A system for recovering vanadium from a chromium-removal underflow of a sodium vanadium solution and a method thereof

Abstract

This invention relates to a system for recovering vanadium from the underflow of vanadium sodium vanadium solution after chromium removal, comprising: a settling tank, the lower side and bottom of which are connected to a first pump and a second pump, respectively; a vanadium removal tank, the top of which is connected to the second pump, containing a first agitator and a first steam loop, and the bottom of which is connected to a third pump; a slurry tank, the top of which has a feed inlet, containing a second agitator and a second steam loop, and the bottom of which is connected to a fourth pump, the fourth pump being connected to the top of the vanadium removal tank via a first branch pipe; a dilution tank, the top of which is connected to a second branch pipe, containing a third agitator, and the bottom of which is connected to a fifth pump; a buffer tank, the bottom of which is connected to the top of the dilution tank; and a plate frame having an inlet and an outlet, the third pump and the fifth pump being connected to the inlet respectively, and the outlet connecting to a pipe forming a cross-shaped pipe that connects to the top of the vanadium removal tank, the settling tank, and the dilution tank respectively. Furthermore, this invention also relates to a corresponding method. This invention can reduce vanadium loss and production costs.

Description

Technical Field

[0001] This invention belongs to the field of hydrometallurgical technology, and more specifically, relates to a system and method for recovering vanadium from the underflow of sodium vanadium molten metallurgy for chromium removal. Background Technology

[0002] Currently, the process route for producing vanadium-aluminum grade vanadium powder, V2O599.8-P vanadium powder, and battery-grade vanadium powder using vanadium slag sodium leaching solution as raw material is as follows: The vanadium-containing leaching solution, after purification and impurity removal by calcium chloride, is first treated with aluminum sulfate to remove silicon, and then the solution is treated with aluminum sulfate to remove chromium. After removing silicon and chromium, the solution is subjected to vanadium precipitation to obtain AMV. After centrifugation, washing, and drying, it is then calcined. The obtained vanadium powder meets the V2O599.8-P index in the YB / T 5304-2017 standard and the customer's individual requirements.

[0003] However, after chromium removal from the vanadium-containing leaching solution, a chromium-removed underflow slag is obtained. Due to the fine particle size of the chromium-removed underflow slag, filtration is difficult and the filter cake is not well-formed, resulting in a water content of approximately 60%. Testing revealed that the chromium-removed underflow slag contains approximately 12% vanadium, all of which is pentavalent vanadium. Therefore, the vanadium in this underflow slag must be recovered to reduce vanadium loss.

[0004] In existing technologies, Wang Xuewen's "A Comprehensive Recovery Method for Vanadium-Chromium Salt Solutions" proposes adding a reducing agent to a vanadium-chromium salt solution under suitable pH conditions to reduce pentavalent vanadium and hexavalent chromium to tetravalent vanadium and trivalent chromium. Then, alkali is added to adjust the pH, causing vanadium and chromium to precipitate. This is filtered to obtain vanadium-chromium slag. The slag is then added to an alkaline solution for selective leaching of vanadium. The leachate is then acid-adjusted to precipitate vanadium again, thus achieving effective separation and recovery of vanadium and chromium. However, this method is unsuitable for treating the chromium-removed underflow slag from the high-purity vanadium pentoxide production process, where vanadium is pentavalent and chromium is trivalent.

[0005] Tao Changyuan's paper, "A Method for Separating and Recovering Vanadium and Chromium from Vanadium-Chromium Slag," proposes a method involving impregnation of vanadium-chromium slag with sulfuric acid solution, followed by filtration to obtain a filtrate containing vanadium and chromium ions. Alkali is added to the filtrate to precipitate, yielding a slurry. Excess oxidant is added to the slurry to obtain a mixed solution containing high-valence vanadium and chromium ions. A vanadium-precipitating agent is added under acidic and heated conditions to obtain a vanadium-containing precipitate and filtrate. The vanadium-containing precipitate is calcined to vanadium pentoxide. The filtrate is cooled and allowed to stand, precipitating sodium sulfate crystals and separating the chromium-containing filtrate. The chromium-containing filtrate is then precipitated under alkaline conditions, and the resulting clear liquid is evaporated to obtain sodium chromate crystals. However, this method is complex and time-consuming, making it unsuitable for industrial production.

