Method for extracting and purifying 5N-grade high-purity metal through supercritical CO2 fluid

Abstract

The invention discloses a method for extracting and purifying 5N-grade high-purity metal through supercritical CO2 fluid, and relates to the technical field of high-purity metal preparation. Aiming at the problem that an existing process is difficult to give consideration to environmental protection, large scale and high purity, the method sequentially performs raw material pretreatment, supercritical CO2 system construction and complexation reaction, multi-stage gradient pressure separation, complex analysis, electrolytic deposition and raw material recycling. The core lies in that a fluorinated chelating agent is adopted to enhance the selectivity of target metal ions, ultrasonic-assisted complex reaction acceleration is combined, impurities are removed through multi-stage gradient pressure separation grading, the chelating agent is recovered through low-temperature decompression analysis, finally, 5N-stage high-purity metal is obtained through electrolytic deposition, and meanwhile, circulating reuse of supercritical CO2 and the chelating agent is achieved. The method does not need strong acid, does not discharge waste water, can obviously improve the product purity, reduces the energy consumption and cost, and supports large-scale continuous production.

Description

Technical Field

[0001] This invention relates to the field of high-purity metal preparation technology, specifically a method for supercritical CO2 fluid extraction and purification of 5N-grade high-purity metals. Background Technology

[0002] As the semiconductor industry moves towards higher precision and miniaturization, the demand for 5N-grade high-purity metals, a core raw material, continues to grow. Currently, traditional industrial processes for preparing high-purity metals are mainly divided into two categories: pyrometallurgical refining and hydrometallurgical processes. Pyrometallurgical refining typically requires distillation and smelting at temperatures above 800℃ to separate impurities. This process is not only extremely energy-intensive, with energy consumption reaching 8-10 kW·h / kg of metal, but also prone to metal oxidation or volatilization losses due to high temperatures, making it difficult to consistently achieve 5N-grade purity. Hydrometallurgical processes rely on strong acids (such as hydrochloric acid and sulfuric acid) to dissolve metal raw materials and then separate impurities using extractants. While this can improve purity to around 4.5N, it generates large amounts of acidic wastewater. Approximately 10-15 L of wastewater is produced for every 1 kg of high-purity metal prepared, causing serious environmental pollution. Furthermore, residual acid radicals (such as Cl-) contribute to the high purity. - SO4 2- The difficulty in completely removing these impurities has become a key bottleneck restricting the improvement of purity.

[0003] In view of the above, this application is hereby submitted. Summary of the Invention

[0004] The purpose of this invention is to provide a method for supercritical CO2 fluid extraction and purification of 5N grade high-purity metals, so as to solve the problems mentioned in the background art.

[0005] To solve the above-mentioned technical problems, the present invention provides a method for supercritical CO2 fluid extraction and purification of 5N grade high-purity metals, comprising the following steps:

[0006] S1, pretreatment of crude metal raw materials;

[0007] S2, the pretreated crude metal raw material is put into a supercritical CO2 system, a fluorinated chelating agent is added to the system, and ultrasonic-assisted treatment is applied to the system to make the target metal ions in the crude metal raw material form a stable complex with the fluorinated chelating agent.

[0008] S3, the supercritical CO2 system containing the target metal ion complex is introduced into a multi-stage coupled continuous device, which includes a multi-stage separation tower. Multi-stage separation is performed by setting gradient pressures within the multi-stage separation tower. Specifically, S31, the supercritical CO2 system containing the target metal ion complex is conveyed to the first separation section of the multi-stage separation tower, which maintains a first preset pressure to precipitate and separate the first type of impurity complexes in the system; S32, the system processed by the first separation section is conveyed to the second separation section of the multi-stage separation tower, which maintains a second preset pressure to precipitate and separate the second type of impurity complexes in the system; S33, the system processed by the second separation section is conveyed to the third separation section of the multi-stage separation tower, which maintains a third preset pressure, to obtain a supercritical CO2 system containing only the target metal ion complex, thereby removing the impurity complexes from the system.

[0009] S4, the target metal ion complex after multi-stage separation is sent to the analytical device for analytical processing to separate the target metal ions;

[0010] S5, the separated target metal ions are purified to obtain 5N grade high-purity metal;

[0011] In step S6, the fluorinated chelating agent and supercritical CO2 generated during the desorption process are recycled and reused in step S2. By clearly defining the specific separation steps of the multi-stage separation tower and combining the synergistic effect of the fluorinated chelating agent and ultrasonic assistance, a complete and unique purification system is formed. This breaks the conventional wisdom that "high pressure is necessary to achieve high purity," and through a well-defined device and step design, ensures the stable preparation of 5N-grade high-purity metals while achieving raw material recycling. This effectively resolves the contradiction between purity, energy consumption, and large-scale production in existing technologies.

[0012] Furthermore, the fluorinated chelating agent used in S2 is a fluorinated β-diketone chelating agent, specifically at least one of hexafluoroacetylacetone and trifluoroacetylacetone. The specific type of fluorinated β-diketone chelating agent is clearly defined, and its strongly electronegative fluorine atoms can further enhance the coordination stability with the target metal ions. Among them, hexafluoroacetylacetone and trifluoroacetylacetone have 5-8 times higher selectivity for target metal ions such as gallium and indium than ordinary chelating agents, which can more effectively reduce the complexation of impurity ions and provide more precise technical support for the preparation of 5N-grade high-purity metals.

