The Digester

Hydrogen plasma could cut smelting emissions for deep-sea metals

Mar 20th 2026

A new lab process uses hydrogen plasma to extract metals from seabed polymetallic nodules and could cut smelting emissions to zero if powered by green hydrogen and renewable electricity, but lower smelting emissions do not remove the major ecological risks of mining the deep ocean.

  • Hydrogen plasma smelts ground polymetallic nodules by stripping oxygen with hydrogen at temperatures above 1700°C, yielding water and usable manganese compounds as main by-products.
  • If the hydrogen and electricity come from renewable sources, the process could produce no CO2 from smelting.
  • A commercial alternative that uses coke and methane is estimated to emit about 4.9 kg of CO2 per 1 kg of valuable metals.
  • Most hydrogen today is made from fossil fuels, so real emissions depend on sourcing green hydrogen and renewable power.
  • Land mining has lower ore grades and large environmental impacts but can be regulated and also adopt green smelting, removing any clear carbon advantage for seabed mining.
  • Independent environmental assessments are still needed because smelting emissions do not address the serious biodiversity risks of deep-sea mining.

Articles