Preparation method of red mud dry powder

Abstract

The preparation method of the red mud dry powder provided by the embodiment of the invention comprises the following steps: removing coarse particles in red mud slurry to obtain fine particle slurry; adding a calcium additive into the fine particle slurry for chemical reaction to neutralize partial alkalinity of the fine particle slurry and improve particle surface properties of the fine particle slurry to obtain a reaction material; adding a flocculating agent into the reaction material for flocculation treatment to obtain a flocculated material; carrying out solid-liquid separation on the flocculated material to obtain a liquid-phase substance and a solid-phase substance; carrying out dehydration treatment on the solid-phase substance, and controlling the water content of the solid-phase substance; carrying out primary drying on the dehydrated solid-phase substance by taking waste heat as a medium; carrying out secondary drying on the solid-phase substance subjected to primary drying by taking superheated steam as a medium, and synchronously spraying a liquid additive to the surface of the solid-phase substance; and crushing the solid-phase substance subjected to secondary drying to a predetermined particle size to obtain the red mud dry powder.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of light metal metallurgy, and in particular to a preparation method of red mud dry powder. BACKGROUND

[0002] Red mud is a strong alkaline waste residue produced in the process of producing alumina from bauxite, with a global annual discharge of more than 150 million tons, but its comprehensive utilization rate is less than 10%. Red mud is rich in Fe2O3 (20%-45%), Al2O3, SiO2 and other components. Its high water content (25%-40%), strong alkalinity (pH 10-13) and complex chemical composition make it cause environmental risks such as land alkalization and heavy metal pollution when it is long-term stockpiled.

[0003] The existing red mud drying technology (such as natural airing and drum drying) has problems such as high energy consumption, low efficiency, and particle agglomeration after drying, and cannot effectively solve the restriction of red mud alkalinity on subsequent application. In addition, traditional dry powder production relies on natural minerals (such as bentonite and diatomite), which consumes a lot of resources and makes it difficult to realize large-scale resource utilization of red mud. Therefore, it is of great significance to develop a process technology that can effectively solve the problem of particle agglomeration in the red mud drying process, for realizing efficient drying and resource utilization of red mud. SUMMARY

[0004] The present application provides a preparation method of red mud dry powder, to solve the technical problem of how to prevent particle agglomeration in the red mud drying process.

[0005] The present application provides a preparation method of red mud dry powder, comprising:

[0006] Removing coarse particles in the red mud slurry to obtain a fine particle slurry;

[0007] Adding a calcareous additive to the fine particle slurry to perform a chemical reaction, to neutralize part of the alkalinity of the fine particle slurry and improve the particle surface properties of the fine particle slurry, to obtain a reaction material;

[0008] Adding a flocculating agent to the reaction material to perform flocculation treatment, to obtain a flocculated material;

[0009] Performing solid-liquid separation on the flocculated material to obtain a liquid phase material and a solid phase material;

[0010] Performing dewatering treatment on the solid phase material, and controlling the water content of the solid phase material;

[0011] Using waste heat as a medium, performing primary drying on the dewatered solid phase material;

[0012] The secondary drying of the solid phase material is performed by using superheated steam as a medium, and liquid additives are sprayed on the surface of the solid phase material at the same time;

[0013] The secondary dried solid phase material is crushed to a predetermined particle size to obtain red mud drying powder.

[0014] Optionally, the calcareous additive includes at least one of the following: limestone, carbide slag, quicklime, slaked lime; and / or,

[0015] The molar ratio of the calcareous additive to sodium oxide in the fine particle slurry is 2.5:1-3.5:1.

[0016] Optionally, the flocculating agent includes at least one of the following: polyacrylamide, polyaluminum chloride, polymeric ferric sulfate; and / or,

[0017] The mass of the flocculating agent is 0.1-0.3% of the mass of the fine particle slurry.

[0018] Optionally, the liquid additive includes at least one of the following: sodium silicate solution, silica sol, diatomite dispersion, bentonite dispersion; and / or,

[0019] The mass concentration of the liquid additive is 1-3%, and the modulus of the sodium silicate solution is 1-2%.

[0020] Optionally, the particle size D50 of the fine particle slurry is greater than or equal to 90um.

[0021] Optionally, the first drying satisfies that the waste heat temperature is 80-100℃, and the water content of the solid phase material is controlled to be 10-15%; and the second drying satisfies that the superheated steam temperature is 140-280℃, and the water content of the solid phase material is controlled to be less than or equal to 2%.

[0022] Optionally, the predetermined particle size D90 is less than or equal to 15um.

[0023] Optionally, the temperature of the chemical reaction is 60-100℃, and the time of the chemical reaction is 0.5-6.5 hours.

[0024] Optionally, the water content of the dehydrated solid phase material is less than or equal to 25%.

[0025] Optionally, the solid-liquid separation method includes at least one of the following: filtration, centrifugation, and sedimentation; and / or,

[0026] The dehydration treatment method includes at least one of the following: pressure filtration, vacuum filtration, and centrifugal dehydration.

[0027] The above technical solutions provided by the embodiments of the present application have the following advantages compared with the prior art:

[0028] The embodiment of the present application provides a preparation method of red mud dry powder. First, coarse particles in red mud slurry are removed to obtain fine particle slurry, which makes the particle size of the material for subsequent treatment more uniform and reduces the possibility of particle agglomeration. Then, a calcareous additive is added to the fine particle slurry for chemical reaction, neutralizing part of the alkalinity and improving the surface properties of the particles. The calcareous additive reacts with the alkaline components in the red mud to form new compounds, reducing the electrostatic and van der Waals forces between the particles, thereby reducing the tendency of particle agglomeration. Subsequently, a flocculating agent is added to the reacted material, allowing the fine particles to form larger flocculating bodies, facilitating solid-liquid separation. The flocculating bodies are more easily dispersed in the subsequent drying process. Through solid-liquid separation, liquid material (filtrate) and solid material (red mud cake) are obtained, and the sodium oxide in the liquid material can be recovered. The solid material is dewatered by a filter press and then dried by waste heat as a medium to preliminarily reduce the water content. Then, overheat steam is used as a medium for secondary drying, and a liquid additive is sprayed synchronously. Overheat steam drying has high heat transfer efficiency and can quickly reduce the water content; the liquid additive forms a protective film on the surface of the particles, further improving the surface properties of the particles, enhancing the dispersibility and thermal stability, and preventing particle agglomeration during the drying process. Finally, the dried solid material is crushed to a predetermined particle size to obtain red mud dry powder. Through the synergistic effect of chemical neutralization, surface modification, physical drying, and crushing, the problem of particle agglomeration in the red mud drying process is effectively solved from multiple angles such as particle surface property improvement, drying medium selection, and process optimization. BRIEF DESCRIPTION OF DRAWINGS

[0029] The accompanying drawings, which are incorporated into and form a part of the specification, illustrate preferred embodiments of the present application and, together with the description, serve to explain the principles of the application.