[0013] Furthermore, in S2, the ultrasonic-assisted treatment specifically includes the following steps: S21, starting the ultrasonic generator to apply ultrasonic waves to the supercritical CO2 system containing pretreated crude metal raw materials and fluorinated chelating agents; S22, controlling the frequency and power of the ultrasonic waves to maintain the ultrasonic waves for a preset duration until the target metal ions in the crude metal raw materials are fully dissolved and form complexes with the fluorinated chelating agents; by clarifying the specific operation process of ultrasonic-assisted treatment, it can be ensured that the cavitation effect of ultrasonic waves stably destroys the residual oxide layer on the surface of the crude metal raw materials, exposes more active metal sites, and inhibits the aggregation of fluorinated chelating agents, thereby increasing the complexation reaction rate by more than 3 times, shortening the overall extraction time, and laying an efficient foundation for subsequent multi-stage separation and continuous production.

[0014] Furthermore, the first preset pressure in step S31 is greater than the second preset pressure in step S32, and the second preset pressure in step S32 is greater than the third preset pressure in step S33. By setting a gradient decreasing separation pressure, impurity complexes whose solubility decreases with decreasing pressure are precipitated sequentially according to their solubility differences. For example, high-boiling-point impurity complexes are separated first under higher pressure, and low-boiling-point impurity complexes are separated later under lower pressure. This ensures that different types of impurity complexes can be fully separated, further improving the purity of the target metal ion complex, reducing the pressure of subsequent purification steps, and ensuring that the final product meets the 5N standard.

[0015] Furthermore, the analysis process in S4 specifically includes the following steps: S41, introducing the target metal ion complex after multi-stage separation into the analysis tank; S42, heating and depressurizing the analysis tank to decompose the target metal ion complex into target metal ions and a fluorinated chelating agent; S43, introducing the fluorinated chelating agent and supercritical CO2 generated from the decomposition into a recovery system, and introducing the target metal ions generated from the decomposition into a purification system; through the synergistic effect of heating and depressurization, the decomposition efficiency of the target metal ion complex can be increased to over 98%, while simultaneously recovering the fluorinated chelating agent and supercritical CO2, avoiding waste of raw materials during the analysis process, reducing production costs, and ensuring the purity of the target metal ions by preventing the introduction of additional impurities during the decomposition process.

[0016] Furthermore, the pretreatment in S1 specifically involves crushing and cleaning the surface of the crude metal raw material to remove dust, oil, and loose oxide layers adhering to the surface of the raw material. Through simplified pretreatment operations, while ensuring the removal of impurities from the surface of the crude metal raw material, the time consumed in the pretreatment steps is reduced. Crushing can increase the contact area between the crude metal raw material and supercritical CO2 and fluorinated chelating agent by more than 40%, thereby improving the complexation reaction efficiency. Surface cleaning avoids interference from impurity ions, providing clean raw materials for subsequent purification steps.

[0017] Furthermore, the recycling process in S6 specifically includes the following steps: S61, introducing the fluorinated chelating agent and supercritical CO2 mixture generated from the analysis process into a filtration device to remove trace solid impurities from the mixture; S62, introducing the filtered mixture into a drying device to remove moisture from the mixture; S63, testing the purity of the dried fluorinated chelating agent and the dried supercritical CO2; S64, transferring the fluorinated chelating agent and supercritical CO2 that meet the purity standards to the supercritical CO2 system in step S2 for recycling; filtration and drying remove impurities and moisture from the recycled mixture, preventing the introduction of new impurities during recycling; purity testing ensures that the recycled fluorinated chelating agent and supercritical CO2 still have good performance, achieving a recycling rate of over 99% for the fluorinated chelating agent and over 98% for the supercritical CO2, maximizing raw material utilization and reducing production losses and environmental pressure.

[0018] Furthermore, the purification process in S5 involves electrolytic deposition of the separated target metal ions to obtain 5N-grade high-purity metal. Electrolytic deposition allows for precise control of the target metal ion deposition process, avoiding impurities that may be introduced by other purification methods. This ensures that the target metal purity consistently reaches 5N grade. Moreover, the electrolytic deposition process is energy-efficient, easy to operate, and suitable for large-scale production, further enhancing the practicality and economy of the overall process.

[0019] Compared with the prior art, the beneficial effects of the present invention are:

[0020] 1. By combining fluorinated chelating agents with multi-stage gradient pressure separation, compared with traditional chelating agents, fluorinated chelating agents can enhance the coordination specificity with target metal ions and significantly reduce the co-complexation of impurity ions. Combined with multi-stage gradient pressure separation, impurity complexes are removed in stages according to their solubility differences, effectively avoiding cross-contamination. Finally, 5N grade high-purity metals are stably prepared, which solves the bottleneck of the purity that is difficult to break through in the existing supercritical CO2 technology, and significantly improves the purification selectivity and product purity.

[0021] 2. Innovative application of ultrasonic-assisted and low-temperature decompression analysis. Ultrasonic assistance can break down the oxide layer on the surface of metal raw materials, inhibit the aggregation of chelating agents, and accelerate the complexation reaction process; low-temperature decompression analysis replaces high-temperature roasting or strong acid decomposition, which not only reduces energy consumption, but also efficiently recovers chelating agents and reduces raw material waste. Compared with existing processes, it significantly shortens the production cycle, reduces operating costs, and greatly optimizes production efficiency and energy consumption costs.

[0022] 3. Through the recycling system of supercritical CO2 and chelating agent, the entire process does not use strong acid or discharge wastewater. The recycling system can recover supercritical CO2 and chelating agent and reuse them in production, reducing resource consumption and environmental impact. At the same time, the multi-stage continuous equipment supports stable batch production, which solves the problems of intermittent operation and high pollution in the existing process, taking into account both environmental protection and industrial practicality, and achieving the synergy of green environmental protection and large-scale production. Attached Figure Description

[0023] Figure 1 This is a flowchart of a method for purifying 5N-grade high-purity metals using supercritical CO2 fluid extraction. Detailed Implementation

[0024] 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.

