We show that platinum (Pt) and palladium (Pd) can be efficiently removed from spent catalytic converters by means of a sintering process involving chloride salts. For Pt, mixing the crushed catalyst in an aqueous solution of chloride salts at catalyst/salt weight ratios ranging from 2.5 to 6.7, followed by drying, and 2-h sintering in the reactor furnace at 1100 °C, results in extraction of 80 ± 4% of the metal. For Pd, the addition of fumed silica to the dry chlorination agents was necessary in order to optimize extraction using fractional factorial design of experiments (DOE). Maximum Pd extraction of 93 ± 5% was achieved at 1100 °C with weight ratios of the catalyst material: CaCl2·2H2O:SiO2 = 1:0.6:1.2. Application of a similar protocol to Pt-containing catalytic converters would be expected to result in a similar high level of extraction efficiency. The primary advantage of the proposed extraction process is that it does not involve hazardous chemicals, strong bases/acids, or corrosive gases, and produces, as a byproduct, only small quantities of nontoxic silicate waste.
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© 2018, The Minerals, Metals & Materials Society.
- Chloride salt extraction
- Factorial analysis
- Precious metal recycling
- Spent catalytic converter