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Geologic hydrogen is discovered in a chromite mine

Geologic hydrogen is discovered in a chromite mine

8 February 2024

The naturally occurring gas appears to be forming from subsurface rock–water interactions and from a leaky fault in deeply buried oceanic crust.

Buildings nestled along a hillside.
Beneath Bulqizë, Albania, lies chromite-rich ore, and researchers recently found naturally occurring hydrogen gas there. Credit: Albinfo/Wikimedia Commons/CC BY-SA 3.0

For all the promise of hydrogen as an alternative energy source, not all of it is created equal. Most commercially produced H2 is a byproduct of fossil-fuel processing, which pollutes the atmosphere with carbon dioxide. So-called green H2 is made by splitting water with energy from solar panels or wind turbines, but that method is expensive.

A much cheaper possibility is extracting naturally occurring H2 from deep underground reservoirs. One well-known site in Mali was discovered in 1987 when well diggers were drilling for water—and others are likely in Oman and Turkey, based on observations of H2 seeps at the surface. As long as the light, reactive element is contained by salt layers or other rock formations that trap gas, it could be burned to produce carbon-free energy. The Malian H2 was of sufficient purity and flowed fast enough to power a 30-kilowatt generator.

Now Laurent Truche of Grenoble Alpes University in France and his colleagues have characterized another source of geologic H2 located in a chromite mine 620 m below Bulqizë, Albania. The flow rate of the H2 deposit is an order of magnitude higher than at similar outgassing sites in Oman and Turkey, and the purity of the flow, about 84% H2 by volume, means that the H2 could readily fuel a gas turbine to produce energy. The company that owns the Bulqizë mine, Albania-based AlbChrome, gave the researchers access to the mine. Working for six years using a network of 38 boreholes, they measured a relatively constant H2 flow rate of some 200 tons annually.

A schematic of the Bulqizë chromite mine.
The schematic of the Bulqizë chromite mine shows (A) the location of the hydrogen-rich fault zone and (B) the various vertical levels where researchers collected outgassing measurements. Credit: From L. Truche et al., Science 383, 618 (2024)

The Bulqizë mine consists predominantly of uplifted oceanic crust, which geologists call an ophiolite. Truche and colleagues identified several types of rocks and minerals in the Bulqizë ophiolite. When exposed to the high pressures and temperatures in the subsurface, the minerals can react with water to form other minerals, methane, and H2. That process appears to be happening now in the mine, but the researchers say that some of the H2, which is leaking from a deep fault zone, may have formed from previous chemical reactions between 160 million to 165 million years ago.

Ophiolites elsewhere may also have H2, but Truche cautions that “one must consider the drawbacks of H2 exploitation. These geological environments harbor a fragile deep biosphere that relies on H2 as an energy source.” Safety is a concern too: Three major gas explosions, the most recent one last year, have rocked the mine since seeping H2 was discovered there in 1992. Although safety precautions have improved, says Truche, “the risk is still there.” (L. Truche et al., Science 383, 618, 2024.)

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