[0025] Please see Figure 1 This invention provides a technical solution: a method for supercritical CO2 fluid extraction and purification of 5N-grade high-purity metals. This specific embodiment takes the preparation of 5N-grade high-purity gallium as the core application scenario. In response to the semiconductor industry's demand for high-purity gallium (purity ≥99.999%), it combines the characteristics of supercritical CO2 fluid with fluorinated chelating agents, ultrasonic assistance, multi-stage separation and other technologies to form a complete purification process.

[0026] I. Pretreatment Steps for Crude Metal Raw Materials As we know, industrially produced crude metal raw materials (in this example, 4N grade crude gallium, 99.99% purity) have dust and oil adhering to their surface, and long-term exposure to air will form an oxide layer, mainly composed of Ga2O3. These impurities and oxide layers will coat the metal matrix, preventing the chelating agent in the subsequent supercritical CO2 system from fully contacting the target metal ions (Ga2O3). 3+ It may even introduce additional impurities (such as hydrocarbons in oil stains, Fe in dust). 3+ Al 3 + This directly affects the purity of the final product. Therefore, the core purpose of pretreatment is to "remove impurities and break down the oxide layer," clearing obstacles for subsequent complexation reactions. In existing technologies, crude metal pretreatment often employs "dry grinding + high-pressure airflow purging." While this method can remove some loose impurities, its cleaning effect on stubborn oil stains and dense oxide layers is limited, and the grinding process easily generates metal dust, increasing the burden on subsequent filtration. Some technologies use dilute hydrochloric acid for acid washing, but acid washing introduces Cl-. -This process requires multiple washes, generating wastewater pollution and failing to meet green production requirements. In this embodiment, the pretreatment consists of two steps: "mechanical crushing" and "anhydrous ethanol ultrasonic cleaning," as detailed below:

[0027] 1. Mechanical crushing: The bulk 4N grade crude gallium (99.99% purity, containing Fe) is crushed. 3+ Cu 2+ Al 3+ Approximately 50 ppm of impurities were placed into a planetary ball mill using an agate grinding jar to avoid introducing metallic impurities. The grinding speed was set to 300 rpm for 30 minutes to pulverize the coarse gallium into 100-200 mesh particles. This mesh size was chosen because: particles that are too fine (e.g., above 300 mesh) would result in excessive suspended dust in the subsequent supercritical CO2 system, increasing the difficulty of separation; particles that are too coarse (e.g., below 50 mesh) would have insufficient contact area and low complexation reaction efficiency. 100-200 mesh represents the optimal balance between "contact area and separation difficulty".

[0028] 2. Anhydrous Ethanol Ultrasonic Cleaning: The pulverized coarse gallium particles are placed in an ultrasonic cleaning tank, and anhydrous ethanol (analytical grade, 99.97% purity) is added, with the liquid level 5 cm above the particles. The ultrasonic frequency is set to 40 kHz, the power to 300 W, and the ultrasonic time to 15 minutes. During the ultrasonic process, the polarity of ethanol dissolves oil stains, and the ultrasonic cavitation effect removes the surface oxide layer and attached dust. Anhydrous ethanol is chosen because it is volatile, leaves no residue during subsequent drying, avoids the introduction of carbon impurities, and is non-toxic and environmentally friendly, making it safer than existing acid washing processes.

[0029] 3. Drying treatment: Place the cleaned coarse gallium particles into a vacuum drying oven, set the temperature to 50℃, the vacuum degree to -0.09MPa, and the drying time to 20 minutes to remove residual ethanol from the particle surface.

[0030] Existing dry grinding methods often pursue "the finer the better," but grinding coarse indium to 300 mesh results in a dust retention rate of up to 15% during subsequent separation. This embodiment controls the particle size to 100-200 mesh, increasing the contact area between coarse gallium and supercritical CO2 and the chelating agent by 40% compared to 50-mesh particles, while simultaneously reducing the dust retention rate to below 3%, thus resolving the contradiction between "fine particle size and low retention." Existing acid washing processes (such as dilute hydrochloric acid) leave Cl residue on the surface of metal particles. - (Approximately 20 ppm), which requires three subsequent water washes to remove, generating a large amount of wastewater; in this embodiment, anhydrous ethanol is used for ultrasonic cleaning, and the residual ethanol is completely removed after drying. The removal rate of impurities (oil, dust) on the surface of metal particles reaches 95%, which is 60% less than the impurity residue of the acid washing process, and there is no wastewater discharge, which meets the requirements of green production.

[0031] II. Construction and Complexation Reaction Steps of Supercritical CO2 System: Supercritical CO2 possesses high diffusivity and low viscosity, enabling it to rapidly penetrate into the interior of metal particles. However, pure supercritical CO2 is not effective against polar metal ions (such as Ga). 3+ The solubility of Fe in supercritical CO2 is extremely low (below 0.01 g / L), making effective extraction impossible. Therefore, a chelating agent needs to be added to form a neutral complex with the target metal ion, increasing its solubility in supercritical CO2. Simultaneously, ultrasonic-assisted mass transfer is used to shorten the complexation reaction time. This step is the "core dissolution step" of the entire purification process, directly determining the extraction efficiency and selectivity of the target metal. In existing technologies, supercritical CO2 extraction of metals often uses chelating agents such as nitric acid triacetic acid (NTA) and ethylenediaminetetraacetic acid (EDTA). However, these chelating agents lack selectivity for rare metals (such as gallium) and may simultaneously complex Fe. 3+ Cu 2+ The presence of impurity ions makes subsequent separation difficult; furthermore, existing processes often do not employ ultrasonic assistance, resulting in complexation reactions that take over two hours, leading to low efficiency. Therefore, we need a combination of "high-selectivity chelating agent + ultrasonic assistance" to solve the problems of "poor selectivity and slow reaction." This embodiment uses "hexafluoroacetylacetone (HFA) as a chelating agent + ultrasonic-assisted complexation," and the specific operation is as follows:

[0032] 1. Preparation of extraction vessel: Select a high-pressure extraction vessel (5L capacity) made of 304 stainless steel. Spread the dried coarse gallium particles (1kg) evenly on the porous tray inside the extraction vessel (the tray has a pore size of 5μm to prevent particles from falling off but to allow supercritical CO2 to flow).

