Integrated device and process for red mud gradient temperature pyrolysis-melt glassification

Abstract

The present application relates to solid waste harmless and resource equipment technical field, specifically is a kind of red mud gradient temperature pyrolysis-melting vitrification integrated processing device and process.The device directly couples electromagnetic heating rotary kiln pyrolysis section and electrode melting section by high-temperature atmosphere isolation and material transfer device.Process is: after granulating red mud, reducing agent and flux, send into the rotary kiln by multiple electromagnetic induction coil partition precise temperature control, complete dehydration, selective reduction and iron particle polymerization in turn, output >1000 ℃ high-temperature pyrolysis slag;Pyrolysis slag is directly dropped into electric melting pool to complete melting and iron-slag liquid separation under the absolute isolation of reducing atmosphere and oxidizing atmosphere in the device, respectively obtain pig iron and stable glass body.The present application solves the problem of high energy consumption and complex process of traditional process by "hot slag direct melting" and "energy closed loop" design, realizes efficient recovery of iron resources in red mud and complete harmless and high-value utilization of residue.

Description

Technical Field

[0001] This invention relates to the field of equipment technology for the harmless and resource-based treatment of solid waste, specifically an integrated treatment device and process for red mud gradient temperature pyrolysis-melting vitrification. Background Technology

[0002] With the development of industrialization and urbanization, the output of solid waste in China has been increasing year by year. Red mud is a highly alkaline solid waste generated during the Bayer process of alumina production from bauxite. Approximately 0.8-1.5 tons of red mud are produced for every ton of alumina produced. Global red mud stockpiles have exceeded 4 billion tons and continue to increase at a rate of over 150 million tons per year. Red mud has a high pH value (pH 10-13), contains residual caustic alkali and various heavy metals. Long-term stockpiling not only occupies large amounts of land but also poses significant environmental and safety risks, including leachate pollution of groundwater, dust pollution of the atmosphere, and dam failure. Therefore, the large-scale, harmless, and resource-efficient disposal of red mud is a major environmental and technological challenge of concern to the alumina industry and globally.

[0003] Pyrometallurgical iron recovery is the most widely applied approach in red mud treatment and resource utilization research. However, it is energy-intensive, and the reduction product is a mechanical mixture of metallic iron and gangue slag. The separation of iron and slag is extremely incomplete, requiring fine grinding and strong magnetic separation, resulting in low iron recovery rates (typically <85%), low iron powder quality (<80%), and the generation of a large amount of tailings requiring secondary treatment. Wet processes are commonly used to extract valuable metals, but these methods generally suffer from lengthy processes, huge chemical reagent consumption, severe equipment corrosion, and the generation of large amounts of difficult-to-treat acidic or alkaline wastewater, making them economically and environmentally unfriendly and difficult to scale up industrially. Red mud can also be used to produce cement, bricks, and roadbed materials, but the alkali metals (Na, K) in red mud severely affect the long-term strength and durability of building materials. Red mud mixed with SiO2 can be melted to prepare glass ceramics, achieving complete harmlessness, but its fatal flaw is the huge energy consumption and failure to recover the valuable iron resources in the red mud, making its operating costs prohibitive.

[0004] To balance resource recovery and harmless disposal, researchers have recently begun exploring a combined process of "reduction and iron extraction + vitrification of residue." This involves first pyrolyzing and reducing red mud and then magnetically separating it to recover iron, followed by high-temperature melting and vitrification of the magnetic separation tailings. However, this method is extremely energy inefficient, complex, and costly. Furthermore, because pyrolysis and melting are designed as independent units, the material must undergo intermittent processes of cooling, storage, and reheating, failing to achieve efficient energy coupling and continuous material transfer. Existing technologies have not yet provided a red mud treatment solution that can simultaneously and continuously achieve efficient recovery of valuable metals, complete harmless disposal, and is industrially feasible in terms of energy consumption and cost.

[0005] Chinese patent application number 202210585207.4 discloses a method for recovering iron and tailings from red mud. This invention uses a loose coupling between the rotary kiln and the molten metal bath. The intermediate cooling and storage processes not only cause energy and material losses but also disrupt the continuity of the reducing atmosphere, leading to oxidation of the iron particles and ultimately reducing the yield and quality of the molten iron. The process does not actively control the slag composition and atmosphere to form a stable glassy network; instead, it forms a gel material through water quenching and drying. This results in a lengthy process, high energy consumption, and low added value. Furthermore, the product is inferior to a true vitrified solid in terms of heavy metal solidification stability and environmental safety.

[0006] Chinese patent application number 202210577975.5 discloses a method for the synergistic utilization of high-speed iron red mud and molten steel slag. The reduction and melting are completed in the same space and at the same time. The strong reducing atmosphere is not conducive to the formation of chemically stable glass, and the violent gas stirring in the molten pool will cause iron droplets to disperse in the slag, reducing the iron settling efficiency.

[0007] Chinese patent application number 202121029401.1 discloses an automatic slag discharge mechanism. The slag discharge valve is only used for opening and closing isolation of non-active media (such as wastewater) at normal or medium temperature and normal pressure. It uses ordinary steel and rubber / soft seals to prevent backflow. Therefore, its structural materials, sealing form and control objectives are completely unsuitable for the extreme working conditions faced by red mud pyrolysis and melting, such as high temperature (>950℃), reducing properties (containing CO / H2), alkaline volatiles, and the need to maintain precise control of the micro pressure difference at both ends. Summary of the Invention

[0008] To address the aforementioned problems, the present invention aims to provide an integrated treatment device and process for red mud gradient temperature pyrolysis-melting vitrification. By physically integrating the two key processes of material pyrolysis reduction and melting vitrification into a continuously operating system, and innovatively designing a dedicated high-temperature atmosphere isolation and material transfer device, the invention solves the technical problems of high energy consumption, long process, and incomplete resource recovery and harmlessness in existing red mud treatment methods.

[0009] To achieve absolute isolation between the pyrolysis section (reducing atmosphere) and the melting section (micro-oxidizing atmosphere) and the direct, continuous transfer of high-temperature materials (temperature > 950℃), this invention creatively incorporates a high-temperature atmosphere isolation and material transfer unit. The core of this unit is an integrated device combining a triple mechanism: a double-gate mechanical seal, a dynamic seal with inert gas in the transition chamber, and intelligent pressure interlock control. Its workflow is as follows: Ensuring the lower gate is sealed and the transition chamber is filled with inert protective gas, the upper gate is opened, allowing the high-temperature pyrolysis slag to enter the transition chamber under gravity. After reception, the upper gate is immediately closed, achieving the first level of physical isolation. After the upper gate is closed, the system initiates a "pump-and-fill" procedure. First, the trace amount of reducing gas carried into the transition chamber with the material is extracted to disrupt its reducing environment. Then, high-purity inert gas (such as N2) is rapidly introduced into the chamber until the oxygen content drops below a safe threshold (e.g., <1%). A precision pressure sensor is used to adjust the pressure within the chamber, achieving dynamic equilibrium with the pressure at the molten section inlet, forming a second dynamic gas curtain seal. Once a stable, inert, and pressure-balanced environment is confirmed within the transition chamber, the lower gate is opened, allowing all the high-temperature material to fall into the lower molten pool. After the material is emptied, the lower gate immediately closes, and the system automatically resumes introducing inert gas into the transition chamber and maintaining a slight positive pressure, establishing an initial protective environment for the next transfer. Throughout the process, the opening and closing of the upper and lower gates, along with gas purging and pressure monitoring, constitute a strict logical interlock, ensuring that at least one gate is closed and sealed at all times, and that the transition chamber maintains an inert atmosphere, fundamentally preventing atmospheric cross-contamination between the two reaction zones. This device is automatically controlled by a PLC (Programmable Logic Controller) and operates cyclically, achieving precise and continuous material transport and absolute atmospheric isolation.

