Pt/Pd Extraction from Industrial Waste

Carrier catalysts are widely used in the chemical and petrochemical industries, such as:

• Anthraquinone process for hydrogen peroxide production

• Urea synthesis

• CO removal from synthesis gas in ammonia production

• Benzene hydrogenation to cyclohexane

• Catalytic combustion of low-concentration volatile organic compounds (VOCs)

• Petroleum refining processes (reforming, isomerization, cracking, hydrogenation, dehydrogenation, etc.)

Among various carrier materials, Al₂O₃ is the most commonly used, with small amounts of SiO₂ and CaCO₃ also employed. The primary active metals are platinum (Pt) and palladium (Pd), forming two main series: Pt/Al₂O₃ and Pd/Al₂O₃. Depending on the application, the Pt/Pd content typically ranges from 0.01% to 0.5%, classifying these as low-grade scrap materials.

Spent Al₂O₃-based catalysts usually exist as 3-5 mm spherical or cylindrical pellets. The carrier’s crystalline structure can be either α-type or γ-type, with significant differences in acid solubility:

• α-type is acid-insoluble

• γ-type is readily soluble in acid

These spent catalysts have a simple composition, primarily involving the recovery of either Pt or Pd individually.

Key to Recovery Technology: Effective Separation of Pt/Pd from the Carrier

The goal is to extract Pt/Pd-enriched concentrates or crude metal. Two main approaches are used:

1. Direct Leaching of Pt/Pd

   • Use acid or other chemical reagents (via stirring, percolation, or soaking) to dissolve Pt/Pd.

   • Then recover the metals from the solution using methods such as:

     • Anion exchange

     • Displacement with zinc (Zn), iron (Fe), or aluminum (Al)

     • Activated carbon adsorption

     • Precipitation with sodium sulfide (Na₂S)

     • Precipitation with ethyl xanthate

2. Leaching the Carrier to Obtain Pt/Pd-Enriched Residue

   • Dissolve the carrier (if γ-Al₂O₃), leaving behind a residue rich in Pt/Pd.

After obtaining Pt/Pd concentrates or crude metal, further refining into pure metal poses no technical difficulty.

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