Continuous refining method and device for titanium dioxide by-product ferrous sulfate

Abstract

This invention provides a continuous refining method and apparatus for ferrous sulfate, a byproduct of titanium dioxide production, comprising the following steps: S1: The raw material is fed into a dissolving tank, and hot water is introduced into the bottom of the dissolving tank. The ferrous sulfate solution enters a buffer tank through a baffle in the dissolving tank, where water is added to dilute the ferrous sulfate solution; S2: The ferrous sulfate solution in the buffer tank is pumped into a purification tank, where iron sheets are added. The solution at the top of the purification tank overflows into a settling tank on the ground, and the clear liquid at the top of the settling tank overflows into a metal membrane filtration system. The clear liquid after metal membrane filtration is sent as the product to a ferrous sulfate storage tank; S3: The concentrated liquid discharged from the metal membrane filtration system and the purification tank is returned to the filter press buffer tank. The pump sends the liquid in the buffer tank to the compressor, and the clear liquid in the filter press is returned to the clear liquid buffer tank. The beneficial effects of this invention are: This method solves the problem of continuous refining of ferrous sulfate in ferric phosphate production enterprises, reduces manual operation, and saves investment and land area.

Description

Technical Field

[0001] This invention belongs to the field of inorganic materials and battery material preparation, and in particular relates to a continuous refining method and apparatus for ferrous sulfate, a byproduct of titanium dioxide production. Background Technology

[0002] Ferric phosphate (FePO4) is a precursor to lithium iron phosphate (LFP), a cathode material for new energy sources. Currently, due to the explosive growth in demand for LFP, the demand for its raw material, ferric phosphate, is also continuously increasing. The main method for large-scale production of ferric phosphate in the market is to precipitate it by reacting a ferrous sulfate solution with phosphate (salt) after oxidation with hydrogen peroxide. The main production processes for ferric phosphate currently include the ferrous sulfate method and the ferrous sulfate method (sodium method and ammonia method). The ferrous sulfate method (ammonia method) is currently the mainstream direction for ferric phosphate production. The ferrous sulfate raw material for this method is mainly ferrous sulfate crystals, a byproduct of titanium dioxide production, which contain various metallic impurities and hydrolyzed titanium sulfate impurities. Refining is required to meet the purity requirements for ferric phosphate production. The industry generally uses a batch method for ferrous sulfate refining, relying on multiple filter presses to obtain a clear ferrous sulfate solution. However, the filter press solution cannot completely remove impurities and cannot provide a stable and continuous output. To maintain a continuous downstream feed, many large storage tanks are needed for storage. The solution is left to settle for about 7-11 days until the pH reaches 2-4, at which point a green and transparent ferrous sulfate solution can be used as a raw material for downstream applications.

[0003] The existing traditional methods for refining ferrous sulfate, a byproduct of titanium dioxide, are as follows:

[0004] Based on downstream production demands, multiple underground dissolving tanks are installed. Water is added and stirred to dissolve ferrous sulfate crystals. After uniform dissolution, the solution is pumped to a refining tank where NaOH solution is added to adjust the pH and remove impurities. The oxidized Fe... 3+ It reacts with alkali to form Fe(OH)₂. 3 After sedimentation, the slurry is pumped to the filter press buffer tank, and then to multiple filter presses. The multiple filter presses operate in sequence, with the following process: feed until the filter chamber is full, press, and discharge. This cycle repeats, and the filter press produces clear liquid intermittently, containing considerable flocculent impurities, especially high levels of Ti. This liquid needs to be allowed to settle in a storage tank for approximately 8-12 days until the pH returns to 2-4. The resulting green, transparent ferrous sulfate solution can then be used as a raw material for downstream applications.

[0005] Given the aforementioned characteristics of filter presses, the entire process cannot achieve continuous production and has low filtration accuracy. It involves a significant amount of manual work in cleaning underground dissolving tanks and finished product storage tanks, which are numerous, occupy a large area, and result in high investment costs. Furthermore, the ferrous sulfate solution process is entirely acidic and highly corrosive, and the multiple large underground dissolving tanks are particularly environmentally unfriendly. Summary of the Invention

[0006] In view of this, the present invention aims to propose a continuous refining method and apparatus for ferrous sulfate, a byproduct of titanium dioxide production, to solve the problems of inability to achieve continuous production, low filtration accuracy, large amount of manual cleaning of underground dissolving tanks and finished product storage tanks, large number of finished product storage tanks occupying a large area, and high investment.

