Environment-friendly titanium dioxide washing system and washing method thereof

Abstract

The present disclosure relates to the field of titanium dioxide production purification technology, and particularly relates to an environment-friendly titanium dioxide washing system and a washing method thereof. The environment-friendly titanium dioxide washing system comprises a pretreatment unit, a closed washing unit and a quality-based recovery circulation unit which are sequentially connected along the material flow direction. The pretreatment unit comprising a modification reaction tank and a modifier metering assembly is arranged to form soft agglomerates with larger particle size from fine particle titanium dioxide before washing, so as to reduce the filtration probability of fine particles from the root, and solve the problem of fine particle filtration. The closed washing unit comprising a diaphragm filter press and a laminated precision filter which are connected in series is arranged to realize double interception. The quality-based recovery circulation unit is arranged to divert the washing wastewater to different recovery pipelines, so as to reduce the wastewater treatment cost and realize the step-by-step utilization of resources.

Description

Technical Field

[0001] This disclosure belongs to the field of titanium dioxide production and purification technology, and particularly relates to an environmentally friendly titanium dioxide washing system and washing method. Background Technology

[0002] Titanium dioxide is currently the highest-performing white inorganic pigment, widely used in coatings, plastics, papermaking, and synthetic fibers. The sulfuric acid process is the mainstream technology for titanium dioxide production. During the production process, the surface of the metatitanic acid particles generated by hydrolysis adsorbs a large number of impurities, including free sulfuric acid, ferrous sulfate, and various soluble metal ions. These impurities need to be removed through a washing process, and the washing effect directly determines the purity, whiteness, and application performance of the final product.

[0003] In related technologies, washing equipment often employs vacuum leaf filters or ordinary plate and frame filter presses. Due to the extremely fine particle size of titanium dioxide, material loss is severe, resulting in raw material depletion and potential environmental pollution. Furthermore, the desalination process utilizes large amounts of water, leading to low recycling rates of washing water and significant water waste. Additionally, the high moisture content of the filter cake results in substantial energy consumption during the calcination process. Moreover, the equipment has low automation levels, requiring manual handling for tasks such as filter cloth maintenance and replacement, filter cake unloading and cleaning, and manual transfer of wastewater or slurry.

[0004] Therefore, developing an environmentally friendly titanium dioxide washing process and method that combines low loss, low water consumption, and high automation is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] This disclosure provides an environmentally friendly titanium dioxide washing system and method, which adopts an integrated architecture of "pre-agglomeration modification - gradient closed washing - graded recycling" to solve the problem of fine particle leakage from the filter at the source, improve washing efficiency and water resource recycling rate, and achieve fully closed and automated clean production.

[0006] In a first aspect, this disclosure provides an environmentally friendly titanium dioxide washing system, comprising a pretreatment unit, a closed washing unit, and a fractional recycling unit connected sequentially along the material flow direction; the pretreatment unit includes a modification reaction tank and a modifier metering component, the modifier metering component being connected to the modification reaction tank, the modification reaction tank being configured to receive titanium dioxide slurry and mix it with a modifier to induce controllable soft agglomeration of fine titanium dioxide particles to form agglomerated slurry; the closed washing unit includes a diaphragm filter press and a disc filter connected in series, the feed end of the diaphragm filter press being connected to the modified reaction tank... The discharge end of the reaction tank is connected to the diaphragm filter press, which is used for solid-liquid separation and washing of the agglomerated slurry. The diaphragm filter press can perform synchronous and coordinated operation of reverse washing and diaphragm pressing. The feed end of the disc-type precision filter is connected to the slurry outlet of the diaphragm filter press, and is used for secondary interception filtration of the slurry. The fractional recycling unit includes an online conductivity detection component and a diversion component. The online conductivity detection component is used to detect the conductivity of the washing wastewater in real time. The diversion component diverts the washing wastewater to different recycling pipelines according to the conductivity detection result.

[0007] In some embodiments, the diaphragm filter press has a forward inlet and a reverse inlet, enabling bidirectional penetration washing; the stacked precision filter is internally equipped with reinforced polyamide plastic filter discs, with a filtration accuracy of 20~200 micrometers.

[0008] In some embodiments, the fractional recycling unit further includes: a first washing recycling pipeline, a second washing recycling pipeline, and a third washing recycling pipeline; the online conductivity detection component includes an online conductivity meter; the diversion component includes intelligent solenoid valves disposed on the first washing recycling pipeline, the second washing recycling pipeline, and the third washing recycling pipeline, and the intelligent solenoid valves are signal-connected to the online conductivity meter.

[0009] In some embodiments, an inorganic membrane module is provided on the first washing and recovery pipeline. The inorganic membrane module is used to enrich and separate titanium dioxide particles in high-concentration wastewater. The concentrated liquid outlet of the inorganic membrane module is connected to the modified reaction tank of the pretreatment unit. The outlet of the second washing and recovery pipeline is connected to the forward inlet of the diaphragm filter press. The outlet of the third washing and recovery pipeline is connected to the equipment flushing system.

