Abstract
Acid mine drainage (AMD) or acid rock drainage (ARD) refers to the effluents from coal and metal mines. AMD is a common phenomenon which occurs naturally as a process of rock weathering, but is increased in large scale due to human activities such as construction contracts (transportation corridors, dam build, etc.) and mining operations. This phenomenon denotes the acidic water that is produced during exposure of sulphide minerals (mainly pyrite) to air and water through a natural process, and creates sulphuric acid. AMD is a hazard to animals, aquatic life and human beings as it increases the acidity and dissolves metals. Preventing and treating AMD is an important issue in a mine site not only during operation life but also after the mine is abandoned.
Highlights
The acidic effluents from active and abandoned mines were called acid mine drainage (AMD)
Mining-influenced water (MIW) is a term used for any water that has been affected in its chemical composition by mineral processing operations
Mining industries are the source of metals and economic activity, and AMD is a big concern for such industries
Summary
The acidic effluents from active and abandoned mines were called acid mine drainage (AMD). Metal and coal deposits contain high levels of sulphide minerals (pyrite, pyrrhotite, chalcopyrite, chalcocite, etc.), which mostly react with water and oxygen, and generate acidic solutions. A general equation is shown below: 4Fe444(+aFFF2qeee)(+(+(+a+aa222qqq)))O+++2(gOOO)222+(((ggg)))4+++H(+444aHqHH)(+((++a→aaqqq)))4→→→Fe444(+aFFF3qeee)(+(+(+a+aa333qqq)))2+++H2222OHHH(2l22)OOO+(((lll)))e+n++eeeerngnneyeerrrgggyyy Either of these reactions can be accelerated by bacteria, which generate energy from the oxidation and may occur suddenly. The ferric cations produced from the previous reaction oxidise new pyrite and the process goes on: FeSFFF2eee(sSSS)222(+((sss)))1+++4F111e444(+aFFF3qeee)(+(+(+a+aa333qqq)))8+++H2888OHHH(2l22)OOO→(((lll)))1→→→5F111e555(+aFFF2qeee)(+(+(+a+aa222qqq)))2+++SO2224−SSS2(OOOaq4−4−4−)2(22((a+aaqqq)))1+++6H111(+666aHqHH)(+((++aaaqqq))). All of these reactions generate an important effect which releases H+, decreases the pH content and holds the solubility of the ferric ion: FeSFFF2eee+SSS22214+++5 O1114445255+OOO22272+++H7227272OHHH222→OOO F→→→e(FOFFeeeH((()OOO3HHH+)))3332+++SO2224−SSS2OOO+4−4−4−2224+++H+444HHH++++e+n++eeeerngnneyeerrrgggyyy
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