Question

What are the main chemical reactions involved in AMD formation?

What is the “initiator reaction” and the “propagation cycle”?

Why is this cyclical nature (regeneration of Fe2+) problematic? How do microbes play a role in these reactions?

What is “yellow boy”? Oxidation of Fe2+ is very slow at low pH values. Why does this reaction occur then in acidic environments?

Answer 1

The main chemical reactions are:

.. (1)

.. (2)

.. (3)

reaction (1) is the initiator reaction. The process becomes cyclic as you can see the production of ferrous ions in reaction (1) aids the production of more ferrous ions from reaction (2) and (3). This cyclic nature is highly problematic as more Fe2+ ions are produced, more H+ ions are also produced.. This increases acidity of water causing serious threats to aquatic life. Microbes play a crucial role in this process since they act as catalyst which can accelerate these reactions which otherwise take place at very slow rates. These microbes can survive even at very low pH and oxygen environment and accelerate the production of H+ ions.

Yellow boy: When chemical are added to neutralise the acid mine water, the ferros ions ar deposited as iron hydroxide which has a yellow color. This is called as yellow boy. This causes coloration of drinking water in nearby areas and also seriously affects marine life.

Even though oxidation of Fe2+ is low at low Ph values, they can still occur due to the presence of microbes. These microbes accelerate the rate of these reactions, increasing the pH of the water.