Processing methods for bauxite used in alumina production

Abstract

This invention relates to a method for processing bauxite for alumina production, and the proposed method pertains to the field of non-ferrous metallurgy. The method for processing bauxite to produce alumina includes: filtering an alumina process slurry obtained after bauxite digestion, wherein the slurry, after leaching, dilution, or thickening, is filtered at a temperature of at least 95°C to obtain a filtrate representing the filtered green liquor and a solid phase of red mud; washing the solid phase of the red mud on a filtration device, wherein the washing is carried out with hot water, preferably at a temperature below 98°C, to achieve specific concentrations of the green liquor and red mud liquid phases; guiding the filtrate to safe filtration and / or precipitation; and supplying the water after washing the red mud to dilute the bauxite digestion slurry and / or dilute the filtrate to obtain a specific concentration of green liquor, wherein the resulting filter cake is waste. This method improves liquid productivity during precipitation and reduces soda consumption, thus increasing the efficiency of alumina production due to savings in soda, heat, and energy, and increasing the yield of smelter-grade alumina.

Description

[0001] This application is a divisional application. The international application number of the original application is PCT / RU2022 / 050278, the international application date is September 6, 2022, the Chinese national application number is 202280008637.8, the entry date into China is June 28, 2023, and the invention title is "Processing method of bauxite for alumina production". Technical Field

[0002] This invention relates to non-ferrous metallurgy, and in particular, to the production of alumina by the Bayer process or the Bayer sintering process, i.e., to a method for improving liquid productivity by effectively separating and washing slurry. Background Technology

[0003] High liquid productivity during sedimentation allows for maintaining a low specific flow rate of the green liquor, thus ensuring low consumption of the main fuel and energy for alumina production. Currently achievable liquid productivity is limited by conventional techniques for thickening and washing red mud in tanks and containers. This technology does not allow for increasing the concentration of the green liquor, thereby increasing productivity, without increasing the alkali loss of the red mud liquid phase. Furthermore, the sedimentation and washing of red mud requires large amounts of liquid, leading to prolonged contact between the solid and liquid phases and autoprecipitation (loss of red mud alumina).

[0004] Many technical solutions have been developed to address the issues of effective mud separation and washing, as well as improving liquid productivity.

[0005] The related technology discloses a method for filtering slurry at the tail end (terminal) of the alumina production process (Abhijeet Bandi, Kausikisaran Misra, N. Nagesh, Uttam Kumar Giri and Rama Chandra Nahak, Improvement of Mud Circuit Efficiency while Processing East Coast Bauxite of India, Proceedings of the 38th International ICSOBA Conference, November 16-18, 2020), which involves filtering the waste slurry in order to dry and store it in a bauxite residue disposal area.

[0006] The disadvantages of this method include the following: - It is impossible to exclude the red mud thickening and washing areas from the production process; - Lack of impact on liquid productivity; - There is a lack of significant savings in resource and energy consumption in alumina production.

[0007] The related technology discloses a method for filtering slurry from the tail end (terminal) of an alumina production process (SedatArslan, Gökhan Kürsat Demir, Bekir Çelikel and Meral Baygül, Implementation and Optimization of Filter Press in Red Mud Washing Process at Eti Aluminum, Proceedings of the 36th International ICSOBA Conference, Belém, Brazil, October 29–November 1, 2018), which involves filtering the waste slurry to dry it and store it in a bauxite residue disposal area.

[0008] The drawbacks of this method include the same problems as in the first example.

[0009] Related technologies disclose a method for improving the production rate of aluminate liquids (Lu Zijian, Zhaoqun, Xieyanli, Bi Shiwen, Yang Yihong, The application of additives in the precipitation of Bayer sodium aluminate liquors, Light Metals, TMS TheMinerals, 2004). This method proposes a scheme to improve the efficiency of the precipitation process by introducing various additives into the process. The additives not only affect the production rate but also the size and quality of the aluminum hydroxide.

[0010] The disadvantages of this method include the following: Using this method, it is impossible to exclude the red mud thickening and washing zones from the production process; - The use of additives can lead to additional contamination of the solution by organic or inorganic impurities, which need to be removed by the solution; - Lack of conservation in the consumption of baking soda and flocculants; - Expensive reagents are required.

