A leaf filter solid-liquid separation process for recovering lithium from sodium aluminate solution

Abstract

A leaf filter solid-liquid separation process for recovering lithium elements from sodium aluminate solution relates to the technical field of alumina production. In this solid-liquid separation process, each working cycle of the leaf filter has three stages: feed filtration, pressure relief backwashing, and mud discharge. In the feed filtration stage, the feed valve is opened to continuously inject crude liquid into the leaf filter, and at the same time, the flocculant addition valve is opened to inject flocculant into the leaf filter, causing the crude liquid to precipitate and quickly adhere to the filter cloth to form mud. The semen filtered through the mud-covered filter cloth flows directly into the filtrate tank through the high-level tank. This solid-liquid separation process takes into account the extraction of lithium and aluminum, eliminates sedimentation separation and the feed mud-covering stage of the leaf filter. First, it can quickly achieve mud on the filter cloth, and then continuously filter out semen to meet the requirements of the production process; second, the semen no longer returns to the mother liquor tank, but flows directly into the filtrate tank, which not only shortens the cycle of the leaf filter and reduces energy consumption, but also greatly improves the solid-liquid separation efficiency of the crude liquid.

Description

Technical Field

[0001] The invention relates to the technical field of alumina production, and in particular to a leaf filter solid-liquid separation process for recovering lithium elements in a sodium aluminate solution. Background Art

[0002] Recent research indicates that lithium resources are associated with bauxite in parts of China. During the alumina production process, the lithium is not extracted, and most of it remains in red mud, which was previously treated as waste. "Research and Progress in Lithium Extraction Using the Bayer Process" (World Nonferrous Metals, March 2024, Part 2) states: "Lithium resources are associated with bauxite in parts of Henan, Yunnan, Guizhou, and Shanxi in my country. The lithium content of bauxite in Henan is generally high. For example, in the Yushan mining area of ​​Xin'an County, Henan Province, the average Li2O content is approximately 0.085%. Lithium minerals are dispersed throughout minerals such as bauxite, kaolinite, and illite. Li Chunchao and others conducted an investigation at the Henan branch of Chinalco and found that approximately 18% of the lithium entered the solution, while over 80% was discharged with the red mud." With the development of new energy vehicles, it is necessary to extract lithium from red mud to increase the overall profitability of mining companies.

[0003] To extract lithium, firstly, the crude liquid (sodium aluminate solution containing floating and suspended matter) must be separated into solid and liquid to obtain red mud containing lithium. Figure 1 and attached Figure 2 In existing alumina production processes, solid-liquid separation of crude liquor occurs in two steps: first, sedimentation to separate the red mud slurry. To accelerate sedimentation, flocculants are typically added to the sedimentation tank. Then, filtration is performed through a leaf filter to obtain the seminal fluid and red mud (see Chinese Patent CN106315644A: A Method and System for Obtaining Seminal Fluid in Alumina Production). The existing leaf filter 1 features a feed valve 11, a relief valve 12, a pressure relief valve 13, and a mud discharge valve 14. The header tank 2 features a reflux valve 21. Each operating cycle of the leaf filter consists of four stages: feed mud entrainment, filtration, pressure relief backwashing, and mud discharge.

[0004] During the feed and sludge stage, the feed valve 11 is first opened, while the pressure relief valve 13 and the overflow valve 12 remain open. This allows the crude liquid in the mother liquor tank to enter the leaf filter 1 tank and reach the overflow height of the overflow pipe. The pressure relief valve 13 and the overflow valve 12 are then closed, and the return valve 21 is opened simultaneously, allowing the semen in the header tank 2 to return to the mother liquor tank. This serves two purposes: first, the circulation of the crude liquid causes the filter cloth to sludge. The filter cloth can only perform preliminary filtration of the crude liquid; only when the sludge layer on the filter cloth reaches a certain thickness can it achieve a fine filtration effect on the crude liquid; second, the incoming liquid compresses the air at the top of the tank, forming a high-pressure air cushion. The sludge stage is concluded when the filtered liquid flowing out of the return valve 21 meets the semen quality standards. The sludge process takes a long time, typically 20-25 minutes.

[0005] During the filtration phase, the return valve 21 is closed and only the feed valve 11 is opened. This is to filter the crude liquid and allow the filtered semen to enter the filtrate tank via the header tank. The filtration phase takes the longest time, typically 60 minutes.