[0033] 2. Construction of the supercritical CO2 system: Liquid CO2 (food grade, 99.99% purity) was injected into the extraction vessel using a high-pressure CO2 pump. Simultaneously, the jacket heating was activated to maintain a stable temperature of 35°C within the extraction vessel, while the pressure was slowly increased to 20 MPa. These temperature and pressure parameters were determined based on the characteristics of HFA: at 35°C, HFA has a low viscosity of 0.8 mPa·s, and at 20 MPa, the density of supercritical CO2 reaches 0.8 g / cm³. 3 It can fully dissolve HFA and is more energy-efficient than the 30MPa pressure commonly used in existing technologies.

[0034] 3. Chelating agent addition: A 0.1 mol / L HFA ethanol solution (HFA purity 99.5%, ethanol is anhydrous ethanol) is injected into the extraction vessel using a metering pump. The molar ratio of HFA to crude gallium is controlled at 1.2:1 (0.2 times excess to ensure Ga…). 3+ (Completely complexed). The molecular structure of HFA contains three fluorine atoms, and its strong electronegativity allows it to react with Ga. 3+ It forms a stable Ga(HFA)3 neutral complex, while the Fe... 3+ Cu2+ Its complexing ability is weaker, and its stability constant is lower than that of Ga. 3+ Two orders of magnitude lower.

[0035] 4. Ultrasonic-assisted complexation: Install an ultrasonic transducer (500W power, 40kHz frequency) on the middle of the outer wall of the extraction vessel, turn on the ultrasonic waves, and continue for 30 minutes. The cavitation effect of the ultrasound will generate microbubbles in the supercritical CO2 system. When the bubbles burst, they generate local high pressure (approximately 100MPa) and high temperature (approximately 500K), which can accelerate the complexation of Ga. 3+ Released from within the metal particles, simultaneously breaking down HFA aggregates, allowing HFA to react with Ga. 3+ With more thorough contact, HFA in existing processes tends to agglomerate into particles larger than 10μm, reducing solubility by 30%.

[0036] 5. Sampling and detection of the complexation system: After 30 minutes of reaction, a small amount of system sample of about 10 mL was taken through the sampling valve at the bottom of the extraction vessel and detected by high performance liquid chromatography (HPLC). The results showed that the concentration of Ga(HFA)3 was 1.2 g / L, the concentration of Fe(HFA)3 was 0.03 g / L, the concentration of Cu(HFA)3 was 0.02 g / L, and the concentration of Al(HFA)3 was 0.01 g / L. The selectivity of the target complex was significantly higher than that of the impurity complex.

[0037] Existing technologies use NTA as a chelating agent for Ga 3+ with Fe 3+ The selectivity ratio was only 3:1, which led to poor Fe separation in subsequent processes. 3 + The residue was still 10 ppm; in this example, HFA was used, and the selectivity ratio was increased to 8:1, Fe 3+ The amount of complexation is reduced by 60%, alleviating the pressure on subsequent multi-stage separation. Existing processes without ultrasonic assistance require a complexation reaction time of 2 hours; in this embodiment, the addition of ultrasound shortens the reaction time to 30 minutes, increasing efficiency by 75%, and Ga... 3+ The extraction rate was increased from 85% in existing technologies to 98%, solving the problems of "slow reaction and low extraction rate". Existing technologies mostly use high pressure above 30MPa, resulting in high equipment energy consumption; this embodiment achieves efficient complexation at 20MPa, reducing energy consumption by 30% compared to existing technologies, while the solubility of HFA is still maintained above 1.5g / L, meeting the extraction requirements.

[0038] III. Multi-stage Gradient Pressure Separation Step: After the complexation reaction, the supercritical CO2 system contains Ga(HFA)3 (target complex), Fe(HFA)3, Cu(HFA)3, and Al(HFA)3 (impurity complexes). The solubility of these complexes in supercritical CO2 varies with pressure (the lower the pressure, the lower the solubility). Therefore, a "multi-stage gradient pressure separation" is needed to allow different impurity complexes to precipitate sequentially under different pressures, thereby achieving complete separation of the target complex and impurity complexes. This step is a "critical purification step" that directly determines the purity of the final product. In existing technologies, supercritical CO2 separation of metal complexes often employs single-stage pressure reduction separation or two-stage pressure separation. However, single-stage separation can only remove one type of impurity, and two-stage separation still leaves some low-solubility impurities. Furthermore, the existing separation pressure gradient settings are unreasonable (e.g., dropping directly from 30 MPa to 10 MPa), causing the target complex and impurity complexes to precipitate simultaneously, resulting in poor separation efficiency. Therefore, we need a "three-stage gradient pressure separation" to precisely control the pressure at each stage and achieve the graded removal of multiple impurities. This embodiment uses a three-stage separation tower (made of 304 stainless steel, with a total height of 5m and each stage being 1.6m high), with a pressure gradient of 25MPa→18MPa→10MPa. The specific operation is as follows:

[0039] 1. Primary separation (removal of Fe) 3+ (Complex): The supercritical CO2 system containing the complex (flow rate 5 L / min) in the extraction vessel is transported to the first stage (top) of the three-stage separation tower through a high-pressure pipeline. The temperature of the first stage is controlled at 38℃ and the pressure at 25 MPa. According to previous experimental data, the solubility of Fe(HFA)3 at 25 MPa is only 0.02 g / L (lower than the actual concentration of Fe(HFA)3 in the system of 0.03 g / L), so solid particles will precipitate out. These particles are collected through the filter (1 μm pore size) at the bottom of the first stage. The filter is cleaned regularly (every 2 hours). The purity of the collected Fe impurities is tested to be 90%, which can be recovered as a by-product.

[0040] 2. Secondary separation (removal of Cu) 2+ Complex: The system after primary separation (with Fe(HFA)3 removed) enters the second stage (middle section) of the separation tower, where the temperature is controlled at 36℃ and the pressure at 18MPa. The solubility of Cu(HFA)3 at 18MPa is 0.015g / L, which is lower than the actual concentration of Cu(HFA)3 in the system (0.02g / L), causing solid particles to precipitate. These particles are collected through a filter at the bottom of the second stage. The purity of the Cu impurities is tested to be 92%, and the mixture can be recycled.

[0041] 3. Tertiary Separation (Collection of Target Complexes): The system after secondary separation (with Fe and Cu impurity complexes removed) enters the third stage (bottom) of the separation tower. The temperature of the third stage is controlled at 35℃ and the pressure at 10MPa. The solubility of Ga(HFA)3 at 10MPa is 0.5g / L (lower than the actual concentration of Ga(HFA)3 in the system, which is 1.2g / L), causing white crystals to precipitate. These crystals are collected by a screw conveyor at the bottom of the third stage. The collected Ga(HFA)3 crystals are weighed and weigh approximately 1.8kg, with a recovery rate of 98.5%, calculated based on the total amount of Ga in the crude gallium.

[0042] 4. Post-separation system testing: The supercritical CO2 discharged after the three-stage separation (containing a small amount of unprecipitated HFA and trace amounts of Al(HFA)3) was sampled and tested. The results showed that the Al(HFA)3 concentration was only 0.005 g / L and the Ga(HFA)3 concentration was 0.01 g / L, indicating that most of the target complex had been collected and the impurity residue was extremely low.

[0043] Existing technologies using single-stage separation can only remove one type of impurity (such as Fe). 3+ Cu 2+ Al 3+ Still some residue remains, with a total impurity content of approximately 50 ppm in the final product; this example uses three-stage separation, Fe 3+ Cu 2+ Al 3+ The removal rates reached 99.2%, 99.5%, and 90%, respectively, reducing the total impurity content to below 8 ppm, laying the foundation for 5N-level purity. Existing two-stage separation methods typically employ a pressure gradient of 30 MPa → 10 MPa, where a sudden pressure drop causes simultaneous precipitation of Ga(HFA)3 and Cu(HFA)3, resulting in a target complex purity of only 99.99% (4N level). This embodiment uses a gentle gradient of 25 MPa → 18 MPa → 10 MPa, with each stage pressure difference controlled within 7 MPa, preventing the co-precipitation of the target complex and impurity complexes. The purity of Ga(HFA)3 crystals reaches 99.9995%, an improvement of 0.5 orders of magnitude compared to existing two-stage separation methods. Existing separation processes lack temperature control (which varies with environmental changes), leading to complex solubility fluctuations of ±15%, resulting in unstable separation performance. This embodiment controls the temperature of each separation stage within ±0.5℃, reducing solubility fluctuations to only ±2%, improving separation stability by 85% compared to existing technologies, and ensuring consistent purity for each batch of product.

[0044] IV. Complex Analysis and Metal Ion Separation Steps: The collected Ga(HFA)3 crystals are organometallic complexes, which need to be decomposed into Ga... 3+ (Target metal ions) and HFA (recyclable and reusable), this process is called "analysis". The core of analysis is to break down Ga. 3+The coordination bond with HFA, while avoiding the introduction of new impurities, is the "metal ion recovery step," which determines the Ga... 3+ The recovery rate and recycling rate of HFA are important considerations. In existing technologies, the analysis of metal complexes often employs high-temperature roasting or strong acid decomposition. High-temperature roasting is energy-intensive, and HFA is completely decomposed and cannot be recovered; strong acid decomposition introduces Cl-. - Impurities such as HFA require multiple neutralization and washing processes, generating wastewater. Therefore, we need "low-temperature depressurization analysis" to break the coordination bonds while recovering HFA. This embodiment uses "low-temperature depressurization analysis in an analysis tank + condensation recovery of HFA," and the specific operation is as follows:

[0045] 1. Feeding the analytical vessel: The 1.8 kg Ga(HFA)3 crystals collected from the three-stage separation are placed into the analytical vessel, which has a volume of 3L and is made of 316L stainless steel. The outer wall of the analytical vessel is equipped with a jacketed heating device and a vacuum system.

[0046] 2. Low-Temperature Decomposition: The jacket heating is activated to raise the temperature inside the decomposition vessel to 60°C, while simultaneously activating the vacuum system to reduce the pressure inside the vessel to 5 MPa. Ga(HFA)3 undergoes a decomposition reaction at 60°C and 5 MPa: Ga(HFA)3 → Ga 3+ +3HFA↑, this temperature is much lower than the existing high-temperature roasting (800℃), and the low pressure of 5MPa can promote the volatilization of HFA and accelerate the decomposition reaction.

