Biological Remediation of Acid Mine DrainageJarno Laitinen M.Sc. Tech., M.Sc. Econ.

Vice PresidentDoranova Oy

Acid Mine Drainage

Background

Acid Mine Drainage– Refers to outflow of acidic waters from mines and tailings– Mainly caused by pyrite oxidation to sulphuric acid– Often contains concentrations of metals and metalloids– And solids, cyanides, explosives, …

Photo: AMD http://clevergreen.co.za/wp-content/uploads/2010/12/acid-mine-drainage.jpg)

Laitinen, Jarno – Acid Mine Drainage @ EuroMining 2013, Tampere (FIN) Slide 3

Properties and Kinetics

Basic Reaction Kinetics

2FeS2 + 2H2O + 7O2 = 2Fe2+ + 4SO42– + 4H+

(aq) Pyrite + water + oxygen = ferrous iron + sulfate + acid

Physico-Chemical properties– Generally, a low pH and above average temperature– At extremes, pH as low as -3.6 and temp. up to 46

deg.C

Laitinen, Jarno – Acid Mine Drainage @ EuroMining 2013, Tampere (FIN) Slide 4

Impacts

Effects to Nature– Impacts ecosystems eg. through

acidity, oxygen depletion, metals precipitation and leaching

– Decreases aquatic life and vegetation

– Long term impacts that can spread wide

– Natural bacteria may assist breakdown of sulphide minerals thus accelerating AMD formation

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Laitinen, Jarno – Acid Mine Drainage @ EuroMining 2013, Tampere (FIN) Slide 5

Managing Acid Mine Drainage

Management Approaches

Laitinen, Jarno – Acid Mine Drainage @ EuroMining 2013, Tampere (FIN) Slide 7

Remediating the changes caused by

AMD plume dispersion

Preventing or minimizing the formation and

spread of AMD

Combining the prevention and

remediation

Prevention by Source Control

Could be implemented by– Sealing/Flooding and Coating the abandoned deep mines

to prevent the oxidation reactions from happening – Applying anionic surfactants to prevent the microbial

actions assisting in dissolving sulphides in the ground , e.g. sodium dodecyl sulphate

– Blending of acid-generating and acid –consuming materials to react producing benign cover, e.g. adding apatite to pyritic mine waste reducing oxidizing of sulfide minerals

Laitinen, Jarno – Acid Mine Drainage @ EuroMining 2013, Tampere (FIN) Slide 8

Abiotic Plume Remediation

Active abiotic treatment systems– Aeration and chemical addition, ion exchange, reverse osmosis– used during production– creates costs in operation / disposal of sludge– needs resources during production

Passive abiotic treatment systems– Based on naturally occurring reactions to decrease metal

concentrations and neutralize acidity– e.g. anoxic limestone drains– requires land area – low maintenance costs, expensive to install– low maintenance need

Laitinen, Jarno – Acid Mine Drainage @ EuroMining 2013, Tampere (FIN) Slide 9

Bacteria are the dark matter of the biological world, with 4 million mostly unknown species in a ton of soil- Edward O. Wilson

Sulphate Reducing Bacteria

Sulphate Reducing Bacteria– Comprise several groups of bacteria that reduce sulphate to

sulphide and produce carbonate which increase the pH.– Uses the biogenic production of hydrogen sulfide to form alkalinity

and to remove metals– This chemically stabilizes the toxic metal ions as solid metal

sulphides

Laitinen, Jarno – Acid Mine Drainage @ EuroMining 2013, Tampere (FIN) Slide 11

Schematic representation of biolgoical sulfate reduction followed by biological partial sulfide oxidatio http://wiki.biomine.skelleftea.se

Biological Plume Remediation

Active biological treatment systems– Off-line sulfidogenic bioreactors– Uses the biogenic production of hydrogen sulfide to form

alkalinity and to remove metals– Reactors are constructed and operated to optimise production

of hydrogen sulphide

Passive biological treatment systems– Aerobic wetlands – Compost reactors (anaerobic wetlands)– Combination of aerobic and anaerobic wetlands– Permeable reactive barriers– Packed bed iron-oxidation bioreactors

Laitinen, Jarno – Acid Mine Drainage @ EuroMining 2013, Tampere (FIN) Slide 12

Aerobic Wetlands

Aerobic Wetlands– are used for treating alkaline mine waters– Effectiveness may be improved by combining with e.g. an anoxic

limestone drain– Removal of arsenic, adsorption onto ferric iron colloids and

possible oxidation from As(III) to As (V) with help of bacteria– is a passive treatment system

Laitinen, Jarno – Acid Mine Drainage @ EuroMining 2013, Tampere (FIN) Slide 13

Photo: Laguna de Rocha, the largest wetland in the urban area in Esteban Echeverría Partido, Argentina.

Compost Bioreactor

Compost Bioreactor– May be used for net acidic and metal-rich mine waters– Use organic materials according to local supply and should not

support any macrophytes – Water runs through the compost and strips of dissolved oxygen– Microbially catalysed reactions cause net alkalinity and

biogenic sulfide

Laitinen, Jarno – Acid Mine Drainage @ EuroMining 2013, Tampere (FIN) Slide 14

Compost bioreactor schematic redrawn adapted from Johnson and Hallberg, 2005

Permeable Reactive Barrier

Permeable reactive barriers– used for treating polluted groundwater on site– using reactive materials e.g. organic solids and limestone– reductive microbiological processes increase alkalinity and

remove metals as sulfides, hydroxides and carbonates – are passive systems

Metal retention. Geoscienceworld.com

Laitinen, Jarno – Acid Mine Drainage @ EuroMining 2013, Tampere (FIN) Slide 15

Permeable Reactive Barrier

Examples of permeable reactive barriers. ITRC 2005

Laitinen, Jarno – Acid Mine Drainage @ EuroMining 2013, Tampere (FIN) Slide 16

Thank you for your interestFor more information:E-mail: jarno.laitinen@doranova.fiPhone: +358 44 355 8236Internet: www.doranova.fi