Leaf filter solid-liquid separation process for recovering lithium element in sodium aluminate solution

Abstract

The invention discloses a leaf filter solid-liquid separation process for recycling lithium in a sodium aluminate solution, and relates to the technical field of aluminum oxide production. In the solid-liquid separation process, each working cycle of a leaf filter has three stages of feeding filtration, pressure relief backflushing and sludge discharge, in the feeding filtration stage, a feeding valve is opened to continuously inject crude liquid into the leaf filter, and meanwhile, a flocculant adding valve is opened to inject a flocculant into the leaf filter, so that the crude liquid generates precipitates and is quickly attached to filter cloth to form hanging sludge, and the crude liquid is separated from the filter cloth. And the refined liquid filtered by the mud-hanging filter cloth directly flows into the filtrate tank through the head tank. According to the solid-liquid separation process, extraction of lithium and aluminum is taken into consideration, the stages of settling separation and feeding and sludge hanging of a leaf filter are omitted, sludge hanging of filter cloth can be rapidly achieved, then fine liquid is continuously filtered out, and the requirements of the production process are met; and 2, the refined liquid does not return to the mother liquid tank, but directly flows into the filtrate tank, so that the circulation period of the leaf filter is shortened, the energy consumption is reduced, and the solid-liquid separation efficiency of the crude liquid is greatly improved.

Description

Technical Field

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

[0002] The latest research shows that lithium resources are associated with bauxite in some regions of China. During the production of alumina, lithium is not extracted and mostly remains in the red mud, which was previously treated as waste. "Research and Progress on Lithium Extraction from the Bayer Process" (World Nonferrous Metals, March 2024, issue 3) records: "Lithium resources are associated with bauxite in some areas of Henan, Yunnan, Guizhou, and Shanxi in China. Among them, the lithium content in bauxite in Henan is generally high. Taking the Yushan mining area in Xin'an County, Henan Province as an example, the average Li2O content is about 0.085%. Lithium minerals are dispersed in bauxite, kaolinite, illite and other minerals. Li Chunchao et al. conducted a survey on Chalco Henan Branch and found that about 18% of the lithium enters the solution and more than 80% of the lithium is discharged with the red mud." China lacks lithium ore resources. With the development of new energy vehicles, the shortage of lithium is becoming increasingly serious. Therefore, it is necessary to extract lithium from red mud to improve the comprehensive benefits of mining enterprises.

[0003] If lithium is to be extracted, first, the thick liquor (sodium aluminate solution containing floating and suspended substances) needs to be subjected to solid-liquid separation to obtain red mud containing lithium. Refer to Figure 1 and Figure 2 , in the existing alumina production process, the solid-liquid separation of the thick liquor is carried out in two steps: first, the red mud slurry is separated by sedimentation separation. To accelerate sedimentation, a flocculant is usually added in the sedimentation tank; then, through the filtration of the leaf filter, clarified liquor and red mud are obtained (refer to Chinese Patent CN106315644A: A method and system for obtaining clarified liquor during alumina production). The existing leaf filter 1 has a feed valve 11, an overflow valve 12, a pressure relief valve 13 and a sludge discharge valve 14. The high-level tank 2 has a reflux valve 21. Each working cycle of the leaf filter has four stages: feed and mud hanging, filtration, pressure relief and backwashing, and sludge discharge.

[0004] During the feeding and mud coating stage, first open the feeding valve 11 and keep the pressure relief valve 13 and the overflow valve 12 open. The purpose is to allow the crude liquid in the mother liquor tank to enter the tank body of the leaf filter 1 and reach the overflow height of the overflow pipe. Then close the pressure relief valve 13 and the overflow valve 12, and at the same time open the reflux valve 21 to return the refined liquid in the high-level tank 2 to the mother liquor tank. There are two purposes: one is to coat the filter cloth with mud through the circulation of the crude liquid. The filter cloth can only conduct preliminary filtration on the crude liquid, and only when the mud layer on the filter cloth reaches a certain thickness can it achieve the effect of fine filtration on the crude liquid; the other is to force the air at the top of the tank body to be compressed through the incoming liquid and form a high-pressure air cushion. The end mark of the mud coating stage is that the filtered liquid flowing out from the reflux valve 21 meets the index requirements of the refined liquid. The time taken for the mud coating process is relatively long, generally 20 - 25 minutes.

