Pretreatment system and pretreatment method for low-grade bauxite

Abstract

The invention belongs to the technical field of metallurgy, and particularly relates to a pretreatment system and a pretreatment method for low-grade bauxite. The pretreatment system provided by the invention is used for heating the low-grade bauxite in stages to gradually realize desulfurization and activation; in the heating process of the first stage, sulfur in the low-grade bauxite is decomposed into gaseous sulfur to be removed; in the second-stage heating process, a crystal structure existing in a kaolinite crystal form between aluminum oxide and silicon dioxide in the low-grade bauxite is destroyed, so that the kaolinite crystal form is converted into amorphous semi-crystalline or amorphous, and the chemical reaction activity of silicon dioxide is improved; the silicon dioxide can easily react with aluminum and caustic soda liquid (sodium hydroxide) to generate sodium aluminosilicate precipitates, and subsequent separation and removal of silicon are facilitated, so that the aluminum-silicon ratio is increased, and recycling of the low-grade bauxite is realized.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of metallurgy, and particularly relates to a pretreatment system and a pretreatment method for low-grade bauxite. BACKGROUND

[0002] In the light non-ferrous metallurgical industry, bauxite with total sulfur content greater than 0.6% is called high-sulfur bauxite, and bauxite with aluminum-silicon ratio less than 6 is called high-silicon bauxite. The aluminum-silicon ratio of low-grade bauxite is only 1-6, and the sulfur content is greater than 0.6%. At present, the reserves of low-grade bauxite are large, and the presence of sulfur will affect the dissolution or sintering process of alumina. In the process of preparing alumina or aluminum hydroxide from low-grade bauxite, sulfur will combine with alkali to form sodium sulfate and crystallize, and the crystallized sodium sulfate will reduce the seed decomposition rate and thus reduce the production capacity of alumina or aluminum hydroxide. In addition, sulfides and thiosulfates will also accelerate the corrosion of equipment and increase the concentration of soluble iron in the solution in the dissolution workshop, ultimately resulting in unqualified alumina or aluminum hydroxide.

[0003] Therefore, how to use low-grade bauxite to efficiently produce alumina or aluminum hydroxide has become a top priority to alleviate the shortage of alumina production ore resources and reduce the dependence on external ore. SUMMARY

[0004] Therefore, the present application provides a pretreatment system and a pretreatment method for low-grade bauxite. The pretreatment system provided by the present application can better reduce the sulfur content after pretreating the low-grade bauxite, and convert the kaolinite crystal form into amorphous semi-crystalline or non-crystalline, which facilitates the subsequent improvement of the aluminum-silicon ratio by alkali immersion, thereby realizing the resource utilization of low-grade bauxite.

[0005] To solve the above technical problems, the present application provides a low-grade bauxite pretreatment system, which comprises a feeding unit, a desulfurization heating furnace, a residence reactor and an activation heating furnace connected in sequence.

[0006] Preferably, a drying preheating unit is arranged between the feeding unit and the desulfurization heating furnace, and the gas outlet of the desulfurization heating furnace is communicated with the inlet of the drying preheating unit.

[0007] The gas outlet of the drying preheating unit is sequentially communicated with a flue gas dust removal and purification unit, a flue gas desulfurization unit and a first induced draft fan.

[0008] The dust outlet of the flue gas dust removal and purification unit is communicated with the inlet of the desulfurization heating furnace.

[0009] Preferably, the activation heating furnace comprises a circulating fluidized bed or a rotary kiln.

[0010] The gas outlet of the activation heating furnace is sequentially communicated with a high-temperature dust remover, a waste heat boiler, a low-temperature dust remover and a second induced draft fan.

[0011] The high-temperature dust collector includes a cyclone dust collector; the low-temperature dust collector includes a bag filter, an electrostatic precipitator, or an electrostatic-bag filter.

