Method for extracting gallium metal element mineral from coal

Abstract

This invention discloses a method for extracting gallium from coal using rare metal extraction technology. Using dry fly ash with a gallium content of 50-80 μg / g as raw material, the method sequentially involves raw material pretreatment, roasting activation, acid leaching, leachate pre-purification, solvent extraction and back-extraction, deep refining, and electrolytic refining to achieve efficient gallium extraction and purification. The core of this method is the destruction of the aluminosilicate lattice through high-temperature roasting activation with soda ash, converting gallium into a soluble state. Impurities are then removed through three stages of deep purification, combined with an alkaline constant-current electrolytic process to prevent impurity co-deposition. This method realizes the resource utilization of low-grade fly ash solid waste, significantly improves the gallium leaching rate and resource recovery rate, and ultimately obtains industrial-grade gallium with high purity.

Description

Technical Field

[0001] This invention relates to the field of rare metal extraction technology, specifically a method for extracting gallium metal from coal. Background Technology

[0002] Gallium, as an important rare metal, is widely used in high-end industrial fields such as semiconductors and electronic devices, and market demand is growing. However, gallium lacks independent deposits and mainly exists in aluminosilicate minerals in an isomorphous form. It is often dispersed and associated with materials such as fly ash, bauxite, and zinc smelting slag, making extraction difficult.

[0003] Existing gallium extraction processes from low-grade fly ash commonly suffer from low gallium leaching rates. Traditional processes often employ direct acid leaching or leaching followed by simple roasting, which fails to effectively disrupt the stable crystal structure of aluminosilicates. This results in gallium trapped within the crystal lattice not being fully converted into a soluble state, leading to low gallium leaching rates and insufficient resource recovery. Furthermore, some processes use inappropriate activators and roasting parameters, further reducing gallium leaching efficiency and increasing extraction costs. Traditional purification processes often employ single purification methods, which cannot completely remove impurities such as iron, aluminum, and trace heavy metals from the leaching solution. During electrolysis, impurity co-deposition easily occurs, resulting in low final gallium purity that fails to meet industrial-grade standards. Additionally, some processes use acidic electrolysis systems, further exacerbating the impurity co-deposition problem and severely impacting product quality stability, failing to meet the requirements of high-end fields such as semiconductors.

[0004] Therefore, we propose a method for extracting gallium metal from coal. Summary of the Invention

[0005] The purpose of this invention is to provide a method for extracting gallium metal from coal, so as to solve the problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a method for extracting gallium metal from coal, comprising the following steps: S1: Select dry fly ash with a gallium content of 50-80μg / g as raw material, and remove large particles of fly ash by screening with a vibrating screen and grinding with a ball mill for later use. S2: Grind dry fly ash and soda ash in a mass ratio of 1:0.4 to 0.7 into a mixer and stir evenly. After stirring, send it into a rotary kiln for heating to 820℃-900℃ and keep it constant for calcination for 1-1.5 hours. Then let it cool naturally to room temperature. S3: Disperse the calcined fly ash and add it to a 3-5 mol / L dilute hydrochloric acid leaching solution. The ratio of dilute hydrochloric acid to fly ash is 6:1-10:1, the leaching temperature is 85-95℃, and the leaching is carried out by stirring for 3-4 hours. This allows the gallium ions in the activated fly ash to react with the acid to generate Ga³⁺ and dissolve into the leaching solution. After leaching, the solution is separated by pressure filtration using a plate and frame filter press to obtain gallium-containing leaching solution and silicon-aluminum filter residue. S4: Add an oxidant to the gallium-containing acid leaching solution and stir thoroughly to oxidize all Fe²⁺ in the leaching solution to Fe³⁺. Then, slowly adjust the pH of the leaching solution to 3.0-3.8 with dilute alkali solution. Let it stand at 60℃ for 30 minutes to allow Fe³⁺ to hydrolyze and form ferric hydroxide precipitate. Finally, filter and separate the precipitate impurities using a vacuum filter to obtain a low-iron gallium-containing refined raw solution. S5: An organic phase is formed by mixing extractant and kerosene at a volume ratio of 15%–25%:75%–85%. The low-iron gallium-containing refined raw solution obtained by pre-purification of the leachate is used as the aqueous phase and added to the extraction tank at a ratio of aqueous phase:organic phase = 1:1–2:1 for extraction. After extraction, the mixture is allowed to stand and separate into layers to obtain gallium-loaded organic phase and raffinate. 0.8 mol / L dilute hydrochloric acid is added to the gallium-loaded organic phase for acid washing to remove impurities. Then, 6 mol / L hydrochloric acid is used as the back-extraction solution and back-extraction is performed at a ratio of organic phase:back-extraction solution = 3:1 to obtain a high-concentration gallium chloride enrichment solution. S6: The high-concentration gallium chloride enriched solution obtained by solvent extraction and back-extraction is adjusted to an alkaline state of pH 8.5-9.0 by adding dilute alkali solution dropwise, so that gallium chloride is converted into sodium gallate. The alkaline solution is then passed through an adsorption column packed with chelating resin for adsorption and impurity removal, so as to fully remove trace heavy metal impurities and residual aluminum and iron impurities in the solution. After adsorption is completed, the solution is filtered to obtain a high-purity sodium gallate electrolyte. S7: Using graphite as the anode and a pure gallium plate as the cathode, high-purity sodium gallate electrolyte is electrolyzed at 40–60℃ and a current density of 50–90 A / m² to obtain high-purity industrial-grade metallic gallium.