[0030] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required in the embodiment or prior art description. Obviously, for those skilled in the art, other related drawings can be derived from these drawings without creative labor.

[0031] Figure 1 A flowchart of a preparation method of red mud dry powder provided by the embodiment of the present application. DETAILED DESCRIPTION

[0032] In order to more clearly illustrate the purposes, technical solutions and advantages of the embodiments of the present application, the technical solutions of the embodiments will be described in detail below with reference to the drawings. Please note that the mentioned embodiments are only examples and not all possible implementations. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0033] The range described herein, such as a numerical range, a ratio range, etc., includes all possible subranges and individual numerical values within the range, for example, a range description of "1 to 6" or "1-6" encompasses all subranges between 1 and 6 (e.g., 1 to 3, 2 to 5, etc.) and individual numbers (e.g., 1, 2, 3, 4, 5, 6) within the range. Unless otherwise specified, the terms "comprises", "comprising", and the like as used herein are specified as "including, but not limited to"; the terms "first", "second", and the like as used herein do not imply actual first and second positions or a sequence of occurrence but are used to distinguish different entities or operations from each other; "and / or" means that multiple cases can exist independently or simultaneously; "at least one", "multiple", "at least one kind", and the like refer to any combination of the corresponding objects, including a single or multiple combinations of the objects. The ratio relationship described herein, such as the mass ratio, the molar ratio, etc., should be understood as the corresponding relationship between the front and the rear in the ratio according to the order of description. The raw materials, reagents, instruments and equipment used herein can be purchased or prepared by existing methods.

[0034] Figure 1 A flow chart of a preparation method of a red mud dry powder provided by the embodiments of the present application.

[0035] See Figure 1 The embodiments of the present application provide a preparation method of a red mud dry powder, which comprises:

[0036] S1, removing coarse particles in red mud slurry to obtain fine particle slurry;

[0037] S2, adding calcium additive to the fine particle slurry to perform chemical reaction, so as to neutralize part of the alkalinity of the fine particle slurry and improve the particle surface properties of the fine particle slurry, and obtain reaction material;

[0038] S3, adding flocculating agent to the reaction material to perform flocculation treatment, and obtain flocculation material;

[0039] S4, performing solid-liquid separation on the flocculation material to obtain liquid phase material and solid phase material;

[0040] S5, performing dewatering treatment on the solid phase material, and controlling the water content of the solid phase material;

[0041] S6, using waste heat as medium to perform primary drying on the dewatered solid phase material; using superheated steam as medium to perform secondary drying on the solid phase material after primary drying, and synchronously spraying liquid additive to the surface of the solid phase material;

[0042] S7, crushing the solid phase material after secondary drying to a predetermined particle size to obtain red mud dry powder.

[0043] Red mud slurry: refers to the mixture of red mud and water formed during the production of alumina. Calcitic additive: refers to a calcium source substance that can chemically react with the basic components in the red mud, used to neutralize the basicity of the red mud. Flocculant: refers to a chemical substance that can make suspended particles aggregate and settle, used to improve the efficiency of solid-liquid separation. Solid-liquid separation: refers to the process of separating solid particles from liquid by physical methods. Waste heat: refers to the excess heat generated during the production process, which can be used as a drying medium. Superheated steam: refers to steam with a temperature higher than the saturation temperature, used in the drying process. Liquid additive: refers to a liquid sprayed on the surface of the particles during the drying process, used to improve the dispersibility and thermal stability of the particles.

[0044] By particle size classification, coarse particles in the red mud slurry are removed, ensuring that the subsequent treatment of red mud particles is fine and uniform, reducing the possibility of particle agglomeration. The calcitic additive chemically reacts with the basic components (such as sodium oxide) in the red mud, neutralizing part of the basicity, while forming a protective layer on the surface of the particles, improving the surface properties of the particles and reducing the electrostatic attraction between the particles. The flocculant makes the fine particles in the slurry aggregate to form larger flocs, facilitating subsequent solid-liquid separation. The flocculated material is separated into liquid and solid phases by methods such as filtration, centrifugation or sedimentation. The water content of the solid phase material is reduced by methods such as pressure filtration, vacuum filtration or centrifugal dewatering, creating conditions for subsequent drying. First-stage drying: pre-drying of the dewatered solid phase material using waste heat, initially reducing the water content. Second-stage drying: further drying of the solid phase material after the first-stage drying using superheated steam, while spraying liquid additives to enhance the dispersibility and thermal stability of the particles. The dried solid phase material is crushed to a predetermined particle size to obtain red mud dry powder.

[0045] In some embodiments, the calcitic additive includes at least one of: limestone, carbide slag, quicklime, slaked lime; and / or,

[0046] The molar ratio of the calcitic additive to sodium oxide in the fine particle slurry is 2.5:1-3.5:1.

