Organic matter removal method

Abstract

The invention discloses an organic matter removal method, which is characterized in that an aluminum oxide production system is independently provided with a set of induction tank device, and the induction tank device is used for storing aluminum hydroxide slurry; aluminum hydroxide slurry in the induction tank is cooled through a plate heat exchanger, meanwhile, materials in the induction tank are continuously circulated through an induction vertical disc filter, and mother liquor with the low organic matter concentration separated out by the induction vertical disc filter returns to an aluminum oxide production system; slurry with high organic matter concentration in the induction tank enters a discharging vertical disc filter, a filter cake of the discharging vertical disc filter is mixed with a fine seed vertical disc mother solution and then enters an induction / finished product flat disc filter, and a filter cake of the induction flat disc filter serves as washed aluminum hydroxide seeds and is sent to the induction tank. And sending the finished product flat plate filter cake as a finished product aluminum hydroxide to a roasting workshop, sending the strong filtrate of the flat plate filter with high organic matter concentration to a causticization process, sending the causticized slurry to a settling washing tank, washing causticized slag, and discharging the washed causticized slag. Through the method, the removal rate of the organic matters can be economically and effectively improved.

Description

Technical Field

[0001] The invention relates to a method for removing organic matter, in particular to a method for removing organic matter in a sodium aluminate solution in a process of producing alumina by the Bayer process, and belongs to the technical field of alumina production. Background Art

[0002] Bauxite is the raw material for the production of alumina. About 90% of the world's alumina is produced from bauxite. There are many types of bauxite and there are also great differences in quality. The properties of alumina and its hydrates largely determine the selection and determination of the production method and process conditions of alumina. In the Bayer process of producing alumina, various organic substances are oxidized and decomposed and react with sodium hydroxide to form sodium oxalate. Sodium oxalate accumulates continuously with the circulation of the solution until it is supersaturated and precipitates, thereby affecting the stable operation of production and product quality, especially causing the product obtained by seed decomposition to be severely refined. Adding an oxidant to the sodium aluminate solution to inhibit the adverse effects of oxalate on the seeding process is a common means in industry. In the circulation process of the sodium aluminate solution, when a large amount of sodium oxalate accumulates, the inhibitory effect of the oxidant is very limited. Therefore, excluding oxalate from the production system is a fundamental measure to solve its impact on production.

[0003] The invention patent CN102092752A applied by Shenyang Aluminum and Magnesium Design Institute Co., Ltd. discloses a process for removing organic matter in alumina production, especially a process for removing oxalate in the Bayer process. It includes continuously sending aluminum hydroxide slurry to the filter cloth of the horizontal belt vacuum filter, and the filter cloth drives the aluminum hydroxide slurry forward, passing through the separation zone, the primary washing zone and the secondary washing zone in turn, and removing the oxalate on the aluminum hydroxide filter cake. The above process flow is a continuous operation with a high degree of automation; and the length of the three zones, the speed of the filter cloth, and the amount of water added to the wash water can be adjusted according to the effect of washing and filtering, and it is widely applicable to slurries with different solid contents and different organic content; the filtrate formed in the separation zone and the primary washing zone can be returned to the Bayer system to recover alkali and alumina, and the primary washing water can be used as the filtrate produced by other processes to reduce the water consumption of the entire production system; and finally, it can effectively reduce the oxalate mixed on the surface of the seed crystal and reduce its harm to the seed. This method is to remove oxalate from the solid surface of aluminum hydroxide. Using the property that oxalate is soluble in hot water and aluminum hydroxide is insoluble in hot water, the oxalate is dissolved in hot water and then filtered out of the system with the filtrate to remove the oxalate solids attached to the fine seed slurry. This method has a large processing capacity but high investment. It is suitable for the production process of Australian ore using high-temperature dissolution technology.

