#EBSstories Trace metals: from the sea floor to the beamline


How does thallium, a rare mineral used in clean energy technology, accumulate in high concentrations in the bottom of the sea? To answer this question, marine geochemist Andrea Koschinsky has come to the ESRF’s ID26.

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“Trace metals are very important because they can play a central biological role in many organisms in the sea, but they are also important in developing modern technology, such as wind power or photovoltaics, to fight against climate change”, explains Andrea Koschinsky, professor of marine geosciences at Jacobs University in Bremen (Germany).

One of these trace metals is thallium, which occurs in ferromanganese crusts and nodules that cover the surface of seafloors throughout the oceans. Thallium is enriched 107 times in ferromanganese deposits compared to seawater, but scientists still do not know the exact geochemical processes responsible for this.

Koschinsky, together with her collaborator and professor of the University Grenoble Alpes Alain Manceau, just finished an experiment on ID26 analysing thallium in ferromanganese mineralisations from the ocean floor.

The samples came from research expeditions in huge vessels where Koschinsky would spend 4-6 weeks taking samples from different oceans using robots that are deployed at the bottom of the sea. The specific location and growth conditions of the samples, ranging from the Pacific, to the Atlantic and Indian oceans, impacts the quantity of thallium found in the deposits.

It was the first time that the technique of X-ray absorption spectroscopy was used to study thallium in its natural environment. Although Koschinsky had to follow the experiment remotely from Bremen due to Covid-19 restrictions, Manceau, who is based in Grenoble, could be on the beamline with the staff. “We’ve already looked at the first data and it looks very promising”, Koschinsky says. And she adds: “With the new EBS and the high-reflectivity crystal analyser, we can now study these metals in their natural habitat and so we’ve been able to separate the thallium from the interfering arsenic, which occurs in significant concentrations in the same sample”. The team hopes the data will help to disentangle the different enrichment mechanisms of the metal in oxic hydrogenetic and suboxic diagenetic ferromanganese deposits.

Andrea Koschinsky onboarad RV SONNELOW.jpg Jayet_ID26_Dec2016-19low.jpg

From the boat to the beamline: Andrea Koschinsky in one of her expeditions (left) and Pieter Glatzel and Blanka Detlefs on ID26 (right). Credits: A. Koschinsky (left) and P. Jayet (right). 

All this information will be useful to learn about the past of our planet and how conditions have changed in the ocean over up to millions of years. It will also be of relevance to mineral extraction and processing. “Extracting thallium from the seafloor is not happening today, but in some years’ time it might be a reality, as it is a scarce metal and used in many electronic or optic applications. The more we know about it, the better we’ll be able to find the best ways to extract it with minimal disturbance to the ecosystem”, concludes Koschinsky.

Text by Montserrat Capellas Espuny.

Video by Montserrat Capellas Espuny and Mark McGee. 

Top image: A piece of ferromanganese crust taken in one of Koschinsky's expeditions. Credit: A. Koschinsky