[0007] Furthermore, in step S1, the screen mesh size of the vibrating screen is 0.1 mm, and the particle size of the fly ash after ball milling is controlled at 200-300 mesh.

[0008] Furthermore, in step S3, the dilute hydrochloric acid is prepared by diluting 36% industrial-grade hydrochloric acid, and the stirring rate is 300 r / min.

[0009] Furthermore, in step S4, the oxidant is industrial-grade hydrogen peroxide with a concentration of 27.5%, and the amount added is 0.5% of the volume of the leachate. The pH value is adjusted using a 2 mol / L dilute sodium hydroxide solution, and the standing temperature is 60°C and the standing time is 30 minutes.

[0010] Furthermore, in step S7, the electrolysis adopts a constant voltage and constant current mode. During the electrolysis process, the pH value of the electrolyte is maintained between 8.5 and 9.0, and the electrolysis time is 2.5 to 3 hours. After the crude gallium is washed with hot water at 80°C, it is melted and slag removed to obtain industrial-grade metallic gallium.

[0011] Compared with the prior art, the beneficial effects of the present invention are: 1. Using dry fly ash with a gallium content of 50-80 μg / g as raw material, this method overcomes the economic challenges of extracting gallium from low-grade fly ash, transforming coal combustion waste into a high-value gallium source, broadening gallium ore supply channels, and realizing the recycling of solid waste resources. Through high-temperature roasting at 820-900℃ with soda ash, the aluminosilicate lattice is completely destroyed, converting gallium into easily soluble sodium gallate, significantly increasing the gallium leaching rate and ensuring full recovery of gallium from the raw material. 2. A three-stage deep purification system is designed, consisting of oxidation precipitation, acid washing for impurity removal, and chelating resin adsorption. In particular, chelating resin adsorption can accurately remove trace heavy metal impurities, ensuring the purity of the electrolyte. An alkaline electrolyte system and constant voltage constant current electrolysis are adopted to avoid co-deposition of impurities in the acidic system. Pure liquid gallium metal is efficiently deposited at the cathode, and the final product purity is ≥99.99%, meeting the standards for high-end industrial applications. Attached Figure Description

[0012] Figure 1 This is a flowchart of the gallium metal extraction process of the present invention; Detailed Implementation