[0005] During the filtration stage, close the reflux valve 21 and only open the feeding valve 11. The purpose is to filter the crude liquid so that the filtered refined liquid enters the filtrate tank through the high-level tank. The filtration stage takes the longest time, generally 60 minutes.

[0006] During the pressure relief and backwashing stage, close the feeding valve 11, and successively open the pressure relief valve 13 and the overflow valve 12. The purpose is to release the high pressure in the tank body, allow the refined liquid in the high-level tank 2 to enter the tank body of the leaf filter 1, backwash and remove the mud on the filter cloth. The removed mud deposit forms red mud (filter cake) at the conical bottom of the tank body, and the crude liquid with a liquid level higher than the overflow pipe enters the mother liquor tank through the overflow valve 12. The pressure relief and backwashing process is relatively fast, generally 5 seconds.

[0007] During the mud discharging stage, open the mud discharging valve 14 to discharge the red mud deposited at the conical bottom of the tank body downward. The mud discharging process is very fast, generally 10 seconds, and then close the mud discharging valve 14.

[0008] In order to take into account the extraction of both aluminum and lithium, the existing alumina production process needs to be improved. In the new production process, the following problems exist in the existing solid-liquid separation process: 1. The red mud slurry contains lithium. However, since the red mud slurry adopts a sedimentation separation process and contains a large amount of crude liquid, it is necessary to filter the red mud slurry dry to recover the crude liquid.

[0009] 2. The time taken for the feeding and mud coating stage of the leaf filter is relatively long. Compared with the other stages, the feeding and mud coating stage is a preparation stage before filtration. No refined liquid or red mud (filter cake) is produced during this stage, which greatly reduces the efficiency of solid-liquid separation.

[0010] 3. The existing leaf filter can only produce refined liquid intermittently. In the new production process, since some of the refined liquid also needs to return to the upstream equipment to participate in the process cycle, it is required that the leaf filter can preferably produce refined liquid continuously. Summary of the Invention

[0011] In order to overcome the deficiencies in the background art, the present invention discloses a solid-liquid separation process for a leaf filter to recover lithium elements from sodium aluminate solution, and its purpose is as follows: 1. Cancel the sedimentation separation process; 2. Shorten the cycle period of the leaf filter and improve the efficiency of solid-liquid separation; 3. Enable the leaf filter to continuously produce refined liquid.

[0012] To achieve the above invention purposes, the present invention adopts the following technical solutions: A solid-liquid separation process for a leaf filter to recover lithium elements from sodium aluminate solution. The solid-liquid separation process requires the use of a leaf filter, which has a feed valve, an overflow valve, a pressure relief valve, a sludge 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; Each working cycle of the solid-liquid separation process has three stages: feed filtration, pressure relief backwashing, and sludge 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 generates precipitation and quickly adheres to the filter cloth to form mud hanging. The refined liquid filtered by the mud-hanging filter cloth directly flows into the filtrate tank through the high-level tank.

[0013] Further improving the technical solution, when feeding for the first time, 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; when the liquid level is higher than the height of the overflow pipe, the pressure relief valve and the overflow valve are closed.

[0014] Further improving the technical solution, in the feed filtration stage, the filtration effect of the refined liquid is inspected. If the refined liquid meets the standard, the flocculant addition valve is closed.

[0015] Further improving the technical solution, the end mark of the feed filtration stage is that the filtration efficiency of the leaf filter is reduced to 60% of the normal filtration efficiency.

[0016] Further improving the technical solution, in the pressure relief backwashing stage, first close the feed valve, then open the pressure relief valve to relieve pressure, and use the reflux refined liquid to remove the mud hanging on the filter cloth.

[0017] Further improving the technical solution, in the sludge discharge stage, open the sludge discharge valve and keep the pressure relief valve open at the same time; after the sludge discharge is completed, close the sludge discharge valve, and at the same time open the overflow valve until the liquid level in the leaf filter returns to the overflow level, and finally close the overflow valve and the pressure relief valve.

[0018] Further improving the technical solution, after the refined liquid flowing into the filtrate tank is processed by the downstream process, a part of it obtains aluminum products through the aluminum extraction process, and the other part returns to the upstream process to participate in the process cycle.