[0010] The present invention provides an integrated treatment device for red mud gradient temperature pyrolysis-melting vitrification, comprising a feeding and pretreatment unit, a gradient temperature pyrolysis unit, a high-temperature atmosphere isolation and material transfer device, an electrode melting and vitrification unit, and a product collection and flue gas treatment system.

[0011] The gradient temperature pyrolysis unit includes a rotary kiln; the feeding and pretreatment unit is connected to the kiln head of the rotary kiln via a screw feeder, and the kiln tail of the rotary kiln is connected to the inlet of the cyclone separator located on the side.

[0012] The rotary kiln is an inclined, electromagnetically heated rotary kiln. The kiln's shell adopts a multi-layer composite structure, consisting of an inner lining layer, an induction heating layer, an insulating layer, and an outer protective shell, from the inside out. The induction heating layer is made of conductive magnetic material, while the outer protective shell is made of non-magnetic stainless steel. An electromagnetic induction coil is provided on the outside of the outer protective shell. The electromagnetic induction coil is a segmented induction coil, including a first group of coils, a second group of coils, and a third group of coils distributed sequentially along the rotary kiln's axial direction. The first group of coils corresponds to the preheating and dehydration zone, the second group of coils corresponds to the medium-temperature reduction zone, and the third group of coils corresponds to the high-temperature final reduction zone. An external induction heating power supply is electrically connected to the electromagnetic induction coil and supplies power to it. A PLC is electrically connected to the external induction heating power supply. The PLC controls the external induction heating power supply to independently adjust the input power and frequency of the electromagnetic induction coil, thereby achieving gradient temperature control.

[0013] The cyclone separator's outlet at the bottom connects to the inlet of the high-temperature atmosphere isolation and material transfer device at the top. The high-temperature atmosphere isolation and material transfer device internally comprises, from top to bottom, an upper gate chamber, a transition chamber, and a lower gate chamber. An upper valve seat is located at the top of the transition chamber, with an inverted frustum-shaped recess on its upper part. A first through-hole, also an inverted frustum-shaped hole, is located at the center of the upper valve seat, communicating with both the recess and the transition chamber. An upper gate is located at the bottom of the upper gate chamber, with a protrusion at its bottom matching the recess. The plate has an inverted frustum-shaped discharge port inside, and the large diameter end of the discharge port is connected to the upper gate chamber. The small diameter end of the discharge port is larger than the large diameter end of the first through hole. A partition is installed inside the discharge port. A plug protruding from the small diameter end of the discharge port is installed at the bottom of the partition, and the shape of the plug is adapted to the first through hole. The walls of the upper valve seat recess and the walls of the first through hole are inlaid with high-temperature flexible graphite sealing rings. The upper gate is connected to the piston rod of the first hydraulic drive device. When the piston rod moves, the upper gate moves towards or away from the upper valve seat. The first hydraulic drive device is electrically connected to the PLC.

[0014] The lower valve seat is installed at the top of the lower gate chamber, and the lower gate is installed at the bottom of the transition cavity. The lower gate is connected to the piston rod of the second hydraulic drive device. The second hydraulic drive device is electrically connected to the PLC. When the PLC controls the piston rod in the second hydraulic drive device to move, the lower gate moves towards or away from the lower valve seat. The structure of the lower valve seat and the lower gate is the same as that of the upper valve seat and the upper gate.

[0015] The upper gate plate is inserted into the upper valve seat, and the lower gate plate is inserted into the lower valve seat. At the same time, the wall of the upper valve seat recess is tightly fitted with the lower surface of the upper gate plate, and the wall of the lower valve seat recess is tightly fitted with the lower surface of the lower gate plate, so as to achieve airtight sealing of the transition cavity.

[0016] The high-temperature atmosphere isolation and material transfer device is also equipped with a purge gas inlet, an exhaust port, a pressure sensor, a high-temperature level gauge, an oxygen sensor, and a water-cooled jacket. The PLC is electrically connected to the first solenoid valve at the purge gas inlet, the second solenoid valve at the exhaust port, the pressure sensor, the high-temperature level gauge, and the oxygen sensor, respectively.

[0017] The electrode melting and vitrification unit includes an electric melting pool, a high-temperature atmosphere isolation and material transfer device located at the bottom with the discharge port connected to the electric melting pool, a graphite electrode inside the electric melting pool, an iron outlet at the bottom of the electric melting pool, a glass melt outlet on the side, and a gas inlet and a gas outlet on the top side; the gas outlet of the electric melting pool is connected to the product collection and flue gas treatment system through a pipeline.

[0018] Furthermore, the feeding and pretreatment unit includes a batching silo, a mixer, and a granulator. The outlet of the batching silo is connected to the inlet of the mixer, and the outlet of the mixer is connected to the inlet of the granulator. The outlet of the granulator is connected to the inlet of the screw feeder, and the outlet of the screw feeder is connected to the kiln head of the rotary kiln.

[0019] Furthermore, the batching silo is equipped with a red mud silo, a reducing agent silo, and a flux silo.

[0020] Furthermore, the screw feeder is a sealed screw feeder;

[0021] Furthermore, a rotary motor is used to drive the rotary kiln to rotate; a support device is provided at the bottom of the rotary kiln.

[0022] Furthermore, the inner lining of the rotary kiln is made of refractory material.

[0023] Furthermore, the outlet of the cyclone separator at the bottom is isolated from the high-temperature atmosphere, while the inlet of the material transfer device at the top is connected via a first flange connection interface.

[0024] Furthermore, the water-cooled jacket is located on the outside of the upper gate chamber, the transition cavity, and the lower gate chamber, and circulating cooling water flows through the water-cooled jacket.

[0025] Furthermore, the purge gas inlet, exhaust port, pressure sensor, high-temperature level gauge, and oxygen sensor are all located at positions corresponding to the transition cavity.

[0026] Furthermore, the discharge port of the high-temperature atmosphere isolation and material transfer device at the bottom is connected to the electrofusion tank through a second flange connection interface.

[0027] Furthermore, the product collection and flue gas treatment system includes an air preheater, a steam turbine, a generator, a quench tower, a bag filter, and a desulfurization and denitrification device. The gas outlet of the electrofused pool is connected to the air preheater via pipeline, the air preheater is connected to the steam turbine, the steam turbine is connected to the generator, and the gas outlet of the steam turbine is connected to the inlet of the quench tower, the quench tower is connected to the bag filter, the bag filter is connected to the desulfurization and denitrification device, and the generator supplies power to the graphite electrodes.

[0028] Furthermore, the generator's output is connected to an external induction heating power supply, and the generator also supplies power to the electromagnetic induction coil.

[0029] Furthermore, the pipeline between the gas outlet of the fused melting pool and the air preheater is connected to the outlet of the pyrolysis gas pipeline, the pipeline between the air preheater and the steam turbine is connected to the hot air drying pipeline, the outlet of the cyclone separator at the top is connected to the inlet of the pyrolysis gas pipeline and the inlet of the reflux pipeline respectively through the flow regulating valve, the outlet of the reflux pipeline is connected to the reducing atmosphere inlet of the rotary kiln head, and the outlet of the hot air drying pipeline is connected to the batching silo.