[0006] During the pressure relief backwash stage, feed valve 11 is closed, and pressure relief valve 13 and relief valve 12 are opened in sequence. This releases the high pressure within the tank, allowing the semen in the high-level tank 2 to enter the leaf filter 1 tank, backwashing the filter cloth. The removed mud is deposited at the conical bottom of the tank, forming red mud (filter cake). The crude liquid with a liquid level higher than the overflow pipe passes through relief valve 12 and enters the mother liquor tank. The pressure relief backwash process is relatively fast, generally taking 5 seconds.

[0007] During the mud discharge phase, the mud discharge valve 14 is opened to allow the red mud deposited at the bottom of the tank cone to be discharged downward. The mud discharge process is very fast, generally taking 10 seconds, and then the mud discharge valve 14 is closed.

[0008] In order to take into account the extraction of aluminum and lithium, the existing alumina production process needs to be improved. In the new production process, the existing solid-liquid separation process has the following problems:

[0009] 1. Red mud slurry contains lithium, but since the red mud slurry adopts sedimentation separation process, it contains a large amount of crude liquid, so the red mud slurry needs to be filtered to recover the crude liquid.

[0010] 2. The feeding and mud-hanging stage of the leaf filter takes a long time. Compared with the other stages, the feeding and mud-hanging stage belongs to the preparation stage before filtration. During this stage, neither semen nor red mud (filter cake) is produced, which greatly reduces the efficiency of solid-liquid separation.

[0011] 3. The existing leaf filter can only produce semen intermittently. In the new production process, since part of the semen needs to return to the upstream equipment to participate in the process cycle, the leaf filter is required to be able to produce semen continuously. Summary of the Invention

[0012] In order to overcome the shortcomings of the background technology, the present invention discloses a leaf filter solid-liquid separation process for recovering lithium from sodium aluminate solution, the purpose of which is to:

[0013] 1. Cancel the sedimentation separation process;

[0014] 2. Shorten the cycle of leaf filter and improve the efficiency of solid-liquid separation;

[0015] 3. Enable the leaf filter to continuously produce semen.

[0016] In order to achieve the above-mentioned object of the invention, the present invention adopts the following technical solutions:

[0017] A leaf filter solid-liquid separation process for recovering lithium from sodium aluminate solution. The solid-liquid separation process requires a leaf filter, which has a feed valve, a relief valve, a pressure relief valve, a mud discharge valve, and a flocculant addition valve. The upstream equipment of the leaf filter is a mother liquor tank, and the downstream equipment includes a high-level tank, a filtrate tank, and a filter cake tank.

[0018] Each working cycle of the solid-liquid separation process has three stages: feed filtration, pressure relief backwashing, and mud discharge. In the feed filtration stage, the feed valve is opened to continuously inject crude liquid into the leaf filter, and at the same time, the flocculant addition valve is opened to inject flocculant into the leaf filter, so that the crude liquid precipitates and quickly adheres to the filter cloth to form mud. The semen filtered by the mud filter cloth directly flows into the filtrate tank through the high-level tank.

[0019] To further improve the technical solution, during the initial feeding, the feed valve is opened to continuously inject the crude liquid into the leaf filter, and at the same time, the flocculant addition valve is opened to inject the flocculant into the leaf filter; when the liquid level is higher than the height of the overflow pipe, the pressure relief valve and the overflow valve are closed.

[0020] To further improve the technical solution, during the feed filtration stage, the filtration effect of the semen is checked, and if the semen meets the standards, the flocculant addition valve is closed.

[0021] To further improve the technical solution, the end of the feed filtration stage is marked by the filtration efficiency of the leaf filter being reduced to 60% of the normal filtration efficiency.

[0022] To further improve the technical solution, during the pressure relief backwash stage, the feed valve is first closed, and then the pressure relief valve is opened to relieve the pressure, and the backflow semen is used to remove the mud on the filter cloth.

[0023] To further improve the technical solution, during the mud discharge stage, open the mud discharge valve and keep the pressure relief valve open; after the mud discharge is completed, close the mud discharge valve and open the overflow valve until the liquid level in the leaf filter returns to the overflow position, and finally close the overflow valve and the pressure relief valve.

[0024] To further improve the technical solution, after the semen flowing into the filtrate tank is processed by the downstream process, a part of it is processed by the aluminum extraction process to obtain aluminum products, and the other part is returned to the upstream process to participate in the process cycle.

[0025] To further improve the technical solution, the red mud produced in the mud discharge stage enters the filter cake tank and then undergoes a lithium extraction process to obtain lithium products.

[0026] To further improve the technical solution, the flocculants are sodium polyacrylate and polyacrylamide.