[0006] Therefore, existing technologies need to be improved. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the purpose of this invention is as follows: After dilution and boiling, lignocellulose is fed into a plate and frame filter press before the chromium-removing underflow slag, allowing the lignocellulose to form a thin film on the filter plate surface, making the filter cake easier to detach. After dilution and boiling, the lignocellulose is added as a filter aid to the slurry formed from the chromium-removing underflow slag and stirred evenly, facilitating filtration and easy filter cake formation. Vanadium in the chromium-removing underflow, after dilution and plate and frame filtration, is returned directly to the high-purity vanadium pentoxide production line for recovery. If the vanadium content in the filter cake is ≥3% after the first plate and frame filtration of the chromium-removing underflow, the filter cake is returned to the vanadium removal tank for further vanadium removal and pumped back into the plate and frame filter press until the vanadium content in the filter cake is <3%, at which point the filter cake proceeds to the next process.

[0008] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0009] According to one aspect of the present invention, a system for recovering vanadium from the underflow of vanadium sodium vanadium solution after chromium removal is provided, comprising:

[0010] The settling tank has its lower side connected to the first pump via a flow measuring valve, and its bottom connected to the second pump via a first underflow valve.

[0011] The vanadium removal tank has a top connected to a second pump via a pipe. The top of the vanadium removal tank is connected to a first water pipe, a first exhaust pipe, and a buffer hopper. The buffer hopper holds the filter cake that is returned to the vanadium removal tank for further vanadium removal. The interior of the vanadium removal tank is equipped with a first agitator and a first steam loop pipe. The bottom of the vanadium removal tank is connected to a third pump via a second underflow valve.

[0012] The pulping tank has a second water pipe and a second exhaust pipe connected to its top, and a feeding port is provided. Wood cellulose is added through the feeding port. The inside of the pulping tank is equipped with a second agitator and a second steam ring pipe. The second steam ring pipe and the first steam ring pipe are connected to a common steam pipe. The bottom of the pulping tank is connected to a fourth pump through a third underflow valve. The fourth pump is connected to the top of the vanadium removal tank through a first branch pipe, and a first valve is provided on the first branch pipe.

[0013] The dilution tank has its top connected to a second branch pipe connected to a fourth pump, and a second valve installed on the second branch pipe. A third stirrer is installed inside the dilution tank, and the bottom of the dilution tank is connected to a fifth pump via a fourth underflow valve.

[0014] The buffer tank has a third water pipe connected to its top, and its bottom is connected to the top of the dilution tank via a fifth underflow valve.

[0015] The plate frame has an inlet and an outlet. The third pump is connected to the inlet of the plate frame through a pipe equipped with a third valve. The fifth pump is connected to the inlet of the plate frame through a pipe equipped with a fourth valve. The outlet of the plate frame is connected to a cross-shaped pipe and is connected to the top of the vanadium removal tank, the top of the settling tank, and the top of the dilution tank through the fifth, sixth, and seventh valves, respectively.

[0016] In one embodiment of the present invention, a first backflushing water pipe is also connected to the pipe connected to the bottom of the settling tank; a second backflushing water pipe is also connected to the pipe connected to the bottom of the vanadium removal tank.

[0017] In one embodiment of the present invention, a first level gauge is connected to the top of the vanadium removal tank and a first thermometer is installed on the lower side of the vanadium removal tank; a second level gauge is connected to the top of the pulping tank and a second thermometer is installed on the lower side of the pulping tank; a third level gauge is connected to the top of the dilution tank; and a fourth level gauge is connected to the top of the buffer tank.

[0018] In one embodiment of the present invention, the vanadium content in the filter cake returned to the vanadium removal tank for further vanadium removal is ≥3%.

[0019] In one embodiment of the present invention, a first steam ring pipe is provided with a plurality of uniformly distributed small holes facing the bottom center of the vanadium removal tank; a second steam ring pipe is provided with a plurality of uniformly distributed small holes facing the bottom center of the pulping tank.

[0020] In one embodiment of the present invention, the diameter of the small holes is 6 mm.

