Ruthenium Recovery from Spent Catalysts

I. Recovery of Ru from Spent Ru/C and Ru/MgO Catalysts

In the ammonia synthesis industry, Ru/C and Ru/MgO catalysts are widely used due to their high catalytic activity and ability to reduce operating pressure and temperature.

Process for treating spent Ru/C catalysts containing Ba and K:

1. Soak the catalyst in HCl solution for 12 hours to dissolve Ba and K.

2. Add H₂SO₄ to the filtrate to precipitate BaSO₄ (recovery rate > 87%).

3. Concentrate the mother liquor to crystallize KCl (recovery rate > 77%).

4. Incinerate the HCl-leached residue at 800°C for 10 hours.

5. Mix the ash with an equal mass of KOH + KNO₃ (1:1 ratio), then heat to 650°C and melt for 1 hour.

6. After cooling, leach the melt with cold water to remove excess potassium salts.

7. Dissolve the filter residue in hot water (80°C) to obtain a K₂RuO₄ solution.

8. Add a small amount of NaClO and heat to 60°C for 0.5 hours to oxidize.

9. Slowly drip concentrated H₂SO₄, then distill under reduced pressure to collect volatile RuO₄ (golden-yellow).

10. Absorb RuO₄ in 37% HCl solution, then slowly concentrate to obtain RuCl₃·nH₂O (recovery rate: 94.6%).

• Alternatively, absorb RuO₄ in HNO₃ solution to produce Ru(NO₃)₃.

Process for treating spent Ru/MgO catalysts containing Ba and Cs promoters:

1. Dissolve Ba and Cs with 1 mol/L HNO₃ (dissolution rate > 97%); Ru/MgO remains undissolved.

2. Heat with 1 mol/L NH₃·H₂O to 70°C to selectively dissolve MgO, yielding a pure Mg(NO₃)₂ solution (can be converted back to MgO via carbonate for reuse).

3. The HNO₃-insoluble residue is crude metallic Ru (recovery rate > 94%).

II. Direct Production of RuCl₃ from Spent Catalysts

Industries such as chemical catalysis, electronics, and electroplating often use ruthenium trichloride (RuCl₃) directly. Producing RuCl₃ from spent Ru-containing catalysts simplifies the process, reduces reagent consumption, and improves recovery rates.

Example process for producing reagent-grade RuCl₃ from Ru-containing waste (67.9% Ru, with Pt, Ag, Pb as main impurities):

1. Place the waste in a distillation reactor.

2. Add a 30% NaOH solution (5 times the mass of the waste) in three batches while introducing Cl₂ for oxidative distillation (reaction: Ru + NaOH + 4Cl₂ → RuO₄ + 8NaCl + 4H₂O).

3. Use a water absorber (1st stage) to prevent salt splashing, followed by seven串联 stages of 6 mol/L HCl + 0.5% C₂H₅OH solution to absorb volatile RuO₄ (reaction: 2RuO₄ + 20HCl → 2H₂RuCl₅ + 8H₂O + 5Cl₂).

4. Filter the 2nd-stage absorption solution, then slowly concentrate to a syrup-like consistency.

5. Dry gently under infrared light to obtain RuCl₃, then seal (to prevent moisture absorption).

6. Add ethanol as a reducing agent to the primary distillation residue, let stand for 12 hours until colorless, then filter.

7. Treat the remaining residue with HNO₃ to separate Ag and Pb.

8. For the residue (~19% Ru), mix with NaOH and NaClO₃ (mass ratio 3:1:1), then melt at 700°C for 1 hour.

9. Pour the melt into cold water for secondary oxidative distillation to recover additional RuCl₃.

   • The final residue contains minimal Ru.

   • Total Ru recovery rate: 98%.