[0027] After implementing the above technical solution, the beneficial effects produced by the present invention are:

[0028] 1. The new production process eliminates sedimentation separation and relies on leaf filters to achieve solid-liquid separation of crude liquid. Firstly, sedimentation separation is inefficient, and the red mud slurry separated by sedimentation contains a large amount of crude liquid. Secondly, it is to maintain the content of suspended matter and floating matter in the crude liquid to facilitate the rapid mud hanging on the filter cloth. Thirdly, the leaf filter is a dynamic separation method with good solid-liquid separation effect and high efficiency, and the water content of the red mud (filter cake) is low. Fourthly, it is conducive to the extraction of lithium.

[0029] 2. This solid-liquid separation process eliminates the feed mud stage. Firstly, it quickly muds the filter cloth, allowing the semen to be immediately filtered out. Secondly, the semen no longer returns to the mother liquor tank, but flows directly into the filtrate tank. Compared with existing solid-liquid separation processes, this solid-liquid separation process not only shortens the leaf filter cycle and reduces energy consumption, but also significantly improves the leaf filter's solid-liquid separation efficiency for crude liquid.

[0030] 3. The leaf filter can continuously produce semen, meeting the requirements of the new production process. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Attachment Figure 1 Shown is a flow chart of an existing solid-liquid separation process.

[0032] Attachment Figure 2 Shown is a timing diagram of the valves of the existing leaf filter.

[0033] Attachment Figure 3 Shown is a flow chart of the solid-liquid separation process.

[0034] Attachment Figure 4 What is shown is the structural schematic diagram of this leaf filter.

[0035] Attachment Figure 5 Shown is the timing diagram of each valve of this leaf filter.

[0036] In the attached figure: 1. Leaf filter; 11. Feed valve; 12. Overflow valve; 13. Pressure relief valve; 14. Mud discharge valve; 15. Filter cloth; 16. Pressure relief pipe; 17. Overflow pipe; 18. Water ring; 19. Flocculant addition valve; 2. High-level tank; 21. Return valve; 3. Three-way tank; 4. Flocculant storage tank. DETAILED DESCRIPTION

[0037] The preferred embodiments of the present invention are described below with reference to the accompanying drawings. It should be understood by those skilled in the art that these embodiments are only used to explain the technical principles of the present invention and are not intended to limit the scope of protection of the present invention. It should be noted that in the description of the present invention, the terms "front", "back", "up", "down", "left", "right", "vertical", "horizontal", "inside", "outside" and the like indicating directions or positional relationships are used for the directions or positional relationships shown in the accompanying drawings, which are merely for the convenience of description and do not indicate or imply that the device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0038] This solid-liquid separation process is a link in the improved alumina production process. The crude liquid (sodium aluminate solution) dissolved in the upstream process contains suspended matter and floating matter. This solid-liquid separation process is mainly used to separate the crude liquid. The separated fine liquid is used for aluminum refining, and the separated red mud is used for lithium refining.

[0039] Refer to the attached Figure 3 This solid-liquid separation process requires the use of a leaf filter 1, a mother liquor tank, a filter cake tank, a high-level tank 2 and a filtrate tank, wherein the mother liquor tank is the upstream equipment of the leaf filter 1, and the filter cake tank, the high-level tank 2 and the filtrate tank are the downstream equipment of the leaf filter 1.

[0040] Compare with Figure 1 and attached Figure 3 . Due to the need to take into account the extraction of lithium, compared with the existing alumina production process, the improved production process does not have a sedimentation separation process, and the crude liquid dissolved by the upstream process directly enters the mother liquor tank. In order to improve the filtration effect, filter aids such as lime milk can also be added to the mother liquor tank. Part of the semen flowing out of the filtrate tank is treated by the aluminum extraction process to obtain aluminum products, and the other part of the semen is returned to the upstream process to participate in the process cycle. In addition, the red mud in the filter cake tank is not piled up as waste, but is treated by the lithium extraction process to obtain lithium products.

[0041] There are two purposes for canceling the sedimentation separation process: first, sedimentation separation is a natural separation with low separation efficiency, and the red mud slurry separated by sedimentation contains a large amount of crude liquid, which needs to be filtered and dried to recover the crude liquid; second, it is to maintain the content of suspended matter and floating matter in the crude liquid, and prepare in advance for the feed filtration of the leaf filter.