[0021] In one embodiment of the present invention, the first backwash water pipe, the first water pipe, the second backwash water pipe, the second water pipe and the third water pipe are all connected to the pure water main pipe, and the conductivity of the pure water is ≤40uS / cm.

[0022] In one embodiment of the present invention, after the vanadium sodium solution in the settling tank has settled for 48 hours, the flow measuring valve and the first pump are opened to carry out vanadium settling operation.

[0023] According to another aspect of the present invention, a method for recovering vanadium using a system for recovering vanadium from the underflow of vanadium sodium vanadium solution after chromium removal as described above is provided, comprising the following steps:

[0024] Chromium slag is settled in a settling tank to obtain a chromium-free underflow;

[0025] Lignocellulose is added to a pulping tank to prepare a slurry. A portion of the slurry is pumped to a vanadium removal tank and another portion is pumped to a dilution tank.

[0026] The chromium removal underflow is pumped into the vanadium removal tank to mix and stir evenly with the slurry pumped into the vanadium removal tank, thus obtaining a chromium slag slurry.

[0027] The liquid in the buffer tank is added to the dilution tank to dilute the slurry, and the diluted slurry is pumped into the plate and frame filter to form a film on the surface of the plate and frame. The filtered clear liquid is then returned to the buffer tank.

[0028] The chromium slag slurry is pumped into a plate and frame filter press for pressure filtration. The filtrate is returned to the settling tank to recover vanadium, and the filter cake is discharged.

[0029] In one embodiment of the present invention, the method further includes:

[0030] The vanadium content in the filter cake after unloading is tested. If the vanadium content is <3%, the obtained filter cake is sold externally. If the vanadium content is ≥3%, the filter cake is transported to a vanadium removal tank for further processing until the vanadium content in the filter cake is <3%.

[0031] By adopting the above technical solution, the present invention has the following advantages compared with the prior art:

[0032] (1) The present invention can recover vanadium from the chromium removal underflow slag in the production process of high-purity vanadium pentoxide, so as to reduce vanadium loss and production costs.

[0033] (2) In this invention, lignocellulose is mixed with water and boiled for a long time. The boiled lignocellulose slurry is pumped into a dilution tank, mixed with the previous batch of clear liquid, and then pumped into a plate and frame filter to form a thin film on the surface of the filter plate. Then, the chromium-removed underflow slag is pumped into the plate and frame filter for pressing, which is conducive to the removal of the filter cake. The boiled lignocellulose slurry is pumped into the chromium-removed underflow slag to be re-pulped and then pumped into the plate and frame filter for pressing to achieve solid-liquid separation, which is conducive to the formation of the filter cake.

[0034] (3) The present invention adds lignocellulose as a filter aid, which does not introduce new impurities and will not affect the quality of the vanadium powder product.

[0035] (4) The vanadium-containing filtrate recovered by this invention is directly returned to the high-purity vanadium pentoxide production line for reuse.

[0036] (5) The underflow generated by the present invention can be directly filtered and pressed using the production plates and frames of existing production lines, and the filter cake is easy to form and fall off.

[0037] (6) The equipment integration and technology described in this invention can be industrialized, with low labor intensity, high degree of automation, and low production cost. Attached Figure Description

[0038] Figure 1 A schematic diagram of the system for recovering vanadium from the underflow of sodium vanadium leaching solution after chromium removal is shown.

[0039] Figure 2 A schematic flowchart of the method for recovering vanadium from the underflow of vanadium sodium vanadium solution for chromium removal provided by the present invention is shown.

[0040] List of reference numerals

[0041] 1. Settling tank; 2. Flow measuring valve; 3. First pump; 4. First underflow valve; 5. Second pump; 6. First backflushing water pipe; 7. First water pipe; 8. First level gauge; 9. First vent pipe; 10. First agitator; 11. Buffer hopper; 12. First steam loop pipe; 13. Vanadium removal tank; 14. Second underflow valve; 15. Third pump; 16. Second backflushing water pipe; 17. First thermometer; 18. Slurry tank; 19. Second steam loop pipe; 20. Steam pipe; 21. Second water pipe; 22. Second vent pipe; 23. Feed port; 2 4 Second level gauge, 25 Second stirrer, 26 Second thermometer, 27 Third underflow valve, 28 Fourth pump, 29 Flow meter, 30 First valve, 31 Second valve, 32 Third valve, 33 Fourth valve, 34 Dilution tank, 35 Fifth pump, 36 Fourth underflow valve, 37 Third level gauge, 38 Third stirrer, 39 Fifth underflow valve, 40 Buffer tank, 41 Fourth level gauge, 42 Third water pipe, 43 Belt, 44 Plate and frame, 45 Fifth valve, 46 Sixth valve, 47 Seventh valve. Detailed Implementation