[0012] Preferably, the outlet of the activation heating furnace is connected in sequence to the primary cooler and the final cooler; the outlet of the final cooler is connected to the desiliconization unit.

[0013] The primary cooler includes a cyclone cooler, and the final cooler includes a fluidized indirect heat exchanger or a gravity indirect heat exchanger.

[0014] Preferably, the outlet of the residence reactor and the outlet of the primary cooler are respectively connected to the inlet of the activation heating furnace;

[0015] The outlet of the final cooler is connected to the inlet of the primary cooler.

[0016] The present invention also provides a method for pre-processing low-grade bauxite using the pre-processing system described above, comprising the following steps:

[0017] Low-grade bauxite is fed to a desulfurization heating furnace for the first desulfurization, and then fed to a residence reactor for the second desulfurization to obtain desulfurized bauxite.

[0018] The desulfurized bauxite is transported to an activation furnace for activation to obtain desulfurized activated bauxite.

[0019] Preferably, the temperatures for the first and second desulfurization processes are independently 500–700°C, the time for the first desulfurization is 1–10 seconds, and the time for the second desulfurization is 1–10 minutes.

[0020] Preferably, before performing the first desulfurization, the process further includes: preheating the low-grade bauxite using a drying and preheating unit;

[0021] The heat source for preheating comes from the gas produced by the first desulfurization process; after preheating, the gas is further subjected to the first dust removal and the third desulfurization processes in sequence, and then exhausted by a No. 1 induced draft fan.

[0022] Preferably, the activation temperature is 900–1100°C, and the activation time is 1–20 min.

[0023] Preferably, the activated part further includes:

[0024] The activated material is subjected to a first cooling and a second cooling in sequence to obtain the desulfurized activated bauxite.

[0025] The activated gas is subjected to a second dust removal, waste heat recovery and a third dust removal in sequence, and then discharged by a second induced draft fan.

[0026] The pretreatment system provided by this invention uses a staged heating process to gradually achieve desulfurization and activation of low-grade bauxite. In the first stage of heating, sulfur in the low-grade bauxite decomposes into gaseous sulfur and is removed. In the second stage of heating, the crystalline structure of alumina and silica in the low-grade bauxite, existing in the form of kaolinite crystals, is disrupted, transforming the kaolinite crystals into amorphous semi-crystalline or amorphous substances. This increases the chemical reactivity of silica, making it readily react with aluminum and liquid alkali (sodium hydroxide) to form sodium aluminosilicate precipitate, which is easily separated and removed from silica, thereby increasing the aluminum-silicon ratio. The pretreatment system provided by this invention features high capacity, high heat utilization rate, high desulfurization rate, high silica activation rate, small footprint, low labor intensity, and high mechanization, playing a positive role in the efficient development and utilization of high-sulfur, high-silicon bauxite raw materials. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the preprocessing system used in the embodiment. Detailed Implementation

[0028] This invention provides a pretreatment system for low-grade bauxite, comprising a feeding unit, a desulfurization heating furnace, a residence reactor, and an activation heating furnace connected in sequence.

[0029] As a specific embodiment of the present invention, the desulfurization heating furnace may include a suspension roasting furnace; the present invention uses a suspension roasting furnace as a desulfurization heating furnace to ensure sufficient contact between hot flue gas and materials, and has a high heat exchange efficiency.

[0030] In one specific embodiment of the present invention, the residence reactor may include a steel shell structure containing castable material. The steel shell structure includes a material chamber and a gas chamber, each equipped with a gas distribution device. Gas is introduced into the gas chamber, causing the material in the material chamber to fluidize. The residence reactor is a fluidized bed reactor; the introduced compressed air fluidizes the material within it like water. Simultaneously, the material is heated and fed into the activation furnace for combustion support. In this invention, the material from the desulfurization furnace enters the residence reactor and remains there for a certain period. The residence reactor increases the desulfurization time and improves the desulfurization efficiency.