[0042] Refer to the attached Figure 3 and attached Figure 4. The leaf filter 1 has a tank body, in which a filter cloth 15, a pressure relief pipe 16, and an overflow pipe 17 are arranged. The overflow pipe 17 is connected to the mother liquid tank through an overflow valve 12, and the pressure relief pipe 16 is connected to the three-way tank 3 through a pressure relief valve 13. The upper end of the three-way tank 3 is connected to the atmosphere, and the lower end is connected to the mother liquid tank. A water ring 18 is arranged outside the tank body, and the water ring 18 is connected to the liquid inlet end of the high-level tank 2, and the liquid outlet end of the high-level tank 2 is connected to the filtrate tank. A feed valve 11 and a mud discharge valve 14 are arranged at the lower part of the tank body. The feed valve 11 is connected to the mother liquid tank through a feeding pump, and is used to inject crude liquid into the tank body. The mud discharge valve 14 is connected to the filter cake tank, and is used to discharge red mud into the filter cake tank.

[0043] Different from the existing leaf filter 1, the high-level tank 2 is no longer equipped with a reflux valve and a reflux pipe connected to the mother liquid tank; a flocculant addition valve 19 is provided at the lower part of the tank body, and the flocculant addition valve 19 is connected to the flocculant storage tank 4 for injecting flocculant into the tank body.

[0044] Refer to the attached Figure 5 Unlike the existing leaf filter solid-liquid separation process, this solid-liquid separation process only has three stages: feed filtration, pressure relief backwashing, and mud discharge.

[0045] During the initial feeding, the feed valve 11 is opened to continuously inject the crude liquid into the tank of the leaf filter 1. At the same time, the flocculant addition valve 19 is opened to inject flocculant into the tank. When the liquid level is higher than the level of the overflow pipe 17, the pressure relief valve 13 and the overflow valve 12 are closed to bring the crude liquid level to the overflow level, and then the normal working cycle begins.

[0046] During the feed and filtration phase of the normal operating cycle, the feed valve 11 is opened, and the crude liquid is continuously injected into the tank via the feed pump. Simultaneously, the flocculant addition valve 19 is opened to inject flocculant into the tank. In this embodiment, the flocculants are sodium polyacrylate and polyacrylamide, which significantly increase the sedimentation rate, causing suspended matter and floating matter in the crude liquid to quickly settle. As the crude liquid is continuously injected, the air at the top of the tank is compressed, forming a high-pressure air cushion. Under the action of pressure, the crude liquid flows toward the filter cloth 15, where suspended matter, floating matter, and their sediment are trapped and quickly form sludge. After being filtered by the sludge filter cloth 15, the semen flows into the water ring 18 and then flows directly into the filtrate tank through the elbow and the high-level tank 2. Due to the rapid formation of sludge, the filtering effect of the filter cloth 15 is greatly enhanced, and the production of red mud and semen also begins to increase rapidly.

[0047] The present invention can achieve rapid mud attachment of the filter cloth during the process of injecting the crude liquid into the tank body. There are two main reasons for this: on the one hand, the sedimentation separation process is eliminated, and the crude liquid dissolved in the upstream process does not undergo sedimentation separation, resulting in a large amount of suspended matter and floating matter in the crude liquid; on the other hand, after adding the flocculant, the suspended matter and floating matter in the crude liquid are quickly precipitated.

[0048] During the feed filtration phase, the filtration effect of the semen needs to be tested. If the filtration effect of the semen meets the requirements, the flocculant addition valve 19 is closed. The end of the feed filtration phase is marked by the filtration efficiency of the leaf filter falling to 60% of the normal filtration efficiency. A filtration efficiency below 60% means a decrease in the amount of red mud and semen generated per unit time and an increase in energy consumption.

[0049] During the pressure relief and backwash phase, feed valve 11 is first closed, then pressure relief valve 13 is opened to relieve pressure. Once pressure relief valve 13 is opened, compressed air at the top of the tank is discharged through pressure relief pipe 16 and tee tank 3. Semen in header tank 2 enters the tank, creating a backflow. This backwash removes any sludge adhering to filter cloth 15, which then settles at the conical bottom of the tank, forming red mud. The pressure relief process is rapid, typically taking 1-3 seconds, and the end of the process is signaled by the tank pressure dropping to zero.

[0050] During the sludge discharge phase, open sludge discharge valve 14 while keeping pressure relief valve 13 open to allow air to enter the tank. The red mud at the conical bottom of the tank drains downward into the filter cake trough under the action of gravity and pressure, achieving force-free sludge discharge. Due to the pressure from above and the squeezing effect of the conical tank, the discharged red mud has a very low moisture content. The moisture content of the red mud needs to be monitored during the sludge discharge process, and sludge discharge valve 14 is closed when the moisture content increases.

