4. Monitor the real-time pH of the slurry during the coating process of each coating agent;

[0010] S5. Adjust the flow rate of the coating pH regulator according to the real-time pH of the slurry to make the slurry pH meet the target requirements.

[0011] Preferably, Q n =Q*C*x n % / C n ;

[0012] Q n is the flow rate of each coating agent, in m 3 / h; Q is the titanium dioxide slurry flow rate, unit is m 3 / h; C is the titanium dioxide slurry concentration, in g / L; x n % is the coating mass percentage of each coating agent; C n is the concentration of each coating agent, in g / L;

[0013] V n =Q*t n ;

[0014] V n is the volume of the coated tank, in m 3 ;t n is the coating time of each coating agent, in hours.

[0015] Preferably, the coating temperature W of each coating agent is obtained n ;

[0016] The corresponding flow of hot steam is delivered to the corresponding coating tanks to keep the temperature of each coating tank at the target temperature W. n .

[0017] Preferably, the titanium dioxide continuous coating method as described above further comprises the following steps:

[0018] Monitor the real-time temperature W of each coating tank during the coating process ns ;

[0019] According to the real-time temperature W ns The hot steam flow rate delivered to the coating tank is adjusted so that the coating temperature meets the target requirement.

[0020] Preferably, the coated tank comprises an outer tank and an inner tank located inside the outer tank, a stirring device is provided inside the inner tank, a flow port connected to the outer tank is provided at the bottom of the inner tank, and an overflow port is provided at the top of the outer tank;

[0021] The titanium dioxide slurry, the coating agent and the coating pH regulator are first transported to the upper part of the inner tank, then flow from top to bottom in the inner tank, and then transferred from the flow port to the outer tank, flow from bottom to top in the outer tank, and finally overflow from the overflow port; the entire flow time of the material in the coating tank is t n .

[0022] Preferably, before step S3, a slurry adjustment step of adjusting the titanium dioxide sand abrasive slurry to a target concentration C using desalted water is also included, and the slurry adjusted titanium dioxide slurry is continuously transported to the first coating tank at a flow rate Q.

[0023] Preferably, after step S3, the method further includes the step of using a terminal pH regulator to adjust the coated slurry to a terminal pH; this step is performed in a pH adjustment tank, and the adjustment time is t z , the unit is h, the volume of the pH adjustment tank is V z , unit is m 3 ;

[0024] V z =Q*t z ;

[0025] After coating, the slurry is transported to the pH adjustment tank at a flow rate Q, and at the same time, the terminal pH adjuster is also transported to the pH adjustment tank at a corresponding flow rate. The mixed material flows in the pH adjustment tank for a flow time of t z The mixed material is fully mixed during the flow in the pH adjustment tank to complete the pH adjustment.

[0026] Preferably, a coating tank is provided after the pH adjustment tank, and the titanium dioxide slurry after terminal pH adjustment is transported to the coating tank for temporary storage, and the storage time is t c , unit is h;

[0027] The volume of the coated tank is V c , unit is m 3 ;

[0028] V c =Q*t c .

[0029] Preferably, the titanium dioxide is coated with a single aluminum film; the titanium dioxide slurry concentration C is 250 to 400 g / L; the titanium dioxide slurry flow rate Q is 15 to 18 m 3 / L;

[0030] There are two coating agents, namely a first coating agent and a second coating agent; one of the first coating agent and the second coating agent is an acidic aluminum source, and the other is an alkaline aluminum source;

[0031] The coating amount x1% of the acidic aluminum source is 0.9-1.5%, the coating pH is 3.0-4.0, and the coating time t1 is 40-80 minutes; the coating amount x2% of the alkaline aluminum source is 1.5-2.5%, the coating pH is 10.5-12.0, and the coating time t2 is 150-210 minutes.

[0032] Preferably, the coating temperature of the acidic aluminum source is 50-70°C; the coating temperature of the alkaline aluminum source is 50-70°C.

[0033] Preferably, the titanium dioxide is coated with zirconium-aluminum film; the titanium dioxide slurry concentration C is 250-400 g / L; the titanium dioxide slurry flow rate Q is 15-18 m 3 / L;

[0034] There are two coating agents, namely, a first coating agent zirconium source and a second coating agent aluminum source;

[0035] The coating amount x1% of the zirconium source is 0.3-0.8%, the coating pH is 5-6, and the coating time t1 is 25-55min; the coating amount x2% of the aluminum source is 1.2-2.0%, the coating pH is 7-9, and the coating time t2 is 90-150min.

[0036] Preferably, the coating temperature of the zirconium source is 60-80°C; the coating temperature of the aluminum source is 60-80°C.