[0010] In some embodiments, the inorganic membrane module has a double-layer composite structure, with an outer layer of ceramic self-cleaning coating and an inner layer of Al2O3-ZrO2 composite membrane; the membrane pore size is 0.01~0.5μm, the membrane thickness is 50~60μm, and the porosity is 44%~46%.

[0011] In some embodiments, a reverse osmosis device is provided on the third washing and recovery pipeline, and the product water outlet of the reverse osmosis device is connected to the reverse inlet of the diaphragm filter press.

[0012] In some embodiments, a conductivity monitor is installed on the product water outlet pipe of the reverse osmosis unit to control the product water conductivity to ≤10μS / cm.

[0013] In a first aspect, this disclosure provides an environmentally friendly titanium dioxide washing method, employing an environmentally friendly titanium dioxide washing system according to any embodiment of the first aspect, comprising the following steps: Pre-agglomeration modification: Titanium dioxide slurry is fed into a modification reaction tank, a modifier is added, and the mixture is stirred to cause controlled soft agglomeration of the fine titanium dioxide particles, resulting in a modified slurry; Gradient closed washing: The modified slurry is pumped into the diaphragm filter press, first filtered under low pressure to form a uniform filter cake, then the forward washing process is started, using medium-concentration wash water stored in the second washing recovery pipeline to perform forward penetration washing of the filter cake; then the process is switched to the backwashing process, using fresh desalinated water to perform reverse penetration washing from the other side of the filter cake, while the diaphragm pressing process is started, and compressed air is introduced to pre-press the filter cake; Separate graded recovery: The wash water produced by the diaphragm filter press is monitored in real time by the online conductivity meter. When the conductivity is ≥15000μS / cm, the intelligent electromagnetic... The valve automatically opens the first washing and recovery pipeline. After the washing water is intercepted and recovered by the inorganic membrane module, the concentrated slurry is returned to the pretreatment unit. When the conductivity drops below 5000 μS / cm, the second washing and recovery pipeline is automatically opened. The washing water is stored and used for the next batch of forward washing. When the conductivity drops below 100 μS / cm, the third washing and recovery pipeline is automatically opened. After being treated by the reverse osmosis integrated device, the water is used as a fresh demineralized water source or equipment flushing water. Filter cake unloading: After pressing, the filter cake discharged from the diaphragm filter press is sent to the subsequent pulping process. The thin slurry containing trace amounts of titanium dioxide is sent to the disc precision filter for precise interception. The filtrate is treated by the reverse osmosis integrated device, and the conductivity of the product water is ≤10 μS / cm.

[0014] In some embodiments, in the gradient closed washing step, the washing pressure of the forward washing process is 0.6~0.8MPa, and the washing time is 60~100 minutes; the washing pressure of the backwashing process is 3.0~5.0MPa, and the pressing pressure of the diaphragm pressing is 1.3~1.5MPa, and the pressing time is 20~30 minutes.

[0015] In some embodiments, in the pre-agglomeration modification step, the modifier is ammonium bicarbonate, which is added at 0.4% to 0.6% of the dry weight of titanium dioxide, with the pH value controlled at 6.5 to 7.0 and the reaction proceeding at a low speed for 10 to 20 minutes, causing the fine titanium dioxide particles to undergo controllable soft agglomeration, resulting in the modified slurry; or, the modifier is an anionic surfactant, which is added at 0.2% to 0.3% of the dry weight of titanium dioxide, with the pH value controlled at 5.5 to 6.5 and the reaction proceeding at a low speed for 10 to 20 minutes, causing the fine titanium dioxide particles to undergo controllable soft agglomeration through electrostatic adsorption.

[0016] The environmentally friendly titanium dioxide washing system and method provided in this disclosure solves the problem of fine particle filtration by setting up a pretreatment unit including a modified reaction tank and a modifier metering component, which causes fine titanium dioxide particles to form soft agglomerates with larger particle sizes before washing.

[0017] By setting up a closed washing unit that includes a diaphragm filter press connected in series and a disc-type precision filter, dual interception is achieved, the total material loss rate can be controlled below 0.5%, and the interception efficiency of the target pre-agglomerated titanium dioxide particles can reach more than 85%, which greatly reduces raw material waste and reduces the wastewater and solid waste treatment load.

[0018] By setting up a separate recycling and circulation unit, the washing wastewater is diverted to different recycling pipelines, which can reduce the amount of washing wastewater discharged by 80%, reduce wastewater treatment costs, and realize the cascade utilization of resources.

[0019] By employing a synergistic operation that simultaneously performs reverse washing and diaphragm pressing, the process eliminates the need for step-by-step switching, shortening the operation cycle by approximately 30% compared to traditional processes. Simultaneously, the pressing action enhances the mass transfer effect of the washing liquid within the filter cake, increasing the elution rate of soluble impurities by approximately 20%. The final product exhibits soluble iron residues below 10 ppm, chloride ion residues below 50 ppm, and a resistivity consistently above 20,000 Ω·cm, fully meeting the high-purity requirements of the chemical fiber and high-end coating industries, resulting in a significant upgrade in product quality. Attached Figure Description

[0020] To more clearly illustrate the technical solutions of the embodiments of this disclosure, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this disclosure. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a structural block diagram of an environmentally friendly titanium dioxide washing system provided in one embodiment of the present disclosure; Figure 2This is a structural block diagram of another environmentally friendly titanium dioxide washing system provided in one embodiment of the present disclosure; Figure 3 This is a flowchart of an environmentally friendly titanium dioxide washing method provided in one embodiment of the present disclosure.

