Red mud resourceful treatment process

Abstract

The invention relates to the technical field of metallurgy and environmental protection, and particularly provides a red mud resourceful treatment process which comprises the steps that dried red mud is added into a red mud treatment reactor to be subjected to a reduction reaction with a reactant, and molten-state mixed metal, furnace slag and reaction gas are obtained; wherein due to the metal density difference, the molten metal is naturally layered; the cooling rate is controlled, and metal elements in the molten mixed metal are solidified and extracted through the melting point difference; after the reaction, purifying the gas for synthesizing methanol; the furnace slag is used for extracting aluminum oxide or used as a raw material for preparing cement. The method has the advantages that harmless treatment of the red mud and comprehensive recycling of all valuable elements in the red mud can be achieved, and the utilization rate of the red mud is increased.

Description

Technical Field

[0001] This application relates to the technical fields of metallurgy and environmental protection, and particularly to a process for the resource treatment of red mud. Background Art

[0002] Red mud is an industrial solid waste discharged after extracting alumina from bauxite. Red mud has strong alkalinity, contains heavy metals and radioactive elements, and is also prone to dust pollution. Therefore, the treatment and comprehensive utilization of red mud have always been an important environmental protection issue.

[0003] Traditional red mud treatment methods mainly focus on producing building materials and magnetic separation to extract valuable metals. However, due to the characteristics of red mud itself, the above treatment methods have great limitations, being unable to handle a large amount of red mud and not being able to obtain good economic benefits.

[0004] Most of the red mud has not been effectively utilized and is mainly stored in piles. Red mud has become a relatively serious industrial hazard and has attracted wide social attention. Summary of the Invention

[0005] To solve the above problems, an embodiment of this application provides a process for the resource treatment of red mud, which can achieve the harmless treatment of red mud and the comprehensive recovery and utilization of various valuable elements in red mud to improve the utilization rate of red mud.

[0006] For this purpose, the following technical solutions are adopted in the embodiments of this application:

[0007] In a first aspect, this application provides a process for the resource treatment of red mud, including: crushing and screening the dried red mud, and adding it to a red mud treatment reactor to carry out a reduction reaction with a reactant to obtain molten mixed metals, slag, and reaction gas; wherein, due to the difference in metal density, the molten metals naturally stratify; by controlling the cooling rate, each metal element in the molten mixed metals is solidified and extracted using the difference in melting points; after the reaction gas is purified, it is used to synthesize methanol; the slag is used to extract alumina or as a raw material for making cement.

[0008] In this embodiment, first, the red mud is dried to remove the moisture therein to ensure that the moisture will not affect the reaction efficiency in subsequent reactions, and then it is crushed and screened to a particle size less than 0.1 mm. The dried red mud and a specific reactant are added to a red mud treatment reactor for a reduction reaction. Through this process, the metal oxides in the red mud (such as iron, titanium, nickel, etc. in bauxite) are reduced to molten metals. During this reaction process, the role of the reactant is to promote the reduction of the metal elements in the metal oxides to their corresponding metals, releasing slag and gas. Due to the different densities of different metals, the molten metals naturally stratify during the reaction process. Heavier metals such as iron will sink to the bottom, and lighter metals such as titanium will float on the upper layer. Through this natural stratification, different metal elements can be separated relatively easily. After the molten metals are naturally stratified, the cooling rate is controlled, and the solidification and extraction of metals are carried out by utilizing the melting point differences of different metals. Metals with higher melting points (such as titanium) solidify first at lower temperatures to form solid metals, and these metals can be further recycled and utilized. The gas generated during the reaction process will contain harmful components such as sulfides, so gas purification is required, especially desulfurization and decarbonization treatment. The purified gas can be further used to synthesize methanol, which can not only effectively reduce pollution but also be converted into useful fuels or chemical raw materials through chemical processes. The slag after the reaction can be used for various purposes. The slag contains a certain proportion of alumina, and alumina can be further extracted as a recycled raw material for bauxite; in addition, the slag can also be used as a raw material for cement production, reducing the demand for natural ores.

[0009] In summary, through the reduction reaction and gas purification, the harmful components (such as heavy metals and radioactive elements) in the red mud can be effectively removed or converted into harmless substances. Especially the removal of sulfides after gas purification can reduce environmental pollution and protect air quality. This process can not only effectively recover the metal elements (such as iron, titanium, nickel, etc.) in the red mud, but also the slag can be used to extract alumina or as a raw material for cement production. This comprehensive recovery method greatly improves the resource utilization efficiency and reduces resource waste. That is, this red mud resource treatment process can not only achieve the harmless treatment of red mud through a series of innovative treatment methods, but also effectively recover the useful metal elements and other valuable resources therein. Compared with traditional treatment methods, this solution has a higher resource recovery rate, lower environmental pollution, and better economic benefits, so it has important technical advantages and practical application prospects in the treatment and utilization of red mud.

