Recovery of precious metals from catalysts refers to the process of extracting platinum, palladium, rhodium, and other precious metals from spent industrial catalysts using physical, chemical, and biological technologies. The significance of recovering precious metals from catalysts extends beyond economic value (recycling one ton of spent automotive catalysts yields 1-2 kilograms of platinum group metals worth over $120,000, at a cost of only 30%-50% of new mining). It also reduces reliance on mineral resources and mitigates environmental hazards. The EU End-of-Life Vehicles Directive and environmental regulations in multiple countries mandate precious metal recycling, driving the industry toward a closed-loop “production-use-recovery” cycle.
Precious metal catalysts are primarily categorized into heterogeneous catalysts (e.g., solid catalysts for automotive exhaust purification) and homogeneous catalysts (e.g., soluble metal compounds used in chemical reactions). Common recyclable precious metal catalysts include: catalytic converters (containing platinum, palladium, rhodium), petrochemical hydrogenation catalysts (containing molybdenum, nickel, vanadium), fuel cell catalysts (platinum-based), and denitrification environmental catalysts (containing vanadium-titanium group metals).
2025 technological innovation focuses on green and efficient recovery. Microwave-assisted leaching technology overcomes traditional limitations: a novel reactor employs 2450MHz microwave radiation combined with a retractable glass stirring rod, directly addressing the low mass transfer efficiency caused by the high viscosity of ionic liquids. This system integrates a diamond ATR crystal infrared probe for real-time monitoring of reaction solution components and dynamic parameter optimization, significantly enhancing the recovery rates of platinum, palladium, and rhodium.
Bioremediation techniques utilize microorganisms (e.g., Ferriportia oxydans) or fungal mycelium to adsorb platinum nanoparticles, achieving over 90% recovery rates with low energy consumption and zero pollution. Functionalized magnetic nanomaterials (e.g., Fe₃O₄@SiO₂-NH₂) selectively capture precious metal ions through coordination interactions, enabling rapid separation and recycling. Smart recovery systems integrate IoT and machine learning algorithms to dynamically adjust leaching parameters. One enterprise achieved a 12% increase in platinum recovery using AI models.
Continuous optimization of hydrometallurgical processes: Palladium recovery in hydrochloric acid/hydrogen peroxide (HCl/H₂O₂) leaching reached 92.6%. A fullerene core-Pd nanocapsule catalyst, constructed after urea complexation purification, demonstrated ultra-high activity in the reduction of 4-nitrophenol (conversion rate >99% within 3.5 minutes). The integrated process of ionic liquid-diffusion dialysis-MVR evaporation achieves precious metal recovery rates >98%, while maintaining acid recovery ≥80% and enabling resource utilization of crystallized salts.
Precious metal recovery from spent catalysts begins with pretreatment. Spent catalysts undergo crushing, screening, and magnetic separation to isolate the carrier from active components. This is followed by high-temperature calcination (four-stage oxygen-controlled calcination at 50-800°C) to remove carbon deposits and organic matter. Pyrolytic activation occurs under an inert atmosphere to prevent metal volatilization (e.g., rhodium loss above 800°C).
The leaching stage employs selective solvent extraction for precious metals. Common hydrometallurgical solutions include aqua regia, hydrochloric acid-chlorate, or thiourea, where pH and redox potential are controlled to selectively dissolve target metals. An innovative process employs a hydrochloric acid-citric acid-hydrogen peroxide mixed leaching agent. Reaction occurs at 600W microwave power and 200 rpm agitation for 20 minutes, achieving highly efficient dissolution of platinum group metals. After centrifuging the leachate to separate residues, the solution enters the purification stage.
Purification and refining employ multi-stage separation. Adding Na₂SO₃ solution to the leachate removes over 90% of iron impurities (at temperatures ≥303K, pH=1.5-2.0), followed by counter-extraction with NH₄OH to remove copper and zinc. Solvent extraction using phosphine-based (Cyanex 923) or amine-based extractants sequentially separates palladium and platinum. Electrochemical deposition selectively deposits metals at controlled potentials, achieving 99.95% purity. The final products are high-purity metals or directly usable alloys (e.g., ferro-molybdenum, ferro-nickel).
Identifying precious metals in spent catalysts requires combining source analysis with rapid detection. Automotive three-way catalytic converters (from vehicles in the US, Germany, France, etc., with mileage of 110,000-220,000 km) typically contain platinum, palladium, and rhodium. The ceramic honeycomb carrier must be crushed to a particle size ≤1 mm for testing. Petrochemical catalysts (hydrogenation, cracking catalysts) contain molybdenum, nickel, and vanadium, while fuel cell catalysts are primarily platinum-based.
ICP-OES (Inductively Coupled Plasma Optical Emission Spectroscopy) is the standard method for quantitative analysis, enabling precise determination of metal content (e.g., original catalyst containing 0.126% Pd). DONGSHENG's extensive experience in precious metal recycling indicates a correlation between catalyst form and precious metal content: ceramic-supported catalysts predominantly contain platinum group metals, while activated carbon supports are commonly used for gold and silver adsorption recovery.
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