Acid
mine drainage (air asam tambang in Bahasa Indonesia) is water that commonly contaminated
when pyrite, chalcopyrite or any iron
sulfides, then highly exposed and reacts with air and water. This contaminant form
sulfuric acid and dissolved iron. Some of or all of this iron contaminated can
precipitate to form the red, orange, or yellow sediments that falls in the
bottom of streams containing mine drainage. This kind of solutions is highly
acid runoff and dissolves some of heavy metal particle such as lead, mercury,
cooper that might be dispersion into ground or surface water. The intends
action of certain bacteria (commonly sulfuric and an aerob bacteria) in acid
mine drainage process also influenced the rate and degree of acid water.
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Acid Mine Drainage Reaction for Pyrite
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Acid Mine Drainage Reaction Ferrous Iron
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Acid Mine Drainage Reaction for Hydrolysis Iron
Acid
mine drainage caused some of environmental problem in mining atmosphere, It
disrupts growth and reproduction of aquatic plants and animals, diminishes
valued recreational fish species, degrades surface and groundwater drinking
supplies, and causes acid corrosion of infrastructure like wastewater pipes.
The degree of acid water can reach 3 or 4 pH.
Yellowboy
as result of Acid Mine Drainage
Mining
known as an activity that produced acid mine drainage, both of underground and
open pit mine. Beside acid mine water that come out from coal mine, ore mine
(ex: cooper and gold mine, lead mine) also. More over, acid mine from gold mine
more dangerous that coal mine. Drainage from these ore mines can contain high
levels of these metals.
Acid
mine at Tinto River, Spain
Two
condition that highly impact acid mine drainage were chemical and physical
condition. Some of chemical parameters that influenced of contaminating acid
mine drainage were pH, temperature, oxygen concentration, dissolved water, Fe3+
ionic activity, and land area of sulfuric
that exposed. Mean while physical parameter were acid reaction rate,
weather, rock permeability, porous ground pressure and hydrologic condition.
The
danger of acid mine that contaminating ground and surface water
There are two commonly method that applied to
eliminate or reduce by acidity and heavy metals components. They are passive
treatment that uses alkaline chemicals to neutralize acid-polluted waters and
passive treatment method uses a treatment system that employs naturally
occurring chemical and biological reactions to minimize acid mine drainage with
little maintenance.
Active
treatment system:
Some
method of active treatment system were using limestone (calcium carbonate)
which is to enrich water with calcium then rise up the pH into balance. The
advantages of using limestone include low cost, ease of use, and formation of a
dense, easily handled sludge. The disadvantages include slow reaction time,
loss in efficiency of the system because of coating of the limestone particles
with iron precipitates, difficulty in treating acid mine drainage with a high
ferrous-ferric ratio, and ineffectiveness in removing manganese.
Others
method using a hydrated lime (calcium hydroxide) as neutralizing agent that
match to applied in coal mining because it is easy and safe to use, effective,
and relatively inexpensive. The disadvantages is the sludge. Soda Ash (sodium
carbonate) that seems match to small acid mine water treatment that flows but
it is poor of settling the properties of sludge. Caustic soda that use for
manganese acid mine water but it is dangerous to environment because of hard to
handling the chemical, poor sludge properties and hard freeze in cold
water.
The
passive treatments:
Passive
treatment is a treatment that occurred in wetland area and still a new
technology. Passive treatments can be combined with several technologies to
treats difficult effluents. Some of commonly passive treatment that applied on
are aerobic wetland, anaerobic wetland, successive alkalinity producing system,
anoxic limestone drains, and limestone pond.
Anoxic Limestone Drains is simply constructed passive treatment method
that uses open ditches filled with limestone (anoxic drains are covered). The
dissolution of limestone adds alkalinity and raising pH, but a coating of
limestone by iron and aluminum precipitates affects the performance of this
treatment method.
Anoxic
Limestone Drains Method
Aerobic
wetlands are typically designed to promote precipitation of iron hydroxide.
Limestone can be added to the organic substrate for additional treatment via
limestone dissolution. The wetlands are usually 1 to 6 acres in size, but
depend upon the flow rate and may require periodic dredging. These treatments
are limited to cases where the discharge has a pH greater than 4 and are often
used as a final polishing treatment.
Anaerobic
wetlands used to neutralizing acid rate and reduce metals particle to the
sulfide form. Anaerobic wetlands may be lined or unlined shallow ponds filled
with organic matter, such as compost, and underlain by limestone gravel. Microorganisms
such as anaerobic bacteria, facilitate this reaction by first consuming oxygen,
alkalinity and H2S are produced. If the system is improperly sized,
if flow dries up, or if extended low temperatures are encountered, the
microorganisms will die and the performance will be decreased. Some anaerobic
wetlands discharge a sulfide “sewage” effluent.
The advantages of passive treatment for acid
mine drainage are:
·
do not require electrical power
·
do not require any mechanical
equipment, hazardous chemicals, or buildings
·
do not require daily operation and
maintenance
·
are more natural and aesthetic in
their appearance and may support plants and wildlife
·
are less expensive
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