Return water treatment method for red mud storage yard of aluminum oxide plant

Abstract

A red mud storage yard backwater treatment method for an aluminum oxide plant belongs to the technical field of aluminum oxide production and comprises the following steps: step 1, aeration precipitation: red mud backwater in a red mud storage yard backwater tank enters an aeration tank through a backwater pump, and a submersible aerator is arranged in the aeration tank for mixed aeration; step 2, neutralization: neutralizing the alkaline red mud return water by adding concentrated sulfuric acid; step 3, mixing, flocculation, precipitation and sand filtration; and step 4, manganese sand filtration: oxidizing low-valence iron ions and low-valence manganese ions in the water into high-valence iron ions and high-valence manganese ions by using an oxidation method, and then removing the high-valence iron ions and high-valence manganese ions through adsorption and filtration, so that the content of iron and manganese in the water is reduced, the chromaticity is reduced, and the water is discharged after reaching the standard. According to the method, stable and harmless discharge of the red mud storage yard backwater is achieved through the combined process, the environmental protection risk caused by disordered discharge of the red mud storage yard backwater is completely eradicated, the engineering investment of the red mud storage yard backwater pool is saved, and the method has wide application prospects and practical value.

Description

Technical Field

[0001] The present invention belongs to the technical field of alumina production, and particularly relates to a method for treating red mud yard return water in an alumina plant. Background Art

[0002] In an alumina plant, a return water pool is set up in the red mud yard to collect the rainfall in the yard's water collection area, that is, rainwater does not accumulate in the storage area of the red mud yard. However, the initial rainwater that falls on the yard surface inevitably carries alkali due to washing the surface layer and cannot be directly discharged. Theoretically, the rainwater collected in the return water pool can be returned to the alumina plant through a return water pump and reused in the process flow, thereby correspondingly reducing the consumption of fresh water and alkali in the alumina process. In fact, the acceptance capacity of the alumina process system is limited. If it is ensured that the red mud return water is not discharged externally, the volume of the return water pool must be enlarged, and the rainwater that can be accommodated during heavy rain will also increase. However, if the volume is too large, the project investment will increase, and the return water pool will be idle most of the time, resulting in waste. Currently, for alumina projects at home and abroad, especially in tropical countries such as Indonesia and Guinea or in the southern regions of China, the rainfall during the rainy season is very large, far greater than the evaporation rate, and the consumption capacity of the return water in the alumina plant is limited. It is very unrealistic to infinitely increase the volume of the return water pool.

[0003] When the red mud yard is in normal return water, the alkali concentration is very high, and the pH value can reach up to 13 - 14. The pH value of the rainwater washing the yard surface is 10 - 12. Currently, at home and abroad, the return water of the red mud yard is simply neutralized with acid and then discharged. However, the actual water quality of the red mud yard return water is very complex. Not only does the pH value exceed the standard, but simple acid neutralization treatment cannot effectively eliminate environmental protection risks. Summary of the Invention

[0004] In view of the above-mentioned drawbacks and deficiencies of the prior art, the present invention provides a method for treating red mud yard return water in an alumina plant, which realizes the stable and harmless discharge of the red mud yard return water through a combined process, completely eliminates the environmental protection risks brought by the disorderly external discharge of the red mud yard return water, saves the project investment of the red mud yard return water pool, and has broad application prospects and practical value.

[0005] In order to achieve the above object, the main technical solutions adopted by the present invention include: A method for treating red mud yard return water in an alumina plant. For the complex water quality of the red mud yard in the alumina plant, through the combined process of aeration precipitation, neutralization, coagulation, precipitation, sand filtration, and manganese sand filtration, the harmless discharge of the red mud yard return water is realized, and the occurrence of environmental protection risks is fundamentally eliminated. The specific steps include: Step 1: Aeration precipitation The red mud return water in the red mud yard return water pool enters the aeration tank through a return water pump. A submersible aerator is installed in the aeration tank for aeration and stirring to ensure that the iron ions in the red mud return water are fully contacted and oxidized with the oxygen in the air, and then iron oxide precipitates are formed, thereby removing a large amount of iron ions.

[0006] Step 2: Neutralization The effluent from the aeration sedimentation tank enters the neutralization tank, and concentrated sulfuric acid is added to neutralize the alkaline red mud return water, adjusting the pH to 6.5 - 7.5.

[0007] Step 3: Mixing, flocculation, sedimentation, sand filtration The neutralized red mud return water is lifted into the coagulation unit. By adding a coagulant and a flocculation aid, the suspended solids in the water form larger - sized flocs. After sedimentation in the sedimentation unit, the suspended solid particles are separated from the water by gravity; then it enters the sand filtration unit, and quartz sand granular filter media is used to intercept the suspended particles in the water, thereby further reducing the turbidity of the water; the coagulation, sedimentation, and sand filtration adopt an integrated water purifier, which is a high - turbidity and large - capacity water treatment equipment that organically combines pipeline mixing, swirl reaction, suspended clarification, inclined tube sedimentation, high - efficiency filtration, sludge thickening, etc.