[0031] As a specific embodiment of the present invention, the activation heating furnace may include a circulating fluidized bed or a rotary kiln.

[0032] In this invention, air and fuel are introduced into the combustion chamber of the desulfurization heating furnace, and the fuel and air are mixed and burned in the combustion chamber to provide heat for the desulfurization heating furnace; air and fuel are introduced into the combustion chamber of the activation heating furnace, and the fuel and air are mixed and burned in the combustion chamber to provide heat for the activation heating furnace.

[0033] In this invention, the desulfurization heating furnace can rapidly heat low-grade bauxite materials to the first desulfurization temperature, and the flue gas has a large contact area with the low-grade bauxite materials, resulting in fast heat transfer; the residence reactor can keep the materials conveyed from the desulfurization heating furnace warm and desulfurize them, increasing the desulfurization time and making the sulfur removal more thorough.

[0034] In one specific embodiment of the present invention, a drying and preheating unit may be provided between the feeding unit and the desulfurization heating furnace, and the gas outlet of the desulfurization heating furnace is connected to the inlet of the drying and preheating unit. The present invention utilizes the hot flue gas generated in the desulfurization heating furnace as a heat source to preheat low-grade bauxite, thereby improving energy utilization.

[0035] In one specific embodiment of the present invention, the outlet of the drying and preheating unit is sequentially connected to the flue gas dust removal and purification unit, the flue gas desulfurization unit, and the No. 1 induced draft fan; the dust outlet of the flue gas purification and dust removal unit is connected to the inlet of the desulfurization heating furnace; the flue gas dust removal and purification unit may include a dry dust collector, which may include a bag filter, an electrostatic precipitator, a cyclone separator, or a gravity dust collector. The present invention does not impose special requirements on the device of the flue gas desulfurization unit; conventional flue gas desulfurization devices in the art can be used. The present invention purifies and desulfurizes the preheated flue gas before venting it, and returns the dust generated after purification to the desulfurization heating furnace for further desulfurization; thus achieving the recycling of thermal energy.

[0036] In one specific embodiment of the present invention, the outlet of the activated heating furnace is sequentially connected to a high-temperature dust collector, a waste heat boiler, a low-temperature dust collector, and a second induced draft fan; the high-temperature dust collector may include a cyclone dust collector; the low-temperature dust collector may include a bag filter, an electrostatic precipitator, or an electrostatic-bag filter.

[0037] In one specific embodiment of the present invention, the discharge port of the activation heating furnace is sequentially connected to a primary cooler and a final cooler; the discharge port of the final cooler is connected to a desilication unit; the primary cooler includes a cyclone cooler, which can be a four-stage cyclone cooler; the final cooler includes a fluidized bed indirect heat exchanger or a gravity indirect heat exchanger. The present invention utilizes the primary and final coolers to cool and lower the temperature of the activated material before it can be conveyed to the desilication unit for desilication.

[0038] In one specific embodiment of the present invention, the outlet of the residence reactor and the outlet of the primary cooler are respectively connected to the inlet of the activation furnace. The present invention can fully utilize the heat in the hot gases generated at the outlets of the residence reactor and the primary cooler. In another specific embodiment of the present invention, the outlet of the final cooler is connected to the inlet of the primary cooler. In yet another specific embodiment of the present invention, the primary cooler involves heat exchange between air and material; the final cooler involves heat exchange between the material and water, and the final cooler is a fluidized bed cooler. In yet another specific embodiment of the present invention, the primary cooler can be a four-stage cyclone cooler. The present invention introduces compressed air into the residence reactor, which fluidizes the material entering the residence reactor, promoting desulfurization; the present invention also introduces compressed air into the air chamber of the final cooler, which fluidizes the material entering the final cooler, promoting heat exchange.