[0007] To achieve the above objectives, the technical solution of the present invention is implemented as follows:

[0008] A continuous purification method for ferrous sulfate, a byproduct of titanium dioxide production, characterized by comprising the following steps:

[0009] S1: The raw material is sent to the dissolving tank, and hot water is introduced into the bottom of the dissolving tank. The ferrous sulfate solution enters the buffer tank through the baffle of the dissolving tank. Water is added to the baffle to dilute the ferrous sulfate solution.

[0010] S2: The ferrous sulfate solution in the buffer tank is pumped into the impurity removal tank. Iron sheets are added to the impurity removal tank. The solution at the top of the impurity removal tank overflows into the ground settling tank. The clear liquid at the top of the settling tank overflows into the metal membrane filtration system. The clear liquid after metal membrane filtration is sent to the ferrous sulfate storage tank as a product.

[0011] S3: The concentrated liquid discharged from the metal membrane filtration system and the impurity removal tank is returned to the filter press buffer tank. The pump sends the liquid in the tank to the compressor, and the clear liquid in the filter press is returned to the clear liquid buffer tank.

[0012] Furthermore, the raw material in step S1 is ferrous sulfate heptahydrate; the temperature of the hot water introduced into the dissolving tank in step S1 is 60-90℃; and the salt layer height in the dissolving tank is 2-4.5m.

[0013] Furthermore, in step S1, the flow rate of the baffled tank needs to be controlled at 0.1 to 0.3 m / s, the temperature of the ferrous sulfate solution in the baffled tank is at least 50 to 70°C, and the concentration of ferrous sulfate in the baffled tank is 20 to 23%.

[0014] Furthermore, the metal membrane filtration system in steps S2 and S3 is a cross-flow filtration system, the pore size of the metal membrane is 30-100 nm, and the metal membrane is 316L metal powder sintered felt.

[0015] In step S2, a patch is added to control the pH of the ferrous sulfate solution between 2 and 4.

[0016] Preferably, the metal membrane filtration system adopts a two-stage or three-stage series filtration method, with a membrane surface flow velocity of 1 to 5 m / s.

[0017] An apparatus used in a continuous refining method for ferrous sulfate, a byproduct of titanium dioxide production, includes a dissolving tank, a buffer tank, a removal tank, a settling tank, a metal membrane filtration system, and a finished product tank.

[0018] The dissolving tank is connected to the buffer tank via a baffle. The buffer tank is connected to the impurity removal tank via a first pipe. The top of the impurity removal tank is connected to the settling tank via a first overflow pipe. The top of the settling tank is connected to the metal membrane filtration system via a second overflow pipe. The metal membrane filtration system is connected to the aging tank via a pipe. The bottom of the metal membrane filtration system and the settling tank are connected to the filter press assembly.

[0019] Furthermore, the dissolving tank is a semi-underground dissolving tank. The bottom of the dissolving tank is equipped with several water outlet pipes and a main pipe. The water outlet pipes are arranged sequentially on the main pipe, and several nozzles are installed on the water outlet pipes.

[0020] The baffle is a hollow structure, with its two ends connected to the dissolving tank and the buffer tank, respectively. The baffle is equipped with several staggered baffles, preferably with a spacing of 300-600 mm between the baffles.

[0021] A concentration meter is installed inside the baffle tank, and an inlet pipe is installed at the top of the baffle tank, with a regulating valve on the inlet pipe;

[0022] The flow velocity in the baffled tank is controlled at 0.1–0.3 m / s, the temperature of the ferrous sulfate solution in the baffled tank is not lower than 50–70℃, and the concentration of ferrous sulfate in the baffled tank is 20–23%.

[0023] Furthermore, the solution buffer tank is a semi-underground concrete structure, and a stirrer is provided inside the solution buffer tank. Preferably, the stirring speed of the stirrer is 10-30 rpm. An automatic weighing feeder is provided on the top of the impurity removal tank. The automatic weighing feeder is provided with iron sheets. Preferably, the iron sheets are irregularly shaped cold-rolled iron sheets from automobiles.