[0013] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0014] Please see Figure 1 This invention provides a technical solution: a method for extracting gallium metal from coal, comprising the following steps: S1: Dry fly ash with a gallium content of 50-80 μg / g is selected as raw material. Large particles of fly ash are removed by screening with a vibrating screen and then ground in a ball mill for later use. The fly ash is screened through a vibrating screen with a screen aperture of 0.1 mm to accurately remove large particles of fly ash and inert impurities such as quartz sand. This avoids these impurities from hindering reaction contact, consuming reagents, or affecting product purity in subsequent roasting and leaching processes. S2: Grind the dry fly ash and soda ash in a mass ratio of 1:0.4 to 0.7 and mix them evenly in a mixer. After mixing, send the mixture into a rotary kiln and heat it to 820℃-900℃, maintaining a constant temperature for calcination for 1-1.5 hours. Then, allow it to cool naturally to room temperature. Using soda ash as an activator, gradually heat the mixture in the rotary kiln to 820℃-900℃ and maintain a constant temperature for 1-1.5 hours. This temperature range is the optimal temperature for the metathesis reaction between soda ash and the aluminosilicate minerals in the fly ash, effectively destroying... The stable lattice structure of aluminosilicate breaks the isomorphic state of gallium within the lattice, transforming the gallium encapsulated within the lattice into acid-soluble sodium gallate. Simultaneously, it converts impurities such as aluminum in fly ash into soluble aluminates, achieving "destabilization and activation" of gallium. This lays a crucial foundation for the subsequent acid leaching process. The calcination time is controlled at 1-1.5 hours to ensure the metathesis reaction proceeds fully and to avoid unreacted aluminosilicate residues that could reduce the gallium extraction rate. After calcination, natural cooling to room temperature prevents the high-temperature material from rapidly shrinking and agglomerating upon cooling. S3: The calcined fly ash is broken up and added to a 3-5 mol / L dilute hydrochloric acid leaching solution. The ratio of dilute hydrochloric acid to fly ash is 6:1 to 10:1, and the leaching temperature is 85-95℃. The leaching is carried out with continuous stirring for 3-4 hours, so that the gallate in the activated fly ash reacts with the acid to generate Ga³⁺ and dissolves into the leaching solution. After leaching, the solution is separated by plate and frame filter press to obtain gallium-containing leaching solution and silicon-aluminum filter residue. The sodium gallate generated by calcination and activation undergoes an acid-base neutralization reaction with dilute hydrochloric acid to generate water-soluble gallium trichloride, so that Ga³⁺ is fully dissolved in the leaching solution. At the same time, precise control of acid concentration, liquid-solid ratio and leaching temperature can effectively inhibit the excessive dissolution of impurities such as aluminum and iron in fly ash, reduce the processing pressure of subsequent purification and impurity removal processes, and reduce reagent consumption.

