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A joint team of researchers has made a ground-breaking discovery with the potential to have a significant impact on the sustainable recovery of rare earth elements (REEs), which are in increasing demand for use in green energy technologies. The team found that humble eggshell waste can recover REES from water, offering a new, environmentally friendly method for their extraction.

Researchers from Trinity College Dublin’s School of Life Sciences and iCRAG, the Irish Research Center for Applied Geosciences, have just published their findings in the journal ACS Omega.

REEs, which are essential to technologies used in electric cars and wind turbines, for example, are in increasing demand but in relative short supply. As a result, scientists must find new ways to extract them from the environment – ​​and in sustainable ways, as current methods are often harmful.

Here, researchers discovered that the calcium carbonate (calcite) in eggshells can effectively absorb and release these valuable REEs from water.

The researchers placed eggshells in REE-containing solutions at varying temperatures from a balmy 25°C to a scorching 205°C and for varying periods of time up to three months. They found that the elements can enter the eggshells by diffusion along calcite boundaries and the organic matrix, and at higher temperatures, the rare earth elements build new minerals on the surface of the eggshells.

At 90°C, the eggshell surface helped restore formations of a rare-earth compound called cozoite. As things got hotter, the eggshells underwent a complete transformation, with the calcite shells dissolving and being replaced by polycrystalline cozoite. And at the highest temperature of 205°C, this mineral gradually transforms into bastnasite, the stable rare earth carbonate mineral used by the industry to extract REEs for technological applications.

This innovative method suggests that waste eggshells can be repurposed as a low-cost, environmentally friendly material to help meet the growing demand for REES, as eggshells trap individual rare earth elements in their structure over time.

Lead author Dr. Rémy Rato says: “This study presents a potentially innovative use of waste materials that not only offers a sustainable solution to the problem of rare earth recovery, but is also consistent with the principles of circular economy and waste valorization.” “

Principal investigator Prof. Juan Diego Rodríguez-Blanco highlighted the wider implications of the findings, adding: “By turning eggshell waste into a valuable resource for the recovery of rare earth elements, we are addressing critical environmental concerns associated with traditional extraction methods, and we contribute to the development of greener technologies’.