Selective recovery of gold, palladium, or platinum from acidic waste solution

End-of-life electrical and electronic equipment is the potential secondary resource for economically-viable precious metals (PMs), e.g., gold (Au), palladium (Pd), or platinum (Pt). The hydrometallurgical processes produce acidic leachates during the recovery of PMs from waste sources, while the selective recovery of Au, Pd, or Pt from such a matrix is challenging either due to the chemical similarities of elements or complexities in the sources and matrices. A total of nine solid-phase extraction (SPE) systems, all claimed to designed for separation of PMs from complex matrices, was evaluated at varying solution pH (≤2 to 10) based on the selectivity towards Au, Pd, or Pt. The observation was used to develop a technique for selective Au, Pd, or Pt separation from acidic waste solutions using a macrocycle-equipped SPE. The feed solution flow-rates, eluent-type or compositions has been optimized to achieve maximum separation efficiency of the target analytes. The relative affinity of the macrocycles in solid-phase towards the ions (Pd > Au > Pt) is the core phenomenon of the proposed technique, and the host-guest type interaction is expected to be more stable than the resin-based separation processes. Furthermore, application of the macrocycle-equipped SPE system is advantageous regarding economics as it minimizes the impact of coexisting ions in the matrix and provides unaltered separation performance for several loading-elution cycles.