INTRODUCTIONImagine production of ARD. Thesereactions make low pH
INTRODUCTIONImagine going fishing on a cool Autumn day, the trees are all differentshades 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 plantand animal life are gone. This is by no means a recent phenomenon. This is dueto the effects of acid rock drainage (ARD). This is a problem that has beenoccurring since ancient times, but it was not until the 1800’s when fast growingindustrialization and heavy mining that it caught alot of attention.Acid rock drainage is the term used to describe leachate, seepage, ordrainage that has been affected by the natural oxidation of sulfur mineralscontained in rock which is exposed to air and water.
The major components ofARD formation are reactive sulfide minerals, oxygen, and water. Biologicalactivity and reactions is what is responsible for the production of ARD. Thesereactions make low pH water that has the ability to mobilize heavy metalscontained in geological materials with which it comes in contact. “ARD causes adevastating impact on the quality of the ground or surface water it dischargesto. (Ellison & Hutchison)”ACID MINE DRAINAGEWithin the mining process there are several sources that cause ARD. Nomatter 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 decadesafter the sulfide containing material is disturbed or deposited. ARD has beenassociated with mines since mining began. When ARD occurs due to the effects ofmining it is called acid mine drainage, or AMD. The coal mining industry herein the eastern United States has been associated with a major source of AMD fordecades. When water comes in contact with pyrite in coal and the rocksurrounding it, chemical reactions take place which cause the water to gainacidity and to pick up iron, manganese and aluminum. Water that comes intocontact with coal has a orange-red yellow and sometimes white color. The metalsstay in the solution beneath the earth due to the lack of oxygen.
When thewater comes out of the mine or the borehole it reacts with the oxygen in the airor some that may be deposited in the stream and deposits the iron, manganese andaluminum and deposits it on the rocks and the stream bed. Each of the chemicalsin acid mine drainage is toxic to fish and aquatic insects in moderateconcentrations. At real high concentrations all plant life is killed.”Underground mines that are likely to result in ARD are those wheremining is located above the water table.
(Kelly 1988)” Most of the mines arealso located in mountainous terrain. “Underground workings usually result in aground water table that has been lowered significantly and permanently. (Kelly1988)” Mining also helps in the breaking of rock exposing more surface area tooxidation.OTHER SOURCES OF ARDARD is not necessarily confined to these mining activities.
“Anyprocess, natural or anthropogenic, that exposes sulfide- bearing rock to air andwater will cause it to occur. (Ellison & Hutchison)” There are examples ofnatural ARD where springs produce acidic water. These are found near outcropsof sulfide-bearing rock, but not all exposing sulfide rock will result in ARDformation. “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 causeleakage. (Ellison & Hutchison 1992)”CHEMISTRY”The most important factor in determining the extent of the acid minedrainage is not the pH, but the total acidity. (Ellison &Hutchison 1992)” Totalacidity is a measure of the excess amount of H+ ions over other ions in thesolution. A high acidity is accompanied by a low pH in AMD.
This is whatseparates AMD from acid rain, which has a low pH and a low acidity. Thesedifferences are due to the sources of acid in different ecosystems.A buffer, as we learned in class, “is a compound that tends to maintainthe pH of a solution over a narrow range as small amounts of acid or base areadded.(Rhankin 1996)”This is also a substance that can also be either an acidor a base. A low pH has a lot of bad effects on the “bicarbonate bufferingsystem.”(Kelly 1988) At low pH solutions carbonate and bicarbonate are changedover to carbonic acid and then on to water and carbon dioxide. Because of thiswater looses its ability to buffer the pH of the water and plants in and aroundthe water that use the bicarbonate in the process of photosynthesis.
Anothereffect of low pH is the increase in the rate of the decomposition of clayminerals and carbonates, releasing toxic metals such as aluminum and silica. Ironically however, Aluminum silicates can aid in the “buffering” of pH.HEAVY METALSThe presence of high concentrations of heavy metals from acid minedrainage is just as much a threat to the environment as acidity is. Whensulfide is oxidized, heavy metal ions are released into the water.
