Recycling system and method for flat-bottom settling tank scabs in aluminum oxide production

Abstract

The invention provides a system and a method for recovering scabs in a flat-bottom settling tank in aluminum oxide production. The system is formed by sequentially connecting a blanking funnel (4), a spiral mixer (5) with a washing water injection port (6) at a feeding end, a mill (3), a sewage tank (1) with a stirrer, a vertical pipeline pump (2), a last washing tank (8) and an underflow pump (9). The recovery method comprises the following steps: feeding blocky scabs into a spiral mixer through a blanking funnel, mixing the blocky scabs with washing water, and crushing until the particle size of 80% of particles is below 400 meshes to form slurry; after the slurry flows into a sewage tank and is stirred, the slurry is conveyed to a feed port of a last washing tank by a vertical pipeline pump; settling and separating in the last washing tank, returning overflow to a production system to recover Al2O3 and Na2O, and outputting and stacking concentrated red mud through an underflow pump. Through physical crushing and directional injection of the last washing tank, the recovery rate of Al2O3 and Na2O in scabs exceeds 90%, ineffective circulation and transportation pollution are eliminated, the content of alkali in a red mud attached liquid is reduced, and therefore the service life of a storage yard is prolonged, and the production cost is reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of alumina production, and in particular relates to a system and method for recovering scabs in a flat-bottomed sedimentation tank, which are used for efficiently recovering Al2O3 and Na2O in the sedimentation scabs. Background Art

[0002] In the Bayer process for alumina production, the separation and washing of red mud are crucial process steps, with the core equipment being the separation and washing settling tanks. To address the challenges of transporting high-solids, high-viscosity red mud slurries, flat-bottom settling tanks are typically used, combined with a powerful pumping system to achieve efficient, stable, and high-concentration underflow discharge. Currently, during the operation of flat-bottom settling tanks, a dense scab layer inevitably forms and hardens on the tank walls, bottom, and agitator. This scab is primarily composed of alkaline alumina hydrates (such as gibbsite and boehmite), silicon-containing minerals, and small amounts of iron, titanium, and calcium compounds. It is characterized by high hardness, strong adhesion, and low solubility. Over time, the scab layer thickens, significantly reducing the effective settling volume, increasing stirring resistance, and increasing energy consumption. In severe cases, the settling tank may even be shut down for manual cleaning.

[0003] The industry's conventional approach to treating sedimentation tank scab is to crush and excavate it during downtime and maintenance using mechanical equipment such as forklifts and jackhammers. The resulting large amounts of massive or plate-like sedimentation scab are typically directly stored as solid waste in red mud dumps or dams. This approach has significant drawbacks: First, the scab still contains a considerable amount of recyclable Al2O3 and Na2O. Direct storage means these valuable resources are permanently wasted, increasing production costs and resource consumption. Second, if the scab is not thoroughly cleaned or improperly disposed of, some of the scab fragments may re-enter the raw ore slurry or return to the sedimentation system, causing an ineffective cycle of Al2O3 and Na2O in the production process. This not only prevents effective recovery but also interferes with the sedimentation process, reducing washing efficiency. If the separated Al2O3 and Na2O are transported by truck to the raw material mining area and re-entered the production process along with the raw ore, leakage during transportation is likely to occur, causing environmental pollution.

[0004] To address the scarring problem, existing technologies, such as patent CN101574700B, propose installing a slurry and rotary screen near the sedimentation tank. This method uses a wash solution to flush the accumulated mud at the bottom of the sedimentation tank, separating the red mud slurry from the scarring. However, the scarring still requires manual removal, and direct and effective recovery of Al2O3 and Na2O from the scarring is not achieved. Patent CN115591298A discloses separating the red mud slurry from the scarring layer by injecting water and stirring, with the scarring discharged from a specific outlet. However, this method also lacks a means of subsequent resource utilization for the discharged scarring. Patent CN108672446B proposes a chemical cleaning technology that incorporates a scarring cleaner within the sedimentation tank. This technology dissolves some of the scarring components and returns them to the process, but it primarily targets emerging scarring and has limited effectiveness against accumulated, thick, hard, historical scarring layers. Furthermore, this solution requires additional alkali solution preparation and a heater, resulting in high operating costs.