[0015] S4: Add an oxidant to the gallium-containing acid leaching solution and stir thoroughly to oxidize all Fe²⁺ in the leaching solution to Fe³⁺. Then, slowly adjust the pH of the leaching solution to 3.0–3.8 with a dilute alkaline solution. Small amounts of Fe²⁺, Al³⁺, and other impurities remain in the acid leaching solution. Fe²⁺ can non-selectively bind with the extractant, affecting the gallium extraction efficiency; therefore, oxidation treatment is necessary first. Add 27.5% industrial-grade hydrogen peroxide (0.5% of the leaching solution volume) to the leaching solution. Hydrogen peroxide, as a highly efficient oxidant, can oxidize all Fe²⁺ in the leaching solution at room temperature. The solution is Fe³⁺, and no new impurities are introduced. Then, the pH of the leachate is slowly adjusted to 3.0-3.8 with 2 mol / L sodium hydroxide dilute alkaline solution. This pH range is the optimal range for Fe³⁺ hydrolysis. Fe³⁺ will undergo hydrolysis to form ferric hydroxide (Fe(OH)3) precipitate, which is insoluble in water, while Ga³⁺ and Al³⁺ remain in a dissolved state, achieving the initial separation of iron impurities from gallium. The solution is then left to stand at 60℃ for 30 minutes to allow Fe³⁺ to hydrolyze and form ferric hydroxide precipitate. Finally, the solution is separated by vacuum filtration to remove the precipitate impurities and obtain a low-iron gallium-containing refined raw solution. S5: An organic phase is formed by mixing the extractant and kerosene at a volume ratio of 15%–25%:75%–85%. High-concentration hydrochloric acid can disrupt the coordination bonding between the extractant and Ga³⁺, causing Ga³⁺ to transfer from the organic phase to the back-extraction solution. The low-iron gallium-containing refined raw solution obtained from the pre-purification of the leachate is used as the aqueous phase and added to the extraction tank at a ratio of aqueous phase:organic phase = 1:1–2:1 for extraction. Stirring ensures full contact between the aqueous and organic phases. Utilizing the selective adsorption of Ga³⁺ by the extractant, Ga³⁺ is selectively transferred from the aqueous phase. The gallium is transferred to the organic phase, while most impurities such as Al³⁺ remain in the aqueous phase, achieving preliminary enrichment and separation of gallium. After extraction, the phases are allowed to stand and separate, resulting in a gallium-loaded organic phase and a raffinate. 0.8 mol / L dilute hydrochloric acid is added to the gallium-loaded organic phase for acid washing to remove impurities. Then, 6 mol / L hydrochloric acid is used as the back-extraction solution, and back-extraction is performed at a ratio of organic phase to back-extraction solution of 3:1. The high concentration of hydrochloric acid can destroy the coordination binding between the extractant and Ga³⁺, causing Ga³⁺ to transfer from the organic phase to the back-extraction solution, resulting in a high concentration of gallium chloride enriched solution. S6: The high-concentration gallium chloride enriched solution obtained by solvent extraction and back-extraction is adjusted to an alkaline state of pH 8.5-9.0 by adding dilute alkali solution dropwise, so that gallium chloride is converted into sodium gallate, forming a homogeneous and stable alkaline solution, which creates suitable conditions for subsequent chelation adsorption. The alkaline solution is then passed through an adsorption column packed with chelating resin for adsorption and impurity removal. The chelating resin has specific coordination groups and has a strong selective adsorption capacity for trace heavy metal impurities and residual Al³⁺ and Fe³⁺ in the solution. These impurities can be fully adsorbed and fixed on the resin, while sodium gallate does not react with the chelating resin and passes smoothly through the adsorption column, thus fully removing trace heavy metal impurities and residual aluminum and iron impurities in the solution. After adsorption is completed, the solution is filtered to obtain a high-purity sodium gallate electrolyte. S7: Using graphite as the anode and a pure gallium plate as the cathode, high-purity sodium gallate electrolyte is electrolyzed at 40–60℃ and a current density of 50–90 A / m². Gallium ions in the electrolyte move towards the cathode under the influence of the electric field, gain electrons on the cathode surface and undergo a reduction reaction to generate liquid metallic gallium, which is deposited on the cathode surface. At the anode, water oxidation occurs to generate oxygen and hydroxide ions, thus avoiding impurities from depositing at the anode and affecting product purity, resulting in high-purity industrial-grade metallic gallium.

[0016] Reference embodiment: In step S1, the screen aperture of the vibrating screen is 0.1 mm, and the particle size of the fly ash after ball milling is controlled at 200-300 mesh, which significantly increases the specific surface area of ​​the fly ash, so that the soda ash and fly ash particles can fully contact each other during subsequent roasting and activation, ensuring a uniform and thorough activation reaction. At the same time, it provides favorable conditions for the rapid dissolution of gallium in the acid leaching process.

[0017] Reference Example: In step S3, the dilute hydrochloric acid is prepared by diluting 36% industrial-grade hydrochloric acid, and the stirring rate is 300 r / min.

[0018] Reference Example: In step S4, the oxidant is industrial-grade hydrogen peroxide with a concentration of 27.5%, and the amount added is 0.5% of the volume of the leachate. The pH value is adjusted by using a 2 mol / L dilute sodium hydroxide solution. The standing temperature is 60°C and the standing time is 30 minutes.

[0019] Reference Example: In step S7, electrolysis adopts a constant voltage and constant current mode. During the electrolysis process, the pH value of the electrolyte is maintained between 8.5 and 9.0, and the electrolysis time is 2.5 to 3 hours. After the crude gallium is washed with hot water at 80°C to remove the electrolyte and trace impurities attached to the surface, it is then subjected to melting and slag removal treatment to remove trace floating slag impurities in the crude gallium, and finally high-purity industrial-grade metallic gallium is obtained, which meets the requirements of industrial applications.

