A method and system for red mud separation and washing in alumina production

Abstract

The application provides a method and system for separating and washing red mud in alumina production, which comprises the following steps: pretreating a red mud slurry to improve the filtration performance of the red mud slurry; filtering the pretreated red mud slurry under a set filtration condition to form a red mud filter cake; during the filtration process, when the thickness of the dewatered red mud filter cake reaches a set thickness, dewatering the red mud filter cake to reduce the moisture content of the dewatered red mud filter cake; performing multi-stage countercurrent washing on the dewatered red mud filter cake to obtain a countercurrent washing liquid; performing purification treatment and concentration treatment on the countercurrent washing liquid, and recycling the countercurrent washing liquid subjected to the purification treatment and concentration treatment as a washing liquid to the multi-stage countercurrent washing step. The problem of low resource recycling rate in the red mud separation and washing process in alumina production is effectively solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of metallurgy, and particularly relates to a method and system for separating and washing red mud in alumina production. BACKGROUND

[0002] In the process of alumina production, the separation and washing of red mud is one of the key links. As a solid waste produced in the process of alumina production, the red mud contains not only a large amount of recoverable alkali liquor, but also valuable metal components such as scandium and titanium. The recovery of these components is of great significance to improve resource utilization and reduce production cost.

[0003] Traditional red mud separation and washing processes usually adopt a mode of combining a settling tank with a drum vacuum filter, a plate-and-frame filter press and the like. However, these traditional processes have the following problems: low separation efficiency, poor filtration performance, low resource recovery rate and high environmental risk. In recent years, although efficient solid-liquid separation technology has been introduced, in the context of alumina red mud treatment, there are still the following problems: insufficient resource recovery and utilization rate: although the solid-liquid separation technology improves the separation efficiency, in actual application, the alkali liquor and valuable metal components in the washing liquor cannot be fully recovered, resulting in that the resource recovery and utilization rate is still low. Incomplete washing liquor treatment: the existing washing liquor treatment process cannot effectively remove suspended solids and colloidal impurities, affecting the recycling efficiency of the washing liquor. Lack of systematic and collaborative optimization: in the existing technology, there is a lack of systematic and collaborative optimization scheme for the pretreatment of red mud slurry, optimization of solid-liquid separation parameters, multi-stage countercurrent washing and recycling of washing liquor and the like, and it is difficult to realize efficient and green production of the red mud separation and washing process. SUMMARY

[0004] The present application provides a method and system for separating and washing red mud in alumina production, to solve the technical problem of how to improve the resource recovery and utilization rate of the red mud separation and washing process in alumina production.

[0005] In a first aspect, the embodiments of the present application provide a method for separating and washing red mud in alumina production, comprising:

[0006] Pretreating a red mud slurry to improve the filtration performance of the red mud slurry;

[0007] Filtering the pretreated red mud slurry under a set filtration condition to form a red mud filter cake;

[0008] During the filtration process, when the thickness of the dewatered red mud filter cake reaches a set thickness, dewatering the red mud filter cake to reduce the moisture content of the red mud filter cake;

[0009] Multi-stage countercurrent washing the dewatered red mud filter cake to obtain a countercurrent washing liquor;

[0010] The counter-current washing liquid is subjected to purification treatment and concentration treatment, and the counter-current washing liquid subjected to the purification treatment and concentration treatment is recycled as a washing liquid to the multi-stage counter-current washing step.

[0011] Optionally, the red mud slurry is subjected to pretreatment to improve the filtration performance of the red mud slurry, which comprises:

[0012] The temperature of the red mud slurry is adjusted to 60-100℃, and the pH value of the red mud slurry is adjusted to 9-13;

[0013] A dispersant is added to the red mud slurry subjected to temperature adjustment and pH value adjustment to improve the filtration performance of the red mud slurry.

[0014] Optionally, the dispersant comprises at least one of the following: sodium polyacrylate, sodium lignosulfonate, polyoxyethylene polyoxypropylene block copolymer, alkyl naphthalene sulfonate formaldehyde condensate, phenol sulfonic acid naphthalene sulfonic acid formaldehyde condensate sodium salt, polyvinyl pyrrolidone, sodium hexametaphosphate, naphthalene sulfonate formaldehyde condensate, polyacrylic acid, carboxymethyl cellulose, carboxymethyl cellulose derivative; and / or,

[0015] The mass of the dispersant is 0.01%-0.5% of the mass of the red mud slurry.

[0016] Optionally, the set filtration conditions comprise: filtration pressure of 0.1-2.0 MPa, feed flow rate of 1-50 m 3 / h, and filtration time of 5-180 min. 3

[0017] Optionally, the pressure of the dewatering is 0.1-2.5 MPa; and / or,

[0018] The moisture content of the red mud filter cake subjected to the dewatering is ≤40%.

[0019] Optionally, the red mud filter cake subjected to the dewatering is subjected to multi-stage counter-current washing to obtain a counter-current washing liquid, which comprises:

[0020] The red mud filter cake subjected to the dewatering is subjected to 4-6 stages of washing, wherein the temperature of the washing liquid of each stage of counter-current washing is 65-85℃, the time of each stage of counter-current washing is 10-20 min, and the solid-liquid mass ratio of each stage of counter-current washing is 3:1-5:1.

[0021] The washing liquid discharged from a previous stage of counter-current washing is used as the washing liquid of a subsequent stage of counter-current washing to realize multi-stage counter-current washing, and a counter-current washing liquid is obtained.

[0022] ​Optionally, the countercurrent washing liquid is subjected to a purification treatment and a concentration treatment, and the countercurrent washing liquid subjected to the purification treatment and the concentration treatment is recycled as a washing liquid to the multi-stage countercurrent washing step, comprising:

[0023] The countercurrent washing liquid is subjected to a purification treatment by ultrafiltration membrane filtration to remove suspended solids and colloidal impurities in the countercurrent washing liquid;

[0024] The countercurrent washing liquid subjected to the ultrafiltration membrane filtration is subjected to a concentration treatment by multi-effect evaporation to concentrate the countercurrent washing liquid to 20% to 30% of the initial volume;

[0025] The countercurrent washing liquid subjected to the concentration treatment is recycled as a washing liquid to the multi-stage countercurrent washing step.

[0026] Optionally, the parameters of the ultrafiltration membrane filtration include a filtration pressure of 0.055 MPa to 0.5 MPa and an ultrafiltration membrane pore size of 0.005 μm to 0.2 μm.

[0027] Optionally, the multi-effect evaporation includes 2-effect to 6-effect evaporation, wherein the first-effect evaporation includes a temperature of 90°C to 120°C and a pressure of 0.1 MPa to 0.2 MPa, and the last-effect evaporation includes a temperature of 60°C to 80°C and a pressure of 0.01 MPa to 0.05 MPa.

