A comprehensive extraction method for associated metals such as aluminum, titanium, gallium and rare earth in coal-bearing strata

Abstract

The present invention provides a comprehensive extraction method for aluminum, titanium, gallium, and rare earth metals co-existing in coal-bearing strata. This method belongs to the field of mineral extraction technology and addresses the problem that there has been little research on the extraction process of titanium, gallium, aluminum, and rare earth metals from coal gangue and fly ash, resulting in the lack of a mature extraction method. The present invention comprises the following steps: S1, preparation of a roasted product; S2, preparation of a dried pre-calcined mixture; S3, preparation of a calcined mixed product; S4, acid leaching; S5, extraction of rare earths; S6, precipitation; S7, extraction of titanium; S8, extraction; S9, extraction of gallium; S10, extraction of aluminum; and S11, waste liquid treatment. The extraction method of the present invention not only reduces the generation of industrial waste, but also transforms waste into valuables, and is environmentally friendly. Compared with traditional extraction processes for single metal elements, the present invention achieves the comprehensive extraction of multiple metals including aluminum, titanium, gallium, and rare earths through a series of carefully designed steps, thereby improving the efficiency of raw material utilization.

Description

Technical Field

[0001] The invention belongs to the technical field of mineral extraction, in particular to a method for comprehensively extracting metals such as aluminum, titanium, gallium and rare earth co-existing in coal-bearing strata. Background Art

[0002] Strategic metal mineral resources play a vital role in national economic development and national defense security. Coal, a special sedimentary organic rock formed under specific geological conditions, can be enriched with strategic metals and form large or super-large metal deposits. With the continuous discovery of strategic coal-measure metal deposits, countries around the world are beginning to attach great importance to these coal-measure strategic metal minerals.

[0003] However, wastes such as coal seam gangue and fly ash generated during coal mine production and utilization have caused serious environmental pollution. Although these wastes contain strategic metal resources such as aluminum, titanium, gallium, and rare earth elements, most of them are of low grade and difficult to handle, resulting in a large amount of waste of precious and usable strategic metal elements.

[0004] Therefore, there is an urgent need to explore a comprehensive utilization method for strategic metal elements in coal gangue and fly ash to transform waste into valuable resources and resolve environmental pollution.

[0005] Currently, aluminum is primarily extracted using alkaline processes to produce alumina, including the Bayer process, sintering, and combined processes. Gallium is primarily extracted from recycled Bayer aluminum smelting fluid, zinc smelting waste, fly ash, and other sources, using extraction and recovery methods. Titanium is primarily utilized by smelting ilmenite concentrate in electric furnaces to produce acid-soluble high-titanium slag, which is then used to produce titanium dioxide using the sulfuric acid process. Rare earth elements are typically extracted using acid leaching, alkaline leaching, and salt leaching.

[0006] However, there is little research on the extraction process of titanium, gallium, aluminum and rare earth metals from coal gangue and fly ash, and a relatively mature extraction method has not yet been formed. Therefore, for the comprehensive development and utilization of strategic metals in coal gangue and fly ash, it is urgent to establish a complete extraction process flow and economical and applicable extraction methods. Summary of the Invention

[0007] The purpose of the present invention is to address the above-mentioned problems in the existing technology and to propose a comprehensive extraction method for the co-existing metals aluminum, titanium, gallium and rare earth in coal-bearing strata.

[0008] The object of the present invention can be achieved by the following technical solution: a comprehensive extraction method of aluminum, titanium, gallium and rare earth metals co-existing in coal-bearing strata, the comprehensive extraction method comprising the following steps:

[0009] S1: preparing a calcined product: mixing coal gangue and fly ash and grinding the mixture to obtain a ground mixture; and calcining the ground mixture to obtain a calcined product, wherein the average particle size of the ground mixture is less than 0.5 mm;

[0010] During the roasting operation, the roasting temperature is greater than 850°C;

[0011] The purpose of roasting is to remove organic matter from coal gangue and fly ash through high-temperature treatment. At the same time, the chemical form of rare earth elements can be changed to exist in the form of ion adsorption, carbonate binding, and silicate binding, making them easier to be extracted in subsequent steps. In addition, the roasting process can also help decompose minerals in coal formations and release more extractable metals.

[0012] Average particle size less than 0.5mm: Controlling the average particle size of the grinding mixture below 0.5mm can increase the specific surface area of ​​the material, thereby improving roasting efficiency. Refining can promote more uniform heat treatment and make roasting more thorough, which helps to improve the subsequent metal extraction efficiency and purity.

[0013] Calcination temperature is greater than 850℃: Coal gangue and fly ash contain a large amount of organic matter and inorganic minerals. At high temperatures above 850℃, organic matter (such as residual carbon and volatile organic compounds in coal) will be completely decomposed or burned, thereby reducing the interference of organic matter on the metal extraction process; in addition, certain inorganic components (such as clay minerals and sulfides) will also undergo phase changes or chemical reactions at this temperature, which is beneficial to changing the occurrence form of the metal and making it easier for subsequent chemical extraction.