[0022] Explanation of reference numerals in the attached figures: 1. Modification reaction tank; 2. Modifier metering assembly; 3. Diaphragm filter press; 4. Disc filter; 5. Online conductivity detection assembly; 6. Diversion assembly; 7. First washing and recovery pipeline; 8. Second washing and recovery pipeline; 9. Third washing and recovery pipeline; 100. Pretreatment unit; 200. Sealed washing unit; 300. Separate recycling and circulation unit. Detailed Implementation

[0023] To enable those skilled in the art to better understand the technical solutions in this disclosure, the technical solutions in the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this disclosure, and not all embodiments. Based on the embodiments in this disclosure, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this disclosure.

[0024] It should be noted that many specific details are set forth in the following description in order to provide a full understanding of this disclosure. However, this disclosure may also be implemented in other ways different from those described herein. Therefore, the scope of protection of this disclosure is not limited to the specific embodiments disclosed below.

[0025] like Figure 1 As shown, the environmentally friendly titanium dioxide washing system provided in this embodiment includes a pretreatment unit 100, a closed washing unit 200, and a fractional recycling and circulation unit 300 connected sequentially along the material flow direction. Each unit is connected to the control signal through pipelines to form a closed-loop operation system, which can realize continuous and automated washing, impurity removal, and resource recovery of titanium dioxide slurry.

[0026] The pretreatment unit 100 is the core functional unit of this system to prevent loss at the source. Its core function is to modify the titanium dioxide slurry before the formal washing process, and increase the equivalent particle size of fine particles through controllable soft agglomeration, thereby reducing the risk of filter penetration in the subsequent filtration process from the source.

[0027] The pretreatment unit 100 includes a modified reaction tank 1 and a modifier metering component 2, which is connected to the modified reaction tank 1.

[0028] For example, the modification reaction tank 1 adopts a vertical cylindrical tank structure. The main body of the tank is made of acid and alkali resistant 316L stainless steel. The inner wall can be lined with a polypropylene layer according to the working conditions to adapt to the acidic or weakly alkaline working conditions of the titanium dioxide slurry and avoid tank corrosion caused by long-term operation. The top of the modification reaction tank 1 has a main feed inlet for receiving titanium dioxide slurry from the upstream hydrolysis process. The upper part of the side wall of the tank has a modifier feed inlet, and the bottom of the tank has a discharge outlet, which is connected to the downstream closed washing unit 200 through a discharge pipeline.

[0029] For example, the outlet end of the modifier metering component 2 is connected to the modifier inlet of the modification reaction tank 1. The modifier metering component 2 is used to quantitatively add the modifier into the modification reaction tank 1, so that the titanium dioxide slurry entering the tank is fully mixed with the modifier, thereby inducing the fine titanium dioxide particles to undergo controllable soft agglomeration and forming agglomerate structures with larger particle sizes.

[0030] In some embodiments, the modified reaction tank 1 is configured to receive titanium dioxide slurry and mix it with a modifier. In actual operation, the slurry stays in the modified reaction tank 1 for a set reaction time. The slurry and the modifier are uniformly mixed by stirring. The soft agglomeration reaction is completed under a suitable pH environment, and finally the agglomerated slurry is formed and transported to the downstream washing process.

[0031] In this embodiment, by setting up an independent pretreatment modification step before the washing process, the traditional approach of relying solely on filtration equipment to intercept particles is broken. By controlling the particle size itself at the source, the equivalent particle size of fine particles is effectively increased without altering the original crystal form and product performance of titanium dioxide. This lays the foundation for reducing filtration loss and improving filtration efficiency in subsequent processes. Simultaneously, the use of metering components to precisely control the amount of modifier added avoids problems such as hard agglomeration due to excessive modifier or poor modification effect due to insufficient addition, ensuring the controllability and stability of the soft agglomeration process.

[0032] The closed washing unit 200 is the core functional unit of this system for achieving deep washing and impurity removal. It adopts a fully enclosed structural design and a two-stage filtration interception architecture, which combines high-efficiency washing, deep dehydration and low material loss.

[0033] The 200-unit closed washing system is a fully enclosed structure. The filter housing is made of stainless steel or plastic-lined steel tubing, and the flange connections use a fully enclosed flange fastening structure. All inlet / outlet water and backwashing pipelines use sealed welded or standard quick-connect interfaces with sealing gaskets. There are no exposed open cavities throughout the entire process, ensuring complete isolation of the internal cavity from the outside environment during operation. The sealing system uses EPDM rubber sealing rings as the main sealing element, with multiple sealing structures at the connection between the filter disc inner support and the filter housing, flange connections, and backwash valve interfaces. This adapts to the acid and alkaline conditions of titanium dioxide slurry, ensuring no leakage and no waste gas escape during operation. A dedicated exhaust port is located at the top of the filter cavity, connecting to the existing waste gas collection system in the workshop via a closed pipeline. This system collects any dust- and acid-containing waste gas overflowing from the cavity, treats it through an alkaline washing spray and dust removal process, and then discharges it in compliance with standards, achieving near-zero waste gas overflow.