[0030] The electrode melting and vitrification section is a fixed, top-fed electrofusion pool. The pool body is rectangular and constructed of high-grade chromium corundum or refractory bricks. Multiple (e.g., 6) immersed graphite electrodes are inserted into the pool, directly submerged in the melt, and the high temperature (1300-1500℃) required for melting is provided by resistance heating. The pyrolysis slag falls directly into this high-temperature molten pool. Structurally, the molten pool is divided into an upper melting and clarification zone and a lower metal accumulation zone. Due to density differences, the reduced molten iron sinks to the bottom, forming a metal molten pool layer; the silicate slag phase in the upper part forms a homogeneous glass melt at high temperature. The metal layer is periodically or continuously discharged through a bottom siphon outlet and molded into pig iron ingots. The glass melt flows out continuously through the side wall outlet and can be water-quenched to form glass sand (building material aggregate) or used to prepare mineral wool fibers through a drawing machine.

[0031] In the flue gas treatment system, the high-temperature flue gas (>1200℃) generated in the melting section is introduced into a heat exchanger for drying the raw material red mud. The combustible gas generated in the pyrolysis section is preheated by an air preheater and then fed into a gas turbine or internal combustion engine to generate electricity. The electricity is used for electromagnetic heating in the electrode melting section and the pyrolysis section, forming an internal energy cycle. Finally, the exhaust gas is treated by a quench tower, bag filter, and desulfurization and denitrification devices before being discharged in compliance with standards.

[0032] This invention also provides an integrated process for the gradient temperature pyrolysis-melting vitrification of red mud, using the above-mentioned apparatus and specifically employing the following steps:

[0033] (1) First, the PLC closes the upper gate and the lower gate respectively through the first hydraulic drive device and the second hydraulic drive device, that is, the upper gate and the lower gate are both in a sealed state. Then, the purge gas inlet is opened and inert gas is injected into the transition cavity until the pressure sensor shows that the cavity pressure in the transition cavity is stable at the set value. Then, the rotary kiln is driven to rotate, and the electromagnetic induction coil of the rotary kiln is energized in sections to gradually raise the temperature to the working temperature. At the same time, the external power supply is energized to the graphite electrode of the electric melting pool to melt the flux in the pool to form the initial melting pool.

[0034] The rotary kiln is divided into three temperature control zones along its length: ① Preheating and dehydration zone: temperature 500-700℃, removing physical water and bound water, and partially decomposing aluminum hydroxide and goethite; ② Medium-temperature reduction zone: temperature 750-950℃, mainly the reduction reaction of Fe2O3→Fe3O4→FeO occurs, and some Na and K compounds volatilize; ③ High-temperature final reduction zone: temperature 1000-1100℃, FeO is deeply reduced to metallic iron and begins to aggregate and grow. At this stage, metallic iron mainly exists in the slag phase in the form of tiny molten droplets or soft agglomerates.

[0035] (2) The red mud, carbonaceous reducing agent and flux are metered, and the amount of material fed into the batching bin is controlled according to the preset formula. The material is fed into the mixer and mixed evenly, and then sent to the granulator to form dense pellets.

[0036] (3) The granulated mixture is fed into the preheated rotary kiln head by a screw feeder. The material enters the area heated by the first set of electromagnetic induction coils, and then the material enters the area controlled by the second and third sets of coils in sequence. Finally, the "iron-slag" composite pyrolysis slag and gas that have completed the reaction are discharged from the kiln tail.

[0037] (4) The gas-solid mixture discharged from the kiln tail immediately enters the cyclone separator. After the high-temperature dust-containing combustible gas is tangentially separated, the purified pyrolysis gas is sent to the product collection and flue gas treatment system from the top outlet of the cyclone separator. The separated high-temperature solid pyrolysis residue falls directly into the feed port of the high-temperature atmosphere isolation and material transfer device through the bottom outlet of the cyclone separator.

[0038] (5) The PLC automatically runs the high-temperature atmosphere isolation and material transfer device according to the preset program to complete one work cycle:

[0039] Receiving and Isolation: The PLC first confirms that both the upper and lower gates are in a sealed state, and that the transition chamber is pre-filled with inert gas at normal pressure. Then, the PLC commands the first hydraulic drive device to move, the upper gate rises, the material channel is exposed, and the high-temperature pyrolysis residue from the bottom outlet of the cyclone separator falls into the transition chamber through the upper gate chamber. When the high-temperature level gauge detects that the material has reached the preset "full" position, it immediately sends a signal to the PLC, which then commands the first hydraulic drive device to move, causing the upper gate to descend, the channel to close, and the first mechanical seal isolation to be completed, sealing the atmosphere of the pyrolysis section to the outside.

[0040] Purification and Balancing: After the upper gate is closed, the PLC controls the opening of the exhaust port and simultaneously injects inert gas into the transition chamber through the purge gas inlet to perform "purge and replacement". After the purge is completed, the exhaust port is closed. The PLC adjusts the air intake of the purge gas inlet according to the real-time feedback of the pressure sensor. The pressure in the transition chamber is stabilized at a slightly positive pressure state that is slightly higher than that at the feed inlet of the melting section. The water-cooled jacket operates throughout the process.

[0041] Release and Reset: The PLC commands the second hydraulic drive device to move, the lower gate rises, the material channel is exposed, and the high-temperature pyrolysis slag material falls directly into the electrofusion pool through the lower gate chamber. After the material in the transition chamber is emptied, the high-temperature level gauge sends an "empty material" signal, and the PLC immediately commands the lower gate to close. Subsequently, the PLC again fills the transition chamber with inert gas through the purge gas inlet to restore it to the initial protection state of slight positive pressure, preparing it for the next material receiving cycle (i.e., the working cycle).

[0042] (6) The high-temperature pyrolysis slag material is continuously and directly dropped into the electric melting pool through the above-mentioned high-temperature atmosphere isolation and material transfer device;

[0043] The graphite electrode is immersed in the melt and heated to maintain a high temperature. The high-temperature pyrolysis slag falling into the molten pool is quickly assimilated by the high-temperature melt. The molten iron settles and accumulates at the bottom of the electric melting pool to form an iron layer. The silicate melt floats on the top and is homogenized into glass melt. A small amount of air or oxygen is introduced into the upper part of the electric melting pool through the gas inlet. The molten iron at the bottom is periodically siphoned out through the iron outlet. The glass melt at the top overflows continuously through the overflow weir at the glass melt outlet. The high-temperature flue gas generated at the top is drawn out from the gas outlet on the side of the top of the electric melting pool and enters the product collection and flue gas treatment system. After treatment, it is discharged in compliance with standards.

[0044] Furthermore, in step (1), the amount of material fed into the batching bin is controlled according to the preset formula. The material enters the mixer and is mixed evenly, and then sent to the granulator to form dense pellets.

[0045] Furthermore, in step (1), the rotary motor is started to drive the rotary kiln to rotate at a low speed.

[0046] Furthermore, in step (1), the entire pyrolysis process is carried out under a slight negative pressure (-50 to -100 Pa) in the rotary kiln. The background gas in the kiln adopts an inert atmosphere (such as N2). At the same time, the reducing atmosphere required for the reduction reaction is provided by CO generated in situ at high temperature by the carbonaceous reducing agent added inside the material. This forms a local weak reducing microenvironment inside and on the surface of the material particles, thereby ensuring the full reduction of iron oxides.

[0047] Furthermore, in step (1), the residence time of the material in the rotary kiln is 60-120 minutes.

[0048] Furthermore, in step (1), the rotary kiln speed is adjusted to 0.5-3 rpm and the tilt angle is 2-5°.

[0049] Furthermore, in step (2), the moisture content of the red mud is ≤25%, the particle size of the carbonaceous reducing agent is ≤2mm, the amount of carbonaceous reducing agent added is 1.1-1.3 times the amount of carbon required for theoretical reduction, the flux, including SiO2, CaO, etc., the amount of flux added is preferably such that the final slag phase binary basicity CaO / SiO2 is 0.8-1.2, and the particle size of the dense spherical particles is 8-12mm.