[0014] S2: preparing a dry pre-calcined mixture: pulverizing the calcined product to obtain a pulverized calcined product having an average particle size of 250-325 mesh, uniformly mixing the pulverized calcined product with a sintering agent to obtain an initial pre-calcined mixture, adding deionized water to the initial pre-calcined mixture, and uniformly mixing to obtain a hydrous pre-calcined mixture, placing the hydrous pre-calcined mixture in a vacuum drying oven and drying it at 50° C.-70° C. until the quality is stable, thereby obtaining a dry pre-calcined mixture;

[0015] The sintering agent is sodium carbonate;

[0016] In the initial pre-calcined mixture, the calcined product is crushed to a sintering agent in a weight ratio of 1:1-2.5;

[0017] In the aqueous pre-calcined mixture, the weight ratio of the initial mixture to deionized water is 1:0.5-2;

[0018] The sintering agent is sodium carbonate: Chemical activity: The choice of sodium carbonate as a sintering agent is that sodium carbonate reacts with the minerals in fly ash or coal seam gangue at high temperature, destroying the crystal structure of the minerals, allowing the metal elements therein to be released and generating metal-containing soluble compounds. This step is the prerequisite for metal extraction and creates conditions for subsequent acid leaching treatment.

[0019] Economic Benefit: Sodium carbonate is a relatively low-cost, readily available chemical, which makes it economically advantageous for large-scale industrial applications.

[0020] Environmental impact: Compared with other possible sintering agents, the use of sodium carbonate has relatively less negative impact on the environment. By-products produced during the calcination process, such as carbon dioxide, can be captured and reused to a certain extent through modern technology, reducing the impact on the environment.

[0021] 250-325 mesh crushed calcined product: This particle size range can ensure that the material is sufficiently fine, so that it can show higher reactivity in subsequent chemical reactions, and also helps the uniform mixing and reaction of the sintering agent.

[0022] Drying at 50-70°C until the quality is stable: Drying within this temperature range can effectively remove moisture without causing changes in chemical composition or pre-sintering, ensuring the quality and reactivity of the mixture.

[0023] The ratio of the crushed calcined product to the sintering agent is 1:1-2.5: the adjustment of the ratio of the crushed calcined product to the sintering agent is to ensure the full progress of the reaction, while controlling the sintering properties of the calcined mixture to improve the sintering performance of the material and the subsequent chemical reaction effect.

[0024] The addition of deionized water is used to adjust the fluidity and plasticity of the mixture to ensure that the mixture can be better mixed and uniform.

[0025] S3: preparing a calcined mixed product: calcining the dried pre-calcined mixture, and then pulverizing the mixture to obtain a calcined mixed product with an average particle size of 250-325 mesh;

[0026] 250-325 mesh calcined mixed product: increased surface area: smaller particle size can significantly increase the total surface area, thereby increasing the effective area in contact with the acid leaching solution and accelerating the release and extraction process of metal ions;

[0027] Improved reaction rate: Finer particle size helps increase the rate of chemical reactions, making the pickling process more efficient and shortening the required processing time;

[0028] Balance energy consumption and efficiency: In actual operation, excessive crushing will lead to increased energy consumption, while too coarse particle size will reduce reaction efficiency. Therefore, choosing a particle size of 250-325 mesh is to find a balance between energy consumption and reaction efficiency.

[0029] S4 acid leaching treatment: the calcined mixed product is placed in an oxalic acid solution with a concentration of 85%, and the acid leaching reaction is carried out at 200°C. After the acid leaching time is 24-100 hours, an acid leaching product is obtained;

[0030] The acid leaching product is filtered to obtain a leaching filtrate containing aluminum, titanium, and gallium and a residue containing rare earth elements;

[0031] The choice of 85% oxalic acid solution for pickling treatment at 200°C is mainly based on the following considerations:

[0032] 1. Selectivity of oxalic acid: Rare earth elements react with strong acids. As an organic acid, oxalic acid has a strong metal dissolving ability at high concentrations. In particular, it can effectively dissolve aluminum, titanium, and gallium without reacting with rare earth elements, and has a good separation effect, thereby achieving effective separation of metals and rare earth elements.

[0033] 2. Effect of temperature: At a temperature of 200°C, the reactivity of oxalic acid and the metal dissolution rate can be significantly improved. Under high temperature conditions, the ionic strength and reactivity of oxalic acid are enhanced, which helps to accelerate the release process of metal ions and makes aluminum, titanium, and gallium metals more easily dissolved. This temperature is the optimal temperature obtained in experiments and actual operations. It can not only ensure a good metal extraction rate, but also control the evaporation and decomposition of oxalic acid, reducing the loss of oxalic acid.

[0034] 3. Selection of oxalic acid concentration: The oxalic acid concentration of 85% is based on the balance between achieving efficient metal extraction and controlling costs. Higher oxalic acid concentrations are beneficial to improving the dissolution rate of metals, but too high a concentration will increase material costs. Therefore, 85% is regarded as an optimized choice between efficiency and cost.

[0035] S5 extracts rare earths: uniformly adds ammonia water to the residue containing rare earth elements, adjusts the pH value to 2-3, filters after the reaction is completed to obtain rare earth hydroxide solids, and calcines the rare earth hydroxide solids to obtain rare earth oxides;

[0036] After the rare earth oxides and sodium fluoride are evenly mixed, electrolysis is performed at 800-1000°C to obtain rare earth metals and rare earth electrolysis waste liquid.

[0037] In the electrolysis operation, sodium fluoride is used as the electrolyte, graphite is used as the anode, and molybdenum rod or tungsten rod is used as the cathode. The electrolysis voltage is 5V:

[0038] The reason for adding ammonia water is that a weak base is used to react with rare earth elements to form rare earth hydroxides. Ammonia water will not bring other ionic impurities. Ammonia water is volatile and will be completely removed in the subsequent calcination process, which is beneficial to the enrichment and purification of rare earths.

