15. Acid mine drainage and gold Cynanidation

Question 1

Charge-balanced Equation for Oxidation of Pyrite

Answer 1

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

Question 2

What valence change does pyrite have in ferrite hydroxide?

Answer 2

+2 to +3

Question 3

Is Fe getting oxidized or reduced

Answer 3

Iron is getting oxidized, because valence number increases

Question 4

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

Answer 4

Oxygen

Question 5

How many moles of H is released?

Answer 5

16 moles

Question 6

When does oxidation of pyrite occur?

Answer 6

During pyrite weathering at or near the surface of the earth

Question 7

What can pyrite weathering be sped up by

Answer 7

Accelerated by mining and quarrying

Question 8

What is the colour of Ferric hydroxide

Answer 8

Yellow orange
Insoluble
Precipitate

Question 9

Where else can pyrite be found

Answer 9

In shales
Interceded with coal seams
Especially in marine coastal swamps

Question 10

What does strip mining of pyrite cause

Answer 10

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

Question 11

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

Answer 11

Thiobacillus ferroxidans

Question 12

What are some characteristics of Thiobacillus ferroxidans?

Answer 12

Colourless
Rod shaped
Aerobic
Airborne

Question 13

What does Thiobacillus ferroxidans do

Answer 13

Convert insoluble metals to soluble state

Question 14

Is Thiobacillus ferroxidans acidic or alkalinic?

Answer 14

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

Question 15

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

Answer 15

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

Question 16

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

Answer 16

Large change since it is logarithmic

Question 17

Which fluids have strong, buffering capacity

Answer 17

Fluids in living organisms and seawater

Question 18

Which fluids have weak buffering capacity

Answer 18

Rain water

Question 19

Where are acid soils commonly found?

Answer 19

Rainforests and jungles

Question 20

Where are alkaline soil commonly found

Answer 20

Deserts

Question 21

What effect does rainfall have on soil pH?

Answer 21

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

Question 22

What is the pH level of clean rain water?

Answer 22

5.6-5.7

Question 23

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

Answer 23

Acidic 5.5-7

Question 24

sulphide minerals like pyrite that are underwater will not Weather significantly

Answer 24

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

Question 25

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

Answer 25

Gossan

Question 26

What are some treatments for acid mine drainage

Answer 26

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

Question 27

What are some long-term treatments for acid mine drainage

Answer 27

1. Bacteria inhibition 2. Physical by water cover or dry cover 3.desulfurization 4. Chemical barrier passivation either by inorganic or organic coating 5. Electro chemical cover.

Question 28

What is water cover and dry cover

Answer 28

Water cover: flooding under water, storage of spoils Dry cover: using soil, organic materials, synthetic materials, and vegetation

Question 29

What is an organic and inorganic coating?

Answer 29

Inorganic: silica, phosphate, alkaline compound Organic: lipids ,fatty acid, oxalic acid

Question 30

What are dry covers used for?

Answer 30

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

Question 31

What is the current approach to AMD?

Answer 31

Delay or prevent oxidation

Question 32

Limitations: physical barrier

Answer 32

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

Question 33

Limitations: bactericides

Answer 33

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

Question 34

Limitations: chemical barriers

Answer 34

Good at preventing AMD

Question 35

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

Answer 35

Silica

Question 36

How does acid reach lakes?

Answer 36

-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

Question 37

Acid mine drainage hazards

Answer 37

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

Question 38

What are some physical properties of gold

Answer 38

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

Question 39

Gold is usually bonded with which metal

Answer 39

Silver

Question 40

What role does cyanide play in gold processing?

Answer 40

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

Question 41

What temperature is the smelter

Answer 41

1600 degrees celsius

Question 42

What are impurities in the smelting process called

Answer 42

Slag

Question 43

How often is gold cyanidation used

Answer 43

90% of gold production

Question 44

What is the chemical formula of gold dissolution

Answer 44

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

Question 45

Remediation of the CN formula

Answer 45

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

Question 46

Where did Baia Mare cyanide spill occur

Answer 46

Romania into Somes River

Question 47

When did Baia Mare cyanide spill occur

Answer 47

2000

Question 48

Where did spill reach and what happened

Answer 48

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

Question 49

how did spill occur

Answer 49

Bad weather and bad structure of dams

Question 50

which company is responsible for cyanide spill

Answer 50

Aurul ( Australian )

Question 51

how is the toxicity of cyanide expressed in concentration?

Answer 51

lethal to 50% of exposeed population LC50

Question 52

ways to get cyanide ( 3 categories )

Answer 52

1. Inhalation 2. Ingestion 3. Absorption through eyes and skin

Question 53

Inhalation how much

Answer 53

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

Question 54

Ingestion how much

Answer 54

1-3 mg per kilogram of body weight

Question 55

absorbtion through eyes and skin how much

Answer 55

100 mg per kilo of body weight

Question 56

how does cyanide affect body

Answer 56

- interferes with cell's ability to use oxygen - cellular suffocation - CNS depression and respiratory arrest

Question 57

what has mining industry come up with to combat cyanide exposure

Answer 57

voluntary cyanide codes for management

Question 58

EU needs concentration of cyanide to be at what?

Answer 58

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