A new study suggests using hydrogen plasma to extract metals from deep-sea nodules could reduce carbon emissions compared to traditional methods. This approach aims to make deep-sea mining more sustainable amid growing demand for battery metals. However, critics emphasize the risks to marine biodiversity.
Polymetallic nodules, about the size of tennis balls, litter parts of the ocean floor and contain manganese, nickel, copper, and cobalt—key materials for batteries and wiring in solar panels and electric vehicles. As demand surges, deep-sea mining proposals have sparked controversy over potential damage to the planet's last pristine ecosystems.
Ubaid Manzoor at the Max Planck Institute for Sustainable Materials in Germany led research published in Science Advances, arguing that inevitable mining should use cleaner extraction. "I think there is a good chance that someday people… will mine the nodules," Manzoor said. "So better to have a good process [for extracting metals] after mining than to have one more dirty process."
The proposed method grinds nodules into pellets and processes them in an arc furnace with hydrogen and argon gas, creating plasma hotter than 1700°C. Hydrogen ions strip oxygen from metal oxides, yielding pure alloys and by-products like water, manganese oxide, and manganese silicates usable for batteries and steel. Using green hydrogen from renewable-powered water splitting and renewable electricity for the furnace could eliminate CO2 emissions.
In contrast, The Metals Company, a Canadian firm seeking mining permits, relies on coke and methane, emitting 4.9 kilograms of CO2 per kilogram of metals via kilns and arc furnaces.
Land-based mining offers metals at concentrations 10 times lower than seafloor nodules, often requiring vast earth-moving and sulphuric acid, which can devastate rainforests and rivers. Yet Mario Schmidt at Pforzheim University in Germany contends that regulated land mining with green processes might match deep-sea sustainability on carbon grounds. "We do not see any fundamental advantage for deep-sea mining in terms of carbon footprint," Schmidt said. "The sustainability of deep-sea mining fails because of the threat it poses to the biodiversity of deep-sea flora and fauna."
David Dye at Imperial College London sees potential economic benefits. "In addressing how you would do the extraction metallurgy downstream of actually picking it up off the seabed, you may be able to then open up the business case and the environmental case to make that attractive," he noted.
Manzoor clarifies the work does not endorse mining and calls for thorough environmental studies.