Spent automobile catalytic converters, containing one or more of the platinum-group metals platinum, palladium, or rhodium are treated to recover these metals by leaching with a cyanide solution at a temperature greater than 100 deg. C to form metal-cyanide complexes in solution, removing leached solids from the pregnant solution, and heating the solution to a temperature high enough to decompose the PGM-cyanide complexes and precipitate the metals. Thus, used monolithic catalytic converter material containing 8.4 Pd, 24 pt, and 1.5 Rh oz/ton was crushed to -8 mesh and leached with 5-pct nacn solution at 160 deg. C in an autoclave for 1 h. After filtering and washing, the solution contained 67 pct of the pd, 87 pct of the pt, and 79 pct of the rh in the original sample. Similarly, used pellet- type catalyst containing 6 pd, 14 pt, and 0.8 Rh oz/ton was leached with 1-pct nacn solution in an autoclave at 160 deg. C for 1 h. After filtering and washing, the solution contained 97 pct of the pd, 94 pct of the pt, and 98 pct of the rh in the original sample. To decompose the PGM-cn complexes, the solutions are further heated to at least 200 deg. C and preferably 250 deg. C in an autoclave. High-grade PGM are precipitated, most base metal-cyanide complexes are destroyed, cyanide is decomposed to ammonia and carbonates, and residual cyanide in solution is generally less than 0.2 Ppm.
Chem. Abstr. 117:11,783T, U.S. Patent No. 5,160,711