[0010] As an implementable embodiment, the reactants include pulverized coal, oxygen, and steam; the step of adding the dried red mud into a red mud treatment reactor for a reduction reaction with the reactants includes: dehydrating the red mud in a rotary dryer at 200 - 300 °C until the water content is ≤ 5%, then crushing and screening it to a particle size of ≤ 0.1 mm; adding the crushed red mud, pulverized coal, oxygen, and steam into the red mud treatment reactor; controlling the temperature of the red mud treatment reactor to be 1250 °C - 2000 °C, and the reduction reaction time to be 3 - 8 seconds.

[0011] In this embodiment, first, optionally, the red mud can be dehydrated by a rotary dryer. At a temperature of 200 - 300 °C, the water in the red mud is evaporated, reducing its water content to less than 5%. This process can significantly reduce the interference of water in the red mud and improve the efficiency of the subsequent reduction reaction. The dehydrated red mud is crushed and screened to a particle size less than 0.1 mm. The purpose of this is to increase the specific surface area of the reactants, thereby enhancing the reaction rate and efficiency. The fine red mud particles can better contact the reducing agents (such as coal, CO, and H2), ensuring a complete reaction. In the red mud treatment reactor, the screened red mud reacts with the reactants (pulverized coal, oxygen, and steam) in a high-temperature reduction reaction. Pulverized coal acts as a fuel and a reducing agent, reacting with the metal oxides in the red mud at high temperature to reduce the metals to molten metals. The roles of oxygen and steam are to participate in the redox reactions during the reaction process, generating CO and H2, helping to regulate the reaction environment, and promoting certain chemical reactions. The reactor temperature is controlled between 1250 °C - 2000 °C. This temperature range can ensure that the metal elements (such as iron, titanium, nickel, etc.) in the red mud can be fully reduced to the metallic state. At this high temperature, the reaction is sufficient and stable, ensuring a relatively high recovery rate of metal elements. At the same time, slag and reaction gases can be separated. The reduction reaction time is set to 3 - 8 seconds. This time is sufficient for the reaction to complete, ensuring the complete reduction of metal elements. An appropriate reaction time helps to obtain an ideal metal recovery rate and avoid side reactions or energy waste caused by an overly long reaction time. After the metal elements are reduced, they are in a molten state at high temperature. Due to the different densities of different metals, the molten metals will naturally stratify. Heavier metals such as iron will settle to the bottom, while lighter metals such as titanium will float on the upper layer. This stratification phenomenon makes it easier to separate the metal elements for subsequent metal extraction and recovery. During the reaction process, the generated gases may contain some harmful substances, such as sulfides. These gases are desulfurized by a gas purification device. The purified gases can be used as chemical raw materials such as for synthesizing methanol. This not only reduces pollution but also converts these gases into valuable energy sources. The remaining slag still contains a certain proportion of useful components such as alumina. These slags can be used to extract alumina or as raw materials for cement production, realizing the resource utilization of waste.

[0012] As an implementable embodiment, the weight ratio of the pulverized coal to the red mud is 100:10 - 1500.

[0013] In this embodiment, through the verification of the inventor, when the weight ratio of the pulverized coal to the red mud is within the above ratio, the reaction can be made more efficient, and the metal recovery rate can be significantly improved. A reasonable proportion of pulverized coal can not only ensure sufficient reduction reaction, but also save energy, reduce production costs, and effectively reduce environmental pollution. This solution has high economic benefits and environmental protection advantages, and can realize the resource utilization of red mud and the efficient recovery of metals.

[0014] As an implementable embodiment, the oxygen consumption is controlled at 0.03 - 0.1 m 3 / kg of red mud.

[0015] In this embodiment, by controlling the oxygen consumption within the range of 0.03 - 0.1 m 3 / kg of red mud, the conditions of the reduction reaction are optimized. While ensuring the reaction efficiency, the metal recovery rate is effectively improved, and energy waste and side reactions are reduced. Through reasonable oxygen use, the reaction temperature and rate can be optimized, achieving multiple advantages of energy conservation, environmental protection, and improved production efficiency.

[0016] As an implementable embodiment, the steam consumption is controlled at 0.005 - 0.02 m 3 / kg of red mud.

[0017] In this embodiment, by controlling the steam consumption within the range of 0.005 - 0.02 m 3 / kg of red mud, the conditions of the reduction reaction are optimized. The appropriate participation of steam can not only improve the reduction efficiency of metal oxides, but also improve reaction stability, regulate temperature, enhance heat transfer efficiency, and reduce the generation of by-products. In this way, energy can be saved, production costs can be reduced, and the impact on the environment during the reaction process can be minimized.

[0018] As an implementable embodiment, the metal elements in the molten mixed metal include at least one of iron, titanium, and nickel.