[0034] In this embodiment, the closed washing unit 200 adopts a fully enclosed structure, combined with a top-mounted centralized waste gas collection and external waste gas treatment system, to achieve near-zero emission of acidic waste gas and significantly reduce environmental risks; the entire process is equipped with online detection of pH and conductivity and automatic control of valves and pumps, which can be connected to the plant's decentralized control system to achieve unattended operation, reducing labor and wastewater treatment costs by more than 60%.

[0035] In some embodiments, the closed washing unit 200 includes a diaphragm filter press 3 and a disc-type precision filter 4 connected in series. The feed end of the diaphragm filter press 3 is connected to the discharge end of the modification reaction tank 1 via a pipeline. In a specific pipeline connection, the bottom discharge port of the modification reaction tank 1 is connected to the inlet of a high-pressure feed pump via a feed pipeline, and the outlet of the high-pressure feed pump is connected to the feed main pipe of the diaphragm filter press 3 via a feed pipeline. The high-pressure feed pump provides power for slurry transportation, pumping the modified slurry into the filter chamber inside the diaphragm filter press 3 to complete solid-liquid separation. The disc-type precision filter 4 serves as a secondary interception device, used for secondary interception filtration of the dilute slurry, further capturing the fine titanium dioxide particles that have passed through the filter cloth of the diaphragm filter press 3, reducing the overall material loss of the system.

[0036] For example, the diaphragm filter press 3 is used to perform solid-liquid separation and washing of the agglomerated slurry. During operation, after the slurry enters the filter chamber of the diaphragm filter press 3, the liquid passes through the filter cloth and is discharged from the filter chamber under the action of the feed pressure, while the solid titanium dioxide particles are intercepted by the filter cloth in the filter chamber and gradually accumulate to form a uniform filter cake. After the feeding and cake formation are completed, washing water can be introduced to penetrate and wash the filter cake to remove soluble impurities adsorbed on the surface and in the pores of the filter cake particles.

[0037] The diaphragm filter press 3 can perform synchronous and coordinated operation of reverse washing and diaphragm pressing. That is, the diaphragm filter press 3 has an independent reverse washing passage and a diaphragm pressing air passage. The two passages can be controlled independently and started synchronously. The diaphragm pressing function can be started at the same time as the reverse washing process, so that the washing and dewatering processes are coupled and completed in the same stage without the need for step switching.

[0038] For example, the diaphragm filter press 3 has a forward inlet and a reverse inlet, enabling bidirectional through-washing. During forward washing, washing water enters from the forward inlet, passes through the filter cake and filter cloth in the feeding direction, and exits from the outlet side. During reverse washing, washing water enters from the reverse inlet, passes through the filter cake and filter cloth in the opposite direction to the feeding direction, and exits from the feed side. The bidirectional through-washing design allows the filter cake to be rinsed from two directions, effectively disrupting the impurity concentration gradient inside the filter cake. This avoids the problem of difficult impurity removal and high residue levels near the feed side of the filter cake during unidirectional washing, improving overall washing uniformity and impurity removal efficiency.

[0039] For example, the disc-type precision filter 4 uses a 316L stainless steel shell and multiple sets of reinforced polyamide plastic filter discs are stacked inside. The filtration accuracy is 20~200 microns, and it can be flexibly selected according to the slurry particle size and processing requirements.

[0040] In this embodiment, a diaphragm filter press 3 is used as the main washing equipment, which combines filtration, washing, and pressing dewatering functions. Multiple processes can be completed within the same equipment, reducing equipment footprint and process turnover costs. Through the coordinated operation of reverse washing and pressing, the limitations of the traditional step-by-step process of washing first and then pressing are overcome, improving washing efficiency and dewatering effect. A disc-type precision filter 4 is added as a secondary interceptor to filter the thin slurry generated by the main equipment, forming a dual interception system of "main filter + fine filter," effectively reducing the overall material loss rate of the system. The fully enclosed equipment structure prevents the escape of acidic waste gas during the washing process, improving the environmental performance of the production process and the quality of the workshop working environment.

[0041] In some embodiments, the fractional recycling unit 300 is the core unit of this system for realizing the cascade utilization of water resources and the closed-loop recycling of materials. By real-time detection and fractional diversion of the water quality of washing wastewater, the targeted reuse of water resources of different qualities is realized, thereby maximizing the utilization rate of resources.

[0042] In some embodiments, the fractional recycling unit 300 includes an online conductivity detection component 5 and a diversion component 6. The online conductivity detection component 5 is used to detect the conductivity of the washing wastewater in real time. Specifically, the online conductivity detection component 5 is installed on the main outlet pipe of the diaphragm filter press 3, that is, on the main pipe after all the filtrate discharge pipes of the diaphragm filter press 3 are combined. The detection probe is inserted into the pipe and directly contacts the washing wastewater, allowing for real-time detection of the conductivity value of the discharged washing wastewater. Since the content of soluble impurities (such as sulfates, metal ions, etc.) in the washing wastewater is positively correlated with the conductivity value, the conductivity value can indirectly characterize the impurity concentration and water quality level of the washing wastewater, providing a rapid and reliable basis for diversion control.