[0051] After the sludge is discharged, the sludge discharge valve 14 is closed and the relief valve 12 is opened. During the pressure relief backwash phase, the tank is filled with liquid. Opening the relief valve 12 allows the liquid level to return to the overflow position, preparing for the next working cycle. After the liquid level returns to the overflow position, the relief valve 12 and the pressure relief valve 13 are closed.

[0052] Compare with Figure 2 and attached Figure 5 The existing solid-liquid separation process has a feed mud hanging stage, and the semen in the high-level tank 2 needs to be returned to the mother liquor tank, which not only takes time and consumes energy, but also has the effect of diluting the mother liquor in the mother liquor tank. This solid-liquid separation process eliminates the feed mud hanging stage. First, it can quickly achieve mud hanging on the filter cloth, and then immediately filter out the semen; second, the semen no longer returns to the mother liquor tank, but flows directly into the filtrate tank, greatly increasing the solid-liquid separation efficiency of the leaf filter for coarse liquid.

[0053] Compared to the existing process of 20-25 minutes for the feed-sludge stage and 60 minutes for the filtration stage, each cycle lasts approximately 80-85 minutes. This solid-liquid separation process only takes 65 minutes per cycle, shortening the leaf filter cycle and reducing energy consumption while significantly increasing the efficiency of red mud and semen production. Furthermore, by eliminating the feed-sludge stage, the leaf filter can continuously produce semen, meeting the requirements of the new production process.

[0054] Parts not described in detail are prior art. Although embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the present invention, and the scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A leaf filter solid-liquid separation process for recovering lithium from sodium aluminate solution, characterized by: The solid-liquid separation process requires the use of a leaf filter, which is equipped with a feed valve, an overflow valve, a pressure relief valve, a mud discharge valve, and a flocculant addition valve. The upstream equipment of the leaf filter is a mother liquor tank, and the downstream equipment is a high-level tank, a filtrate tank, and a filter cake tank. The crude liquid dissolved in the upstream process directly enters the mother liquor tank without going through a sedimentation separation process. Each working cycle of the solid-liquid separation process has three stages: feed filtration, pressure relief backwashing, and mud discharge. During the initial feeding, the feed valve is opened to continuously inject crude liquid into the leaf filter, and the flocculant addition valve is opened to inject flocculant into the leaf filter; when the liquid level is higher than the height of the overflow pipe, the pressure relief valve and the overflow valve are closed; in the feed filtration stage, the feed valve is opened to continuously inject crude liquid into the leaf filter, and the flocculant addition valve is opened to inject flocculant into the leaf filter, so that the crude liquid precipitates and quickly adheres to the filter cloth to form mud. The semen filtered by the mud-covered filter cloth directly flows into the filtrate tank through the high-level tank; the red mud generated in the mud discharge stage enters the filter cake tank, and then obtains lithium products through the lithium extraction process.

2. The leaf filter solid-liquid separation process for recovering lithium from sodium aluminate solution according to claim 1, wherein: During the feed filtration stage, the filtration effect of the semen is checked. If the semen meets the standards, the flocculant addition valve is closed.

3. The leaf filter solid-liquid separation process for recovering lithium from sodium aluminate solution according to claim 1, wherein: The sign of the end of the feed filtration stage is that the filtration efficiency of the leaf filter drops to 60% of the normal filtration efficiency.

4. A leaf filter solid-liquid separation process for recovering lithium from sodium aluminate solution as claimed in claim 1, characterized in that: During the pressure relief backwash stage, first close the feed valve, then open the pressure relief valve to relieve the pressure, and use the backflow semen to remove the mud on the filter cloth.

5. The leaf filter solid-liquid separation process for recovering lithium from sodium aluminate solution according to claim 1, characterized in that: During the mud discharge stage, open the mud discharge valve and keep the pressure relief valve open; after the mud discharge is completed, close the mud discharge valve and open the overflow valve until the liquid level in the leaf filter returns to the overflow position, and finally close the overflow valve and the pressure relief valve.

6. The leaf filter solid-liquid separation process for recovering lithium from sodium aluminate solution according to claim 1, wherein: After the semen flowing into the filtrate tank is processed by the downstream process, part of it is processed by the aluminum extraction process to obtain aluminum products, and the other part is returned to the upstream process to participate in the process cycle.

7. The leaf filter solid-liquid separation process for recovering lithium from sodium aluminate solution according to claim 1, characterized in that: The flocculants are sodium polyacrylate and polyacrylamide.

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