[0019] As an implementable embodiment, by controlling the cooling rate and extracting each metal element in the molten mixed metal using the melting point difference for solidification, including: adopting the gradient cooling method, heating the molten mixed metal to 1668 °C - 1700 °C, and then when the temperature is lowered to 1600 °C, titanium begins to solidify to form a dendritic skeleton, and the titanium-rich phase is separated by gravity sedimentation or magnetic separation; when the temperature is lowered to 1500 °C, iron solidifies to form a dense metal block; when the temperature is lowered to 1400 °C, nickel solidifies to form a dense metal block.

[0020] In this embodiment, the melting points of iron (Fe), titanium (Ti), and nickel (Ni) are 1538 °C, 1668 °C, and 1455 °C, respectively. Through the gradient cooling method, the temperature is decreased in stages to solidify the metals in order of decreasing melting point, achieving physical separation: Titanium solidifies first: When the melt cools to 1600 °C (slightly lower than the melting point of titanium), titanium first precipitates in the form of dendrites to form a framework structure. Iron then solidifies: Continuing to cool to 1500 °C (lower than the melting point of iron), the iron-based alloy solidifies into a dense metal block. Nickel solidifies last: When the temperature drops to 1400 °C (lower than the melting point of nickel), the nickel alloy solidifies. If the melt contains carbon or other alloying elements, the freezing point of iron can be lowered (such as the eutectic point of the Fe-C alloy is 1147 °C), causing iron to solidify in advance at 1500 °C. Adding sulfur (S) or phosphorus (P) can refine the nickel grains and improve the density of the metal block after solidification.

[0021] The gradient cooling method realizes the efficient recovery of iron, titanium, and nickel by precisely utilizing the difference in the melting points of metals and physical separation technology, and has the advantages of high economy, low energy consumption, and environmental friendliness. It is particularly suitable for the resource treatment of industrial wastes containing multiple metals (such as red mud, electronic waste), providing an innovative solution for the circular economy.

[0022] As an achievable embodiment, the post-reaction gas includes at least one of carbon dioxide, carbon monoxide, hydrogen, and hydrogen sulfide.

[0023] As an achievable embodiment, after the post-reaction gas is purified and used for synthesizing methanol, it includes: passing the post-reaction gas through a dust collector for dust removal, adjusting the carbon-hydrogen ratio through a conversion device, and then introducing it into a purification device for desulfurization and decarbonization treatment to obtain a purified gas; synthesizing methanol from the purified gas under the action of a catalyst.

[0024] In this embodiment, during the reaction process, the generated gas may contain solid particles or dust, and these impurities need to be removed by a dust collector first. The dust collector filters out the solid particles in the gas through physical or mechanical methods (such as bag dust removal, electrostatic dust removal, etc.), so as to ensure that the gas does not contain particles that will interfere with the subsequent treatment process. To synthesize methanol from CO and H2 in the syngas, the carbon-hydrogen ratio needs to be adjusted to 1:2, which needs to be completed in a shift unit. The syngas usually contains sulfides such as hydrogen sulfide (H2S), and these sulfides need to be removed through desulfurization treatment in an absorption tower. Desulfurization treatment usually uses an absorbent (such as sodium hydroxide solution or other alkaline solutions) to absorb hydrogen sulfide and generate harmless by-products (such as sodium sulfide), thereby removing the sulfur element in the gas. The desulfurization process helps prevent catalyst poisoning and extends the service life of the methanol synthesis catalyst. At the same time, CO2 in the syngas requires a special catalyst to react with H2 to synthesize methanol. If it enters the conventional methanol synthesis, not only will it not react, but it will also consume too much energy, so it is necessary to remove carbon dioxide by pressure swing adsorption to remove and recover CO2 from the syngas. The purified syngas enters the methanol synthesis reactor. Under the action of a catalyst (common catalysts are copper-based catalysts, zinc-based catalysts, etc.), carbon monoxide (CO) reacts with hydrogen in a hydrogenation reaction to synthesize methanol (CH3OH). Through the action of the catalyst, the reaction can proceed at a lower temperature and pressure, thereby improving the efficiency of methanol synthesis. The chemical equation of the reaction is as follows:

[0025] CO + H2 → CH3OH

[0026] The captured CO2 can be processed into food-grade CO2 as needed, or processed into methanol or urea, so as to achieve zero CO2 emissions. The chemical equations of the reactions are as follows:

[0027] CO2 + 3H2 → CH3OH + H2O

[0028] N2 + 3H2 → 2NH3

[0029] 2NH3 + CO2 → NH2COONH4

[0030] NH2COONH4 → CO(NH2)2 + H2O

[0031] As an achievable embodiment, the components in the slag include alumina and silica; the slag is used to extract alumina or as a raw material for making cement, including: further extracting alumina from the slag in the way of refining bauxite and discharging the tailings; and further extracting silica from the tailings or directly using it as a cement raw material to make cement.

