Leaching of petroleum catalysts with cyanide for palladium recovery
The US Bureau of Mines has tested cyanide leaching for recovery of palladium (Pd) from spent petroleum processing catalysts. Three different catalyst samples were supplied by a spent-catalyst processor. These catalysts consisted of a zeolite base and contained 0.4 to 0.7% Pd. During alkaline cyanide leaching, the catalysts exhibited ion-exchange properties due to their zeolite matrices. Hydrogen ions were released from the zeolite in exchange for sodium ions in solution, resulting in a significant decrease in solution pH. This could present a safety hazard because of the potential for release of toxic hydrogen cyanide gas. A pretreatment step where the catalysts were contacted with a 1.0 M sodium hydroxide was found to prevent the pH shift from occurring. Following the sodium hydroxide pretreatment, two stages of leaching at 160 C with solution containing 1% sodium cyanide and 0.1 M sodium hydroxide gave at least 75 and up to 95% Pd recovery. The Pd was quantitatively recovered from the leach solution by thermal decomposition in an autoclave at 250 C for 1 h. The Pd content of the precipitate was over 50%. Thermal decomposition also decreased the total cyanide content of the barren solution to less than 0.2 mg/L. The catalyst leach residues passed the Federal Toxicity Characteristic Leaching Procedure and the California Waste Extraction Test, indicating that landfill disposal of the leach residues would be acceptable.
- OSTI ID:
- 49340
- Resource Relation:
- Other Information: PBD: 1995
- Country of Publication:
- United States
- Language:
- English
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