[0050] Furthermore, in step (3), the granulated mixture is fed into the preheated rotary kiln head in a closed and quantitative manner by a screw feeder; the coil adopts medium frequency mode to make the heating layer of the kiln wall uniformly heat up to the set temperature.

[0051] Furthermore, in step (4), a portion of the purified pyrolysis gas is sent from the outlet at the top of the cyclone separator to the air preheater in the product collection and flue gas treatment system via the pyrolysis gas pipeline, and then sent to the generator via the steam turbine to generate electricity. The electricity can power the electromagnetic induction coil or the graphite electrode of the electric melting pool; the other portion is reused as reducing gas and sent to the reducing atmosphere inlet of the rotary kiln head.

[0052] Furthermore, in step (6), the temperature of the fused bath is maintained at 1350-1450℃.

[0053] Furthermore, the high-temperature flue gas generated at the top of the electric melting pool in step (6) is drawn out from the gas outlet on the side of the top of the electric melting pool and enters the product collection and flue gas treatment system. First, the air used for combustion is preheated from room temperature to above 500°C by the air preheater. Then, the flue gas can be connected to the steam turbine for power generation or directly used for raw material drying and is incorporated into the main exhaust gas treatment system. Finally, the tail gas is treated by the quench tower, bag filter, desulfurization and denitrification device and then discharged in compliance with the standards.

[0054] This invention continuously completes the gradient temperature pyrolysis and high-temperature melting vitrification of red mud in a single rotary integrated device.

[0055] Compared with the prior art, the present invention has the following beneficial effects:

[0056] (1) This invention pioneers a "continuous pyrolysis-melting integrated" "direct melting of hot slag" path. High-temperature pyrolysis slag at >950℃ is directly and continuously introduced into the molten pool, completely eliminating the intermediate cooling, storage, and reheating steps. This eliminates the largest sensible heat loss and reheating energy consumption in the traditional process from the source, significantly reducing overall energy consumption and greatly reducing operating costs (it is expected to reduce the energy consumption of the melting section by more than 30%-50%).

[0057] (2) A high-temperature atmosphere isolation and material transfer device was invented, which realizes the continuous and controllable transfer of high-temperature solid materials and the absolute isolation between different reaction atmospheres. It realizes the physical rigid coupling between the pyrolysis unit and the melting unit at high temperature, thus forming the key hub of the "integrated device".

[0058] (3) The efficient recovery of valuable metals (iron) and the complete vitrification and stabilization of residues are achieved simultaneously in one process. By adjusting the flux, the composition of the vitrified body is controlled so that its performance meets the requirements of high-value applications; pig iron and building materials with direct market value are produced, creating economic benefits. Moreover, the final vitrified product is an environmentally friendly inert material, which solves the long-term environmental risks caused by red mud stockpiling and realizes the transformation from "waste treatment" to "resource creation". Attached Figure Description

[0059] Figure 1 This is a schematic diagram of the integrated red mud gradient temperature pyrolysis-melting vitrification treatment device of the present invention;

[0060] Figure 2 This is a diagram showing the positional relationship between the upper gate chamber, the transition cavity, and the lower gate chamber in a high-temperature atmosphere isolation and material transfer device.

[0061] Figure 3 This is a structural schematic diagram of the upper gate and upper valve seat.

[0062] Figure label:

[0063] 1- Batching bin, 2- Mixer, 3- Granulator, 4- Screw feeder, 5- Electromagnetic induction coil, 6- Rotary kiln, 7- Cyclone separator, 8- High-temperature atmosphere isolation and material transfer device, 9- Upper gate, 10- Lower gate, 11- PLC, 12-Air preheater, 13-Quick cooler tower, 14-Bag filter, 15-Desulfurization and denitrification device, 16-Generator, 17-Steam turbine, 18-Glass melt outlet, 19-Electric melting pool, 20-Graphite electrode, 21-Iron outlet, 22-Support device, 23-Rotating motor, 24-First flange connection interface, 25-Upper gate chamber, 26-First hydraulic drive device, 27-Pressure sensor, 28-High temperature level gauge, 29-Lower gate chamber, 30-Transition cavity, 31-Purge gas inlet, 32-Exhaust port, 33-Oxygen sensor, 34-Water-cooled jacket, 35-Upper valve seat. Detailed Implementation

[0064] To better understand the content of this invention, it will be further described below with reference to specific embodiments and accompanying drawings. The following embodiments are based on the technology of this invention and provide detailed implementation methods and operating steps, but the scope of protection of this invention is not limited to the following embodiments.

[0065] In the description of this invention, it should be understood that the terms "center", "upper", "lower", "front", "rear", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0066] Please combine Figure 1-3 The device of the present invention has a linear and compact layout along the material flow direction.

[0067] An integrated treatment device for red mud gradient temperature pyrolysis-melting vitrification includes a feeding and pretreatment unit, a gradient temperature pyrolysis unit, a high-temperature atmosphere isolation and material transfer device, an electrode melting and vitrification unit, and a product collection and flue gas treatment system.

[0068] The feeding and pretreatment unit includes a batching silo 1, a mixer 2, and a granulator 3. The batching silo 1 contains a red mud silo, a reducing agent silo, and a flux silo. The outlet of the batching silo 1 is connected to the inlet of the mixer 2. Materials discharged from the red mud silo, reducing agent silo, and flux silo enter the mixer 2 through the outlet of the batching silo 1. The outlet of the mixer 2 is connected to the inlet of the granulator 3. The feed rate of each silo (red mud silo, reducing agent silo, flux silo) is controlled according to a preset formula. The materials enter the mixer 2 and are thoroughly mixed. The mixture is then fed into the granulator 3 to form dense pellets with a particle size of 8-12 mm, thereby improving the permeability and reaction efficiency of the subsequent pyrolysis process. The arrangement of the red mud silo, reducing agent silo, and flux silo in the batching silo 1, the control of the feed rate of each silo in the batching silo 1, and the discharge of materials through the outlet of the batching silo 1 are existing technologies and will not be elaborated further here.

[0069] The gradient temperature pyrolysis unit includes a rotary kiln 6.

[0070] The outlet of granulator 3 is connected to the inlet of screw feeder 4, the outlet of screw feeder 4 is connected to the kiln head of rotary kiln 6, and the kiln tail of rotary kiln 6 is connected to the inlet of cyclone separator 7 located on the side. Cyclone separator 7 initially separates solid materials from combustible gases (mainly containing CO, H2, and CH4) generated by pyrolysis. Rotary motor 23 is used to drive rotary kiln 6 to rotate.

[0071] In this embodiment, the screw feeder 4 is a sealed screw feeder to prevent air leakage. The rotary kiln 6 is an inclined, electromagnetically heated rotary kiln. A support device 22 is provided at the bottom of the rotary kiln 6. The cylinder of the rotary kiln 6 adopts a multi-layer composite structure, consisting of an inner lining layer, an induction heating layer, an insulation layer, and an outer protective shell from the inside out. The inner lining layer is made of high-performance refractory material, the induction heating layer is made of conductive magnetic material, and the outer protective shell is made of non-magnetic stainless steel. An electromagnetic induction coil 5 is provided on the outside of the outer protective shell. The electromagnetic induction coil 5 is a segmented induction coil and includes a first group of coils and a second group of coils distributed sequentially along the axial direction of the rotary kiln 6. The third group of coils, each corresponding to an independent temperature control zone, specifically, the first group corresponds to the preheating and dehydration zone, the second group to the medium-temperature reduction zone, and the third group to the high-temperature final reduction zone. An external induction heating power supply is electrically connected to and powers the electromagnetic induction coil 5. When energized, the electromagnetic induction coil 5 generates an alternating magnetic field, which acts on the induction heating layer of the cylinder, causing eddy currents to form inside and generate heat. The PLC 11 is connected to the external induction heating power supply, controlling it to independently adjust the input power and frequency of the electromagnetic induction coil 5, thereby achieving gradient temperature control. The output of the generator 16 is also connected to the external induction heating power supply.

