Acid mine drainage Flashcards
what is AMD
the acidic outflow from metal, coal mines or sometimes sulfide rocks which are exposed to water and oxygen
what it that makes AMD acidic
Pyrite (and other metal-sulfides oxidise)
what is the equation for pyrite
FeS2
why is AMD so bad
acid kills aquatic life and keeps toxic metals dissolved (and therefore more mobile)
what is faster abiotic or biotic oxidation of Fe2+ to Fe3+ and why
biotic - allows for the recycling process to occur which speeds up the rate of pyrite oxidative dissoluion
what enables the recyling process
microorganisms
why do cells oxidise lots of Fe3+
to get enough energy because under acidic conditions iron oxidation produces very little energy - so even a few cells can cause a lot of iron oxidation
how does indirect AMD work
microorganisms generate Fe3+ from dissolved Fe2+ - attachment is not necassary
how does direct AMD work
microorganisms attach to pyrite (by adsorbtion)
Which mirobes do it
Siderophiles and Sulfur lovers
AMD degrades water quality via:
- acid and metals are toxis to aquatic life
- smothers some photosynthesisers
- impairs certain autotrophs
- acids corrode infrastructure
- effects can occur a long way from the actual mine
How to remediate AMD
- Prevention at source
- Treatment downstream
How does Prevention At Source work
- adding alkilinity
- adding phosphate
- growing vegetation and microbes on piles to consume the oxygen and water
- capping piles to block water and oxygen
- flooding to induce anoxia
- applying biocides to kill microorganisms
How does Treatment Downstream work
- divering AMD to water treatment plant or ponds
- adding bases to raise pH
- adding organic substrate to promote SRB and formation of sulfide-minerals
- adding live or dead biomass to adsorb metals
- devierting to wetlands (artificially constructed)
