A survey of corrosivity of underground mine waters from indian coal mines

Abstract

The coal mining industry is facing serious corrosion problems. Millions of litres of water is disposed off from some underground coal mines every day. In this survey, mine water samples from various underground coal mines were collected and analysed in an attempt to correlate the various physicochemical characteristics with their corrosivity. The analyses include determination of the values of pH, alkalinity, acidity, specific conductivity, hardness, total solids, sulphate, chloride, cupric, ferrous and ferric ions. Corrosion rates of steel in minewaters were also measured by weight-loss trial method.

The present survey shows that mine waters are nearly neutral, alkaline, midly acidic and highly acidic in nature. The corrosivity of these vary from mildly to extremely corrosive. An evaluation of minewaters corrosivity using Langelier Saturation Index has also been made but no definite relationship has been found between the corrosion rate and Langelier Saturation Index. A classification of the basis of corrosivity of these mine waters is also made.

Causes of aggressiveness of Fe³⁺, Cu²⁺, SO₄ ²⁻, Cl⁻ in acid mine waters have also been discussed which conclude that corrosion rates were significantly increased by Fe³⁺ and Cu²⁺ due to their reduction to Fe²⁺ and metallic Cu, respectively. Occurrence of these ions in acid mine waters has also been discussed.