[0004] The invention patent CN109292804A applied by Guangxi Huayin Aluminum Co., Ltd. discloses a method for removing oxalate in alumina production, which relates to the technical field of alumina production. Specifically, a special crystallization aid and a CGM crystallization aid are added to the semen, decomposed, filtered to obtain an aluminum hydroxide filter cake, and filtered to obtain oxalate crystals by underflow; the temperature of the first decomposition tank is adjusted to 56-62°C; the temperature of the final decomposition tank is 45-49°C; the amount of the CGM crystallization aid added is 0-25ppm of the semen, and the amount of the special crystallization aid added is 5-30ppm of the semen; the special crystallization aid includes oleic acid 10-30%, C fatty acid 1-5%, and the rest is water according to mass percentage. The removal method adds a special crystallization aid in combination with a CGM crystallization aid to stabilize the oxalate in a spherical form, and then lowers the temperature of the first tank and the temperature of the final tank to reduce the oxalate concentration in the solution and increase the decomposition yield. The method removes oxalate by changing the morphology of oxalate crystals. Oxalate crystals are generally slender needle-shaped, which will clog the filter cloth of the seed filter and the aluminum hydroxide flat disc filter, reducing their operating rate and production capacity. By adding a special crystallization aid to the semen, the oxalate crystals are precipitated in a spherical form, eliminating the effect of needle-shaped oxalate on the filter cloth of the filter, so that it can obtain good filtering performance and achieve the purpose of removing oxalate. The principle of oxalate balling in this method is not clear. From the actual production point of view, only alumina plants using Guangxi bauxite as raw materials can achieve oxalate balling, but this method is not yet universally applicable. Summary of the invention

[0005] The purpose of the present invention is to provide a method for removing organic matter to overcome the deficiencies of the prior art.

[0006] The technical solution of the present invention is an organic matter removal method, comprising the following steps: an alumina production system is independently provided with an induction tank device, the induction tank device is used to store aluminum hydroxide slurry, the aluminum hydroxide slurry in the induction tank mainly comprises: decomposition and classification cyclone bottom flow slurry, induction seed slurry, and washed seed slurry; the aluminum hydroxide slurry in the induction tank is first cooled by a plate heat exchanger to make the organic matter in the tank reach a precipitation state, and at the same time, the material in the induction tank is continuously circulated by an induction vertical disk filter, and the induction vertical disk filter is separated. The mother liquor with lower organic matter concentration is returned to the alumina production system; the slurry with higher organic matter concentration in the induction tank enters the discharge disc filter, the filter cake of the discharge disc filter is mixed with the mother liquor from the fine seed disc and enters the induction / finished product flat disc filter, the filter cake of the induction flat disc filter is sent to the induction tank as the washed aluminum hydroxide seed, the filter cake of the finished flat disc filter is sent to the roasting workshop as the finished aluminum hydroxide, the strong filtrate of the flat disc filter with high organic matter concentration is sent to the causticizing process, the slurry after causticizing is sent to the sedimentation washing tank, and the causticized slag is discharged after washing.

[0007] In the aforementioned method for removing organic matter, the alumina production system needs to be equipped with a separate induction tank device, which can utilize the existing decomposition tank in the alumina production system, or a new storage tank device can be separately provided.

[0008] In the aforementioned method for removing organic matter, the material in the induction tank is continuously circulated by the induction disc filter, and the mother liquor with lower organic matter concentration precipitated by the induction disc filter is returned to the alumina production system. Specifically, the slurry with lower organic matter concentration in the induction tank enters the induction disc filter, and the mother liquor with lower organic matter concentration precipitated by the induction disc filter is returned to the alumina production system. The filter cake of the induction disc filter is mixed with the mother liquor from the fine seed disc in the induction seed mixing tank to form an induced seed slurry, which is then pumped into the induction tank to realize the circulation of the material.

[0009] In the aforementioned method for removing organic matter, the slurry with a higher organic matter concentration in the induction tank enters the discharge disc filter, and the filter cake of the discharge disc filter and the mother liquor from the fine seed disc are mixed in the discharge mixing tank to form a mixed slurry which is then pumped into the induction / finished product flat disc filter.

[0010] In the aforementioned method for removing organic matter, the filter cake of the induced flat disc filter is used as the washed aluminum hydroxide seed and the mother liquor from the fine seed disc is mixed in the washed seed mixing tank to form a washed seed slurry which is then pumped into the induction tank.

