ABSTRACT: Acid mine drainage has a prominent and damaging effect on the environment. This paper outlines the environmental impact, the chemistry behind the acid generation, and methods of treatment. The objective of this paper is to educate the reader about acid mine drainage, and what can be done to reduce this pollutant.
INTRODUCTION/BACKGROUND: Acid mine drainage (AMD) often occurs at abandoned mining sites. Acid generation is the result of combining certain minerals, water, and an oxidant. Sulfide minerals are the most common producers of AMD, but mining waste rock, tailings, and other mining structures also generate AMD. AMD has a low pH and consists of large concentrations of heavy metal and other toxic elements. This pollutant affects both human health and the environment. AMD also occurs …show more content…
Many AMD regions have a pH of 4 or less, which is comparable to battery acid or vinegar. [5] With such an acidic environment, the food web is often destroyed and AMD regions can be completely dead. Aquatic insects are rarely present, thus leaving organisms that feed off them, such as minnows, without food. Fish are also affected by the low pH, especially during the reproduction process. The acidity effects the development of the eggs, metamorphosis is slowed, and the mortality rate rises. [7]
The chemical reaction process of the acid generation can be described using a common sulfide mineral, Pyrite (FeS2). The oxidation of FeS2 breaks down into three components, iron, sulfate, and hydrogen as seen below:
FeS_2+7/2 O_2+H_2 O→Fe^(2+)+2SO_4^(2-)+2H^+ 1/2(1)
These three dissolved compounds raise the acidity of the water and decrease the pH, unless neutralized. The ferrous iron, provided enough oxygen, will oxidize to ferric iron, which will reduce the pH level and act as an oxidant to additional pyrite.
INTRODUCTION/BACKGROUND: Acid mine drainage (AMD) often occurs at abandoned mining sites. Acid generation is the result of combining certain minerals, water, and an oxidant. Sulfide minerals are the most common producers of AMD, but mining waste rock, tailings, and other mining structures also generate AMD. AMD has a low pH and consists of large concentrations of heavy metal and other toxic elements. This pollutant affects both human health and the environment. AMD also occurs …show more content…
Many AMD regions have a pH of 4 or less, which is comparable to battery acid or vinegar. [5] With such an acidic environment, the food web is often destroyed and AMD regions can be completely dead. Aquatic insects are rarely present, thus leaving organisms that feed off them, such as minnows, without food. Fish are also affected by the low pH, especially during the reproduction process. The acidity effects the development of the eggs, metamorphosis is slowed, and the mortality rate rises. [7]
The chemical reaction process of the acid generation can be described using a common sulfide mineral, Pyrite (FeS2). The oxidation of FeS2 breaks down into three components, iron, sulfate, and hydrogen as seen below:
FeS_2+7/2 O_2+H_2 O→Fe^(2+)+2SO_4^(2-)+2H^+ 1/2(1)
These three dissolved compounds raise the acidity of the water and decrease the pH, unless neutralized. The ferrous iron, provided enough oxygen, will oxidize to ferric iron, which will reduce the pH level and act as an oxidant to additional pyrite.