[0028] In a second aspect, the embodiments of the present application provide a system for separating and washing red mud in alumina production, which is used to execute the method of any one of the first aspect, comprising:

[0029] The pretreatment unit comprises a slurry storage tank, a temperature adjusting device, a pH adjusting device, a dispersant adding device, and a stirring system; the temperature adjusting device is used to adjust the temperature of the red mud slurry to a preset temperature range; the pH adjusting device is used to adjust the pH value of the red mud slurry to a preset pH range; the dispersant adding device is used to add a dispersant to the red mud slurry; and the stirring system is used to mix the dispersant and the red mud slurry;

[0030] The liquid filter unit is a chamber liquid filter, which is provided with a pressure control system, a variable frequency feeding system, a filter cake thickness monitoring device, and a pressing mechanism; the pressure control system is used to control the filtration pressure and the dewatering pressure; the variable frequency feeding system is used to control the feeding flow of the red mud slurry; the filter cake thickness monitoring device is used to monitor the thickness of the red mud filter cake; and the pressing mechanism is used to dewater the red mud filter cake;

[0031] The multi-stage countercurrent washing unit is composed of 4 to 6 washing tanks connected in series; each washing tank is provided with a temperature control device, a stirring system and a liquid level control system; the temperature control device is used to control the temperature of the washing liquid; the stirring system is used to contact the washing liquid with the red mud filter cake; and the liquid level control system is used to control the liquid level of the washing liquid;

[0032] The washing liquid treatment and circulation unit comprises an ultrafiltration membrane filtration device, a multi-effect evaporation concentration device, a liquid storage tank and a delivery pump group; the ultrafiltration membrane filtration device is used to perform ultrafiltration membrane filtration on the countercurrent washing liquid; the multi-effect evaporation concentration device is used to concentrate the countercurrent washing liquid subjected to the ultrafiltration membrane filtration; the liquid storage tank is used to store the countercurrent washing liquid subjected to the concentration treatment; and the delivery pump group is used to send the countercurrent washing liquid subjected to the concentration treatment back to the multi-stage countercurrent washing unit;

[0033] The monitoring and control system is composed of a sensor array, an industrial control computer and automatic control software; the sensor array is used to collect temperature, pressure, liquid level and pH value signals; the industrial control computer is used to receive and process the signals collected by the sensor array; and the automatic control software is used to control the operating parameters of the pretreatment unit, the liquid filter unit, the multi-stage countercurrent washing unit and the washing liquid treatment and circulation unit according to the processed signals.

[0034] Compared with the prior art, the above technical solution provided by the embodiments of the present application has the following advantages:

[0035] The embodiment of the present application provides a method for separating and washing red mud in alumina production. First, the filtration performance of the red mud slurry is improved by pretreatment, so that the subsequent filtration operation is more efficient, and the foundation for the whole separation and washing process is laid. Then, the pretreated red mud slurry is filtered under the set filtration conditions to form a red mud filter cake. When the thickness of the red mud filter cake reaches the set value, the red mud filter cake is dehydrated in time to reduce the moisture content of the red mud filter cake, which not only reduces the burden of subsequent treatment, but also improves the drying efficiency of the red mud, and provides better conditions for subsequent washing operation. The present application adopts a multi-stage countercurrent washing technology. Countercurrent washing can make the washing liquid fully contact with the red mud, maximize the recovery of valuable components such as aluminum and sodium remaining in the red mud, and reduce the amount of washing liquid. Through multi-stage countercurrent washing, the washing effect is further improved, and the recovery of valuable components is more complete. Finally, the countercurrent washing liquid is purified and concentrated to realize the recycling of the washing liquid, which not only reduces the wastewater discharge, but also reduces the production cost and improves the comprehensive utilization rate of resources. Overall, the present application optimizes each link of red mud separation and washing, from pretreatment, filtration and dehydration to multi-stage countercurrent washing and recycling of washing liquid, forming an efficient resource recycling system, effectively solving the problem of low resource recycling rate in the red mud separation and washing process in alumina production, and having significant economic and environmental benefits. BRIEF DESCRIPTION OF DRAWINGS

[0036] The accompanying drawings, which are incorporated into and form part of the specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the application.

[0037] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required in the embodiment or prior art description. Obviously, for those skilled in the art, no creative work is needed to derive other related drawings from these drawings.

[0038] Figure 1 A flowchart of a method for separating and washing red mud in alumina production provided by the embodiment of the present application. DETAILED DESCRIPTION

[0039] In order to more clearly illustrate the purpose, technical scheme and advantages of the embodiments of the present application, the technical scheme of the embodiments will be described in detail below with reference to the drawings. Please note that the mentioned embodiments are only examples, not all possible implementations. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present application.

[0040] The range descriptions described herein, such as numerical range, ratio range, etc., include all possible subranges and single values within the range, for example, the range description of "1 to 6" or "1~6" covers all subranges (such as 1 to 3, 2 to 5, etc.) and single numbers (such as 1, 2, 3, 4, 5, 6) between 1 and 6. Unless otherwise specifically stated, the terms "include", "contain" and the like used herein mean "including but not limited to"; the terms "first", "second" and the like used herein only serve to distinguish different entities or operations, and do not imply actual sequence or association; "and / or" means that multiple cases can exist independently or simultaneously; "at least one", "multiple", "at least one" and the like refer to any combination of the corresponding objects, including single or multiple combinations of the objects. The ratio relationships involved herein, such as mass ratio, molar ratio, etc., should be understood as the corresponding relationship between the front and the rear in the ratio according to the description order. The raw materials, reagents, instruments and equipment used herein can be purchased or prepared by existing methods.

[0041] Figure 1 A flow chart of a method for separating and washing red mud in alumina production provided by the embodiments of the present application.

[0042] See Figure 1 , in a first aspect, the embodiments of the present application provide a method for separating and washing red mud in alumina production, comprising:

[0043] S1, pretreating the red mud slurry to improve the filtration performance of the red mud slurry;

[0044] S2, filtering the pretreated red mud slurry under a set filtration condition to form a red mud filter cake;

[0045] S3, during the filtration process, when the thickness of the dewatered red mud filter cake reaches a set thickness, dewatering the red mud filter cake to reduce the moisture content of the red mud filter cake;

[0046] S4, multi-stage countercurrent washing the dewatered red mud filter cake to obtain a countercurrent washing liquid;

[0047] S5, purifying and concentrating the countercurrent washing liquid, and recycling the countercurrent washing liquid after the purification and concentration as a washing liquid to the multi-stage countercurrent washing step.

[0048] Red mud slurry refers to the mixture containing solid particles and liquid generated after extracting alumina from bauxite through processes such as Bayer process or sintering process in the production of alumina. Its main components include silicon dioxide, aluminum oxide, calcium oxide, iron oxide, etc. Red mud slurry is usually alkaline, with high silicon and calcium content and certain radioactivity. Pretreatment: Adjust the temperature, pH value and add dispersant to the red mud slurry to improve its filtration performance. Filtration: Make the red mud slurry pass through the filter medium to form red mud filter cake under the set process conditions (pressure, flow rate, time). Dewatering: When the red mud filter cake reaches a certain thickness, apply pressure to remove water from the red mud filter cake, reducing the moisture content. Multi-stage countercurrent washing: Use the countercurrent principle to improve the recovery rate of alkali and valuable metals through multi-stage washing process. Purification and concentration treatment: Filter and evaporate the washing liquid to remove impurities and recover valuable components for recycling. Moisture content refers to the water content in the material, usually expressed as a percentage (%). In the production of alumina, the moisture content of red mud filter cake refers to the percentage of water in the red mud filter cake.