[0043] The diversion component 6 diverts washing wastewater to different recycling pipelines based on the conductivity detection results. The control terminal of the diversion component 6 is connected to the online conductivity detection component 5, which can receive real-time conductivity detection data and automatically switch the flow path according to the preset control logic, so as to introduce washing wastewater of different water quality into the corresponding recycling pipeline and realize the recycling of different water quality.

[0044] In this embodiment, conductivity is used as the detection index for water quality classification. This method offers fast detection response, real-time online continuous monitoring, and eliminates the need for manual sampling and testing, thus meeting the requirements of automated continuous production. The diversion component 6 automatically diverts wastewater according to its quality, enabling refined classification and recycling of washing wastewater. This avoids the reduction in reuse value caused by mixing washing water of different qualities, providing a foundation for subsequent tiered reuse and effectively improving the recycling rate of water resources.

[0045] like Figure 2 As shown, in some embodiments, the fractional recycling unit 300 further includes a first washing recycling pipeline 7, a second washing recycling pipeline 8, and a third washing recycling pipeline 9. The three pipelines constitute three independent water flow channels for fractional recycling, corresponding to the recycling of washing wastewater at high, medium, and low concentration levels, respectively.

[0046] For example, an inorganic membrane module is installed on the first washing and recovery pipeline 7. The inorganic membrane module is used to enrich and separate titanium dioxide particles in high-concentration wastewater. The first washing and recovery pipeline 7 corresponds to the recovery channel for high-concentration washing wastewater. This part of the wastewater is generated in the early stage of washing. The wastewater not only contains high concentrations of soluble salts, but also carries some fine titanium dioxide slurry. Therefore, it is necessary to first perform solid-liquid separation to recover the solid materials.

[0047] The outlet of the second washing and recovery pipeline 8 is connected to the forward inlet of the diaphragm filter press 3. The second washing and recovery pipeline 8 corresponds to the recovery channel of medium-concentration washing wastewater. This part of the wastewater is generated in the middle of the washing process. The soluble impurities in the wastewater have been greatly reduced, and the water quality meets the water requirements for forward washing. Therefore, after recovery, it can be directly used as water for the next batch of forward washing.

[0048] The outlet of the third washing and recovery pipeline 9 is connected to the equipment flushing system. A reverse osmosis unit is installed on the third washing and recovery pipeline 9, and the product water outlet of the reverse osmosis unit is connected to the reverse inlet of the diaphragm filter press 3. Although the low-concentration washing wastewater in the third washing and recovery pipeline 9 has a low impurity content, it still cannot meet the desalination water quality standards required for reverse washing. Therefore, a reverse osmosis unit is installed to perform deep purification treatment. For example, the reverse osmosis unit is connected in series on the third washing and recovery pipeline 9. Before entering the reverse osmosis unit, the low-concentration wastewater passes through a pretreatment unit such as a security filter and a precision filter to remove suspended solids. Then, it is pressurized by a high-pressure pump and enters the reverse osmosis membrane element. Under high pressure, water molecules permeate through the reverse osmosis membrane, while residual trace amounts of salt and small molecule impurities are intercepted by the membrane layer on the concentrate side, thereby producing high-purity product water. The product water outlet of the reverse osmosis unit is connected to the reverse washing inlet pipeline of the diaphragm filter press 3 through a recycled water pipeline. The deeply purified product water can be used as a supplementary source of fresh desalination water and reused in the reverse washing process, which has the highest water quality requirements. By using a reverse osmosis device to deeply purify low-concentration washing wastewater to the level of desalinated water, it can be reused in the reverse washing process, realizing a closed-loop circulation of high-quality washing water, further reducing the consumption of fresh desalinated water and lowering production costs.

[0049] In this embodiment, an inorganic membrane module is used to recover materials from high-concentration wastewater. This concentrates the titanium dioxide particles entrained in the wastewater and returns them to the front end of the system for reprocessing, achieving a closed-loop material circulation and further reducing the total material loss rate. Medium-concentration wastewater is directly reused in the forward washing process, realizing the tiered utilization of medium-quality water resources and reducing fresh water consumption in the forward washing process. Clean water is reused in auxiliary processes such as equipment rinsing, maximizing the reuse of water resources across all stages and significantly reducing the overall fresh water consumption and wastewater discharge of the system.

[0050] In some embodiments, the online conductivity detection component 5 includes an online conductivity meter. The detection probe of the online conductivity meter is inserted into the interior of the main water outlet pipe. The probe is in direct contact with the washing wastewater and can detect the conductivity value of the wastewater in real time and continuously, and convert the detection signal into a standard electrical signal and transmit it to the control system.

