Recovery of Precious Metals from Secondary Sources

The synthesis of dione and dithione ligands (1,4-dimethyl-2,3-piperazinedione, 1,4-dimethyl- 2,3-perhydrodiazepinedione, 1,4-dimethyl- 2,3-piperazinedithione, and 1,4-dimethyl-2,3- perhydrodiazepinedithione) and their iodine adducts (1,4-dimethyl-2,3-piperazinedithione/ triiodide, 1,4-dimethyl-2,3-perhydrodiazepinedithione/ bisdiiodine), for the dissolution of Pd and Pt was investigated. 1,4-dimethyl-2,3-piperazinedione, 1,4-dimethyl-2,3-perhydrodiazepinedione, and 1,4-dimethyl-2,3-piperazinedithione were successfully synthesised using conventional methods. 1,4-dimethyl-2,3-piperazinedione and 1,4-dimethyl-2,3- perhydrodiazepinedione were also synthesised mechanochemically while 1,4-dimethyl-2,3- piperazinedithione can be synthesised sonochemically.

The adduct 1,4-dimethyl-2,3- piperazinedithione/triiodide was also successfully synthesised. The mild conditions which would lead to the dissolution of Pd, Pt, and Au were examined. The best results were achieved in DESs, where metal solutions up to 200 mM (Reline 200) and 300 mM (Ethaline 200) were obtained, using a Pd:iodine ratio of 1:4.