A process was investigated for the recovery of terbium (Tb), lanthanum (La) and cerium (Ce) from the HydroWEEE leaching residue by dissolution in concentrated methanesulphonic acid (MSA), a green solvent known for its high thermal stability, low toxicity and biodegradability. The stare-of-the-art treatment technologies for terbium recovery involve long leaching times and harsh conditions, due to the difficulty of dissolving rare-earth phosphates. With this novel approach, milder conditions can be used for the dissolution step. A paper has been published in the journal RSC Advances based on these results (L. Gijsemans, F. Forte, B. Onghena and K. Binnemans, RSC Adv., 2018, 8, 26349-26355).
Figure 1. Rare earths recovery from lamp phosphor waste by leaching with methanesulfonic acid.
An alternative approach for the recovery of Tb, La and Ce from the HydroWEEE residue is an integrated process based on roasting in the presence of sodium carbonate, followed by leaching with mineral acids. These results have been presented at the ERES conference (28th_31st May 2017, Santorini, Greece). Furthermore, a paper has been recently submitted to a peer reviewed journal.
During the ERES conference, an integrated route for yttrium (Y) and europium (Eu) recovery from waste cathode ray tubes (CRT) phosphors was presented as well. To avoid the release of toxic H2S gas, a roasting step is applied which allows to convert zinc sulfide into zinc oxide, afterwards removed by leaching with acetic acid. Rare earths are then recovered by dissolution in methanesulfonic acid. A paper based on these results has been recently submitted to a peer- reviewed journal.
Two routes were investigated for the recovery of lanthanum (La) and cerium (Ce) from spent NiMH batteries. The flow-sheets (based on a combination of pyro- and ionometallurgical processes) have been presented during the 4th International Symposium on Enhanced Landfill Mining (5th_6th February 2018, Mechelen, Belgium).
Finally, a route has been developed for Y and Eu recovery from the mixed oxide obtained by the HydroWEEE process by solvent extraction with a phosphonium ionic liquid. These results are also topic of an upcoming publication.
In Task 1.4, the investigated routes have been compared and the best one was selected for further upscaling.
Figure 2. Flow-sheet of the selected route (lanthanum and cerium recovery from NiMH batteries).