Discarded oyster shells may pull rare earth metals from polluted water

Discarded oyster shells may pull rare earth metals from polluted water

Recent research conducted by a team at Trinity College Dublin has identified a cost-effective and sustainable strategy for mitigating water pollution. This innovative approach utilizes oyster shells, which are often discarded after consumption and subsequently end up in landfills. The findings, published in the journal Science of the Total Environment, reveal that these waste seashells—particularly oyster shells—can effectively extract and eliminate rare earth elements from contaminated water. Remarkably, this process occurs naturally, leading to the formation of stable mineral crystals.

What are rare earth elements, and why are they increasingly problematic?

Rare earth elements serve as crucial components in various cutting-edge technologies, including wind turbines, electric vehicles, and smartphones. However, their extraction and processing pose significant environmental risks, especially when these metals infiltrate water supplies. The geopolitical implications are also noteworthy, as the production of these strategic materials is dominantly concentrated in a limited number of countries, while the demand continues to escalate.

The presence of rare earth elements in aquatic ecosystems can lead to the degradation of microorganisms, as well as harm to plants and animals. Therefore, it is imperative to develop effective and sustainable methods for removing these elements from water, making this an urgent environmental imperative.

What have the researchers discovered?

In their laboratory studies, the research team subjected crushed shells from mussels, cockles, and oysters to solutions enriched with rare earth elements. The results indicated that the shells initiate a chemical reaction whereby the minerals within the shell dissolve, allowing them to be replaced with new minerals that incorporate the rare earth elements. Essentially, the shells serve as a "template," facilitating the conversion of dissolved metals into solid mineral crystals that are securely housed within the shell material.

Notably, oyster shells exhibited superior performance among the materials tested. Their unique microstructure enhanced the chemical reaction's depth, enabling them to capture significantly higher amounts of rare earth elements compared to other shell types. These findings suggest that shell waste could be a viable, low-cost, and eco-friendly option for treating contaminated water and even recovering valuable metals from industrial effluents.

What is the impact of this work?

Dr. Rémi Rateau, a member of Trinity's School of Natural Sciences and the study's first author, remarked, "Among the most exciting aspects of this discovery is that even modest quantities of shell waste could extract substantial amounts of rare earth metals from polluted water, thus creating a palpable environmental impact with as little as a few kilograms of oyster shells."

"The global aquaculture industry generates millions of tons of shell waste annually, a significant portion of which is discarded or sent to landfills. By repurposing this waste, we can provide both a means for environmental remediation and a sustainable recycling pathway."

Dr. Juan Diego Rodriguez-Blanco, Principal Investigator of the project and also from Trinity's School of Natural Sciences, added, "What makes this discovery particularly promising is that the process is driven entirely by mineral reactions—the shells naturally convert dissolved rare earth elements into new solid minerals. This means that the process is straightforward and does not require extensive financial investment or complex technical equipment."

"Understanding these reactions will enable us to devise low-cost and eco-friendly approaches to extract critical metals from contaminated waters while simultaneously adding value to a prevalent waste product."

A deeper dive into the science

In interactions with rare-earth-rich solutions, the calcium carbonate minerals present in the shells undergo dissolution, which is followed by the crystallization of new rare earth carbonate minerals. This transformation occurs in a series of stages: calcium carbonate → lanthanite → kozoite → hydroxylbastnäsite, with kozoite being the predominant product under the tested conditions.

Throughout the reaction, a coating of rare earth carbonate crystals develops on the shell grains. In the cases of mussel and cockle shells, this coating quickly becomes impermeable, inhibiting further reactions and leaving a significant portion of the original shell intact. Conversely, the porous microstructure of oyster shells enables the reaction to persist throughout the entire grain, allowing for a nearly complete replacement of the original calcium carbonate.

As a result, oyster shells achieved the highest performance levels, with a rare earth uptake reaching approximately 1.5 grams of rare earth metals per gram of oyster shell. In practical terms, even small amounts of shell waste have the potential to remove significant quantities of rare earth elements from contaminated water—indicating that a few kilograms of shell waste could capture kilograms of dissolved rare earth elements from polluted sources rich in these materials.

Dr. Rodriguez-Blanco further noted, "The research also demonstrated that various rare earth elements are integrated into the crystals during different growth phases, suggesting the potential for developing environmentally friendly rare earth separation technologies in the future."

Publication details

Rémi Rateau et al, Sustainable rare earth capture using seashell carbonates: Mineralogical pathways and comparative uptake behaviour of mussel, cockle, and oyster shells, Science of The Total Environment (2026). DOI: 10.1016/j.scitotenv.2026.181698