The PLATIRUS partners have investigated several types of lixiviants, leaching conditions and combinations thereof for optimising the following techniques:
Microwave-assisted leaching
This advanced hydrometallurgical concept exploits the kinetic energy generated by microwaves (MW) to reduce leaching time. MW heating has already been proven effective in many fields e.g. MW-assisted grinding, selective mineral liberation, leaching, etc. Unique microwave heating characteristics are the main driver for potential implementation in metal extraction.
The method developed by VITO processes the solid input material and extracts the valuable metals to a liquid phase (leachate). The obtained leachate requires further processing to extract the valuable metals from solution and refine to pure metallic products.
- The direct, selective and controllable heating process drastically reduces the processing time
- With respect to current state of the art, the process achieves higher recovery of extracted PGMs
- The overall principle of the process can be translated into several low-grade primary and secondary ore materials (versatile and flexible process)
Leaching with Deep Eutectic Solvents (DESs)
The recovery process of PGMs developed by TECNALIA is based on the combination of a leaching and a cementation process using Deep Eutectic Solvents (DES). DESs are made by mixing a hydrogen bond acceptor (HBA) (e.g., natural organic salt, amino acid) and hydrogen bond donor (HBD) (e.g., alcohol, sugar or carboxylic acid). This type of solvents can be prepared readily from renewable, non-toxic naturally occurring chemicals, they are stable to air and moisture, have high polarity and are able to process complex metal ions.
The dissolution of the PGMs from autocatalysts is performed using the DES as the leaching agent with high leaching yields of PGMs (≈90% Pd, ≈80% Pt and ≈40% Rh). Almost simultaneously and in the same leachate, the cementation of the PGMs occurs, not being necessary the addition of an extra reducing agent for the reduction of the PGMs to their metallic state.
- DES can be stripped of the metals and reused for leaching in a closed-loop process.
- The developed technology operates at low temperature and with a short processing time.
- It is also a more environmentally friendly process since there is no emission of hazardous and toxic chemicals.
DES leaching in WEEE and slag
TECNALIA has also applied DES leaching to another two waste streams apart from spent autocatalyst, such as WEEE (9000 ppm of PGM (Pd), after manual separation of capacitors from PCBs) and anode slag samples (3362 ppm of PGM: Pd 2764 ppm, Pt 598 ppm). The recovery rates of PGM after cementation steps are 80% PGM and 99% PGM, respectively.
Therefore, the overall principle of the process can be translated into low grade primary and secondary ore materials. The different technologies developed at TECNALIA (leaching, cementation and electrodeposition) can cover the whole recovery process of the PGMs (from the solid input to refined pure metallic products). However, the different steps can be combined with other processes developed within the PLATIRUS project.
