The rapid growth of the electric vehicle market and renewable energy infrastructure has created a massive surge in demand for rare earth elements. These 17 metallic elements are vital for the production of high performance magnets and energy efficient lighting, yet their supply remains fragile.
Currently, the world recycles less than 1 percent of these materials, largely because separating them from one another is an environmental and technical nightmare. Traditional industrial methods rely on repeated solvent extraction steps that consume large amounts of water and chemicals.
A recent patent WO2025003082A1 from ETH Zurich describes a new chemical process that could change this dynamic by using the unique structural properties of thiometallate complexes to isolate these metals more efficiently.
The core challenge in rare earth processing is the chemical similarity between the elements. Most rare earths exist in a stable trivalent oxidation state, meaning they react in nearly identical ways during standard chemical processing. This makes precise separation extremely difficult.
While some researchers have tried using light or specific electrical potentials to separate them, these methods often suffer from low efficiency or require toxic materials like mercury. The innovation described in the new patent moves away from these traditional hurdles by exploiting how different rare earth metals form specific molecular structures with varying levels of solubility.
How structural variance enables separation
The process starts by converting a mixture of rare earth compounds into what are known as thiometallate complexes. In this system, rare earth metal ions react with sulfur based compounds like tetrathiotungstate or tetrathiomolybdate in an organic donor solvent, such as acetonitrile.
The researchers discovered that the resulting complexes do not all look the same at the molecular level. Depending on the specific metal involved, the chemistry produces different arrangements, including dimeric, monomeric, or polymeric structures.
This structural difference is the key to the entire separation process. Because these different molecular shapes have vastly different solubilities, some metals will stay dissolved in the liquid while others will form a solid precipitate that can be easily filtered out.
The data shows that the solubility can differ by around an order of magnitude depending on which metal is used and what its oxidation state is. This provides a clear pathway for engineers to pull specific metals out of a complex mixture in just a few steps.
Isolating europium through internal reduction
The process is particularly effective for recovering europium, which is a critical and expensive component used in red lamp phosphors. Europium has the highest reduction potential among rare earths, and the ETH Zurich process takes advantage of this through a mechanism called internal reduction. When europium(III) reacts with the thiometallate ligands, it is reduced to europium(II) by a sulfur atom in the ligand itself. This reaction can happen naturally in ambient daylight or at temperatures above negative 20 degrees Celsius.
Once it is reduced, the europium forms a coordination polymer where the metal centers are linked together by sulfur atoms. This polymeric structure is much less soluble than the complexes formed by other metals like yttrium.
In laboratory experiments, this method separated europium from yttrium with a separation factor of more than 2300. This high level of selectivity suggests that high purity materials can be obtained without the dozens of extraction cycles required by current industrial standards.
A path toward circular electronics recycling
To prove the practical value of this chemistry, the researchers tested the system on waste from commercial fluorescent lamps. They treated crushed glass from the bulbs with an acid to extract the phosphor materials and then applied the thiometallate separation process. The results were impressive, showing a recovery efficiency of over 98 percent for europium from the lamp extract. This shows that the process can handle the complex mixtures found in real world electronic waste.
The final part of the process involves converting the isolated complexes back into useful industrial materials. By reacting the solid precipitates with ammonium oxalate, the researchers can recover rare earth oxalates. These are then heated, or calcined, at temperatures between 500 and 1200 degrees Celsius to produce rare earth oxides.
This step also allows the original thiometallate compounds to be recycled and used again in the first step of the process. This circular approach reduces chemical waste and could make rare earth recycling much more economically viable for the global industry.
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