Acid mine drainage remediation options: a review
Section snippets
Acid mine drainage: nature of the problem
Acidic sulfur-rich wastewaters are the by-products of a variety of industrial operations such as galvanic processing and the scrubbing of flue gases at power plants (Johnson, 2000). The major producer of such effluents is, however, the mining industry. Waters draining active and, in particular, abandoned mines and mine wastes are often net acidic (sometimes extremely so). Such waters typically pose an additional risk to the environment by the fact that they often contain elevated concentrations
“Source control” vs. “migration control” options
Given the axiom that “prevention is better than cure”, it is generally preferable, although not always pragmatic, to preclude the formation of AMD in the first instance. Such techniques are known collectively as “source control” measures (Fig. 1) and will be described only briefly.
In as much as both oxygen and water are required to perpetuate the formation of AMD, it follows that by excluding either (or both) of these, it should be possible to prevent or minimise AMD production. One way in
Active technologies
The most widespread method used to mitigate acidic effluents is an active treatment process involving addition of a chemical-neutralising agent (Coulton et al., 2003b). Addition of an alkaline material to AMD will raise its pH, accelerate the rate of chemical oxidation of ferrous iron (for which active aeration, or addition of a chemical oxidising agent such as hydrogen peroxide, is also necessary), and cause many of the metals present in solution to precipitate as hydroxides and carbonates.
Significant biological processes
The basis of bioremediation of AMD derives from the abilities of some microorganisms to generate alkalinity and immobilise metals, thereby essentially reversing the reactions responsible for the genesis of AMD. While in aerobic wetlands constructed to treat AMD, macrophytes such as Typha and Phragmites spp. are the most obvious forms of life present, their direct roles in improving water quality have been questioned (Johnson and Hallberg, 2002).
Microbiological processes that generate net
Active biological systems: sulfidogenic bioreactors
Off-line sulfidogenic bioreactors represent a radically different approach for remediating AMD (Johnson, 2000, Boonstra et al., 1999). These engineered systems have three potential advantages over passive biological remediation: (i) their performance is more predictable and readily controlled; (ii) they allow heavy metals, such as copper and zinc, present in AMD to be selectively recovered and reused; and (iii) concentrations of sulfate in processed waters may be significantly lowered. On the
Remediation options: factors in decision making
The choice of which option to use to remediate AMD is dictated by a number of economical and environmental factors. Sometimes the true environmental cost of a remediation system is not immediately apparent. One such cost is the amount of fossil fuel energy needed to transport liming materials, often long distances from source to mine sites (such as at the Wheal Jane mine in Cornwall, where the lime is transported several hundred kilometres from a site in the midlands of England). Traditionally,
Acknowledgements
The authors would like to acknowledge the financial support received from the LINK directorate (Grants # BTL/70/21 and 5/BRM18412) in supporting their research programmes into bioremediation of mine waters.
References (31)
- et al.
Biological treatment of acid mine drainage
- et al.
Biodiversity of acidophilic microorganisms
Adv. Appl. Microbiol.
(2001) - et al.
The microbiology of acidic mine waters
Res. Microbiol.
(2003) - et al.
Ecological engineering methods for acid-mine drainage treatment of coal wastes
Resour. Conserv. Recycl.
(1991) - et al.
The Geco process: a new high density sludge treatment for acid mine drainage
- et al.
An arsenic(III)-oxidizing bacterial population: selection, characterization, and performance in reactors
J. Appl. Microbiol.
(2002) - et al.
A full-scale porous reactive wall for prevention of acid mine drainage
Ground Water Monit. Remediat.
(1997) Coal Mining and Water Quality
(1995)- et al.
Wheal Jane mine water active treatment plant-design, construction and operation
Land Contam. Reclam.
(2003) - et al.
The design and optimization of active mine water treatment plants
Land Contam. Reclam.
(2003)