[0047] The main role of calcium additives is to neutralize the strong alkalinity of red mud and improve the chemical properties of the particle surface, thereby reducing particle agglomeration. Limestone is a common calcium additive with relatively low price and wide availability. It will decompose into calcium oxide (CaO) during the reaction, which will then undergo a neutralization reaction with the alkaline components in the red mud. Calcium carbide slag is a byproduct of calcium carbide production, and its main component is also calcium oxide. As an industrial waste slag, using calcium carbide slag not only achieves resource recycling, but also reduces production costs. Quicklime has strong alkalinity and can quickly neutralize the alkaline components in the red mud. Its reaction speed is fast and the effect is significant, but the dosage needs to be strictly controlled to avoid excessive neutralization leading to other problems. The alkalinity of hydrated lime is slightly weaker than that of quicklime, but it can still effectively neutralize the alkalinity of red mud. It is relatively mild during the reaction and is suitable for treating red mud that is sensitive to alkalinity. The molar ratio of calcium additives to sodium oxide in red mud is controlled between 2.5:1 and 3.5:1. The strong alkalinity of red mud mainly comes from sodium oxide (Na2O) and other alkaline components. By controlling the molar ratio of calcium additives to sodium oxide, the alkalinity of red mud can be effectively neutralized, thereby reducing the adverse effects on subsequent drying and application processes. After the reaction of calcium additives with the components in red mud, new compounds are formed on the surface of the particles, improving the surface properties of the particles. A suitable molar ratio can ensure the best modification effect on the surface of the particles, reduce the agglomeration tendency between particles, and avoid other adverse reactions caused by excessive calcium additives. Choosing the right molar ratio can also maximize the use of calcium additives while ensuring technical effectiveness, reducing production costs. Especially when using industrial waste such as calcium carbide slag as calcium additives, it can better achieve resource recycling, meet environmental protection and sustainable development requirements.

[0048] Using limestone as a calcium additive, the molar ratio is 3:1.

[0049] Using calcium carbide slag as a calcium additive, the molar ratio is 2.5:1.

[0050] Using quicklime as a calcium additive, the molar ratio is 3.5:1.

[0051] Using hydrated lime as a calcium additive, the molar ratio is 3:1.

[0052] Using a mixture of limestone and calcium carbide slag as a calcium additive, the molar ratio is 3:1.

[0053] Using a mixture of quicklime and hydrated lime as a calcium additive, the molar ratio is 3.5:1.

[0054] In some embodiments, the flocculant includes at least one of: polyacrylamide, polyaluminum chloride, polyferric sulfate; and / or,

[0055] The mass of the flocculant is 0.1-0.3% of the mass of the fine particle slurry.

[0056] The main role of the flocculant is to aggregate fine particles together through bridging to form larger flocs, facilitating subsequent solid-liquid separation and drying. Polyacrylamide is a high-molecular polymer with a large number of active groups (such as amide groups and carboxyl groups). These groups can be adsorbed on the surface of red mud particles through electrostatic attraction and van der Waals force, forming a layer of high-molecular film. Polyaluminum chloride is an inorganic high-molecular flocculant that mainly undergoes electrostatic neutralization with the negative charges on the surface of red mud particles through the hydrolysis of polynuclear aluminum ions, while also aggregating particles together through bridging. Polyferric sulfate is an inorganic high-molecular flocculant that mainly undergoes electrostatic neutralization with the negative charges on the surface of red mud particles through the hydrolysis of polynuclear iron ions, while also aggregating particles together through bridging. The mass of the flocculant is recommended to be controlled between 0.1%-0.3% of the mass of the fine particle slurry. This proportion range has three aspects. First, it can effectively promote the flocculation of red mud particles, forming larger flocs, facilitating subsequent solid-liquid separation. If the amount of flocculant is insufficient, the flocculation effect is not obvious, which may lead to uneven dispersion of particles, affecting the subsequent drying process. If the amount of flocculant is too much, not only will it increase the cost, but it may also introduce too many impurities, affecting the quality of the final product. Second, it can save costs to the maximum extent while ensuring technical effects. The cost of flocculants is relatively high, so reasonable control of the amount is of great significance to reduce production costs. Third, it can ensure that the flocs maintain appropriate strength during the subsequent drying process, avoiding the re-dispersion or agglomeration of particles during the drying process. Examples:

[0057] Polyacrylamide is used as the flocculant, and the addition amount is 0.2% of the mass of the fine particle slurry.

[0058] Polyaluminum chloride is used as the flocculant, and the addition amount is 0.1% of the mass of the fine particle slurry.

[0059] Polyferric sulfate is used as the flocculant, and the addition amount is 0.3% of the mass of the fine particle slurry.

[0060] A mixture of polyacrylamide and polyaluminum chloride is used as the flocculant, and the addition amount is 0.2% of the mass of the fine particle slurry.

[0061] A mixture of polyacrylamide and polyferric sulfate is used as the flocculant, and the addition amount is 0.3% of the mass of the fine particle slurry.

[0062] A mixture of polyaluminum chloride and polyferric sulfate is used as the flocculant, and the addition amount is 0.1% of the mass of the fine particle slurry.

[0063] In some embodiments, the liquid aid comprises at least one of: a sodium silicate solution, a silica sol, a diatomite dispersion, a bentonite dispersion; and / or,

[0064] The mass concentration of the liquid aid is 1-3%, and the modulus of the sodium silicate solution is 1-2%.

[0065] The modulus refers to the molar ratio of silicon dioxide (SiO2) to sodium oxide (Na2O) in the sodium silicate solution. The liquid aid has a wide range of choices, mainly including sodium silicate solution, silica sol, diatomite dispersion, and bentonite dispersion, etc. These aids can effectively improve the surface properties of red mud particles through different chemical and physical mechanisms. Sodium silicate solution can form a silicon-oxygen network structure (Si-O-Si) at high temperatures, which can wrap red mud particles and enhance the thermal stability and dispersibility of the particles. Silica sol is a colloidal solution formed by dispersing nano-sized silica particles in water. During the drying process, the silica particles in the silica sol form a uniform protective film on the surface of the red mud particles, enhancing the dispersibility and thermal stability of the particles. Diatomite is a natural siliceous mineral with a porous structure and large specific surface area. Diatomite dispersion can fill the gaps between red mud particles, forming a stable particle structure and enhancing the dispersibility and thermal stability of the particles. Bentonite is a layered silicate mineral with good adsorption and swelling properties. Bentonite dispersion can form an adsorption film on the surface of red mud particles, enhancing the dispersibility and thermal stability of the particles. The mass concentration of the liquid aid is controlled within 1-3%, and the modulus of the sodium silicate solution is controlled within 1-2%. This proportion range can first form a uniform protective film on the surface of red mud particles, enhancing the dispersibility and thermal stability of the particles. If the amount of liquid aid is insufficient, the formation of the protective film is incomplete, which may lead to particle agglomeration. If the amount of liquid aid is too large, not only will it increase the cost, but it may also introduce too many impurities, affecting the performance of the final product. Second, it can save costs to the maximum extent while ensuring technical effects. The cost of liquid aid is relatively high, so reasonable control of the amount is of great significance to reducing production costs. Third, it can ensure that the particles maintain appropriate dispersibility and thermal stability during the subsequent drying process, avoiding particle re-agglomeration during the drying process.