[0020] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method of extracting gallium metal element mineral from coal, characterized by, Includes the following steps: S1: Select dry fly ash with a gallium content of 50-80μg / g as raw material, and remove large particles of fly ash by screening with a vibrating screen and grinding with a ball mill for later use. S2: Grind dry fly ash and soda ash in a mass ratio of 1:0.4 to 0.7 into a mixer and stir evenly. After stirring, send it into a rotary kiln for heating to 820℃-900℃ and keep it constant for calcination for 1-1.5 hours. Then let it cool naturally to room temperature. S3: Disperse the calcined fly ash and add it to a 3-5 mol / L dilute hydrochloric acid leaching solution. The ratio of dilute hydrochloric acid to fly ash is 6:1-10:1, the leaching temperature is 85-95℃, and the leaching is carried out by stirring for 3-4 hours. This allows the gallium ions in the activated fly ash to react with the acid to generate Ga³⁺ and dissolve into the leaching solution. After leaching, the solution is separated by pressure filtration using a plate and frame filter press to obtain gallium-containing leaching solution and silicon-aluminum filter residue. S4: Add an oxidant to the gallium-containing acid leaching solution and stir thoroughly to oxidize all Fe²⁺ in the leaching solution to Fe³⁺. Then, slowly adjust the pH of the leaching solution to 3.0-3.8 with dilute alkali solution. Let it stand at 60℃ for 30 minutes to allow Fe³⁺ to hydrolyze and form ferric hydroxide precipitate. Finally, filter and separate the precipitate impurities using a vacuum filter to obtain a low-iron gallium-containing refined raw solution. S5: An organic phase is formed by mixing extractant and kerosene at a volume ratio of 15%–25%:75%–85%. The low-iron gallium-containing refined raw solution obtained by pre-purification of the leachate is used as the aqueous phase and added to the extraction tank at a ratio of aqueous phase:organic phase = 1:1–2:1 for extraction. After extraction, the mixture is allowed to stand and separate into layers to obtain gallium-loaded organic phase and raffinate. 0.8 mol / L dilute hydrochloric acid is added to the gallium-loaded organic phase for acid washing to remove impurities. Then, 6 mol / L hydrochloric acid is used as the back-extraction solution and back-extraction is performed at a ratio of organic phase:back-extraction solution = 3:1 to obtain a high-concentration gallium chloride enrichment solution. S6: The high-concentration gallium chloride enriched solution obtained by solvent extraction and back-extraction is adjusted to an alkaline state of pH 8.5-9.0 by adding dilute alkali solution dropwise, so that gallium chloride is converted into sodium gallate. The alkaline solution is then passed through an adsorption column packed with chelating resin for adsorption and impurity removal, so as to fully remove trace heavy metal impurities and residual aluminum and iron impurities in the solution. After adsorption is completed, the solution is filtered to obtain a high-purity sodium gallate electrolyte. S7: Using graphite as the anode and a pure gallium plate as the cathode, high-purity sodium gallate electrolyte is electrolyzed at 40–60℃ and a current density of 50–90 A / m² to obtain high-purity industrial-grade metallic gallium.

2. The method for extracting gallium metal element mineral products from coal according to claim 1, characterized in that, In step S1, the screen mesh size of the vibrating screen is 0.1 mm, and the particle size of the fly ash after ball milling is controlled at 200-300 mesh.

3. The method for extracting gallium metal element mineral products from coal according to claim 1, characterized in that, In step S3, the dilute hydrochloric acid is prepared by diluting 36% industrial-grade hydrochloric acid, and the stirring rate is 300 r / min.

4. The method for extracting gallium metal element mineral products from coal according to claim 1, characterized in that, In step S4, the oxidant is industrial-grade hydrogen peroxide with a concentration of 27.5%, and the amount added is 0.5% of the volume of the leachate. The pH value is adjusted by using a 2 mol / L dilute sodium hydroxide solution. The standing temperature is 60°C and the standing time is 30 minutes.

5. The method of claim 1, wherein the method is characterized by: In step S7, the electrolysis adopts a constant voltage and constant current mode. During the electrolysis process, the pH value of the electrolyte is maintained between 8.5 and 9.0, and the electrolysis time is 2.5 to 3 hours. After the crude gallium is washed with hot water at 80°C, it is melted and slag is removed to obtain industrial-grade metallic gallium.

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