Drainage Essay, Research Paper
The Cause and Effects of Acid Mine Drainage
INTRODUCTION
Imagine going fishing on a cool Autumn day, the trees are all different
shades of orange, brown and red and the birds are singing their beautiful songs,
but their is a serious problem because when you arrive at the river all plant
and animal life are gone. This is by no means a recent phenomenon. This is due
to the effects of acid rock drainage (ARD). This is a problem that has been
occurring since ancient times, but it was not until the 1800’s when fast growing
industrialization and heavy mining that it caught alot of attention.
Acid rock drainage is the term used to describe leachate, seepage, or
drainage that has been affected by the natural oxidation of sulfur minerals
contained in rock which is exposed to air and water. The major components of
ARD formation are reactive sulfide minerals, oxygen, and water. Biological
activity and reactions is what is responsible for the production of ARD. These
reactions make low pH water that has the ability to mobilize heavy metals
contained in geological materials with which it comes in contact. “ARD causes a
devastating impact on the quality of the ground or surface water it discharges
to. (Ellison & Hutchison)”
ACID MINE DRAINAGE
Within the mining process there are several sources that cause ARD. No
matter what activities occur, ARD usually occurs when certain conditions are met.
These conditions are the factors that limit or accelerate the release of ARD.
The initial release of ARD can occur anywhere from a few months to many decades
after the sulfide containing material is disturbed or deposited. ARD has been
associated with mines since mining began. When ARD occurs due to the effects of
mining it is called acid mine drainage, or AMD. The coal mining industry here
in the eastern United States has been associated with a major source of AMD for
decades. When water comes in contact with pyrite in coal and the rock
surrounding it, chemical reactions take place which cause the water to gain
acidity and to pick up iron, manganese and aluminum. Water that comes into
contact with coal has a orange-red yellow and sometimes white color. The metals
stay in the solution beneath the earth due to the lack of oxygen. When the
water comes out of the mine or the borehole it reacts with the oxygen in the air
or some that may be deposited in the stream and deposits the iron, manganese and
aluminum and deposits it on the rocks and the stream bed. Each of the chemicals
in acid mine drainage is toxic to fish and aquatic insects in moderate
concentrations. At real high concentrations all plant life is killed.
“Underground mines that are likely to result in ARD are those where
mining is located above the water table. (Kelly 1988)” Most of the mines are
also located in mountainous terrain. “Underground workings usually result in a
ground water table that has been lowered significantly and permanently. (Kelly
1988)” Mining also helps in the breaking of rock exposing more surface area to
oxidation.
OTHER SOURCES OF ARD
ARD is not necessarily confined to these mining activities. “Any
process, natural or anthropogenic, that exposes sulfide- bearing rock to air and
water will cause it to occur. (Ellison & Hutchison)” There are examples of
natural ARD where springs produce acidic water. These are found near outcrops
of sulfide-bearing rock, but not all exposing sulfide rock will result in ARD
formation. “Acid drainage will not occur if sulfide minerals are nonreactive,
the rock contains sufficient alkaline material to neutralize any acid produced,
or the climate is arid and there is not adequate rainfall infiltration to cause
leakage. (Ellison & Hutchison 1992)”
CHEMISTRY
“The most important factor in determining the extent of the acid mine
drainage is not the pH, but the total acidity. (Ellison &Hutchison 1992)” Total
acidity is a measure of the excess amount of H+ ions over other ions in the
solution. A high acidity is accompanied by a low pH in AMD. This is what
separates AMD from acid rain, which has a low pH and a low acidity. These
differences are due to the sources of acid in different ecosystems.
A buffer, as we learned in class, “is a compound that tends to maintain
the pH of a solution over a narrow range as small amounts of acid or base are
added.(Rhankin 1996)” This is also a substance that can also be either an acid
or a base. A low pH has a lot of bad effects on the “bicarbonate buffering
system.”(Kelly 1988) At low pH solutions carbonate and bicarbonate are changed
over to carbonic acid and then on to water and carbon dioxide. Because of this
water looses its ability to buffer the pH of the water and plants in and around
the water that use the bicarbonate in the process of photosynthesis. Another
effect of low pH is the increase in the rate of the decomposition of clay
minerals and carbonates, releasing toxic metals such as aluminum and silica.
Ironically however, Aluminum silicates can aid in the “buffering” of pH.