[0024] The impurity removal tank is equipped with a pH tester, which controls the pH of the ferrous sulfate solution in the impurity removal tank between 2 and 4 by controlling the amount of iron added;

[0025] The first axial flow pump is installed on the first pipeline.

[0026] Furthermore, the top of the impurity removal tank is provided with several evenly distributed first overflow ports, and a return pipe is provided at the first overflow port. The first overflow pipe is set on the return pipe, and the other end of the first overflow pipe is connected to the settling tank.

[0027] The return pipeline is equipped with a second axial flow pump and a first valve. The second axial flow pump has a feed rate of 20 to 50 times that of the first axial flow pump.

[0028] An eccentric agitator is installed inside the top of the impurity removal tank. The agitation speed of the eccentric agitator is 10-30 rpm. The eccentric agitator is a paddle agitator.

[0029] The bottom of the trough is equipped with a bottom sludge rake with a rotation speed of 0.03 to 0.06 rpm.

[0030] Furthermore, the metal membrane filtration system includes a clear liquid buffer tank and a metal membrane filter. The settling tank is connected to the clear liquid buffer tank through a second overflow pipe. The clear liquid buffer tank is connected to the metal membrane filter through a third pipe. A third axial flow pump is installed on the third pipe. The clear liquid filtered by the metal membrane filter flows into the finished product tank through a fourth pipe. Nitrogen gas is introduced into the finished product tank.

[0031] The bottom of the settling tank is connected to the filter press assembly via a fifth pipe, and a second valve is installed on the fifth pipe;

[0032] The bottom of the metal membrane filter is connected to the filter press assembly via a pipe;

[0033] The metal membrane has a pore size of 30–100 nm and is made of 316L sintered metal powder felt. Through backwashing with the clarified liquid, the membrane flux can be restored to 90–100%. Membrane regeneration is easy and quick, ensuring continuous process operation and significantly improving production efficiency. The clarified liquid from membrane filtration is sent as a product to the ferrous sulfate storage tank.

[0034] Preferably, the metal membrane filtration system adopts a two-stage or three-stage series filtration method, with a membrane surface flow velocity of 1 to 5 m / s.

[0035] Furthermore, the filter press assembly includes a filter press buffer trough and a filter press machine. The bottom of the settling tank is connected to the filter press buffer trough through a fifth pipe. The filter press buffer trough is connected to the filter press machine through a sixth pipe. A filter press feed pump is installed on the sixth pipe. The filtrate of the filter press is connected to the clear liquid buffer tank through a seventh pipe. A filter residue conveyor belt is installed at the bottom of the filter press.

[0036] The filter press has a pressing function, and the filter cloth has a filtration accuracy of 1-20 microns. The concentrated liquid discharged from the metal membrane discharge tank and the concentrated liquid discharged from the bottom of the impurity removal tank are returned to the filter press buffer tank. The concentrated liquid is pumped to the filter press, which has a pressing function. The clear liquid from the filter press is returned to the metal membrane system feed buffer tank. The unloaded filter cake is conveyed to the warehouse by a conveyor belt.

[0037] Compared with existing technologies, the continuous refining method and apparatus for ferrous sulfate, a byproduct of titanium dioxide production, described in this invention has the following advantages:

[0038] This invention involves adding iron sheets to the impurity removal tank to reduce ferric iron, thereby increasing product yield and reducing flocculent content. The rational design of the impurity removal and settling tanks reduces the flocculent content entering the metal membrane and improves the stable operation of the metal membrane system. The selection of a high-precision metal membrane ensures that the filtered clear liquid meets the quality requirements for ferrous sulfate in battery-grade ferric phosphate. Finally, the slurry is filtered using a filter press, resolving the issues associated with returning the slurry to the dissolving tank. Attached Figure Description

[0039] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0040] Figure 1 This is a schematic diagram of a continuous refining apparatus for ferrous sulfate, a byproduct of titanium dioxide, as described in an embodiment of the present invention.

[0041] Figure 2 This describes a method for preparing ferrous sulfate, a byproduct of titanium dioxide production, in existing technologies.