[0042] It should be understood that the embodiments of the invention shown in the exemplary embodiments are merely illustrative. Although only a few embodiments have been described in detail in this invention, those skilled in the art will readily recognize that various modifications are possible without substantially departing from the teachings of the invention. Accordingly, all such modifications should be included within the scope of the invention. Other substitutions, modifications, variations, and deletions can be made to the design, operating conditions, and parameters of the following exemplary embodiments without departing from the spirit of the invention.

[0043] like Figure 1 As shown, the present invention provides a system for recovering vanadium from the underflow of vanadium sodium vanadium solution after chromium removal, comprising:

[0044] Settling tank 1, the lower part of settling tank 1 is connected to the first pump 3 through flow measuring valve 2, and the bottom of settling tank 1 is connected to the second pump 5 through the first bottom flow valve 4;

[0045] The top of the vanadium removal tank 13 is connected to the second pump 5 via a pipe. The top of the vanadium removal tank 13 is connected to the first water pipe 7, the first exhaust pipe 9 and the buffer hopper 11. The buffer hopper 11 holds the filter cake that is returned to the vanadium removal tank for further vanadium removal. The interior of the vanadium removal tank 13 is equipped with the first agitator 10 and the first steam ring pipe 12. The bottom of the vanadium removal tank 13 is connected to the third pump 15 via the second underflow valve 14.

[0046] The pulping tank 18 has a second water pipe 21 and a second exhaust pipe 22 connected to its top and a feed port 23 for adding lignocellulose. The pulping tank 18 is equipped with a second agitator 25 and a second steam ring pipe 19. The second steam ring pipe 19 and the first steam ring pipe 12 are connected to a common steam pipe 20. The bottom of the pulping tank 18 is connected to a fourth pump 28 through a third underflow valve 27. The fourth pump 28 is connected to the top of the vanadium removal tank 13 through a first branch pipe. A first valve 30 is provided on the first branch pipe.

[0047] The top of the dilution tank 34 is connected to the second branch pipe connected to the fourth pump 28. The second branch pipe is equipped with a second valve 31. The inside of the dilution tank 34 is equipped with a third stirrer 38. The bottom of the dilution tank 34 is connected to the fifth pump 35 through the fourth underflow valve 36.

[0048] The buffer tank 40 has a third water pipe 42 connected to its top, and its bottom is connected to the top of the dilution tank 34 via a fifth underflow valve 39.

[0049] The plate frame 44 has an inlet and an outlet. The third pump 15 is connected to the inlet of the plate frame 44 through a pipe equipped with a third valve 32. The fifth pump 35 is connected to the inlet of the plate frame 44 through a pipe equipped with a fourth valve 33. The outlet of the plate frame 44 is connected to a cross-shaped pipe and is connected to the top of the vanadium removal tank 13, the top of the settling tank 1, and the top of the dilution tank 40 through the fifth valve 45, the sixth valve 46, and the seventh valve 47, respectively.

[0050] In the above system, a first backwash water pipe 6 is also connected to the pipe connected to the bottom of the settling tank 1; a second backwash water pipe 16 is also connected to the pipe connected to the bottom of the vanadium removal tank 13.

[0051] In the above system, the top of the vanadium removal tank 13 is also connected to a first level gauge 8 and the lower part of the vanadium removal tank 13 is equipped with a first thermometer 17; the top of the pulping tank 18 is also connected to a second level gauge 24 and the lower part of the pulping tank 18 is equipped with a second thermometer 26; the top of the dilution tank 34 is also connected to a third level gauge 37; and the top of the buffer tank 40 is also connected to a fourth level gauge 41.

[0052] In the above system, the vanadium content in the filter cake returned to the vanadium removal tank 13 for further vanadium removal is ≥3%.