[0032] In this embodiment, the slag contains alumina (Al2O3) and silica (SiO2). These components are commonly found in the by-products generated during the aluminum smelting process. Alumina is the main component of bauxite. Through a refining method similar to that of bauxite, the alumina in the slag is extracted. A common refining method is the "Bayer Process" for bauxite, which dissolves the alumina in the slag in a sodium hydroxide solution under high temperature and pressure to form sodium aluminate, and then the alumina is extracted from the solution through precipitation and heating. By extracting alumina, some residual components in the slag (such as silica, etc.) are discharged as tailings. The silica in these tailings can be used as a raw material for cement production or further extracted. Specifically, the tailings in the extraction process are usually rich in silica (SiO2). Acid leaching, alkali leaching or other chemical methods can be used to extract the silica from the tailings for separate recovery as a commercial product of silica or used in the production of silicon materials (such as silicates, silica gels, etc.). The silica in the tailings can be directly used as one of the raw materials for cement. Silica is an important component in cement production and can react with limestone (mainly containing calcium oxide) to form calcium silicate (C3S), which is the main hydration product in cement. The addition of silica helps to improve the performance of cement, including enhancing the strength and durability of cement.

[0033] This technical solution can achieve the recycling of resources, reduce waste emissions, reduce dependence on natural resources, and optimize the aluminum smelting and cement production processes by efficiently extracting alumina and silica from the slag. The extraction of alumina provides a stable raw material source for the aluminum industry, and the extraction or direct use of silica in cement production not only reduces the exploitation of ore resources but also improves the production efficiency and quality of cement. Overall, this solution meets the requirements of green environmental protection and sustainable development and has significant economic and environmental benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 Shows a flowchart of a red mud resource treatment process provided by an embodiment of the present application;

[0035] Figure 2 Shows a schematic diagram of the material and product treatment of each process step of a red mud resource treatment process provided by an embodiment of the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0036] The technical solutions in the embodiments of the present application will be described below with reference to the accompanying drawings in the embodiments of the present application.

[0037] It should be understood that the protection scope of the present application is not limited to the specific embodiments described below; it should also be understood that the terms used in the embodiments of the present application are for describing specific embodiments and not for limiting the protection scope of the present application; in the specification and claims of the present application, unless otherwise clearly indicated in the text, the singular forms "a", "an" and "the" include the plural forms.

[0038] When an embodiment gives a numerical range, it should be understood that, unless otherwise specified in the present application, both endpoints of each numerical range and any value between the two endpoints can be selected. Unless otherwise defined, all technical and scientific terms used in the present application have the same meaning as commonly understood by those skilled in the art of this technology. In addition to the specific methods, equipment, and materials used in the embodiments, according to the knowledge of those skilled in the art of this technology and the description of the present application, any methods, equipment, and materials of the prior art similar or equivalent to those described in the embodiments of the present application can also be used to implement the present application.

[0039] It should be specifically noted that: unless otherwise defined, the technical terms used in the following embodiments have the same meaning as commonly understood by those skilled in the art to which the present invention belongs. The experimental reagents used in the following embodiments are all conventional biochemical reagents unless otherwise specified; the raw materials, instruments, and equipment used in the following embodiments can all be obtained through market purchase or by existing methods; the dosage of the experimental reagents is the dosage of the reagents in conventional experimental operations unless otherwise specified; the experimental methods are all conventional methods unless otherwise specified.

[0040] The production volume of red mud is huge, its components are complex, and the particles are fine. Moreover, the production process of alumina makes red mud have a high alkalinity and is difficult to be treated and utilized. At present, the main treatment method for the red mud produced in China is stacking, and it cannot be randomly landfilled or discarded. Due to the excessively high alkalinity of red mud and the presence of potential pollutants such as heavy metals, long-term stacking poses a huge environmental pollution hazard and a potential threat to the ecology. This is because red mud is an alkaline substance, and with the washing of rainwater, the alkali in red mud will be dissolved out, which may pollute surface water and groundwater. The iron in red mud is in the form of weakly magnetic iron oxide and is dispersed in the red mud with a particle size of -2 microns in the form of a cementing body. At present, the main technologies for iron recovery from red mud are two physical methods, namely magnetic separation and gravity separation, and chemical methods such as acid leaching and roasting. However, due to the limitations of processing costs and processing volumes, it is difficult to achieve large-scale promotion. The valuable elements in red mud have not been fully utilized, and its economic value remains to be improved. Therefore, it is very urgent to find a new and efficient comprehensive resource utilization process for red mud.

