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Environmental Pollution (Rhoda) > AMD > Flashcards

AMD Flashcards

1
Q

What are the 4 meanings of AMD

A

Acid mine drainage, alkaline mine drainage, abandoned mine drainage, active mine drainage

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2
Q

In what locations is AMD a serious problem

A

Areas with a history of coal mining and hard rock mining

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3
Q

How is AMD generated

A

Geochemical oxidation of sulphide mineral that release heavy metal ions and acids into surface and ground waters

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4
Q

Name 2 common forms of sulphide associated with mining

A

Pyrite and marcasite (FeS2)

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5
Q

what are the three reactions involved in the oxidation of pyrite

A

oxidation of pyrite releases iron II ions and hydrogen ions
Iron II ions are oxidised to iron III ions
Iron III ions are hydrolysed to iron III hydroxide and hydrogen ions

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6
Q

What bacterium catalyses oxidation of pyrite

A

Thiobacillus ferrooxidans

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7
Q

What is the consequence of iron III hydroxide to aquatic life

A

turns run off an orange or red colour and kills aquatic life.

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8
Q

Where is Wheal jane mine located

A

Cornwall

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9
Q

What happened to the water table at Wheal Jane mine

A

was lowered by 400m by regular pumping during its productive life.

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10
Q

What did Wheal Jane mine produce

A

Tin copper zinc and lead

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11
Q

When did the pumping of water from the mine stop and what did this result in

A

march 1991.

Resulted in a build up of mine water containing cadmium nickel, arsenic, copper and lead.

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12
Q

who monitored the mine and what did they prupose?

A

NRA - NAtional rivers authority later became environment agency.
Proposed wheal jane mine needed an AMD discharge by the end of the year (1991)

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13
Q

What did the owners of the mine (Carnon Consolidate Ltd) do in September 1991

A

abandoned the mine, no longer under obligation to carry out works with respect to ADM.
NRA was not notified of the abandonment till 31st october

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14
Q

Why was discharge of the mine halted and what catastrophe happened next?

A

pumping to the tailings dam was stopped becausse of high winds and the dam was full
13th january 1992 - a presumed underground collapsse led to the break of an adit plug releasing millions of gallons of contaminated water into the Carnon River and Restronguet Creek.
high quantities of zinc and cadmium released

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15
Q

Why was the collapse of the mine not initially detrimental to aquatic life?

A

The area around the Carnon River had consistently failed environment quality standards for many years due to the local geology and hundreds of years of mining, therefore the diversity of aquatic life was low.

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16
Q

What where the 2 resident species to the upper/middle Restronguet Creek?

A

Nereis diversicolor - polychaete

Scrobicular plana - bivalve

17
Q

What was the effect on drinking water?

A

deemed unfit to consume. bottled water required

18
Q

What did the NRA do following the january 1992 discharge ? How did it work?

A

funded a new treatment plant

  • this used lime to neutralise the water and percipitate dissolved metals.
  • treated water was passed to Clemows Valley Tailings Dam where sludge containing metallic hydroxides was allowed to settle
  • clarified water decanted in Clemows stream
19
Q

What does lime do to AMD?

A

raises the pH

20
Q

What were the issues concerning method of clarifing water from Wheal Jane mine into Tailings dam

A

Strong winds blowing across the dam caused the remobilization of the sewage sludge. The effluent then became unacceptable for discharge

21
Q

Ore milling halted in March 1998, what effects did this have on the treatment of AMD?

A

sand from the mill previously mixed with the minewater sludge and increased the density of the material, helping to keep the sludge settled at the bottom, this effect was then removed and effluent was unacceptible for discharge.

22
Q

In October 2000 a new improved treatment works was completed, how does it work?

A

-Minewater and sludge from clarifier tanks mixed in Pre-reaction tanks (Provides thicker sludge at end process)
- Lime slurry is added raising the pH, causing the ppt of metal hydroxides within the reaction tanks.
- Flocculent added and causes the settlement of sludge in the clarifier tanks.
This treatment plant creates a far denser sludge than the previous plant. This sludge is then sent to the dam and enclosed within purpose built ‘Paddocks’
Paddock idea allows the water to be collected and sent back for treatment allowing the dam to be dried out and restored to a more natural state.

23
Q

The environment agency constructed a passive treatment system, however there were issues, what were these?

A
  • Too much land was required
  • passive plant could only deal with 6 litres a second but some 330 L/s needed to be treated
  • land available is inadequate for a full scale plant
  • less controllable and consistent than a chemical treatment plant.
24
Q

What were the stages in the passive treatment system?

A
  • Anoxic Pond (prevents deposition of metals)
  • Anoxic limestone drain (adds alkalinity)
  • Aerobic Cell (removes iron etc as iron hydroxides, Thiobacillus is a catalyst. Typha plant species take up hydroxides)
  • Anaerobic cell (Bacteria, desulfovibro, reduces sulphate to sulphides which combine with the metals to form insoluble products)
  • Rock Matrix (algae grow and remove manganese, BOD)
    fed into the Carnon River
25
Q

Define these terms: Anoxic, Aerobic, Anaerobic

A

Anoxic- lack of o2
Aerobic - with o2
Anaerobic - without o2

26
Q

what are the associated issues with the anoxic limestone drain in the passive treatment system?

A

longevity of treatment.
calcium carbonate ppt clogs up the pores.
high flow and acid levels can be too high for effective treatment.

27
Q

How are the Pittsburgh coal beds contributing to AMD

A

coal deposits close to the surface around the Peters Creek watershed has led to extensive mining throughout the area.
Due to a lack of environmental laws spoil piles remain unreclaimed throughout the watershed and abandoned mines workings have partially flooded.
as water percolates through pyrite laden area, AMD results. This further dissolves aluminium and P.

28
Q

Modern mining companies claim that new techniques protect against AMD, why may this be untrue?

A

AMD often takes several years to develop. Recent mines that have not yet contaminated nearby waters do not yet provide proof that these ores can be mined safely.

29
Q

What is the rate determining step in oxidation of pyrite?

A

microbial oxidation of iron II ions to Iron III ions

30
Q

what is the limiting factor for acidity of pyrite

A

oxygen

31
Q

what are the impacts of mining?

A

increases the oxygen content, speeds up movement of water through the system, creating acidic conditions.
Bacteria thrive in acidic conditions and catalyse reaction, increasing acidity.

32
Q

what is the APP of a rock

A

acid producing potential - calculated from the sulphur content.

33
Q

what is the static test?

A

this calculated the net effect of APP - ANC

34
Q

What is the ANC of a rock?

A

acid neutralising capacity - calculated from calcium carbonate content

35
Q

what are the static test limitations?

A

does not take into account the rate of reaction

acid may generated away from neutralising capacity

36
Q

what is the Kinetic test ?

A

This simulates the conditions underground.
crushed rock placed in a chamber and exposed alternately to ambient and 100% humidity air. rinced with distilled water and pH, metal content evaluated once a week. provides predictions.

37
Q

How can you prevent AMD?

A
  • minimize water circulation through the mine by covering with an impermeable cap
  • dispose of material under water
  • treat AMD with crushed limestone in a passive anoxic limestone drain
38
Q

what are the problems associated with AMD?

A
  • surface water pollution
  • localised flooding of structures built on mines
  • overflowing of sewers by mine water inflows (clogging)
  • pollution of overlying aquifiers
  • mine gas emissions
  • subsidence
  • acidity

Environmental Pollution (Rhoda) (7 decks)

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