Biogeochemistry of Acid Drainage

This chapter begins with a discussion on the sulfur cycle on a global scale. It then focuses on smaller scales and the associated complexity within which iron sulfide oxidation occurs. The chapter describes the nanoenvironment scale where bacteria such as Acidithiobacillus ferrooxidans, a common rod-shaped acidophile, exists. At the scale of a bacterium, electrons are transferred in a series of redox reactions to energize iron- and sulfide-oxidizing microbes. Various microbial processes, the generation of acid drainage under pH-neutral conditions, and genetic studies are reviewed. The chapter talks about microbial growth conditions, and reviews microbial processes. Today some of the highest incidences of acid drainage occur at the countless abandoned mine sites throughout the world and at operational mines where sulfide oxidation mitigation measures have failed to prevent the release of acid drainage to downgradient surface waters.