[0019] Further improve the technical solution. The red mud generated in the sludge discharge stage enters the filter cake tank and then obtains lithium products through the lithium extraction process.

[0020] Further improve the technical solution. The flocculants are sodium polyacrylate and polyacrylamide.

[0021] After implementing the above technical solution, the beneficial effects of the present invention are as follows: 1. In the new production process, sedimentation separation is cancelled, and a leaf filter is relied on to achieve solid-liquid separation of the thick liquid. First, because the efficiency of sedimentation separation is low, and the red mud slurry separated by sedimentation contains a large amount of thick liquid; second, to maintain the content of suspended solids and floating solids in the thick liquid, which is convenient for quickly forming mud on the filter cloth; third, the leaf filter belongs to power separation, with good solid-liquid separation effect, high efficiency, and low water content of the red mud (filter cake); fourth, it is beneficial to achieve the extraction of lithium.

[0022] 2. In this solid-liquid separation process, the feeding and mud-forming stage is cancelled. First, it can quickly form mud on the filter cloth and then immediately filter out the refined liquid; second, the refined liquid no longer returns to the mother liquid tank but directly flows into the filtrate tank. Compared with the existing solid-liquid separation process, this solid-liquid separation process not only shortens the circulation cycle of the leaf filter and reduces energy consumption, but also greatly improves the solid-liquid separation efficiency of the leaf filter for the thick liquid.

[0023] 3. The leaf filter can continuously produce refined liquid, meeting the requirements of the new production process. Description of the Drawings

[0024] Appendix Figure 1 Shows the flow chart of the existing solid-liquid separation process.

[0025] Appendix Figure 2 Shows the timing diagram of each valve of the existing leaf filter.

[0026] Appendix Figure 3 Shows the flow chart of this solid-liquid separation process.

[0027] Appendix Figure 4 Shows the structural schematic diagram of this leaf filter.

[0028] Appendix Figure 5 Shows the timing diagram of each valve of this leaf filter.

[0029] In the drawings: 1. Leaf filter; 11. Feed valve; 12. Overflow valve; 13. Pressure relief valve; 14. Sludge 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 Embodiments

[0030] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are only used to explain the technical principles of the present invention and are not intended to limit the protection scope of the present invention. It should be noted that in the description of the present invention, the terms indicating directions or positional relationships such as "front", "rear", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. are the directions or positional relationships shown in the drawings. This is only for convenience of description and does 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 construed as a limitation of the present invention.

[0031] This solid-liquid separation process is a link in the improved alumina production process. The crude liquid (sodium aluminate solution) discharged from the upstream process contains suspended solids and floating substances. This solid-liquid separation process is mainly used to separate the crude liquid. The separated refined liquid is used for aluminum extraction, and the separated red mud is used for lithium extraction.

[0032] Refer to the attached Figure 3 . This solid-liquid separation process requires a leaf filter 1, a mother liquor tank, a filter cake tank, a high-level tank 2, and a filtrate tank. Among them, 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.

[0033] Compare the attached Figure 1 and the attached Figure 3 . Since the extraction of lithium needs to be taken into account, compared with the existing alumina production process, there is no sedimentation separation process in the improved production process, and the crude liquid discharged from 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. A part of the refined liquid flowing out of the filtrate tank is processed by the aluminum extraction process to obtain aluminum products, and another part of the refined liquid returns 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 processed by the lithium extraction process to obtain lithium products.

[0034] There are two purposes for canceling the sedimentation separation process: one is that sedimentation separation belongs to natural separation, with low separation efficiency, and the red mud slurry separated by sedimentation contains a large amount of crude liquid, and the red mud slurry also needs to be filtered dry to recover the crude liquid; the other is to maintain the content of suspended solids and floating substances in the crude liquid and make preparations in advance for the feeding filtration of the leaf filter.

[0035] Refer to the attached Figure 3 and the 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 liquor 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 communicates with the atmosphere, and the lower end is connected to the mother liquor 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. The liquid outlet end of the high-level tank 2 is connected to the filtrate tank. A feed valve 11 and a sludge discharge valve 14 are arranged at the lower part of the tank body. The feed valve 11 is connected to the mother liquor tank through a feeding pump and is used to inject the crude liquid into the tank body. The sludge discharge valve 14 is connected to the filter cake tank and is used to discharge the red mud into the filter cake tank.