[0049] By adjusting the temperature and pH value, and adding dispersant, the flowability of red mud slurry is improved, the viscosity is reduced, and the filtration efficiency is improved. Under the set pressure, flow rate and time, the red mud slurry passes through the filter medium to form red mud filter cake. By monitoring the thickness of the red mud filter cake in real time, dewatering is ensured at the best opportunity. When the red mud filter cake reaches the set thickness, pressure is applied for dewatering, reducing the moisture content of the red mud filter cake and improving the resource recovery rate. Using multi-stage countercurrent washing process, the alkali and valuable metal components are recovered step by step to improve the recovery rate. Impurities are removed by ultrafiltration membrane filtration, and the washing liquid is concentrated by multi-effect evaporation to realize the recycling of resources. Example:

[0050] Adjust the temperature of the red mud slurry to 70°C, the pH value to 11, and add 0.1% sodium polyacrylate.

[0051] The filtration pressure is set to 0.6 MPa, the feed flow rate is 12 m 3 / h, and the filtration time is 20 min.

[0052] The dewatering pressure is 1.0 MPa, and the moisture content of the red mud filter cake is reduced to 30%.

[0053] Four-stage countercurrent washing is adopted, with the temperature of each stage of countercurrent washing liquid being 75°C, the time being 15 min, and the solid-liquid mass ratio being 4:1.

[0054] The ultrafiltration membrane filtration pressure is 0.2 MPa, and the pore size is 0.1 μm.

[0055] The multi-effect evaporator adopts 3 effects, with the evaporation temperature of the first effect being 105°C and the pressure being 0.15 MPa; the evaporation temperature of the last effect being 75°C and the pressure being 0.03 MPa.

[0056] The temperature of the red mud slurry is adjusted to 85°C and the pH value is adjusted to 12, and 0.05% of sodium lignosulfonate is added.

[0057] The filtration pressure is set to 0.4 MPa, the feed flow rate is 8 m 3 / h, and the filtration time is 15 min.

[0058] The dewatering pressure is 0.8 MPa, and the moisture content of the red mud filter cake is reduced to 35%.

[0059] Six stages of countercurrent washing are used, and the temperature of the countercurrent washing liquid in each stage is 80°C, the time is 20 min, and the solid-liquid mass ratio is 5:1.

[0060] In some embodiments, the red mud slurry is pretreated to improve the filtration performance of the red mud slurry, including:

[0061] The temperature of the red mud slurry is adjusted to 60°C to 100°C, and the pH value of the red mud slurry is adjusted to 9 to 13;

[0062] A dispersant is added to the red mud slurry that has been temperature-adjusted and pH-adjusted to improve the filtration performance of the red mud slurry.

[0063] The temperature of the red mud slurry is adjusted to 60°C to 100°C to improve the flowability of the slurry, reduce the viscosity, and improve the filtration efficiency. The pH value of the red mud slurry is adjusted to 9 to 13 to optimize the filtration performance and reduce the chemical reactions that may occur during the filtration process. A dispersant (such as sodium polyacrylate or sodium lignosulfonate) is added to the red mud slurry to improve the filtration performance of the slurry. The dispersant improves the filtration efficiency by reducing the viscosity of the slurry and improving the dispersibility of the red mud particles. Examples:

[0064] The temperature of the red mud slurry is adjusted to 70°C, the pH value is adjusted to 11, and 0.1% of sodium polyacrylate is added.

[0065] The temperature of the red mud slurry is adjusted to 85°C, the pH value is adjusted to 12, and 0.05% of sodium lignosulfonate is added.

[0066] The temperature of the red mud slurry is adjusted to 65°C, the pH value is adjusted to 10, and 0.01% of sodium polyacrylate is added.

[0067] The temperature of the red mud slurry is adjusted to 95°C, the pH value is adjusted to 13, and 0.02% of sodium lignosulfonate is added.

[0068] The temperature of the red mud slurry is adjusted to 75°C, the pH value is adjusted to 11.5, and 0.03% of sodium polyacrylate is added.

[0069] The temperature of the red mud slurry is adjusted to 80°C, the pH value is adjusted to 12.5, and 0.04% of sodium lignosulfonate is added.

[0070] The temperature of the red mud slurry is adjusted to 60°C, the pH value to 9.5, and 0.05% of polyvinylpyrrolidone is added.

[0071] The temperature of the red mud slurry is adjusted to 100°C, the pH value to 13.5, and 0.06% of naphthalenesulfonate formaldehyde condensate is added.

[0072] The temperature of the red mud slurry is adjusted to 72°C, the pH value to 10.5, and 0.07% of polyacrylic acid is added.

[0073] The temperature of the red mud slurry is adjusted to 88°C, the pH value to 12.8, and 0.08% of methylcellulose is added.

[0074] In some embodiments, the dispersant includes at least one of: sodium polyacrylate, sodium lignosulfonate, polyoxyethylene polyoxypropylene block copolymer, alkyl naphthalene sulfonate formaldehyde condensate, naphthalenesulfonic acid formaldehyde condensate sodium salt, polyvinylpyrrolidone, sodium hexametaphosphate, naphthalenesulfonate formaldehyde condensate, polyacrylic acid, methylcellulose, methylcellulose derivatives; and / or,

[0075] The mass of the dispersant is 0.01% to 0.5% of the mass of the red mud slurry.

[0076] These dispersants, such as sodium polyacrylate or sodium lignosulfonate, work by adsorbing onto the surface of the red mud particles, reducing van der Waals forces between the particles, and improving the dispersibility of the particles. The amount of dispersant used is 0.01% to 0.5% of the mass of the red mud slurry, which ensures that the dispersant effectively improves the filtration performance of the red mud slurry while avoiding excessive use that would increase costs and potentially have negative effects. Examples:

[0077] 0.1% of sodium polyacrylate is added.

[0078] 0.05% of sodium lignosulfonate is added.

[0079] 0.01% of polyoxyethylene polyoxypropylene block copolymer is added.

[0080] 0.02% of alkyl naphthalene sulfonate formaldehyde condensate is added.

[0081] 0.03% of naphthalenesulfonic acid formaldehyde condensate sodium salt is added.

[0082] 0.04% of polyvinylpyrrolidone is added.

[0083] 0.05% of sodium hexametaphosphate is added.

[0084] 0.06% of naphthalenesulfonate formaldehyde condensate is added.

[0085] Add 0.07% polyacrylic acid.

[0086] Add 0.08% methylcellulose.

[0087] In some embodiments, the set filtration conditions include: a filtration pressure of 0.1 MPa to 2.0 MPa, a feed flow rate of 1 m 3 / h to 50 m 3 / h, and a filtration time of 5 min to 180 min.