[0039] Electrolysis is performed at 800°C-1000°C: The temperature selection for the electrolysis operation is based on the chemical properties of the rare earth elements and the physical properties of sodium fluoride. Within the temperature range of 800°C to 1000°C, sodium fluoride acts as an electrolyte, forming a good ionic conductor in the electrolytic cell, thereby promoting the effective transfer of current. In addition, this temperature range helps the mixture of rare earth oxides and sodium fluoride maintain a certain fluidity during the electrolysis process, allowing rare earth metals to be smoothly precipitated at the cathode. High-temperature electrolysis is one of the key conditions for achieving efficient extraction and purification of rare earth elements, as it ensures the progress of the electrolysis reaction and the smooth deposition of rare earth metals.

[0040] The choice of graphite as the anode is based on its good electrical conductivity and stability at high temperatures. During the electrolysis process, graphite can withstand extreme environments without being corroded or damaged, which is very important in metal extraction.

[0041] Sodium fluoride is chosen as the electrolyte because it can provide the necessary ions to promote the flow of current during the electrolysis process. It can form a stable electrolyte environment in the electrolytic cell, which contributes to the successful electrolytic extraction of rare earth metals.

[0042] The choice of molybdenum rod or tungsten rod as cathode is based on their excellent mechanical strength and stability at high temperature. These materials can maintain stable physical and chemical properties during high-temperature electrolysis, which is conducive to metal extraction.

[0043] The electrolysis voltage is set at 5V based on the optimization of the power conversion efficiency and metal extraction efficiency during the electrolysis process. Too high a voltage will increase energy consumption. The electrolysis voltage of 5V is an optimized choice that takes into account energy efficiency and cost while ensuring effective metal extraction.

[0044] S6 precipitation: titrating the sodium hydroxide solution into the leaching filtrate containing aluminum, titanium, and gallium by titration, adjusting the pH value to 12.8, and filtering after the reaction to obtain a titanium hydroxide precipitate and a separation filtrate rich in aluminum and gallium;

[0045] The reason for adding sodium hydroxide solution until the pH reaches 12.8 is that in a strong alkaline environment, titanium can precipitate from the solution in the form of titanium hydroxide, while aluminum and gallium remain in the solution under this pH condition, achieving effective separation between the metals through simple and practical chemical regulation.

[0046] S7 titanium extraction: calcining the titanium hydroxide precipitate to obtain titanium oxide powder;

[0047] Titanium oxide powder is pressed into shape and sintered to prepare a cathode; graphite is selected as the anode; calcium chloride is used as the electrolyte; a titanium or graphite crucible is used as the container; and electrolysis is performed at 800°C-1000°C to obtain titanium metal and titanium electrolysis waste liquid;

[0048] Using titanium oxide as cathode: Titanium oxide is used as cathode because during the electrolysis process, titanium oxide can be directly reduced to metallic titanium through electrolytic reduction. In the electrolysis reaction, titanium ions obtain electrons and are reduced to titanium metal and deposited at the cathode. This process effectively extracts metallic titanium directly from the oxide.

[0049] Graphite is chosen as the anode due to its good electrical conductivity and chemical stability. At high temperatures, graphite does not easily react with the electrolyte or the generated oxygen, which ensures the stability of the electrolysis process.

[0050] Calcium chloride, as an electrolyte, provides good ion conductivity at high temperatures. Calcium chloride can dissolve titanium oxide and act as a conductive medium during the electrolysis process, which helps the reduction of titanium and the progress of the electrolysis process.

[0051] Titanium or graphite crucibles are used because they exhibit good chemical stability and do not react with other substances during high-temperature electrolysis. Titanium crucibles can prevent any potential metal contamination, while graphite crucibles are selected for their excellent temperature and corrosion resistance.

[0052] Electrolysis is performed at 800-1000°C: this temperature range ensures good conductivity of the electrolyte and proper reaction kinetics of the reactants. Within this temperature range, calcium chloride remains molten, promoting ion transfer and effective reduction of titanium. In addition, this temperature range helps reduce evaporation losses of materials while ensuring the energy efficiency of the reaction.

[0053] S8 extraction: adding an alkaline extractant to the separation filtrate rich in aluminum and gallium, and performing a three-stage countercurrent extraction operation at room temperature to obtain a gallium-rich extract phase and an aluminum-rich raffinate phase after separation;

[0054] The alkaline extractant is 7-alkyl-8-hydroxyline, which is more suitable for the extraction environment and subsequent alkaline leaching operation.

[0055] The three-stage countercurrent extraction operation can effectively utilize the extractant and improve the extraction efficiency by performing extraction in stages. In each stage, the extractant and the metal-containing solution flow in different directions. This countercurrent design allows the extractant to be reused repeatedly, increasing the chance of contact with the target metal ions, thereby improving the extraction efficiency and purity. In addition, this method is also beneficial to reduce the amount of extractant used and the treatment cost of the treated waste liquid.

[0056] S9: extracting gallium: distilling the gallium-rich extract phase to remove 7-alkyl-8-hydroxy phenoline in the gallium-rich extract phase to obtain a gallium-containing product;

[0057] The gallium-containing product is placed in a sodium hydroxide solution for alkaline leaching to obtain a sodium gallate-sodium hydroxide solution.

[0058] Under a 40°C environment, platinum is used as the cathode and anode, sodium gallate-sodium hydroxide solution is used as the electrolyte, and an electrode refining method is used to perform electrolysis to obtain gallium metal and gallium electrolysis waste liquid.