[0039] Figure 1 This is a schematic diagram of the pretreatment system used in the embodiment. Specifically: the discharge port of the feeding unit is connected to the inlet of the drying and preheating unit through material pipe 1; the discharge port of the drying and preheating unit is connected to the inlet of the desulfurization heating furnace through material pipe 2; the discharge port of the desulfurization heating furnace is connected to the inlet of the residence reactor through material pipe 3; the discharge port of the residence reactor is connected to the inlet of the activation heating furnace through material pipe 4; the discharge port of the activation heating furnace is connected to the inlet of the primary cooler through material pipe 5; the discharge port of the primary cooler is connected to the inlet of the final cooler through material pipe 6; and the discharge port of the final cooler sends the product to the desiliconization unit through material pipe 7. The gas outlet of the desulfurization heating furnace merges with material pipe 1 through flue gas pipe 8 and is connected to the inlet of the drying and preheating unit; the gas outlet of the drying and preheating unit is connected to the inlet of the flue gas dust removal and purification unit through flue gas pipe 9; and the gas outlet of the flue gas dust removal and purification unit is connected to... Flue gas pipe 10 is connected to the inlet of the flue gas desulfurization unit. The outlet of the flue gas desulfurization unit is connected to the inlet of the No. 1 induced draft fan through flue gas pipe 11. The outlet of the No. 1 induced draft fan is connected to the atmosphere through flue gas pipe 12. The outlet of the residence reactor is connected to the inlet of the activation heating furnace through air pipe 14 (used for the outlet of the primary cooler) via air pipe 13. The outlet of the final cooler is connected to the inlet of the primary cooler through air pipe 20. The outlet of the activation heating furnace is connected to the inlet of the high-temperature dust collector through flue gas pipe 15. The outlet of the high-temperature dust collector is connected to the inlet of the waste heat boiler through flue gas pipe 16. The outlet of the waste heat boiler is connected to the inlet of the low-temperature dust collector through flue gas pipe 17. The outlet of the low-temperature dust collector is connected to the inlet of the No. 2 induced draft fan through flue gas pipe 18. The outlet of the No. 2 induced draft fan is connected to the atmosphere through flue gas pipe 19.

[0040] The present invention also provides a method for pre-processing low-grade bauxite using the pre-processing system described above, comprising the following steps:

[0041] Low-grade bauxite is fed to a desulfurization heating furnace for the first desulfurization, and then fed to a residence reactor for the second desulfurization to obtain desulfurized bauxite.

[0042] The desulfurized bauxite is transported to an activation furnace for activation to obtain desulfurized activated bauxite.

[0043] This invention involves feeding low-grade bauxite through a feeding unit to a desulfurization heating furnace for primary desulfurization, followed by a secondary desulfurization process in a residence reactor to obtain desulfurized bauxite. In one specific embodiment of this invention, the sulfur content in the low-grade bauxite can be above 0.6%, or even 1-2%; the aluminum-silicon ratio in the low-grade bauxite can be 1-6, specifically 2, 3, 4, or 5.

[0044] In one specific embodiment of the present invention, before the first desulfurization, the method further includes: preheating the low-grade bauxite using a drying and preheating unit; the heat source for preheating comes from the gas generated during the first desulfurization. In another specific embodiment of the present invention, the temperature of the preheated material can be 150–200°C.

[0045] In one specific embodiment of the present invention, the preheating process may further include: subjecting the preheated gas to a first dust removal and a third desulfurization process in sequence, and then exhausting it using a No. 1 induced draft fan; the dust content of the flue gas after the first dust removal can be 5 mg / Nm³. 3 The following values ​​can also be 1–5 mg / Nm 3 Specifically, it can be expressed as 4 mg / Nm 3 3mg / Nm 3 or 2mg / Nm 3 The present invention has no special requirements for the conditions of the first dust removal, and can be carried out in accordance with conventional methods in the art; the third desulfurization can be wet desulfurization or dry desulfurization; the present invention has special requirements for both wet desulfurization and dry desulfurization, and can be carried out in accordance with conventional methods in the art.

