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Supercritical CO₂ Precious Metal Extraction Process 1. Feedstock Preparation• Material Type: E-waste such as printed circuit boards, connectors, or other components with gold, silver, or platinum group metal (PGM) coatings.• Pre-treatment: The material is shredded or crushed to increase surface area and ensure better contact with the supercritical CO₂.• Loading: The processed material is loaded into a high-pressure extraction vessel (e.g., 10 liters in volume).2. System Pressurization and Heating• CO₂ Supply: Liquid CO₂ is stored in a tank and pumped into the system using a high-pressure CO₂ pump.• Transition to Supercritical State: The extraction vessel is heated to around 31°C and pressurized to 74 bar (or higher), converting CO₂ into its supercritical state—a phase where it behaves like both a gas and a liquid.3. Solvent Enhancement (Optional)• A ligand or co-solvent (e.g., tributyl phosphate or other metal-binding agents) may be introduced to increase the affinity of supercritical CO₂ for metal ions, enhancing metal solubility and selectivity.4. Extraction Phase• Supercritical CO₂ circulates through the extraction vessel.• It dissolves or leaches the precious metal coatings from the substrate materials.• This process typically takes about 1 hour per cycle, depending on conditions and metal type.5. Separation and Collection• The metal-rich CO₂ exits the extraction chamber and passes through a separator (often a pressure drop device or cooling unit).• The pressure is reduced or temperature altered, causing the dissolved metals to precipitate out.• Metals are collected in a collector trap or via filtration.6. CO₂ Recovery and Recirculation• The now-clean CO₂ is re-condensed and recycled back into the system.• This closed-loop design minimizes waste and makes the process highly sustainable and cost-efficient.7. Metal Refinement• The precipitated metals can be further refined using conventional metallurgical techniques such as electrolysis or melting.Advantages of the Process• Non-toxic: No cyanide or mercury is used.• Eco-friendly: CO₂ is recyclable and has minimal environmental impact.• Efficient: Targets only the precious metals with minimal damage to other materials.• Scalable: Can be used in small modular setups or scaled for industrial throughput. |
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