[0088] Setting the filtration pressure in the range of 0.1 MPa to 2.0 MPa, the adjusted pressure can optimize the filtration speed, thereby improving the quality of red mud filter cake. Higher pressure can increase the flow rate of slurry through the filter medium, thereby improving the filtration efficiency. For example, at a lower pressure of 0.1 MPa to 0.5 MPa, it is suitable for thinner slurry or preliminary filtration stage; while at a higher pressure of 1.0 MPa to 2.0 MPa, it is suitable for thicker slurry or scenarios requiring rapid formation of red mud filter cake. Appropriate pressure can ensure uniform formation of red mud filter cake, reduce the porosity of red mud filter cake, and improve the compactness of red mud filter cake, thereby reducing the moisture content of red mud filter cake. Controlling the feed flow rate in the range of 1 m 3 / h to 50 m 3 / h ensures uniform entry of slurry into the filter medium, forming a uniform red mud filter cake. By controlling the feed flow rate, it ensures uniform distribution of slurry on the entire filter medium, avoiding local overload or insufficient flow. For example, a low flow rate of 1 m 3 / h to 10 m 3 / h is suitable for small-scale or fine filtration operations; while a high flow rate of 30 m 3 / h to 50 m 3 / h is suitable for large-scale production, requiring rapid formation of red mud filter cake. Uniform feed flow rate helps to form a uniform red mud filter cake, reducing the non-uniformity of red mud filter cake thickness, thereby improving filtration efficiency and red mud filter cake quality. Setting the filtration time to 5 min to 180 min, according to the characteristics of the slurry and the performance of the filtration equipment, determines the optimal filtration time to improve filtration efficiency. Shorter filtration time (such as 5 min to 30 min) is suitable for high concentration, high filtration efficiency slurry, which can quickly form red mud filter cake; while longer filtration time (such as 120 min to 180 min) is suitable for low concentration slurry, which can reduce the filtration amount of filter cloth in the plate and frame, reduce the loss, and prolong the service life of the filter cloth, thereby forming a uniform red mud filter cake. By adjusting the filtration time, it ensures that the solid particles in the slurry are fully settled to form a dense red mud filter cake, while avoiding the increase of energy consumption and the decrease of production efficiency caused by too long filtration time. Example:

[0089] The filtration pressure is set to 0.6 MPa, and the feed flow rate is 12 m 3 / h, with a filtration time of 20 min.

[0090] The filtration pressure was set at 0.4 MPa, with a feed flow of 8 m 3 / h, with a filtration time of 15 min.

[0091] The filtration pressure was set at 1.0 MPa, with a feed flow of 20 m 3 / h, with a filtration time of 30 min.

[0092] The filtration pressure was set at 0.8 MPa, with a feed flow of 15 m 3 / h, with a filtration time of 25 min.

[0093] The filtration pressure was set at 1.2 MPa, with a feed flow of 25 m 3 / h, with a filtration time of 35 min.

[0094] The filtration pressure was set at 1.5 MPa, with a feed flow of 30 m 3 / h, with a filtration time of 40 min.

[0095] The filtration pressure was set at 0.5 MPa, with a feed flow of 10 m 3 / h, with a filtration time of 18 min.

[0096] The filtration pressure was set at 1.8 MPa, with a feed flow of 35 m 3 / h, with a filtration time of 50 min.

[0097] The filtration pressure was set at 0.3 MPa, with a feed flow of 5 m 3 / h, with a filtration time of 10 min.

[0098] The filtration pressure was set at 2.0 MPa, with a feed flow of 50 m 3 / h, with a filtration time of 180 min.

[0099] In some embodiments, the pressure of the dewatering is from 0.1 MPa to 2.5 MPa; and / or,

[0100] The moisture content of the dewatered red mud filter cake is < 40%.

[0101] When the red mud cake reaches the set thickness, a pressure of 0.1 MPa to 2.5 MPa is applied for dewatering. Through the action of pressure, the moisture content of the red mud cake is reduced. The applied pressure is transmitted to the red mud cake through the pressing mechanism, so that the water in the red mud cake is squeezed out. Higher pressure can remove water more effectively, but too high pressure can cause the red mud cake to be excessively compacted, affecting subsequent processing. By adjusting the dewatering pressure, the moisture content of the red mud cake can be controlled. Specifically, a pressure of 0.1 MPa to 0.5 MPa is suitable for thinner red mud cake, which can gently remove water; while a pressure of 1.0 MPa to 2.5 MPa is suitable for thicker red mud cake, which can more thoroughly remove water. By controlling the dewatering pressure and time, the moisture content of the red mud cake is reduced to below 40%, improving the resource recovery rate. Reducing the moisture content of the red mud cake can reduce the difficulty and cost of subsequent processing, improve the recovery rate of alkali liquor and valuable metals, and reduce resource waste. Examples:

[0102] The dewatering pressure is 1.0 MPa, and the moisture content of the red mud cake is reduced to 30%.

[0103] The dewatering pressure is 0.8 MPa, and the moisture content of the red mud cake is reduced to 35%.

[0104] The dewatering pressure is 1.2 MPa, and the moisture content of the red mud cake is reduced to 32%.

[0105] The dewatering pressure is 1.5 MPa, and the moisture content of the red mud cake is reduced to 33%.

[0106] The dewatering pressure is 0.5 MPa, and the moisture content of the red mud cake is reduced to 38%.

[0107] The dewatering pressure is 2.0 MPa, and the moisture content of the red mud cake is reduced to 31%.

[0108] The dewatering pressure is 0.3 MPa, and the moisture content of the red mud cake is reduced to 39%.

[0109] The dewatering pressure is 2.5 MPa, and the moisture content of the red mud cake is reduced to 34%.

[0110] The dewatering pressure is 0.7 MPa, and the moisture content of the red mud cake is reduced to 36%.

[0111] The dewatering pressure is 1.8 MPa, and the moisture content of the red mud cake is reduced to 37%.

[0112] In some embodiments, the red mud cake subjected to the dewatering is subjected to multi-stage countercurrent washing, obtaining a countercurrent washing liquid, comprising:

[0113] The dewatered red mud filter cake is subjected to 4 to 6 stages of countercurrent washing, wherein the temperature of the washing liquid for each stage of countercurrent washing is 65 to 85°C, the time for each stage of countercurrent washing is 10 to 20 minutes, and the solid-liquid mass ratio for each stage of countercurrent washing is 3:1 to 5:1.

[0114] The washing liquid discharged from the previous stage of countercurrent washing is used as the washing liquid for the subsequent stage of countercurrent washing to achieve multi-stage countercurrent washing, thereby obtaining countercurrent washing liquid.

[0115] Through 4 to 6 stages of countercurrent washing, the alkali liquor and valuable metal components in the red mud filter cake are gradually recovered in the multi-stage washing process, which has been proven to effectively reduce the residual manganese sulfate in the red mud and improve the recovery rate. The specific operation of multi-stage countercurrent washing is as follows: first, the dewatered red mud filter cake is subjected to multi-stage washing, and the temperature of the washing liquid for each stage of countercurrent washing is controlled at 65 to 85°C, the time is 10 to 20 minutes, and the solid-liquid mass ratio is 3:1 to 5:1. The setting of these parameters ensures that the alkali liquor and valuable metal components can be fully dissolved in the washing process. The temperature range of 65 to 85°C can ensure sufficient dissolution speed while avoiding the increase in energy consumption or component decomposition that may be caused by excessively high temperature. The washing time of 10 to 20 minutes ensures sufficient contact and reaction time, and the control of the solid-liquid mass ratio ensures sufficient contact between the washing liquid and the red mud while avoiding resource waste caused by excessive liquid.