[0011] The closest method to the claimed method is a method for processing low-quality bauxite into alumina (Patent KZ No. 13802, publication date: December 15, 2003). In this method, red mud is directly filtered in several stages after thickening. The filtrate from each stage is re-slurried with the filtrate from the subsequent filtration stage. The re-slurried mud is heated to a temperature not exceeding 95°C, and it is ensured that a caustic alkali (Na₂O) is used in the first stage. 苛性碱A final stage involves supplying hot water to the red mud slurry at a concentration not exceeding 135 g / L, and filtration is performed with a caustic alkali to alumina ratio not lower than that corresponding to the equilibrium green liquor. The number of filtration stages is determined by the residual alkali content in the final stage's filtered red mud liquid phase. This method reduces specific consumption of hot water for red mud washing, losses of aluminum hydroxide and alkali, and flocculant consumption. It also allows for a reduction in the production space required in the mud loop.

[0012] The disadvantages of this method include the following: - This process is expected to involve several stages of filtration, which increases the amount of equipment required to implement the process several times over; - The degree of washing of the mud with the filtrate from subsequent stages is low, which reduces the efficiency of the process and increases the loss of alkali; - Thickening still exists in the production process, which does not allow for the complete elimination of solid alumina loss due to autoprecipitation, and the complete abandonment of the use of flocculants; -with Na2O 苛性碱 The liquid concentration should not exceed 135 g / L, as this is not the optimal parameter for achieving maximum liquid productivity. - The relatively low filtration temperature below 95°C results in additional loss of alumina from the liquid due to automatic sedimentation and the low resistance of the cloth. Summary of the Invention

[0013] The objective of this invention is to develop a cost-effective method for increasing the liquid production rate of alumina from bauxite by increasing its concentration and reducing the caustic alkali to alumina ratio. This is achieved by replacing the thickening and washing of red mud with filtration and washing on a filtration device, thereby reducing the specific consumption of hot water for mud washing, thus increasing the concentration and reducing the caustic alkali to alumina ratio. The resulting green liquor with a higher concentration and lower caustic alkali to alumina ratio is then processed according to existing alumina production processes. Furthermore, this method significantly reduces the loss of soluble alumina and alkali in the liquid phase of the mud.

[0014] The technical benefits lie in increasing precipitation productivity and reducing soda consumption, thereby improving the efficiency of alumina production and increasing the output of smelting-grade alumina by saving soda, heat and energy.

[0015] The technical effect is achieved through a method of processing bauxite to produce alumina, which includes the filtration of slurry (bauxite digestion slurry, diluted slurry, or thickened slurry) using filtration equipment to achieve high-speed separation of the solid and liquid phases. The filtrate, representing the green liquor, is then supplied to a safety filtration unit to remove residual solids, while a portion of the filtrate, upon reaching a specified quality in terms of solid particle content, can be directly sent to precipitation. After safety filtration, the liquid is directed to precipitation to extract aluminum hydroxide. The resulting filter cake from the slurry filtration is washed on a filter in a pressing layer with hot water, preferably not exceeding 98°C, to separate the solid and liquid phases of the slurry through washing. The wash water from the filter cake washing is directed to dilute the bauxite digestion slurry to achieve a specific concentration of green liquor. The filter cake is waste suitable for storage in the slurry treatment area using dry, semi-dry, or wet methods.

[0016] The proposed "direct filtration" slurry method will reduce alumina loss by avoiding the automatic sedimentation of the green liquor in the thickening-washing system, thus reducing the consumption of hot water for washing. This, in the case of a high slurry washing coefficient, will increase the concentration of the green liquor, reduce the caustic alkali to alumina ratio, and improve liquid productivity. Increased liquid productivity will reduce the specific flow rate of liquid produced per ton of alumina, which will increase alumina production output and reduce costs in key performance indicators.