[0051] In some embodiments, the diversion component 6 includes intelligent solenoid valves installed on the first washing recovery pipeline 7, the second washing recovery pipeline 8, and the third washing recovery pipeline 9. These intelligent solenoid valves are connected to an online conductivity meter. Specifically, the main outlet pipeline of the diaphragm filter press 3 is divided into three branches via a T-joint, corresponding to the inlets of the first washing recovery pipeline 7, the second washing recovery pipeline 8, and the third washing recovery pipeline 9, respectively. Each branch is equipped with an intelligent solenoid valve, and all three valves are electrically connected to the control system. Based on the real-time values ​​transmitted by the online conductivity meter, the control system controls the opening and closing of the three solenoid valves according to preset threshold logic, ensuring that only the recovery pipeline corresponding to the water quality level is open at any given time, thereby achieving automatic diversion of washing wastewater.

[0052] In this embodiment, three independent recycling pipelines are used to handle washing wastewater of different qualities, achieving three-level classification and recycling of the wastewater and providing a clear water flow path for subsequent cascade reuse. An automatic control scheme using an online conductivity meter and intelligent solenoid valves enables fully automated operation of the diversion process, eliminating the need for manual water quality assessment and valve switching. This improves the system's automation level and the timeliness and accuracy of diversion, avoiding the lag and errors of manual operation.

[0053] like Figure 3 As shown, the method for washing titanium dioxide using the above system includes the following steps S1-S4: S1: Pre-agglomeration modification: Titanium dioxide slurry is fed into a modification reaction tank, a modifier is added and stirred to react, so that the fine titanium dioxide particles undergo controllable soft agglomeration, and the modified slurry is obtained.

[0054] S2: Gradient closed washing: The modified slurry is pumped into the diaphragm filter press. First, it is fed at low pressure and filtered to form a uniform filter cake. Then, the forward washing process is started, and the filter cake is washed in the forward through using the medium-concentration wash water stored in the second washing recovery pipeline. Then, the process is switched to the backwashing process, and the filter cake is washed in the reverse through using fresh desalinated water from the other side. At the same time, the diaphragm pressing process is started, and compressed air is introduced to pre-press the filter cake.

[0055] S3: Differentiated cascade recovery: The washing water produced by the diaphragm filter press is monitored in real time by the online conductivity meter. When the conductivity is ≥15000μS / cm, the intelligent solenoid valve automatically opens the first washing recovery pipeline. After the washing water is intercepted and recovered by the inorganic membrane module, the concentrated slurry is returned to the pretreatment unit. When the conductivity drops below 5000μS / cm, the second washing recovery pipeline is automatically opened. The washing water is stored and used for the next batch of forward washing process. When the conductivity drops below 100μS / cm, the third washing recovery pipeline is automatically opened. After being treated by the reverse osmosis integrated device, it is used as a fresh demineralized water source or equipment flushing water.

[0056] S4: Filter cake unloading: After pressing, the filter cake discharged from the diaphragm filter press is sent to the subsequent pulping process. The thin slurry containing trace amounts of titanium dioxide is sent to a disc-type precision filter for precision interception. The filtrate is treated by the aforementioned reverse osmosis integrated device, and the conductivity of the produced water is ≤10μS / cm.

[0057] In some embodiments, in step S1, the modifier is ammonium bicarbonate. Ammonium bicarbonate is added at 0.4% to 0.6% of the dry weight of titanium dioxide, the pH value is controlled at 6.5 to 7.0, and the reaction is carried out at a low speed for 10 to 20 minutes to cause the fine particles of titanium dioxide to undergo controllable soft agglomeration, thereby obtaining the modified slurry.

[0058] In some embodiments, in step S1, the modifier is an anionic surfactant. The anionic surfactant is added at 0.2% to 0.3% of the dry weight of titanium dioxide. The pH value is controlled at 5.5 to 6.5, and the reaction is carried out at a low speed for 10 to 20 minutes. The fine titanium dioxide particles are controlled to agglomerate through electrostatic adsorption.

[0059] In some embodiments, in step S2, the washing pressure of the forward washing process is 0.6~0.8MPa, and the washing time is 60~100 minutes; the washing pressure of the backwashing process is 3.0~5.0MPa, and the pressing pressure of the diaphragm pressing is 1.3~1.5MPa, and the pressing time is 20~30 minutes.

[0060] In some embodiments, in step S3, when the conductivity is ≥15000μs / cm, corresponding to the initial high-salt washing stage, the wastewater contains some slurry, a large amount of free sulfuric acid and soluble metal salts. The wastewater flows into the high-concentration slurry recovery pipeline, and titanium dioxide particles are recovered by the inorganic membrane module. The concentrated slurry is returned to the modified reaction tank 1 for recycling.

[0061] When the conductivity is 5000~15000μs / cm, corresponding to the intermediate salt transition washing stage, the salt content in the wastewater is greatly reduced. The wastewater flows into the intermediate concentrated wash water recovery pipeline and is stored in the intermediate wash water storage tank for use in the next batch of forward washing process.

[0062] When the conductivity is ≤100μs / cm, corresponding to the final fine washing stage, the wastewater quality is close to the desalination standard. The wastewater flows into the clean water reuse pipeline and is sent to the clean water reuse tank as equipment flushing water.

[0063] In some embodiments, in step S4, the slurry containing trace amounts of titanium dioxide discharged from the diaphragm filter press 3 is sent to the disc-type precision filter 4 for secondary interception filtration. After interception, the concentration of titanium dioxide in the slurry is reduced from about 5% to below 0.5%, and the interception efficiency for pre-agglomerated titanium dioxide particles can reach more than 85%. The filtered clear liquid is sent to the reverse osmosis unit for deep treatment, and the conductivity of the produced water is ≤10μs / cm. It can be used as fresh demineralized water to supplement the reverse washing process.