[0116] The principle of countercurrent washing is to use the washing liquid after the previous stage of washing as the washing liquid for the subsequent stage. Specifically, fresh washing liquid is used for the first stage of washing, and the washing liquid after the first stage of washing is used to wash the red mud filter cake in the second stage, and so on. Since the washing liquid from the previous stage has dissolved a certain amount of alkali liquor and valuable metal components, these components will continue to contact the red mud filter cake in the subsequent washing process, further dissolving more valuable components. This step-by-step utilization method enables the alkali liquor and valuable metal components in the washing liquid to be maximally recovered while reducing the amount of fresh washing liquid. Through multi-stage countercurrent washing, the washing liquid of each stage fully contacts the red mud filter cake, enabling the alkali liquor and valuable metal components in the red mud to be gradually dissolved and recovered in the multi-stage washing process. This countercurrent principle effectively improves resource recovery rate while reducing washing liquid consumption and production cost. In addition, countercurrent washing can effectively reduce impurity accumulation, ensuring the quality of the washing liquid and further enhancing resource recovery effect. Example:

[0117] 4 stages of countercurrent washing are adopted, and the temperature of the washing liquid for each stage of countercurrent washing is 75°C, the time is 15 minutes, and the solid-liquid mass ratio is 4:1.

[0118] 5 stages of countercurrent washing are adopted, and the temperature of the washing liquid for each stage of countercurrent washing is 80°C, the time is 20 minutes, and the solid-liquid mass ratio is 5:1.

[0119] The 6-stage countercurrent washing is adopted, the temperature of each stage of countercurrent washing liquid is 70°C, the time is 10 min, and the solid-liquid mass ratio is 3:1.

[0120] The 4-stage countercurrent washing is adopted, the temperature of each stage of countercurrent washing liquid is 85°C, the time is 18 min, and the solid-liquid mass ratio is 4:1.

[0121] The 5-stage countercurrent washing is adopted, the temperature of each stage of countercurrent washing liquid is 72°C, the time is 12 min, and the solid-liquid mass ratio is 3:1.

[0122] The 6-stage countercurrent washing is adopted, the temperature of each stage of countercurrent washing liquid is 82°C, the time is 16 min, and the solid-liquid mass ratio is 5:1.

[0123] The 4-stage countercurrent washing is adopted, the temperature of each stage of countercurrent washing liquid is 78°C, the time is 14 min, and the solid-liquid mass ratio is 4:1.

[0124] The 5-stage countercurrent washing is adopted, the temperature of each stage of countercurrent washing liquid is 83°C, the time is 19 min, and the solid-liquid mass ratio is 5:1.

[0125] The 6-stage countercurrent washing is adopted, the temperature of each stage of countercurrent washing liquid is 73°C, the time is 11 min, and the solid-liquid mass ratio is 3:1.

[0126] The 4-stage countercurrent washing is adopted, the temperature of each stage of countercurrent washing liquid is 84°C, the time is 17 min, and the solid-liquid mass ratio is 4:1.

[0127] In some embodiments, the multi-stage countercurrent washing comprises 4 to 6 stages of countercurrent washing.

[0128] The first stage of countercurrent washing uses fresh washing liquid to wash the red mud filter cake, which has the highest concentration of residual alkali and valuable metal components. Fresh washing liquid can maximize the dissolution of these components. In the countercurrent washing process, fresh washing liquid is first used to wash the red mud filter cake, which has the highest concentration of residual alkali and valuable metal components. According to relevant research, the use of five-stage countercurrent leaching can maximize the dissolution of these components, achieving comprehensive utilization of red mud and alkali. The washing liquid after the first stage flows into the second stage to wash the red mud filter cake in the second stage. Since the washing liquid has already dissolved a certain amount of alkali and valuable metal components, these components will continue to contact and dissolve with the residual components in the red mud filter cake during the second stage of washing. By analogy, the washing liquid of each stage carries the dissolved components of the previous stage, and the valuable components in the red mud filter cake are recovered step by step. Through four to six stages of countercurrent washing, the alkali and valuable metal components in the red mud filter cake are gradually recovered in the multi-stage washing process. Through four to six stages of countercurrent washing, the alkali and valuable metal components in the red mud filter cake are gradually recovered in the multi-stage washing process, which has been proven to effectively reduce the residual manganese sulfate in the red mud and improve the recovery rate. This countercurrent principle keeps the concentration gradient of the components in the washing liquid at a high level, thereby maximizing the recovery efficiency.

[0129] Example: The multi-stage countercurrent washing includes four, five, and six stages of countercurrent washing.

[0130] In some embodiments, the countercurrent washing liquid is subjected to purification treatment and concentration treatment, and the countercurrent washing liquid subjected to the purification treatment and concentration treatment is recycled as washing liquid to the multi-stage countercurrent washing step, comprising:

[0131] The countercurrent washing liquid is subjected to purification treatment by ultrafiltration membrane filtration to remove suspended solids and colloidal impurities in the countercurrent washing liquid;

[0132] The countercurrent washing liquid subjected to the ultrafiltration membrane filtration is subjected to concentration treatment by multiple-effect evaporation to concentrate the countercurrent washing liquid to 20% to 30% of the initial volume;

[0133] The countercurrent washing liquid subjected to the concentration treatment is recycled to the multi-stage countercurrent washing step.

[0134] Ultrafiltration membrane: GE Water, Model: UF-1000. Multiple-effect evaporator: SPX Flow, Model: EV-2000.

[0135] Ultrafiltration membrane filtration is a key step in achieving purification of the countercurrent washing liquid. Ultrafiltration membrane filtration technology not only optimizes the quality of the washing liquid, but also effectively reduces the mixing of impurities in subsequent processing, ensuring smooth operation of the entire process.

[0136] Multi-effect evaporation concentration utilizes the secondary steam generated in the previous effect as a heat source through multi-effect evaporators, achieving multi-stage utilization of thermal energy, thereby significantly improving energy utilization and reducing energy consumption. This process concentrates the filtered countercurrent scrubbing liquid to 20-30% of the initial volume, effectively reducing steam consumption, saving energy, and achieving significant economic benefits. The core of multi-effect evaporation lies in its efficient energy utilization method. Through the series operation of multiple evaporators, the steam of the previous effect is used as the heat source of the next effect, thereby achieving step-by-step utilization of energy, significantly improving evaporation efficiency, and reducing energy consumption. Multi-effect evaporation concentration not only reduces the volume of the scrubbing liquid and increases its concentration, but also creates conditions for the recycling of the scrubbing liquid. The concentration of alkali and valuable metal components in the concentrated scrubbing liquid is significantly increased, which not only improves the resource recovery efficiency, but also reduces the difficulty and cost of subsequent processing.

[0137] Recycling is one of the innovations of the present application. The concentrated countercurrent scrubbing liquid is returned to the multi-stage countercurrent scrubbing process, realizing the recycling of the scrubbing liquid. This process not only reduces the amount of fresh water used and reduces production costs, but also reduces wastewater discharge and is environmentally friendly. Through recycling, the alkali and valuable metal components in the scrubbing liquid can be recycled multiple times, further improving the resource recovery rate. At the same time, recycling reduces the dependence on fresh scrubbing liquid, reducing water resource consumption and wastewater treatment costs during production.

[0138] In some embodiments, the parameters of the ultrafiltration membrane filtration include a filtration pressure of 0.055 MPa to 0.5 MPa and an ultrafiltration membrane pore size of 0.005 μm to 0.2 μm.

