Zn-vapor pretreatment for acid leaching of platinum group metals from automotive catalytic converters

• Zn vapor pretreatment is proposed for the recovery of precious metal catalysts.
• Extraction of the metals from simulated catalysts is examined in acid solutions.
• Enhancement of the extraction by the pretreatments is observed in aqua regia.
• Hydrochloric acid is also found able to dissolve precious metals.
• Effects of pretreatments are discussed from the viewpoint of catalyst structure.

To recover platinum group metals (PGMs) from spent automotive catalytic converters with a smaller environmental load, a Zn-vapor treatment prior to acid leaching was previously proposed. Because PGMs and Zn form alloys which dissolve easily, the pretreatment is believed to reduce the use of both chemical agents and processing time. In this study, effects of this treatment on PGM leaching were examined using simulated catalysts. Leaching tests in aqua regia demonstrated that Zn-vapor treatment enhanced the dissolution of PGMs, and was especially effective on Rh. Pretreatments were also found to enhance PGM extractions in hydrochloric acid depending on the conditions. Reactions on Zn-treated catalysts in the solution are discussed based on these results.

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