Waste from former European coal mining activities contains rare earths. A study published in Scientific Reports analyzed four samples from Spain, Poland and Slovenia: the results show real mineral potential, but there is a problem... for now.
Rare earths encompass several elements used in magnets, electronics and certain energy technologies. Their total concentration varied from 159.72 to 221.89 parts per million depending on the sample. Here, one part per million corresponds to roughly one gram of material per tonne of waste.
A piece of coal in front of a coal-fired power plant.
Image Wikimedia
The richest sample came from the Spanish site of La Matona, with 221.89 parts per million. The researchers therefore selected it for additional tests: they tried to concentrate the rare earths using low-energy methods such as gravity, magnetism, static electricity or flotation.
These physical methods unfortunately produced only negligible enrichment. The rare earths were not concentrated in an easily separated fraction. Analyses show that they occur as rare, very fine mineral phases, closely mixed with quartz and minerals rich in aluminum and silicon.
The team also tested several chemical solutions to dissolve the targeted elements. Water and acetic acid, the main acid in vinegar, proved ineffective here too. Hydrochloric acid heated to 60 °C increased the dissolved amounts, but without reaching a level deemed suitable for practical recovery under the studied conditions.
These observations currently prevent the direct transformation of these residues into a new industrial source. The measured contents remain interesting for documenting European secondary resources. However, the low concentration and the close association with other minerals complicate the treatments and could increase the consumption of chemicals.
The study focuses on four specific materials and tests carried out in the laboratory. It therefore does not rule out other, more favorable coal wastes. Future work will need to target other sites or develop more selective processes.