A method and system for dewatering red mud based on coupling of solid waste filter aid and gradient pressure filtration

Abstract

The present application relates to a kind of bauxite residue solid waste treatment technical field, especially in kind based on solid waste filter aid and gradient filter pressing coupling bauxite dewatering method and system.The dewatering method includes the following steps: pretreatment is carried out to bauxite, adjust bauxite slurry pH value;Industrial solid waste is crushed, calcined, pulverized and made into solid waste base material, and the solid waste base material is compounded with chemical filter aid to make composite solid waste filter aid;Pretreated bauxite slurry is mixed with composite solid waste filter aid evenly;Gradient filter pressing is carried out to the mixed material, and the gradient filter pressing at least includes filter pressing initial stage, filter pressing middle stage and filter pressing later stage, and the pressure applied in each stage is successively increased, and filter cake and filtrate are obtained after filter pressing;The filter cake after filter pressing is dried, and dewatered bauxite is obtained.The method can realize the efficient, energy-saving removal of bauxite moisture, and provide technical support for subsequent resource utilization of bauxite.

Description

Technical Field

[0001] This invention relates to the field of red mud solid waste treatment technology, and in particular to a red mud dewatering method and system based on the coupling of solid waste filtration aid and gradient pressure filtration. Background Technology

[0002] Red mud is a major industrial solid waste generated during alumina production. Its dewatering treatment is a crucial preliminary step for its subsequent resource utilization. The core principle is to remove free and bound water from the red mud through a combination of physical and chemical methods, reducing its moisture content to meet the requirements for resource utilization in red mud-based cementitious materials and road engineering materials. The working principle of the red mud dewatering method involves first pre-treating the red mud slurry to remove impurities and adjust its state; then adding filter aids to improve its filtration characteristics; subsequently, a filter press removes most of the water to form a filter cake; and finally, a drying device deeply dries the filter cake, completing the overall red mud dewatering process.

[0003] Currently, commercially available red mud dewatering systems mainly consist of a pretreatment unit, a filter aid unit, a filter press unit, and a drying unit, all connected by pipelines. The pretreatment unit primarily removes large impurities from the red mud slurry and adjusts the pH level. The filter aid unit is typically an independent feeding tank, delivering the filter aid to the feed end of the pretreatment unit or filter press unit via pipelines. The filter press unit uses a single, constant pressure to filter the red mud slurry, allowing water to pass through the filter cloth to form filtrate, while solid particles are retained to form a filter cake. The drying unit uses a conventional hot air drying structure to dry the filter cake after filter pressing at high temperatures, further reducing the moisture content of the red mud. In actual operation, the red mud slurry is first fed into the pretreatment unit to remove large impurities and adjust its basic state. Then, a filter aid is added in proportion, and the mixed slurry is fed into the filter press unit for filtration. The resulting filter cake is then dried in the drying unit, ultimately yielding dewatered red mud.

[0004] Existing red mud dewatering methods have revealed numerous technical problems in practical applications: First, existing filtration processes all employ a single-pressure filtration mode, requiring frequent changes and increasing equipment maintenance costs. If the pressure is too high in the initial stages of filtration, fine red mud particles can clog the filter cloth, causing filtration channel failure. If the pressure is insufficient in the later stages, bound water within the red mud particles cannot be effectively removed, resulting in a persistently high moisture content in the filter cake, failing to meet the requirements for red mud resource utilization. Furthermore, while some existing technologies attempt to use solid waste for red mud filtration or employ gradient filtration, these standalone solid waste filtration technologies lack coupling design with the filtration process. The pore structure of the filter aid cannot be fully utilized, and filter cake clogging remains. Separate gradient filtration technologies, without the synergistic effect of solid waste filtration, cannot fundamentally improve the filtration characteristics of red mud particles, resulting in limited improvement in dewatering efficiency.

[0005] Secondly, there are obvious defects in the selection and addition of filter aids. Existing methods mostly use traditional chemical filter aids such as single polyaluminum chloride and polyacrylamide. These filter aids not only have poor mixing uniformity with red mud slurry, making it difficult to fully exert the filter aid effect, but also easily introduce secondary pollution. At the same time, existing methods lack targeted filter aid preparation, which cannot realize the resource utilization of industrial solid waste and increases the cost of using filter aids.

[0006] Secondly, the lack of coordinated design means that the pretreatment, filtration, filtration, and drying units operate independently without a unified parameter control and linkage mechanism. Uneven mixing of the filter aid and red mud slurry directly affects the subsequent filtration efficiency. Uneven distribution of filter cake thickness during filtration leads to fluctuations in dewatering efficiency, and the energy of filtration and drying cannot be effectively linked, resulting in significant heat energy waste and high overall energy consumption. Furthermore, the hot air generated during drying is directly discharged, resulting in low energy utilization. Summary of the Invention

[0007] This invention aims to solve the technical problems of existing red mud dewatering methods, such as the high cost and secondary pollution caused by filter aids, low filtration efficiency leading to high filter cake moisture content, inability to utilize solid waste as a resource, lack of coordination between steps resulting in energy waste, and poor equipment adaptability and maintainability. It also addresses the problems of poor coupling and limited dewatering effect in existing solid waste filtration aid and gradient filtration related improvement technologies. Therefore, it provides a highly efficient red mud dewatering method with high dewatering efficiency, low energy consumption, no secondary pollution, and the ability to realize solid waste resource utilization, as well as strong coordination and wide adaptability, to meet the industrial needs of large-scale resource utilization of red mud.

[0008] To achieve the above objectives, the embodiments of the present invention provide the following technical solutions: A red mud dewatering method based on the coupling of solid waste filtration aid and gradient pressure filtration includes the following steps: Pre-treatment of red mud involves adjusting the pH value of the red mud slurry. Industrial solid waste is crushed, calcined, and pulverized to produce solid waste base material, which is then compounded with chemical filter aids to produce composite solid waste filter aids. The pretreated red mud slurry was mixed evenly with the composite solid waste filter aid. The mixed materials are subjected to gradient filtration, which includes at least an initial stage, a middle stage and a later stage of filtration, with the pressure applied in each stage increasing sequentially. After filtration, filter cake and filtrate are obtained. The filter cake after pressure filtration is dried to obtain dehydrated red mud.

[0009] Further, the pretreatment steps include: stirring the red mud evenly, and then adding a pH adjuster to adjust the pH value to 8.5-10.5.

[0010] Furthermore, the pH adjuster is a compound system of sodium bicarbonate and potassium dihydrogen phosphate, with a mass ratio of 2-3:1, and the amount added is 0.5-1.2 wt% of the dry weight of red mud.

[0011] Furthermore, the preparation steps of the composite solid waste filter aid include: crushing industrial solid waste to a particle size of no more than 20 mm, calcining it at 800-900℃ for 2-3 hours, cooling it and then pulverizing it to a particle size of no more than 100 mesh to obtain solid waste base material; and compounding the solid waste base material with polyaluminum chloride and sodium carboxymethyl cellulose at a mass ratio of 8-12:3-5:1.

[0012] Furthermore, the industrial solid waste is one or a mixture of two of fly ash and slag, and the amount of the composite solid waste filter aid added is 1.5-3.0 wt% of the dry weight of the red mud.