[0066] Using sodium silicate solution as the liquid aid, the concentration is 2%, and the modulus is 1.5%.

[0067] Using silica sol as the liquid aid, the concentration is 1.5%, and the modulus is 1%.

[0068] Using diatomite dispersion as the liquid aid, the concentration is 1%, and the modulus is 2%.

[0069] Using bentonite dispersion as the liquid aid, the concentration is 3%, and the modulus is 1%.

[0070] A mixture of sodium silicate solution and silica sol is used as the liquid aid, with a concentration of 2% and a modulus of 1.5%.

[0071] A mixture of diatomite dispersion and bentonite dispersion is used as the liquid aid, with a concentration of 3% and a modulus of 1%.

[0072] In some embodiments, the fine particle slurry has a particle size D50 ≥ 90um.

[0073] Particle size D50 refers to the median value of the particle size distribution, i.e., half of the particles have a diameter less than or equal to the D50 value, and the other half have a diameter greater than or equal to the D50 value. In the preparation of red mud dry powder, controlling the particle size D50 of the fine particle slurry ≥ 90um has the following effects: reducing agglomeration: larger particle size (D50 ≥ 90um) means that the contact area between particles is relatively small, and the interaction forces between particles such as van der Waals forces and electrostatic forces are relatively weak, thereby reducing the possibility of particle agglomeration during the drying process. This helps to improve the drying efficiency and ensure that the dried powder has good dispersibility. Increase the drying speed: larger particles have a relatively small specific surface area, and the water evaporation speed is relatively fast, thereby increasing the drying speed and reducing energy consumption. Facilitate crushing: larger particle size makes it easier to break the dried particles during crushing, and the particle size distribution after crushing is more uniform, which can better meet the requirements of subsequent applications. Improve product performance: larger particle size helps to form a more stable particle structure, enhancing the mechanical strength and thermal stability of the particles. This makes the final red mud dry powder have better performance in applications such as building materials, soil conditioners and industrial fillers. Reduce the loss of fine particles: larger particle size reduces the loss of fine particles during solid-liquid separation, improving the recovery rate of red mud, thereby achieving efficient use of resources. Example:

[0074] Use a hydrocyclone to classify the particle size of the red mud slurry, remove the coarse particles in the red mud slurry, and control the particle size D50 of the fine particle slurry to be 90um.

[0075] Use a screening device to classify the particle size of the red mud slurry, remove the coarse particles in the red mud slurry, and control the particle size D50 of the fine particle slurry to be 95um.

[0076] Use a combination of hydrocyclone and screening device to classify the particle size of the red mud slurry, remove the coarse particles in the red mud slurry, and control the particle size D50 of the fine particle slurry to be 100um.

[0077] Use a hydrocyclone to classify the particle size of the red mud slurry, remove the coarse particles in the red mud slurry, and control the particle size D50 of the fine particle slurry to be 92um.

[0078] The red mud slurry is subjected to particle size classification using a screening device to remove coarse particles from the red mud slurry, and the particle size D50 of the fine particle slurry is controlled to be 98 um.

[0079] The red mud slurry is subjected to particle size classification using a hydrocyclone to remove coarse particles from the red mud slurry, and the particle size D50 of the fine particle slurry is controlled to be 96 um.

[0080] In some embodiments, the first-stage drying satisfies: the waste heat temperature is 80-100℃, and the moisture content of the solid phase material is controlled to be 10-15%; the second-stage drying satisfies: the superheated steam temperature is 140-280℃, and the moisture content of the solid phase material is controlled to be ≤2%.

[0081] The first-stage drying and the second-stage drying are two key steps in the preparation process of red mud dry powder, which respectively realize the dehydration treatment of the red mud solid phase material through different drying media and temperature conditions. The drying parameters (temperature and moisture content control) of these two stages are crucial to ensure the quality and performance of the red mud dry powder. The selection of the first-stage drying waste heat temperature is based on the balance between the physical properties of the red mud and the drying efficiency. The temperature range of 80-100℃ can ensure sufficient heat transfer to evaporate water quickly, and also will not be too high to cause the rapid solidification of the particle surface, thereby affecting the further evaporation of the internal moisture. The moisture content of the red mud is controlled to be 10-15% in the first-stage drying to ensure that the red mud has appropriate humidity before entering the second-stage drying. This humidity range can ensure that the red mud particles will not be broken due to excessive drying in the subsequent high-temperature drying process, and also ensure that enough moisture is removed to create good conditions for the second-stage drying. The selection of the superheated steam temperature of the second-stage drying is based on the chemical properties of the red mud and the drying requirements. The temperature range of 140-280℃ can ensure sufficient heat transfer to evaporate water quickly, and also will not be too high to cause the particle surface to be excessively carbonized or sintered, affecting the dispersibility and thermal stability of the particles. The moisture content of the red mud is controlled to be below 2% in the second-stage drying to ensure the performance of the red mud dry powder in subsequent applications. Low moisture content can prevent the particles from absorbing moisture during storage and use, while improving the stability and durability of the product. Examples:

[0082] The first-stage drying temperature is 80℃, and the moisture content is controlled to be 10%; the second-stage drying temperature is 140℃, and the moisture content is controlled to be 2%.

[0083] The first-stage drying temperature is 90℃, and the moisture content is controlled to be 12%; the second-stage drying temperature is 160℃, and the moisture content is controlled to be 1.5%.

[0084] The first-stage drying temperature is 100℃, and the moisture content is controlled to be 15%; the second-stage drying temperature is 180℃, and the moisture content is controlled to be 1%.

[0085] The first-stage drying temperature is 85°C, and the moisture content is controlled at 11%; the second-stage drying temperature is 200°C, and the moisture content is controlled at 1.8%.

