How to Recover Platinum and Rhodium from Industrial Glass Production Waste

Platinum-rhodium crucibles, bushing plates, and spinnerets melt glass and glass fibers at high temperatures (1200–1300°C) for extended periods. During operation, some platinum and rhodium oxidize into PtO₂ and Rh₂O₃, which then volatilize and either seep into furnace refractory bricks or become trapped in glass slag. These materials typically contain:

• 46–54% SiO₂

• 39–50% Al₂O₃

• ~2% CaO + MgO

• ~2000 g/t Pt

• ~200 g/t Rh

Since directly leaching platinum and rhodium with oxidative acids proves difficult, standard methods first separate silicon-aluminum and aluminum oxides to concentrate the precious metals. Workers mix the waste slag with sodium carbonate and sinter it at around 1000°C, converting the oxides into sodium silicate and sodium aluminate through these reactions:

1. Na₂CO₃ + 2SiO₂ → Na₂O·2SiO₂ + CO₂

2. Na₂CO₃ + Al₂O₃ → Na₂O·Al₂O₃ + CO₂

3. Na₂CO₃ + 6SiO₂ + Al₂O₃ → Al₂O₃·6SiO₂ + CO₂

Next, they grind the molten material in a ball mill and treat the slurry with hydrochloric acid to dissolve the sodium silicate and sodium aluminate:

• Na₂O·2SiO₂ + 2HCl + H₂O → 2NaCl + 2H₂SiO₃

• Na₂O·Al₂O₃ + 8HCl → 2AlCl₃ + 2NaCl + 4H₂O

• Na₂O·Al₂O₃·6SiO₂ + 8HCl + 2H₂O → 2AlCl₃ + 2NaCl + 6H₂SiO₃

To improve solid-liquid separation, they add a flocculant to help the fine particles settle. After filtration, aluminum powder displaces residual metals from the solution, leaving a filtrate with <0.004 g/L Pt, which they discard.

The remaining insoluble residue, now enriched with platinum group metals, undergoes hydrofluoric acid treatment to remove residual silica. This step yields a concentrate with roughly 50% platinum and rhodium.

Finally, they dissolve the concentrate using aqua regia or HCl + NaClO₃ and then refine the metals through selective precipitation or solvent extraction, producing pure platinum and rhodium products.

Key Improvements:

1. Reduced Passive Voice – Changed passive constructions (e.g., "are subjected to" → "melt," "is mixed" → "workers mix").

2. Varied Sentence Starters – Avoided repetitive openings.

3. Shorter Sentences – Split long sentences for clarity.

4. Added Transitions – Used words like next, finally, since to improve flow.

5. Bullet Points for Readability – Organized compositional data clearly.

This version is more engaging and easier to follow while maintaining technical accuracy. Let me know if you'd like any further refinements!