[0013] Furthermore, in the mixing process, a double-helix stirring method is used, with a stirring speed of 100-180 r / min and a stirring time of 15-30 minutes.

[0014] Furthermore, in the gradient pressure filtration step, plate and frame pressure filtration is used, and the filter cloth is a modified filter cloth with a pore size of 5-10μm.

[0015] Furthermore, the initial pressure of the filter press is 0.5-0.8 MPa, and the filtration time is within 10 minutes; the pressure in the middle stage of the filter press is 1.2-1.5 MPa, and the filtration time is 10-30 minutes; the pressure in the later stage of the filter press is 1.8-2.2 MPa, and the filtration time is 30-60 minutes; the filter cake thickness is controlled to be 10-20 mm during the filter press process.

[0016] Furthermore, the drying process employs waste heat recovery hot air circulation, with a drying temperature of 80-120℃ and a drying time of 2-3 hours, reducing the moisture content of the dehydrated red mud to below 4%.

[0017] This invention also provides a red mud dewatering system based on the coupling of solid waste filtration aid and gradient pressure filtration, comprising: The red mud pretreatment unit is used to pretreat red mud and adjust the pH value of the red mud slurry. The composite solid waste filter aid preparation unit is used to crush, calcine and grind industrial solid waste to make solid waste base material, and then combine the solid waste base material with chemical filter aid to make composite solid waste filter aid. The mixing unit is used to mix the pretreated red mud slurry with the composite solid waste filter aid evenly. A gradient filtration unit is used to perform gradient filtration on the mixed material. The gradient filtration includes at least an initial stage, a middle stage and a later stage of filtration, and the pressure applied in each stage increases sequentially. After filtration, filter cake and filtrate are obtained. The low-temperature drying unit is used to dry the filter cake after pressure filtration to obtain dehydrated red mud.

[0018] One or more technical solutions provided in the embodiments of the present invention have at least the following technical effects or advantages: 1. This method involves compounding industrial solid waste, after crushing, calcining, and pulverizing, with a chemical filter aid. The resulting filter aid has a porous structure. After mixing, these porous particles disperse between the red mud particles, acting as a skeletal support during the pressure filtration process. This prevents the filter cake from becoming over-compacted and clogging the water flow channels, while the pores themselves can also adsorb some water. Based on this, by setting three progressively increasing pressure stages, a lower pressure in the initial stage of pressure filtration prevents the rapid accumulation of fine red mud particles on the filter cloth surface, preventing the formation of a dense clogging layer and maintaining unobstructed filtration channels. Increasing the pressure in the middle stage accelerates the removal of free water, while the higher pressure in the later stage acts on the interior of the filter cake, breaking down the agglomeration structure between the red mud particles and squeezing out the bound water adsorbed on the particle surface. Compared to existing methods, this method combines the preparation of the composite solid waste filter aid with gradient pressure filtration, rather than simply adding the filter aid before pressure filtration or using gradient pressure alone. These two techniques work synergistically during the filter press process. The composite solid waste filter aid improves the filtration characteristics of the material, creating conditions for efficient dewatering through gradient filtration. Meanwhile, the staged pressurization of gradient filtration fully utilizes the pore structure and adsorption properties of the composite solid waste filter aid. The combined effect of these two techniques improves the efficiency of the entire dewatering process, reducing the final moisture content of the filter cake to a low level while shortening the filtration time. This method solves the problems of low filtration efficiency, high filter cake moisture content, high filter aid cost, and the potential for secondary pollution in existing technologies. Furthermore, using industrial solid waste as a raw material for the filter aid achieves resource utilization of solid waste and reduces dependence on single chemical filter aids.

[0019] 2. High dewatering efficiency and stable performance: Through the coupling effect of solid waste filtration and gradient pressure filtration, the problems of filter cloth clogging and high filter cake moisture content are effectively solved. The final dewatered red mud moisture content is ≤4%, which fully meets the requirements for resource utilization of red mud-based cementitious materials, road engineering materials, etc. At the same time, the filter cake thickness is uniform, the dewatering efficiency is stable, and the processing capacity is increased by 40-60% compared with the existing system, making it suitable for large-scale industrial applications.

[0020] 3. Solid waste resource utilization and controllable cost: The composite solid waste filter aid is prepared by using industrial solid waste (fly ash, slag), realizing the on-site resource utilization of solid waste. This not only reduces solid waste stockpiling pollution, but also reduces the cost of filter aid by more than 30%. Low-temperature drying and waste heat recovery reduce the overall system energy consumption by more than 35%, resulting in low equipment maintenance costs and a significant reduction in comprehensive treatment costs.

[0021] 4. Environmentally friendly and free of secondary pollution: The system uses a mild alkaline regulator to avoid wastewater pollution caused by strong acid neutralization; the composite solid waste filter aid has no harmful components, and the entire process has no toxic or harmful substances discharged, which is in line with the concept of green and environmentally friendly development and realizes the clean and resource-based treatment of red mud.

[0022] 5. High degree of automation and easy operation: The intelligent control unit realizes the automated and coordinated operation of each unit, and can monitor and adjust the operating parameters in real time, reducing manual intervention; the touch screen operation interface is simple, which is convenient for staff to operate and maintain, reduces labor costs, and is suitable for the transformation and upgrading of existing red mud treatment production lines.

[0023] 6. High adaptability and wide range of applications: It can be applied to various types of red mud produced by Bayer process, sintering process and combined process, and is not limited by the initial moisture content and particle size of red mud; the system has a compact structure and can be flexibly adjusted according to the processing capacity. It is suitable for both new production lines and the modification of existing dewatering systems, and has a wide range of application scenarios.

[0024] 7. High equipment stability and long service life: The core equipment is made of corrosion-resistant materials and is adapted to the strong alkaline properties of red mud; the filter cloth is modified and equipped with a cleaning device to reduce clogging and wear; the linkage design of each unit reduces the operating load of the equipment, extends the service life of the equipment, and reduces the cost of equipment replacement and maintenance.

[0025] Advantages of additional aspects of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. The drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. In addition, the dimensions or spacing between the components are exaggerated to show the position of each component, and the schematic diagrams are for illustrative purposes only.

[0027] Figure 1 This is a flowchart of a red mud dewatering method based on the coupling of solid waste filtration aid and gradient pressure filtration provided in an embodiment of the present invention. Detailed Implementation

[0028] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Furthermore, it should be understood that when the terms include and / or encompass are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0029] This invention proposes a red mud dewatering method based on the coupling of solid waste filtration aid and gradient pressure filtration. It is applicable to the large-scale dewatering treatment of red mud generated during the Bayer process for alumina production. It can realize the coupling of solid waste resource utilization and efficient red mud dewatering, and solve problems such as low dewatering efficiency, high energy consumption, high filter cake moisture content, and easy secondary pollution. It achieves efficient and energy-saving removal of moisture from red mud, provides equipment support for the subsequent resource utilization of red mud, and promotes the large-scale resource utilization of red mud.

[0030] like Figure 1 As shown, the red mud dewatering method includes the following steps: S100 pretreats the red mud, adjusts the pH value of the red mud slurry, and improves the initial state of the red mud slurry, laying the foundation for subsequent filtration aid and pressure filtration processes.