[0037] The continuous coating method and system provided in the present application not only realize the continuous coating of titanium dioxide and improve the production capacity, but also fully guarantee the coating effect and improve the product quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 It is a structural schematic diagram of the coating tank provided by the present application;

[0039] Figure 2 It is a structural schematic diagram of the titanium dioxide continuous coating system provided by the present application;

[0040] Figure 3 This is a TEM image of titanium dioxide obtained by coating using the continuous coating method provided by the present application;

[0041] Figure 4This is the TEM image of titanium dioxide obtained by coating using the traditional coating method;

[0042] Among them, 1-slurry mixing tank; 2-coating tank; 21-inner tank; 22-outer tank; 23-feeding port; 24-overflow port; 25-flow port; 3-pH adjusting tank; 4-post-coating tank; 5-stirring device; 7-desalting water delivery pipeline; 8-titanium dioxide slurry delivery pipeline; 9-pH adjusting agent delivery pipeline; 10-coating agent delivery pipeline; 11-control valve; 12-pH detection sensor; 13-temperature detection sensor; 14-steam delivery main pipe; 15-steam delivery branch pipe. DETAILED DESCRIPTION

[0043] The titanium dioxide continuous coating method provided in the present application comprises the following steps:

[0044] S1. Obtain the titanium dioxide slurry concentration C, the number of coating agents n and the coating sequence, and the concentration C of each coating agent n 、The coating amount of each coating agent x n %, coating time t of each coating agent n , the coating pH of each coating agent and the concentration of each coating pH adjusting agent.

[0045] The titanium dioxide slurry concentration C adopts the appropriate concentration of titanium dioxide coating, which is generally 250-400g / L.

[0046] Common coating types of titanium dioxide include aluminum coating, silicon coating, silicon aluminum coating, zirconium aluminum coating, etc. The number of coating agents, coating sequence, and coating agent concentration C n , coating agent coating amount x n %, coating agent coating time t n , coating pH and coating pH regulator concentration are determined according to actual coating requirements.

[0047] S2. Confirm the flow rate Q of titanium dioxide slurry and the flow rate Q of each coating agent n , the flow rate of each coating pH regulator, the number of coating tanks n and the volume V of each coating tank n The number of coating tanks corresponds to the number of coating agents, that is, there are as many coating tanks as there are coating agents.

[0048] Specific:

[0049] The flow rate Q of titanium dioxide slurry should be appropriate. It should not be too large to affect the uniformity of mixing with the coating agent, nor too small to reduce production efficiency. It can be determined according to the titanium dioxide coating capacity. Preferably:

[0050] Q = m / (24*C)*1000;

[0051] Q is the titanium dioxide slurry flow rate, unit is m 3 / h; m is the titanium dioxide coating capacity, unit is t / d; C is the titanium dioxide slurry concentration, unit is g / L, calculated in titanium dioxide; the titanium dioxide coating capacity m can be set according to raw materials and customer needs.

[0052] Q n =Q*C*x n % / C n ;

[0053] Q n is the flow rate of each coating agent, in m 3 / h;x n % is the mass percentage of each coating agent; the coating amount is generally the mass percentage of the oxide of the coating element in the titanium dioxide in the titanium dioxide slurry;

[0054] C n is the concentration of each coating agent, in g / L, calculated as the oxide of the coating element; C is the concentration of titanium dioxide slurry, in g / L;

[0055] V n =Q*t n ;

[0056] V n is the volume of the coated tank, in m 3 ;t n is the coating time of each coating agent, in hours.

[0057] The flow rate of titanium dioxide slurry is determined according to the production capacity and concentration of titanium dioxide slurry, and the flow rate of each coating agent is determined according to the coating amount and concentration of each coating agent. Since the coating time required for each coating agent is different, in order to achieve continuous coating, the volume of the corresponding coating tank is also set to be different. The flow rate of each pH regulator can be preliminarily determined by combining the current hydrogen ion concentration in titanium dioxide slurry, coating agent and pH regulator, as well as the flow rate of titanium dioxide slurry, coating agent flow rate and coating pH.

[0058] S3. Continuously convey titanium dioxide slurry, the first coating agent and the first coating pH adjuster to the first coating tank with a volume of V1 according to the titanium dioxide slurry flow rate Q, the first coating agent flow rate Q1 and the first coating pH adjuster flow rate respectively; each material flows in the first coating tank, and after the flow time reaches t1, it is continuously discharged to the second coating tank with a volume of V2, and at the same time, the second coating agent and the second coating pH adjuster are continuously conveyed to the second coating tank according to the second coating agent flow rate Q2 and the second coating pH adjuster flow rate, and the above steps are followed until the conveyance of all coating agents is completed; the materials are fully mixed and reacted during the flow of each coating tank to complete the coating.

[0059] The above-mentioned coating stages are carried out simultaneously in different coating tanks, and the feeding and homogenization steps of the traditional method are unified into one step, thereby realizing the continuous coating of titanium dioxide. Compared with single-batch coating, the steps are simplified and the production efficiency is improved. However, at the same time, the present application adopts a continuous coating method. During the entire coating process, the slurry is in a continuous flow process. Therefore, the material in the tank body can be easily discharged from the tank body when the mixing is uneven and the reaction is insufficient. Preferably, the coating tank of the present application adopts an inner and outer double-layer tank body. Specifically, Figure 1 As shown, the coating tank includes an outer tank 22 and an inner tank 21 located inside the outer tank, a stirring device 5 is provided inside the inner tank, a feed port 23 is provided at the top of the inner tank, a flow port 25 connected to the outer tank is provided at the bottom of the inner tank, and an overflow port 24 is provided at the top of the outer tank.