[0042] Explanation of reference numerals in the attached figures:

[0043] 1. Dissolving tank; 2. Buffer tank; 3. Impurity removal tank; 4. Settling tank; 5. Finished product tank; 6. First pipeline; 7. First axial flow pump; 8. First valve; 9. Filter residue conveyor belt; 10. Return pipeline; 11. First overflow pipeline; 12. Second axial flow pump; 13. Clear liquid buffer tank; 14. Metal membrane filter; 15. Second overflow pipeline; 16. Third pipeline; 17. Third axial flow pump; 18. Fourth pipeline; 19. Fifth pipeline; 20. Second valve; 21. Filter press buffer tank; 22. Filter press machine; 23. Sixth pipeline; 24. Filter press feed pump; 25. Seventh pipeline. Detailed Implementation

[0044] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0045] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0046] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art will understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0047] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0048] A continuous refining method for ferrous sulfate, a byproduct of titanium dioxide production, is characterized by the following steps: S1: The raw material is fed into a dissolving tank 1, and hot water is introduced into the bottom of the dissolving tank 1. The ferrous sulfate solution enters a buffer tank 2 through a baffle in the dissolving tank 1. Water is added to the baffle to dilute the ferrous sulfate solution; S2: The ferrous sulfate solution in the buffer tank 2 is pumped into a purification tank 3. Iron sheets are added to the purification tank 3. The solution at the top of the purification tank 3 overflows into a settling tank 4. The clear liquid at the top of the settling tank 4 overflows into a metal membrane filtration system. The clear liquid after metal membrane filtration is sent as a product to a ferrous sulfate storage tank; S3: The concentrated liquid discharged from the metal membrane filtration system and the purification tank 3 is returned to the filter press buffer tank 21. The pump sends the liquid in the tank to the compressor. The clear liquid in the filter press is returned to the clear liquid buffer tank 13.

[0049] The raw material in step S1 is ferrous sulfate heptahydrate; the temperature of the hot water introduced into dissolving tank 1 in step S1 is 60–90°C; the salt layer height in dissolving tank 1 is 2–4.5 m. The flow rate in the baffle tank in step S1 needs to be controlled at 0.1–0.3 m / s, the temperature of the ferrous sulfate solution in the baffle tank is at least 50–70°C, and the concentration of ferrous sulfate in the baffle tank is 20–23%.

[0050] The metal membrane filtration system in steps S2 and S3 is a cross-flow filtration system. The pore size of the metal membrane is 30-100 nm, and the metal membrane is 316L metal powder sintered felt. In step S2, a patch is added to control the pH of the ferrous sulfate solution at 2-4.

[0051] In practice, the metal membrane filtration system adopts a two-stage or three-stage series filtration method, with a membrane surface flow velocity of 1 to 5 m / s.

[0052] An apparatus for a continuous refining method of ferrous sulfate, a byproduct of titanium dioxide production, includes a dissolving tank 1, a buffer tank 2, a removal tank 3, a settling tank 4, a metal membrane filtration system, and a finished product tank 5. The dissolving tank 1 is connected to the buffer tank 2 via a baffle plate. The buffer tank 2 is connected to the removal tank 3 via a first pipe 6. The top of the removal tank 3 is connected to the settling tank 4 via a first overflow pipe. The top of the settling tank 4 is connected to the metal membrane filtration system via a second overflow pipe. The metal membrane filtration system is connected to the finished product tank via a pipe. The bottom of the metal membrane filtration system and the settling tank 4 are connected to a filter press assembly.

[0053] The dissolving tank 1 is a semi-underground dissolving tank 1. Several outlet pipes and a main pipe are located at the bottom of the dissolving tank 1. The outlet pipes are sequentially connected to the main pipe, and several nozzles are installed on the outlet pipes. The baffle is a hollow structure, with its two ends connected to the dissolving tank 1 and the buffer tank, respectively. Several staggered baffles are installed inside the baffle, preferably with a spacing of 300–600 mm between the baffles. A concentration meter is installed inside the baffle, and an inlet pipe with a regulating valve is located at the top of the baffle. The flow velocity in the baffle is controlled at 0.1–0.3 m / s, the temperature of the ferrous sulfate solution in the baffle is not lower than 50–70℃, and the concentration of ferrous sulfate in the baffle is 20–23%.