[0139] The pore size of the ultrafiltration membrane ranges from 0.005 μm to 0.2 μm, which can effectively remove suspended solids and colloidal impurities in the scrubbing liquid. If these impurities are not removed, they may cause scaling, clogging, and other problems during subsequent evaporation concentration, affecting the normal operation and service life of the equipment. Through the physical screening action of the ultrafiltration membrane, the clarity of the scrubbing liquid is significantly improved, creating good conditions for subsequent evaporation concentration. During the filtration process, the filtration pressure is controlled within the range of 0.055 MPa to 0.5 MPa, which can ensure the filtration efficiency and avoid damage to the membrane caused by excessive pressure.

[0140] In some embodiments, the multi-effect evaporation includes 2 to 6 effects, wherein the first effect evaporation includes a temperature of 90-120°C and a pressure of 0.1-0.2 MPa, and the last effect evaporation includes a temperature of 60-80°C and a pressure of 0.01-0.05 MPa.

[0141] By 2 to 6 effect multi-effect evaporation, each evaporator utilizes the secondary steam generated by the previous stage, reducing the consumption of fresh steam, significantly improving the evaporation efficiency and reducing energy consumption. The first-stage evaporation temperature is 90-120°C, and the pressure is 0.1-0.2 MPa. The first-stage evaporation is the initial stage of the entire multi-effect evaporation process, using fresh steam as the heat source, through high-temperature and high-pressure evaporation, the washing liquid is preliminarily concentrated. High-temperature and high-pressure conditions can quickly evaporate the water in the washing liquid, while generating a large amount of secondary steam to provide heat for the subsequent evaporator. The last-stage evaporation temperature is 60-80°C, and the pressure is 0.01-0.05 MPa. The last-stage evaporation is the final stage of the multi-effect evaporation process, through low-temperature and low-pressure evaporation, the washing liquid is further concentrated. Low-temperature and low-pressure conditions can effectively utilize the secondary steam generated by the previous stage, reducing energy consumption, while avoiding the decomposition of components or increasing energy consumption caused by high temperature and high pressure. Example:

[0142] The ultrafiltration membrane filtration pressure is 0.2 MPa, the pore size is 0.1 μm, and the multi-effect evaporator adopts 3 effects. The first-stage evaporation temperature is 105°C, and the pressure is 0.15 MPa. The last-stage evaporation temperature is 75°C, and the pressure is 0.03 MPa.

[0143] The ultrafiltration membrane filtration pressure is 0.1 MPa, the pore size is 0.05 μm, and the multi-effect evaporator adopts 4 effects. The first-stage evaporation temperature is 110°C, and the pressure is 0.18 MPa. The last-stage evaporation temperature is 70°C, and the pressure is 0.02 MPa.

[0144] The ultrafiltration membrane filtration pressure is 0.3 MPa, the pore size is 0.15 μm, and the multi-effect evaporator adopts 5 effects. The first-stage evaporation temperature is 115°C, and the pressure is 0.2 MPa. The last-stage evaporation temperature is 72°C, and the pressure is 0.04 MPa.

[0145] The ultrafiltration membrane filtration pressure is 0.4 MPa, the pore size is 0.2 μm, and the multi-effect evaporator adopts 6 effects. The first-stage evaporation temperature is 120°C, and the pressure is 0.22 MPa. The last-stage evaporation temperature is 78°C, and the pressure is 0.05 MPa.

[0146] The ultrafiltration membrane filtration pressure is 0.15 MPa, the pore size is 0.08 μm, and the multi-effect evaporator adopts 3 effects. The first-stage evaporation temperature is 100°C, and the pressure is 0.12 MPa. The last-stage evaporation temperature is 68°C, and the pressure is 0.01 MPa.

[0147] The ultrafiltration membrane filtration pressure is 0.25 MPa, the pore size is 0.12 μm, and the multi-effect evaporator adopts 4 effects. The first-stage evaporation temperature is 108°C, and the pressure is 0.16 MPa. The last-stage evaporation temperature is 74°C, and the pressure is 0.03 MPa.

[0148] The ultrafiltration membrane filtering pressure is 0.35 MPa, the pore size is 0.18 μm, the multi-effect evaporator adopts 5 effects, the evaporation temperature of the first effect is 112 ℃, and the pressure is 0.19 MPa; the evaporation temperature of the last effect is 76 ℃, and the pressure is 0.04 MPa.

[0149] The ultrafiltration membrane filtering pressure is 0.45 MPa, the pore size is 0.22 μm, the multi-effect evaporator adopts 6 effects, the evaporation temperature of the first effect is 118 ℃, and the pressure is 0.23 MPa; the evaporation temperature of the last effect is 80 ℃, and the pressure is 0.05 MPa.

[0150] The ultrafiltration membrane filtering pressure is 0.05 MPa, the pore size is 0.02 μm, the multi-effect evaporator adopts 2 effects, the evaporation temperature of the first effect is 90 ℃, and the pressure is 0.1 MPa; the evaporation temperature of the last effect is 60 ℃, and the pressure is 0.01 MPa.

[0151] The ultrafiltration membrane filtering pressure is 0.5 MPa, the pore size is 0.25 μm, the multi-effect evaporator adopts 6 effects, the evaporation temperature of the first effect is 120 ℃, and the pressure is 0.25 MPa; the evaporation temperature of the last effect is 80 ℃, and the pressure is 0.05 MPa.

[0152] In a second aspect, the embodiments of the present application provide a system for separating and washing red mud in alumina production, which is used to execute the method of any one of the first aspect, and comprises:

[0153] The pretreatment unit comprises a slurry storage tank, a temperature adjusting device, a pH adjusting device, a dispersant adding device and a stirring system; the temperature adjusting device is used to adjust the temperature of the red mud slurry to a preset temperature range; the pH adjusting device is used to adjust the pH value of the red mud slurry to a preset pH range; the dispersant adding device is used to add a dispersant to the red mud slurry; and the stirring system is used to mix the dispersant with the red mud slurry.

[0154] The liquid filter unit is a chamber type liquid filter, which is provided with a pressure control system, a variable frequency feeding system, a filter cake thickness monitoring device and a squeezing mechanism; the pressure control system is used to control the filtering pressure and the dewatering pressure; the variable frequency feeding system is used to control the feeding flow of the red mud slurry; the filter cake thickness monitoring device is used to monitor the thickness of the red mud filter cake; and the squeezing mechanism is used to dewater the red mud filter cake.

[0155] The multi-stage countercurrent washing unit is composed of 4 to 6 washing tanks connected in series; each washing tank is provided with a temperature control device, a stirring system and a liquid level control system; the temperature control device is used to control the temperature of the washing liquid; the stirring system is used to contact the washing liquid with the red mud filter cake; and the liquid level control system is used to control the liquid level of the washing liquid.

[0156] The washing liquid treatment and circulation unit comprises an ultrafiltration membrane filtering device, a multi-effect evaporation concentration device, a liquid storage tank and a delivery pump group; the ultrafiltration membrane filtering device is used for ultrafiltration membrane filtering of the countercurrent washing liquid; the multi-effect evaporation concentration device is used for concentrating the countercurrent washing liquid filtered by the ultrafiltration membrane; the liquid storage tank is used for storing the countercurrent washing liquid subjected to concentration treatment; and the delivery pump group is used for sending the countercurrent washing liquid subjected to concentration treatment back to the multi-stage countercurrent washing unit.