[0060] The titanium dioxide slurry, coating agent and coating pH regulator are first transported to the upper part of the inner tank, and then flow from top to bottom in the inner tank. During the flow, they are fully mixed and reacted under the action of the stirring device, and then transferred from the flow port to the outer tank, flow from bottom to top in the outer tank, and finally automatically discharged from the overflow port; the entire flow time of the material in the coating tank is t n The material flow direction is shown by the arrow. Compared with the single-layer tank, the inner and outer double-layer coating tank prolongs the slurry flow path and residence time, which can make the coating reaction more complete and the coating more uniform, thus effectively solving the above technical problems.

[0061] Traditionally, titanium dioxide slurry is transported between different tanks by pumps. The material can be easily pumped out when the reaction is not complete, affecting the uniformity of the coating. This application uses a double-layer tank to automatically discharge the slurry by overflow. When the slurry reaches the overflow port, it must pass through the inner tank and the outer tank, which fully guarantees the residence time of the material in the tank, making the reaction more complete and the film layer more uniform.

[0062] S4. Monitor the real-time slurry pH during the coating process of each coating agent.

[0063] S5. Adjust the flow rate of the coating pH regulator according to the real-time slurry pH.

[0064] The coating needs to be carried out under suitable pH conditions. Traditional coatings, such as the single Al coating described in the background technology, only limit the coating amount of aluminum sulfate and sodium aluminate. Affected by factors such as material batches, slurry concentration, stirring time, etc., even if the same amount of aluminum sulfate and sodium aluminate are added, the coating pH between batches will change, exceeding the suitable pH range, thereby affecting the coating effect. The present application monitors the pH of each coating stage, and adjusts the flow rate of the coating pH regulator in real time according to the monitoring results to ensure that the coating pH is always in the appropriate range, thereby improving the coating effect.

[0065] Since the pH adjuster flow rate is adjusted according to the real-time pH of the slurry, a value can be estimated based on experience when initially determining the pH adjuster flow rate, and then the pH adjuster flow rate can be adjusted in real time based on the pH test results. This can also ensure that the coating pH is always within an appropriate range, thereby reducing the amount of calculations.

[0066] It is generally known to those skilled in the art that titanium dioxide coating requires not only a suitable pH but also a suitable temperature. Therefore, the present application also includes the following steps:

[0067] Get the coating temperature W of each coating agent n ;

[0068] The corresponding flow of hot steam is delivered to the corresponding coating tanks to keep the temperature of each coating tank at the target temperature W. n , improve the coating effect.

[0069] Further preferably, the present application further comprises the following steps:

[0070] Monitor the real-time temperature W of each coating tank during the coating process ns ; and according to the monitoring temperature W ns Adjust the hot steam flow delivered to the coating tank to ensure that the coating temperature is always within the appropriate range to ensure the coating effect.

[0071] The titanium dioxide slurry for coating, especially the titanium dioxide slurry produced by the sulfuric acid process, generally needs to be sand-milled to make the titanium dioxide particle size meet the coating requirements. The titanium dioxide slurry obtained by sand-milling has a higher concentration, while the titanium dioxide slurry required for coating has a lower concentration, generally 250-400 g / L. Therefore, before step S3, the present application also includes a slurry adjustment step of using desalted water to adjust the titanium dioxide sand-milled slurry to the target concentration C. This step is performed in a slurry adjustment tank, and the slurry-adjusted titanium dioxide slurry is continuously transported to the first coating tank at a flow rate Q. Partial coating requires adjusting the pH of the titanium dioxide slurry during the slurry adjustment process, and at this time, an appropriate amount of pH regulator needs to be added to the slurry adjustment tank.

[0072] The slurry in the slurry mixing tank can be directly transported to the first coating tank. At this time, in order to ensure the uniformity of slurry mixing, the slurry mixing tank can also use a double-layer tank like the coating tank, and the volume of the slurry mixing tank is determined according to the slurry mixing time.

[0073] The slurry can also be prepared by a prefabricated method, and continuously transported to the first coating tank at a corresponding flow rate.

[0074] Downstream customers have different requirements for the pH of titanium dioxide. In addition, in order to facilitate water washing, the pH of titanium dioxide generally needs to be adjusted to an appropriate range after coating. Therefore, preferably, the present application further includes a step of using a terminal pH regulator to adjust the coated slurry to a terminal pH after step S3; this step is performed in a pH adjustment tank, and the adjustment time is t z , the unit is h, the volume of the pH adjustment tank is Vz , unit is m 3 ;

[0075] V z =Q*t z ;

[0076] After coating, the slurry is transported to the pH adjustment tank at a flow rate of Q. At the same time, the terminal pH adjuster is also transported to the pH adjustment tank at a corresponding flow rate. The mixed material flows in the pH adjustment tank for a flow time of t z The mixed materials are fully mixed during the flow in the pH adjustment tank to complete the pH adjustment.