[0053] In the above system, the first steam ring pipe 12 is provided with a plurality of evenly distributed small holes facing the bottom center of the vanadium removal tank 13; the second steam ring pipe 19 is provided with a plurality of evenly distributed small holes facing the bottom center of the pulping tank 18.

[0054] In the above system, the diameter of the pinhole is 6mm.

[0055] In the above system, the first backwash water pipe 6, the first water pipe 7, the second backwash water pipe 16, the second water pipe 21 and the third water pipe 42 are all connected to the pure water main pipe, and the conductivity of the pure water is ≤40uS / cm.

[0056] In the above system, after the vanadium sodium solution in the settling tank 1 has settled for 48 hours, the flow measuring valve 2 and the first pump 3 are opened to carry out vanadium precipitation.

[0057] In addition, such as Figure 2 As shown, the present invention provides a method for recovering vanadium using the vanadium-removing underflow system of vanadium sodium vanadium solution as described above, comprising the following steps:

[0058] Chromium slag is settled in a settling tank to obtain a chromium-free underflow;

[0059] Lignocellulose is added to a pulping tank to prepare a slurry. A portion of the slurry is pumped to a vanadium removal tank and another portion is pumped to a dilution tank.

[0060] The chromium removal underflow is pumped to the vanadium removal tank and mixed evenly with the slurry pumped to the vanadium removal tank to obtain chromium slag slurry.

[0061] The liquid in the buffer tank is added to the dilution tank to dilute the slurry, and the diluted slurry is pumped into the plate and frame filter to form a film on the surface of the plate and frame. The filtered clear liquid is then returned to the buffer tank.

[0062] The chromium slag slurry is pumped into a plate and frame filter press for pressure filtration. The filtrate is returned to the settling tank to recover vanadium, and the filter cake is discharged.

[0063] The above method also includes:

[0064] The vanadium content in the filter cake after unloading is tested. If the vanadium content is <3%, the obtained filter cake is sold externally. If the vanadium content is ≥3%, the filter cake is transported to a vanadium removal tank for further processing until the vanadium content in the filter cake is <3%.

[0065] The technical solutions of the present invention will be described in detail below through specific embodiments.

[0066] like Figure 1-2 As shown, after the sodium vanadium solution reacts with the chromium removal agent, it is fed into settling tank 1 to settle the chromium slag. After 48 hours of settling, the flow measuring valve 2 can be opened and the first pump 3 can be started to perform vanadium precipitation.

[0067] The chromium removal underflow in settling tank 1 needs to be cleaned regularly. Open the first underflow valve 4 and start the second pump 5 to pump the chromium removal underflow in settling tank 1 into vanadium removal tank 13. If opening the first underflow valve 4 and starting the second pump 5 cannot smoothly discharge the chromium removal underflow in settling tank 1, open the first backflushing water pipe 6 to backflush it and help the underflow in settling tank 1 to be discharged. After the underflow can be discharged smoothly, close the first backflushing water pipe 6.

[0068] When the liquid level in the vanadium removal tank 13 submerges the lower blades of the first agitator 10, the first agitator 10 is started to agitate the liquid in the vanadium removal tank 13. Chromium removal underflow is pumped into the vanadium removal tank 13 until the specified liquid level is reached, then the first underflow valve 4 and the second pump 5 are closed. After stopping the pumping of chromium removal underflow into the vanadium removal tank 13, the first water pipe 7 is opened to add water into the tank until the specified liquid level is reached, then the first water pipe 7 is closed. The third underflow valve 27 and the first valve 30 are opened, the second valve 31 is closed, and the fourth pump 28 is started to pump the specified amount of lignocellulose slurry into the vanadium removal tank 13. The valve on the steam pipe 20 to the vanadium removal tank 13 is opened, and the liquid in the vanadium removal tank 13 is heated to 70°C with the first agitator 10 running through the first steam ring pipe 12. This temperature is maintained for ≥0.5 hours. After reaching the constant temperature time, the fourth valve 33 can be opened and closed, the third valve 32 can be opened, the second underflow valve 14 can be opened, and the third pump 15 can be started to pump the slurry in the vanadium removal tank 13 into the plate and frame filter 44 for pressure filtration. If a blockage occurs between the bottom of the vanadium removal tank 13 and the third pump 15, the second backwash water pipe 16 can be opened to clear the blockage. The first steam ring pipe 12 is a stainless steel ring pipe and is connected to the steam pipe 20; the first steam ring pipe 12 has multiple evenly distributed diameters at the center of the bottom of the cone of the vanadium removal tank 13. The total area of ​​all the small holes on the first steam ring pipe 12 is greater than the cross-sectional area of ​​the first steam ring pipe 12 to avoid pressure buildup and jetting. The first steam ring pipe 12 is placed on a support composed of multiple protruding supports evenly distributed on the same horizontal plane of the inner wall of the vanadium removal tank 13. The distance between the first steam ring pipe 12 and the inner wall of the vanadium removal tank 13 is approximately 20 mm. The first level gauge 8 is installed on the top of the vanadium removal tank 13 to detect the liquid level inside the tank. The first exhaust pipe 9 is connected to the main exhaust pipe and is used to remove the gas generated during the production process inside the tank. The buffer hopper 11 is installed on the top of the vanadium removal tank 13 to hold the filter cake returned to the vanadium removal tank 13 for further vanadium removal. The first thermometer 17 is installed on the lower side of the vanadium removal tank 13 to detect the temperature of the liquid inside the tank.