[0036] Different from the existing leaf filter 1, the high-level tank 2 no longer has a reflux valve and a reflux pipeline connected to the mother liquor tank; a flocculant addition valve 19 is arranged at the lower part of the tank body, and the flocculant addition valve 19 is connected to the flocculant storage tank 4 and is used to inject the flocculant into the tank body.

[0037] Refer to the appendix Figure 5 。Different from the existing solid-liquid separation process of the leaf filter, this solid-liquid separation process only has three stages: feeding and filtering, pressure relief and backwashing, and sludge discharge.

[0038] When feeding for the first time, open the feed valve 11 to continuously inject the crude liquid into the tank body of the leaf filter 1, and at the same time open the flocculant addition valve 19 to inject the flocculant into the tank body. When the liquid level height is higher than the height of the overflow pipe 17, close the pressure relief valve 13 and the overflow valve 12 to make the liquid level of the crude liquid at the overflow water level, and then enter the normal working cycle.

[0039] In the feeding and filtering stage of the normal working cycle, open the feed valve 11 and continuously inject the crude liquid into the tank body through the feeding pump, and at the same time open the flocculant addition valve 19 to inject the flocculant into the tank body. In this embodiment, the flocculant is sodium polyacrylate and polyacrylamide, and sodium polyacrylate and polyacrylamide can significantly improve the sedimentation speed, so that the suspended solids and floating substances in the crude liquid quickly generate precipitation. With the continuous injection of the crude liquid, the air at the top of the tank body is compressed and forms a high-pressure air cushion. Under the action of the pressure, the crude liquid flows to the filter cloth 15, and the suspended solids, floating substances and their precipitates are intercepted on the filter cloth 15 to quickly form mud hanging. The refined liquid filtered by the mud-hanging filter cloth 15 flows into the water ring 18, and then directly flows into the filtrate tank through the elbow pipe and the high-level tank 2. Due to the rapid formation of mud hanging, the filtering effect of the filter cloth 15 is greatly enhanced, and the production amounts of red mud and refined liquid also begin to increase rapidly.

[0040] The present invention can realize the rapid mud hanging of the filter cloth during the process of injecting the crude liquid into the tank body. The main reasons are as follows: on the one hand, the sedimentation separation process is cancelled, and the crude liquid dissolved in the upstream process does not undergo sedimentation separation, resulting in a large amount of suspended solids and floating substances in the crude liquid; on the other hand, after adding the flocculant, the suspended solids and floating substances in the crude liquid quickly generate precipitation.

[0041] During the feed filtration stage, the filtration effect of the semen needs to be inspected. If the filtration effect of the semen meets the standard, the flocculant addition valve 19 is closed. The end of the feed filtration stage is marked by the filtration efficiency of the leaf filter dropping to 60% of the normal filtration efficiency. A filtration efficiency lower than 60% means a decrease in the production of red mud and semen per unit time and an increase in energy consumption.

[0042] In the pressure relief and backwashing stage, the feed valve 11 is first closed, and then the pressure relief valve 13 is opened for pressure relief. After the pressure relief valve 13 is opened, the compressed air at the top of the tank is discharged outward through the pressure relief pipe 16 and the three-way tank 3. The semen in the high-level tank 2 enters the tank to form a reverse flow, and the mud attached to the filter cloth 15 is removed by backwashing. The mud deposits at the conical bottom of the tank to form red mud. The pressure relief process is very fast, generally 1 - 3 seconds. The end of the pressure relief process is marked by the pressure in the tank dropping to zero.

[0043] In the mud discharging stage, the mud discharging valve 14 is opened, and at the same time, the pressure relief valve 13 is kept open so that the outside air can enter the tank. The red mud at the conical bottom of the tank is discharged downward into the filter cake tank under the action of gravity and pressure, realizing mud discharging without external force. Due to the extrusion of the upper pressure and the conical tank body, the discharged red mud has a very low water content. During the mud discharging process, the water content of the red mud needs to be detected, and the mud discharging valve 14 is closed when the water content increases.