[0017] Introducing the proposed method will have many advantages, namely, it will be able to achieve the following: -Replacing the existing two operations of thickening and washing red mud in tanks and containers with a single operation, namely filtration and washing on the filtration equipment, will reduce the loss of alumina caused by automatic sedimentation; - By reducing the water content in the treatment slurry and returning the filtrate obtained from filter cake washing to alumina production, the loss of soluble alkali and alumina in the liquid phase of the treatment slurry is reduced by 60-75% compared to current levels; - Reduce heat consumption from waste liquid evaporation by increasing the concentration of green liquor, reduce fuel consumption in the sintering zone by increasing the share of the Bayer loop (for the Bayer sintering combined process), and reduce or completely eliminate flocculant consumption by eliminating the use of flocculants for thickening and washing. - Reduce the consumption of electricity and compressed air by decreasing the specific flow rate of liquid in the sedimentation and evaporation zones, reducing the share of the sintering circuit (as a special case of alumina production via the Bayer sintering process), and replacing the tanks and pumping equipment in the thickening-washing zone with filter presses.

[0018] This method is supplemented by its implementation methods.

[0019] In a specific embodiment of the invention, the slurry obtained after bauxite digestion is used as a filtration slurry. The filtrate is sent to a stirred collection tank to be mixed with wash water from mud washing. The mixed liquid is further sent to a liquid safety filter, where a portion of the strong filtrate, after reaching a specified mass in terms of solid particle content, can be directly provided to the sedimentation tank after dilution with water. The filter cake is washed with hot water in a pressing layer. The wash water from the filter cake washing is directed to a stirred tank to dilute the filtrate. The washed filter cake is re-slurryed with water and pumped to the mud treatment area, or stored as a filter cake using dry or semi-dry methods.

[0020] In a specific embodiment of the invention, the thickened slurry obtained by thickening the diluted slurry is used as a filtration slurry. The thickener overflow is sent for liquid safety filtration. The filtrate is sent to a stirred collection tank and then to a liquid safety filtration system, where a portion of the strong filtrate, after reaching a specified mass in terms of solid particle content, can be directly supplied to sedimentation. The filter cake is washed with hot water in a pressing layer. The wash water from the filter cake washing is supplied to a stirrer (dilution stirrer) to obtain a diluted slurry. The washed filter cake is re-slurryed with water and pumped to a slurry treatment area, or stored as a filter cake using dry or semi-dry methods. Attached Figure Description

[0021] Figure 1 , 2 Figures 3 and 4 show alternative arrangements for the process flow diagram used to process bauxite to produce alumina.

[0022] The difference between alternative arrangements lies in the properties of the filter slurry.

[0023] Figure 1 A process flow diagram for filtering and washing diluted slurry is shown.

[0024] The diluted slurry supplied to the filter is obtained by digesting the raw slurry. The bauxite slurry obtained by digesting the raw slurry is diluted with wash water provided by washing the filter cake with water. The slurry is then fed to the filter for separation and washing of the solid phase. The initial diluted slurry supplied to the filter press is preferably at a temperature up to 110°C, and the solid particle content in the slurry is approximately 40-110.0 kg / m³. 3 .

[0025] The filtrate (green liquid) is supplied to a liquid safety filtration unit to remove solid particles. This process is carried out until a suitable mass is achieved (Fe2O3 content not exceeding 0.016 g / dm³). 3 After that, a portion of the filtrate can bypass the safety filtration and be directly supplied to the precipitate.

[0026] The red mud cake obtained during filtration is washed with water to remove the green liquor (specific water consumption is not less than 2.0 m). 3 / t dry mud). The hot water temperature is preferably not more than 98°C. Wash water (from washing) obtained in the filter cake washing stage is provided to dilute the slurry after bauxite digestion. The washed red mud with a moisture content of 25-30% W is re-slurryed with water returned from the mud treatment area and then pumped to the mud treatment area in the form of slurry or filter cake.

[0027] Figure 2 The process flow diagram for filtering and washing the slurry after bauxite digestion is shown.

[0028] The initial slurry used for filtration is obtained by digesting the feed slurry. The slurry obtained during the digestion process is fed to the filter press to separate and wash the solid phase. The initial bauxite slurry fed to the filter press after digestion reaches temperatures as high as 120°C, and the solid particle content in the slurry is approximately 50-180.0 kg / m³. 3 The filtrate (strong green solution) is diluted with washing water to obtain the specified liquid concentration. The resulting green solution is then supplied to a safety filtration unit to remove solid particles. The solution is then filtered to achieve a suitable mass (Fe₂O₃ content not exceeding 0.016 g / dm³). 3 After that, a portion of the filtrate can be transferred for dilution to obtain the specified concentration, and then bypassed for use in the precipitation.

