Wetlands for Wetlands for remediation of remediation of

acid-mine drainageacid-mine drainageAlyssa ShielAlyssa Shiel

OverviewOverview Define acid-mine Define acid-mine

drainagedrainage Constructed Constructed

wetlands as wetlands as passive passive treatment treatment systemssystems

Acid-tolerant Acid-tolerant aquatic plantsaquatic plants

Benhar ironstone Benhar ironstone mine spoil in mine spoil in Central ScotlandCentral Scotland

Acid-mine drainageAcid-mine drainage

Drainage flowing from or caused by Drainage flowing from or caused by mining that is typically highly acidic mining that is typically highly acidic with elevated metal levelswith elevated metal levels

Increased concentrations of cadmium, Increased concentrations of cadmium, nickel, lead, zinc, copper and sulfatesnickel, lead, zinc, copper and sulfates

The primary source of freshwater The primary source of freshwater metal contaminationmetal contamination

Associated with land contamination Associated with land contamination and sparse vegetationand sparse vegetation

May leach into surrounding May leach into surrounding watercourseswatercourses

Acid-mine drainageAcid-mine drainage

Lowers pH, between Lowers pH, between 2.0 and 3.02.0 and 3.0

Contaminates water Contaminates water with oils, cyanides, with oils, cyanides, acids and alkaliesacids and alkalies

Reduces buffering Reduces buffering capacity capacity

Alters phosphorus Alters phosphorus availabilityavailability

Solubilizes some Solubilizes some heavy metalsheavy metals

Constructed wetlands as Constructed wetlands as treatment systemstreatment systems

Viable treatment Viable treatment system for many mining system for many mining regions of the worldregions of the world

Passive, low-cost Passive, low-cost remediationremediation

GoalsGoals Removal of iron from Removal of iron from

the water columnthe water column Removal of other Removal of other

metalsmetals Sulfate reductionSulfate reduction Alleviation of extreme Alleviation of extreme

acidic conditionsacidic conditions

Acid tolerant aquatic Acid tolerant aquatic speciesspecies

Typha sp.Typha sp. (cattails) (cattails) SphagnumSphagnum dominates dominates

Found to accumulate ironFound to accumulate iron Green algaesGreen algaes

Chlamydomonas aplanataChlamydomonas aplanata (<3)(<3)

Blue-green algaesBlue-green algaes Spirulina nordstedtiiSpirulina nordstedtii (4.9) (4.9)

DiatomsDiatoms Navicula nivalisNavicula nivalis (3.0) (3.0)

(M. Kelly, 1988)

(Heal and Salt, 1999)

•Acidic metal-rich drainage from reclaimed ironstone mine spoil

•12 month evaluation of a constructed wetland system

Benhar ironstone spoil Benhar ironstone spoil heap in Central Scotlandheap in Central Scotland

Benhar before Benhar before remediationremediation

Ironstone spoilIronstone spoil Characterized by pH 2.7 and 247 mg/l total FeCharacterized by pH 2.7 and 247 mg/l total Fe Highly acidic with elevated metal concentrationsHighly acidic with elevated metal concentrations Acidity may mobilize iron, manganese, aluminum Acidity may mobilize iron, manganese, aluminum

and other metalsand other metals Although mining ceased early in the 20th Although mining ceased early in the 20th

Century, the Bing has remained mostly Century, the Bing has remained mostly unvegetated due to the highly acidic and infertile unvegetated due to the highly acidic and infertile spoilspoil

Mine drainage was polluting a small watercourse Mine drainage was polluting a small watercourse which leads into the River Almondwhich leads into the River Almond

Ironstone spoilIronstone spoil

Iron pyrites in ironstone and coal Iron pyrites in ironstone and coal spoil are oxidized to form sulfuric spoil are oxidized to form sulfuric acid when exposed to air and wateracid when exposed to air and water

At pH above 4, acid production At pH above 4, acid production proceeds slowly and is controlled by proceeds slowly and is controlled by the rate of oxygen diffusion into the the rate of oxygen diffusion into the spoilspoil

Below pH 4, an alternative oxidation Below pH 4, an alternative oxidation pathway exists involving the pathway exists involving the bacterium bacterium Thiobacillus ferrooxidansThiobacillus ferrooxidans

TreatmentTreatment Creating an aesthetically-pleasing Creating an aesthetically-pleasing

landformlandform Treatment with dried pelleted sewage Treatment with dried pelleted sewage

sludge, limestone and peatsludge, limestone and peat After which trees were plantedAfter which trees were planted Betula Betula

pubescens pubescens and and Alnus glutinosaAlnus glutinosa (common (common alderalder))

Construction of settling pond and surface Construction of settling pond and surface flow wetland to receive spoil drainageflow wetland to receive spoil drainage Mushroom compost substrateMushroom compost substrate Cattails Cattails (Typha latifolia).(Typha latifolia).

ReclamationReclamation Acidity, iron, Acidity, iron,

manganese and manganese and aluminum aluminum concentrations concentrations declineddeclined

Removed on average Removed on average 33% of acidity and 20-33% of acidity and 20-40% of metal inputs40% of metal inputs

Removal rates Removal rates decreased in the winterdecreased in the winter

Enabled vegetation Enabled vegetation establishmentestablishment

Effect was spatially Effect was spatially variablevariable

SummarySummary

Constructed wetlands offer an Constructed wetlands offer an inexpensive, passive treatment for inexpensive, passive treatment for acid-mine drainageacid-mine drainage

Several acid-tolerant aquatic species Several acid-tolerant aquatic species including including SphagnumSphagnum and and Typha sp.Typha sp.

Benhar mine spoil Benhar mine spoil Site historySite history Treatment Treatment Results Results