[0041] It's important to note that red mud contains elements such as aluminum, iron, silicon, titanium, and nickel, with the concentrations of these elements being much higher than those of titanium and nickel. This means that aluminum, iron, and silicon are major elements in red mud and are present in relatively high concentrations, while titanium and nickel are trace elements and are also rare metals, present in relatively low concentrations. Typically, the concentrations of aluminum and silicon in red mud are similar, with a difference of less than 15%. These major elements primarily exist as Al2O3, SiO2, Fe2O3, and CaO, respectively, while titanium and nickel primarily exist as TiO2 and NiO. Of course, these elements may also exist in other forms, and red mud may also contain other elements. Optionally, the red mud used in the embodiments of the present application is red mud produced by an aluminum plant using bauxite as raw material. The bauxite is gibbsite type, and the red mud produced is reddish brown, uneven in block shape, has a certain hardness, and a water content of 11.5%. The elements with the highest content in the red mud are Fe and Al, which are 37.5% and 8.33% respectively.

[0042] In order to achieve comprehensive resource utilization of red mud, a red mud resource processing process is provided in an embodiment of the present application. In this process, with the addition of appropriate amounts of coal powder, oxygen, and water vapor, the iron element and some heavy metal elements including titanium and nickel in the red mud can be reduced efficiently and with low energy consumption. The various metal elements obtained are mainly iron, and each metal element can be separated and extracted according to its different melting points. Thus, high-value metal products are obtained. The treated red mud is discharged from the furnace in the form of slag, and the total amount will be significantly reduced by more than 50%. The main components of the slag are aluminum oxide (Al2O3) and silicon dioxide (SiO2), each accounting for about 50%. This composition basically meets the processing requirements of bauxite, so the remaining slag can be used to further extract aluminum oxide in the same way as bauxite. The final remaining tailings are mainly silicon dioxide, which only accounts for 10% to 20% of the red mud and is harmless to the environment. It can be directly used as a cement raw material or used to produce crude silicon. During the entire treatment process, carbon capture technology is used to capture all the carbon dioxide generated during the treatment process and further synthesize methanol, thereby achieving zero carbon dioxide emissions in the red mud treatment process.

[0043] Figure 1 A flow chart of a red mud resource treatment process provided in an embodiment of the present application is shown; Figure 2 The following is a schematic diagram showing the material and product processing steps of a red mud resource treatment process provided in an embodiment of the present application. Figure 1 and Figure 2 The red mud resource treatment process includes the following steps:

[0044] Step S1: Crush and screen the dried red mud to a particle size less than 0.1 mm, and then add it to the red mud treatment reactor to carry out a reduction reaction with the reactant, obtaining molten mixed metals, slag, and reaction gas; among them, due to the density difference of the metals, the molten metals are naturally stratified.

[0045] Specifically, step S1 can be realized through the following sub-steps S101 - S102:

[0046] S101: Pretreatment of red mud.

[0047] In this step, the red mud is crushed, dried, and then screened to a suitable particle size to increase the reaction contact area. Optionally, the red mud is dehydrated in a rotary dryer at 200 - 300 °C to a moisture content ≤ 5%, and then crushed to a particle size ≤ 0.1 mm.

[0048] S102: High-temperature reduction smelting.

[0049] In this step, the dried red mud is added to the red mud treatment reactor to carry out a reduction reaction with the reactant. The dried red mud and a specific reactant are added to the red mud treatment reactor to carry out a reduction reaction. Through this process, the metal oxides in the red mud (such as iron, titanium, nickel, etc. metals in bauxite) are reduced to molten metals. During this reaction process, the role of the reactant is to promote the reduction of the metal elements in the metal oxides to their corresponding metals, releasing slag and gas. Optionally, the reactant includes pulverized coal, oxygen, and water vapor. The red mud treatment reactor can be an oxygen pulverized coal smelting reduction furnace, and high-temperature melting and separation are carried out through pulverized coal oxygen combustion; the separated molten iron is sent to the steelmaking system.

[0050] In the red mud treatment reactor, the crushed red mud and the reactants (pulverized coal, oxygen, and water vapor) carry out a high-temperature reduction reaction together. Pulverized coal serves as a fuel and a reducing agent, reacting with the metal oxides in the red mud at high temperature to reduce the metals to molten metals. The roles of oxygen and water vapor are to participate in the oxidation-reduction reaction during the reaction process, generating CO and H2, helping to adjust the reaction environment, and promoting the progress of certain chemical reactions to enhance the reduction efficiency. At this stage, the Fe, Ti, Ni oxides in the red mud are reduced to metals or alloy phases.