[0054] The solution buffer tank 2 is a semi-underground concrete structure. The solution buffer tank 2 is equipped with a stirrer. Preferably, the stirring speed of the stirrer is 10-30 rpm. The top of the impurity removal tank 3 is equipped with an automatic weighing feeder. The automatic weighing feeder is equipped with iron sheets. Preferably, the iron sheets are irregularly shaped cold-rolled iron sheets from automobiles. The impurity removal tank 3 is equipped with a pH tester. By controlling the amount of iron sheets added, the pH of the ferrous sulfate solution in the impurity removal tank 3 is controlled to be between 2 and 4. The first axial flow pump 7 is installed on the first pipeline 6.

[0055] The top of the impurity removal tank 3 is provided with several evenly distributed first overflow ports. A return pipe 10 is provided at the first overflow port. The first overflow pipe 11 is set on the return pipe 10. The other end of the first overflow pipe is connected to the settling tank 4. A second axial flow pump 12 and a first valve 8 are provided on the return pipe 10. The second axial flow pump 12 is 20 to 50 times the feed rate of the first axial flow pump 7. An eccentric agitator is provided inside the top of the impurity removal tank 3. The agitation speed of the eccentric agitator is 10 to 30 rpm. The eccentric agitator is a paddle agitator. A bottom sludge rake is provided at the bottom of the settling tank. The rotation speed is 0.03 to 0.06 rpm.

[0056] The metal membrane filtration system includes a clear liquid buffer tank 13 and a metal membrane filter 14. A settling tank 4 is connected to the clear liquid buffer tank 13 via a second overflow pipe 15. The clear liquid buffer tank 13 is connected to the metal membrane filter 14 via a third pipe 16. A third axial flow pump 17 is installed on the third pipe 16. The clear liquid filtered by the metal membrane filter 14 flows into the finished product tank 5 via a fourth pipe 18. Nitrogen gas is introduced into the finished product tank 5. The bottom of the settling tank 4 is connected to the filter press assembly via a fifth pipe 19. A second valve 20 is installed on the fifth pipe 19. The bottom of the metal membrane filter 14 is connected to the filter press assembly via a pipe.

[0057] The metal membrane has a pore size of 30–100 nm and is made of 316L sintered metal powder felt. Through backwashing with the clarified liquid, the membrane flux can be restored to 90–100%. Membrane regeneration is easy and quick, ensuring continuous process operation and significantly improving production efficiency. The clarified liquid from membrane filtration is sent as a product to the ferrous sulfate storage tank.

[0058] Preferably, the metal membrane filtration system adopts a two-stage or three-stage series filtration method, with a membrane surface flow velocity of 1 to 5 m / s.

[0059] The filter press assembly includes a filter press buffer tank 21 and a filter press machine 22. The bottom of the settling tank 4 is connected to the filter press buffer tank 21 via a fifth pipe 19. The filter press buffer tank 21 is connected to the filter press machine 22 via a sixth pipe 23. A filter press feed pump 24 is installed on the sixth pipe 23. The filtrate from the filter press is connected to the clear liquid buffer tank 13 via a seventh pipe 25. A filter cake conveyor belt 9 is installed at the bottom of the filter press. The filter press has a pressing function, and the filter cloth has a filtration accuracy of 1-20 microns. The concentrated liquid discharged from the metal membrane discharge tank 3 and the concentrated liquid discharged from the bottom of the impurity removal tank 3 are returned to the filter press buffer tank 21. The concentrated liquid is pumped to the filter press, which has a pressing function. The clear liquid from the filter press is returned to the metal membrane system feed buffer tank 2. The unloaded filter cake is conveyed to the warehouse via a conveyor belt.

[0060] Example 1:

[0061] like Figure 1 As shown, ferrous sulfate heptahydrate is delivered to the dissolving tank by a forklift. The dissolving tank is a concrete structure with a salt layer height of 4.5m. 70℃ hot water is evenly applied from bottom to top through a distributor and nozzles to dissolve the ferrous sulfate heptahydrate. The ferrous sulfate solution then enters a buffer tank through a baffled trough. Water is added to the baffled trough to dilute the ferrous sulfate solution. A concentration meter is installed in the baffled trough, and an automatic water addition regulating valve is used to ensure the ferrous sulfate concentration is maintained at 22% (wt). The baffled trough is hollow and equipped with a cover plate. The bottom inner wall is staggered with baffles spaced 400mm apart. The flow velocity in the baffled trough is controlled at 0.2m / s, the temperature of the ferrous sulfate solution in the baffled trough is not lower than 68℃, and the ferrous sulfate concentration in the baffled trough is 22%.