[0064] Example 1 This embodiment uses ammonium bicarbonate as a modifier, suitable for weakly acidic titanium dioxide slurry systems, and is applicable to large-scale production scenarios. The material to be washed is metatitanic acid slurry after sulfuric acid hydrolysis. The system is weakly acidic, and the initial filtrate solid content is about 1%. Ammonium bicarbonate is added at 0.5% of the dry weight of titanium dioxide, and the reaction pH is adjusted to 6.5-7.0. The reaction is carried out at low speed for 15 minutes to complete soft agglomeration. The modified slurry is sent to diaphragm filter press 3 for filtration into cake. It is then washed with recycled medium-concentration water at 0.3 MPa for 15 minutes in a forward wash. Subsequently, reverse washing is switched and diaphragm pressing is started simultaneously. The washing wastewater is diverted and recycled according to the conductivity threshold. The high-concentration water is recycled after recovering titanium dioxide through an inorganic membrane module, the medium-concentration water is reused in the forward wash process, and the clear water is reused as rinsing water. The downstream dilute slurry is intercepted by a disc-type precision filter 4, and the clear liquid is further treated by a reverse osmosis unit for reuse.

[0065] In this embodiment, the solid content of the modified filter press filtrate is reduced to approximately 0.5%; the total loss rate of titanium dioxide in the system is ≤0.5%; the amount of washing wastewater discharged is reduced by 80% compared to traditional processes; the operation cycle is shortened by approximately 30%; the elution rate of soluble impurities is increased by approximately 20%; and the residual iron impurities in the finished product are less than 10 ppm, and the residual chloride ions are less than 50 ppm. This method does not introduce organic impurities, and there is no risk of yellowing during subsequent calcination, making it suitable for low-cost large-scale production.

[0066] Example 2 This embodiment uses sodium dodecylbenzenesulfonate (DBS) as a modifier, suitable for neutral or weakly alkaline titanium dioxide slurry systems, corresponding to high-end refined titanium dioxide production scenarios. The material to be washed is a neutral titanium dioxide slurry with an initial filtration filtrate solid content of approximately 1%. DBS is added at 0.2%–0.3% of the dry weight of titanium dioxide, the reaction pH is adjusted to 5.5–6.5, and the reaction is carried out with low-speed stirring for 15 minutes to complete soft agglomeration. The subsequent washing, fractionation and recovery, and deep purification processes are the same as in Example 1.

[0067] In this embodiment, the solid content of the modified filter press filtrate is reduced to about 0.2%, and the soft agglomeration and anti-filtration effects are better. At the same time, the introduced surfactant can assist the dispersion performance of subsequent products, making it suitable for the production of high-end titanium dioxide with higher product quality requirements.

[0068] It is readily understood that those skilled in the art can combine, split, or reorganize the embodiments provided in this disclosure to obtain other embodiments, none of which exceed the protection scope of this disclosure.

[0069] The above detailed embodiments further illustrate the purpose, technical solutions, and beneficial effects of the embodiments of this disclosure. It should be understood that the above are merely specific embodiments of the embodiments of this disclosure and are not intended to limit the protection scope of the embodiments of this disclosure. Any modifications, equivalent substitutions, improvements, etc., made on the basis of the technical solutions of the embodiments of this disclosure should be included within the protection scope of the embodiments of this disclosure.

Claims

1. An environmentally friendly titanium dioxide washing system, characterized in that, It includes a pretreatment unit (100), a closed washing unit (200) and a fractional recycling unit (300) connected sequentially along the material flow direction. The pretreatment unit (100) includes a modified reaction tank (1) and a modifier metering component (2). The modifier metering component (2) is connected to the modified reaction tank (1). The modified reaction tank (1) is configured to receive titanium dioxide slurry and mix it with the modifier to induce the titanium dioxide fine particles to undergo controllable soft agglomeration to form agglomerated slurry. The closed washing unit (200) includes a diaphragm filter press (3) and a disc-type precision filter (4) connected in series. The feed end of the diaphragm filter press (3) is connected to the discharge end of the modified reaction tank (1) via a pipeline. The diaphragm filter press (3) is used to perform solid-liquid separation and washing on the agglomerated slurry. The diaphragm filter press (3) can perform synchronous and coordinated operation of reverse washing and diaphragm pressing. The feed end of the disc-type precision filter (4) is connected to the slurry outlet of the diaphragm filter press (3) and is used to perform secondary interception filtration on the slurry. The fractional recycling unit (300) includes an online conductivity detection component (5) and a diversion component (6). The online conductivity detection component (5) is used to detect the conductivity of the washing wastewater in real time, and the diversion component (6) diverts the washing wastewater to different recycling pipelines according to the conductivity detection result.

2. The environmentally friendly titanium dioxide washing system according to claim 1, characterized in that, The diaphragm filter press (3) has a forward liquid inlet and a reverse liquid inlet, which can perform bidirectional penetration washing; the stacked precision filter (4) is equipped with a reinforced polyamide plastic filter disc, with a filtration accuracy of 20~200 micrometers.