[0059] In the alkali leaching process, the concentration of sodium hydroxide solution is 200g / ml, and according to the solid-liquid ratio, the gallium-containing product: sodium hydroxide solution is 1g: 20-40ml; the alkali leaching process time is 2-6 hours;

[0060] Electrolysis is performed using electrode refining at 40°C: Electrode refining is an effective method for purifying metals through electrolysis. It can reduce metals from their compounds and can be carried out at lower temperatures, making it more environmentally friendly and energy-efficient than traditional high-temperature smelting processes. For relatively active metals such as gallium, the electrode refining method can provide a mild and precisely controlled environment to obtain high-purity metallic gallium. 40°C is a relatively mild temperature that can effectively promote the electrolysis reaction while avoiding unnecessary side reactions or material damage that may be caused by excessively high temperatures. In addition, this temperature is conducive to maintaining the stability of the solution and the effective extraction of gallium.

[0061] Platinum is a very stable metal with good chemical stability and electrical conductivity. Using platinum as an electrode can ensure the smooth progress of the electrolysis process, while preventing the electrode material from decomposing into the solution and maintaining the high purity of the gallium extraction process.

[0062] Sodium hydroxide concentration: A concentration of 200 g / ml was chosen to ensure that there was sufficient sodium hydroxide in the solution to react with the gallium-containing product, thereby effectively converting the gallium into dissolved sodium gallate. This concentration was high enough to increase the reaction rate and gallium dissolution efficiency, but not so high as to cause an increase in solution viscosity or unwanted side reactions.

[0063] S10: Aluminum extraction: titration of ammonia into the aluminum-rich raffinate phase is performed, and the pH value is adjusted to 5. After the reaction is completed, filtration is performed to obtain an aluminum hydroxide product;

[0064] The aluminum hydroxide product is calcined to obtain an aluminum oxide product;

[0065] The aluminum oxide product is pressed into shape to prepare a cathode, and a graphite rod is used as an anode. Electrolysis is performed in an environment of 550°C using a molten salt electrolyte to obtain metallic aluminum and aluminum electrolysis waste liquid;

[0066] The molten salt electrolyte is a mixture of calcium chloride and sodium chloride;

[0067] The reason for titrating ammonia into the aluminum-rich raffinate phase using titration and adjusting the pH value to 5 is: the purpose of using the titration method is to accurately control the pH of the reaction environment, thereby promoting the separation of aluminum in the form of precipitation; aluminum ions exist as metaaluminate in strong bases, and the use of weak bases can completely precipitate aluminum ions and avoid incomplete precipitation. The choice of adjusting the pH value to 5 is based on the chemical properties of aluminum and precipitation conditions. At a pH value of 5, aluminum ions are precipitated in the form of aluminum hydroxide. This pH value is the optimal condition for the beginning of aluminum hydroxide precipitation and can effectively separate aluminum.

[0068] In an environment of 550°C, a mixture of calcium chloride and sodium chloride is selected as the molten salt electrolyte: the mixture of calcium chloride and sodium chloride has a low melting point, good electrical conductivity and relatively stable chemical properties. The use of this mixture can be used for electrolysis at a lower operating temperature, reducing energy consumption while ensuring the efficiency and stability of the electrolysis process. The mixture of calcium chloride and sodium chloride can lower the melting point of the electrolyte and improve the electrolysis efficiency. The temperature selection of 550°C is based on the needs of the molten salt electrolysis process. At this temperature, the electrolyte formed by calcium chloride and sodium chloride can maintain a good molten state, thereby effectively conducting electricity and promoting the reduction reaction of aluminum oxide.

[0069] S11 waste liquid treatment: mixing the filtered waste liquid in step S10 with the rare earth electrolysis waste liquid in step S5, the titanium electrolysis waste liquid in step S7, the gallium electrolysis waste liquid in step S9, and the aluminum electrolysis waste liquid in step S10 to obtain a mixed waste liquid, introducing carbon dioxide into the mixed waste liquid for acidification, and then filtering the mixed waste liquid to obtain calcium carbonate and a gallium-containing solution;

[0070] Calcium carbonate is added to dilute hydrochloric acid to react and calcium chloride is obtained;

[0071] After the gallium-containing solution is acidified by introducing carbon dioxide, it is filtered to obtain a gallium hydroxide and sodium carbonate solution;

[0072] The sodium carbonate solution is evaporated to dryness to obtain sodium carbonate crystals.

[0073] In the above-mentioned comprehensive extraction method of co-existing metals aluminum, titanium, gallium and rare earth from coal-bearing strata, in step S3, during the calcination operation of the dried pre-calcined mixture, the calcination temperature is 950°C-1100°C and the calcination time is 1-2 hours.

[0074] Within the temperature range of 950℃-1100℃, the inorganic components in the roasted product can be effectively promoted to react with the sintering agent sodium carbonate to produce a form that is easy to extract by acid leaching. This temperature range ensures the complete decomposition of organic matter in the mixture, and also enables some refractory mineral phases to be converted into more active phases, facilitating subsequent metal extraction. Too low a temperature is not enough to promote the effective progress of these chemical reactions, while too high a temperature will lead to unnecessary energy consumption or excessive sintering of the material, affecting subsequent processing.

[0075] In the above-mentioned comprehensive extraction method of co-existing metals aluminum, titanium, gallium and rare earth from coal-bearing strata, in step S5, during the calcination operation of the rare earth hydroxide solid, the calcination temperature is 1000-1100° C. and the calcination time is 1-2 hours.