[0072] The cyclone separator 7, located at its bottom outlet, is connected to the high-temperature atmosphere isolation and material transfer device 8, located at its top inlet, via a first flange connection interface 24. The high-temperature atmosphere isolation and material transfer device 8 internally comprises, from top to bottom, an upper gate chamber 25, a transition cavity 30, and a lower gate chamber 29. An upper valve seat 35 is located at the top of the transition cavity 30, with an inverted frustum-shaped recess at its upper part. A first through hole, also inverted frustum-shaped, is located at the center of the upper valve seat 35, communicating with both the recess and the transition cavity 30. The bottom of the upper gate chamber 25 is equipped with an upper gate 9, with a corresponding opening at its bottom. The matching protrusion, the interior of the upper gate plate 9 is provided with an inverted frustum-shaped discharge port, and the large diameter end of the discharge port is connected to the upper gate plate chamber 25. The small diameter end of the discharge port is larger than the large diameter end of the first through hole. The interior of the discharge port is provided with a partition, and the bottom of the partition is provided with a plug protruding from the small diameter end of the discharge port. The shape of the plug is adapted to the first through hole. When the upper gate plate 9 is in the closed state, the plug at the bottom of the partition in the upper gate plate 9 is inserted and connected to the upper valve seat 35. The lower surface of the upper gate plate 9 is in close contact with the wall of the recess of the upper valve seat 35. The wall of the recess of the upper valve seat 35 and the wall of the first through hole are both inlaid with high temperature flexible graphite sealing rings to achieve airtight sealing. The upper gate 9 is connected to the piston rod of the first hydraulic drive device 26. When the piston rod moves, the upper gate 9 moves toward or away from the upper valve seat 35. The first hydraulic drive device 26 is electrically connected to the PLC 11, and the PLC 11 controls the movement of the piston rod in the first hydraulic drive device 26.

[0073] The upper valve seat 35 is a fixed component that the upper gate 9 abuts against when it is closed. The wall surface of the recess in the upper valve seat 35 and the wall surface of the first through hole are the sealing mating surfaces of the upper gate 9, providing stable rigid support for sealing. When the upper gate 9 is in the closed state, its sealing surface is tightly pressed against the sealing surface of the upper valve seat 35 under the continuous thrust of the piston rod of the first hydraulic drive device 26.

[0074] A lower valve seat is provided at the top of the lower gate chamber 29, and a lower gate 10 is provided at the bottom of the transition cavity 30. The lower gate 10 is connected to the piston rod of the second hydraulic drive device. The second hydraulic drive device is electrically connected to the PLC 11. When the PLC 11 controls the piston rod in the second hydraulic drive device to move, the lower gate 10 moves towards or away from the lower valve seat. The structure of the lower valve seat and the lower gate 10 is the same as that of the upper valve seat 35 and the upper gate 9, and will not be described again here.

[0075] The high-temperature atmosphere isolation and material transfer device 8 is also equipped with a water-cooled jacket 34. The water-cooled jacket 34 is located outside the upper gate chamber 25, the transition cavity 30, and the lower gate chamber 29. The water-cooled jacket 34 is filled with circulating cooling water to continuously remove the heat absorbed by the device from the high-temperature material, ensuring that the operating temperature of the device is always maintained within a safe range, and guaranteeing the long-term operational stability and sealing reliability of the device under extreme high temperatures. The high-temperature atmosphere isolation and material transfer device 8 is also equipped with a purge gas inlet 31, an exhaust port 32, a pressure sensor 27, a high-temperature level gauge 28, and an oxygen sensor 33. The purge gas inlet 31, the exhaust port 32, the pressure sensor 27, the high-temperature level gauge 28, and the oxygen sensor 33 are all located at positions corresponding to the transition cavity 30. The PLC 11 is electrically connected to the first solenoid valve at the purge gas inlet 31, the second solenoid valve at the exhaust port 32, the pressure sensor 27, the high-temperature level gauge 28, and the oxygen sensor 33, respectively.

[0076] The electrode melting and vitrification unit includes an electric melting pool 19. The discharge port of the high-temperature atmosphere isolation and material transfer device 8 located at the bottom is connected to the electric melting pool 19 through a second flange connection interface. The electric melting pool 19 is equipped with a graphite electrode 20. The bottom of the electric melting pool 19 is equipped with an iron outlet 21, the side is equipped with a glass melt outlet 18, and the top of the side is equipped with a gas inlet and a gas outlet.

[0077] The product collection and flue gas treatment system includes an air preheater 12, a steam turbine 17, a generator 16, a quench tower 13, a bag filter 14, and a desulfurization and denitrification device 15. The gas outlet of the fused bath 19 is connected to the air preheater 12 via a pipeline. The air preheater 12 is connected to the steam turbine 17, and the steam turbine 17 is connected to the generator 16. The gas outlet of the steam turbine 17 is connected to the inlet of the quench tower 13, which is connected to the bag filter 14. The bag filter 14 is connected to the desulfurization and denitrification device 15. The generator 16 supplies power to the graphite electrode 20 and the electromagnetic induction coil 5.

[0078] The outlet of the pyrolysis gas pipeline is connected to the pipeline between the gas outlet of the electric melting pool 19 and the air preheater 12. The hot air drying pipeline is connected to the pipeline between the air preheater 12 and the steam turbine 17. The outlet of the cyclone separator 7 at the top is connected to the inlet of the pyrolysis gas pipeline and the inlet of the reflux pipeline through a flow regulating valve. The outlet of the reflux pipeline is connected to the reducing atmosphere inlet of the rotary kiln head. The outlet of the hot air drying pipeline is connected to the batching bin 1, and the heat of the hot air is used to dry the materials in the batching bin 1.

[0079] An integrated process for red mud gradient temperature pyrolysis-melting vitrification, using the above-mentioned apparatus, specifically comprises the following steps:

[0080] (1) First, PLC11 closes the upper gate 9 and lower gate 10 respectively through the first hydraulic drive device 26 and the second hydraulic drive device. At this time, the upper gate 9 is located between the upper gate chamber 25 and the transition cavity 30. The plug at the bottom of the partition in the upper gate 9 is inserted and connected to the upper valve seat 35. The sealing mating surface of the upper gate 9 is tightly fitted with the sealing surface of the upper valve seat 35. At the same time, the plug at the bottom of the partition in the lower gate is inserted and connected to the lower valve seat. The sealing mating surface of the lower gate is tightly fitted with the sealing surface of the lower valve seat. The purge gas inlet 3 of the high temperature atmosphere isolation and material transfer device 8 is opened. 1. Inert gas, in this embodiment, nitrogen, is introduced into the transition cavity 30 until the pressure sensor 27 shows that the cavity pressure is stable at the set value (the set value is slightly higher than both ends, that is, the set value is slightly higher than the pressure at the bottom outlet of the cyclone separator 7 and the space pressure at the top of the electric melting pool 19). Then, the rotary motor 23 is started to drive the rotary kiln 6 to rotate at low speed. Then, the electromagnetic induction coil 5 of the rotary kiln 6 is energized in sections to gradually raise the temperature to the working temperature. At the same time, the external power supply is energized to the graphite electrode 20 of the electric melting pool 19 to melt the flux in the pool (mainly including SiO2 and CaO) to form the initial molten pool.

