Two different approaches have been investigated by the PLATIRUS partners – solid separation and liquid-liquid separation. The approaches are discussed in more detail below.
Separation via hybrid structured sorbents
This technology can reduce the volume to be treated by liquid-liquid extraction by pre-concentrating the PGMs in the eluent. By this process, PGM’s are separated from the metal hindering or prohibiting the recovery process. The loaded sorbents are then regenerated to recover the adsorbed PGMs and allow their reuse.
VITO has developed novel sorbents from hybrid structured materials. The structured metal oxide support gives the desired porosity, mechanical and thermal stability. An organic scavenger group is grafted on the support to make the material selective for PGM recovery.
- By this process, the targeted secondary PGM particles are up-concentrated by a factor of 10 – 100.
- PGMs in diluted solutions can be recovered selectively by a low-energy-intensive process.
- The developed material can be regenerated after the stripping to enable reuse of the sorbents.
Non-conventional liquid-liquid extraction
Separation using ionic liquids (ILs), also called non-conventional liquid-liquid extraction, deploys solvents entirely consisting of ions that can replace the conventional molecular organic solvents used in “classic” solvent extraction. KUL and Tecnalia have worked in PLATIRUS on the separation and purification of PGM mixtures using ILs.
This process enables the production of nitrate solutions of PGMs that can be used to produce new catalysts. Alternatively, the output of the process (i.e. individual solutions of PGMs) can serve as input for the GDEx process (explained in the Recovery processes).
- Compared to conventional hydrometallurgy, it can work effectively at similar temperatures
- Compared to other processes reported in the literature so far, it is highly selective
- It does not require the use of volatile or flammable compounds thus, eliminates their associated hazards
- No solvent loss, chemistry remains in balance and therefore, the ionic liquid can be reused