[0076] During the extraction process of rare earth elements, rare earth hydroxide solids need to be calcined to convert into more stable rare earth oxides. At a temperature of 1000-1100°C, rare earth hydroxides can be completely decomposed into oxides. This temperature range is based on the optimal calcination conditions for the transformation of rare earth hydroxides into rare earth oxides, ensuring the completeness of the reaction and the purity of the product.

[0077] In the above-mentioned comprehensive extraction method of co-existing metals aluminum, titanium, gallium, and rare earth from coal-bearing strata, in step S7, during the calcination of the titanium hydroxide precipitate, the calcination temperature is 1000-1150° C. and the calcination time is 1-2 hours;

[0078] In the electrolysis operation for extracting titanium metal, the electrolysis voltage is 2.8-3.2V.

[0079] Calcination temperature is 1000-1150℃: This temperature range can ensure the complete dehydration and decomposition of titanium hydroxide, converting it into high-valent oxides of titanium. This high-valent oxide form is crucial for the subsequent electrolytic extraction process because it ensures that titanium can be effectively reduced during the electrolysis process. This temperature range is selected to maximize the purity and stability of the oxide while avoiding unnecessary energy consumption or excessive sintering of the material due to excessively high temperatures.

[0080] The electrolysis voltage of 2.8-3.2V used in the electrolytic extraction of titanium metal is determined based on the electrochemical properties of titanium in calcium chloride electrolyte. This voltage range is sufficient to reduce titanium oxide to titanium metal at the cathode while avoiding the waste of electrical energy caused by excessively high voltage. The electrolysis process of titanium involves relatively complex electron transfer and chemical reactions. A suitable electrolysis voltage can effectively promote the reduction of titanium oxide and maintain high reduction efficiency and product purity. Too low an electrolysis voltage is insufficient to drive the reaction.

[0081] In the above-mentioned comprehensive extraction method of co-existing metals aluminum, titanium, gallium, and rare earth from coal-bearing strata, in step S9, during the distillation operation of the gallium-rich extract phase, the distillation temperature is 422°C;

[0082] In the electrolysis operation for extracting gallium metal, the electrolysis current is 200mA / L and the electrolysis voltage is 4V.

[0083] The reason for choosing a distillation temperature of 422°C is to ensure that the target product is completely evaporated and collected during the distillation process. Since the boiling point of the target product is 421.22°C, choosing a slightly higher distillation temperature can ensure that the product can be effectively separated from the mixture without wasting energy.

[0084] During the electrolytic extraction of gallium metal, an electrolysis current of 200mA / L and an electrolysis voltage of 4V are set to ensure high efficiency and high purity of the electrolysis process. This current density and voltage are selected based on the electrochemical properties of gallium in the electrolyte, ensuring that gallium metal can be effectively reduced from the sodium gallate-sodium hydroxide solution during the electrolysis process. The relatively mild electrolysis current of 200mA / L effectively controls the speed and heat generation of the electrolysis process, avoiding excessive electrolysis speeds that could degrade the quality of the gallium metal. The electrolysis voltage of 4V is determined based on the electrode potential of gallium and the desired overpotential. This voltage ensures efficient gallium reduction while limiting unwanted electrochemical side reactions, such as the undesirable deposition of other elements in the solution or excessive hydrogen production.

[0085] In the above-mentioned comprehensive extraction method of co-existing metals aluminum, titanium, gallium and rare earth from coal-bearing strata, in step S10, the aluminum hydroxide product is calcined at a temperature of 1000-1100° C. for 1-2 hours.

[0086] In the electrolysis operation for extracting metallic aluminum, the electrolysis voltage is 3.2V.

[0087] The temperature range of 1000-1100℃ is selected in the process of calcining aluminum hydroxide to produce alumina, mainly to ensure the complete decomposition and dehydration of aluminum hydroxide to form high-purity alumina. The temperature in this process needs to be high enough to promote the transformation of hydroxide to oxide while avoiding excessive sintering.

[0088] The electrolysis voltage of 3.2V used in the electrolysis process for extracting metallic aluminum is determined based on the electrochemical behavior of aluminum in the molten salt electrolyte (a mixture of sodium chloride and calcium chloride) used. This voltage is sufficient to cause the electrolytic reduction reaction of aluminum to occur in the electrolytic cell, that is, the reduction of aluminum oxide at the cathode to produce metallic aluminum. This electrolysis voltage is set to maximize the production efficiency and purity of aluminum while avoiding unnecessary side reactions, such as excessive consumption of electrolyte or excessive generation of oxygen at the anode. In addition, maintaining the electrolysis voltage at 3.2V can maintain the stability of the electrolysis process, optimize energy consumption, and ensure the effective use of energy in the electrolysis process. Too low an electrolysis voltage may lead to a decrease in the reduction efficiency of aluminum, while too high an electrolysis voltage may increase energy consumption and may cause overheating or structural damage to the electrolytic cell.

[0089] Compared with the existing technology, the comprehensive extraction method of co-existing metals aluminum, titanium, gallium and rare earth in coal-bearing strata has the following beneficial effects:

[0090] 1. Comprehensive extraction and efficient resource utilization: By reusing coal gangue and fly ash, this method not only reduces the generation of industrial waste but also turns waste into treasure, which is environmentally friendly. Compared with traditional extraction processes for single metal elements, this invention achieves the comprehensive extraction of multiple metals such as aluminum, titanium, gallium and rare earth elements through a series of carefully designed steps, improves the utilization efficiency of raw materials, and reduces the cost and time required to extract these elements separately.