[0077] The next process after coating is filter pressing, which is to separate the solid and liquid of the slurry. The present application also provides a post-coating tank after the pH adjustment tank. The titanium dioxide slurry after terminal pH adjustment is transported to the post-coating tank for temporary storage, which is convenient for subsequent filter pressing production.

[0078] Storage time is t c , unit is h;

[0079] The volume of the tank after coating is V c , unit is m 3 ;

[0080] V c =Q*t c .

[0081] As can be understood by those skilled in the art, the volume of the tank after coating can also be appropriately expanded to meet the demand for higher storage time.

[0082] The present application further arranges a slurry mixing tank, a pH adjustment tank and a post-coating tank of corresponding volumes before and after the coating tank, so that the entire coating process is in a continuous state, further improving the coating efficiency.

[0083] The coating method provided in this application is suitable for titanium dioxide coating, which is mostly wet coating in the prior art, and is better applied to non-dense coating. Dense films such as dense silicon coating require a long time, high temperature, higher requirements on flow rate and tank volume, and limited production conditions.

[0084] In the continuous coating method provided by the present application, titanium dioxide slurry and coating agent are continuously transported to the coating tank in proportion, the proportion of titanium dioxide and coating agent is always the same during the flow from the inside to the outside of the coating tank, the mixing is uniform, the coating time is also fully guaranteed, the coating reaction is relatively sufficient, and the coating pH and temperature are always consistent. Therefore, the coating uniformity and density are good, the product quality is better than traditional intermittent production, and there is no difference between batches.

[0085] The present application provides an optimal titanium dioxide single aluminum continuous coating method, the production capacity m is designed to be about 120t (the production capacity includes the coating element, but the coating element is generally less in content and can be ignored. When calculating, 120t is calculated based on the titanium dioxide content), the titanium dioxide slurry concentration C used is 250-400g / L; the titanium dioxide slurry flow rate Q is 15-18m 3 / L. Titanium dioxide slurry can be selected from sulfuric acid process titanium dioxide slurry and chloride process titanium dioxide slurry.

[0086] There are two coating agents, namely the first coating agent and the second coating agent; one of the first coating agent and the second coating agent is an acidic aluminum source, and the other is an alkaline aluminum source. When sulfuric acid titanium dioxide slurry is used, the first coating agent is an acidic aluminum source, and when chloride titanium dioxide slurry is used, the first coating agent is an alkaline aluminum source.

[0087] Acidic aluminum sources include aluminum sulfate, aluminum chloride, etc., and alkaline aluminum sources include sodium aluminate, potassium aluminate, etc.

[0088] The coating amount x1% of the acidic aluminum source is 0.9-1.5%, the coating pH is 3.0-4.0, and the coating time t1 is 40-80 min; the coating amount x2% of the alkaline aluminum source is 1.5-2.5%, the coating pH is 10.5-12.0, and the coating time t1 is 150-210 min.

[0089] More preferably, the coating temperature of the acidic aluminum source is 50-70°C; the coating temperature of the alkaline aluminum source is 50-70°C.

[0090] The present application also provides a preferred titanium dioxide zirconium aluminum continuous coating method, the production capacity m is designed to be about 120t, the titanium dioxide slurry concentration C used is 250-400g / L; the titanium dioxide slurry flow rate Q is 15-18m 3 / L. Titanium dioxide slurry can be selected from sulfuric acid process titanium dioxide slurry and chloride process titanium dioxide slurry.

[0091] There are two coating agents, namely a first coating agent zirconium source and a second coating agent aluminum source.

[0092] The zirconium source may be zirconium oxychloride, zirconium sulfate, zirconium chloride, etc., and the aluminum source may be sodium aluminate, potassium aluminate, etc.

[0093] The coating amount x1% of the zirconium source is 0.3-0.8%, the coating pH is 5-6, and the coating time t1 is 25-55min; the coating amount x2% of the aluminum source is 1.2-2.0%, the coating pH is 7-9, and the coating time t2 is 90-150min.

[0094] More preferably, the coating temperature of the zirconium source is 60-80°C; the coating temperature of the aluminum source is 60-80°C.

[0095] After testing, it was found that the flow rate of the above-mentioned single aluminum coating and zirconium aluminum dual coating slurry was appropriate, the pH and temperature of the coating process were effectively controlled, continuous coating could be carried out for a long time without interruption, and the products produced had a more uniform and dense coating layer than those produced by the traditional intermittent method.

[0096] Based on the above method, the present application also provides a titanium dioxide continuous coating system, such as Figure 2 As shown, along the flow direction of titanium dioxide slurry, it includes a slurry mixing tank 1, several coating tanks 2 and a pH adjustment tank 3 connected in sequence. The slurry mixing tank, coating tank and pH adjustment tank all adopt an inner and outer double-layer tank body, specifically including an outer tank 22 and an inner tank 21 located in the outer tank, a stirring device 5 is provided in the inner tank, a feed port 23 is provided at the top of the inner tank, a flow port 25 connected to the outer tank is provided at the bottom of the inner tank, and an overflow port 24 is provided at the top of the outer tank. Titanium dioxide slurry, coating agent, pH adjuster and other materials enter the corresponding inner tank from the top of the inner tank, flow from top to bottom in the inner tank, and are fully mixed under the action of the stirring device, transferred to the outer tank through the flow port, flow from bottom to top in the outer tank, and finally automatically discharged from the overflow port when reaching the overflow port. The flow time of the material in the entire tank body is the slurry mixing time / coating time / pH adjustment time.