[0029] The red mud cake obtained during filtration is washed with water to remove the green liquor (specific water consumption is not less than 2.0 m). 3 / t dry mud). The hot water temperature is preferably not more than 98°C. The wash water obtained in the filter cake washing stage is sent to dilute the strong green liquor. The washed red mud with a moisture content of 25-30% W is re-slurryed with water returned from the mud treatment area, and then pumped to the mud treatment area in the form of slurry or filter cake.

[0030] Figure 3 A process flow diagram for the filtration and washing of thickened slurry is shown.

[0031] The initial thickened slurry used for filtration is obtained by digesting the raw material slurry. The slurry obtained after digesting the raw material slurry is diluted with wash water obtained from washing the filter cake with water. The diluted slurry undergoes thickening. During the thickening process, two products are obtained: a clear liquid and a thickened slurry. The clear liquid is sent to a safety filtration unit to remove solid particles. The thickened slurry is fed to a filter to separate and wash the solid phase. The initial thickened slurry supplied to the filter press is at a temperature of approximately 100-105°C, and the solid particle content in the slurry is 400-800 kg / m³. 3 .

[0032] The filtrate (green liquid) is sent to a liquid safety filtration unit to remove solid particles.

[0033] The red mud cake obtained during filtration is washed with water to remove the green liquor (specific water consumption is not less than 2.0 m). 3 / t dry mud). The hot water temperature is preferably not more than 98°C. The wash water obtained in the filter cake washing stage is sent to the digested slurry for dilution. The washed red mud with a moisture content of 25-30% W is re-slurryed with water returned from the mud treatment area, and then pumped to the mud treatment area in the form of slurry or filter cake. Detailed Implementation

[0034] This method is intended for the production of alumina from bauxite processing. The method includes high-speed separation and washing of the alumina production slurry obtained from bauxite digestion. Filtration of the slurry (bauxite digestion slurry, diluted slurry, or thickened slurry) is carried out using a filtration device at a temperature of at least 95°C, preferably 95-120°C. The filter cake is washed on a filter at a water temperature not exceeding 98°C, with a specific hot water consumption of at least 2.0 m³. 3 / t mud.

[0035] The specific implementation method in terms of equipment involves using the following filtration equipment: centrifuge, filter press, high-pressure filter, belt filter press.

[0036] The filtrate obtained during the slurry filtration stage is provided for additional purification operations, namely safety filtration, or directly to sedimentation. Wash water from the washing stage is used to dilute the initial slurry or the filtrate to achieve a specific concentration of green liquor. After the washing stage, the filter cake is re-slurryed and pumped to the mud treatment area, or transported in dried form to the mud treatment area for dry storage.

[0037] Therefore, the proposed method for producing alumina from bauxite provides high-speed separation and washing of the slurry, which allows for increased concentration of green liquor, reduced loss of soluble alumina and alkali, and thus improved efficiency in alumina production.

[0038] The following examples illustrate the proposed method.

[0039] Example 1

[0040] The bauxite digestion slurry was diluted with wash water from the sludge washing process on a filter. The slurry was diluted with wash water to obtain a liquid phase concentration of 160 g / L based on caustic alkali, with a liquid caustic alkali to alumina molar ratio of 1.73 (unchanged from the reference). The resulting diluted slurry was filtered at 8 atm and 105°C to obtain filtrate and filter cake. The filter cake was washed with hot water at 80°C. The amount of hot water provided for washing was sufficient to achieve a Na₂O concentration of [missing information]. 苛性碱The filtrate concentration was 160 g / L. Losses of soluble alumina and alkali were reduced by 64% by weight. The filtrate (green liquor) underwent precipitation, and liquid productivity increased by 5.0 kg / m³. 3 .