[0091] 2. Efficient and simple operation process: By directly mixing fly ash and gangue and adopting the calcination-acid leaching separation and purification method, the present invention eliminates the complicated sorting steps, simplifies the extraction process, and saves energy and labor costs.

[0092] 3. Improve metal extraction rate and purity: This method not only effectively improves the extraction rate of the target metal but also significantly improves the purity of the metal by optimizing the conditions of key steps such as roasting, acid leaching, and electrolysis (such as temperature, time, electrolysis voltage, etc.), meeting the needs of industry and scientific research for high-purity metal materials.

[0093] 4. Environmental friendliness and waste liquid resource utilization: In terms of waste liquid treatment, the present invention effectively reduces the emission of hazardous waste through the waste liquid recovery step. In particular, the introduction of carbon dioxide to recover valuable components from the waste liquid reduces the burden on the environment and realizes the resource utilization of useful components in the waste liquid.

[0094] 5. Reduce energy consumption and costs: While improving material utilization, the method of the present invention accurately controls key process parameters, effectively reduces energy consumption, simplifies the extraction process and uses common reagents, further reduces production costs, and has significant economic benefits.

[0095] In summary, the present invention provides an advanced method for the comprehensive extraction of multiple valuable metals from coal-bearing strata in an efficient, economical and environmentally friendly manner, thereby achieving efficient utilization of resources and sustainable development of the environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0096] Figure 1 It is a comprehensive extraction flow chart of the present invention.

[0097] Figure 2 It is a waste liquid treatment flow chart of the present invention. DETAILED DESCRIPTION

[0098] The following are specific embodiments of the present invention and the accompanying drawings to further describe the technical solutions of the present invention, but the present invention is not limited to these embodiments.

[0099] like Figure 1 As shown, a comprehensive extraction method for metals co-existing in coal-bearing strata, aluminum, titanium, gallium, and rare earth, comprises the following steps:

[0100] S1: preparing a calcined product: mixing coal gangue and fly ash and grinding the mixture to obtain a ground mixture; and calcining the ground mixture to obtain a calcined product, wherein the average particle size of the ground mixture is less than 0.5 mm;

[0101] During the roasting operation, the roasting temperature is greater than 850°C;

[0102] S2: preparing a dry pre-calcined mixture: pulverizing the calcined product to obtain a pulverized calcined product having an average particle size of 250-325 mesh, uniformly mixing the pulverized calcined product with a sintering agent to obtain an initial pre-calcined mixture, adding deionized water to the initial pre-calcined mixture, and uniformly mixing to obtain a hydrous pre-calcined mixture, placing the hydrous pre-calcined mixture in a vacuum drying oven and drying it at 50° C.-70° C. until the quality is stable, thereby obtaining a dry pre-calcined mixture;

[0103] The sintering agent is sodium carbonate;

[0104] In the initial pre-calcined mixture, the calcined product is crushed to a sintering agent in a weight ratio of 1:1-2.5;

[0105] In the aqueous pre-calcined mixture, the weight ratio of the initial mixture to deionized water is 1:0.5-2;

[0106] S3 prepares a calcined mixed product: the dried pre-calcined mixture is calcined, and after the calcination operation is completed, a calcined mixed product with an average particle size of 250-325 mesh is obtained; during the calcination operation, the calcination temperature is 1000° C. and the calcination time is 1-2 hours.

[0107] S4 acid leaching treatment: the calcined mixed product is placed in an oxalic acid solution with a concentration of 85%, and the acid leaching reaction is carried out at 200°C. After the acid leaching time is 24-100 hours, an acid leaching product is obtained;

[0108] The acid leaching product is filtered to obtain a leaching filtrate containing aluminum, titanium, and gallium and a residue containing rare earth elements;

[0109] S5 extracts rare earths: uniformly adds ammonia water to the residue containing rare earth elements, adjusts the pH value to 2-3, filters after the reaction is completed to obtain rare earth hydroxide solids, and calcines the rare earth hydroxide solids to obtain rare earth oxides;

[0110] In the calcination operation, the calcination temperature is 1050°C and the calcination time is 1-2 hours;

[0111] After the rare earth oxides and sodium fluoride are evenly mixed, electrolysis is performed at 800-1000°C to obtain rare earth metals and rare earth electrolysis waste liquid.

[0112] In the electrolysis operation, sodium fluoride is used as the electrolyte, graphite is used as the anode, and molybdenum rod or tungsten rod is used as the cathode. The electrolysis voltage is 5V:

[0113] S6 precipitation: titrating the sodium hydroxide solution into the leaching filtrate containing aluminum, titanium, and gallium by titration, adjusting the pH value to 12.8, and filtering after the reaction to obtain a titanium hydroxide precipitate and a separation filtrate rich in aluminum and gallium;

[0114] S7 titanium extraction: calcining the titanium hydroxide precipitate to obtain titanium oxide powder; in the calcination process, the calcination temperature is 1050° C. and the calcination time is 1-2 hours;

[0115] Titanium oxide powder is pressed into shape and sintered to prepare a cathode; graphite is selected as the anode; calcium chloride is used as the electrolyte; a titanium or graphite crucible is used as the container; electrolysis is carried out at an environment of 800°C-1000°C to obtain titanium metal and titanium electrolysis waste liquid; wherein the electrolysis voltage is 2.8-3.2V.