3. The environmentally friendly titanium dioxide washing system according to claim 2, characterized in that, The fractional recycling circulation unit (300) further includes: a first washing recycling pipeline (7), a second washing recycling pipeline (8) and a third washing recycling pipeline (9), the online conductivity detection component (5) includes an online conductivity meter; the diversion component (6) includes intelligent solenoid valves installed on the first washing recycling pipeline (7), the second washing recycling pipeline (8) and the third washing recycling pipeline (9), and the intelligent solenoid valves are signal-connected to the online conductivity meter.

4. The environmentally friendly titanium dioxide washing system according to claim 3, characterized in that, An inorganic membrane module is installed on the first washing and recovery pipeline (7). The inorganic membrane module is used to enrich and separate titanium dioxide particles in high-concentration wastewater. The concentrated liquid outlet of the inorganic membrane module is connected to the modified reaction tank (1) of the pretreatment unit (100). The outlet of the second washing and recovery pipeline (8) is connected to the forward inlet of the diaphragm filter press (3). The outlet of the third washing and recovery pipeline (9) is connected to the equipment flushing system.

5. The environmentally friendly titanium dioxide washing system according to claim 4, characterized in that, The inorganic membrane module has a double-layer composite structure, with an outer layer of ceramic self-cleaning coating and an inner layer of Al2O3-ZrO2 composite membrane; the membrane pore size is 0.01~0.5μm, the membrane thickness is 50~60μm, and the porosity is 44%~46%.

6. The environmentally friendly titanium dioxide washing system according to claim 3, characterized in that, The third washing and recovery pipeline (9) is equipped with a reverse osmosis device, and the product water outlet of the reverse osmosis device is connected to the reverse liquid inlet of the diaphragm filter press (3).

7. The environmentally friendly titanium dioxide washing system according to claim 6, characterized in that, The reverse osmosis unit is equipped with a conductivity monitor on the product water outlet pipe to control the product water conductivity to ≤10μS / cm.

8. An environmentally friendly titanium dioxide washing method, employing the environmentally friendly titanium dioxide washing system according to any one of claims 1-7, characterized in that, Includes the following steps: Pre-agglomeration modification: Titanium dioxide slurry is fed into a modification reaction tank, a modifier is added and stirred to react, so that the fine titanium dioxide particles undergo controllable soft agglomeration to obtain the modified slurry; Gradient closed washing: The modified slurry is pumped into the diaphragm filter press. First, it is fed at low pressure and filtered to form a uniform filter cake. Then, the forward washing process is started, and the filter cake is washed through the medium concentration of wash water stored in the second washing recovery pipeline. Then, the process is switched to the backwash process, and the filter cake is washed through the other side of the filter cake with fresh desalinated water. At the same time, the diaphragm pressing process is started, and compressed air is introduced to pre-press the filter cake. Separate cascade recovery: The washing water produced by the diaphragm filter press is monitored in real time by the online conductivity meter. When the conductivity is ≥15000μS / cm, the intelligent solenoid valve automatically opens the first washing recovery pipeline. After the washing water passes through the inorganic membrane module to intercept and recover titanium dioxide particles, the concentrated slurry is returned to the pretreatment unit. When the conductivity drops below 5000μS / cm, the second washing recovery pipeline is automatically opened. The washing water is stored and used for the next batch of forward washing process. When the conductivity drops below 100μS / cm, the third washing recovery pipeline is automatically opened. After being treated by the reverse osmosis integrated device, it is used as a fresh demineralized water source or equipment flushing water. Filter cake unloading: After pressing, the filter cake discharged from the diaphragm filter press is sent to the subsequent pulping process. The thin slurry containing trace amounts of titanium dioxide is sent to a disc-type precision filter for precise interception. The filtrate is treated by the aforementioned reverse osmosis integrated device, and the conductivity of the produced water is ≤10μS / cm.

9. The environmentally friendly titanium dioxide washing method according to claim 8, characterized in that, In the gradient closed washing step, the washing pressure of the forward washing process is 0.6~0.8MPa and the washing time is 60~100 minutes; the washing pressure of the backwashing process is 3.0~5.0MPa; the pressing pressure of the diaphragm pressing is 1.3~1.5MPa and the pressing time is 20~30 minutes.

10. The environmentally friendly titanium dioxide washing method according to claim 8, characterized in that, In the pre-agglomeration modification step, the modifier is ammonium bicarbonate. Ammonium bicarbonate is added at 0.4% to 0.6% of the dry weight of titanium dioxide, the pH value is controlled at 6.5 to 7.0, and the reaction is carried out at a low speed for 10 to 20 minutes to cause controllable soft agglomeration of the fine titanium dioxide particles, thereby obtaining the modified slurry. or, The modifier is an anionic surfactant. The anionic surfactant is added at 0.2% to 0.3% of the dry weight of titanium dioxide. The pH value is controlled at 5.5 to 6.5, and the reaction is carried out at a low speed for 10 to 20 minutes. The fine titanium dioxide particles are controlled to agglomerate through electrostatic adsorption.

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