[0041] Example 2

[0042] The bauxite digestion slurry was filtered at 8 atm and 120°C to obtain filtrate and filter cake. The filter cake was washed with hot water at 98°C. The amount of hot water supplied for washing resulted in a concentration of 160 g / L in the mixture of the digested slurry filtrate and the wash water from the filter cake washing, calculated as caustic alkali, while the caustic alkali to alumina molar ratio in the liquid was 1.68 (a decrease of 0.05 units compared to the reference). The loss of soluble alumina and alkali was reduced by 69% by weight. The mixture of filtrate and wash water (green liquor) underwent precipitation, and the liquid productivity increased by 15.0 kg / m³. 3 .

[0043] Example 3

[0044] The bauxite slurry, after being digested, was diluted with wash water obtained from washing the slurry on a filter in an extrusion layer. The slurry was diluted with wash water to obtain a liquid phase concentration of 160 g / L based on caustic alkali, with a caustic alkali to alumina molar ratio of 1.68 (a decrease of 0.05 units compared to the reference). The resulting diluted slurry underwent thickening. The clarified portion was separated from the thickened portion. The resulting thickened slurry was filtered at 8 atm and 95°C to obtain a filtrate and a filter cake. The filter cake was washed with hot water at 95°C. The amount of hot water supplied for washing was [amount missing] to obtain a Na₂O [concentration missing]. 苛性碱 The concentration of the diluted slurry was 160 g / L. The molar ratio of caustic alkali to alumina in the liquid was 1.68, indicating no alumina loss due to autoprecipitation. Losses of soluble alumina and alkali were reduced by 61% by weight. The filtrate and the clarified portion from the thickened diluted slurry were combined and precipitated, resulting in a 12.4 kg / m³ increase in liquid productivity. 3 .

[0045] Example 4

[0046] The bauxite digestion slurry was diluted with wash water from the sludge washing process on a filter. The slurry was diluted with wash water to obtain a liquid concentration of 160 g / L based on caustic alkali, with a caustic alkali to alumina ratio of 1.65. The resulting diluted slurry was filtered at 6 atm and 105°C to obtain filtrate and filter cake. The filter cake was washed with hot water at 90°C. The amount of hot water supplied for washing was [amount missing] to obtain a solution of Na₂O. 苛性碱The filtrate concentration was 160 g / L. Losses of soluble alumina and alkali were reduced by 59% by weight. The filtrate (green liquor) underwent precipitation, and liquid productivity increased by 12.0 kg / m³. 3 .

[0047] Example 5

[0048] The bauxite digestion slurry was diluted with wash water from centrifugal washing of mud. The diluted slurry was used to obtain a liquid phase concentration of 160 g / L based on caustic alkali (as Na₂O), with a caustic alkali to alumina molar ratio of 1.65. The resulting diluted slurry was thickened in a thickener, during which the clarified and thickened portions were separated. The resulting thickened slurry was centrifuged at 95°C to obtain a centrifuged filtrate and a filter cake. The filter cake was washed with hot water at 95°C. The amount of hot water used for washing was sufficient to obtain a Na₂O concentration of 160 g / L. 苛性碱 The concentration of the diluted slurry was 160 g / L. The molar ratio of caustic alkali to alumina in the liquid was 1.65, indicating no alumina loss due to autoprecipitation. Losses of soluble alumina and alkali were reduced by 60% by weight. The centrifugal filtrate from the centrifuge and the clarified portion after thickening the diluted slurry were combined, filtered on a safety filter unit, and the mixture then underwent precipitation, resulting in an increase in liquid productivity of 13.5 kg / m³. 3 .

[0049] Example 6

[0050] The bauxite slurry, after digestion, was diluted with wash water from the slurry washing process on a filter in an extrusion layer. The slurry was diluted with wash water to obtain a liquid phase concentration of 160 g / L based on caustic alkali, with a caustic alkali to alumina molar ratio of 1.64 (a decrease of 0.09 units compared to the reference). The resulting diluted slurry underwent thickening. The clarified portion was separated from the thickened portion. The resulting thickened slurry was filtered at 3 atm and 95°C to obtain a filtrate and a filter cake. The filter cake was washed with hot water at 98°C. The amount of hot water supplied for washing was [amount missing] to obtain a Na₂O [concentration missing]. 苛性碱 The diluted slurry concentration was 160 g / L. The molar ratio of caustic alkali to alumina in the liquid was 1.64, indicating no alumina loss due to autoprecipitation. Losses of soluble alumina and alkali were reduced by 57% by weight. After thickening the diluted slurry, the centrifuged filtrate and clarified portion were combined and filtered on a safety filtration unit. The mixture underwent precipitation, and the liquid yield increased by 14.4 kg / m³. 3 .