[0097] The present application provides a titanium dioxide slurry delivery pipeline 8 between the front and rear tanks for delivering the titanium dioxide slurry.

[0098] The present application also includes a desalted water delivery pipeline 7, several pH regulator delivery pipelines 9, and a coating agent delivery pipeline 10 for delivering corresponding materials. A control valve 11 is also provided on the delivery pipeline for controlling the material delivery flow rate.

[0099] The present application also includes a plurality of pH detection sensors 12, which are used to detect the pH of the titanium dioxide slurry from the slurry mixing tank, the coating tank and the pH adjustment tank. The pH detection sensor 12 is interlocked with the control valve of the pH adjuster delivery pipeline. When the detected pH does not meet the target requirements, it can be fed back to the control valve to timely adjust the pH adjuster delivery flow.

[0100] Preferably, a post-coating tank 4 is provided behind the pH adjustment tank 3 to store the titanium dioxide slurry after coating and pH adjustment. A stirring device is also provided in the post-coating tank 4 to continuously stir the titanium dioxide slurry so that the titanium dioxide slurry is continuously in a uniformly dispersed state to prevent the slurry from agglomerating. When the slurry in the post-coating tank reaches a certain volume, it is transported to the next process, i.e., the filter press, for filtration.

[0101] Preferably, the present application is provided with a temperature regulating system for regulating the slurry mixing tank 1 and the coating tank 2 to be at a target temperature.

[0102] Furthermore, the temperature regulation system includes a hot steam delivery main pipe 14, several steam delivery branch pipes 15 respectively connected to the slurry mixing tank 1 and the coating tank 2, and several temperature detection sensors 13; the several temperature detection sensors are respectively used to detect the temperature of the titanium dioxide slurry from the slurry mixing tank 1 and the coating tank 2; each steam delivery branch pipe 15 is provided with a control valve for adjusting the hot steam delivery amount according to the detection information of the temperature detection sensor, thereby adjusting the temperature of the slurry mixing tank and the coating tank.

[0103] Furthermore, the end of the steam delivery branch pipe connected to the coating tank is directly connected to the outer tank, and hot steam is first delivered to the outer tank. The end of the steam delivery branch pipe is connected to the outer tank, which can leave enough space for the inner tank, expand the area of ​​the stirring device, improve the stirring effect, and then improve the coating effect.

[0104] The pH detection sensor and the temperature detection sensor are preferably arranged on the titanium dioxide slurry conveying pipeline between the front and rear tanks.

[0105] Therefore, the continuous coating method and system provided in the present application not only realize the continuous coating of titanium dioxide and improve the production capacity, but also fully guarantee the coating effect and improve the product quality.

[0106] Example 1

[0107] This embodiment adopts Figure 2 The system shown in the figure performs continuous coating production of titanium dioxide, and specifically includes the following steps:

[0108] S1. In this embodiment, the titanium dioxide powder adopts a single Al coating, and the production capacity is designed to be 120 t / d. The titanium dioxide slurry concentration is designed to be 300 g / L (in terms of titanium dioxide), and the slurry mixing temperature is designed to be 50-60°C.

[0109] First, aluminum sulfate is used as the first coating agent, the coating amount is 1.1% (calculated as the mass percentage of aluminum oxide to titanium dioxide in the slurry), the coating pH is 3.4-3.6, the coating time is 1 hour, the concentration of aluminum sulfate solution (calculated as aluminum oxide) is 100 g / L, the coating temperature is 60°C, the first pH adjuster is NaOH, and the concentration of the first pH adjuster is 120 g / L.

[0110] Then sodium aluminate was used as the second coating agent, the coating amount was 1.9% (calculated as the mass percentage of alumina to titanium dioxide in the slurry), the second pH adjuster was NaOH, the concentration of the second pH adjuster was 120 g / L, the coating pH was 11.3-11.5, the coating time was 3 hours, the concentration of sodium aluminate solution was 160 g / L (calculated as alumina), and the coating temperature was 60°C.

[0111] After coating, sulfuric acid was used to adjust the slurry pH to 6.6-7.0, the sulfuric acid concentration was 160 g / L, and the pH adjustment time was 1 hour.

[0112] After pH adjustment, the storage time in the coated tank is 5 hours.

[0113] S2. After calculation, the titanium dioxide slurry flow rate Q = m / (24*C)*1000 = 16.7m 3 / h;

[0114] Aluminum sulfate flow rate Q1 = Q*C*x1% / C1 = 0.55m 3 / h;

[0115] Sodium aluminate flow rate Q2 = Q*C*x2% / C2 = 0.58m 3 / h;

[0116] The volume of the slurry mixing tank is 16.7m 3 ;

[0117] The volume of the first coating tank V1 = Q*t1 = 16.7m 3 ;

[0118] The volume of the second coating tank V2 = Q*t2 = 50m 3 ;

[0119] pH adjustment tank volume V z =Q*t z =16.7m 3 ;

[0120] Tank volume after coating V c =Q*t c =83.5m 3 .