[0031] S200 processes industrial solid waste through crushing, calcination, and pulverization to produce solid waste base material. This solid waste base material is then compounded with chemical filter aids to create a composite solid waste filter aid. This approach abandons the traditional method of using a single chemical filter aid. By modifying industrial solid waste and then compounding it with chemical filter aids to form a composite solid waste filter aid, it not only achieves the resource utilization of industrial solid waste but also solves the problems of secondary pollution and high cost associated with traditional chemical filter aids.

[0032] The S300 mixes the pretreated red mud slurry with the composite solid waste filter aid evenly, allowing the filter aid to play its role effectively and solving the problem of poor filtration effect caused by uneven mixing after the addition of existing filter aids.

[0033] The S400 performs gradient pressure filtration on the mixed material. This gradient pressure filtration includes at least three stages: initial, middle, and final stages, with the pressure increasing sequentially in each stage. The resulting product is a filter cake and filtrate. This staged pressure-increasing filtration method replaces the traditional single constant pressure filtration. Different pressures are matched to the material characteristics at different stages of filtration, solving the problems of easy clogging of the filter cloth under high pressure in the initial stage and inability to remove bound water under low pressure in the later stage.

[0034] The S500 dries the filter cake after pressure filtration to obtain dehydrated red mud, achieving the final removal of moisture from the red mud and solving the problem of incomplete dehydration caused by poor connection between existing drying and pressure filtration.

[0035] This method forms a complete red mud dewatering process system by sequentially performing pretreatment, preparation of composite solid waste filter aid, uniform mixing, gradient pressure filtration, and drying. It addresses the technical problems of existing red mud dewatering methods, such as extensive pretreatment processes, lack of synergy between filter aid and pressure filtration, unreasonable pressure control during pressure filtration, and poor integration between the drying process and preceding steps. Pretreatment provides a suitable material state for filtration aid and pressure filtration, while the composite solid waste filter aid constructs a good filtration channel for gradient pressure filtration. Gradient pressure filtration reduces the processing load for drying. These processes are matched to form a linked process system, improving the overall efficiency of red mud dewatering. The core process of this method is the coupled design of the composite solid waste filter aid preparation and gradient pressure filtration. The porous structure of the composite solid waste filter aid forms drainage channels in the filter cake, providing a good filtration foundation for the staged pressurization of gradient pressure filtration. The staged pressurization of gradient pressure filtration fully utilizes the porous structure of the composite solid waste filter aid to gradually remove free and bound water from the red mud. The synergistic effect of the two processes alleviates the filter cloth clogging problem, while effectively removing moisture from the red mud.

[0036] Furthermore, the pretreatment steps include stirring the red mud evenly and adjusting the pH value to 8.5-10.5. Adjusting the pH value to a weakly alkaline range is based on the alkaline characteristics of the red mud itself. Using this range can change the charge state on the surface of the red mud particles, reduce the agglomeration between particles, and make the particles more evenly dispersed in the slurry, which is beneficial to the contact and interaction between the subsequent filter aid and the red mud particles.

[0037] Furthermore, the pH adjuster is a compound system of sodium bicarbonate and potassium dihydrogen phosphate, with a mass ratio of 2-3:1, and the amount added is 0.5-1.2 wt% of the dry weight of red mud.

[0038] Existing technologies typically use strong acids such as sulfuric acid or hydrochloric acid to adjust pH. However, strong acids react violently with alkaline red mud, easily leading to localized over-acidity and structural damage to the red mud. Furthermore, the introduced acid radicals remain in the filter cake or filtrate, causing secondary pollution. This method utilizes a mild acid-base buffer system: sodium bicarbonate is weakly alkaline, and potassium dihydrogen phosphate is weakly acidic. The combination forms a buffer system in the red mud slurry, stabilizing the pH within the desired weakly alkaline range and preventing drastic pH fluctuations. Simultaneously, the phosphate ions in potassium dihydrogen phosphate react with calcium ions in the red mud to form calcium phosphate precipitates. These precipitates provide some flocculation, assisting the composite solid waste filter aid in improving the filtration performance of the red mud. The addition amount is controlled at 0.5-1.2 wt%, achieving the goal of pH adjustment without excessively introducing other ions.

[0039] Furthermore, the preparation steps of the composite solid waste filter aid include: crushing industrial solid waste to a particle size of no more than 20 mm, calcining it at 800-900℃ for 2-3 hours, cooling it and then pulverizing it to a particle size of no more than 100 mesh to obtain solid waste base material; and compounding the solid waste base material with polyaluminum chloride and sodium carboxymethyl cellulose at a mass ratio of 8-12:3-5:1.

[0040] Crushing to 20mm facilitates uniform heat transfer during subsequent calcination. The selection of calcination temperature and time is based on the characteristics of industrial solid waste. Taking fly ash and slag as examples, calcination within the range of 800-900℃ can burn off the residual carbon components and simultaneously transform the mineral phase, forming an active material with a porous structure. The porosity can be increased to 35-50%, the specific surface area reaches 15-25m² / g, and the pore size distribution is mainly mesopores of 10-100nm. This porous structure is conducive to adsorbing moisture and forming drainage channels in the filter cake. If the temperature is too low or the time is too short, the carbon components will not burn off completely, and the pore structure will not develop fully; if the temperature is too high or the time is too long, it will cause particle sintering, which will destroy the pore structure. Crushing to no more than 100 mesh is to obtain a suitable particle size. If the particle size is too large, the specific surface area is small and the adsorption performance is poor; if the particle size is too fine, it will easily clog the filter cloth. The calcined and pulverized solid waste base material is compounded with polyaluminum chloride and sodium carboxymethyl cellulose. Polyaluminum chloride, as an inorganic flocculant, can neutralize the surface charge of red mud particles and promote the aggregation of fine particles into larger flocs. Sodium carboxymethyl cellulose, as an organic polymer, can play a bridging flocculation role, while increasing the viscosity of the slurry and reducing particle sedimentation. The three are compounded to form an inorganic-organic composite filter aid system, which has multiple functions such as charge neutralization, bridging flocculation and skeleton support, and the effect is better than using any one of them alone.

[0041] Furthermore, the industrial solid waste is one or a mixture of two of fly ash and slag, and the amount of the composite solid waste filter aid added is 1.5-3.0 wt% of the dry weight of the red mud.

[0042] Fly ash and slag are major industrial solid wastes generated by coal-fired power plants and steel mills. They are widely available, inexpensive, and possess certain pozzolanic activity and a porous structure, making them suitable as filter aid materials. The recommended addition amount is 1.5-3.0 wt%. Too low a dosage will result in insignificant filter aid effect, while too high a dosage will increase costs and cause excessive filter cake thickness, thus reducing filter press efficiency. This range allows for full utilization of the filter aid effect without excessively increasing treatment costs.

[0043] Furthermore, in the mixing process, a double-helix stirring method is used, with a stirring speed of 100-180 r / min and a stirring time of 15-30 minutes.