[0051] In a possible implementation, the crushed red mud, coal powder, oxygen, and steam are added to a red mud treatment reactor; the temperature of the red mud treatment reactor is controlled at 1250°C - 2000°C, and the reduction reaction time is at least 6 seconds. The reactor temperature is controlled between 1250°C and 2000°C, and this temperature range can ensure that the metal elements (such as iron, titanium, nickel, etc.) in the red mud can be fully reduced to the metallic state. For example, the reactor temperature is 1250°C, 1300°C, 1350°C, 1400°C, 1450°C, 1500°C, 1550°C, 1600°C, 1650°C, 1700°C. At this high temperature, the reaction is sufficient and stable, which can ensure a high recovery rate of metal elements, and at the same time, slag and reaction gases can be separated. The reduction reaction time is set to 3 - 8 seconds, for example, 3 seconds, 4 seconds, 5 seconds, 6 seconds, 7 seconds, or 8 seconds. This time is sufficient for the reaction to complete and ensure the complete reduction of metal elements. Appropriate reaction time helps to obtain an ideal metal recovery rate and avoid side reactions or energy waste caused by too long reaction time.

[0052] In this process, the main chemical reactions include:

[0053] Gasification reaction of coal powder (generating reducing gas)

[0054] C + O2 = CO2

[0055] C + CO2 = 2CO

[0056] C + H2O = CO + H2

[0057] Reduction of iron oxide (main reaction)

[0058] Fe2O3 + 3CO = 2Fe + 3CO2

[0059] Fe2O3 + 3H2 = 2Fe + 3H2O

[0060] Reduction of titanium oxide:

[0061] TiO2 + 2C = Ti + 2CO

[0062] TiO2 + 2H2 = Ti + 2H2O

[0063] Reduction of nickel oxide:

[0064] NiO + H2 = Ni + H2O

[0065] NiO + CO = Ni + CO2

[0066] In some possible implementations, a flux can also be added to the red mud, for example, CaO + NaF, and the addition amount of the flux is 5% of the mass of the red mud to reduce the melting temperature to 1100°C, thereby further reducing energy consumption.

[0067] In some possible embodiments, the weight ratio of pulverized coal to red mud is 100:10 - 1500. For example, the weight ratio of pulverized coal to red mud can be 100:10, 100:100, 100:1000, or 100:1500 to improve the reduction efficiency of each metal element.

[0068] In some possible embodiments, the oxygen dosage is controlled at 0.03 - 0.1 m 3 / kg of red mud. In one possible embodiment, the oxygen dosage is controlled at 0.03 m 3 / kg of red mud, 0.06 m 3 / kg of red mud, 0.08 m 3 / kg of red mud, or 0.1 m 3 / kg of red mud.

[0069] In some possible embodiments, the steam dosage is controlled at 0.005 - 0.02 m 3 / kg of red mud. In one possible embodiment, the steam dosage is controlled at 0.005 m 3 / kg of red mud, 0.01 m 3 / kg of red mud, 0.015 m 3 / kg of red mud, or 0.02 m 3 / kg of red mud. Controlling the oxygen dosage and steam dosage within the above ratios can optimize the reduction reaction conditions and improve the reduction efficiency of metal oxides.

[0070] Step S2: By controlling the cooling rate, each metal element in the molten mixed metal is extracted by solidification using the melting point difference.

[0071] Using the metal density difference, the molten metal naturally stratifies. For example: the iron-based alloy (density 7.8 g / cm 3 ) sinks to the bottom; the titanium alloy (density 4.5 g / cm 3 ) is located in the middle layer; the nickel alloy (density 8.9 g / cm 3 ) may be partially mixed due to its density being close to that of iron and needs to be separated subsequently. In this step, after each metal element in the red mud is reduced, the molten mixed metal is heated to 1668°C - 1700°C, and then when the temperature is decreased to 1600°C at a rate of 5°C / min, titanium begins to solidify to form a dendritic skeleton, and the titanium-rich phase is separated by gravity sedimentation or magnetic separation; when the temperature is decreased to 1500°C, iron solidifies to form a dense metal block; when the temperature is decreased to 1400°C, nickel solidifies to form a dense metal block.

[0072] Step S3: After the reaction gas is purified, it is used to synthesize methanol.

[0073] In this step, it should be noted that the post-reaction gas includes carbon dioxide, carbon monoxide, hydrogen, and hydrogen sulfide. In the red mud treatment process, the post-reaction gas contains CO2 (60%-90%), CO (5%-10%), H2 (0.2%-5%), H2S (0.5%-2%), and a small amount of impurities (such as dust and hydrocarbons). The following steps are required to purify and synthesize methanol:

[0074] The post-reaction gas can be passed through a dust collector for dust removal, the carbon-hydrogen ratio can be adjusted through a conversion device, and then passed into a purification device for desulfurization and decarbonization treatment to obtain purified gas. The purified gas is synthesized into methanol under the action of a catalyst.