[0116] S8 extraction: adding an alkaline extractant to the separation filtrate rich in aluminum and gallium, and performing a three-stage countercurrent extraction operation at room temperature to obtain a gallium-rich extract phase and an aluminum-rich raffinate phase after separation;

[0117] The alkaline extractant is 7-alkyl-8-hydroxyline;

[0118] S9 Gallium Extraction: Distilling the gallium-rich extract phase to remove 7-alkyl-8-hydroxyline from the gallium-rich extract phase to obtain a gallium-containing product; during the distillation process, the distillation temperature is 422° C.;

[0119] The gallium-containing product is placed in a sodium hydroxide solution for alkaline leaching to obtain a sodium gallate-sodium hydroxide solution.

[0120] Under a 40°C environment, platinum was used as the cathode and anode, and sodium gallate-sodium hydroxide solution was used as the electrolyte. Electrolysis was performed using an electrode refining method to obtain gallium metal and gallium electrolysis waste liquid. During the electrolysis operation, the electrolysis current was 200mA / L and the electrolysis voltage was 4V.

[0121] In the alkali leaching process, the concentration of sodium hydroxide solution is 200g / ml, and according to the solid-liquid ratio, the gallium-containing product: sodium hydroxide solution is 1g: 20-40ml; the alkali leaching process time is 2-6 hours;

[0122] S10: Aluminum extraction: titration of ammonia into the aluminum-rich raffinate phase is performed, and the pH value is adjusted to 5. After the reaction is completed, filtration is performed to obtain an aluminum hydroxide product;

[0123] The aluminum hydroxide product is calcined to obtain an aluminum oxide product; during the calcination process, the calcination temperature is 1000° C. and the calcination time is 1-2 hours;

[0124] The alumina product is pressed and formed into a cathode, and a graphite rod is used as an anode. Electrolysis is carried out in an environment of 550°C using a molten salt electrolyte to obtain metallic aluminum and aluminum electrolysis waste liquid. During the electrolysis operation, the electrolysis voltage is 3.2V.

[0125] The molten salt electrolyte is a mixture of calcium chloride and sodium chloride;

[0126] like Figure 2 As shown, S11 waste liquid treatment: the filtered waste liquid in step S10 is mixed with the rare earth electrolysis waste liquid in step S5, the titanium electrolysis waste liquid in step S7, the gallium electrolysis waste liquid in step S9, and the aluminum electrolysis waste liquid in step S10 to obtain a mixed waste liquid, carbon dioxide is introduced into the mixed waste liquid for acidification, and then a filtering operation is performed to obtain calcium carbonate and a gallium-containing solution;

[0127] Calcium carbonate is added to dilute hydrochloric acid to react and calcium chloride is obtained;

[0128] After the gallium-containing solution is acidified by introducing carbon dioxide, it is filtered to obtain a gallium hydroxide and sodium carbonate solution;

[0129] The sodium carbonate solution is evaporated to dryness to obtain sodium carbonate crystals.

[0130] The specific embodiments described herein are merely illustrative of the spirit of the invention. Those skilled in the art to which the invention pertains may make various modifications or additions to the described specific embodiments or substitute them in a similar manner, but will not deviate from the spirit of the invention or exceed the defined scope. Although the invention has been described and described in detail in the accompanying drawings and the foregoing description, such illustrations and descriptions are considered to be illustrative or exemplary rather than restrictive. It should be understood that within the scope of the following claims, changes and modifications may be made by those of ordinary skill in the art. Specifically, the present invention encompasses additional embodiments having any combination of features from the different embodiments described above. With respect to the use of the expression "generally" or "substantially", this patent application should be understood to disclose features and values ​​that also fully satisfy these features and values, i.e., without the aforementioned characterization as "generally" or "substantially".

[0131] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood in a broad sense. For example, they may refer to fixed, detachable, or integral connections; mechanical or electrical connections; direct or indirect connections through an intermediate medium; and internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on the specific circumstances.