[0011] In the aforementioned method for removing organic matter, the aluminum hydroxide slurry in the induction tank is cooled by a plate heat exchanger to ensure that the slurry temperature in the tank is ≤55°C; the solid content of the slurry in the induction tank is 500-900g / L; and the induction time of the slurry in the induction tank is 8-15 hours.

[0012] The beneficial effects of the present invention are as follows: compared with the prior art, the method for removing organic matter in the process of producing alumina by the Bayer process of the present invention can economically and effectively improve the organic matter removal rate, improve the quality of alumina, have strong operability, simple process flow, low investment and operating costs, and reduce the overall cost of alumina production. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It is a simplified process flow diagram of the present invention. DETAILED DESCRIPTION

[0014] The present invention is further described below in conjunction with the accompanying drawings and embodiments, but they are not intended to limit the present invention.

[0015] Embodiment of the present invention: A method for removing organic matter is used to remove the organic matter produced by Bayer process alumina The organic matter in the sodium aluminate solution includes the following steps: the alumina production system is equipped with a set of induction tank device, which is used to store aluminum hydroxide slurry. The aluminum hydroxide slurry in the induction tank mainly includes: decomposition and classification cyclone bottom flow slurry, induction seed slurry, and washed seed slurry. The aluminum hydroxide slurry in the induction tank is first cooled by a plate heat exchanger to make the organic matter in the tank reach a precipitation state. At the same time, the induction disc filter is used to continuously circulate the material in the induction tank. The mother liquor with a lower organic concentration precipitated by the induction disc filter is returned to the alumina production system to achieve the purpose of diluting the organic concentration of the alumina production system. The slurry with higher organic matter concentration in the induction tank enters the discharge disc filter, the filter cake of the discharge disc filter is mixed with the mother liquor from the fine seed disc and enters the induction / finished product flat disc filter, the filter cake of the induction flat disc filter is sent to the induction tank as the washed aluminum hydroxide seed, the filter cake of the finished flat disc filter is sent to the roasting workshop as the finished aluminum hydroxide, the strong filtrate of the flat disc filter with high organic matter concentration is sent to the causticizing tank for causticizing process, the slurry after causticizing is sent to the sedimentation washing tank, and the causticized slag is discharged after washing.

[0016] In the whole structure, the induction disc filter realizes the continuous induction circulation of the materials in the induction tank. The discharge disc filter is responsible for discharging the aluminum hydroxide slurry with a high organic concentration in the induction tank. The induction flat disc filter is responsible for washing the aluminum hydroxide seeds, and the finished product flat disc filter is responsible for discharging the finished aluminum hydroxide.

[0017] The alumina production system needs to set up a set of induction tank device separately. The induction tank device can use the existing decomposition tank in the alumina production system, or a new storage tank device can be set up separately.

[0018] The method of using the induction disc filter to continuously circulate the material in the induction tank, and returning the mother liquor with lower organic concentration precipitated by the induction disc filter to the alumina production system is as follows: the slurry with lower organic concentration in the induction tank enters the induction disc filter, and the mother liquor with lower organic concentration precipitated by the induction disc filter is returned to the alumina production system, and the filter cake of the induction disc filter is mixed with the mother liquor from the fine seed disc in the induction seed mixing tank to form an induction seed slurry, which is then pumped into the induction tank to realize the circulation of the material.

[0019] The slurry with higher organic matter concentration in the induction tank enters the discharge disc filter, and the filter cake of the discharge disc filter is mixed with the mother liquor from the fine seed disc in the discharge mixing tank to form a mixed slurry which is then pumped into the induction / finished product flat disc filter.

[0020] The filter cake of the induced flat disc filter is used as the washed aluminum hydroxide seed and the mother liquor from the fine seed disc is mixed in the washed seed mixing tank to form the washed seed slurry which is then pumped into the induction tank.