[0044] The double-helix stirring method enables the material to form a composite axial and radial flow within the mixing vessel, avoiding dead zones and ensuring sufficient contact and dispersion of the composite solid waste filter aid with the red mud slurry. Too low a speed or too short a time results in uneven mixing, causing the filter aid to clump together and fail to function effectively. Too high a speed or too long a time will destroy the existing floc structure, reducing filtration performance. Within this parameter range, the filter aid can be uniformly dispersed in the red mud slurry, allowing its porous particles to fully contact the red mud particles, maximizing adsorption and flocculation, and preparing for subsequent pressure filtration.

[0045] Furthermore, in the gradient pressure filtration step, a plate and frame filter press is used, and the filter cloth is a modified filter cloth with a pore size of 5-10μm; the pressure in the initial stage of pressure filtration is 0.5-0.8MPa, and the pressure filtration time is within 10 minutes; the pressure in the middle stage of pressure filtration is 1.2-1.5MPa, and the pressure filtration time is 10-30 minutes; the pressure in the later stage of pressure filtration is 1.8-2.2MPa, and the pressure filtration time is 30-60 minutes; the filter cake thickness is controlled to be 10-20mm during the pressure filtration process.

[0046] Plate and frame filter presses are a common type of equipment for red mud dewatering, suitable for treating slurries with high solids content. The filter cloth pore size should be selected between 5-10 μm. If the pore size is too small, the filtration resistance is high and the filtration speed is slow; if the pore size is too large, fine particles can easily penetrate the filter cloth, causing turbidity in the filtrate. Simultaneously, particles embedded in the filter cloth pores can cause blockages that are difficult to clean. Using polytetrafluoroethylene (PTFE) coated modified filter cloth can reduce the adhesion between the filter cloth surface and red mud particles, reducing particle adhesion and embedding on the filter cloth surface, and extending the service life of the filter cloth.

[0047] The setting of pressure stages is the core of gradient pressure filtration. Initially, maintain 0.5-0.8 MPa for 10 minutes. At this stage, the filter cake is not yet fully formed, and the lower pressure prevents fine particles from rapidly depositing on the filter cloth surface to form a dense layer, allowing sufficient channels for water to drain. In the middle stage, maintain 1.2-1.5 MPa for 10-30 minutes. During this time, the filter cake gradually thickens, and increasing the pressure overcomes the filter cake resistance to squeeze out free water. In the later stage, maintain 1.8-2.2 MPa for 30-60 minutes. At this point, most of the free water has been removed, and higher pressure is needed to act on the interior of the filter cake, removing capillary water and some bound water between particles. The coordination of time and pressure ranges ensures that each stage is effective without excessively prolonging the cycle.

[0048] If the filter cake is too thin, the single processing capacity will be small and the equipment utilization rate will be low. If the filter cake is too thick, the internal moisture discharge path will be long and the moisture in the center will be difficult to remove, resulting in uneven and high overall moisture content. A filter cake thickness of 10-20mm can achieve a balance between processing capacity and dewatering effect.

[0049] Furthermore, the drying process employs waste heat recovery hot air circulation, with a drying temperature of 80-120℃ and a drying time of 2-3 hours, reducing the moisture content of the dehydrated red mud to below 4%.

[0050] Waste heat recovery hot air circulation refers to the process where a portion of the hot air discharged from the drying chamber is returned to the drying chamber for reuse after heat exchange, thus recovering heat and reducing energy consumption. The drying temperature is selected at 80-120℃ because most of the moisture in the red mud has been removed after pressure filtration. The remaining moisture mainly consists of adsorbed water inside the particles and a small amount of capillary water, which can be removed by prolonged contact with hot air at a lower temperature, eliminating the need for high-temperature drying. This avoids increased energy consumption and adverse effects on the mineral structure of the red mud caused by high temperatures. A drying time of 2-3 hours ensures sufficient evaporation of moisture. Once the moisture content is reduced to below 4%, the red mud meets the requirements for raw material moisture content in resource utilization scenarios such as red mud-based cementitious materials.

[0051] Based on the above dewatering method, this embodiment also proposes a red mud dewatering system based on the coupling of solid waste filtration aid and gradient pressure filtration, including: The red mud pretreatment unit is used to pretreat red mud and adjust the pH value of the red mud slurry. The composite solid waste filter aid preparation unit is used to crush, calcine and grind industrial solid waste to make solid waste base material, and then combine the solid waste base material with chemical filter aid to make composite solid waste filter aid. The mixing unit is used to mix the pretreated red mud slurry with the composite solid waste filter aid evenly. A gradient filtration unit is used to perform gradient filtration on the mixed material. The gradient filtration includes at least an initial stage, a middle stage and a later stage of filtration, and the pressure applied in each stage increases sequentially. After filtration, filter cake and filtrate are obtained. The low-temperature drying unit is used to dry the filter cake after pressure filtration to obtain dehydrated red mud.

[0052] Intelligent control unit, used to control the coordinated operation of various units; Each unit is connected in sequence through conveying pipelines to form a closed-loop dewatering process, realizing integrated treatment of red mud from pretreatment to final dewatering.

[0053] Specifically: 1. Red mud pretreatment unit.

[0054] The red mud pretreatment unit includes a stirring and conditioning tank and a pH adjuster feeding device. The pH adjuster feeding device is installed on the stirring and conditioning tank and is used to add an alkaline adjuster into the stirring and conditioning tank to adjust the pH value of the red mud slurry to 8.5-10.5. The stirring and conditioning tank is equipped with a stirring component with a stirring speed of 60-120 r / min and a stirring time of 10-20 min to ensure the homogenization of the red mud slurry.

[0055] The alkaline regulator is a compound system of sodium bicarbonate and potassium dihydrogen phosphate with a mass ratio of 2-3:1. The amount added is 0.5-1.2 wt% of the dry weight of red mud. This avoids secondary pollution caused by traditional strong acid neutralization and destroys the agglomeration structure of red mud particles, reducing water binding.

[0056] Furthermore, the stirring and conditioning tank of the red mud pretreatment unit and the mixing kettle of the mixing unit are both made of corrosion-resistant material (316L stainless steel) to avoid the strong alkalinity of the red mud slurry from corroding the equipment and extend the service life of the equipment.

[0057] 2. Composite solid waste filter aid preparation unit.

[0058] The composite solid waste filter aid preparation unit includes a solid waste crushing device, a calcination device, a crushing and screening device, and a mixing device, used to prepare industrial solid waste into a composite solid waste filter aid to realize the resource utilization of solid waste; the discharge port of the solid waste crushing device is connected to the inlet of the calcination device, the discharge port of the calcination device is connected to the inlet of the crushing and screening device, and the discharge port of the crushing and screening device is connected to the inlet of the mixing device; the mixing device is also connected to a chemical filter aid feeding device, used to compound the solid waste base material with the chemical filter aid to form a composite solid waste filter aid.

[0059] The industrial solid waste is one or a combination of two of fly ash and slag. The preparation process of the solid waste base material is as follows: the industrial solid waste is crushed to a particle size ≤20mm by a solid waste crushing device, fed into a calcination device, calcined at 800-900℃ for 2-3 hours, cooled, and then fed into a crushing and screening device to be crushed to a particle size ≤100 mesh to obtain the solid waste base material. The composite solid waste filter aid is composed of the solid waste base material, polyaluminum chloride, and sodium carboxymethyl cellulose, with a mass ratio of 8-12:3-5:1. The amount of composite solid waste filter aid added is 1.5-3.0wt% of the dry weight of red mud.