HEAVY METALS
The presence of high concentrations of heavy metals from acid mine
drainage is just as much a threat to the environment as acidity is. When
sulfide is oxidized, heavy metal ions are released into the water. “The key
concept in this case is the specialization of the metal distinguishes between ?
filterable’ and ?particulate’ fraction of a metal.(Kelly 1988)” Filterable
means that particles can be trapped by a filter. The particulate fraction of
the metal includes solid minerals, crystals, and metals that set up into
organisms.
The presence of heavy metals in the aquatic environment can have a
serious effect on the plants and animals in an ecosystem. Plants uptake the
metals and because plants are at the bottom of the food chain, these metals are
passed on to animals. The animals become contaminated with the metals through
eating and drinking. There are actually some types of algae that actually
thrive in harsh metal environments because they are not affected by the toxicity
and therefore they have no competition. These types of species are blue-green
algae: Plectonema, and green algae: Mougeoutia, Stigeoclonium, and Holmidium
rivular (Kelly 1988). These species are the exception because there are “very
few aquatic plants known to be naturally tolerant to heavy metals.(Kelly 1988)”
LAWS AND REGULATIONS
Recently, many laws and regulations have been passed to help treat and
control the acid mine drainage. The EPA has helped establish new limits and
regulations such as no net acidity of drainage (pH between 6-9), average total
iron content of discharge must be less than 3 mg/L, and the average total
manganese content less than 2 mg/L. Processes used now to prevent acid
discharge are proper filtering equipment and drainage ponds that contain acid
rock indefinitely. The most common methods of treating acid mine drainage are
through chemical and biological processes.(Klepper 1989)
The Appalachian Clean Stream Initiative was established by the Office of
Surface Mining (OSM) and is trying to clean up acid drainage by combining the
efforts of citizen groups, corporations and government agencies. President of
the OSM, Robert Uram said, “Private organizations both grassroots and national
have joined, in addition to government programs at the federal, state, and local
levels.”
“The most effective way to control acid generation is to prevent its
initiation.(Siwik 1989)” The biggest part of the reclamation and restoration is
to research into the use of peat/wetland treatment for heavy metal removal from
acid mine drainage.(Siwik 1989) According to the EPA standards, many of the
mines will have to be designed and operated to meet the standard of “zero
discharge” from the mines. CHEMICAL TREATMENT
Chemical treatment is the most common method used to eliminate acid
drainage from abandoned underground mines. There is three major working parts
that do just this; complexion, oxidation, and reduction”(Kelly 1989)
Neutralization of acid water with lime is a common practice. Chemicals commonly
used in neutralization techniques are lime and sodium bicarbonate or “costic
soda.” Other examples of substances that have been found to reduce acid mine
drainage are bactericides including antibiotics, detergents, heavy metals and
food preservatives. Antibiotics and heavy metals are to costly and to dangerous
to the surrounding aquatic life. Alconex, an inexpensive detergent, and sodium
laurel sulfate both are found to reduce acid in mine drainage.
BIOLOGICAL TREATMENT
Some choose to use biological treatment to treat acid mine drainage and these
ways can include: Biodegration of a chemical into basic oxidation products such
as carbon dioxide, water, and nitrogen. To me, a very interesting way of
treating acid mine drainage successfully and also high metal removal. The
reason for this is that the plants that are in the wetland are anaerobic and
therefore the rates of decomposition and mineralization of organic matter from
the plants of the wetlands is slowed, and organic matter tends to accumulate on
the surface of sediments. Wetland, therefore can gather and transform organic
material and nutrients.(Bastian 1993) Natural and constructed wetland have been
used to treat wastewater. The first one that was ever constructed was in 1982.
There are over 200 systems in Appalachia alone.(Bastian 1993)
Even though this is safer for the ecosystem it is found that at most
sites, chemical treatment is still necessary to meet efficient standards, but
the costs of chemical treatment is greatly reduced with the initial biological
treatment. Most operators find that the costs of the construction of the
wetlands are made up within one year due to the money saved on chemicals.
CONCLUSION
In conclusion, acid rock drainage is a big problem all throughout the
world due to alot of industrialization and mining. This is not only a serious
problem around the world, it touches home here, especially here in Appalachia,
but it seems to be under or getting under control with all the new regulations
and standards the EPA is setting. Low pH and a high acidity level is harmful
to us our wildlife and our plants. With the help of more education and more
research it will not have to be a problem for our future.