Researchers crushed mussel, cockle and oyster shells collected from a Dublin beach and added them to polluted water; the experiment cleaned the water while recovering valuable metals

Researchers have identified a potentially low-cost way to clean water contaminated with rare earth metals — using discarded seashells instead of added chemicals.

A team from the Department of Geology at Trinity College Dublin and iCRAG (Irish Centre for Research in Applied Geosciences) found that oyster shells can remove rare earth elements from polluted water by transforming them into new solid minerals. The process could potentially address two problems at once: water contamination and the growing volume of shell waste generated by the aquaculture industry. The research was published in the peer-reviewed journalScience of the Total Environment.

How the shell-based process works

The researchers collected mussel, cockle and oyster shells from a beach in Dublin. They cleaned, dried and crushed the shells into small grains before exposing them to solutions containing three rare earth elements: lanthanum, neodymium and dysprosium. The concentrations were deliberately selected to represent heavily contaminated water.


The chemistry behind the process is relatively straightforward. Seashells are primarily made of calcium carbonate. When exposed to rare-earth-rich water, the calcium carbonate gradually dissolves and is replaced by new solid minerals incorporating the rare earth elements. In other words, the shells do not simply absorb the metals like a sponge. Instead, the original shell is gradually transformed, mineral by mineral, into a new material containing the rare earth elements.

“The process is entirely mineral-driven – the shells naturally transform dissolved rare earth elements into new solid minerals,” principal investigator Juan Diego Rodriguez-Blanco said. He added that the process does not require substantial financial investment or sophisticated technical equipment.

The findings suggest that shell waste could potentially become a useful raw material for treating contaminated water.

Why oyster shells performed better

The three types of shells did not behave in exactly the same way.

Oyster shells proved to be the most effective because of their porous, layered microstructure. This structure allowed the dissolve-and-replace reaction to penetrate deeper into the shell grains.

Mussel and cockle shells behaved differently. A new mineral crust formed rapidly on their outer surfaces, eventually becoming impermeable and preventing the reaction from progressing into the interior.

As a result, more than half of the original mussel and cockle shell remained unchanged after the outer layer became sealed. The finding highlights how the microscopic structure of a material can determine whether a seemingly simple chemical process works effectively.

Why rare earth metals matter

Rare earth elements are essential to many modern technologies. They are used in permanent magnets found in wind turbines and electric motors, as well as in electronics and other high-tech components. Recovering these elements is increasingly important because conventional mining and processing can be costly and environmentally damaging. Industrial activities can also generate wastewater containing dissolved metals.

The shell-based approach offers an intriguing possibility: instead of treating shell waste as something to discard, it could potentially be used to recover valuable metals while simultaneously reducing contamination in wastewater.

The scale of the waste problem is considerable. As first author Rémi Rateau noted, the global aquaculture industry generates millions of tonnes of shell waste each year, much of which is discarded or sent to landfill. Rateau also said that relatively small quantities of shell waste could potentially remove substantial amounts of rare earth metals from contaminated water, highlighting the possibility of turning an abundant waste product into a useful resource.

A promising result, but not yet an industrial solution

Though the research had promising results, its real-life usage is still debatable. For instance, the experiment was conducted at temperatures ranging from 25°C to 205°C, with reactions continuing for as long as three months. It conducted under controlled laboratory conditions and the rare earth concentrations were intentionally high, and real industrial wastewater is considerably more complicated. It can contain mixtures of competing ions, organic compounds and fluctuating pH levels that could affect the reaction.

The researchers therefore emphasize that further testing is needed. Pilot-scale experiments using genuine industrial wastewater would be necessary before the approach could be considered a practical cleanup technology. For now, the findings represent a promising lead rather than a ready-to-deploy solution. Still, the underlying idea is notable. A material that is widely treated as waste could potentially help remove strategically important metals from contaminated water while recovering those metals in solid form.

However, as Rodriguez-Blanco put it, the research could help scientists “start designing” low-cost strategies for removing critical metals from contaminated water while giving new value to a major waste product. That wording is fitting: the study may not have produced a finished technology, but it points toward a surprisingly simple way of turning two environmental problems — shell waste and metal contamination — into part of the same solution.