American Scientist

To the Editors:

I enjoyed Roger P. Smith’s article “A Short History of Hydrogen Sulfide” (January–February). Many may not know that the gas plays productive roles in several geologic settings. First, hydrogen sulfide occurs as a minor constituent in most natural gas deposits and must be removed. It is then oxidized to elemental sulfur, a process that produces virtually the sole source of sulfur in North America. Previously, “biogenic” sulfur had to be mined by the Frasch process primarily in Gulf Coast salt domes.

Hydrogen sulfide also plays an important role in forming metallic- sulfide ores of zinc, lead and copper. The bearing fluids of these base metals must encounter a source of hydrogen sulfide (either biogenic or magmatic) along their flow path to precipitate metal-sulfide minerals. Alternatively, volcanic hydrogen sulfide helps form ores of gold and silver, as the precious metals form stable aqueous complexes with hydrogen sulfide, greatly enhancing their solubility in ore fluids. Precious metals often precipitate when the hydrogen sulfide is destroyed by a number of processes, including boiling, which puts hydrogen sulfide into the vapor phase. Hydrogen sulfide can also be oxidized by certain bacteria to make sulfuric acid, which is thought to be important in cave formation. Volcanic hydrogen sulfide from hot springs at mid-ocean ridges becomes the basis for complex biological communities where chemosynthetic (chemical producing) bacteria use it and carbon dioxide. Finally, we use hydrogen sulfide produced by stimulating sulfate-reducing bacteria to remediate groundwater contaminated by metals, arsenic and radionuclides (US Patent 5,833,855). With hydrogen sulfide, one should consider its good, bad and smelly aspects!

Jim Saunders
Auburn University