[0121] The first pH regulator delivery flow rate, the second pH regulator delivery flow rate and the sulfuric acid delivery flow rate are preliminarily determined according to production experience. The first pH regulator delivery flow rate, the second pH regulator delivery flow rate and the sulfuric acid delivery flow rate are 0.05m 3 / h、0.05m 3 / h and 0.36m 3 / h.

[0122] S3. In the slurry mixing tank, the sand abrasive slurry (sand abrasive slurry is sulfuric acid slurry with a concentration of 600g / L) and desalted water are continuously transported. The transport flow rate of the sand abrasive slurry and desalted water is 8.35m 3 / h, under the action of the stirring device, titanium dioxide slurry that meets the concentration requirements is obtained, and then 3 / h is discharged through the overflow port and flows to the first coating tank. At the same time, the 3 / h conveying aluminum sulfate solution and 0.05m3 / h transports the first pH adjuster to the first coating tank, the material flows from the inner tank to the outer tank, and then is discharged through the overflow port and transported to the second coating tank. The material stays in the first coating tank for 1 hour;

[0123] While the titanium dioxide slurry is being transported from the first coating tank to the second coating tank, 3 / h conveying sodium aluminate solution and 0.05m 3 / h transports the second pH adjuster to the second coating tank, the material flows from the inner tank to the outer tank, and then is transported to the pH adjustment tank through the overflow port, and the material stays in the second coating tank for 3h;

[0124] While the titanium dioxide slurry is being transported from the second coating tank to the pH adjustment tank, 3 / h transports sulfuric acid solution to the pH adjustment tank, and after staying for 1 hour, it is discharged to the coating tank for temporary storage.

[0125] During the entire coating process, steam of corresponding flow rates is delivered to the slurry mixing tank, the first coating tank and the second coating tank respectively, so that the temperature of each tank is maintained within the required range.

[0126] S4. Use pH detection sensors and temperature detection sensors to monitor the temperature and pH of each tank in the coating process in real time. When the real-time monitored temperature and pH exceed the required range, adjust the flow rate of hot steam and pH regulator accordingly. For example, when it is detected that the temperature of the slurry mixing tank exceeds 60°C, the flow rate of hot steam delivered to the slurry mixing tank is reduced accordingly through the control valve.

[0127] S5. The slurry in the coating tank is transported to the filter press for filtration, and then flashed and steamed to obtain a single aluminum coated titanium dioxide product. Samples are taken for TEM transmission electron microscopy testing, and the results are as follows: Figure 3 shown.

[0128] Through the above method, the daily production capacity of Al-coated titanium dioxide can reach 120t.

[0129] Comparative Example 1

[0130] First, the qualified sulfuric acid titanium dioxide slurry after sand grinding is put into the coating tank, and desalted water is added to adjust the concentration to 300g / L, and then 1.1% aluminum sulfate is added. The aluminum sulfate is added for 30 minutes and homogenized for 30 minutes after addition. Then 1.9% sodium aluminate is added. The sodium aluminate is added for 60 minutes and homogenized for 120 minutes after addition. Then sulfuric acid is added to adjust the end point pH to 6.6-7.0. The sulfuric acid is added for 30 minutes and homogenized for 30 minutes after addition. Then, filter pressing, flash evaporation and steam powder are performed to obtain the finished titanium dioxide powder. Samples are taken for TEM transmission electron microscope detection. The results are as follows: Figure 4 shown.

[0131] After the entire coating is completed, the slurry is pumped into the next process and re-filled for the next coating.

[0132] from Figures 3-4 It can be seen that the uniformity of the titanium dioxide obtained by the continuous coating method of the present application is better than that of the titanium dioxide obtained by the traditional intermittent coating method.

[0133] To achieve a daily production capacity of 120t using traditional methods, the coating tank volume needs to reach 120m 3 Under this volume condition, production is subject to certain restrictions.

[0134] Example 2

[0135] S1. In this embodiment, the titanium dioxide powder adopts Zr / Al coating, and the designed production capacity is 120t / d. The titanium dioxide slurry adopts sulfuric acid method titanium dioxide slurry, the concentration is designed to be 300g / L (in terms of titanium dioxide), and the slurry mixing temperature is designed to be 60-75°C.

[0136] First, zirconium dichloride is used as the first coating agent, the coating amount is 0.5% (calculated as the mass percentage of zirconium oxide to titanium dioxide in the slurry), the coating pH is 5-6, the coating time is 40 minutes, the concentration of zirconium dichloride solution (calculated as zirconium oxide) is 100 g / L, the coating temperature is 70°C, the first pH adjuster is NaOH, and the concentration of the first pH adjuster is 280 g / L.