[0062] The solution buffer tank is a semi-underground concrete structure equipped with a stirrer, preferably at a speed of 20 rpm. The stirred solution is pumped to an above-ground impurity removal tank. Iron sheets, irregularly shaped and cold-rolled from automotive materials, are weighed and added to the top of the impurity removal tank via an automatic lift. The impurity removal tank uses a circulating axial flow pump for back-mixing to prevent the deposition of flocculent matter on the iron sheets, which would affect the reaction rate. Multiple overflow ports are evenly distributed at the top of the impurity removal tank; the overflows are collected and piped into the axial flow pump, pressurized, and then discharged to the bottom of the impurity removal tank. The flow rate of the axial flow pump is preferably 50 times the feed rate of the impurity removal tank.

[0063] By controlling the amount of iron added, the pH of the ferrous sulfate solution in the impurity removal tank is controlled at 3.

[0064] The solution at the top of the impurity removal tank overflows into the above-ground settling tank. The settling velocity of the flocculent material in the settling tank is 0.1 m / s. The settling tank is equipped with a bottom sludge rake, the rotation speed of which is controlled at 0.03 rpm.

[0065] The clear liquid overflowing from the top of the settling tank flows into the feed circulation tank of the metal membrane system. The incoming material from the circulation tank mixes with the concentrated circulating liquid discharged from the metal membrane system and is then pumped into the metal membrane for filtration. The metal membrane filtration is a cross-flow filtration system with a pore size of 20 nm. The metal membrane is made of 316L sintered metal powder felt. The metal membrane employs a two-stage or three-stage series filtration method, with a membrane surface velocity of 5 m / s. The metal membrane has automatic backwashing and online chemical cleaning functions. Through backwashing with the clear liquid, the membrane flux can be restored to 99%. The membrane filtration clear liquid is sent as product to the ferrous sulfate storage tank.

[0066] The concentrated liquid discharged from the metal membrane and the concentrated liquid discharged from the bottom of the impurity removal tank are returned to the filter press buffer tank. The concentrated liquid is then pumped to the filter press, which has a pressing function and a filter cloth filtration accuracy of 10 microns. The clear liquid from the filter press is returned to the metal membrane system feed buffer tank. The unloaded filter cake is conveyed to the warehouse by a conveyor belt.

[0067] Explanation of the principle of this invention:

[0068] Comparison of this invention with traditional old processes

[0069] Dissolution optimization

[0070] The old process used an intermittent dissolution method. Solid FeSO4·7H2O raw material was directly discharged into the dissolution tank, and the corresponding amount of condensate was introduced according to the amount of raw material added for dissolution. The dissolution tank needed to be equipped with a stirrer for stirring. After the raw material was completely dissolved, the dissolved solution in the tank was pumped downstream. This process has obvious drawbacks. First, it cannot be operated continuously. It can only be discharged after the raw material in the entire dissolution tank is completely dissolved, requiring a lot of manpower and multiple large-capacity dissolution tanks to achieve batch discharge. Second, the composition of the raw material fluctuates greatly, and it is difficult to precisely control the amount of raw material and water added. Moreover, because the dissolution tank is large, there may even be local undissolved areas, resulting in a high product defect rate.

[0071] This invention employs a continuous dissolution method. First, an appropriate amount of FeSO4·7H2O raw material is added to a dissolution tank to form a salt layer of a certain height. The condensate is then introduced to the bottom of the salt layer, flowing upwards through it and overflowing from the top of the tank to the downstream. Once the salt layer height is ensured, the overflowing salt solution is the saturated solution. Water is then quantitatively added to dilute the solution to the desired concentration based on a calculated concentration. This process allows for continuous operation, streamlines the equipment, requires minimal personnel, and enables precise control of the product concentration.

