A team of researchers from Trinity College Dublin’s School of Natural Sciences and iCRAG, the Ireland Research Centre in Applied Geosciences, has determined that eggshell waste can be used to recover rare earth elements (REEs) from water.

According to the researchers, the approach promises to offer an environmentally friendly method for extracting the REEs necessary for developing the permanent magnets used in electric cars and wind turbines. Current methods used for extracting REEs are damaging to the environment and are chemical-intensive. As such, the researchers developed a sustainable approach to extract them from the environment.

Discovering that the calcium carbonate in eggshells can absorb and separate the REEs from water, the team put eggshells in solutions that contained REEs at varying temperatures — ranging from 77° F to 401° F — for periods up to three months.

During those experiments, the REEs entered the eggshell via diffusion along calcite boundaries. At higher temperatures, REEs reportedly formed new minerals on the surface of the eggshells.

Specifically, kozoite was detected in small concentrations at 194° F after one day, then subsequently amounting to a few weight percent after two weeks and close to 100% after 80 days.

Further, at 329° F, kozoite gradually replaced calcite, and after two days, only kozoite remained, the researchers explained.

At 401° F there was an emergence and subsequently a gradual increase of hydroxylbastnäsite. The researchers added that bastnäsite is a stable rare earth carbonate mineral that is used to extract REEs for technology applications.

In addition to the eggshell calcite being a potential sustainable sorbent for REE, the team also discovered that at higher temperatures, it is also a potential precipitant.

“The dissolution–precipitation reaction also generates minor grain-scale REE partitioning, which, if magnified, could be exploited as an environmentally friendly technique for REE separation,” the team said.

The findings are detailed in the article “Utilization of Eggshell Waste Calcite as a Sorbent for Rare Earth Element Recovery,” which appears in the journal ACS Omega.

To contact the author of this article, email mdonlon@globalspec.com