[0060] Furthermore, in the composite solid waste filter aid preparation unit, the industrial solid waste is prepared by mixing fly ash and slag in a mass ratio of 1:1, the preferred calcination temperature is 850℃, the preferred calcination time is 2.5h, and the preferred particle size of the solid waste base material is 80-100 mesh; in the composite solid waste filter aid, the preferred mass ratio of solid waste base material, polyaluminum chloride, and sodium carboxymethyl cellulose is 10:4:1, and the preferred addition amount is 2.0-2.5wt% of the dry weight of red mud.

[0061] 3. Hybrid unit.

[0062] The mixing unit includes a mixing kettle, a metering and conveying device, and an online monitoring device. The metering and conveying device is connected to the stirring and conditioning tank of the red mud pretreatment unit and the mixing device of the composite solid waste filter aid preparation unit, respectively, and is used to accurately convey the homogenized red mud slurry and the composite solid waste filter aid into the mixing kettle in a certain proportion. The online monitoring device is installed on the mixing kettle and is used to monitor the mixing uniformity of the slurry in the mixing kettle in real time and feed it back to the intelligent control unit. The mixing kettle is equipped with a double spiral stirring component with a stirring speed of 100-180 r / min and a stirring time of 15-30 min to ensure that the composite solid waste filter aid and the red mud slurry are fully mixed, so that the pore adsorption and flocculation dispersion effects of the filter aid can be fully exerted.

[0063] 4. Gradient pressure filtration unit.

[0064] The gradient filtration unit is the core unit, including a gradient filter press, a filter cloth cleaning device, a filter cake thickness detection device, and a pressure regulating device. The gradient filter press adopts a plate and frame structure with multiple filter plates inside. The surface of the filter plates is covered with modified filter cloth (treated with polytetrafluoroethylene coating, with a pore size of 5-10μm) to reduce filter cloth clogging and improve filtration efficiency. The pressure regulating device is connected to the gradient filter press to realize gradient pressure control during the filtration process. The specific gradient pressure is set as follows: 0.5-0.8MPa in the initial stage of filtration (0-10min), 1.2-1.5MPa in the middle stage of filtration (10-30min), and 1.8-2.2MPa in the later stage of filtration (30-60min). By applying gradient pressure, filter cloth clogging caused by high initial pressure is avoided, while ensuring that bound water inside the red mud is fully removed in the later stage.

[0065] The filter cloth cleaning device is connected to the gradient filter press and is used to clean the filter cloth regularly to prevent clogging and extend its service life. The filter cake thickness detection device is installed at the discharge end of the gradient filter press to monitor the filter cake thickness in real time (controlled within 10-20mm) and feed it back to the intelligent control unit. The intelligent control unit adjusts the filtration parameters to ensure uniform filter cake thickness and improve dewatering efficiency. The filter cake discharge port of the gradient filter press is connected to the low-temperature drying unit.

[0066] Furthermore, the gradient pressure of the gradient filtration unit is preferably set as follows: 0.6-0.7 MPa in the initial stage of filtration (0-10 min), 1.3-1.4 MPa in the middle stage of filtration (10-30 min), and 1.9-2.1 MPa in the later stage of filtration (30-60 min); the filter cloth pore size is preferably 6-8 μm, and the filter cake thickness is preferably 12-18 mm.

[0067] 5. Low-temperature drying unit.

[0068] The low-temperature drying unit includes a low-temperature drying chamber, a hot air circulation device, and a moisture content detection device. The inlet of the low-temperature drying chamber is connected to the filter cake outlet of the gradient filter press unit, used to receive the red mud filter cake and perform low-temperature drying. The hot air circulation device is installed inside the low-temperature drying chamber and adopts a waste heat recovery structure to recycle the hot air generated during the drying process, reducing energy consumption. The moisture content detection device is installed at the outlet of the low-temperature drying chamber to monitor the moisture content of the dewatered red mud in real time and feed it back to the intelligent control unit, which adjusts the drying temperature and drying time. The drying temperature of the low-temperature drying chamber is set to 80-120℃, and the drying time is 2-3 hours to ensure that the final moisture content of the dewatered red mud is ≤4%.

[0069] Furthermore, the drying temperature of the low-temperature drying unit is preferably 90-110℃, the waste heat recovery rate of the hot air circulation device is ≥80%, ensuring further reduction in energy consumption; the detection accuracy of the moisture content detection device is ≤0.1%, ensuring that the moisture content of the dehydrated red mud meets the standard.

[0070] 6. Intelligent control unit.

[0071] The intelligent control unit includes a PLC controller, a touch screen, and a data acquisition module. The data acquisition module is connected to the pH meter of the red mud pretreatment unit, the online monitoring device of the mixing unit, the filter cake thickness detection device and pressure sensor of the gradient filter press unit, and the moisture content detection device and temperature sensor of the low-temperature drying unit, respectively, for collecting the operating parameters of each unit. The PLC controller is connected to the actuators (stirring components, conveying devices, pressure regulating devices, hot air circulation devices, etc.) of each unit, for automatically adjusting the operating parameters of each unit according to the collected parameters, so as to realize the automated and coordinated operation of the system. The touch screen is used to manually set operating parameters and view the system operating status, which facilitates operation and maintenance.

[0072] This system overcomes the limitations of existing red mud dewatering systems where each unit operates independently. It constructs a solid waste filter aid-gradient pressure filtration coupling system, achieving synergistic advancement of solid waste resource utilization and efficient red mud dewatering, and has the following advantages: 1. This is the first time that solid waste filter aids and gradient filtration have been deeply coupled, rather than simply superimposed. The porous structure of the composite solid waste filter aid (fly ash and slag-based) can serve as a filter cake skeleton, reducing filter cloth clogging and providing a good filtration channel for gradient filtration. Gradient filtration uses staged pressurization: low pressure in the initial stage to avoid filter cloth clogging, medium pressure in the middle stage to promote the removal of free water, and high pressure in the later stage to remove bound water. The synergistic effect of these two methods results in a 25-35% reduction in filter cake moisture content and a 40-60% increase in filtration efficiency compared to existing single-pressure filtration systems.

[0073] 2. Filter aid base material is prepared using industrial solid waste (fly ash, slag) to replace traditional chemical filter aids, realize the resource utilization of solid waste, and reduce the cost of filter aids by more than 30%. At the same time, the solid waste base material is compounded with polyaluminum chloride and sodium carboxymethyl cellulose to form a synergistic filter aid system, which has adsorption, flocculation and dispersion functions, solving the problems of poor filtration effect and easy clogging of filter cloth by single filter aids.

[0074] 3. The system integrates six major units: red mud pretreatment, composite solid waste filter aid preparation, precision mixing, gradient filtration, low-temperature drying, and intelligent control, forming a closed-loop integrated system with each unit working in synergy. The intelligent control unit collects parameters from each unit in real time and automatically adjusts operating parameters to achieve seamless connection between pretreatment, filtration aid, filtration, and drying. At the same time, the low-temperature drying unit uses waste heat recovery to further reduce system energy consumption, resulting in an overall energy consumption reduction of more than 35% compared to existing systems.