[0046] In one specific embodiment of the present invention, the temperature of the first desulfurization can be 500–700℃, or 550–650℃; the time of the first desulfurization can be 1–10 seconds, specifically 2 seconds, 3 seconds, 4 seconds, 5 seconds, 6 seconds, 7 seconds, 8 seconds, or 9 seconds; the temperature of the second desulfurization can be 500–700℃, or 550–650℃; the temperature of the second desulfurization can be 20–35℃ lower than the temperature of the first desulfurization, specifically 25℃ or 30℃ lower; the time of the second desulfurization can be 1–10 minutes, specifically 2 minutes, 3 minutes, 4 minutes, 5 minutes, 6 minutes, 7 minutes, 8 minutes, or 9 minutes. In the first and second desulfurization processes of the present invention, sulfur in low-grade bauxite combines with oxygen and leaves the material as sulfur dioxide, entering the flue gas. After the first and second desulfurization processes, the desulfurization rate of this invention is greater than 90%, specifically 92% or 95%; the sulfur content in the desulfurized bauxite can be less than 0.1%, specifically 0.1% or 0.08%.

[0047] After obtaining desulfurized bauxite, the present invention transports the desulfurized bauxite to an activation furnace for activation, thereby obtaining desulfurized activated bauxite. In one specific embodiment of the present invention, the activation temperature can be 900–1100℃, specifically 950℃, 1000℃, 1050℃, or 1080℃; the activation time can be 1–20 min, specifically 3 min, 5 min, 8 min, 10 min, 13 min, 15 min, or 18 min.

[0048] As a specific embodiment of the present invention, the activated part may further include:

[0049] The activated material is subjected to a first cooling and a second cooling in sequence to obtain the desulfurized activated bauxite.

[0050] The activated gas is subjected to a second dust removal, waste heat recovery and a third dust removal in sequence, and then discharged by a second induced draft fan.

[0051] In one specific embodiment of the present invention, the first cooling temperature can be 180-220°C, specifically 200°C; the second cooling temperature can be 75-85°C, specifically 80°C.

[0052] In one specific embodiment of the present invention, the content in the flue gas after the second dust removal can be 10 mg / Nm³. 3 The following values ​​can also be 1–10 mg / Nm³. 3 Specifically, it can be expressed as 9 mg / Nm 3 8mg / Nm 3 7mg / Nm 3 6mg / Nm3 5mg / Nm 3 4mg / Nm 3 3mg / Nm 3 or 2mg / Nm 3 The content in the flue gas after the third dust removal process can be 5 mg / Nm³. 3 The following values ​​can also be 1–5 mg / Nm 3 Specifically, it can be expressed as 4 mg / Nm 3 3mg / Nm 3 or 2mg / Nm 3 The present invention does not impose special requirements on the conditions for the second and third dust removal processes; conventional methods in the field can be used.

[0053] In one specific embodiment of the present invention, the temperature of the flue gas after waste heat recovery can be 145-155°C, specifically 150°C.

[0054] The pretreatment method provided by this invention can remove sulfur from low-grade bauxite and also change the crystal form of silica, which exists as kaolinite crystals in low-grade bauxite, into amorphous semi-crystalline or amorphous material that is easily soluble in liquid alkali. In the desilication unit, it can react with aluminum in bauxite and sodium in liquid alkali to form sodium aluminosilicate precipitate, thereby achieving the purpose of removing silica; thus realizing the resource utilization of low-grade bauxite.

[0055] To further illustrate the present invention, the technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0056] Example 1

[0057] use Figure 1 The pretreatment system shown is used to pretreat low-grade bauxite. The desulfurization heating furnace is a suspension roasting furnace, the residence reactor is a fluidized bed reactor (including a steel shell structure containing castable material, a material chamber and a gas chamber set in the steel shell structure, and gas distribution devices are set in the gas chamber and the material chamber respectively), the activation heating furnace is a circulating fluidized bed, the primary cooler is a four-stage cyclone cooler, the final cooler adopts a fluidized bed indirect heat exchanger, the flue gas dust removal and purification unit is a bag filter, the flue gas desulfurization unit is a wet desulfurization device (including a desulfurization tower), the high-temperature dust collector is a cyclone dust collector, and the low-temperature dust collector is a bag filter.