[0069] The second steam loop 19, second exhaust pipe 22, second level gauge 24, second agitator 25, and second thermometer 26 are installed in the same position, manner, and function as the first steam loop 12, first exhaust pipe 9, first level gauge 8, first agitator 10, and first thermometer 17. The feed inlet 23 is flared and installed on the top of the pulping tank 18. Its valve is opened, and lignocellulose is added to the pulping tank 18 through the feed inlet 23. The second water pipe 21 is connected to the top of the pulping tank 18. After opening the valve on the second water pipe 21 and adding the specified amount of water to the pulping tank 18, the second agitator 25 is started, and the specified amount of lignocellulose is added to the pulping tank 18 through the feed inlet 23. Then, the steam valve of the steam pipe 20 to the pulping tank 18 is opened, and the liquid in the tank is heated to boiling and then kept at a constant temperature for ≥2 hours through the second steam loop 19. After the constant temperature time is reached, the third underflow valve 27 and the fourth pump 28 can be opened to pump the prepared lignocellulose slurry to the vanadium removal tank 13 or the dilution tank 34.

[0070] After closing the first valve 30 and opening the second valve 31, open the third underflow valve 27 and start the fourth pump 28 to deliver the prepared lignocellulose slurry to the dilution tank 34 in the specified amount. Then open the fifth underflow valve 39 to discharge the specified amount of clear liquid from the buffer tank 40 into the dilution tank 34. Start the third agitator 38, and after the liquid in the dilution tank 34 has been stirred for 5 minutes, open the fourth underflow valve 36 and start the fifth pump 35 to pump the diluted lignocellulose slurry into the plate frame 44. The third level gauge 37 is installed on the top of the dilution tank 34 to detect the liquid level inside the tank.

[0071] After closing valves 45 and 46, opening valve 47, closing valve 32, and opening valve 33, the fourth underflow valve 36 is opened, and pump 35 is started to pump the diluted wood fiber slurry into the filter cake 44. The boiled wood cellulose is trapped on the surface of the filter cake 44, forming a thin film that ensures easy detachment during filter cake discharge. The filtered clear liquid is returned to the buffer tank 40 for use in the wood cellulose preparation in the dilution tank 34, reducing wastewater generation and thus production costs. If the clear liquid volume exceeds the preparation volume, valve 45 is opened and valve 47 is closed to return the excess clear liquid to the vanadium removal tank 13 to reduce the vanadium concentration in the chromium removal underflow. If the clear liquid volume is less than the preparation volume, the third water pipe 42 is opened to meet the preparation volume requirements. A fourth level gauge 41 is installed on the top of the buffer tank 40 to detect the liquid level inside the tank.

