The Cause And Effects Of Acid Mine 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.