[0075] 4. The gradient filter press uses modified filter cloth (PTFE coating), combined with a filter cloth cleaning device, which effectively reduces filter cloth clogging and extends the service life of the filter cloth; the filter cake thickness detection device is linked with the pressure regulating device to ensure uniform filter cake thickness and improve dewatering stability; each core piece of equipment is made of corrosion-resistant material, which is suitable for the strong alkaline properties of red mud, extending the service life of the equipment and reducing maintenance costs.

[0076] 5. The entire system generates no toxic or harmful substances. The composite solid waste filter aid enables the resource utilization of industrial solid waste. The alkaline regulator adopts a mild compound system to avoid wastewater pollution caused by strong acid neutralization, thus achieving the coordinated development of solid waste treatment, resource recycling, and green environmental protection.

[0077] The effectiveness of the present invention will be verified below with reference to specific embodiments and comparative examples: Example 1 A red mud dewatering method based on the coupling of solid waste filtration aid and gradient pressure filtration, wherein the dewatering method and operating parameters are as follows: 1. Red mud pretreatment: The mixing and conditioning tank is made of 316L stainless steel, and the stirring speed is 90 r / min; the pH adjustment agent feeding device adds sodium bicarbonate and potassium dihydrogen phosphate compound regulator (mass ratio 2.5:1), the amount of which is 0.8 wt% of the dry weight of red mud, adjusts the pH of the slurry to 9.5, and stirs for 15 min to obtain homogeneous red mud slurry.

[0078] 2. Preparation of composite solid waste filter aid: Industrial solid waste is prepared by mixing fly ash and slag in a mass ratio of 1:1, crushing them to a particle size of ≤20mm using a solid waste crushing device, and then feeding them into a calcination device. The mixture is calcined at 850℃ for 2.5h, cooled, and then crushed to 80-100 mesh using a pulverizing and screening device to obtain solid waste base material. In a mixing device, solid waste base material, polyaluminum chloride, and sodium carboxymethyl cellulose are mixed in a mass ratio of 10:4:1, with an addition amount of 2.2wt% of the dry weight of red mud, to prepare a composite solid waste filter aid.

[0079] 3. Precise mixing: The mixing vessel adopts a double spiral stirring component with a stirring speed of 150 r / min; the metering and conveying device accurately delivers the homogeneous red mud slurry and composite solid waste filter aid to the mixing vessel in proportion; the online monitoring device monitors the mixing uniformity in real time; and the mixing is carried out for 25 minutes to ensure that the two are fully mixed.

[0080] 4. Gradient Filtration: The gradient filter press is a plate and frame type, and the filter cloth is a modified filter cloth with polytetrafluoroethylene coating and a pore size of 7μm. The gradient pressure is set as follows: initial 5min, 0.65MPa; middle 10min, 1.35MPa; and final 30min, 2.0MPa. The filter cake thickness detection device controls the filter cake thickness to 15mm, and the filter cloth cleaning device cleans the filter cloth every 30min. The filtration time is 45min, and red mud filter cake is obtained.

[0081] 5. Low-temperature drying: The drying temperature of the low-temperature drying oven is 100℃, and the waste heat recovery rate of the hot air circulation device is 85%. The moisture content detection device monitors the moisture content in real time. After drying for 2.5 hours to constant weight, the final dehydrated red mud is obtained. The moisture content is 3.1%.

[0082] 6. Intelligent control: The system adopts a PLC controller, a data acquisition module to collect parameters of each unit in real time, a touch screen to set operating parameters, and automatically adjusts the operating status of each unit to achieve automated and coordinated operation of the system.

[0083] Example 2 A red mud dewatering method based on the coupling of solid waste filtration aid and gradient pressure filtration is proposed. The dewatering method is basically the same as that in Example 1, except that the operating parameters are as follows: 1. The amount of pH adjuster added for red mud pretreatment is 1.0 wt% of the dry weight of red mud, the pH is adjusted to 10.5, the stirring speed is 120 r / min, and the stirring time is 20 min; the alkaline adjuster is sodium bicarbonate and potassium dihydrogen phosphate in a mass ratio of 3:1.

[0084] 2. Preparation of composite solid waste filter aid: The industrial solid waste is slag, calcined at 900℃ for 3 hours, and the particle size of the solid waste base material is ≤100 mesh; the mass ratio of the composite solid waste filter aid is 12:5:1, and the addition amount is 2.5wt% of the dry weight of red mud.

[0085] 3. Precise mixing: The stirring speed is 180 r / min and the stirring time is 30 min to ensure uniform mixing.

[0086] 4. Gradient pressure filtration: The filter cloth pore size is 8μm, and the gradient pressure is set as follows: 0.7MPa in the initial stage, 1.4MPa in the middle stage, and 2.1MPa in the later stage; the filter cake thickness is 18mm, and the filtration time is 50min; the filter cloth cleaning device cleans the filter cloth every 25min.

[0087] 5. Low-temperature drying: Drying temperature 110℃, waste heat recovery rate 82%, drying time 2h, final dehydrated red mud moisture content 2.7%.

[0088] Example 3 A red mud dewatering method based on the coupling of solid waste filtration aid and gradient pressure filtration is proposed. The dewatering method is basically the same as that in Example 1, except that the operating parameters are as follows: 1. Red mud pretreatment: The amount of pH adjuster added is 0.5 wt% of the dry weight of red mud, the pH is adjusted to 8.5, the stirring speed is 60 r / min, and the stirring time is 10 min; the alkalinity adjuster is sodium bicarbonate and potassium dihydrogen phosphate in a mass ratio of 2:1.

[0089] 2. Preparation of composite solid waste filter aid: The industrial solid waste is fly ash, calcined at 800℃ for 2 hours, and the particle size of the solid waste base is 80 mesh; the mass ratio of the composite solid waste filter aid is 8:3:1, and the addition amount is 1.5wt% of the dry weight of red mud.

[0090] 3. Precise mixing: The stirring speed is 100r / min and the stirring time is 15min to ensure uniform mixing.

[0091] 4. Gradient pressure filtration: The filter cloth pore size is 6μm, and the gradient pressure is set as follows: 0.6MPa in the initial stage, 1.3MPa in the middle stage, and 1.9MPa in the later stage; the filter cake thickness is 12mm, and the filtration time is 45min; the filter cloth cleaning device cleans the filter cloth every 35min.

[0092] 5. Low-temperature drying: Drying temperature 80℃, waste heat recovery rate 80%, drying time 3h, final dehydrated red mud moisture content 3.7%.

[0093] Example 4 A red mud dewatering method based on the coupling of solid waste filtration aid and gradient pressure filtration is proposed. The dewatering method is basically the same as that in Example 1, except that the operating parameters are as follows: 1. Red mud pretreatment: The amount of pH adjuster added is 0.9 wt% of the dry weight of red mud, the pH is adjusted to 10.0, the stirring speed is 100 r / min, and the stirring time is 15 min; the alkalinity adjuster is sodium bicarbonate to potassium dihydrogen phosphate in a mass ratio of 2.5:1.