[0086] The first-stage drying temperature is 95°C, and the moisture content is controlled at 13%; the second-stage drying temperature is 220°C, and the moisture content is controlled at 1.2%.

[0087] The first-stage drying temperature is 98°C, and the moisture content is controlled at 14%; the second-stage drying temperature is 240°C, and the moisture content is controlled at 1.6%.

[0088] In some embodiments, the predetermined particle size D90≤15μm.

[0089] Particle size D90 refers to the value at which 90% of the particles in a particle size distribution have a diameter less than or equal to that value. It is an important statistical parameter for characterizing the size distribution of a particle population, and can intuitively reflect the fineness of the particle population. Controlling the predetermined particle size D90≤15μm of the dried red mud powder means that the particle size is relatively uniform, which can reduce the particle size difference between particles. This makes the dried red mud powder better mixed with other materials in subsequent applications (such as building materials, soil conditioners, industrial fillers, etc.), forming a uniform composite material. Small particles (D90≤15μm) are easier to disperse during the drying process, reducing the possibility of agglomeration. This helps to improve the uniformity and stability of the product, avoiding inconsistent performance due to particle agglomeration. Smaller particle size (D90≤15μm) means higher specific surface area, which improves the reactivity of the dried red mud powder. In building materials, higher reactivity can enhance the adhesion and strength of the material; in soil conditioners, it can better improve soil structure and fertility. Small particles (D90≤15μm) have a higher specific surface area, which can provide more adsorption sites, improving the adsorption performance of the dried red mud powder. This makes it better able to adsorb other substances in industrial filler applications, improving the overall performance of the material. Smaller particle size (D90≤15μm) makes the dried red mud powder easier to mix with other materials during processing, reducing energy consumption and equipment wear during processing.

[0090] The dried solid material is pulverized to a particle size D90 of 10μm using an air jet mill.

[0091] The dried solid material is pulverized to a particle size D90 of 12μm using a ball mill.

[0092] The dried solid material is pulverized to a particle size D90 of 15μm using a hammer crusher.

[0093] The dried solid material is pulverized to a particle size D90 of 11μm using a combination of an air jet mill and a ball mill.

[0094] The dry solid-phase material is pulverized to a particle size D90 of 13 pm using a combination of a ball mill and a hammer crusher.

[0095] The dry solid-phase material is pulverized to a particle size D90 of 14 pm using an air jet mill.

[0096] In some embodiments, the temperature of the chemical reaction is 60-100°C, and the time of the chemical reaction is 0.5-6.5 hours.

[0097] By reasonably setting the temperature and time of the chemical reaction, the strong alkalinity of the red mud can be effectively neutralized, and the surface properties of the particles can be improved, thereby creating good conditions for subsequent drying and pulverization processes. The chemical reaction rate is closely related to the temperature. Within the temperature range of 60-100°C, the reaction rate of the calcareous additive (such as limestone, quicklime, etc.) with the alkaline components (such as sodium hydroxide, calcium hydroxide, etc.) in the red mud is moderate. If the temperature is too low, the reaction rate is slow, and it is difficult to complete the neutralization reaction in a short time; if the temperature is too high, the reaction may be too violent, and even side reactions may be triggered, affecting the reaction effect. The red mud contains various metal oxides and hydrates, which can participate in chemical reactions well within the temperature range of 60-100°C. At the same time, this temperature range will not cause the structure of the red mud particles to change dramatically, thereby ensuring the dispersibility and stability of the particles. The chemical reaction requires sufficient time to ensure that the reactants are in sufficient contact and complete the reaction. The time range of 0.5-6.5 hours can ensure that the calcareous additive and the alkaline components in the red mud are fully reacted to achieve the desired neutralization effect. If the time is too short, the reaction will not be complete, which may result in incomplete neutralization of the alkalinity of the red mud; if the time is too long, not only will the production cost increase, but other impurities or side reactions may also be introduced. Examples:

[0098] The reaction temperature is 60°C, and the reaction time is 6.5 hours.

[0099] The reaction temperature is 80°C, and the reaction time is 3 hours.

[0100] The reaction temperature is 100°C, and the reaction time is 0.5 hours.

[0101] The reaction temperature is 70°C, and the reaction time is 5 hours.

[0102] The reaction temperature is 90°C, and the reaction time is 2 hours.

[0103] The reaction temperature is 75°C, and the reaction time is 4 hours.

[0104] In some embodiments, the water content of the solid-phase material after dehydration is ≤25%.

[0105] The moisture content refers to the percentage of water mass in the total mass of the material, and is commonly used to describe the degree of dryness of a material. Controlling the moisture content of the solid-phase material after dewatering to be ≤25% has important implications for the subsequent drying process and the performance of the final product. Controlling the moisture content of the solid-phase material after dewatering to be below 25% can prevent particle agglomeration, and higher moisture content can lead to particle agglomeration during the drying process, forming larger particle groups. By controlling the moisture content to be below 25%, this agglomeration phenomenon can be reduced, ensuring good dispersion of the particles during the drying process. Lower moisture content helps achieve more uniform drying results, avoiding uneven drying due to high local moisture. Lower moisture content can reduce particle expansion and cracking caused by water evaporation during high-temperature drying, thereby improving the thermal stability of the particles. Example:

[0106] Dewatering treatment using a filter press, controlling the moisture content to be 20%.

[0107] Dewatering treatment using a vacuum filter, controlling the moisture content to be 22%.

[0108] Dewatering treatment using a centrifugal dewatering machine, controlling the moisture content to be 25%.

[0109] Dewatering treatment using a combination of filter press and vacuum filter, controlling the moisture content to be 21%.

[0110] Dewatering treatment using a combination of vacuum filter and centrifugal dewatering machine, controlling the moisture content to be 23%.

[0111] Dewatering treatment using a combination of filter press and centrifugal dewatering machine, controlling the moisture content to be 24%.

[0112] In some embodiments, the solid-liquid separation method includes at least one of the following: filtration, centrifugation, sedimentation; and / or,

[0113] The dewatering method includes at least one of the following: filter pressing, vacuum filtration, centrifugal dewatering.