[0072] Impurity Removal Optimization

[0073] Fe 2+ It is easily oxidized in air to form Fe. 3+ The old process involved adding NaOH to make Fe... 3+ Fe(OH)3 precipitate is formed and then pumped to a filter press for removal. On the one hand, similar to the dissolution section, pH can only be adjusted in batches, making continuous operation impossible and requiring significant manpower; on the other hand, Fe... 3+ Removing the filter press by forming Fe(OH)3 precipitate results in a significant loss of raw materials, greatly reducing their utilization rate. Furthermore, the large amount of precipitate not only easily clogs the pipeline system, increasing the frequency of maintenance, but also leads to the commissioning of more filter press equipment and the generation of more filter cake solid waste. The filter press filtrate needs to stand for 7–11 days after entering the finished product tank before being sent downstream.

[0074] This invention removes impurities by adding iron sheets. In the impurity removal tank, sufficient contact between the solution and the iron sheets is ensured, along with adequate reaction time. The solution at the top of the tank overflows into a settling tank above ground, and the clear liquid at the top overflows and is sent to a metal membrane for filtration. The concentrated liquid at the bottom of the tank is sent to a filter press for further processing. The entire process operates continuously, significantly improving production efficiency and avoiding raw material loss. Furthermore, the amount of sediment is greatly reduced, decreasing the use of the filter press and the generation of solid waste. The metal membrane has a pore size of 20 nm, providing a filtration precision far exceeding that of a filter press, and the filtrate can be directly sent downstream without prolonged settling.

[0075] The process comparison is shown in the table below:

[0076]

[0077]

[0078] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A continuous refining process of titanium white by-product ferrous sulfate characterized by: The method comprises the following steps: S1: raw materials are sent to a dissolving tank, hot water is introduced into the bottom of the dissolving tank, and ferrous sulfate solution is introduced into a buffer tank through a baffle tank of the dissolving tank, water is added in the baffle tank to dilute the ferrous sulfate solution; S2: the ferrous sulfate solution in the buffer tank is pumped into a removal tank, iron pieces are added into the removal tank, the solution at the top of the removal tank overflows to a ground tank, the clear liquid at the top of the ground tank overflows to a metal membrane filtration system, and the clear liquid filtered by the metal membrane filtration system is sent to a ferrous sulfate storage tank as a product; S3: the concentrated liquid discharged from the metal membrane filtration system and the removal tank is returned to a buffer tank of a filter press, the liquid in the buffer tank is pumped to a compressor, and the clear liquid in the filter press is returned to a clear liquid buffer tank.

2. The continuous refining method of titanium dioxide by-product ferrous sulfate according to claim 1, characterized by: The raw materials in the step S1 are ferrous sulfate heptahydrate; The temperature of the hot water introduced into the dissolving tank in the step S1 is 60-90°C, and the salt layer height of the dissolving tank is 2-4.5 m.

3. The continuous refining method of titanium dioxide by-product ferrous sulfate according to claim 1, characterized by: The flow rate of the baffle tank in the step S1 needs to be controlled at 0.1-0.3 m / s, the temperature of the ferrous sulfate solution in the baffle tank is at least 50-70°C, and the concentration of the ferrous sulfate solution in the baffle tank is 20-23%.

4. The continuous refining method of titanium dioxide by-product ferrous sulfate according to claim 1, characterized by: The metal membrane filtration system in the step S2 and the step S3 is a cross-flow filtration, the pore size of the metal membrane is 30-100 nm, and the metal membrane is a 316L metal powder sintered felt; The iron pieces are added in the step S2 to control the pH of the ferrous sulfate solution at 2-4.

5. The continuous refining method of titanium dioxide by-product ferrous sulfate according to claim 4, characterized in that: The metal membrane filtration system adopts a two-stage series or three-stage series filtration mode, and the flow rate of the membrane surface is 1-5 m / s.

6. The apparatus for use in a continuous process for the refining of titanium white by-product ferrous sulfate according to any one of claims 1 to 5, characterized in that: The method comprises a dissolving tank, a buffer tank, a removal tank, a ground tank, a metal membrane filtration system, and a product tank. The dissolving tank is connected with the buffer tank through a baffle tank, the buffer tank is connected with the removal tank through a first pipeline, the top of the removal tank is connected with the ground tank through a first overflow pipe, the top of the ground tank is connected with the metal membrane filtration system through a second overflow pipe, the metal membrane filtration system is connected with the product tank through a pipeline, and the bottom of the metal membrane filtration system and the ground tank is connected with a filter press assembly.

