The surprising power of seashells: how oyster waste can recapture rare earth elements

On many coastlines around the world, piles of discarded oyster and mussel shells are a common sight — the leftovers of a global seafood industry that produces millions of tonnes of waste each year. At the same time, hidden in rocky deposits far from the coast, a very different sort of resource — rare earth elements — is plentiful. These metals are in soaring demand as they are essential for technologies such as wind turbines, electric vehicles, and most modern electronics.

My team’s new research explores an interesting connection between this waste and the critically needed rare earth elements. We found that common seashells, particularly oyster shells, can capture and trap rare earth elements from water. In doing so, the seashells transform from waste into a potential tool for cleaning up pollution linked to the green energy transition.

People in Japan often describe rare earth elements as the “vitamins of modern industry” because, like vitamins in the body, they are essential for many modern technologies but only small amounts are needed. Extracting and processing rare earth minerals them can generate contaminated wastewater, where these elements may leak into the environment.

In our labs at Trinity College Dublin, we have been investigating whether seashell waste could help address this problem. We collected oyster, mussel and cockle shells from Irish beaches, cleaned them and crushed them into small grains. These fragments were then placed in water containing rare earth elements — specifically lanthanum, neodymium and dysprosium — at concentrations similar to those found in severe industrial contamination.

What happens next is not immediately visible to the naked eye, but under the microscope it is striking – and beautiful. At the surface of each shell grain, a chemical reaction begins. The calcium carbonate that makes up the shell starts to dissolve, while new minerals containing rare earth elements begin to crystallise in its place. Over time, a thin layer forms, like a kind of mineral “skin” that coats the grain.

Using a high-resolution microscope, we observed this process in detail. Tiny crystals first appear as needle-like structures, then grow and merge into a continuous crust. In some cases, this crust eventually blocks further reaction, effectively shutting down the process.

But not all shells behave the same way: oyster shells, it turns out, have a unique internal structure. They are made of thin layers and porous, chalky regions that allow water and dissolved elements to circulate more freely. This means the reaction does not stop at the surface. Instead, it continues inward, gradually replacing the entire shell.

Under the right conditions, 1g of oyster shells can capture and lock away up to around 1.5g of the rare earth elements present in the solution. Rather than simply sticking to the surface, these elements become part of a new, stable carbonate mineral.

From pollution control to resource recovery

Many materials used in water treatment rely on adsorption, the process whereby contaminants bind or “adsorb” to a surface. But in this case, it’s a process called full mineral transformation that incorporates the rare earth elements into solid crystals. This makes them far less likely to be released back into the environment.

Once captured, these elements could follow different paths. The material could be potentially processed further to recover the metals. Because they are concentrated in a solid phase, established chemical extraction methods could, in principle, be used to recycle them. Potentially, those waste shells could be used not only to clean up pollution, but also to recover valuable resources that would otherwise be lost.

There is no shortage of seashells. Nature makes them for free. Global shellfish aquaculture produces vast quantities of shell waste each year, much of which ends up in landfill or stockpiled near coastlines. Crushed shells could be used in filtration systems, treatment beds or permeable barriers, where contaminated water flows through reactive material. These approaches are already commonly used in water treatment, for example for the removal of heavy metals from seawater.

The challenge lies in maintaining efficiency. Some shell types quickly develop impermeable coatings that limit their effectiveness. Our results suggest that oyster shells, thanks to their structure, are particularly well suited to overcoming this limitation.

Making this technology work on a larger scale will depend less on finding new materials and more on designing systems that let as much water as possible come into contact with the active surfaces, while preventing those surfaces from becoming blocked or less effective over time.

This approach alone will not reduce the need for mining rare earth elements. Global demand for these materials is vast and growing very rapidly. However, that does not make this solution insignificant. It can help support a less wasteful and more “circular” approach to critical materials by offering a way to capture rare earth elements from waste streams, reduce environmental contamination and potentially recover part of what is currently lost during processing.

Scaling this approach from the lab to real-world applications requires testing under more complex conditions, as industrial wastewaters contain mixtures of metals, variable chemistry and flowing systems. Pilot-scale studies are needed to assess performance, durability and how quickly shell fragments develop a rare earth-rich mineral coating, like an armour, that blocks further reaction with the water.

Practical questions also matter: how much processing (cleaning, crushing) is truly necessary, and can it be done cost-effectively at scale? If rare earth recovery is the goal, efficient methods must be developed to extract them from the newly formed minerals. Addressing these challenges will determine whether this becomes a viable large-scale solution.

Juan Diego Rodriguez-Blanco receives funding from Science Foundation Ireland (Research Ireland), Geological Survey Ireland and the Environmental Protection Agency (Ireland).