[0008] Step 4: Manganese sand filtration The final effluent enters the manganese sand filter. Using the oxidation method, the ferrous ions and manganous ions in the water are further oxidized into ferric ions and manganic ions, and then removed through adsorption filtration, achieving the purpose of further reducing the iron and manganese content in the water and further reducing the chromaticity, thereby ensuring the full compliance discharge of the red mud return water.

[0009] Further, the submersible aerator described in Step 1 uses a self - suction aeration method for aeration, with an aeration volume of 200 m 3 / h, and the aeration time does not exceed 2 h. The aerator motor rotates the impeller at high speed, generating centrifugal force, which makes a negative pressure area form at the impeller inlet, thus sucking in air and water. After the air and water are mixed in a certain proportion in the mixing chamber, they are ejected along the tangent direction of the impeller under the action of centrifugal force and diffuse in the circumferential direction to form a convection cycle. The tiny bubbles have a large specific surface area and a slow rising speed, thus ensuring the full mixing and stirring of oxygen and water and improving the aeration efficiency.

[0010] Further, 98% industrial concentrated sulfuric acid is used for acid - base neutralization in Step 2, and the dosing amount depends on the pH value of the raw water, with a dosing amount of 1 - 3 L / m 3 .

[0011] Further, the coagulant and flocculation aid described in Step 3 are polyaluminum chloride and anionic polyacrylamide respectively. The dosing amount depends on the suspended solid concentration of the raw water. The dosing amount of polyaluminum chloride is 50 - 100 mg / L, and the dosing amount of anionic polyacrylamide is 5 - 10 mg / L.

[0012] Further, the filtration rate of the manganese sand filter described in Step 4 depends on the raw water quality parameters and ranges from 8 to 10 m / h; the manganese sand filter automatically controls the combined air-water backwashing according to time, with the water backwashing intensity being 13 - 16 L / (m 2 ·s), and the air scrubbing intensity being 15 - 18 L / (m 2 ·s).

[0013] Further, the sludge generated by the aeration sedimentation tank and the integrated water purifier is directly transported to the red mud yard.

[0014] Further, the qualified water after treatment can be used as the solvent preparation water for the chemical dosing device and the backwashing water for the filter.

[0015] The beneficial effects of the present invention are as follows: 1. The present invention adopts a combined process, with a simple overall process and strong operability, which can ensure the continuous and stable discharge of the excess red mud yard return water up to the standard, completely eliminating environmental protection risks.

[0016] 2. The present invention ensures the qualified external discharge of the excess red mud yard return water, thereby effectively reducing the effective volume and idle rate of the yard return water tank, saving capital construction investment.

[0017] 3. The sludge generated by the present invention is directly discharged into the red mud yard without further treatment, saving costs.

[0018] 4. The qualified water after treatment by the present invention is used as the solvent preparation water for the chemical dosing device and the backwashing water for the filter, saving energy and water. Description of the Drawings

[0019] Figure 1 It is a schematic diagram of the method for treating the red mud yard return water in an alumina plant according to the present invention. Detailed Embodiments

[0020] For better explaining the present invention and facilitating understanding, the present invention will be described in detail below in conjunction with the drawings and through specific embodiments.

[0021] As Figure 1 shown, the present invention provides a method for treating the red mud yard return water in an alumina plant, including process units such as aeration sedimentation, neutralization, mixing, flocculation, sedimentation, sand filtration, and manganese sand filtration. The specific steps of the embodiment of the present invention include: Step 1: Aeration sedimentation The red mud return water in the red mud yard return water tank enters the aeration tank through a return water pump. A submersible aerator is installed in the aeration tank for aeration through self-priming aeration, and the aeration volume reaches 200 m 3 / h, control the aeration time not to exceed 2 h. The aerator motor rotates the impeller at high speed, generating centrifugal force, which creates a negative pressure area at the impeller inlet, thus sucking in air and water. After the air and water are mixed in a certain proportion in the mixing chamber, they are ejected along the tangent direction of the impeller under the action of centrifugal force and diffuse in the circumferential direction to form a convection cycle. The tiny bubbles have a large specific surface area and a slow rising speed, ensuring sufficient contact and oxidation between the iron ions in the red mud return water and the oxygen in the air, and then forming iron oxide precipitates. Moreover, the aeration and agitation cause the iron oxide particles to collide with other impurities or suspended solids in the water, thus promoting the formation of precipitates.

[0022] Step 2: Neutralization The effluent from the aeration sedimentation tank enters the neutralization tank, and 98% industrial concentrated sulfuric acid is added to neutralize the alkaline red mud return water, adjusting the pH to 6.5 - 7.5. The dosage of concentrated sulfuric acid depends on the pH value of the raw water, and the dosage is 1 - 3 L / m 3 .