“The keyconcept in this case is the specialization of the metal distinguishes between filterable’ and particulate’ fraction of a metal.(Kelly 1988)” Filterablemeans that particles can be trapped by a filter. The particulate fraction ofthe metal includes solid minerals, crystals, and metals that set up intoorganisms.The presence of heavy metals in the aquatic environment can have aserious effect on the plants and animals in an ecosystem. Plants uptake themetals and because plants are at the bottom of the food chain, these metals arepassed on to animals. The animals become contaminated with the metals througheating and drinking. There are actually some types of algae that actuallythrive in harsh metal environments because they are not affected by the toxicityand therefore they have no competition.
These types of species are blue-greenalgae: Plectonema, and green algae: Mougeoutia, Stigeoclonium, and Holmidiumrivular (Kelly 1988). These species are the exception because there are “veryfew aquatic plants known to be naturally tolerant to heavy metals.(Kelly 1988)”LAWS AND REGULATIONSRecently, many laws and regulations have been passed to help treat andcontrol the acid mine drainage. The EPA has helped establish new limits andregulations such as no net acidity of drainage (pH between 6-9), average totaliron content of discharge must be less than 3 mg/L, and the average totalmanganese content less than 2 mg/L. Processes used now to prevent aciddischarge are proper filtering equipment and drainage ponds that contain acidrock indefinitely. The most common methods of treating acid mine drainage arethrough chemical and biological processes.(Klepper 1989)The Appalachian Clean Stream Initiative was established by the Office ofSurface Mining (OSM) and is trying to clean up acid drainage by combining theefforts of citizen groups, corporations and government agencies.
President ofthe OSM, Robert Uram said, “Private organizations both grassroots and nationalhave joined, in addition to government programs at the federal, state, and locallevels.””The most effective way to control acid generation is to prevent itsinitiation.(Siwik 1989)” The biggest part of the reclamation and restoration isto research into the use of peat/wetland treatment for heavy metal removal fromacid mine drainage.(Siwik 1989) According to the EPA standards, many of themines will have to be designed and operated to meet the standard of “zerodischarge” from the mines. CHEMICAL TREATMENTChemical treatment is the most common method used to eliminate aciddrainage from abandoned underground mines. There is three major working partsthat do just this; complexion, oxidation, and reduction”(Kelly 1989) Neutralization of acid water with lime is a common practice. Chemicals commonlyused in neutralization techniques are lime and sodium bicarbonate or “costicsoda.
” Other examples of substances that have been found to reduce acid minedrainage are bactericides including antibiotics, detergents, heavy metals andfood preservatives. Antibiotics and heavy metals are to costly and to dangerousto the surrounding aquatic life. Alconex, an inexpensive detergent, and sodiumlaurel sulfate both are found to reduce acid in mine drainage.
BIOLOGICAL TREATMENTSome choose to use biological treatment to treat acid mine drainage and theseways can include: Biodegration of a chemical into basic oxidation products suchas carbon dioxide, water, and nitrogen. To me, a very interesting way oftreating acid mine drainage successfully and also high metal removal. Thereason for this is that the plants that are in the wetland are anaerobic andtherefore the rates of decomposition and mineralization of organic matter fromthe plants of the wetlands is slowed, and organic matter tends to accumulate onthe surface of sediments. Wetland, therefore can gather and transform organicmaterial and nutrients.(Bastian 1993) Natural and constructed wetland have beenused 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 mostsites, chemical treatment is still necessary to meet efficient standards, butthe costs of chemical treatment is greatly reduced with the initial biologicaltreatment. Most operators find that the costs of the construction of thewetlands are made up within one year due to the money saved on chemicals.CONCLUSIONIn conclusion, acid rock drainage is a big problem all throughout theworld due to alot of industrialization and mining. This is not only a seriousproblem 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 regulationsand standards the EPA is setting.Low pH and a high acidity level is harmfulto us our wildlife and our plants.
With the help of more education and moreresearch it will not have to be a problem for our future.