[0072] After a thin film forms on the surface of the plate and frame filter 44, close the fifth valve 45 and the seventh valve 47, open the sixth valve 46, close the fourth valve 33, open the second underflow valve 14, and start the third pump 15. Pump the pre-treated chromium-removed underflow from the vanadium removal tank 13 to the plate and frame filter 44 for pressure filtration. The filtrate is returned to the settling tank for vanadium recovery. After the filter cake from the plate and frame filter 44 is unloaded, it falls onto the conveyor belt 43, where a sample is taken to test its vanadium content. If the vanadium content in the filter cake is <3%, the conveyor belt 43 reverses to transport the filter cake to the next process. If the vanadium content in the filter cake is ≥3%, the conveyor belt 43 rotates forward to transport the filter cake to the buffer hopper 11, and then returns it to the vanadium removal tank 13. After pulping and vanadium removal, it is pumped back into the plate and frame filter for pressure filtration until the vanadium content in the filter cake is <3%. The filter cake is then returned to the vanadium removal tank 13, and there is no need to add boiled lignocellulose.

[0073] Preferably, the first backwash water pipe 6, the first water pipe 7, the second backwash water pipe 16, the second water pipe 21, and the third water pipe 42 are all connected to the pure water main pipe. The pure water is obtained by removing impurities from domestic water through two stages of reverse osmosis and EDI, and the water quality requirement is a conductivity ≤40uS / cm.

[0074] In the aforementioned system and application operations, specifically, the settling tank 1 has a cylindrical diameter of 4.4m, a height of 10.0m, a bottom conical height of 2.5m, and a distribution cylinder diameter of 0.5m, extending 8m into the tank. The vanadium removal tank 13 has a cylindrical diameter of 3.0m, a height of 3.5m, and an elliptical arc bottom (0.6m high), with a single-batch liquid preparation volume of 20m³. 3 The pulping tank has a cylindrical body with a diameter of 1.8m, a height of 2.5m, and an elliptical arc bottom (0.5m high). The single-batch liquid preparation volume is 5m³. 3 The dilution tank 34 has a diameter of 1.6m, a height of 2.5m, and an elliptical arc bottom (0.5m high). The volume of liquid prepared in a single batch is 4m³. 3 The buffer tank 40 has a cylindrical diameter of 1.6m, a height of 2.5m, and a conical bottom with a height of 1m. It can receive a single volume of 5m³ of clear liquid. 3 The slab frame is 100m. 2 .

[0075] In the above system and application operation, specifically, 50 kg of lignocellulose and 5 m³ of co-prepared liquor are added in a single batch to pulping tank 18. 3 The boiled lignocellulose was pumped into dilution tank 34 in a single batch, approximately 0.5 ml. 3 Dilute to 4m in dilution tank 34. 3 After a single application to the board frame, the diluted lignocellulose slurry is 4m³. 3 The boiled lignocellulose was pumped into vanadium removal tank 13 in a single batch, approximately 2m³. 3 The underflow from the chromium removal tank 1 is pumped into the vanadium removal tank in a single operation, approximately 5m³. 3 The filter cake after plate and frame filtration has a moisture content of approximately 35%.

[0076] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of the present invention. Any modifications or equivalent substitutions made to the present invention without departing from the spirit and scope thereof should be covered within the protection scope of the claims of the present invention.

