Issues

Question 1

Acid mine drainage
come from

Answer 1

sulfide rocks exposed to water adn o2
Pyrite-FeS2 (main cause)
ferrihydrite encrustation

Question 1

Acid mine drainage
mechanism

Answer 1

fe2 oxidises to fe3
produce acid (H)
Fe3+ oxidises pyrite
FeS2+Fe3+ - Fe2+ +SO4- (can only happen at pH>4.5)
lower pH Fe3 stays dissolved
higher pH Fe3 precipitates as ferrihydrite

Question 2

Acid mine drainage
mechanism 2

Answer 2

fe oxidising aciophillic bacteria (pyrite dissolution, rapid)
pyrite generates Fe2
bacterial generates Fe3
so acid generation

Question 3

Acid mine drainage
EFFECTS

Answer 3

TOXIC
acidity change (auto impaired)
colour change (photo impaired)
corrode infrastructure

Question 4

Acid mine drainage
prevention

Answer 4

add alkalinity before pH<4.5
cover- water and o2 don’t get to it

Question 5

Acid mine drainage
remediation

Answer 5

treatment downstream, each pond different base to absorb metals
move to wetlands,low matinance, self sustaining

Question 6

Bioleaching

Answer 6

acid mine drainage done on purpose and controlled
to recover valuable metals from low grade sulfides ores

Question 7

Bioleaching
methods

Answer 7

dump-add acid and microorg to rocks
heap (controlled version)-add air and crush rocks, spray with sulfuric acid, bacteria and nutrience, then solution run off into proccessing plant (purify target metals)

Question 8

Bioremediation

Answer 8

microorganisms transform contaminants into benign or less mobile form
remove, degrade, immobilise

Question 9

Bioremediation
strategies

Answer 9

1. stimulate natural microbial community -aeration, nutrient, add PED/TEA
2. Add surfactants to enhance microbial attachment
3. add microorganisms

Question 10

Bioremediation
Techniques in situ

Answer 10

permeable reactive barrier -need to work out flow paths to treat contamination, regenerated easier
or injection well- nutrience and pH adjustors

Question 11

Bioremediation of organic contaminant

Answer 11

degrade the contaminant by chemohetero (PED is contaminant)
aeration sitmulate aerobic chemohetro
nutrient and electon shuttles

Question 12

Bioremediation of Metals

Answer 12

immobilize contaminant to protect spreading to ground water
alter oxidation state to less mobile via anaerobic chemohetero

Question 13

Last step of bioleaching heap

Answer 13

Fe2+ rich liquid is oxidised by microorganisms in ponds and added back to heap as it is acidic
Acidithiobacillus ferrooxidans

Question 14

bioleaching optimisation

Answer 14

recycle iron with oxidising bacteria
optimum pH
permeability
nutrients not being limited but nuterience
temp