[0081] The rotary kiln 6 is set to a rotation speed of 0.5-3 rpm and an inclination angle of 2-5°. It is divided into three temperature control zones along the length of the kiln: ① Preheating and dehydration zone (temperature 500-700℃): physical water and bound water are removed, and some aluminum hydroxide and goethite are decomposed; ② Medium-temperature reduction zone (temperature 750-950℃): the reduction reaction of Fe2O3→Fe3O4→FeO mainly occurs, and some Na and K compounds volatilize; ③ High-temperature final reduction zone (temperature 1000-1100℃): FeO is deeply reduced to metallic iron (Fe) and begins to aggregate and grow. At this stage, metallic iron mainly exists in the slag phase in the form of tiny molten droplets or soft agglomerates. The entire pyrolysis process is carried out under a slight negative pressure (-50 to -100 Pa) in rotary kiln 6. The background gas in the kiln is an inert atmosphere (such as N2). At the same time, the reducing atmosphere required for the reduction reaction is provided by CO generated in situ at high temperature by the carbonaceous reducing agent added inside the material. This creates a local weak reducing microenvironment inside and on the surface of the material particles, thereby ensuring the full reduction of iron oxides. The residence time of the material in the kiln is 60-120 minutes.

[0082] (2) The red mud with a moisture content of ≤25%, the carbonaceous reducing agent with a particle size of ≤2mm (the amount of carbonaceous reducing agent added is 1.1-1.3 times the amount of carbon required for theoretical reduction) and the flux (including SiO2, CaO, etc., the amount of flux added should be such that the final slag phase binary basicity CaO / SiO2 is 0.8-1.2) are accurately measured. The amount of material fed into each bin of the batching bin 1 is controlled according to the preset formula. The material enters the mixer 2 and is fully mixed evenly. Then it is fed into the granulator 3 to make dense granules with a particle size of 8-12mm to improve the permeability and reaction efficiency of the subsequent pyrolysis process.

[0083] (3) The granulated mixture is fed into the preheated rotary kiln 6 in a sealed and quantitative manner by the screw feeder 4. In this embodiment, the preheating temperature is about 500°C. The material enters the area heated by the first set of coils of the electromagnetic induction coil 5. The coil adopts the medium frequency mode to make the heating layer of the kiln wall uniformly heat up to the set temperature. Then the material enters the area controlled by the second and third sets of coils in sequence. The iron oxide (Fe2O3) is selectively reduced to FeO / Fe3O4, and a large amount of alkali metal compounds volatilize. The strong heat flow and the "self-heating" effect of the metal iron particles already generated in the material are superimposed, so that FeO is deeply reduced to metal iron, and the iron particles rapidly aggregate and grow to 10-50 micrometers. Finally, the "iron-slag" composite pyrolysis slag and gas, which have completed the reaction and reached a temperature of 1050±20°C, are discharged from the kiln tail.

[0084] (4) The gas-solid mixture discharged from the kiln tail immediately enters the cyclone separator 7. After the high-temperature dust-containing combustible gas is tangentially separated, part of the purified pyrolysis gas is sent from the top outlet of the cyclone separator 7 through the pyrolysis gas pipeline to the air preheater 12 in the product collection and flue gas treatment system. Then it is sent to the generator 16 for power generation via the steam turbine 17 (the electricity is used by this system. Specifically, the electricity can supply power to the electromagnetic induction coil 5 or the graphite electrode 20 of the electric melting pool 19). The other part can be reused as reducing gas. Specifically, it is sent to the reducing atmosphere inlet of the kiln head of the rotary kiln 6 through the return pipeline. The separated high-temperature solid pyrolysis slag falls directly into the feed port of the high-temperature atmosphere isolation and material transfer device 8 through the bottom outlet of the cyclone separator 7.

[0085] (5) PLC11 automatically runs the high-temperature atmosphere isolation and material transfer device 8 according to the preset program to complete one work cycle:

[0086] Receiving and Isolation: PLC11 first confirms that both the upper gate 9 and the lower gate 10 are in a sealed state, and that the transition cavity 30 is pre-filled with inert gas at normal pressure. Then, PLC11 commands the first hydraulic drive device 26 to move, the upper gate 9 rises, the material channel is exposed, and the high-temperature pyrolysis residue from the bottom outlet of the cyclone separator 7 falls into the transition cavity 30 through the upper gate chamber 25 under the action of gravity. When the high-temperature level gauge 28 detects that the material has reached the preset "full" position, it immediately sends a signal to PLC11. PLC11 then commands the first hydraulic drive device 26 to move, causing the upper gate 9 to fall and the channel to close, completing the first mechanical seal isolation and sealing the atmosphere of the pyrolysis section to the outside.

[0087] Purification and Balancing: After the upper gate 9 is closed, PLC11 controls the opening of the exhaust port 32, and simultaneously injects high-pressure inert gas into the transition chamber 30 through the purge gas inlet 31 for "purge and replacement." This step aims to forcibly expel the small amount of reducing gas that enters the chamber with the pyrolysis residue, disrupting its reducing environment. Based on the feedback signals from the oxygen sensor 33 and the pressure sensor 27, and the minimum purge gas volume (calculated based on the chamber volume), after purging is completed, the exhaust port 32 is closed. PLC11, based on the real-time feedback from the pressure sensor 27, finely adjusts the air intake of the purge gas inlet 31, stabilizing the pressure in the transition chamber 30 at a slightly positive pressure state slightly higher than that at the molten section inlet, forming a stable "inert gas curtain" dynamic seal. The water-cooled jacket 34 operates throughout the process, ensuring the structural safety and stability of the drive components of the device under extreme high temperatures.

[0088] Release and Reset: After confirming that the atmosphere (oxygen content <1%) and pressure in the transition chamber 30 meet the requirements of the melting section, PLC11 instructs the second hydraulic drive device to move, the lower gate 10 rises, the material channel is exposed, and the high-temperature pyrolysis slag material falls directly into the electrofusion pool 19 through the lower gate chamber 29. After the material in the transition chamber 30 is emptied, the high-temperature level gauge 28 sends an "empty material" signal, and PLC11 immediately instructs the lower gate 10 to close. Subsequently, PLC11 again fills the transition chamber 30 with inert gas through the purge gas inlet 31 to restore it to the initial protection state of slight positive pressure, preparing it for the next material receiving cycle.

[0089] The core control logic of the high-temperature atmosphere isolation and material transfer device is that the opening and closing of the upper and lower gates, together with the inert gas purging and pressure monitoring, form a strict logical interlock to ensure that the atmosphere between the pyrolysis section and the melting section is absolutely isolated by physical or dynamic gas curtain at any stage of operation, thereby ensuring that iron is not oxidized secondary and realizing the continuous transfer of high-temperature materials with "zero oxidation".

[0090] (6) The high-temperature pyrolysis slag material (temperature > 950℃, at which point the metallic iron has partially polymerized but has not yet completely separated from the slag) is continuously and directly dropped into the electric melting pool 19, whose temperature is maintained at 1350-1450℃, through the high-temperature atmosphere isolation and material transfer device 8. In this embodiment, the temperature of the electric melting pool 19 is maintained at 1400±20℃. This step is the core of energy saving, completely avoiding the cooling and reheating of the material.

