Turning Old CFL Bulbs into a Treasure Trove of Europium

Redacción HC
10/09/2025

Recovering rare earth elements (REEs) from electronic waste has long been a tantalizing yet elusive goal. These metals are critical for clean energy technologies, from wind turbines and electric vehicles to high-performance displays. However, traditional mining and extraction processes are energy-intensive, environmentally damaging, and often geopolitically fraught. Now, a new study in Nature Communications unveils a promising method to selectively recover europium—a highly valued REE—from discarded compact fluorescent lamps (CFLs) using an innovative redox-active ligand.

The Challenge of Recovering Rare Earths

Global demand for REEs is surging, yet recycling accounts for ≤1% of total supply. Europium, in particular, is scarce in natural ores (0.05–0.10% by weight) but abundant in old fluorescent lamp phosphors—up to 230 kg per ton of phosphor powder. This makes CFL waste an exceptionally rich “urban mine.”

The main hurdle is separating europium from chemically similar elements, especially yttrium, which often co-occurs in lamp phosphors. Conventional separation techniques rely on solvent extraction or ion exchange, which can be costly, inefficient, and environmentally harmful.

A Redox Twist: The Tetrathiotungstate Ligand

Researchers from ETH Zürich and the Paul Scherrer Institut, led by Victor Mougel, have developed a direct, low-energy method for europium recovery. The process hinges on tetrathiotungstate (WS₄²⁻), an inorganic ligand capable of inducing an internal electron transfer that converts europium from its +3 oxidation state [Eu(III)] to +2 [Eu(II)].

Under ambient light or gentle heating in acetonitrile, the ligand triggers a striking yellow-to-red color change, followed by precipitation of an insoluble Eu(II) coordination polymer: [NEt₄]₂[Eu²⁺(WS₄)₂].

The reaction is highly selective—yttrium remains dissolved while europium drops out as a solid. At low temperature and in the dark, the reaction halts, confirming the light-activated redox mechanism.

Remarkable Selectivity and Efficiency

In lab tests with model mixtures of europium and yttrium, the method achieved separation factors (S_Eu/Y) as high as 3,583, far surpassing conventional approaches (typically S_Eu/Y between 2 and 100). Applied to real CFL phosphor powder—with a natural europium-to-yttrium ratio of 1:13.6—the method still achieved S_Eu/Y ≈ 1,043 and recovered 98.9% of the europium without any pre-treatment beyond simple acid dissolution.

Once isolated, the europium-containing precipitate can be processed into commercial-grade Eu₂O₃ via oxalate precipitation and calcination, with a purity of around 90%. Importantly, the tetrathiotungstate ligand can be recovered and reused, closing the loop for a more sustainable process.

Implications for Critical Mineral Supply Chains

Europium is listed as a critical raw material by both the United States and the European Union. The EU’s Critical Raw Materials Act sets a target of recycling 25% of critical minerals by 2030. This “one-pot” process, with its high selectivity, minimal energy requirements, and potential for reagent recycling, aligns perfectly with these policy goals.

If integrated into existing e-waste processing facilities, particularly those handling fluorescent lamps, the technique could bolster secondary supply chains, reduce environmental impacts from mining, and provide economic incentives for collection and recycling.

Beyond Europium: A Gateway to Other REEs?

While the study focuses on europium, the authors note that the method could be adapted for other REEs with favorable redox chemistry. This opens the door to broader applications in recycling valuable elements from e-waste, potentially transforming how we approach resource recovery in the clean energy era.

Conclusion

From a discarded light bulb to a near-pure rare earth oxide, this new method offers a bright spot in the challenging field of e-waste recycling. By harnessing the unusual chemistry of tetrathiotungstate ligands, researchers have demonstrated that high-purity europium recovery is not just a lab curiosity but a scalable, economically viable solution.

Call to action: Governments, industry, and recyclers should explore pilot projects to integrate this method into national e-waste strategies, especially in regions where fluorescent lighting is still prevalent.