[0114] By reasonably selecting and optimizing the solid-liquid separation method (such as filtration, centrifugation, sedimentation) and the dewatering method (such as filter pressing, vacuum filtration, centrifugal dewatering), the excess water in the red mud can be effectively removed, the moisture content of the solid-phase material (red mud filter cake) can be reduced, the efficiency of the subsequent drying process can be improved, the particle agglomeration phenomenon can be reduced, and the thermal stability and performance of the product can be enhanced. Example:

[0115] Using filtration for solid-liquid separation, using filter pressing for dewatering, and using an air jet mill for pulverization.

[0116] Using centrifugation for solid-liquid separation, using vacuum filtration for dewatering, and using a ball mill for pulverization.

[0117] Solid-liquid separation is performed using a sedimentation method, dewatering treatment is performed using a centrifugal dewatering method, and pulverization is performed using a hammer crusher.

[0118] Solid-liquid separation is performed using a combination of filtration and centrifugation, dewatering treatment is performed using a combination of pressure filtration and vacuum filtration, and pulverization is performed using a combination of an air jet mill and a ball mill.

[0119] Solid-liquid separation is performed using a combination of centrifugation and sedimentation, dewatering treatment is performed using a combination of vacuum filtration and centrifugal dewatering, and pulverization is performed using a combination of a ball mill and a hammer crusher.

[0120] Solid-liquid separation is performed using a combination of filtration and sedimentation, dewatering treatment is performed using a combination of pressure filtration and centrifugal dewatering, and pulverization is performed using a combination of an air jet mill and a hammer crusher.

[0121] The present application will be further described in conjunction with specific examples. It should be understood that these examples are only used to illustrate the present application and not used to limit the scope of the present application. The experimental methods in the following examples, if the specific conditions are not indicated, are generally determined according to the industry standards. If there is no corresponding industry standard, the determination is made according to the general international standards, the conventional conditions, or the conditions suggested by the manufacturers.

[0122] Example 1

[0123] The red mud slurry 1000 ml is removed from coarse particles by a hydrocyclone, with a particle size D50 = 90 μm controlled.

[0124] Limestone is added to the fine particle slurry at a Ca / Na molar ratio of 2.5:1, the reaction temperature is 60°C, and the reaction time is 6 hours.

[0125] After the reaction is completed, polyacrylamide (PAM, 0.1 wt%) is added for flocculation, and a filtrate is obtained by filtration, and the filtrate is recovered with sodium oxide.

[0126] The filter cake is dewatered by a filter press, with a water content of 25% controlled, and is fed into a primary dryer, with waste heat as a medium, and a temperature of 100°C controlled, and the water content after drying is 10%.

[0127] The secondary drying is performed, with superheated steam as a medium, a temperature of 140°C, and a liquid additive (sodium silicate solution, concentration 1%, modulus 2) sprayed synchronously, and the water content is controlled to 2%.

[0128] Finally, the dried product is pulverized by an air jet mill to a particle size D90 = 13 μm, and 312 grams of red mud dry powder is obtained.

[0129] Example 2

[0130] The red mud slurry 1000 ml is removed from coarse particles by a hydrocyclone, with a particle size D50 = 95 μm controlled.

[0131] Limestone was added to the fine particle slurry at a Ca / Na molar ratio of 3.0:1, the reaction temperature was 80°C, and the reaction time was 4 hours.

[0132] After the reaction was completed, polyacrylamide (PAM, 0.2wt%) was added for flocculation, and a filtrate was obtained by filtration, and sodium oxide was recovered from the filtrate.

[0133] The filter cake was dewatered by a filter press, the water content was controlled at 24%, and was sent into a primary dryer, the medium was waste heat, the temperature was controlled at 90°C, and the water content after drying was 12%.

[0134] The secondary drying was performed with superheated steam as the medium, the temperature was 260°C, liquid additives (sodium silicate solution, concentration 2%, modulus 1.5) were sprayed synchronously, and the water content was controlled at 1.5%.

[0135] Finally, the dried product was crushed to a particle size D90=12μm by an air jet mill, and 324 grams of red mud dry powder was obtained.

[0136] Example 3

[0137] The red mud slurry 1000ml was removed by a hydrocyclone, the particle size D50=100μm was controlled, and the coarse particles were removed.

[0138] Limestone was added to the fine particle slurry at a Ca / Na molar ratio of 3.5:1, the reaction temperature was 100°C, and the reaction time was 1 hour.

[0139] After the reaction was completed, polyacrylamide (PAM, 0.3wt%) was added for flocculation, and a filtrate was obtained by filtration, and sodium oxide was recovered from the filtrate.

[0140] The filter cake was dewatered by a filter press, the water content was controlled at 25%, and was sent into a primary dryer, the medium was waste heat, the temperature was controlled at 80°C, and the water content after drying was 13%.

[0141] The secondary drying was performed with superheated steam as the medium, the temperature was 280°C, liquid additives (sodium silicate solution, concentration 3%, modulus 1) were sprayed synchronously, and the water content was controlled at 2%.

[0142] Finally, the dried product was crushed to a particle size D90=14μm by an air jet mill, and 331 grams of red mud dry powder was obtained.

[0143] Example 4

[0144] The red mud slurry 1000ml was removed by a hydrocyclone, the particle size D50=92μm was controlled, and the coarse particles were removed.

[0145] Calcium carbide slag was added to the fine particle slurry at a Ca / Na molar ratio of 2.8:1, the reaction temperature was 70°C, and the reaction time was 5 hours.

[0146] After the reaction is completed, polyacrylamide (PAM, 0.15wt%) is added for flocculation, and a filtrate is obtained by filtration, and sodium oxide is recovered from the filtrate.

[0147] The filter cake is dewatered by a filter press, the water content is controlled to be 23%, and is sent into a first-stage drying machine, the medium is waste heat, the temperature is controlled to be 95°C, and the water content after drying is 11%.

[0148] The second-stage drying is performed by using superheated steam as the medium, the temperature is 200°C, liquid additives (sodium silicate solution, concentration 1.5%, modulus 1.8) are sprayed synchronously, and the water content is controlled to be 1.8%.

[0149] Finally, the dried product is crushed to a particle size D90=12.5μm by using an air flow mill, and 320 grams of red mud dry powder is obtained.