Claims

1. A system for recovering vanadium from the underflow of sodium vanadium hydroxide solution after chromium removal, characterized in that, Include: A settling tank, the lower part of which is connected to a first pump via a flow measuring valve, and the bottom of which is connected to a second pump via a first underflow valve; a first backflushing water pipe is also connected to the pipe connected to the bottom of the settling tank. The vanadium removal tank has its top connected to a second pump via a pipe. The top of the tank is connected to a first water pipe, a first exhaust pipe, and a buffer hopper. The buffer hopper holds filter cake that is returned to the tank for further vanadium removal. The tank's interior is equipped with a first agitator and a first steam ring pipe. The bottom of the tank is connected to a third pump via a second underflow valve. A second backflushing water pipe is also connected to the pipe at the bottom of the tank. The first steam ring pipe has multiple evenly distributed small holes, each with a diameter of 6mm, facing the center of the bottom of the tank. The total area of ​​all the holes on the first steam ring pipe is greater than the cross-sectional area of ​​the first steam ring pipe. The first steam ring pipe rests on a support structure composed of multiple protruding supports evenly distributed on the same horizontal plane of the inner wall of the vanadium removal tank. The pulping tank has a second water pipe and a second exhaust pipe connected to its top, and a feeding port for adding lignocellulose. The feeding port is funnel-shaped and installed on the top of the pulping tank. Inside the pulping tank, a second agitator and a second steam ring pipe are installed. The second steam ring pipe and the first steam ring pipe are connected to a common steam pipe. The second steam ring pipe has multiple evenly distributed small holes, each with a diameter of 6 mm, facing the center of the bottom of the pulping tank. The bottom of the pulping tank is connected to a fourth pump via a third underflow valve. The fourth pump is connected to the top of the vanadium removal tank via a first branch pipe, and a first valve is installed on the first branch pipe. The dilution tank has its top connected to a second branch pipe connected to the fourth pump, the second branch pipe being equipped with a second valve, a third stirrer installed inside the dilution tank, and its bottom connected to a fifth pump via a fourth underflow valve. A buffer tank, the top of which is connected to a third water pipe, and the bottom of which is connected to the top of the dilution tank via a fifth underflow valve; The plate frame has an inlet and an outlet. A third pump is connected to the inlet of the plate frame via a pipe equipped with a third valve. A fifth pump is connected to the inlet of the plate frame via a pipe equipped with a fourth valve. The outlet of the plate frame is connected to a cross-shaped pipe that is connected to the top of the vanadium removal tank, the top of the settling tank, and the top of the dilution tank via fifth, sixth, and seventh valves, respectively. When the fifth and sixth valves are closed and the seventh valve is open, the diluted wood fiber slurry is pumped into the plate frame, and the filtered clear liquid is returned to the buffer tank. When the fifth and seventh valves are closed and the sixth valve is open, the chromium slag slurry in the vanadium removal tank is pumped to the plate frame for pressure filtration, and the filtrate is returned to the settling tank.

2. The system for recovering vanadium from the underflow of sodium vanadium solution after chromium removal according to claim 1, characterized in that, The top of the vanadium removal tank is also connected to a first level gauge and the lower side of the vanadium removal tank is equipped with a first thermometer; the top of the pulping tank is also connected to a second level gauge and the lower side of the pulping tank is equipped with a second thermometer; the top of the dilution tank is also connected to a third level gauge; and the top of the buffer tank is also connected to a fourth level gauge.

3. The system for recovering vanadium from the underflow of sodium vanadium hydroxide solution after chromium removal according to claim 1, characterized in that, The vanadium content in the filter cake returned to the vanadium removal tank for further vanadium removal is ≥3%.

4. The system for recovering vanadium from the underflow of sodium vanadium solution after chromium removal according to claim 1, characterized in that, The first backwash water pipe, the first water pipe, the second backwash water pipe, the second water pipe and the third water pipe are all connected to the pure water main pipe, and the conductivity of the pure water is ≤40uS / cm.

5. The system for recovering vanadium from the underflow of vanadium sodium vanadium solution after chromium removal according to claim 1, characterized in that, After the sodium vanadium solution in the settling tank has settled for 48 hours, the flow meter valve and the first pump are opened to carry out vanadium settling operations.

6. A method for recovering vanadium using the system for recovering vanadium from the chromium removal underflow of vanadium sodium vanadium solution according to any one of claims 1-5, comprising the following steps: Chromium slag is settled in a settling tank to obtain a chromium-free underflow; Lignocellulose is added to a pulping tank to prepare a slurry. A portion of the slurry is pumped to a vanadium removal tank and another portion is pumped to a dilution tank. The chromium removal underflow is pumped into the vanadium removal tank to mix and stir evenly with the slurry pumped into the vanadium removal tank, thus obtaining a chromium slag slurry. The liquid in the buffer tank is added to the dilution tank to dilute the slurry, and the diluted slurry is pumped into the plate and frame filter to form a film on the surface of the plate and frame. The filtered clear liquid is then returned to the buffer tank. The chromium slag slurry is pumped into a plate and frame filter press for pressure filtration. The filtrate is returned to the settling tank to recover vanadium, and the filter cake is discharged.

7. The method according to claim 6, characterized in that, The method further includes: The vanadium content in the filter cake after unloading is tested. If the vanadium content is <3%, the obtained filter cake is sold externally. If the vanadium content is ≥3%, the filter cake is transported to the vanadium removal tank for further processing until the vanadium content in the filter cake is <3%.

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