[0157] The monitoring and control system comprises a sensor array, an industrial control computer and automatic control software; the sensor array is used for collecting temperature, pressure, liquid level and pH value signals; the industrial control computer is used for receiving and processing the signals collected by the sensor array; and the automatic control software is used for controlling the operation parameters of the pretreatment unit, the liquid filter unit, the multi-stage countercurrent washing unit and the washing liquid treatment and circulation unit according to the processed signals.

[0158] The application will be further described in conjunction with specific examples. It should be understood that these examples are only used to illustrate the application and not used to limit the scope of the application. The experimental methods not specified in the following examples are generally determined according to the industry standards. If there is no corresponding industry standard, the general international standards, conventional conditions or the conditions suggested by the manufacturers are used.

[0159] Example 1

[0160] The dewatered red mud filter cake is subjected to 4-stage countercurrent washing.

[0161] The temperature of the washing liquid of each stage is maintained at 75℃, and the washing time is 15 min.

[0162] The solid-liquid mass ratio is controlled to be 4:1, so as to ensure that the washing liquid and the red mud filter cake are fully contacted.

[0163] The washing liquid after the washing of the previous stage is used as the washing liquid of the next stage, so as to realize countercurrent washing.

[0164] Example 2

[0165] The dewatered red mud filter cake is subjected to 5-stage countercurrent washing.

[0166] The temperature of the washing liquid of each stage is maintained at 80℃, and the washing time is 18 min.

[0167] The solid-liquid mass ratio is controlled to be 5:1, so as to ensure that the washing liquid and the red mud filter cake are fully contacted.

[0168] The washing liquid after the washing of the previous stage is used as the washing liquid of the next stage, so as to realize countercurrent washing.

[0169] Example 3

[0170] The dewatered red mud filter cake is subjected to 6 stages of countercurrent washing.

[0171] The temperature of the countercurrent washing liquid is maintained at 85°C, and the washing time is 20 min.

[0172] The solid-liquid mass ratio is controlled to be 3:1, so as to ensure that the washing liquid fully contacts the red mud filter cake.

[0173] The washing liquid after the previous stage of washing is used as the washing liquid for the next stage, so as to realize countercurrent washing.

[0174] Example 4

[0175] The dewatered red mud filter cake is subjected to 4 stages of countercurrent washing.

[0176] The temperature of the countercurrent washing liquid is maintained at 65°C, and the washing time is 10 min.

[0177] The solid-liquid mass ratio is controlled to be 5:1, so as to ensure that the washing liquid fully contacts the red mud filter cake.

[0178] The washing liquid after the previous stage of washing is used as the washing liquid for the next stage, so as to realize countercurrent washing.

[0179] Example 5

[0180] The dewatered red mud filter cake is subjected to 5 stages of countercurrent washing.

[0181] The temperature of the countercurrent washing liquid is maintained at 70°C, and the washing time is 12 min.

[0182] The solid-liquid mass ratio is controlled to be 4:1, so as to ensure that the washing liquid fully contacts the red mud filter cake.

[0183] The washing liquid after the previous stage of washing is used as the washing liquid for the next stage, so as to realize countercurrent washing.

[0184] Example 6

[0185] The dewatered red mud filter cake is subjected to 6 stages of countercurrent washing.

[0186] The temperature of the countercurrent washing liquid is maintained at 80°C, and the washing time is 15 min.

[0187] The solid-liquid mass ratio is controlled to be 3:1, so as to ensure that the washing liquid fully contacts the red mud filter cake.

[0188] The washing liquid after the previous stage of washing is used as the washing liquid for the next stage, so as to realize countercurrent washing.

[0189] Comparative Example 1

[0190] The dewatered red mud filter cake is subjected to single-stage washing.

[0191] The temperature of the washing liquid is maintained at 75°C, and the washing time is 15 min.

[0192] The solid-liquid mass ratio is controlled to be 4:1, ensuring that the washing liquid fully contacts the red mud filter cake.

[0193] Comparative Example 2

[0194] The dewatered red mud filter cake is subjected to single-stage washing.

[0195] The temperature of the washing liquid is maintained at 80°C, and the washing time is 20 min.

[0196] The solid-liquid mass ratio is controlled to be 5:1, ensuring that the washing liquid fully contacts the red mud filter cake.

[0197] Comparative Example 3

[0198] The dewatered red mud filter cake is subjected to single-stage washing.

[0199] The temperature of the washing liquid is maintained at 65°C, and the washing time is 10 min.

[0200] The solid-liquid mass ratio is controlled to be 3:1, ensuring that the washing liquid fully contacts the red mud filter cake.

[0201] Effect data: The effect data in Examples 1 to 6 and Comparative Examples 1 to 3 are shown in Table 1.

[0202] Experimental method for effect data:

[0203] 1. Alkali liquor recovery rate determination:

[0204] The concentration of alkali liquor in the washing liquid is determined by a chemical analysis method, and the alkali liquor recovery rate is calculated. Formula:

[0205]

[0206] 2. Valuable metal recovery rate determination: The concentration of valuable metals (such as scandium and titanium) in the washing liquid is determined by a spectral analysis method, and the valuable metal recovery rate is calculated. Formula:

[0207]

[0208] 3. Red mud filter cake moisture content determination: The moisture content of the red mud filter cake is determined by a drying method. Formula:

[0209]

[0210] Table 1

[0211]

[0212] Through the above effect data table, the differences between different embodiments and comparative examples can be intuitively compared. The following conclusions can be drawn:

[0213] Lye recovery rate: The lye recovery rates of examples 1 to 6 are all above 95%, with the highest reaching 98%, while the lye recovery rates of comparative examples 1 to 3 are all below 90%, with the highest only being 86%. This shows that the multi-stage countercurrent washing process of the present application can significantly improve the recovery efficiency of lye.

[0214] Valuable metal recovery rate: The valuable metal recovery rates of examples 1 to 6 are between 22% and 30%, while the valuable metal recovery rates of comparative examples 1 to 3 are all below 20%, with the highest only being 16%. This shows that the multi-stage countercurrent washing process of the present application also has a significant advantage in recovering valuable metals.

[0215] Red mud filter cake moisture content: The red mud filter cake moisture contents of examples 1 to 6 are all below 30%, with the lowest reaching 25%, while the red mud filter cake moisture contents of comparative examples 1 to 3 are all above 33%, with the highest reaching 36%. This shows that the multi-stage countercurrent washing process of the present application can effectively reduce the moisture content of red mud filter cake and improve resource recovery rate.

[0216] Examples 1 to 6 successfully achieved differentiated control of recovery rate and moisture content by fine-tuning the number of stages, washing liquid temperature, time, and solid-liquid mass ratio of multi-stage countercurrent washing. For example, example 3 (6-stage countercurrent washing, 85°C, 20min, solid-liquid mass ratio 3:1) has the highest lye recovery rate (98%), the highest valuable metal recovery rate (30%), and the lowest red mud filter cake moisture content (25%), indicating that the process is best under these conditions. In contrast, comparative examples 1 to 3 lack the multi-stage recovery advantage of countercurrent washing due to the use of single-stage washing process, resulting in low resource recovery efficiency and high red mud filter cake moisture content, thus again proving the excellent performance of the multi-stage countercurrent washing process of the present application.