[0094] 2. Preparation of composite solid waste filter aid: Industrial solid waste is prepared by mixing fly ash and slag at a mass ratio of 1.2:1, calcining at 860℃ for 2.6h, and the particle size of the solid waste base material is 90 mesh; the mass ratio of the composite solid waste filter aid is 11:4.5:1, and the addition amount is 2.3wt% of the dry weight of red mud.

[0095] 3. Precise mixing: The stirring speed is 160 r / min and the stirring time is 28 min to ensure uniform mixing.

[0096] 4. Gradient pressure filtration: filter cloth pore size 7.5μm, gradient pressure set as follows: initial 0.68MPa, middle 1.38MPa, and later 2.05MPa; filter cake thickness 16mm, filtration time 48min; filter cloth cleaning device cleans every 28min.

[0097] 5. Low-temperature drying: Drying temperature 105℃, waste heat recovery rate 86%, drying time 2.2h, final dehydrated red mud moisture content 2.9%.

[0098] Example 5 A red mud dewatering method based on the coupling of solid waste filtration aid and gradient pressure filtration is proposed. The dewatering method is basically the same as that in Example 1, except that the operating parameters are as follows: 1. Red mud pretreatment: The amount of pH adjuster added is 0.95 wt% of the dry weight of red mud, the pH is adjusted to 10.2, the stirring speed is 110 r / min, and the stirring time is 18 min; the alkalinity adjuster is sodium bicarbonate to potassium dihydrogen phosphate in a mass ratio of 2.8:1.

[0099] 2. Preparation of composite solid waste filter aid: Industrial solid waste is prepared by mixing fly ash and slag at a mass ratio of 0.8:1, calcining at 880℃ for 2.7h, and the particle size of the solid waste base material is 95 mesh; the mass ratio of the composite solid waste filter aid is 11.5:4.2:1, and the amount added is 2.4wt% of the dry weight of red mud.

[0100] 3. Precise mixing: The stirring speed is 170 r / min and the stirring time is 26 min to ensure uniform mixing.

[0101] 4. Gradient pressure filtration: filter cloth pore size 7.2μm, gradient pressure set as follows: initial 0.67MPa, middle 1.36MPa, and later 2.02MPa; filter cake thickness 17mm, filtration time 46min; filter cloth cleaning device cleans every 26min.

[0102] 5. Low-temperature drying: The drying temperature is 108℃, the waste heat recovery rate is 84%, the drying time is 2.1h, and the final dehydrated red mud moisture content is 2.8%.

[0103] Example 6 A red mud dewatering method based on the coupling of solid waste filtration aid and gradient pressure filtration is proposed. The dewatering method is basically the same as that in Example 1, except that the operating parameters are as follows: 1. Red mud pretreatment: The amount of pH adjuster added is 0.7wt% of the dry weight of red mud, the pH is adjusted to 9.0, the stirring speed is 80r / min, and the stirring time is 12min; the alkalinity adjuster is sodium bicarbonate to potassium dihydrogen phosphate in a mass ratio of 2.2:1.

[0104] 2. Preparation of composite solid waste filter aid: The industrial solid waste is fly ash, calcined at 820℃ for 2.2h, and the particle size of the solid waste base is 85 mesh; the mass ratio of the composite solid waste filter aid is 9:3.5:1, and the addition amount is 1.8wt% of the dry weight of red mud.

[0105] 3. Precise mixing: The stirring speed is 120 r / min and the stirring time is 18 min to ensure uniform mixing.

[0106] 4. Gradient pressure filtration: The filter cloth pore size is 6.5μm, and the gradient pressure is set as follows: 0.62MPa in the initial stage, 1.32MPa in the middle stage, and 1.95MPa in the later stage; the filter cake thickness is 14mm, and the filtration time is 45min; the filter cloth cleaning device cleans the filter cloth every 32min.

[0107] 5. Low-temperature drying: The drying temperature is 88℃, the waste heat recovery rate is 81%, the drying time is 2.8h, and the final dehydrated red mud moisture content is 3.4%.

[0108] Example 7 A red mud dewatering method based on the coupling of solid waste filtration aid and gradient pressure filtration is proposed. The dewatering method is basically the same as that in Example 1, except that the operating parameters are as follows: 1. Red mud pretreatment: The amount of pH adjuster added is 0.85 wt% of the dry weight of red mud, the pH is adjusted to 9.8, the stirring speed is 95 r / min, and the stirring time is 16 min; the alkalinity adjuster is sodium bicarbonate to potassium dihydrogen phosphate in a mass ratio of 2.6:1.

[0109] 2. Preparation of composite solid waste filter aid: Industrial solid waste is prepared by mixing fly ash and slag at a mass ratio of 1.1:1, calcining at 855℃ for 2.4h, and the particle size of the solid waste base material is 85-95 mesh; the mass ratio of the composite solid waste filter aid is 10.5:4.2:1, and the addition amount is 2.1wt% of the dry weight of red mud.

[0110] 3. Precise mixing: The stirring speed is 140 r / min and the stirring time is 22 min to ensure uniform mixing.

[0111] 4. Gradient pressure filtration: filter cloth pore size 7.1μm, gradient pressure set as follows: initial 0.64MPa, middle 1.34MPa, and later 2.01MPa; filter cake thickness 15.5mm, filtration time 42min; filter cloth cleaning device cleans every 29min.

[0112] 5. Low-temperature drying: Drying temperature 102℃, waste heat recovery rate 85%, drying time 2.3h, final dehydrated red mud moisture content 3.0%.

[0113] Example 8 A red mud dewatering method based on the coupling of solid waste filtration aid and gradient pressure filtration is proposed. The dewatering method is basically the same as that in Example 1, except that the operating parameters are as follows: 1. Red mud pretreatment: The amount of pH adjuster added is 0.92 wt% of the dry weight of red mud, the pH is adjusted to 10.1, the stirring speed is 105 r / min, and the stirring time is 17 min; the alkalinity adjuster is sodium bicarbonate to potassium dihydrogen phosphate in a mass ratio of 2.7:1.

[0114] 2. Preparation of composite solid waste filter aid: Industrial solid waste is prepared by mixing fly ash and slag at a mass ratio of 0.9:1, calcining at 870℃ for 2.5h, and the particle size of the solid waste base material is 90-100 mesh; the mass ratio of the composite solid waste filter aid is 11.2:4.3:1, and the addition amount is 2.35wt% of the dry weight of red mud.

[0115] 3. Precise mixing: The stirring speed is 165 r / min and the stirring time is 25 min to ensure uniform mixing.

[0116] 4. Gradient pressure filtration: The filter cloth pore size is 7.3μm, and the gradient pressure is set as follows: 0.66MPa in the initial stage, 1.37MPa in the middle stage, and 2.03MPa in the later stage; the filter cake thickness is 16.5mm, and the filtration time is 47min; the filter cloth cleaning device cleans the filter cloth every 27min.

[0117] 5. Low-temperature drying: The drying temperature is 106℃, the waste heat recovery rate is 84.5%, the drying time is 2.15h, and the final dehydrated red mud moisture content is 2.85%.