7. The continuous refining device for titanium dioxide by-product ferrous sulfate according to claim 6, characterized in that: The dissolving tank is a semi-underground dissolving tank. The bottom of the dissolving tank is provided with a plurality of water outlet pipelines and a total pipeline, the water outlet pipelines are sequentially arranged on the total pipeline, and a plurality of nozzles are arranged on the water outlet pipelines. The baffle tank has a hollow structure, the two ends of the baffle tank are communicated with the dissolving tank and the buffer tank respectively, and a plurality of baffles are arranged in the baffle tank. A concentration instrument is arranged in the baffle tank, a water inlet pipe is arranged at the top of the baffle tank, and an adjusting valve is arranged on the water inlet pipe. The flow rate of the baffle tank is controlled at 0.1-0.3 m / s, the temperature of the ferrous sulfate solution in the baffle tank is not less than 50-70°C, and the concentration of the ferrous sulfate solution in the baffle tank is 20-23%.

8. The continuous refining device for titanium dioxide by-product ferrous sulfate according to claim 7, characterized in that: The distance between the baffles is 300-600 mm.

9. The continuous refining device for titanium dioxide by-product ferrous sulfate according to claim 6, characterized in that: The buffer tank is a semi-underground concrete structure, a stirrer is arranged in the buffer tank, an automatic weighing feeder is arranged at the top of the removal tank, and the automatic weighing feeder is provided with iron pieces. A pH tester is arranged in the removal tank, the amount of the added iron pieces is controlled to control the pH of the ferrous sulfate solution in the removal tank at 2-4. A first axial flow pump is arranged on the first pipeline.

10. The continuous refining device for titanium dioxide by-product ferrous sulfate according to claim 9, characterized in that: The iron pieces are irregularly shaped iron pieces for automobile cold rolling.

11. The continuous refining device of ferrous sulfate by-product of titanium dioxide according to claim 9, characterized in that: The stirring speed of the stirrer is 10-30 rpm.

12. The continuous refining device of ferrous sulfate by-product of titanium dioxide according to claim 7, characterized in that: The top of the impurity removal tank is provided with a plurality of first overflow ports uniformly distributed, a reflux pipeline is arranged at the first overflow port, a first overflow pipeline is arranged on the reflux pipeline, and the other end of the first overflow pipeline is connected with the settling tank; A second axial flow pump and a first valve are arranged on the reflux pipeline, and the second axial flow pump is 20-50 times of the first axial flow pump in feeding amount; An eccentric stirrer is arranged in the top of the impurity removal tank, the stirring speed of the eccentric stirrer is 10-30 rpm, and the eccentric stirrer is a paddle stirrer; A bottom rake is arranged at the bottom of the settling tank, and the rotating speed of the bottom rake is 0.03-0.06 rpm.

13. The continuous refining device of ferrous sulfate by-product of titanium dioxide according to claim 6, characterized in that: The metal membrane filtration system comprises a clear liquid buffer tank and a metal membrane filter, the settling tank is connected with the clear liquid buffer tank through a second overflow pipeline, the clear liquid buffer tank is connected with the metal membrane filter through a third pipeline, a third axial flow pump is arranged on the third pipeline, and the clear liquid filtered by the metal membrane filter flows into a finished product tank through a fourth pipeline; The bottom of the settling tank is connected with a filter press assembly through a fifth pipeline, and a second valve is arranged on the fifth pipeline; The bottom of the metal membrane filter is connected with the filter press assembly through a pipeline; The pore size of the metal membrane is 30-100 nm, and the metal membrane is a 316L metal powder sintered felt.

14. The continuous refining device for titanium dioxide by-product ferrous sulfate according to claim 6, characterized in that: The filter press assembly comprises a filter press buffer tank and a filter press machine, the bottom of the settling tank is connected with the filter press buffer tank through a fifth pipeline, the filter press buffer tank is connected with the filter press machine through a sixth pipeline, a filter press feeding pump is arranged on the sixth pipeline, the filtrate of the filter press is connected with the clear liquid buffer tank through a seventh pipeline, and the bottom of the filter press is provided with a filter residue conveying belt; The filter press has a pressing function, and the filter cloth has a filtering precision of 1-20 microns.

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