[0217] Examples 1 to 6 not only improved resource recovery rate, but also significantly reduced the moisture content of red mud filter cake, reducing the cost and environmental risk of subsequent processing. For example, example 6 (6-stage countercurrent washing, 80°C, 15min, solid-liquid mass ratio 3:1) has a good overall effect, with a lye recovery rate of 97%, a valuable metal recovery rate of 26%, and a red mud filter cake moisture content of 26%, achieving a good balance between resource recovery and cost efficiency. Comparative examples 1 to 3 have low resource recovery rate and high red mud filter cake moisture content, not only increasing the difficulty and cost of subsequent processing, but also possibly leading to resource waste and increased environmental risk.

[0218] In summary, the multi-stage countercurrent washing process provided by the embodiments of the present application can significantly improve the recovery rate of lye and valuable metals, while reducing the moisture content of the red mud filter cake, and reducing the cost and environmental risk of subsequent processing, by optimizing parameters such as washing liquid temperature, washing time and solid-liquid mass ratio.

[0219] The above description is merely that of the embodiments of the application, so that those skilled in the art can understand or implement the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to these embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for separating and washing red mud produced from alumina, characterized in that, The method includes: The red mud slurry is pretreated to improve its filtration performance. The pretreated red mud slurry is filtered under set filtration conditions to form a red mud filter cake; During the filtration process, when the thickness of the red mud filter cake reaches a set thickness, the red mud filter cake is dehydrated to reduce the moisture content of the dehydrated red mud filter cake; the moisture content of the dehydrated red mud filter cake is ≤40%. The dehydrated red mud filter cake is subjected to multi-stage countercurrent washing to obtain countercurrent washing liquid; The countercurrent washing liquid is purified and concentrated, so that the purified and concentrated countercurrent washing liquid is returned to the multi-stage countercurrent washing step for recycling. The pretreatment of the red mud slurry to improve its filtration performance includes: The temperature of the red mud slurry is adjusted to 60°C to 100°C, and the pH value of the red mud slurry is adjusted to 9 to 13. A dispersant is added to the red mud slurry after temperature and pH adjustment to improve the filtration performance of the red mud slurry; The dispersant comprises at least one of the following: sodium polyacrylate, sodium lignosulfonate, polyoxyethylene-polyoxypropylene block copolymer, alkyl naphthalene sulfonate formaldehyde condensate, sodium salt of phenol sulfonate naphthalene sulfonate formaldehyde condensate, polyvinylpyrrolidone, sodium hexametaphosphate, naphthalene sulfonate formaldehyde condensate, polyacrylic acid, carboxymethyl cellulose, and carboxymethyl cellulose derivatives. The mass of the dispersant is 0.01% to 0.5% of the mass of the red mud slurry; The process of performing multi-stage countercurrent washing on the dehydrated red mud filter cake to obtain a countercurrent washing solution includes: The dehydrated red mud filter cake is subjected to 4 to 6 stages of washing, wherein the temperature of the washing liquid in each countercurrent washing stage is 65°C to 85°C, the time of each countercurrent washing stage is 10 min to 20 min, and the solid-liquid mass ratio of each countercurrent washing stage is 3:1 to 5:

1. The washing liquid discharged from the previous stage of countercurrent washing is used as the washing liquid for the next stage of countercurrent washing to achieve multi-stage countercurrent washing and obtain countercurrent washing liquid.

2. The method according to claim 1, characterized in that, The set filtration conditions include: filtration pressure of 0.1 MPa to 2.0 MPa, and feed flow rate of 1 m³ / min. 3 / h to 50m 3 / h, filtration time is 5min to 180min; The dehydration pressure is from 0.1 MPa to 2.5 MPa.

3. The method according to claim 1, characterized in that, The purification and concentration of the countercurrent washing liquid, so that the purified and concentrated countercurrent washing liquid is returned to the multi-stage countercurrent washing step for recycling, includes: The countercurrent washing liquid is purified by ultrafiltration membrane filtration to remove suspended solids and colloidal impurities. Multi-effect evaporation is used to concentrate the countercurrent washing liquid filtered through the ultrafiltration membrane to 20% to 30% of its initial volume. The concentrated countercurrent washing liquid is returned to the multi-stage countercurrent washing step for recycling.

4. The method according to claim 3, characterized in that, The parameters for ultrafiltration membrane filtration include: a filtration pressure of 0.055 MPa to 0.5 MPa and an ultrafiltration membrane pore size of 0.005 μm to 0.2 μm.

5. The method according to claim 3, characterized in that, The multi-effect evaporation includes 2 to 6 effects, wherein the first effect evaporation includes the following parameters: temperature of 90°C to 120°C and pressure of 0.1 MPa to 0.2 MPa, and the last effect evaporation includes the following parameters: temperature of 60°C to 80°C and pressure of 0.01 MPa to 0.05 MPa.

6. A system for separating and washing red mud produced from alumina, used to perform the method according to any one of claims 1 to 5, characterized in that, include: Pretreatment unit: The pretreatment unit includes a slurry storage tank, a temperature control device, a pH control device, a dispersant addition device, and a stirring system; The temperature regulating device is used to regulate the temperature of the red mud slurry to a preset temperature range; the pH regulating device is used to regulate the pH value of the red mud slurry to a preset pH range; the dispersant adding device is used to add a dispersant to the red mud slurry; the stirring system is used to mix the dispersant with the red mud slurry. Liquid filtration unit: The liquid filtration unit is a chamber-type liquid filtration unit, which is equipped with a pressure control system, a variable frequency feeding system, a filter cake thickness monitoring device, and a pressing mechanism; the pressure control system is used to control the filtration pressure and dewatering pressure; the variable frequency feeding system is used to control the feed flow rate of the red mud slurry; The filter cake thickness monitoring device is used to monitor the thickness of the red mud filter cake; the pressing mechanism is used to dehydrate the red mud filter cake. Multi-stage countercurrent washing unit: The multi-stage countercurrent washing unit consists of 4 to 6 washing tanks connected in series; each washing tank is equipped with a temperature control device, a stirring system and a liquid level control system; the temperature control device is used to control the temperature of the washing liquid; the stirring system is used to bring the washing liquid into contact with the red mud filter cake; the liquid level control system is used to control the liquid level of the washing liquid. Washing liquid treatment and circulation unit: The washing liquid treatment and circulation unit includes an ultrafiltration membrane filtration device, a multi-effect evaporation and concentration device, a storage tank, and a transfer pump set; the ultrafiltration membrane filtration device is used to filter the countercurrent washing liquid using ultrafiltration membrane; the multi-effect evaporation and concentration device is used to concentrate the countercurrent washing liquid after ultrafiltration membrane filtration; the storage tank is used to store the concentrated countercurrent washing liquid; the transfer pump set is used to send the concentrated countercurrent washing liquid back to the multi-stage countercurrent washing unit; Monitoring and Control System: The monitoring and control system consists of a sensor array, an industrial control computer, and automated control software; the sensor array is used to collect temperature, pressure, liquid level, and pH signals; the industrial control computer is used to receive and process the signals collected by the sensor array; the automated control software is used to control the operating parameters of the pretreatment unit, liquid filter unit, multi-stage countercurrent washing unit, and washing liquid treatment and circulation unit according to the processed signals.

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