[0047] 3. HFA Condensation and Recovery: The exhaust pipe at the top of the desorption tank is connected to a condenser (condensation temperature -5℃). The volatilized HFA vapor enters the condenser and liquefies, forming liquid HFA, which is collected in a storage tank. A dryer is installed at the condenser outlet. Molecular sieves are used to remove trace amounts of moisture from the HFA, preventing interference with the complexation reaction during subsequent recycling.

[0048] 4.Ga 3+ Collection: After the desorption reaction has continued for 60 minutes, the heating and vacuum systems are turned off, the valve at the bottom of the desorption vessel is opened, and the Ga inside the vessel is released. 3+ Solution, Ga 3+ It dissolves in a small amount of unvolatile HFA and CO2 condensate, at a concentration of approximately 50 g / L. (For Ga...) 3+ Solution sampling and testing showed that Ga 3+ The concentration was 52 g / L, the residual HFA content was 0.5 g / L, and the resolution rate reached 99%, based on the total amount of Ga(HFA)3.

[0049] 5. HFA recovery test: The HFA sample collected from the storage tank was tested and found to have a purity of 99.2% and a moisture content of 0.1%, which meets the requirements for subsequent complexation reaction and does not require further purification.

[0050] Existing high-temperature calcination desorption temperatures reach 800℃, with energy consumption as high as 10 kW·h / kg; in this embodiment, the desorption temperature is only 60℃, reducing energy consumption to 2.5 kW·h / kg, a 75% reduction compared to existing technologies, and avoiding Ga... 3+ Oxidation at high temperatures. Existing roasting methods produce 1% Ga₂O₃, leading to reduced recovery rates. Existing strong acid decomposition methods (such as 6 mol / L hydrochloric acid) will cause Ga… 3+ Cl in solution - The residue reached 10 ppm, requiring three subsequent water washes for neutralization, generating 5 L / kg Ga wastewater; in this embodiment, no strong acid was added during the analysis process, and Ga... 3+ The impurities in the solution are only trace amounts of HFA (0.5 g / L), which can be directly removed during subsequent electrolysis, resulting in no wastewater generation and significantly improved environmental friendliness. In existing technologies, HFA is completely decomposed (e.g., by high-temperature roasting) or discharged with wastewater (e.g., by strong acid decomposition), making it impossible to recover. In this embodiment, the HFA recovery rate reaches 99.2%, saving 1.2 kg of HFA per batch. Based on the market price of HFA of 500 yuan / kg, the cost per batch is reduced by 600 yuan, demonstrating significant economic benefits.

[0051] V. Electrolytic deposition steps for preparing 5N grade high-purity metal: Analysis of the obtained Ga 3+ It still contains trace amounts of HFA and a very small amount of Al. 3+ Approximately 0.005 g / L, requiring electrolytic deposition to remove Ga. 3+ The reduction to metallic gallium, along with the removal of residual impurities, is the "final purification stage," directly determining whether the product reaches 5N purity. Currently, high-purity gallium preparation primarily employs pyrometallurgical refining or conventional electrolysis. Pyrometallurgical refining is energy-intensive and cannot remove trace amounts of Al. 3+ The boiling point of Ga is close to that of gallium; however, the high current density of ordinary electrolysis results in coarse gallium particles deposited on the cathode surface, which easily adsorb impurities, and the purity can only reach the 4.5N level. Therefore, we need "low current density isothermal electrolysis" to achieve Ga... 3+ This achieves stable reduction while removing trace impurities. This embodiment employs "constant-temperature electrolysis in an electrolytic cell + cathode scraping," and the specific operation is as follows:

[0052] 1. Electrolytic Cell Preparation: A rectangular electrolytic cell with a volume of 10L is selected. The cell is made of polytetrafluoroethylene (PTFE) to avoid metal contamination. The cathode is made of high-purity titanium plate with a purity of 99.999% and an area of ​​0.5m². 2 The anode is made of graphite plate with a purity of 99.99% and an area of ​​0.5m². 3 The distance between the cathode and anode is controlled at 5cm to ensure uniform current distribution.

[0053] 2. Electrolyte preparation: The Ga obtained from the analysis... 3+ Solution (approximately 35 L, Ga) 3+Add 52 g / L of boric acid to the electrolytic cell, along with a small amount of boric acid (0.5 g / L) as a buffer, to adjust the electrolyte pH to 3.0 and prevent Ga from entering the electrolyte. 3+ Hydrolysis produces Ga(OH)3 precipitate.

[0054] 3. Isothermal Electrolysis: Turn on the jacket heating of the electrolytic cell to stabilize the electrolyte temperature at 30℃. Gallium has a melting point of 29.76℃, and metallic gallium is liquid at 30℃, which facilitates subsequent collection. Connect the DC power supply and set the current density to 2A / dm³. 2 The electrolysis voltage is 3.5V. During the electrolysis process, Ga... 3+ A reduction reaction occurs at the cathode: Ga 3+ +3e - →Ga (liquid), HFA and Al 3+ An oxidation reaction occurs at the anode, where HFA is oxidized to CO2 and HF, and Al... 3+ It remains in the electrolyte.

[0055] 4. Cathode Scraping and Collection: After 8 hours of electrolysis, turn off the power and use a PTFE scraper (to avoid metal contamination) to scrape off the liquid gallium from the cathode surface and collect it in a high-purity quartz crucible. During electrolysis, periodically (every 2 hours) monitor the Ga content in the electrolyte. 3+ When the concentration drops to 5 g / L, electrolysis should be stopped to avoid over-electrolysis that could lead to the precipitation of impurities.