[0021] The aluminum hydroxide slurry in the induction tank is cooled by a plate heat exchanger to ensure that the slurry temperature in the tank is ≤55°C. The solubility of organic matter decreases at low temperatures, thereby facilitating the precipitation of organic matter. The solid content of the slurry in the induction tank is 500-900g / L. Within this solid content range, organic matter is easy to precipitate. The slurry induction time in the induction tank is 8-15 hours to ensure that the organic matter in the slurry can be fully induced to precipitate.

[0022] In order to verify the effectiveness of the method of the present invention, an alumina plant with an annual output of 2.2 million tons is used as an example. The plant uses a high-temperature dissolution process to treat Australian ore, and the TOC content in the ore is 0.22%. The plant is equipped with 2 V = 11000m 3 Induction tank, 3 units F=240m 2 Induction disc filter, 4 units F=240m 2 1 set of vertical disc filter with a capacity of 180m 2 Induction plate filter, 2 units F=180m 2 Finished flat disc filter. The solid content of the slurry in the induction tank is 650g / L, the slurry temperature in the tank is 50-55℃, and the induction time is 12 hours.

[0023] The achieved results are as follows: The removal capacity of the organic matter removal process is 8-10 tons / day.

[0024] Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments, or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for removing organic matter, characterized in that: The invention comprises the following steps: an alumina production system is provided with an induction tank device, the induction tank device is used for storing aluminum hydroxide slurry, the aluminum hydroxide slurry in the induction tank mainly comprises: decomposition and classification cyclone bottom flow slurry, induction seed slurry and washed seed slurry; the aluminum hydroxide slurry in the induction tank is first cooled by a plate heat exchanger to make the organic matter in the tank reach a precipitation state, and at the same time, the material in the induction tank is continuously circulated by an induction disc filter, and the mother liquor with a low organic matter concentration precipitated by the induction disc filter is returned to the alumina production system; the slurry with a high organic matter concentration in the induction tank enters the discharge disc filter, the filter cake of the discharge disc filter is mixed with the mother liquor from the fine seed disc and then enters the induction / finished product flat disc filter, the filter cake of the induction disc filter is sent to the induction tank as the washed aluminum hydroxide seed, the filter cake of the finished flat disc filter is sent to the roasting workshop as the finished aluminum hydroxide, the strong filtrate of the flat disc filter with a high organic matter concentration is sent to the causticizing process, the slurry after causticizing is sent to the sedimentation washing tank, and the causticized slag is discharged after washing.

2. The method for removing organic matter according to claim 1, characterized in that: The alumina production system needs to set up a set of induction tank device separately. The induction tank device can use the existing decomposition tank in the alumina production system, or a new storage tank device can be set up separately.

3. The method for removing organic matter according to claim 1, characterized in that: The method of using the induction disc filter to continuously circulate the material in the induction tank, and returning the mother liquor with lower organic concentration precipitated by the induction disc filter to the alumina production system is as follows: the slurry with lower organic concentration in the induction tank enters the induction disc filter, and the mother liquor with lower organic concentration precipitated by the induction disc filter is returned to the alumina production system, and the filter cake of the induction disc filter is mixed with the mother liquor from the fine seed disc in the induction seed mixing tank to form an induction seed slurry, which is then pumped into the induction tank to realize the circulation of the material.

4. The method for removing organic matter according to claim 1, characterized in that: The slurry with higher organic matter concentration in the induction tank enters the discharge disc filter, and the filter cake of the discharge disc filter is mixed with the mother liquor from the fine seed disc in the discharge mixing tank to form a mixed slurry which is then pumped into the induction / finished product flat disc filter.

5. The method for removing organic matter according to claim 1, characterized in that: The filter cake of the induced flat disc filter is used as the washed aluminum hydroxide seed and the mother liquor from the fine seed disc is mixed in the washed seed mixing tank to form the washed seed slurry which is then pumped into the induction tank.

6. The method for removing organic matter according to claim 1, characterized in that: The aluminum hydroxide slurry in the induction tank is cooled by a plate heat exchanger to ensure that the slurry temperature in the tank is ≤55°C; the solid content of the slurry in the induction tank is 500-900g / L; and the induction time of the slurry in the induction tank is 8-15 hours.

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