AMD Flashcards
What are the 4 meanings of AMD
Acid mine drainage, alkaline mine drainage, abandoned mine drainage, active mine drainage
In what locations is AMD a serious problem
Areas with a history of coal mining and hard rock mining
How is AMD generated
Geochemical oxidation of sulphide mineral that release heavy metal ions and acids into surface and ground waters
Name 2 common forms of sulphide associated with mining
Pyrite and marcasite (FeS2)
what are the three reactions involved in the oxidation of pyrite
oxidation of pyrite releases iron II ions and hydrogen ions
Iron II ions are oxidised to iron III ions
Iron III ions are hydrolysed to iron III hydroxide and hydrogen ions
What bacterium catalyses oxidation of pyrite
Thiobacillus ferrooxidans
What is the consequence of iron III hydroxide to aquatic life
turns run off an orange or red colour and kills aquatic life.
Where is Wheal jane mine located
Cornwall
What happened to the water table at Wheal Jane mine
was lowered by 400m by regular pumping during its productive life.
What did Wheal Jane mine produce
Tin copper zinc and lead
When did the pumping of water from the mine stop and what did this result in
march 1991.
Resulted in a build up of mine water containing cadmium nickel, arsenic, copper and lead.
who monitored the mine and what did they prupose?
NRA - NAtional rivers authority later became environment agency.
Proposed wheal jane mine needed an AMD discharge by the end of the year (1991)
What did the owners of the mine (Carnon Consolidate Ltd) do in September 1991
abandoned the mine, no longer under obligation to carry out works with respect to ADM.
NRA was not notified of the abandonment till 31st october
Why was discharge of the mine halted and what catastrophe happened next?
pumping to the tailings dam was stopped becausse of high winds and the dam was full
13th january 1992 - a presumed underground collapsse led to the break of an adit plug releasing millions of gallons of contaminated water into the Carnon River and Restronguet Creek.
high quantities of zinc and cadmium released
Why was the collapse of the mine not initially detrimental to aquatic life?
The area around the Carnon River had consistently failed environment quality standards for many years due to the local geology and hundreds of years of mining, therefore the diversity of aquatic life was low.
What where the 2 resident species to the upper/middle Restronguet Creek?
Nereis diversicolor - polychaete
Scrobicular plana - bivalve
What was the effect on drinking water?
deemed unfit to consume. bottled water required
What did the NRA do following the january 1992 discharge ? How did it work?
funded a new treatment plant
- this used lime to neutralise the water and percipitate dissolved metals.
- treated water was passed to Clemows Valley Tailings Dam where sludge containing metallic hydroxides was allowed to settle
- clarified water decanted in Clemows stream
What does lime do to AMD?
raises the pH
What were the issues concerning method of clarifing water from Wheal Jane mine into Tailings dam
Strong winds blowing across the dam caused the remobilization of the sewage sludge. The effluent then became unacceptable for discharge
Ore milling halted in March 1998, what effects did this have on the treatment of AMD?
sand from the mill previously mixed with the minewater sludge and increased the density of the material, helping to keep the sludge settled at the bottom, this effect was then removed and effluent was unacceptible for discharge.
In October 2000 a new improved treatment works was completed, how does it work?
-Minewater and sludge from clarifier tanks mixed in Pre-reaction tanks (Provides thicker sludge at end process)
- Lime slurry is added raising the pH, causing the ppt of metal hydroxides within the reaction tanks.
- Flocculent added and causes the settlement of sludge in the clarifier tanks.
This treatment plant creates a far denser sludge than the previous plant. This sludge is then sent to the dam and enclosed within purpose built ‘Paddocks’
Paddock idea allows the water to be collected and sent back for treatment allowing the dam to be dried out and restored to a more natural state.
The environment agency constructed a passive treatment system, however there were issues, what were these?
- Too much land was required
- passive plant could only deal with 6 litres a second but some 330 L/s needed to be treated
- land available is inadequate for a full scale plant
- less controllable and consistent than a chemical treatment plant.
What were the stages in the passive treatment system?
- Anoxic Pond (prevents deposition of metals)
- Anoxic limestone drain (adds alkalinity)
- Aerobic Cell (removes iron etc as iron hydroxides, Thiobacillus is a catalyst. Typha plant species take up hydroxides)
- Anaerobic cell (Bacteria, desulfovibro, reduces sulphate to sulphides which combine with the metals to form insoluble products)
- Rock Matrix (algae grow and remove manganese, BOD)
fed into the Carnon River