[0005] In summary, there is an urgent need to specifically treat the large amount of accumulated solid hard sedimentation scars that have formed in the flat-bottom sedimentation tank, economically and efficiently recover the Al2O3 and Na2O contained therein, and reintegrate them into the production process to realize resource utilization recycling technology and systems. Summary of the Invention

[0006] In view of the above-mentioned problems existing in the prior art, the present invention provides a recovery system for scabs in a flat-bottomed sedimentation tank for alumina production, comprising: a feed hopper (4) located near the bottom of the flat-bottomed sedimentation tank; a spiral mixer (5), a feed port of which is arranged below the feed hopper (4); a wash water injection port (6), arranged in the feed hopper (4) area or the feed end of the spiral mixer (5); a mill (3), a feed port of which is connected to the discharge port of the spiral mixer (5), and the discharge port is used to discharge slurry; a sewage tank (1) containing stirring, a feed port of which is located below the discharge port of the mill (3); a vertical pipeline pump (2), an inlet of which is connected to the bottom outlet of the sewage tank (1) containing stirring through a pipeline; a final washing tank (8), a feed port of which is connected to the vertical pipeline pump outlet pipe (10); and an underflow pump (9), an inlet of which is connected to the bottom outlet of the final washing tank (8) through a pipeline.

[0007] Furthermore, the washing water in the washing water injection port (6) comes from the dilute alkali solution in the washing sedimentation tank in the alumina production process, with a concentration of 4 to 8 g / L and a temperature of 80 to 85°C.

[0008] Furthermore, the mill (3) is a ball mill or a rod mill, and the sewage tank (1) containing stirring is a pit-type tank.

[0009] The present invention also provides a method for recovering scars from a flat-bottomed sedimentation tank in an alumina production process, comprising the following steps:

[0010] Step 1, scab crushing and slurrying: the blocky or compacted sedimentation scab (7) is fed into the spiral mixer (5) through the feeding funnel (4), and washing water is added through the washing water injection port (6). After mixing in the spiral mixer (5), it is fed to the mill (3) and pulverized in the mill (3) to form a slurry;

[0011] Step 2: Temporary storage and transportation of slurry: The slurry obtained in step 1 is introduced into a sewage tank (1) containing stirring, and after stirring, it is pressurized and transported by a vertical pipeline pump (2);

[0012] Step 3: Directional recovery and separation: The slurry transported in step 2 is injected into the final washing tank (8) through the vertical pipeline pump outlet pipe (10) for sedimentation separation, and the red mud is discharged from the system through the underflow pump (9). The dissolved Al2O3 and Na2O are returned to the alumina production process through the overflow port of the final washing tank (8) for recycling.

[0013] Furthermore, in the slurry after being crushed by the mill (3) in step 1, more than 80% of the particles have a particle size of less than 400 mesh.

[0014] The method of the present invention has the following advantages:

[0015] 1) Efficient recovery of valuable components: Through the initial slurrying process in a spiral mixer combined with forced grinding in a mill, the massive and compacted red mud scabs are effectively broken down to an appropriate fineness, fully exposing and dissolving the Al2O3 and Na2O contained within them. This allows for efficient recovery in the final washing tank, improving the recovery rates of alumina and alkali.

[0016] 2) Completely avoid ineffective circulation: The treated red mud scab slurry is directly and completely sent to the end of the red mud washing process (the final washing tank). After the valuable components are recovered, the inert red mud solids are then pumped to the red mud dam for storage through the underflow pump. This completely blocks the possibility of red mud scab returning to the original ore pulp preparation or front-end separation and sedimentation process, eliminating the resulting ineffective circulation, additional equipment load and production efficiency loss;

[0017] 3) Reduce labor and secondary pollution: The entire processing process is mechanized and continuous, requiring only forklift loading, avoiding the heavy labor of manual cleaning and external disposal of scab blocks on the screen and potential secondary pollution problems in the existing technology;

