Acid mine drainage is accelerated and perpetuated by acidophilic bacteria such as Thiobacillus which derive energy from the oxidation of inorganic compounds. But nature always seeks balance and provides the means to correct the problem.
Bacteria such as Desulfovibrio are sulphate reducers which reverse the effects of the acidophiles. They oxidize organic materials by using the sulphate ion as an electron acceptor. This produces sulphide (S-) which reacts with metal ions, immobilizing both the sulphur and metals as metal sulphides and bicarbonate ions which buffer the pH around neutrality, further inducing the precipitation of metals.
Boojum research puts this process of Acid Reduction Using Microbiology (ARUM) to work on mine sites.
Sulphate-reducing bacteria (SRB) are ubiquitous in the environment. They thrive in the midst of rich deposits of organic carbon and in the absence of oxygen. For example, sediments at the bottom of water bodies are ideal habitats for SRB, as are wet, humus-rich soils. Unfortunately, such habitats are scarce on mine sites where soils are pushed aside by heavy equipment or buried by waste rock.
Frequently, the first task undertaken on-site by Boojum is to recreate an environment within which ARUM can occur. Drainage ditches and erosion gullies are damned to slow the escape of contaminated water. Organic matter is added to the resulting pond to begin the formation of anaerobic sediments. Sloping tailings deposits are terraced to hold moisture and provide a foothold for naturally-occurring indigenous plants which begin to build up soils. Floating Wetlands and muskegs may be utilized to reduce acidity and lower the level of contamination in mine run-off and groundwater.
ARUM was developed with the assistance of the Canadian MEND program. Technical reports are available at MEND and Laurentian Library.