Wetlands for remediation of acidmine drainage Alyssa Shiel

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Wetlands for remediation of acid-mine drainage Alyssa Shiel

Wetlands for remediation of acid-mine drainage Alyssa Shiel

Overview n n Define acid-mine drainage Constructed wetlands as passive treatment systems Acid-tolerant aquatic

Overview n n Define acid-mine drainage Constructed wetlands as passive treatment systems Acid-tolerant aquatic plants Benhar ironstone mine spoil in Central Scotland

Acid-mine drainage Drainage flowing from or caused by mining that is typically highly acidic

Acid-mine drainage Drainage flowing from or caused by mining that is typically highly acidic with elevated metal levels n Increased concentrations of cadmium, nickel, lead, zinc, copper and sulfates n The primary source of freshwater metal contamination n Associated with land contamination and sparse vegetation n May leach into surrounding watercourses n

Acid-mine drainage n n n Lowers p. H, between 2. 0 and 3. 0

Acid-mine drainage n n n Lowers p. H, between 2. 0 and 3. 0 Contaminates water with oils, cyanides, acids and alkalies Reduces buffering capacity Alters phosphorus availability Solubilizes some heavy metals

Constructed wetlands as treatment systems n n n Viable treatment system for many mining

Constructed wetlands as treatment systems n n n Viable treatment system for many mining regions of the world Passive, low-cost remediation Goals n Removal of iron from the water column n Removal of other metals n Sulfate reduction n Alleviation of extreme acidic conditions

Acid tolerant aquatic species n n Typha sp. (cattails) Sphagnum dominates n Found to

Acid tolerant aquatic species n n Typha sp. (cattails) Sphagnum dominates n Found to accumulate iron n Green algaes n Chlamydomonas aplanata (<3) n Blue-green algaes n Spirulina nordstedtii (4. 9) n Diatoms n Navicula nivalis (3. 0) (M. Kelly, 1988)

Benhar ironstone spoil heap in Central Scotland • Acidic metal-rich drainage from reclaimed ironstone

Benhar ironstone spoil heap in Central Scotland • Acidic metal-rich drainage from reclaimed ironstone mine spoil • 12 month evaluation of a constructed wetland system (Heal and Salt, 1999)

Benhar before remediation

Benhar before remediation

Ironstone spoil n n n Characterized by p. H 2. 7 and 247 mg/l

Ironstone spoil n n n Characterized by p. H 2. 7 and 247 mg/l total Fe Highly acidic with elevated metal concentrations Acidity may mobilize iron, manganese, aluminum and other metals Although mining ceased early in the 20 th Century, the Bing has remained mostly unvegetated due to the highly acidic and infertile spoil Mine drainage was polluting a small watercourse which leads into the River Almond

Ironstone spoil Iron pyrites in ironstone and coal spoil are oxidized to form sulfuric

Ironstone spoil Iron pyrites in ironstone and coal spoil are oxidized to form sulfuric acid when exposed to air and water n At p. H above 4, acid production proceeds slowly and is controlled by the rate of oxygen diffusion into the spoil n Below p. H 4, an alternative oxidation pathway exists involving the bacterium Thiobacillus ferrooxidans n

Treatment Creating an aesthetically-pleasing landform n Treatment with dried pelleted sewage sludge, limestone and

Treatment Creating an aesthetically-pleasing landform n Treatment with dried pelleted sewage sludge, limestone and peat n After which trees were planted Betula pubescens and Alnus glutinosa (common alder) n Construction of settling pond and surface flow wetland to receive spoil drainage n Mushroom compost substrate n Cattails (Typha latifolia). n

Reclamation n n Acidity, iron, manganese and aluminum concentrations declined Removed on average 33%

Reclamation n n Acidity, iron, manganese and aluminum concentrations declined Removed on average 33% of acidity and 20 -40% of metal inputs Removal rates decreased in the winter Enabled vegetation establishment Effect was spatially variable

Summary Constructed wetlands offer an inexpensive, passive treatment for acid-mine drainage n Several acid-tolerant

Summary Constructed wetlands offer an inexpensive, passive treatment for acid-mine drainage n Several acid-tolerant aquatic species including Sphagnum and Typha sp. n Benhar mine spoil n Site history n Treatment n Results n