[0018] 4) Improve the on-site environment: timely cleaning and treatment of sedimentation tank scarring will help maintain the normal operation and cleaning cycle of the sedimentation tank, reduce on-site mud accumulation, and improve the production environment;

[0019] 5) Effective recycling of resources: All red mud scab materials are processed within the system, the valuable components are recovered and the inert components are discharged, realizing the full quantification and rational utilization of resources and reducing production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a schematic structural diagram of a system for recovering scars from a flat-bottomed sedimentation tank in the production of aluminum oxide according to the present invention;

[0021] Explanation of the accompanying symbols: 1. Sewage tank with stirring; 2. Vertical pipeline pump; 3. Grinding mill; 4. Feeding funnel; 5. Spiral mixer; 6. Washing water inlet; 7. Sedimentation scar; 8. Last washing tank; 9. Underflow pump; 10. Vertical pipeline pump. DETAILED DESCRIPTION

[0022] like Figure 1 As shown, the scar recovery system of the present invention is arranged near the flat bottom settling tank of alumina production, and comprises:

[0023] The discharge funnel 4 is arranged below the flat bottom sedimentation tank and is used to receive the sedimentation scars 7 to be processed which are transported by equipment such as forklifts;

[0024] The wash water inlet 6 is used to inject wash water into the lower feeding funnel 4. The wash water comes from the dilute alkali solution in the washing sedimentation tank in the alumina production process, with a concentration of 4-8 g / L and a temperature of 80-85°C. The wash water is used to moisten and dilute the sedimentation scars, reduce their viscosity, assist in crushing and slurrying, and dissolve some soluble substances such as Na2O;

[0025] The spiral mixer 5 is connected to the outlet end of the discharge funnel 4, and forcibly mixes, preliminarily moistens, and breaks up the massive sedimentation scab 7 falling from the discharge funnel 4 with the added wash water 6. The spiral mixer 5 transports the material through the rotation of the spiral blades and realizes the preliminarily slurrying of the scab and the wash water, forming a slurry mixture suitable for processing by the mill 3, thereby improving the mill efficiency and reducing the risk of clogging;

[0026] Mill 3, using a ball mill or rod mill and other crushing equipment, is used to grind the massive or hardened sedimentation scabs into a suitable particle size, ensuring that the Al2O3 and Na2O contained in the scabs can be fully dissolved or released, and effectively separated in the subsequent sedimentation washing;

[0027] The sewage tank 1 with stirring is used to receive and temporarily store the sedimentation and scabbing slurry that has undergone preliminary treatment. The agitator provided in the tank is in continuous operation to prevent the solid particles in the slurry from settling and agglomerating, thereby maintaining a uniform suspension state of the material and creating conditions for subsequent pumping;

[0028] The vertical pipeline pump 2 is installed at the bottom outlet of the sewage tank 1, and its inlet is connected to the outlet of the sewage tank 1. It is used to pressurize the evenly stirred sedimentation slurry in the sewage tank 1 and stably transport it to the last washing tank 8 through its outlet pipe 10;

[0029] The final washing tank 8 is located at the end of the red mud washing process and is the last washing and settling tank before the red mud is discharged. Its function is to receive the sedimentation slurry delivered by the vertical pipeline pump 2 through the vertical pipeline pump outlet pipe 10, so that the red mud particles in the slurry can be settled here. The washed red mud is sent to the red mud dam for storage through the underflow pump 9, and the dissolved Al2O3 and Na2O are returned to the production system through overflow for utilization.

[0030] The system achieves physical crushing of sedimentation scabs, slurry transportation and directional recovery of effective components through the coordinated work of the above equipment. The specific steps of the sedimentation scab recovery process include:

[0031] Step 1. System startup preparation: Start the agitator in the sewage tank (1) to ensure that the slurry received later in the tank remains in a suspended state. Open the valve of the wash water inlet (6) to allow the wash water to enter the discharge funnel (4) area or the spiral mixer (5) at the set flow rate. Start the drive device of the spiral mixer (5) to start the rotation of its spiral blades. Start the drive device of the mill (3) to put the mill into operation. Start the vertical pipeline pump (2), establish the delivery pressure, and deliver the material (initially water or low-concentration slurry) to the last washing tank (8) through the vertical pipeline pump outlet pipe (10). This step ensures that all equipment is in normal operation before feeding.

