Have we found a greener way to do deep-sea mining?

The process of extracting metals from ore using hydrogen could make deep-sea mining of valuable materials more sustainable than mining on land, a new study claims.

Rows ocean floor dotted with nodules the size of tennis balls. These polymetallic nodules are composed primarily of manganese with small amounts of nickel, copper and cobalt, among other elements. As solar energy and electric vehicle construction boom, demand for these metals is growing as they are vital components of batteries and wiring. But plans to mine polymetallic nodules are controversial because harvesting operations could potentially harm the deep seabed, one of the last intact ecosystems on Earth.

Despite this, some researchers suspect that deep-sea mining will eventually occur. “I think there's a good chance that someday people… will mine for nodules,” he says. Ubaid Manzoor at the Max Planck Institute for Sustainable Materials in Germany. “So it's better to have a good process [for extracting metals] after mining rather than having another messy process.”

Metallurgical companya Canadian deep-sea mining company that has applied for a deep-sea mining permit from the Trump administration, plans to extract metals using a fossil fuel-based approach using coke and methane. His process involves placing the nodules first in a kiln and then in an electric arc furnace—a greener alternative to a traditional blast furnace. Despite this, the company says its approach will result in 4.9kg of carbon dioxide emissions for every 1kg of valuable metals.

Manzoor and his colleagues have found a way to reduce emissions associated with mining. Their system does not include the furnace. Instead, the nodules will be crushed into smaller granules and placed directly into an arc furnace, which also contains hydrogen and argon. High-energy electrons flowing from the electrode in the oven to the pellets knock electrons out of the hydrogen gas molecules, forming a plasma that can be heated to temperatures in excess of 1700°C.

The hydrogen ions in the plasma then react with the oxygen in the granules, removing oxides from the alloy and leaving behind pure metal. Besides water, the only byproducts are manganese oxide and manganese ligates, which can be used to make batteries and steel.

If the hydrogen gas used in the furnace is “green”—that is, it is produced by splitting water with electricity from renewable sources—and the electricity to run the furnace is generated from renewable sources, then the process should not emit CO2, according to the researchers. Today, the vast majority of hydrogen is produced using fossil fuels.

Metals such as manganese are found both on land and on the seabed, but in concentrations about 10 times lower. Mining them on land involves moving large volumes of earth, and extracting the metal from the ore is often done using sulfuric acid. This process can lead to the destruction of tropical forests and polluted rivers.

However, land-based mining could be better regulated to prevent environmental destruction, and metal smelting could be done using green hydrogen and renewable electricity rather than fossil fuels, he argues. Mario Schmidt at the University of Pforzheim in Germany. At this point, vacuuming up nodules from the seafloor is not necessarily more sustainable.

“We don't see any fundamental benefit from deep sea mining in terms of carbon emissions,” he says. “The sustainability of deep-sea mining is failing because of the threat it poses to the biodiversity of deep-sea flora and fauna.”

But the process developed by Manzoor and his colleagues could help deep-sea mining become more economically viable, according to David Dye at Imperial College London.

“By deciding how you go about extracting the metallurgy after actually collecting it from the seabed, you can perhaps then uncover the business case and the environmental case to make it attractive,” he says.

Manzoor stresses that the study is not intended to promote deep-sea mining and the environmental impacts need to be fully examined.