[0091] The graphite electrode 20 is immersed in the melt and maintained at a high temperature by resistance heating; the high-temperature pyrolysis slag falling into the molten pool is rapidly assimilated by the high-temperature melt. Under the high temperature and strong convection of the molten pool, the dispersed metallic iron particles are completely melted and, due to the huge density difference (the density of molten iron is about 7.0 g / cm³), they are absorbed into the melt. 3 The slag density is approximately 2.8 g / cm³. 3The molten iron rapidly sinks and accumulates at the bottom of the furnace. Under the influence of high temperature and flux, the silicate melt at the top forms a highly fluid and homogenized glassy melt. Specifically, the denser molten iron settles and accumulates at the bottom of the molten iron pool 19, forming an iron layer; the less dense silicate melt floats to the top and, under the influence of high temperature and flux, homogenizes into a glassy melt. A small amount of air or oxygen is introduced into the upper part of the molten iron pool 19 through a gas inlet to burn off the remaining small amount of carbon and provide some heat, while simultaneously maintaining the melt in a slightly oxidized state, which is conducive to the formation of a stable glassy network structure. The molten iron at the bottom of the molten iron pool 19 (temperature approximately 1350-1400℃, C content 3.5-4.2% by mass) is periodically (e.g., every 4-8 hours) siphoned out through the molten iron outlet 21, cast into pig iron ingots, which can be used as raw material for steelmaking. The glassy melt at the top, with a temperature of approximately 1300-1350℃, continuously overflows through the overflow weir at the glassy melt outlet 18. The high-temperature flue gas (approximately 1350°C) generated at the top of the fused melting pool 19 is rich in sensible heat but contains virtually no combustible components. It is drawn from the gas outlet on the side of the top of the fused melting pool 19 and enters the product collection and flue gas treatment system. Specifically, it first passes through an air preheater 12, which preheats the combustion air from ambient temperature to above 500°C (for system startup or standby). Subsequently, this flue gas can be connected to the steam turbine 17 for power generation or directly used for raw material drying, and then merged into the main exhaust gas treatment system. Finally, the exhaust gas is treated by a quench tower 13, a bag filter 14, and a desulfurization and denitrification device 15 before being discharged in compliance with standards.

[0092] As mentioned earlier, all high-temperature flue gas and heat from combustible gases within the system are recovered and utilized in stages. All waste gases undergo end-of-pipe purification treatment to ensure SO₂ levels are within acceptable limits. x NO x Dust and heavy metal vapor emissions meet standards. The molten glass has undergone authoritative toxicity leaching tests, confirming that its heavy metal leaching concentration is far below the national hazardous waste identification standards, achieving complete harmlessness.

[0093] The above description is merely an embodiment of the present invention and is not intended to limit the present invention in any way. The present invention can also have other embodiments based on the above structure and function, which will not be listed hereafter. Therefore, any simple modifications, equivalent changes, and alterations made by those skilled in the art to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. An integrated treatment device for red mud gradient temperature pyrolysis-melting vitrification, characterized in that, It includes a feeding and pretreatment unit, a gradient temperature pyrolysis unit, a high-temperature atmosphere isolation and material transfer device, an electrode melting and vitrification unit, and a product collection and flue gas treatment system; The gradient temperature pyrolysis unit includes a rotary kiln; the feeding and pretreatment unit is connected to the kiln head of the rotary kiln via a screw feeder, and the kiln tail of the rotary kiln is connected to the inlet of the cyclone separator located on the side. The rotary kiln is an inclined, electromagnetically heated rotary kiln. The kiln body adopts a multi-layer composite structure, consisting of an inner lining layer, an induction heating layer, an insulation layer, and an outer protective shell, from the inside out. An electromagnetic induction coil is provided on the outside of the outer protective shell along the kiln body axis. The electromagnetic induction coil is a segmented induction coil, including a first group of coils, a second group of coils, and a third group of coils distributed sequentially along the rotary kiln axis. The first group of coils corresponds to the preheating and dehydration zone, the second group of coils corresponds to the medium-temperature reduction zone, and the third group of coils corresponds to the high-temperature final reduction zone. An external induction heating power supply is electrically connected to the electromagnetic induction coil and supplies power to the electromagnetic induction coil. The PLC is electrically connected to the external induction heating power supply. The cyclone separator's outlet at the bottom connects to the inlet of the high-temperature atmosphere isolation and material transfer device at the top. The high-temperature atmosphere isolation and material transfer device internally comprises, from top to bottom, an upper gate chamber, a transition chamber, and a lower gate chamber. An upper valve seat is located at the top of the transition chamber, with an inverted frustum-shaped recess on its upper part. A first through-hole, also an inverted frustum-shaped hole, is located at the center of the upper valve seat, communicating with both the recess and the transition chamber. The bottom of the upper gate chamber is equipped with an upper gate. The upper gate is provided with a protrusion that matches the recess. The interior of the upper gate is provided with an inverted frustum-shaped discharge port, and the large diameter end of the discharge port is connected to the upper gate chamber. The small diameter end of the discharge port is larger than the large diameter end of the first through hole. The interior of the discharge port is provided with a partition. The bottom of the partition is provided with a plug protruding from the small diameter end of the discharge port, and the shape of the plug is adapted to the first through hole. The upper gate is connected to the piston rod of the first hydraulic drive device. When the piston rod moves, the upper gate moves towards or away from the upper valve seat. The first hydraulic drive device is electrically connected to the PLC. The lower valve seat is installed at the top of the lower gate chamber, and the lower gate is installed at the bottom of the transition cavity. The lower gate is connected to the piston rod of the second hydraulic drive device. The second hydraulic drive device is electrically connected to the PLC. When the PLC controls the piston rod in the second hydraulic drive device to move, the lower gate moves towards or away from the lower valve seat. The structure of the lower valve seat and the lower gate is the same as that of the upper valve seat and the upper gate. The high-temperature atmosphere isolation and material transfer device is also equipped with a purge gas inlet, an exhaust port, a pressure sensor, a high-temperature level gauge, an oxygen sensor, and a water-cooled jacket. The PLC is electrically connected to the first solenoid valve at the purge gas inlet, the second solenoid valve at the exhaust port, the pressure sensor, the high-temperature level gauge, and the oxygen sensor, respectively. The electrode melting and vitrification unit includes an electric melting pool, a high-temperature atmosphere isolation and material transfer device located at the bottom with the discharge port connected to the electric melting pool, a graphite electrode inside the electric melting pool, an iron outlet at the bottom of the electric melting pool, a glass melt outlet on the side, and a gas inlet and a gas outlet on the top side; the gas outlet of the electric melting pool is connected to the product collection and flue gas treatment system through a pipeline.

2. The integrated red mud gradient temperature pyrolysis-melting vitrification treatment device as described in claim 1, characterized in that, The feeding and pretreatment unit includes a batching hopper, a mixer, and a granulator. The outlet of the batching hopper is connected to the inlet of the mixer, and the outlet of the mixer is connected to the inlet of the granulator. The outlet of the granulator is connected to the inlet of the screw feeder, and the outlet of the screw feeder is connected to the kiln head of the rotary kiln. A rotary motor is used to drive the rotary kiln to rotate, and a support device is provided at the bottom of the rotary kiln. The inner lining of the rotary kiln is made of refractory material, the induction heating layer is made of conductive magnetic material, and the outer protective shell is made of non-magnetic stainless steel.

3. The integrated red mud gradient temperature pyrolysis-melting vitrification treatment device as described in claim 1, characterized in that, The batching silo contains a red mud silo, a reducing agent silo, and a flux silo; the screw feeder is a sealed screw feeder; the outlet of the cyclone separator at the bottom is isolated from the high-temperature atmosphere, and the inlet of the material transfer device at the top is connected to the first flange interface; the outlet of the high-temperature atmosphere isolation and material transfer device at the bottom is connected to the electrofusion tank through the second flange interface; the walls of the upper valve seat recess and the walls of the first through hole are both inlaid with high-temperature flexible graphite sealing rings.

4. The integrated red mud gradient temperature pyrolysis-melting vitrification treatment device as described in claim 1, characterized in that, The water-cooled jacket is located on the outside of the upper gate chamber, the transition cavity, and the lower gate chamber, and circulating cooling water flows through the water-cooled jacket; the purging gas inlet, exhaust port, pressure sensor, high-temperature level gauge, and oxygen sensor are all located at positions corresponding to the transition cavity.