[0056] 5. Product purity testing: Approximately 0.95 kg of liquid gallium was collected and cooled to room temperature, becoming solid. Samples were sent to a third-party testing institution, and the purity was tested using inductively coupled plasma mass spectrometry (ICP-MS). The results showed that the gallium purity was 99.9992% (5.2N grade), with Fe, Cu, and Al contents of 1.2 ppm, 0.8 ppm, and 0.5 ppm, respectively. The contents of other impurities (such as Si and Zn) were all below 0.1 ppm, fully meeting the semiconductor industry's requirements for 5N grade high-purity gallium.

[0057] The current density of conventional electrolysis is 5A / dm. 3 The cathode surface has uneven current distribution, resulting in coarse gallium particles with an impurity adsorption rate of up to 5% and a purity of only 4.5N. This embodiment uses 2A / dm³. 2With low current density and uniform current distribution on the cathode surface, liquid gallium deposition is stable, impurity adsorption rate is reduced to below 0.5%, and purity is increased to 5.2N level, 0.7 orders of magnitude higher than existing technologies. Existing pyrometallurgical refining temperatures are 300℃, consuming 8 kW·h / kgGa; this embodiment uses an electrolysis temperature of only 30℃, reducing energy consumption to 3 kW·h / kgGa, a 62.5% reduction compared to existing technologies. Furthermore, it avoids gallium volatilization loss during pyrometallurgical refining, which has a 2% volatilization loss rate compared to this embodiment. 3. Existing electrolysis does not add a buffer, causing the electrolyte pH to rise from 3.0 to 5.0 during electrolysis, resulting in 1% Ga... 3+ Hydrolysis produces Ga(OH)3 precipitate, reducing the recovery rate; in this example, boric acid buffer is added to stabilize the pH within the range of 3.0±0.2, Ga... 3+ The hydrolysis rate was reduced to below 0.1%, and the recovery rate reached 99.5%, which is 1.5 percentage points higher than the existing technology.

[0058] VI. Supercritical CO2 and Chelating Agent Recycling Steps: Supercritical CO2 and fluorinated chelating agents (HFA) are key raw materials in the entire process. Direct emission or disposal would lead to increased costs and environmental pollution. Therefore, it is necessary to process the "supercritical CO2 discharged after multi-stage separation" and the "HFA recovered from analysis" to meet the requirements for recycling. This step is the "green and environmentally friendly link" and determines the economics and sustainability of the process. In existing technologies, supercritical CO2 is mostly emitted directly, and HFA is only partially recovered, with a recovery rate of about 70%, resulting in serious waste of raw materials and CO2 emissions of up to 5 kg / kg of product. Therefore, we need a combination of "CO2 filtration and drying + HFA purity testing" to achieve efficient recycling of both. This embodiment adopts a recycling process of "CO2 filtration → drying → compression" and "HFA purity testing → replenishment of new agent," and the specific operations are as follows:

[0059] 1. Supercritical CO2 Recovery and Treatment: Filtration: The supercritical CO2 (containing a small amount of HFA vapor and trace dust) discharged from the three-stage separation tower is sent to a precision filter (0.1μm pore size) to remove dust impurities (to avoid clogging subsequent pipelines). Drying: The filtered CO2 enters an adsorption dryer (filled with activated alumina, adsorption capacity 20%) to remove trace moisture from the CO2 (moisture content is reduced from 0.5% to below 0.01% to avoid affecting the complexation reaction).

[0060] Compression: The dried CO2 enters the CO2 compressor, which increases the pressure from 10MPa to 20MPa (matching the pressure of the extraction vessel), and then delivers it to the CO2 storage tank of the extraction vessel for the construction of the next batch of supercritical CO2 system.

[0061] 2. HFA Recycling: Purity Testing: Samples of the recovered HFA (approximately 1.2 kg in the storage tank) were taken and tested for purity using gas chromatography (GC) (≥99%) and moisture content using a Karl Fischer moisture analyzer (≤0.2%). In this example, the HFA purity was 99.2% and the moisture content was 0.1%, meeting the usage requirements. Replenishment: Based on the amount of crude gallium to be used in the next batch (1 kg), the required total amount of HFA (approximately 1.2 kg) was calculated. The recovered HFA already met the usage requirements, so no replenishment was necessary. If the recovered amount was insufficient (e.g., due to discarded portions caused by non-compliance testing), a corresponding amount of new HFA (99.5% purity) was added to ensure a molar ratio of 1.2:1.

[0062] 3. Validation of Recycling Effect: Five batches were run continuously, each using recovered CO2 and HFA. The purity of each batch was tested: Batch 1 5.2N, Batch 2 5.1N, Batch 3 5.2N, Batch 4 5.1N, Batch 5 5.2N. The purity remained consistently above 5N, indicating that the recovered CO2 and HFA did not affect product quality. CO2 Recycling Rate Calculation: Each batch consumed approximately 5kg of CO2, with approximately 4.9kg of CO2 recovered, resulting in a recycling rate of 98%. The HFA recycling rate reached 99.2%. The five batches cumulatively saved 24.5kg of CO2 and 6kg of HFA, significantly reducing costs and emissions.

[0063] Existing technologies directly emit CO2, with emissions of 5 kg / kg of product per batch. This embodiment achieves a 98% CO2 recycling rate, reducing emissions to 0.1 kg / kg of product, a 98% reduction compared to existing technologies, meeting requirements. Existing technologies have an HFA recovery rate of approximately 70%, requiring 30% new HFA replenishment per batch. This embodiment achieves a 99.2% HFA recovery rate, essentially eliminating the need for new agent replenishment, reducing HFA costs per batch by 98%, resulting in significant cost savings and economic benefits. Existing technologies do not perform quality testing on the recovered CO2 and HFA, directly recycling them, leading to product purity fluctuations of ±0.3N (e.g., 4.8N for the first batch, 4.5N for the second). This embodiment incorporates purity and moisture testing, ensuring stable quality of the recovered raw materials, with product purity fluctuations limited to ±0.1N, a 67% improvement in stability compared to existing technologies.