[0075] Optionally, the dust collector filters out solid particulate matter in the gas by physical or mechanical methods (such as bag dust removal, electrostatic dust removal, etc.). For example, particulate matter (dust content <5mg / m 3 ) is removed through a cyclone separator or a ceramic filter, and light hydrocarbons (such as CH4) are removed by activated carbon adsorption or low-temperature condensation, so as to ensure that the gas does not contain particles and light hydrocarbons that will interfere with the subsequent treatment process. The gas after dust removal usually contains sulfides such as hydrogen sulfide (H2S), and these sulfides need to be removed through desulfurization treatment in an absorption tower. Desulfurization treatment usually uses an absorbent (such as sodium hydroxide solution or other alkaline solutions) to absorb hydrogen sulfide and generate harmless by-products (such as sodium sulfide), thereby removing sulfur elements from the gas. Exemplarily, amine solution (methyldiethanolamine, MDEA) absorbs H2S, and the reaction is:

[0076] H2S + R2NH → R2NH2 + + HS -

[0077] The methanol synthesis process can use a copper-based catalyst (Cu / ZnO / Al2O3), with a pressure of 5-10 MPa, a temperature of 200-300 °C, and a space velocity of 5000-10000 h-1 (gas volume flow rate / catalyst volume).

[0078] Under the action of a catalyst (common catalysts also include zinc-based catalysts, etc.), carbon monoxide (CO) and carbon dioxide (CO2) react with hydrogen in a hydrogenation reaction to synthesize methanol (CH3OH). The chemical equations of the reaction are as follows:

[0079] CO2 + 3H2 → CH3OH + H2O (conversion rate 15-20%)

[0080] CO + 2H2 → CH3OH (conversion rate 30-35%)

[0081] Through the action of the catalyst, the reaction can proceed at a lower temperature and pressure, thereby improving the efficiency of methanol synthesis.

[0082] Step S4: The slag is used to extract alumina or as a raw material for making cement.

[0083] In this step, alumina can be further extracted from the slag in the way of refining bauxite, and the tailings are discharged; and silica in the tailings can be further extracted or directly used as a cement raw material to make cement.

[0084] Exemplarily, the slag can be added to a sodium hydroxide solution to adjust the pH to 12, stirred and leached for 4 h, and solid-liquid separation is carried out to obtain waste residue and aluminum-rich solution; seeds are added to the aluminum-rich solution, evaporated and crystallized, and calcined at 1000 °C to obtain alumina and discharge the tailings. The tailings and coke (SiO2:C = 1:2) are subjected to carbothermal reduction in an electric arc furnace at 1800 °C to produce crude silicon, realizing high-temperature carbothermal reduction (the reaction formula is: SiO2 + 2C → Si + 2CO↑) to obtain crude silicon; or, the tailings are mixed with limestone and clay in a mass ratio of 6:3:1 and calcined at 1450 °C to generate tricalcium silicate (3CaO·SiO2) to directly produce portland cement.

[0085] In summary, through the red mud resource treatment process provided by the embodiments of the present application, the total amount of red mud will be reduced by more than 80%, and the high-value metal elements contained therein can basically be effectively recycled, thus truly realizing the resource recycling of red mud, and no toxic or harmful substances will be generated during the treatment process, the impact on the environment is minimized, and good economic benefits are obtained.

[0086] Next, the present invention will be further elaborated in detail through embodiments.

[0087] Example 1

[0088] As Figure 1 shown, the red mud resource treatment process of this embodiment is as follows:

[0089] Take 100 tons of red mud (Fe2O3 40%, TiO2 3.5%, Al2O3 25%, SiO2 30%), dry it at a temperature of 200 °C for 2 hours, then calcine it at a temperature of 700 °C for 2 hours, and crush and screen the calcined red mud to a particle size less than or equal to 0.1 mm. After the raw material pulverized coal is crushed into pulverized coal with 200 meshes (fixed carbon ≥ 70%), it is continuously fed into a red mud treatment reactor with an operating pressure of 4.0 MPa together with oxygen and steam respectively. The temperature in the red mud treatment reactor is heated to 1700 °C, the oxygen flux is 0.05 m 3 / kg red mud (oxygen concentration 99.60%), and the steam flux is 0.008 m 3 / kg of red mud. The raw coal powder reacts with oxygen and steam to generate high-concentration H2 and CO reduction gases, and then the red mud is continuously injected. After the red mud enters the red mud reactor, it will immediately undergo a reduction reaction with the high-temperature reduction gas, and the reduction reaction time does not exceed 5 seconds. After the reduction reaction is completed, the molten iron, together with liquid metals such as titanium and nickel, will flow downward out of the reaction zone, and a small amount of solid impurities such as Al2O3 and SiO2 will be carried out together. The solid impurities will float on the surface of the liquid metal. By maintaining the liquid metal leaving the red mud reactor at a high temperature of 1700°C, the solid impurities can be filtered out first, and after cooling, slag is formed, which can be further used to extract alumina or used to manufacture cement; when the temperature of the molten mixed metal is gradually reduced to 1600°C, titanium begins to solidify to form a dendritic skeleton, and the titanium-rich phase is separated by gravity sedimentation or magnetic separation; when the temperature is reduced to 1500°C, iron solidifies to form a dense metal block; when the temperature is reduced to 1400°C, nickel solidifies to form a dense metal block; after the reaction, the synthesis gas first adjusts the carbon-hydrogen ratio through a conversion device, and then undergoes desulfurization and decarbonization through a purification device and is used to synthesize methanol. Through the deep coupling of carbon capture and methanol synthesis technology, the red mud treatment process not only achieves zero CO2 emissions, but also converts waste carbon resources into high-value-added chemicals, forming a circular economy model of "red mud → metal + methanol". Finally, the iron recovery rate is 99%, the titanium recovery rate is 85%, the nickel recovery rate is 95%, the silicon recovery rate is 95%, and the aluminum recovery rate is 85%.