[0118] Example 9 A red mud dewatering method based on the coupling of solid waste filtration aid and gradient pressure filtration is proposed. The dewatering method is basically the same as that in Example 1, except that the operating parameters are as follows: 1. Red mud pretreatment: The amount of pH adjuster added is 0.65 wt% of the dry weight of red mud, the pH is adjusted to 9.2, the stirring speed is 85 r / min, and the stirring time is 13 min; the alkalinity adjuster is sodium bicarbonate to potassium dihydrogen phosphate in a mass ratio of 2.3:1.

[0119] 2. Preparation of composite solid waste filter aid: The industrial solid waste is a mixture of slag and fly ash in a mass ratio of 1:0.9, calcined at 830℃ for 2.3h, with a particle size of 82-88 mesh; the composite solid waste filter aid has a mass ratio of 9.5:3.8:1 and is added at 1.7wt% of the dry weight of red mud.

[0120] 3. Precise mixing: The stirring speed is 130 r / min and the stirring time is 20 min to ensure uniform mixing.

[0121] 4. Gradient pressure filtration: The filter cloth pore size is 6.8μm, and the gradient pressure is set as follows: 0.63MPa in the initial stage, 1.33MPa in the middle stage, and 1.97MPa in the later stage; the filter cake thickness is 14.5mm, and the filtration time is 42min; the filter cloth cleaning device cleans once every 31min.

[0122] 5. Low-temperature drying: Drying temperature 95℃, waste heat recovery rate 82%, drying time 2.6h, final dehydrated red mud moisture content 3.3%.

[0123] Comparative Example Using the Bayer red mud from Example 1 as raw material, a comparative experiment was conducted between the existing red mud dewatering system and the system of the present invention. The specific groupings are as follows: Comparative Example 1: Using the existing single pressure filtration method (no solid waste filter aid, single pressure 1.6MPa), with other conditions consistent with Example 1, the final red mud moisture content was 33.2%, the processing capacity was 1.2t / h, and the energy consumption was 85kWh / t.

[0124] Comparative Example 2: Using existing methods plus a single composite solid waste filter aid (without gradient pressure filtration), and with other conditions consistent with Example 1, the final red mud moisture content was 10.5%, the treatment capacity was 1.5 t / h, and the energy consumption was 78 kWh / t.

[0125] Comparative Example 3: Using the existing method plus gradient pressure filtration (without solid waste as filter aid), and with other conditions consistent with Example 1, the final red mud moisture content was 9.8%, the processing capacity was 1.6 t / h, and the energy consumption was 75 kWh / t.

[0126] Comparative experimental results show that, using the red mud dewatering method based on solid waste filtration aid and gradient pressure filtration coupling of this invention, with the parameters of Example 1, the final red mud moisture content is 3.1%, the processing capacity is 2.2 t / h, and the energy consumption is 55 kWh / t. Compared with existing dewatering methods, the dewatering effect and processing capacity are significantly improved, and the energy consumption is significantly reduced, effectively solving many limitations of existing red mud dewatering methods.

[0127] While the specific embodiments of the present invention have been described above, they are not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative effort based on the technical solutions of the present invention are still within the scope of protection of the present invention.

Claims

1. A red mud dewatering method based on the coupling of solid waste filtration aid and gradient pressure filtration, characterized in that, Includes the following steps: Pre-treatment of red mud involves adjusting the pH value of the red mud slurry. Industrial solid waste is crushed, calcined, and pulverized to produce solid waste base material, which is then compounded with chemical filter aids to produce composite solid waste filter aids. The pretreated red mud slurry was mixed evenly with the composite solid waste filter aid. The mixed materials are subjected to gradient filtration, which includes at least an initial stage, a middle stage and a later stage of filtration, with the pressure applied in each stage increasing sequentially. After filtration, filter cake and filtrate are obtained. The filter cake after pressure filtration is dried to obtain dehydrated red mud.

2. The red mud dewatering method based on the coupling of solid waste filtration aid and gradient pressure filtration as described in claim 1, characterized in that, The pretreatment steps include: stirring the red mud evenly, and then adding a pH adjuster to adjust the pH value to 8.5-10.

5.

3. The red mud dewatering method based on the coupling of solid waste filtration aid and gradient pressure filtration as described in claim 2, characterized in that, The pH adjuster is a compound system of sodium bicarbonate and potassium dihydrogen phosphate, with a mass ratio of 2-3:1, and the amount added is 0.5-1.2 wt% of the dry weight of red mud.

4. The red mud dewatering method based on the coupling of solid waste filtration aid and gradient pressure filtration as described in claim 1, characterized in that, The preparation steps of the composite solid waste filter aid include: crushing industrial solid waste to a particle size of no more than 20 mm, calcining it at 800-900℃ for 2-3 hours, cooling it and then pulverizing it to a particle size of no more than 100 mesh to obtain solid waste base material; and compounding the solid waste base material with polyaluminum chloride and sodium carboxymethyl cellulose at a mass ratio of 8-12:3-5:

1.

5. The red mud dewatering method based on the coupling of solid waste filtration aid and gradient pressure filtration as described in claim 4, characterized in that, The industrial solid waste is one or a mixture of two of fly ash and slag, and the amount of the composite solid waste filter aid added is 1.5-3.0 wt% of the dry weight of red mud.

6. The red mud dewatering method based on the coupling of solid waste filtration aid and gradient pressure filtration as described in claim 1, characterized in that, The mixing process involves a double-helix stirring method with a stirring speed of 100-180 r / min and a stirring time of 15-30 minutes.

7. The red mud dewatering method based on the coupling of solid waste filtration aid and gradient pressure filtration as described in claim 1, characterized in that, The gradient pressure filtration step uses plate and frame filtration, and the filter cloth is a modified filter cloth with a pore size of 5-10μm.

8. The red mud dewatering method based on the coupling of solid waste filtration aid and gradient pressure filtration as described in claim 1, characterized in that, The initial pressure of the filter press is 0.5-0.8 MPa, and the filtration time is within 10 minutes; the pressure in the middle stage of the filter press is 1.2-1.5 MPa, and the filtration time is 10-30 minutes; the pressure in the later stage of the filter press is 1.8-2.2 MPa, and the filtration time is 30-60 minutes; the filter cake thickness is controlled to be 10-20 mm during the filter press process.

9. The red mud dewatering method based on the coupling of solid waste filtration aid and gradient pressure filtration as described in claim 1, characterized in that, The drying process employs waste heat recovery hot air circulation, with a drying temperature of 80-120℃ and a drying time of 2-3 hours, reducing the moisture content of the dehydrated red mud to below 4%.

10. A red mud dewatering system based on the coupling of solid waste filtration aid and gradient pressure filtration, characterized in that, include: The red mud pretreatment unit is used to pretreat red mud and adjust the pH value of the red mud slurry. The composite solid waste filter aid preparation unit is used to crush, calcine and grind industrial solid waste to make solid waste base material, and then combine the solid waste base material with chemical filter aid to make composite solid waste filter aid. The mixing unit is used to mix the pretreated red mud slurry with the composite solid waste filter aid evenly. A gradient filtration unit is used to perform gradient filtration on the mixed material. The gradient filtration includes at least an initial stage, a middle stage and a later stage of filtration, and the pressure applied in each stage increases sequentially. After filtration, filter cake and filtrate are obtained. The low-temperature drying unit is used to dry the filter cake after pressure filtration to obtain dehydrated red mud.

Images