[0032] Step 2, scab treatment and recovery: The operator uses a forklift or other tools to dig out the block or compacted sedimentation scab (7) to be cleaned and recovered from the flat bottom sedimentation tank and load it into the discharge funnel (4). The sedimentation scab (7) meets the continuously added wash water in the spiral mixer (5). The spiral blades forcibly break up and shear the scab blocks, and fully mix and wet them with the wash water to form a preliminary slurry mixture, which is then continuously fed into the feed port of the mill (3). In the mill (3), the mixture is impacted and ground by the grinding media, and the sedimentation scab is crushed to the target particle size. The grinding process fully exposes the Al2O3 (in the form of sodium aluminosilicate, etc.) and Na2O (in the form of alkali, etc.) wrapped inside the scab, and dissolves into the liquid phase under the action of the wash water. The qualified slurry after grinding flows into the pre-started sewage tank (1) by gravity. The agitator in the sewage tank (1) continuously stirs to maintain a uniform suspension state of the slurry. The activated vertical pipeline pump (2) continuously extracts the sedimentation scar slurry in the sewage tank (1), and after pressurization, stably pumps it to the feed port of the last washing tank (8) through the vertical pipeline pump outlet pipe (10).

[0033] Step 3, final washing and component separation: The sedimentation slurry entering the final washing tank (8) is subjected to sedimentation separation in the tank. Al2O3 and Na2O dissolved in the liquid phase are returned to the alumina production process (such as the previous stage washing or decomposition process) with the washing overflow and are effectively recovered. The solid red mud particles are concentrated at the bottom of the tank to form an underflow. The concentrated red mud underflow is transported to the red mud dam for storage by the underflow pump (9) according to the normal production process. At this point, the valuable components Al2O3 and Na2O in the sedimentation slurry are effectively recovered, and the inert red mud solids are discharged from the system, avoiding the ineffective circulation, equipment wear and waste of resources caused by the sedimentation slurry directly or indirectly re-entering the raw ore production process without treatment.

[0034] Example 1

[0035] Settling scars: The existing flat bottom settling tank has a diameter of 42 meters and an operating cycle of 70-80 days. There are eight separation tanks in total. Each time the settling tank is cleaned and parked, the height of the settled red mud is about 0.8 to 1 meter. One flat bottom settling tank can settle about 1000m of red mud. 3 about.

[0036] Process parameters:

[0037] The target particle size of the mill is more than 80% of the particles are less than 400 mesh; the washing water (6) is a 80℃ dilute alkali solution (concentration 4-8g / L) from the washing sedimentation tank in the alumina production process, with a flow rate of 80m 3 / h; the speed of the spiral mixer (5) is 60 rpm; the stirring speed of the sewage tank (1) is 100 rpm; the flow rate of the vertical pipeline pump (2) is 110 m 3 / h.

[0038] The system was started according to the process steps of the present invention, with continuous loading by forklift, and the scab treatment capacity was approximately 25 tons / hour (dry basis). The slurry was transported to the final washing tank (8) for sedimentation separation. The overflow Na2O concentration was stable, indicating that Na2O was effectively dissolved and recovered; the underflow solids content was normal and was discharged to the red mud dam by the underflow pump (9). The system operated stably and without blockage.

[0039] Example 2

[0040] The sedimentation scar to be treated comes from the same source as in Example 1, but the scar hardness is higher.

[0041] The target particle size of the mill is more than 80% of the particle size is less than 200 mesh, and the finer particle size ensures the release of components in the hard scar; the flow rate of the washing water (6) is 85℃ dilute alkali solution, and the flow rate is 70m 3 / h, reduce the amount of water to maintain the appropriate concentration of the slurry; the speed of the spiral mixer (5) is 65rpm to enhance the mixing and breaking effect; the flow rate of the vertical pipeline pump (2) is 100m 3 / h.