Claims

1. A comprehensive extraction method for the co-existing metals aluminum, titanium, gallium and rare earth in coal-bearing strata, characterized in that: The comprehensive extraction method comprises the following steps: S1: preparing a calcined product: mixing coal gangue and fly ash and grinding the mixture to obtain a ground mixture; and calcining the ground mixture to obtain a calcined product, wherein the average particle size of the ground mixture is less than 0.5 mm; During the roasting operation, the roasting temperature is greater than 850°C; S2: preparing a dry pre-calcined mixture: pulverizing the calcined product to obtain a pulverized calcined product having an average particle size of 250-325 mesh, uniformly mixing the pulverized calcined product with a sintering agent to obtain an initial pre-calcined mixture, adding deionized water to the initial pre-calcined mixture, and uniformly mixing to obtain a hydrous pre-calcined mixture, placing the hydrous pre-calcined mixture in a vacuum drying oven and drying it at 50° C.-70° C. until the quality is stable, thereby obtaining a dry pre-calcined mixture; The sintering agent is sodium carbonate; In the initial pre-calcined mixture, the calcined product is crushed to a sintering agent in a weight ratio of 1:1-2.5; In the aqueous pre-calcined mixture, the weight ratio of the initial mixture to deionized water is 1:0.5-2; S3: preparing a calcined mixed product: calcining the dried pre-calcined mixture, and then pulverizing the mixture to obtain a calcined mixed product with an average particle size of 250-325 mesh; In step S3, the dried pre-calcined mixture is calcined at a temperature of 950° C. to 1100° C. for 1 to 2 hours. S4 acid leaching treatment: the calcined mixed product is placed in an oxalic acid solution with a concentration of 85%, and the acid leaching reaction is carried out at 200°C. After the acid leaching time is 24-100 hours, an acid leaching product is obtained; The acid leaching product is filtered to obtain a leaching filtrate containing aluminum, titanium, and gallium and a residue containing rare earth elements; S5 extracts rare earths: uniformly adds ammonia water to the residue containing rare earth elements, adjusts the pH value to 2-3, filters after the reaction is completed to obtain rare earth hydroxide solids, and calcines the rare earth hydroxide solids to obtain rare earth oxides; After the rare earth oxide and sodium fluoride are uniformly mixed, electrolysis is performed at 800°C-1000°C to obtain rare earth metals and rare earth electrolysis waste liquid; In the electrolysis operation, sodium fluoride is used as the electrolyte, graphite is used as the anode, and molybdenum rod or tungsten rod is used as the cathode. The electrolysis voltage is 5V: In step S5, during the calcination of the rare earth hydroxide solid, the calcination temperature is 1000-1100° C. and the calcination time is 1-2 hours; S6 precipitation: titrating the sodium hydroxide solution into the leaching filtrate containing aluminum, titanium, and gallium by titration, adjusting the pH value to 12.8, and filtering after the reaction to obtain a titanium hydroxide precipitate and a separation filtrate rich in aluminum and gallium; S7 titanium extraction: calcining the titanium hydroxide precipitate to obtain titanium oxide powder; Titanium oxide powder is pressed into shape and sintered to prepare a cathode; graphite is selected as the anode; calcium chloride is used as the electrolyte; a titanium or graphite crucible is used as the container; and electrolysis is performed at 800°C-1000°C to obtain titanium metal and titanium electrolysis waste liquid; S8 extraction: adding an alkaline extractant to the separation filtrate rich in aluminum and gallium, and performing a three-stage countercurrent extraction operation at room temperature to obtain a gallium-rich extract phase and an aluminum-rich raffinate phase after separation; The alkaline extractant is 7-alkyl-8-hydroxyline; S9: extracting gallium: distilling the gallium-rich extract phase to remove 7-alkyl-8-hydroxy phenoline in the gallium-rich extract phase to obtain a gallium-containing product; The gallium-containing product is placed in a sodium hydroxide solution for alkaline leaching to obtain a sodium gallate-sodium hydroxide solution. Under a 40°C environment, platinum is used as the cathode and anode, sodium gallate-sodium hydroxide solution is used as the electrolyte, and an electrode refining method is used to perform electrolysis to obtain gallium metal and gallium electrolysis waste liquid. In the alkali leaching process, the concentration of sodium hydroxide solution is 200g / ml, and according to the solid-liquid ratio, the gallium-containing product: sodium hydroxide solution is 1g: 20-40ml; the alkali leaching process time is 2-6 hours; S10: Aluminum extraction: titration of ammonia into the aluminum-rich raffinate phase is performed, and the pH value is adjusted to 5. After the reaction is completed, filtration is performed to obtain aluminum hydroxide product and filtered waste liquid; The aluminum hydroxide product is calcined to obtain an aluminum oxide product; The aluminum oxide product is pressed into shape to prepare a cathode, and a graphite rod is used as an anode. Electrolysis is performed in an environment of 550°C using a molten salt electrolyte to obtain metallic aluminum and aluminum electrolysis waste liquid; The molten salt electrolyte is a mixture of calcium chloride and sodium chloride; S11 waste liquid treatment: mixing the filtered waste liquid in step S10 with the rare earth electrolysis waste liquid in step S5, the titanium electrolysis waste liquid in step S7, the gallium electrolysis waste liquid in step S9, and the aluminum electrolysis waste liquid in step S10 to obtain a mixed waste liquid, introducing carbon dioxide into the mixed waste liquid for acidification, and then filtering the mixed waste liquid to obtain calcium carbonate and a gallium-containing solution; Calcium carbonate is added to dilute hydrochloric acid to react and calcium chloride is obtained; After the gallium-containing solution is acidified by introducing carbon dioxide, it is filtered to obtain a gallium hydroxide and sodium carbonate solution; The sodium carbonate solution is evaporated to dryness to obtain sodium carbonate crystals.

2. The method for comprehensive extraction of co-existing metals such as aluminum, titanium, gallium and rare earth from coal-bearing strata according to claim 1, characterized in that: In step S7, during the calcination of the titanium hydroxide precipitate, the calcination temperature is 1000-1150° C. and the calcination time is 1-2 hours; In the electrolysis operation for extracting titanium metal, the electrolysis voltage is 2.8-3.2V.

3. The method for comprehensive extraction of co-existing metals such as aluminum, titanium, gallium and rare earth from coal-bearing strata according to claim 1, characterized in that: In step S9, during the distillation operation of the gallium-rich extract phase, the distillation temperature is 422° C.; In the electrolysis operation for extracting gallium metal, the electrolysis current is 200mA / L and the electrolysis voltage is 4V.

4. The method for comprehensive extraction of co-existing metals aluminum, titanium, gallium and rare earth from coal-bearing strata according to claim 1, characterized in that: In step S10, the aluminum hydroxide product is calcined at a temperature of 1000-1100° C. for 1-2 hours. In the electrolysis operation for extracting metallic aluminum, the electrolysis voltage is 3.2V.

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