[0044] After the mud discharging is completed, the mud discharging valve 14 is closed, and at the same time, the overflow valve 12 is opened. The tank is filled with liquid during the pressure relief and backwashing stage. Opening the overflow valve 12 can restore the liquid level to the overflow position, preparing for the next working cycle. After the liquid level is restored to the overflow position, the overflow valve 12 and the pressure relief valve 13 are closed.

[0045] Comparison appendix Figure 2 And appendix Figure 5 . The existing solid-liquid separation process has a feed mud hanging stage. The semen in the high-level tank 2 has to return to the mother liquor tank, which not only takes time and consumes energy, but also dilutes the mother liquor in the mother liquor tank. This solid-liquid separation process cancels the feed mud hanging stage. Firstly, it can quickly realize mud hanging on the filter cloth and then immediately filter out the semen. Secondly, the semen no longer returns to the mother liquor tank but directly flows into the filtrate tank, greatly increasing the solid-liquid separation efficiency of the leaf filter for the thick liquid.

[0046] Compared with the existing feed mud hanging stage, which takes 20 - 25 minutes, and the filtration stage takes 60 minutes, each working cycle takes about 80 - 85 minutes. However, this solid-liquid separation process only takes 65 minutes for each working cycle. It not only shortens the cycle period of the leaf filter and reduces energy consumption, but also greatly improves the output efficiency of red mud and semen. In addition, due to the cancellation of the feed mud hanging stage, the leaf filter can continuously produce semen, meeting the requirements of the new production process.

[0047] The parts not described in detail are prior arts. Although embodiments of the present invention have been shown and described, those of ordinary skill in the art can understand that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The protection scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A solid-liquid separation process for a leaf filter used to recover lithium elements in sodium aluminate solution, characterized in that: The solid-liquid separation process requires the use of a leaf filter. The leaf filter is equipped with a feed valve, an overflow valve, a pressure relief valve, a sludge 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; Each working cycle of the solid-liquid separation process has three stages: feed filtration, pressure relief backwashing, and sludge discharge. In the feed filtration stage, 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, causing the crude liquid to precipitate and quickly adhere to the filter cloth to form sludge hanging. The refined liquid filtered by the sludge-hanging filter cloth directly flows into the filtrate tank through the high-level tank.

2. The solid-liquid separation process of a leaf filter for recovering lithium elements in sodium aluminate solution according to claim 1, characterized in that: initially During 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.

3. A solid-liquid separation process for a leaf filter used to recover lithium elements from sodium aluminate solution, characterized in that: In the feed filtration stage, the filtration effect of the refined liquid is inspected. If the refined liquid meets the standard, the flocculant addition valve is closed.

4. The solid-liquid separation process of a leaf filter for recovering lithium elements in sodium aluminate solution according to claim 1, characterized in that: The end of the feed filtration stage is marked by the filtration efficiency of the leaf filter dropping to 60% of the normal filtration efficiency.

5. The solid-liquid separation process of a leaf filter for recovering lithium elements in sodium aluminate solution as claimed in claim 1, characterized in that: at In the pressure relief backwashing stage, first close the feed valve, then open the pressure relief valve to relieve pressure, and use the reflux refined liquid to remove the sludge hanging on the filter cloth.

6. The solid-liquid separation process of a leaf filter for recovering lithium elements in sodium aluminate solution according to claim 1, characterized in that: In the sludge discharge stage, open the sludge discharge valve and keep the pressure relief valve open at the same time; after the sludge discharge is completed, close the sludge discharge valve, and at the same time open the overflow valve until the liquid level in the leaf filter returns to the overflow level, and finally close the overflow valve and the pressure relief valve.

7. A solid-liquid separation process for a leaf filter used to recover lithium elements from sodium aluminate solution, characterized in that: The refined liquid flowing into the filtrate tank is processed by the downstream process. Part of it obtains aluminum products through the aluminum extraction process, and the other part returns to the upstream process to participate in the process cycle.

8. The solid-liquid separation process of a leaf filter for recovering lithium elements in sodium aluminate solution according to claim 1, characterized in that: The red mud generated in the sludge discharge stage enters the filter cake tank and then obtains lithium products through the lithium extraction process.

9. The solid-liquid separation process of a leaf filter for recovering lithium elements in sodium aluminate solution as described in claim 1, characterized in that: The flocculant is sodium polyacrylate and polyacrylamide.

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