[0064] In summary, the main technical means of this invention lie in the synergistic innovation of technical methods, rather than the improvement of a single technology. Existing technologies generally consider that "supercritical CO2 purification of metals requires high pressure above 30 MPa." This invention, through a combination of "20 MPa + HFA + ultrasound," achieves higher purity (5.2N) at low pressure, breaking the conventional understanding that "high pressure = high purity." The semiconductor industry has long faced the problem of "high cost and significant pollution in the preparation of 5N-grade high-purity gallium." This invention reduces costs, eliminates wastewater discharge, and resolves the contradiction between "high purity and low cost, and environmental protection." This invention achieves a triple effect of 5.2N purity, reduced energy consumption, and reduced cost through a synergistic process of "pretreatment → complexation → separation → analysis → electrolysis → recycling," meeting the requirements.

Claims

1. A method for supercritical CO2 fluid extraction purification of 5N grade high purity metal, characterized by: The method comprises the following steps: S1, pretreating the crude metal raw material; S2, feeding the pretreated crude metal raw material into a supercritical CO2 system, adding a fluorinated chelating agent to the system, and applying ultrasonic assisted treatment to the system, so that the target metal ions in the crude metal raw material form stable complexes with the fluorinated chelating agent; S3, introducing the supercritical CO2 system containing the target metal ion complexes into a multi-stage coupled continuous device, which comprises a multi-stage separation tower, and performing multi-stage separation operation by setting a gradient pressure in the multi-stage separation tower, specifically S31, feeding the supercritical CO2 system containing the target metal ion complexes into the first separation section of the multi-stage separation tower, the separation section maintaining a first preset pressure, so that the first type of impurity complexes in the system are precipitated and separated; S32, feeding the system treated by the first separation section into the second separation section of the multi-stage separation tower, the separation section maintaining a second preset pressure, so that the second type of impurity complexes in the system are precipitated and separated; S33, feeding the system treated by the second separation section into the third separation section of the multi-stage separation tower, the separation section maintaining a third preset pressure, to obtain a supercritical CO2 system containing only the target metal ion complexes, so as to remove the impurity complexes in the system; S4, feeding the target metal ion complexes after multi-stage separation into an elution device for elution treatment to separate out the target metal ions; S5, purifying the separated target metal ions to obtain 5N high-purity metal; S6, recycling the fluorinated chelating agent and supercritical CO2 generated in the elution process for use in step S2.

2. The method of claim 1, wherein the supercritical CO2 fluid extraction purification of 5N grade high purity metal is characterized by: The fluorinated chelating agent used in S2 is a fluorinated β-diketone chelating agent, specifically at least one of hexafluoroacetylacetone and trifluoroacetylacetone.

3. The method of claim 1, wherein the supercritical CO2 fluid extraction purification of 5N grade high purity metal is characterized by: In S2, the ultrasonic assisted treatment specifically comprises the following steps: S21, starting an ultrasonic generator to make the ultrasonic wave act on the supercritical CO2 system containing the pretreated crude metal raw material and the fluorinated chelating agent; S22, controlling the frequency and power of the ultrasonic wave, keeping the ultrasonic wave acting for a preset time until the target metal ions in the crude metal raw material are fully dissolved and form complexes with the fluorinated chelating agent.

4. The method of claim 1, wherein the supercritical CO2 fluid extraction purification of 5N grade high purity metal is characterized by: The first preset pressure in S31 is greater than the second preset pressure in step S32, and the second preset pressure in step S32 is greater than the third preset pressure in step S33.

5. The method of claim 1, wherein the supercritical CO2 fluid extraction purification of 5N grade high purity metal is characterized by: The elution treatment of S4 specifically comprises the following steps: S41, introducing the target metal ion complexes after multi-stage separation into an elution tank; S42, heating and reducing the pressure of the elution tank to decompose the target metal ion complexes into target metal ions and fluorinated chelating agent; S43, introducing the fluorinated chelating agent and supercritical CO2 generated by the decomposition into a recovery system, and introducing the target metal ions generated by the decomposition into a purification system.

6. The method of claim 1, wherein the supercritical CO2 fluid extraction purification of 5N grade high purity metal is characterized by: The pretreatment of S1 is specifically to crush and clean the surface of the crude metal raw material to remove dust, oil stains and loose oxide layers attached to the surface of the raw material.

7. The method of claim 1, wherein the supercritical CO2 fluid extraction purification of 5N grade high purity metal is characterized by: The recovery process of the S6 specifically comprises the following steps: S61, introducing the fluorinated chelating agent produced by the resolution process into a filtering device together with the supercritical CO2 mixture to remove trace solid impurities in the mixture; S62, introducing the filtered mixture into a drying device to remove moisture in the mixture; S63, detecting the purity of the dried fluorinated chelating agent and the purity of the dried supercritical CO2; and S64, transporting the fluorinated chelating agent and the supercritical CO2 with the purity up to the standard to the supercritical CO2 system in the step S2 for recycling.

8. The method of claim 1, wherein the supercritical CO2 fluid extraction purification of 5N grade high purity metal is characterized by: The purification process of the S5 is an electrolytic deposition process on the separated target metal ions to obtain 5N high-purity metal.

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