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Geology 308 for Final > 15. Acid mine drainage and gold Cynanidation > Flashcards

15. Acid mine drainage and gold Cynanidation Flashcards

1
Q

Charge-balanced Equation for Oxidation of Pyrite

A

4FeS2 + 15O2 + 14H2O → 4Fe(OH)3 + 8SO42- + 16H+

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2
Q

What valence change does pyrite have in ferrite hydroxide?

A

+2 to +3

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3
Q

Is Fe getting oxidized or reduced

A

Iron is getting oxidized, because valence number increases

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4
Q

What is the most common oxidizing agent in environment in the atmosphere?

A

Oxygen

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5
Q

How many moles of H is released?

A

16 moles

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6
Q

When does oxidation of pyrite occur?

A

During pyrite weathering at or near the surface of the earth

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7
Q

What can pyrite weathering be sped up by

A

Accelerated by mining and quarrying

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8
Q

What is the colour of Ferric hydroxide

A

Yellow orange
Insoluble
Precipitate

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9
Q

Where else can pyrite be found

A

In shales
Interceded with coal seams
Especially in marine coastal swamps

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10
Q

What does strip mining of pyrite cause

A

Acidification of local surface waters due to oxidation of pyrite by exposure to oxygen and water

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11
Q

What bacteria helps oxidation of pyrite to ferric oxide and hydrogen ions

A

Thiobacillus ferroxidans

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12
Q

What are some characteristics of Thiobacillus ferroxidans?

A

Colourless
Rod shaped
Aerobic
Airborne

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13
Q

What does Thiobacillus ferroxidans do

A

Convert insoluble metals to soluble state

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14
Q

Is Thiobacillus ferroxidans acidic or alkalinic?

A

Highly acidophilic (1.5-2.0)
Obtains energy through oxidation of iron

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15
Q

What are some coal and metal inferiors sulfide deposited around the world

A

Coal
Copper
Copper-lead-zinc
Lead-zinc
Gold
Uranium
Silver
Tin
Nickel

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16
Q

Does a small change in ph scale represent small or large change

A

Large change since it is logarithmic

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17
Q

Which fluids have strong, buffering capacity

A

Fluids in living organisms and seawater

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18
Q

Which fluids have weak buffering capacity

A

Rain water

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19
Q

Where are acid soils commonly found?

A

Rainforests and jungles

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20
Q

Where are alkaline soil commonly found

A

Deserts

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21
Q

What effect does rainfall have on soil pH?

A

Rainwater naturally combines with carbon dioxide in the atmosphere to form a weak acid (h2co3)

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22
Q

What is the pH level of clean rain water?

A

5.6-5.7

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23
Q

What is the natural pH range for most plants? Is it acidic or alkaline?

A

Acidic 5.5-7

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24
Q

sulphide minerals like pyrite that are underwater will not Weather significantly

A

True, this is because they are not exposed to oxygen as much as if it was above water

25
Q

What is the geological name for a rusty exposure of rock?

A

Gossan

26
Q

What are some treatments for acid mine drainage

A
  1. Add a buffer material like limestone.
  2. Limit the area of exposed rock.
  3. Compacting acid generating rock.
  4. Covering the rock with sealing layers
27
Q

What are some long-term treatments for acid mine drainage

A
  1. Bacteria inhibition
  2. Physical by water cover or dry cover
    3.desulfurization
  3. Chemical barrier passivation either by inorganic or organic coating
  4. Electro chemical cover.
28
Q

What is water cover and dry cover

A

Water cover: flooding under water, storage of spoils

Dry cover: using soil, organic materials, synthetic materials, and vegetation

29
Q

What is an organic and inorganic coating?

A

Inorganic: silica, phosphate, alkaline compound

Organic: lipids ,fatty acid, oxalic acid

30
Q

What are dry covers used for?

A

To minimize the production of acidic effluents from sulphide bearing waste, the bottom becomes impermeable but groundwater can exit down

31
Q

What is the current approach to AMD?

A

Delay or prevent oxidation

32
Q

Limitations: physical barrier

A

What dry barriers have short term effectiveness.

Wet: specific to where inundation is established, high maintenance cost

Dry: plastic liners are expensive and rarely used for large volumes of waste to clean the room

33
Q

Limitations: bactericides

A

Suppress oxidation, but are only effective on fresh tailings and short-lived
Not permanent solution
Toxic to aquatic organisms

34
Q

Limitations: chemical barriers

A

Good at preventing AMD

35
Q

What is the most promising stable, acid, resistant, and long, lasting coating in organic coatings

A

Silica

36
Q

How does acid reach lakes?

A

-Acid will leach from rock as long as the source rock is exposed to air and water until sulphides are leached out

  • process that lasts hundreds and thousands of years
  • Acid is carried off mine site by rainwater and surface drainage, deposited into nearby streams and rivers
37
Q

Acid mine drainage hazards

A

Physical, chemical and biological degradation of stream habitats
Affects fishes, and those who eat it

38
Q

What are some physical properties of gold

A

Malleable
Soft
Pounded thin
drawn out to make a thin wire
doesn’t rust or tarnish

39
Q

Gold is usually bonded with which metal

A

Silver

40
Q

What role does cyanide play in gold processing?

A

Helps extract gold from other metals, and leach to surrounding water

41
Q

What temperature is the smelter

A

1600 degrees celsius

42
Q

What are impurities in the smelting process called

A

Slag

43
Q

How often is gold cyanidation used

A

90% of gold production

44
Q

What is the chemical formula of gold dissolution

A

4 Au(s) + 8 NaCN(aq) + O2(g) + 2H2O(l)→ 4 NaAu(CN)2 + 4 NaOH(aq)

45
Q

Remediation of the CN formula

A

CN− + [O] → OCN−
OCN− + 2H2O → HCO−3 + NH3

46
Q

Where did Baia Mare cyanide spill occur

A

Romania into Somes River

47
Q

When did Baia Mare cyanide spill occur

A

2000

48
Q

Where did spill reach and what happened

A

Reached Tisza and Danube
Killing large numbers of fish in Hungary and Romania
Worst disaster since chernobyl

49
Q

how did spill occur

A

Bad weather and bad structure of dams

50
Q

which company is responsible for cyanide spill

A

Aurul ( Australian )

51
Q

how is the toxicity of cyanide expressed in concentration?

A

lethal to 50% of exposeed population LC50

52
Q

ways to get cyanide ( 3 categories )

A
  1. Inhalation
  2. Ingestion
  3. Absorption through eyes and skin
53
Q

Inhalation how much

A

Gaseous hydrogen cyanide
100-300 parts per million
death in 10-60 minutes

54
Q

Ingestion how much

A

1-3 mg per kilogram of body weight

55
Q

absorbtion through eyes and skin how much

A

100 mg per kilo of body weight

56
Q

how does cyanide affect body

A
  • interferes with cell’s ability to use oxygen
  • cellular suffocation
  • CNS depression and respiratory arrest
57
Q

what has mining industry come up with to combat cyanide exposure

A

voluntary cyanide codes for management

58
Q

EU needs concentration of cyanide to be at what?

A

cannot discharge more than 10ppm
financial guarantees for clean up as well

Geology 308 for Final (11 decks)

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