[0150] Example 5

[0151] The red mud slurry 1000ml is removed by a hydrocyclone, the particle size D50=98μm is controlled, and coarse particles are removed.

[0152] The quicklime is added in the fine particle slurry according to the Ca / Na molar ratio 3.2:1, the reaction temperature is 90°C, and the reaction time is 2 hours.

[0153] After the reaction is completed, polyacrylamide (PAM, 0.25wt%) is added for flocculation, and a filtrate is obtained by filtration, and sodium oxide is recovered from the filtrate.

[0154] The filter cake is dewatered by a filter press, the water content is controlled to be 22%, and is sent into a first-stage drying machine, the medium is waste heat, the temperature is controlled to be 85°C, and the water content after drying is 10.5%.

[0155] The second-stage drying is performed by using superheated steam as the medium, the temperature is 250°C, liquid additives (sodium silicate solution, concentration 2.5%, modulus 1.2) are sprayed synchronously, and the water content is controlled to be 1.2%.

[0156] Finally, the dried product is crushed to a particle size D90=13.5μm by using an air flow mill, and 328 grams of red mud dry powder is obtained.

[0157] Example 6

[0158] The red mud slurry 1000ml is removed by a hydrocyclone, the particle size D50=94μm is controlled, and coarse particles are removed.

[0159] The quicklime is added in the fine particle slurry according to the Ca / Na molar ratio 3.1:1, the reaction temperature is 75°C, and the reaction time is 3 hours.

[0160] After the reaction is completed, polyacrylamide (PAM, 0.2wt%) is added for flocculation, and a filtrate is obtained by filtration, and sodium oxide is recovered from the filtrate.

[0161] The filter cake is dewatered by a filter press, the water content is controlled at 24%, and is sent to a first-stage drying machine, using waste heat as the medium, the temperature is controlled at 92°C, and the water content after drying is 11.5%.

[0162] The second-stage drying is performed using superheated steam as the medium, the temperature is 220°C, and liquid additives (sodium silicate solution, concentration 2%, modulus 1.6) are sprayed synchronously, and the water content is controlled at 1.4%.

[0163] Finally, the dried product is pulverized to a particle size D90=12.8 μm by an air flow mill, and 326 grams of red mud dry powder is obtained.

[0164] Comparative Example 1

[0165] The red mud slurry 1000 ml is treated by a hydrocyclone, and the coarse particles are removed, with the particle size D50=90 μm.

[0166] Without adding calcium-based additives, flocculation treatment is directly performed, polyacrylamide (PAM, 0.1 wt%) is added for flocculation, and the filtrate is obtained by filtration, and the sodium oxide is recovered from the filtrate.

[0167] The filter cake is dewatered by a filter press, the water content is controlled at 25%, and is sent to a first-stage drying machine, using waste heat as the medium, the temperature is controlled at 100°C, and the water content after drying is 10%.

[0168] The second-stage drying is performed using superheated steam as the medium, the temperature is 140°C, and no liquid additives are sprayed, and the water content is controlled at 2%.

[0169] Finally, the dried product is pulverized to a particle size D90=15 μm by an air flow mill, and 305 grams of red mud dry powder is obtained.

[0170] Comparative Example 2

[0171] The red mud slurry 1000 ml is treated by a hydrocyclone, and the coarse particles are removed, with the particle size D50=95 μm.

[0172] Limestone is added in the fine particle slurry according to a Ca / Na molar ratio of 3.0:1, the reaction temperature is 80°C, and the reaction time is 4 hours.

[0173] After the reaction is completed, polyacrylamide (PAM, 0.2 wt%) is added for flocculation, and the filtrate is obtained by filtration, and the sodium oxide is recovered from the filtrate.

[0174] The filter cake is dewatered by a filter press, the water content is controlled at 24%, and is sent to a first-stage drying machine, using waste heat as the medium, the temperature is controlled at 90°C, and the water content after drying is 12%.

[0175] Only the first-stage drying is performed, and no second-stage drying is performed, and the dry powder is obtained.

[0176] Finally, the dry product is pulverized by jet mill to a particle size D90 = 18 μm, to obtain 315 grams of red mud dry powder.

[0177] Finally, the dry product is pulverized by jet mill to a particle size D90 = 18 μm, to obtain 315 grams of red mud dry powder.

[0178] Comparative Example 3

[0179] The red mud slurry 1000 ml is passed through a hydrocyclone to remove coarse particles, with a particle size D50 = 100 μm.

[0180] Limestone is added to the fine particle slurry at a Ca / Na molar ratio of 3.5:1, with a reaction temperature of 100°C and a reaction time of 1 hour.

[0181] After the reaction is complete, polyacrylamide (PAM, 0.3 wt%) is added for flocculation, and a filtrate is obtained by filtration, from which sodium oxide is recovered.

[0182] The filter cake is dewatered by a filter press, with a water content of 25%, and is fed into a primary dryer, with waste heat as the medium, at a temperature of 80°C, and a water content of 13% after drying.

[0183] The secondary drying is performed with superheated steam as the medium, at a temperature of 280°C, with simultaneous spraying of a liquid additive (sodium silicate solution, concentration 3%, modulus 1), with a water content of 2%.

[0184] No pulverization is performed, and the dry powder is obtained directly.

[0185] Effect data: The effect data in Examples 1 to 6 and Comparative Examples 1 to 3 are shown in Table 1.

[0186] Experimental method for effect data:

[0187] 1. Particle size D90 measurement

[0188] Instrument: Laser particle size analyzer

[0189] Method: The red mud powder sample after drying is placed in the laser particle size analyzer, and the particle size distribution data is recorded by measuring according to the instrument operating procedure, and the D90 value is calculated.

[0190] 2. Water content measurement

[0191] Instrument: Oven Method: Accurately weigh about 10 grams of red mud powder sample after drying, and place it in an oven preheated to 105°C, and dry to constant weight. Calculate the water content of the sample.

[0192] 3. Observation of particle agglomeration

[0193] Instrument: Scanning electron microscope (SEM)

[0194] Method: After the dried red mud powder sample is treated with gold spraying, it is placed in a scanning electron microscope to observe the agglomeration of the particles and record the dispersion state of the particles.