[0137] Then sodium aluminate is used as the second coating agent, the coating amount is 1.8% (calculated as the mass percentage of alumina to titanium dioxide in the slurry), the second pH adjuster is aluminum sulfate, the concentration of the second pH adjuster is 100g / L, the coating pH is 7.5-8.5, the coating time is 2h, the concentration of sodium aluminate solution is 160g / L (calculated as alumina), and the coating temperature is 70°C.

[0138] After coating, sulfuric acid was used to adjust the slurry pH to 6.5-6.8, the sulfuric acid concentration was 160 g / L, and the pH adjustment time was 1 hour.

[0139] After pH adjustment, the storage time in the coated tank is 5 hours.

[0140] S2. After calculation, the titanium dioxide slurry flow rate Q = m / (24*C)*1000 = 16.7m 3 / h;

[0141] Zirconium dichloride flow rate Q1 = Q*C*x1% / C1 = 0.25m 3 / h;

[0142] Sodium aluminate flow rate Q2 = Q*C*x2% / C2 = 0.56m 3 / h;

[0143] The volume of the slurry mixing tank is 16.7m 3 ;

[0144] The volume of the first coating tank V1 = Q*t1 = 11.1m 3 ;

[0145] The volume of the second coating tank V2 = Q*t2 = 33.4m 3 ;

[0146] pH adjustment tank volume V z =Q*t z =16.7m 3 ;

[0147] Tank volume after coating V c =Q*t c =83.5m 3 .

[0148] The first pH adjuster delivery flow rate, the second pH adjuster delivery flow rate and the sulfuric acid delivery flow rate are preliminarily determined according to production experience. The first pH adjuster delivery flow rate, the second pH adjuster delivery flow rate and the sulfuric acid delivery flow rate are 0.52m 3 / h、0.4m 3 / h and 0.14m 3 / h.

[0149] S3. In the slurry mixing tank, the sand abrasive slurry (sand abrasive slurry is sulfuric acid slurry with a concentration of 600g / L) and desalted water are continuously transported. The transport flow rate of the sand abrasive slurry and desalted water is 8.35m 3 / h, under the action of the stirring device, titanium dioxide slurry that meets the concentration requirements is obtained, and then 3 / h is discharged through the overflow port and flows to the first coating tank. At the same time, the 3 / h transport of zirconium oxychloride solution and 0.52m 3 / h transports the first pH regulator to the first coating tank, the material flows from the inner tank to the outer tank, and then is discharged through the overflow port and transported to the second coating tank. The material stays in the first coating tank for 40 minutes;

[0150] While the titanium dioxide slurry is being transported from the first coating tank to the second coating tank, 3 / h conveying sodium aluminate solution and 0.4m 3 / h transports the second pH regulator to the second coating tank, the material flows from the inner tank to the outer tank, and then is transported to the pH adjustment tank through the overflow port, and the material stays in the second coating tank for 2h;

[0151] While the titanium dioxide slurry is being transported from the second coating tank to the pH adjustment tank, 3 / h transports sulfuric acid solution to the pH adjustment tank, and after staying for 1 hour, it is discharged to the coating tank for temporary storage.

[0152] During the entire coating process, steam of corresponding flow rates is delivered to the slurry mixing tank, the first coating tank and the second coating tank respectively, so that the temperature of each tank is maintained within the required range.

[0153] S4. Use pH detection sensors and temperature detection sensors to monitor the temperature and pH of each tank in the coating process in real time. When the real-time monitored temperature and pH exceed the required range, adjust the flow rate of hot steam and pH regulator accordingly. For example, when it is detected that the temperature of the slurry mixing tank exceeds 70°C, the flow rate of hot steam delivered to the slurry mixing tank is reduced accordingly through the control valve.

[0154] Although preferred embodiments of the present invention have been described, additional changes and modifications may be made to these embodiments by those skilled in the art once the basic inventive concepts are known. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention. Obviously, those skilled in the art may make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A titanium dioxide continuous coating method, characterized in that: The following steps are involved: S1. Obtain the titanium dioxide slurry concentration C, the number of coating agents n and the coating sequence, and the concentration C of each coating agent n 、The coating amount of each coating agent x n %, coating time t of each coating agent n , the coating pH of each coating agent and the concentration of each coating pH adjusting agent; S2. Confirm the flow rate Q of titanium dioxide slurry and the flow rate Q of each coating agent n , the flow rate of each coating pH regulator, the number of coating tanks n and the volume V of each coating tank n ; The number of coating tanks corresponds to the number of coating agents; S3. Continuously convey titanium dioxide slurry, the first coating agent and the first coating pH adjusting agent to the first coating tank with a volume of V1 according to the titanium dioxide slurry flow rate Q, the first coating agent flow rate Q1 and the first coating pH adjusting agent flow rate respectively; the material flows in the first coating tank, and after the flow time reaches t1, it is continuously discharged to the second coating tank with a volume of V2, and at the same time, the second coating agent and the second coating pH adjusting agent are continuously conveyed to the second coating tank according to the second coating agent flow rate Q2 and the second coating pH adjusting agent flow rate, and the above steps are followed until all n coating agents are added; the material is fully mixed and reacted during the flow of each coating tank to complete the coating; S4. Monitor the real-time pH of the slurry during the coating process of each coating agent; S5. Adjust the flow rate of the coating pH regulator according to the real-time pH of the slurry to make the slurry pH meet the target requirements.