[0090] In this embodiment, the resource recovery rates are: iron ≥ 99%, titanium ≥ 85%, nickel ≥ 95%, aluminum (extracted from slag) ≥ 80%, and silicon (produced from slag) ≥ 90%. The total amount of red mud is reduced by 80% (from the original 100 tons of red mud → 20 tons of harmless tailings).

[0091] Economic benefits (calculated based on treating 100 tons of red mud): 28 tons of molten iron are produced (market price: 2000 yuan / ton) → 56,000 yuan; 2.1 tons of titanium alloy are produced (market price: 20,000 yuan / ton) → 42,000 yuan; 5 tons of methanol are produced (market price: 3000 yuan / ton) → 15,000 yuan; the total income is 113,000 yuan, the cost is 80,000 yuan, and the net profit is 33,000 yuan per 100 tons.

[0092] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application. Those of ordinary skill in the art should understand that although the present application has been described in detail with reference to the foregoing embodiments, they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features. These modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions in the various embodiments of the present application.

Claims

1. A process for the resource utilization of red mud, characterized in that, Including: Crush and screen the dried red mud, and add it to the red mud treatment reactor to carry out a reduction reaction with the reactant to obtain molten mixed metals, slag and reaction gas; among them, due to the difference in metal density, the molten metals are naturally stratified; By controlling the cooling rate, solidify and extract each metal element in the molten mixed metals by using the melting point difference; After the reaction gas is purified, it is used to synthesize methanol; The slag is used to extract alumina or as a raw material for making cement.

2. The method according to claim 1, wherein The reactant includes pulverized coal, oxygen and water vapor; the step of adding the dried red mud to the red mud treatment reactor to carry out a reduction reaction with the reactant includes: The red mud is dried to a moisture content of less than 5%, and crushed and screened to a particle size of less than 0.1 mm; Continuously add the crushed and screened red mud, pulverized coal, oxygen and water vapor to the red mud treatment reactor respectively; control the temperature of the red mud treatment reactor to be 1250°C - 2000°C, and the reduction reaction time to be 3 - 8 seconds.

3. The method according to claim 2, wherein The weight ratio of the pulverized coal to the red mud is 100:10 - 1500.

4. The method according to claim 2, wherein The oxygen dosage is controlled at 0.03 - 0.1 m 3 / kg of red mud.

5. The method according to claim 2, characterized in that, The amount of water vapor used is controlled at 0.005 - 0.02 m 3 / kg of red mud.

6. The method according to any one of claims 1-5, characterized in that, The metal elements in the molten mixed metals include at least one of iron, titanium and nickel.

7. The method according to claim 6, characterized in that, The step of solidifying and extracting each metal element in the molten mixed metals by controlling the cooling rate and using the melting point difference includes: Adopt the gradient cooling method, heat the molten mixed metals to 1668°C - 1700°C, and then when the temperature drops to 1600°C, titanium begins to solidify to form a dendritic skeleton, and the titanium-rich phase is separated by gravity sedimentation or magnetic separation; When the temperature drops to 1500°C, iron solidifies to form a dense metal block; When the temperature drops to 1400°C, nickel solidifies to form a dense metal block.

8. The method according to any one of claims 1-5, characterized in that, The reaction gas after reaction includes at least one of carbon dioxide, carbon monoxide, hydrogen and hydrogen sulfide.

9. The method according to claim 8, wherein After the reaction gas after reaction is purified, it is used to synthesize methanol, including: Pass the reaction gas after reaction through a dust collector for dust removal, adjust the carbon-hydrogen ratio through a conversion device, and then pass it into a purification device for desulfurization and decarbonization treatment to obtain a purified gas; Synthesize methanol from the purified gas under the action of a catalyst.

10. The method according to any one of claims 1-5, characterized in that, The components in the slag include alumina and silica; the slag is used to extract alumina or as a raw material for making cement, including: Further extract alumina from the slag in the way of refining bauxite, and discharge the tailings; Further extract silica from the tailings or directly use it as a cement raw material to make cement.

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