[0042] The remaining process parameters are the same as in Example 1.

[0043] The system was started according to the process steps of the present invention, and the forklift was continuously loaded. The scab treatment capacity dropped slightly to 25 tons / hour (dry basis). The Na2O concentration in the overflow of the final wash tank 8 was comparable to that of Example 1. This shows that even when treating harder scab, Na2O can still be effectively recovered by adjusting the abrasive fineness and the wash water volume, and the underflow discharge is normal.

[0044] Example 3

[0045] The sedimentation scab to be treated is of the same origin as that in Example 1, and mainly comprises scabs formed by the bonding of fine particles.

[0046] Wash water (6) is a dilute alkali solution at 83°C with a flow rate of 85m 3 / h, increasing the water volume to assist in crushing and dissolving; the flow rate of the vertical pipeline pump (2) is 120m 3 The target particle size of the mill, the rotation speed of the spiral mixer (5), and the stirring speed of the agitated sewage tank (1) are the same as those in Example 1.

[0047] The system was started according to the process steps of the present invention, and the forklift was continuously loaded. The scab treatment capacity was increased to 30 tons / hour (dry basis). The overflow of the final washing tank (8) was clear, Na2O was recovered well, and the underflow pump (9) operated smoothly. This shows that for fragile scab, the treatment capacity can be increased by optimizing the washing water volume and the flow parameters of the vertical pipeline pump.

[0048] Table 1 is the flat bottom sedimentation tank scar recovery data table of Examples 1 to 3

[0049]

[0050] The above are preferred embodiments of the present invention. Any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A system for recovering scars from a flat bottom sedimentation tank in an alumina production plant, characterized in that: include: A discharge funnel (4) is located near the bottom of the flat-bottomed sedimentation tank; A spiral mixer (5), the feed port of which is arranged below the discharge funnel (4); A wash water inlet (6) is provided in the region of the discharge hopper (4) or at the feed end of the spiral mixer (5); A mill (3), the feed port of which is connected to the discharge port of the spiral mixer (5), and the discharge port is used to discharge the slurry; A sewage tank (1) containing stirring, the feed port of which is located below the discharge port of the grinding mill (3); a vertical pipeline pump (2), the inlet of which is connected to the bottom outlet of the agitated sewage tank (1) via a pipeline; The final washing tank (8) has a feed port connected to the vertical pipeline pump outlet pipe (10); An underflow pump (9) has an inlet connected to the bottom outlet of the final washing tank (8) via a pipeline.

2. The recovery system according to claim 1, wherein the wash water in the wash water injection port (6) comes from the dilute alkali solution in the washing sedimentation tank in the alumina production process, with a concentration of 4 to 8 g / L and a temperature of 80 to 85°C.

3. The recycling system according to claim 1, characterized in that The mill (3) is a ball mill or a rod mill, and the sewage tank (1) containing stirring is a pit-type tank.

4. A method for recovering scars from a flat-bottomed sedimentation tank for alumina production using the method according to any one of claims 1 to 3, characterized in that: The following steps are involved: Step 1, scab crushing and slurrying: the blocky or compacted sedimentation scab (7) is fed into the spiral mixer (5) through the feeding funnel (4), and washing water is added through the washing water injection port (6). After mixing in the spiral mixer (5), it is fed to the mill (3) and pulverized in the mill (3) to form a slurry; Step 2: Temporary storage and transportation of slurry: The slurry obtained in step 1 is introduced into a sewage tank (1) containing stirring, and after stirring, it is pressurized and transported by a vertical pipeline pump (2); Step 3: Directional recovery and separation: The slurry transported in step 2 is injected into the final washing tank (8) through the vertical pipeline pump outlet pipe (10) for sedimentation separation, and the red mud is discharged from the system through the underflow pump (9). The dissolved Al2O3 and Na2O are returned to the alumina production process through the overflow port of the final washing tank (8) for recycling.

5. The recycling method according to claim 4, characterized in that: In step 1, more than 80% of the particles in the slurry after being crushed by the mill (3) have a particle size of less than 400 mesh.

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