2. The titanium dioxide continuous coating method according to claim 1, characterized in that: Q n =Q*C*x n % / C n ; Q n is the flow rate of each coating agent, in m 3 / h; Q is the titanium dioxide slurry flow rate, unit is m 3 / h; C is the titanium dioxide slurry concentration, in g / L; x n % is the coating mass percentage of each coating agent; C n is the concentration of each coating agent, in g / L; V n =Q*t n ; V n is the volume of the coated tank, in m 3 ; t n is the coating time of each coating agent, in hours.

3. The titanium dioxide continuous coating method according to claim 1, characterized in that: The following steps are also included: Get the coating temperature W of each coating agent n ; The corresponding flow of hot steam is delivered to the corresponding coating tanks to keep the temperature of each coating tank at the target temperature W. n .

4. The titanium dioxide continuous coating method according to claim 3, characterized in that: The following steps are also included: Monitor the real-time temperature W of each coating tank during the coating process ns ; According to the real-time temperature W ns The hot steam flow rate delivered to the coating tank is adjusted so that the coating temperature meets the target requirement.

5. The titanium dioxide continuous coating method according to claim 1, characterized in that: The coated tank comprises an outer tank and an inner tank located inside the outer tank, a stirring device is arranged inside the inner tank, a flow port connected to the outer tank is arranged at the bottom of the inner tank, and an overflow port is arranged at the top of the outer tank; The titanium dioxide slurry, the coating agent and the coating pH regulator are first transported to the upper part of the inner tank, then flow from top to bottom in the inner tank, and then transferred from the flow port to the outer tank, flow from bottom to top in the outer tank, and finally overflow from the overflow port; the entire flow time of the material in the coating tank is t n .

6. The titanium dioxide continuous coating method according to claim 1, characterized in that: Before step S3, a slurry adjustment step of adjusting the titanium dioxide sand-grinding slurry to a target concentration C using desalted water is also included, and the slurry-adjusted titanium dioxide slurry is continuously transported to the first coating tank at a flow rate Q.

7. The titanium dioxide continuous coating method according to claim 1, characterized in that: After step S3, the step of using a terminal pH regulator to adjust the coated slurry to the terminal pH is also included; this step is carried out in a pH adjustment tank, and the adjustment time is t z , the unit is h, the volume of the pH adjustment tank is V z , unit is m 3 ; V z =Q*t z ; After coating, the slurry is transported to the pH adjustment tank at a flow rate Q, and at the same time, the terminal pH adjuster is also transported to the pH adjustment tank at a corresponding flow rate. The mixed material flows in the pH adjustment tank for a flow time of t z The mixed material is fully mixed during the flow in the pH adjustment tank to complete the pH adjustment.

8. The titanium dioxide continuous coating method according to claim 7, characterized in that: A coating tank is also provided after the pH adjustment tank. The titanium dioxide slurry after terminal pH adjustment is transported to the coating tank for temporary storage. The storage time is t c , unit is h; The volume of the coated tank is V c , unit is m 3 ; V c =Q*t c 。 9. The titanium dioxide continuous coating method according to claim 1, characterized in that: The titanium dioxide is coated with a single aluminum film; the titanium dioxide slurry concentration C is 250-400 g / L; the titanium dioxide slurry flow rate Q is 15-18 m 3 / L; There are two coating agents, namely a first coating agent and a second coating agent; one of the first coating agent and the second coating agent is an acidic aluminum source, and the other is an alkaline aluminum source; The coating amount x1% of the acidic aluminum source is 0.9-1.5%, the coating pH is 3.0-4.0, and the coating time t1 is 40-80 minutes; the coating amount x2% of the alkaline aluminum source is 1.5-2.5%, the coating pH is 10.5-12.0, and the coating time t2 is 150-210 minutes.

10. The titanium dioxide continuous coating method according to claim 9, characterized in that: The coating temperature of the acidic aluminum source is 50-70°C; the coating temperature of the alkaline aluminum source is 50-70°C.

11. The titanium dioxide continuous coating method according to claim 1, characterized in that: The titanium dioxide is coated with zirconium-aluminum film; the titanium dioxide slurry concentration C is 250-400 g / L; the titanium dioxide slurry flow rate Q is 15-18 m 3 / L; There are two coating agents, namely, a first coating agent zirconium source and a second coating agent aluminum source; The coating amount x1% of the zirconium source is 0.3-0.8%, the coating pH is 5-6, and the coating time t1 is 25-55min; the coating amount x2% of the aluminum source is 1.2-2.0%, the coating pH is 7-9, and the coating time t2 is 90-150min.

12. The titanium dioxide continuous coating method according to claim 11, characterized in that: The coating temperature of the zirconium source is 60-80°C; the coating temperature of the aluminum source is 60-80°C.

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