[0023] Step 3: Mixing, flocculation, sedimentation, sand filtration The neutralized red mud return water is lifted into the coagulation unit, and a coagulant polyaluminum chloride and a flocculation aid anionic polyacrylamide are added. The dosage depends on the suspended solid concentration of the raw water. The dosage of polyaluminum chloride is 50 - 100 mg / L, and the dosage of anionic polyacrylamide is 5 - 10 mg / L. By adding the coagulant and flocculation aid, the suspended solids in the water form larger flocs. After sedimentation in the sedimentation unit, the suspended solid particles are separated from the water by gravity; then it enters the sand filtration unit, and quartz sand granular filter media is used to intercept the suspended particles in the water, thereby further reducing the turbidity of the water; Coagulation, sedimentation, and sand filtration adopt an integrated water purifier, which is a high-turbidity and large-capacity water treatment equipment that organically combines pipeline mixing, swirl reaction, suspended clarification, inclined tube sedimentation, high-efficiency filtration, sludge thickening, etc.

[0024] Step 4: Manganese sand filtration The final effluent enters the manganese sand filter. The low-valent iron ions and low-valent manganese ions in the water are further oxidized into high-valent iron ions and high-valent manganese ions by the oxidation method, and then removed through adsorption filtration, achieving the purpose of further reducing the iron and manganese content in the water and further reducing the chromaticity, thus ensuring the full compliance discharge of the red mud return water. The filtration rate of the manganese sand filter depends on the raw water quality parameters and takes a value of 8 - 10 m / h; and the air-water combined backwashing is automatically controlled according to time. The water backwashing intensity is 13 - 16 L / (m 2 ·s), and the air scrubbing intensity is 15 - 18 L / (m 2 ·s).

[0025] In this embodiment, the sludge generated by the aeration sedimentation tank and the integrated water purifier is directly transported to the red mud yard without further treatment.

[0026] In this embodiment, the treated qualified water can be used as the water for dissolving drugs in the drug adding device and the backwashing water for the filter. Therefore, only a small amount of water is needed in the startup stage, and no external water source is required during the operation stage.

[0027] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Any modifications, alterations, substitutions, and variations made by those of ordinary skill in the art to the above embodiments fall within the scope of the present invention.

Claims

1. A method for treating red mud backwater in an alumina plant, characterized in that: The steps include: Step 1: Aeration and sedimentation The red mud return water in the red mud dump returns to the aeration tank through the return water pump. The aeration tank is equipped with a submersible aerator for mixed aeration, so that the iron ions in the red mud return water are fully contacted and oxidized with the oxygen in the air to form iron oxide precipitates. Step 2: Neutralization The effluent from the aeration sedimentation tank enters the neutralization tank, where concentrated sulfuric acid is added to neutralize the alkaline red mud return water; Step 3: Mixing, flocculation, sedimentation, sand filtration The neutralized red mud return water is lifted and enters the coagulation unit. By adding coagulants and coagulant aids, the suspended matter in the water forms flocs and settles in the sedimentation unit. Then it enters the sand filtration unit, where quartz sand granular filter media is used to intercept suspended particles in the water. Step 4: Manganese sand filtration The effluent from step 3 enters the manganese sand filter, where the low-valent iron ions and low-valent manganese ions in the water are oxidized into high-valent iron ions and high-valent manganese ions by oxidation, and then removed by adsorption filtration to reduce the iron and manganese content in the water and the chromaticity, and then discharged after meeting the standards.

2. The method for treating red mud dump water from an alumina plant according to claim 1, characterized in that: In step 1, the submersible aerator is used for aeration in a self-priming aeration mode, and the aeration volume is 200m 3 / h, aeration time shall not exceed 2h.

3. The method for treating red mud dump water from an alumina plant according to claim 1, characterized in that: In step 2, 98% industrial concentrated sulfuric acid is used for acid-base neutralization, and the dosage is 1~3L / m 3 .

4. The method for treating red mud dump water from an alumina plant according to claim 1, characterized in that: In the step 3, the coagulant and coagulant aid used are polyaluminium chloride and anionic polyacrylamide respectively, the dosage of polyaluminium chloride is 50-100 mg / L, and the dosage of anionic polyacrylamide is 5-10 mg / L.

5. The method for treating red mud dump water from an alumina plant according to claim 1, characterized in that: In step 3, coagulation, sedimentation and sand filtration are performed using an integrated water purifier.

6. The method for treating red mud dump return water in an alumina plant according to claim 1, characterized in that: In step 4, the filtration rate of the manganese sand filter is 8-10 m / h; the water backwash intensity of the manganese sand filter is 13-16 L / (m 2 ·s), air scrubbing intensity 15~18L / (m 2 ·s).

7. The method for treating red mud dump water from an alumina plant according to claim 1, characterized in that: The sludge produced by the aeration sedimentation tank, coagulation, sedimentation and sand filtration steps is directly transported to the red mud dump.

8. The method for treating red mud dump water from an alumina plant according to claim 1, characterized in that: The qualified water after treatment is used as water for dissolving drugs in dosing devices and water for backwashing filters.

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