[0058] The sulfur content in low-grade bauxite is 1%, and the aluminum-silicon ratio is 1.

[0059] The specific method is as follows:

[0060] Start the No. 1 induced draft fan. The hot flue gas generated after the ambient temperature air is burned in the desulfurization heating furnace returns to the drying and preheating unit to preheat the material to be treated. Then, it is sequentially passed into the flue gas dust removal and purification unit and the flue gas desulfurization unit for the first dust removal and flue gas desulfurization. After that, it is discharged into the air by the No. 1 induced draft fan. Fuel is introduced into the desulfurization heating furnace and mixed with air. The fuel is ignited in the desulfurization heating furnace to achieve ignition. The hot flue gas generated after ignition heats and desulfurizes the low-grade bauxite conveyed by the feeding unit.

[0061] The material, after being heated and desulfurized in a desulfurization furnace, is transported to a residence reactor for heat preservation and desulfurization to obtain desulfurized bauxite.

[0062] The No. 2 induced draft fan is started. The air enters the activation heating furnace through the primary cooler and is mixed with fuel and ignited to activate the desulfurized bauxite. The generated flue gas passes through the high-temperature dust collector, waste heat boiler, and low-temperature dust collector, and undergoes secondary dust removal, waste heat recovery, and tertiary dust removal in sequence before being discharged into the air through the No. 2 induced draft fan.

[0063] Low-grade bauxite is fed into a drying and preheating unit via a feeding unit and preheated to 160°C. The preheated material then enters a desulfurization furnace, where it is heated to 600°C and held for 2 seconds before being discharged into a residence reactor for desulfurization at 580°C for 6 minutes, yielding desulfurized bauxite. The sulfur content in the desulfurized bauxite is 0.08%, with a desulfurization rate of 92%. The sulfur-containing flue gas generated in the desulfurization furnace is returned to the drying and preheating unit to preheat the low-grade bauxite, followed by flue gas dust removal and desulfurization. The dust content in the flue gas after dust removal is 4 mg / Nm³. 3 After desulfurization, the sulfur content in the flue gas meets environmental protection requirements and is discharged into the air by the No. 1 induced draft fan; the dust collected from the flue gas after dust removal and purification is returned to the desulfurization heating furnace.

[0064] The desulfurized bauxite is fed into an activation furnace and heated to 1050℃ for 15 minutes for activation. After activation, it enters a primary cooler for heat exchange with air. The air is preheated to 700℃ and sent into the activation furnace as combustion air. After activation, the product is cooled to 200℃ and then further cooled to 80℃ in a final cooler to obtain desulfurized activated bauxite. The desulfurized activated bauxite is then mixed with a 125g / L hydroxide solution at a liquid-solid ratio of 4:1 for 4 hours, followed by solid-liquid separation to obtain desulfurized and desiliconized bauxite with an aluminum-silicon ratio of 7.

[0065] The high-temperature flue gas generated by the activation heating furnace has a dust content of 10g / Nm³ after being removed by a high-temperature dust collector. 3 After preliminary dust removal, the flue gas enters a waste heat boiler for waste heat recovery, resulting in a flue gas temperature of 150℃. The recovered flue gas is then sent to a low-temperature dust collector for further dust removal, yielding a dust content of 4 mg / Nm³. 3 The flue gas was discharged into the air by the No. 2 induced draft fan.

