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GLGY 308 Final > Acid Mine Drainage and Gold Cyanidation > Flashcards

Acid Mine Drainage and Gold Cyanidation Flashcards

1
Q

Explain the chemical reaction for the oxidation of pyrite

A

4 mols of pyrite react with oxygen and water to release 16 mols of H+

Fe is oxidized (valence increases from +2 to +3)

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2
Q

Most common oxidizing agent in environment

A

O2

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3
Q

Oxidation of pyrite occurs naturally when

A

Pyrite weathers at or near earths surface

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4
Q

Oxidation of pyrite is accelerated by

A

Mining

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5
Q

Ferric oxide (yellow-iron oxide)

A

Yellow-orange precipitate in oxidation of pyrite reaction that smothers organisms living on stream bottom

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6
Q

What is the chemical formula for ferric oxide

A

4Fe(OH)3

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7
Q

Pyrite occurs in shales that can be interbedded with

A

Coal seams

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8
Q

Coal seams are common in shales in

A

Marine coastal swamps

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9
Q

What often causes acidification of local surface waters

A

Strip mining of coal seams - oxidation of pyrite by exposure to O2 and H20 causes release of H+

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10
Q

Thiobacillus ferrooxidans

A

Microbe that catalyzes oxidation of pyrite

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11
Q

Thiobacillus ferrooxidans vs O2 oxidation

A

Thiobacillus ferrooxidans 1,000,000x increased rate

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12
Q

Thiobacillus ferrooxidans convert insoluble metals to

A

Soluble state

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13
Q

Rod-shaped

A

Thiobacillus ferrooxidans

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14
Q

Aerobic, airborne bacteria

A

Thiobacillus ferrooxidans

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15
Q

Thiobacillus ferrooxidans pH preference

A

Highly acidic (pH 1.5-2.0)

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16
Q

Thiobacillus ferrooxidans energy obtaining reaction

A

Oxidation of iron

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17
Q

Logarithmic nature of pH scale

A

Small change in pH = large change in H+ concentration

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18
Q

Buffers

A

Solutions that resist changes in pH by absorbing H+

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19
Q

Have strong buffering capacity

A

Fluids in living organisms and seawater

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20
Q

Common place for alkaline soils

A

Deserts

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21
Q

Common place for acidic soils

A

Rainforests, jungles

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22
Q

How does rain affect pH of soil

A

Combines with Co2 to create weak acid

23
Q

pH of clean rainwater

24
Q

Natural pH range of plants

A

acidic (5.5-7)

25
Q

Sulfide minerals (pyrite) will not weather significantly when

A

Underwater

26
Q

Gossan

A

Rusty exposure of rock

27
Q

Acid mine drainage treatments

A

-add buffer
- limit area of exposed rock
- compact acid-generating rock
- cover rock with sealing layers

28
Q

Buffer material for acid mine drainage

29
Q

Categories of long-term treatments for AMD

A
  1. bacterial inhibition
  2. physical barrier
  3. desulfurization
  4. chemical barrier
  5. electrochemical cover
30
Q

Purpose of AMD treatment

A

Delay or prevent oxidation

31
Q

Physical barriers

A
  • Slow sulfide oxidation
  • short-term
32
Q

Wet vs dry physical barriers

A

Wet: sites with complete induntation and high maintenance costs
Dry: plastic liners expensive and cannot be used for large volumes

33
Q

Bactericides pros and cons

A
  • suppress oxidation
  • short-lived
  • may be toxic to aquatic organisms
34
Q

Most promising, stable, acid-resistant, long lasting chemical barrier

35
Q

Chemical barriers

A

Act on sulfide surfaces

36
Q

Acid will leach from rock as long as

A

Rock is exposed to air and water and sulphides left to leach out

37
Q

Responsible for physical, chemical, and biological degradation of stream habitat

38
Q

Physical properties of gold

A
  • Soft + malleable
  • Doesn’t rust or tarnish
39
Q

Gold usually bonded to

40
Q

Role of cyanide in gold processing

A

Helps extract it from other metals and leach into surrounding water

41
Q

Temperature of gold smelter

42
Q

Slag

A

Impurities in smelting process

43
Q

Used in 90% of gold production

A

Gold cyanidation

44
Q

Why is gold cyanidation controversial

A

Toxic nature of cyanide

45
Q

Date and location of Baia Mare Cyanide Spill

A

2000, Romania into Somes River

46
Q

LC50

A

Lethal dose to 50% of population

47
Q

LC50 for gaseous hydrogen cyanide

A

100-300 ppm, death within 60min

48
Q

LC50 for cyanide ingestion

A

1-3mg per kg body weight

49
Q

LC50 for cyanide absorption through eyes and skin

A

100mg per kg body weight

50
Q

How does cyanide act on the body

A

Interferes with cell’s ability to use oxygen - causing cellular suffocation which leads to the depression of the CNS and respiratory arrest

51
Q

Pros of cyanide

A

Cheap, effective, and biodegradable in sunlight

52
Q

Cyanide banned for gold extraction

A

Montana, Wisconsin, Czech Republic, Hungary

53
Q

European Union response to Baia Mare

A

“the concentration of cyanide must be reduced to the lowest possible level using the best possible techniques”

No discharge of waste containing over 10ppm of cyanide

54
Q

Currently protesting for cyanide ban

GLGY 308 Final (11 decks)

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