[0051] Therefore, the proposed method for improving liquid productivity based on filtration and washing technologies ensures effective washing of soluble alkali and alumina in the slurry, and further improves liquid productivity by increasing their concentration and reducing the caustic alkali to alumina ratio. Consequently, the achieved liquid productivity is 5-15 kg / m³ higher than that obtained by conventional methods. 3 .

[0052] As a general example, the method includes grinding bauxite with evaporated waste liquid, digesting it, diluting the slurry from bauxite digestion, desilicates the green liquor, thickens and / or filters and washes the red mud slurry, extracting aluminum hydroxide from the green liquor, separating the aluminum hydroxide from the waste liquid, further washing and calcining the aluminum hydroxide, sintering the red mud and / or bauxite with soda and limestone, digesting the resulting sinter, thickening and / or filtering and washing the digested sintered slurry to obtain green liquor, and further desilicates and decomposes the green liquor, wherein the filtration of the red mud and the digested sintered slurry is performed immediately before or after thickening. The filtered slurry is washed directly with hot water on a filtration device, the amount of water added specifying the required concentration of the green liquor and filter cake liquid phases, the filter cake being waste, wherein the filtration is carried out at a caustic alkali to alumina ratio not less than the equilibrium green liquor caustic alkali to alumina ratio. This method allows for increased liquid production rates, reduced heat consumption from liquid evaporation, loss of aluminum hydroxide and alkali in red mud, and reduced consumption of flocculants, compressed air, and electricity. The proposed method provides for the simultaneous execution of two technical processes: slurry filtration and washing using the same equipment. In alumina production, several slurries are produced sequentially: the first is a slurry from bauxite digestion, which is diluted with wash water to obtain a diluted slurry. The diluted slurry undergoes thickening to obtain a thickened slurry. The proposed alumina production process is used depending on the type of slurry. In each alumina refinery, the concentration of the green liquor varies and depends on the maximum production rate achieved in the sedimentation zone. For example, for the liquid in the Ural alumina refinery, with Na₂O… 苛性碱 The value is estimated to be in the range of 160-170 g / L.

Claims

1. A method for processing bauxite to produce alumina, the method comprising: - The alumina process slurry obtained after bauxite digestion is filtered, wherein the slurry, after digestion, dilution or thickening, is filtered on a filtration device at a temperature of 95°C to 120°C to obtain a filtrate, wash water and solid phase of red mud representing the filtered green liquor. - The solid phase of the red mud is washed on the filtration device, wherein the washing is carried out with hot water, preferably at a temperature below 98°C, to achieve a specific concentration of green liquor and red mud liquid phase, wherein the filtered green liquor is directed to safe filtration and / or sedimentation, and the wash water after washing the red mud is supplied for diluting the bauxite digested slurry and / or diluting the filtrate to obtain a specific concentration of green liquor, wherein the resulting filter cake is waste, and wherein the filtration of the slurry and the washing of the solid phase of the red mud are carried out on the same filtration device in the direct filtration zone.

2. The method according to claim 1, wherein, The direct filtration zone replaces the conventional red mud circuit and safety filtration zone.

3. The method according to claim 1, wherein, After the bauxite is digested, the slurry is filtered, and the resulting filter cake is washed with hot water.

4. The method according to claim 1, wherein, After dilution of the slurry from bauxite digestion, the slurry is filtered, and the resulting filter cake is washed with hot water.

5. The method according to claim 1, wherein, After the diluted slurry is thickened, the thickened slurry is filtered, and the resulting filter cake is washed with hot water.

6. The method according to claim 1, wherein, The red mud is at least 2.0 m 3 Washing of red mud with hot water at specific consumption.

7. The method according to claim 1, wherein, Filter presses, centrifuges, belt filter presses, and high-pressure filters can be used for the filtration and washing of red mud.

8. The method according to claim 1, wherein, The filtrate bypasses the safety filtration and is supplied directly to the precipitate.

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