[0066] This invention integrates desulfurization and activation, shortening the processing flow and reducing material transportation and heat loss. The pretreatment system provided by this invention features high capacity, high energy utilization, a bauxite desulfurization rate of over 90%, and a high silicon activation rate. The high silicon activity in the product makes it easily leached by liquid alkali, increasing the aluminum-silicon ratio of the raw material, reducing alkali consumption for leaching, and improving the yield of aluminum hydroxide. This invention requires a low roasting temperature for desulfurization, achieves a high activation rate, consumes less heat during activation, occupies a small area, reduces labor intensity, and has a high degree of mechanization. It plays a positive role in the efficient development and utilization of high-sulfur, high-silicon bauxite for alumina production and the disposal of waste low-grade bauxite.

[0067] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. People can obtain other embodiments based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A pretreatment system for low-grade bauxite, characterized in that, It includes a feeding unit, a desulfurization heating furnace, a residence reactor, and an activation heating furnace connected in sequence.

2. The low-grade bauxite pretreatment system according to claim 1, characterized in that, A drying and preheating unit is provided between the feeding unit and the desulfurization heating furnace, and the gas outlet of the desulfurization heating furnace is connected to the inlet of the drying and preheating unit. The air outlet of the drying and preheating unit is connected in sequence to the flue gas dust removal and purification unit, the flue gas desulfurization unit and the No. 1 induced draft fan; The dust outlet of the flue gas purification and dust removal unit is connected to the inlet of the desulfurization heating furnace.

3. The low-grade bauxite pretreatment system according to claim 1, characterized in that, The activation heating furnace includes a circulating fluidized bed or a rotary kiln; The outlet of the activation heating furnace is sequentially connected to a high-temperature dust collector, a waste heat boiler, a low-temperature dust collector, and a second induced draft fan. The high-temperature dust collector includes a cyclone dust collector; the low-temperature dust collector includes a bag filter, an electrostatic precipitator, or an electrostatic-bag filter.

4. The low-grade bauxite pretreatment system according to claim 1, characterized in that, The outlet of the activation heating furnace is connected in sequence to the primary cooler and the final cooler; the outlet of the final cooler is connected to the desiliconization unit. The primary cooler includes a cyclone cooler, and the final cooler includes a fluidized indirect heat exchanger or a gravity indirect heat exchanger.

5. The low-grade bauxite pretreatment system according to claim 1 or 4, characterized in that, The outlet of the residence reactor and the outlet of the primary cooler are respectively connected to the inlet of the activation heating furnace; The outlet of the final cooler is connected to the inlet of the primary cooler.

6. A method for pre-processing low-grade bauxite using the pre-processing system according to any one of claims 1 to 5, characterized in that, Includes the following steps: Low-grade bauxite is fed to a desulfurization heating furnace for the first desulfurization, and then fed to a residence reactor for the second desulfurization to obtain desulfurized bauxite. The desulfurized bauxite is transported to an activation furnace for activation to obtain desulfurized activated bauxite.

7. The method for pretreatment of low-grade bauxite according to claim 6, characterized in that, The temperatures for the first and second desulfurization processes are independently 500–700°C, the time for the first desulfurization process is 1–10 seconds, and the time for the second desulfurization process is 1–10 minutes.

8. The method for pretreatment of low-grade bauxite according to claim 6 or 7, characterized in that, Before the first desulfurization, the process also includes: preheating the low-grade bauxite using a drying and preheating unit; The heat source for preheating comes from the gas produced by the first desulfurization process; after preheating, the gas is further subjected to the first dust removal and the third desulfurization processes in sequence, and then exhausted by a No. 1 induced draft fan.

9. The method for pretreatment of low-grade bauxite according to claim 6, characterized in that, The activation temperature is 900–1100℃, and the activation time is 1–20 min.

10. The method for pretreatment of low-grade bauxite according to claim 6 or 9, characterized in that, The activation process also includes: The activated material is subjected to a first cooling and a second cooling in sequence to obtain the desulfurized activated bauxite. The activated gas is subjected to a second dust removal, waste heat recovery and a third dust removal in sequence, and then discharged by a second induced draft fan.

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