[0195] 4. Thermal stability test

[0196] Instrument: Thermogravimetric analyzer (TGA)

[0197] Method: After the dried red mud powder sample is placed in a thermogravimetric analyzer, it is heated from room temperature to 800℃ at a heating rate of 10℃ / min, and the mass change curve of the sample is recorded to determine the thermal stability of the sample.

[0198] 5. Product yield measurement: The total mass of the dried red mud powder sample is accurately weighed and recorded as the product yield.

[0199] Table 1

[0200]

[0201] Through the above effect data table, the differences between different examples and comparative examples can be intuitively compared. The following conclusions can be drawn:

[0202] Particle size control effect:

[0203] Examples: The particle size D90 of all examples is controlled below 15μm, among which the particle size of example 2 and example 4 is the smallest, which is 12μm and 12.5μm respectively. This shows that by optimizing the type, amount of calcium additive and reaction conditions, the particle size of red mud dry powder can be effectively controlled to meet the demand of fine powder application. Comparative examples: The particle sizes of comparative example 1 and comparative example 2 are 15μm and 18μm respectively, which are obviously larger than the examples. Comparative example 3 does not undergo crushing treatment, and the particle size reaches 100μm, which is much larger than the examples, indicating that the unoptimized process is difficult to realize fine particle size control.

[0204] Moisture content control effect:

[0205] Examples: The moisture content of the examples is controlled below 2%, among which the moisture content of example 5 is the lowest, which is 1.2%. This shows that through the two-stage drying process, especially the superheated steam drying combined with liquid additive spraying, the moisture content of red mud dry powder can be effectively reduced to improve the stability of the product. Comparative examples: The moisture contents of comparative example 1 and comparative example 2 are 2% and 12% respectively, and the moisture content of comparative example 2 is higher due to the absence of secondary drying, indicating that secondary drying is crucial for reducing moisture content.

[0206] Particle agglomeration:

[0207] Example: All examples do not show obvious agglomeration phenomenon, indicating that by adding calcium adjuvant and liquid adjuvant, and optimizing the drying process, the particle agglomeration can be effectively prevented, and the dispersibility of the product can be improved. Comparative example: Comparative example 1, comparative example 2 and comparative example 3 all show obvious agglomeration phenomenon, indicating that when no adjuvant is added or the process is not optimized, the particle agglomeration problem is more serious.

[0208] Thermal stability:

[0209] Example: The thermal stability of all examples is ≥600℃, indicating that by the steam-chemical coupling activation process, the thermal stability of the red mud dry powder can be significantly enhanced, making it suitable for high temperature application scenarios. Comparative example: The thermal stability of comparative example 1, comparative example 2 and comparative example 3 is less than 500℃, indicating that the thermal stability of red mud powder without surface activation treatment is poor.

[0210] Product yield:

[0211] Example: The product yield of example 3 is the highest, which is 331 grams, indicating that under the optimized conditions, higher product yield can be achieved. Comparative example: The product yield of comparative example 3 is 330 grams, which is slightly lower than that of example 3, but the particle size is larger and the agglomeration is serious, indicating that although the yield is high without crushing treatment, the product quality is poor.

[0212] The above is only a specific embodiment of the present application, which enables those skilled in the art to understand or implement the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to these embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features applied herein.

Claims

1. A method for preparing red mud dry powder, comprising: removing coarse particles in a red mud slurry to obtain a fine particle slurry; adding a calcareous auxiliary agent to the fine particle slurry to perform a chemical reaction, to neutralize part of the alkalinity of the fine particle slurry and to improve the particle surface properties of the fine particle slurry, to obtain a reaction material; adding a flocculating agent to the reaction material to perform flocculation treatment, to obtain a flocculated material; performing solid-liquid separation on the flocculated material to obtain a liquid phase material and a solid phase material; performing dewatering treatment on the solid phase material and controlling the water content of the solid phase material; performing primary drying on the dewatered solid phase material using waste heat as a medium; performing secondary drying on the primary dried solid phase material using superheated steam as a medium, and simultaneously spraying a liquid auxiliary agent onto the surface of the solid phase material; pulverizing the secondary dried solid phase material to a predetermined particle size to obtain red mud dry powder.

2. The method for producing red mud dry powder according to claim 1, characterized by, The calcareous auxiliary agent comprises at least one of the following: limestone, carbide slag, quicklime, and slaked lime; and / or, The molar ratio of the calcareous auxiliary agent to sodium oxide in the fine particle slurry is 2.5:1-3.5:

1.

3. The method of producing dried red mud powder according to claim 1, characterized in that, The flocculating agent comprises at least one of the following: polyacrylamide, polyaluminum chloride, and polyferric sulfate; and / or, The mass of the flocculating agent is 0.1-0.3% of the mass of the fine particle slurry.

4. The method of producing dried red mud powder according to claim 1, characterized in that, The liquid auxiliary agent comprises at least one of the following: sodium silicate solution, silica sol, diatomite dispersion, and bentonite dispersion; and / or, The mass concentration of the liquid auxiliary agent is 1-3%, and the modulus of the sodium silicate solution is 1-2%.

5. The method of producing dried red mud powder according to claim 1, characterized in that, The particle size D50 of the fine particle slurry is ≥90um.

6. The method of producing dried red mud powder according to claim 1, characterized in that, The primary drying satisfies: the waste heat temperature is 80-100℃, and the water content of the solid phase material is controlled to be 10-15%; and the secondary drying satisfies: the superheated steam temperature is 140-280℃, and the water content of the solid phase material is controlled to be ≤2%.

7. The method of producing dried red mud powder according to claim 1, characterized in that, The predetermined particle size D90 is ≤15um.

8. The method of producing dried red mud powder according to claim 1, characterized in that, The temperature of the chemical reaction is 60-100℃, and the time of the chemical reaction is 0.5-6.5 hours.

9. The method of producing dried red mud powder according to claim 1, characterized in that, The water content of the dewatered solid phase material is ≤25%.

10. The method of producing dried red mud powder according to claim 1, characterized in that, The solid-liquid separation method comprises at least one of the following: filtration, centrifugation, and sedimentation; and / or, The dewatering treatment method comprises at least one of the following: pressure filtration, vacuum filtration, and centrifugal dewatering.

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