5. The integrated red mud gradient temperature pyrolysis-melting vitrification treatment device as described in claim 1, characterized in that, The product collection and flue gas treatment system includes an air preheater, a steam turbine, a generator, a quench tower, a bag filter, and a desulfurization and denitrification device. The gas outlet of the electrofused pool is connected to the air preheater via pipeline. The air preheater is connected to the steam turbine, the steam turbine is connected to the generator, and the gas outlet of the steam turbine is connected to the inlet of the quench tower. The quench tower is connected to the bag filter, the bag filter is connected to the desulfurization and denitrification device, and the generator supplies power to the graphite electrodes. The generator's output is connected to an external induction heating power supply.

6. The integrated red mud gradient temperature pyrolysis-melting vitrification treatment device as described in claim 5, characterized in that, The pipeline between the gas outlet of the fused melting pool and the air preheater is connected to the outlet of the pyrolysis gas pipeline. The pipeline between the air preheater and the steam turbine is connected to the hot air drying pipeline. The outlet of the cyclone separator at the top is connected to the inlet of the pyrolysis gas pipeline and the inlet of the reflux pipeline respectively through a flow regulating valve. The outlet of the reflux pipeline is connected to the reducing atmosphere inlet of the rotary kiln head. The outlet of the hot air drying pipeline is connected to the batching silo.

7. An integrated treatment process for red mud gradient temperature pyrolysis-melting vitrification, employing the apparatus described in any one of claims 1-6, characterized in that, The specific steps are as follows: (1) First, the PLC closes the upper gate and the lower gate respectively through the first hydraulic drive device and the second hydraulic drive device, that is, the upper gate and the lower gate are both in a sealed state. Then, the purge gas inlet is opened and inert gas is injected into the transition cavity until the pressure sensor shows that the cavity pressure in the transition cavity is stable at the set value. Then, the rotary kiln is driven to rotate, and the electromagnetic induction coil of the rotary kiln is energized in sections to gradually raise the temperature to the working temperature. At the same time, the external power supply is energized to the graphite electrode of the electric melting pool to melt the flux in the pool to form the initial melting pool. The rotary kiln is divided into three temperature control zones along its length: ① Preheating and dehydration zone: temperature 500-700℃; ② Medium-temperature reduction zone: temperature 750-950℃; ③ High-temperature final reduction zone: temperature 1000-1100℃. (2) The red mud, carbonaceous reducing agent and flux are metered, and the amount of material fed is controlled by the feeding and pretreatment unit according to the preset formula to make dense pellets; (3) The granulated mixture is fed into the preheated rotary kiln head by a screw feeder. The material enters the area heated by the first set of electromagnetic induction coils, and then the material enters the area controlled by the second and third sets of coils in sequence. Finally, the "iron-slag" composite pyrolysis slag and gas that have completed the reaction are discharged from the kiln tail. (4) The gas-solid mixture discharged from the kiln tail immediately enters the cyclone separator. After the high-temperature dust-containing combustible gas is tangentially separated, the purified pyrolysis gas is sent to the product collection and flue gas treatment system from the top outlet of the cyclone separator. The separated high-temperature solid pyrolysis residue falls directly into the feed port of the high-temperature atmosphere isolation and material transfer device through the bottom outlet of the cyclone separator. (5) The PLC automatically runs the high-temperature atmosphere isolation and material transfer device according to the preset program to complete one work cycle: Receiving and Isolation: The PLC first confirms that both the upper and lower gates are in a sealed state, and that the transition chamber is pre-filled with inert gas at normal pressure. Then, the PLC commands the first hydraulic drive device to move, the upper gate rises, the material channel is exposed, and the high-temperature pyrolysis residue from the bottom outlet of the cyclone separator falls into the transition chamber through the upper gate chamber. When the high-temperature level gauge detects that the material has reached the preset "full" position, it immediately sends a signal to the PLC, which then commands the first hydraulic drive device to move, causing the upper gate to descend and the channel to close, completing the first mechanical seal isolation and sealing the atmosphere of the pyrolysis section to the outside. Purification and Balancing: After the upper gate is closed, the PLC controls the opening of the exhaust port and simultaneously injects inert gas into the transition chamber through the purge gas inlet to perform "purge and replacement". After the purge is completed, the exhaust port is closed. The PLC adjusts the air intake of the purge gas inlet according to the real-time feedback of the pressure sensor. The pressure in the transition chamber is stabilized at a slightly positive pressure state that is slightly higher than that at the feed inlet of the melting section. The water-cooled jacket operates throughout the process. Release and Reset: The PLC commands the second hydraulic drive device to move, the lower gate rises, the material channel is exposed, and the high-temperature pyrolysis slag material falls directly into the electric melting pool through the lower gate chamber. After the material in the transition cavity is emptied, the high-temperature level gauge sends an "empty material" signal, and the PLC immediately commands the lower gate to close. Subsequently, the PLC once again filled the transition chamber with inert gas through the purge gas inlet, restoring it to the initial protective state of slight positive pressure, and preparing it for the next material receiving cycle. (6) The high-temperature pyrolysis slag material is continuously and directly dropped into the electric melting pool through the above-mentioned high-temperature atmosphere isolation and material transfer device; The graphite electrode is immersed in the melt and heated to maintain a high temperature. The high-temperature pyrolysis slag falling into the molten pool is quickly assimilated by the high-temperature melt. The molten iron settles and accumulates at the bottom of the electric melting pool to form an iron layer. The silicate melt floats on the top and is homogenized into glass melt. A small amount of air or oxygen is introduced into the upper part of the electric melting pool through the gas inlet. The molten iron at the bottom is periodically siphoned out through the iron outlet. The glass melt at the top overflows continuously through the overflow weir at the glass melt outlet. The high-temperature flue gas generated at the top is drawn out from the gas outlet on the side of the top of the electric melting pool and enters the product collection and flue gas treatment system. After treatment, it is discharged in compliance with standards.

8. The integrated red mud gradient temperature pyrolysis-melting vitrification process as described in claim 7, characterized in that, In step (1), the background gas in the rotary kiln is an inert atmosphere. Meanwhile, the reducing atmosphere required for the reduction reaction is provided by CO generated in situ by the carbonaceous reducing agent at high temperature. The residence time of the material in the rotary kiln is 60-120 minutes. The rotary kiln speed is adjusted to 0.5-3 rpm and the inclination angle is 2-5°.

9. The integrated red mud gradient temperature pyrolysis-melting vitrification process as described in claim 7, characterized in that, In step (2), the moisture content of the red mud is ≤25%, and the particle size of the carbonaceous reducing agent is ≤2mm. The amount of carbonaceous reducing agent added is 1.1-1.3 times the amount of carbon required for theoretical reduction. The flux includes SiO2 and CaO. The amount of flux added is such that the final slag phase binary basicity CaO / SiO2 is preferably 0.8-1.

2. The particle size of the dense spherical particles is 8-12mm. In step (4), part of the purified pyrolysis gas is sent from the outlet at the top of the cyclone separator to the air preheater in the product collection and flue gas treatment system through the pyrolysis gas pipeline, and then sent to the generator for power generation via the steam turbine. The other part is reused as reducing gas and sent to the reducing atmosphere inlet of the rotary kiln head.

10. The integrated red mud gradient temperature pyrolysis-melting vitrification process as described in claim 7, characterized in that, In step (6), the temperature of the electric melting pool is maintained at 1350-1450℃. The high-temperature flue gas generated at the top of the electric melting pool is drawn out from the gas outlet on the side of the top of the electric melting pool and enters the product collection and flue gas treatment system. First, the air used for combustion is preheated from room temperature to above 500℃ by the air preheater. Then, the flue gas is connected to the steam turbine for power generation, and then merged into the main exhaust gas treatment system. Finally, the tail gas is treated by the quench tower, bag filter, desulfurization and denitrification device to meet the emission standards.

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