Acid Base Accounting of Overburden and Coal

Abstract

Acid-Base Accounting (ABA) is an analytical procedure that provides values to help assess the acid- or alkaline-producing potential of overburden rocks prior to coal mining. This procedure was developed at West Virginia University in the late 1960s. After the passage of laws requiring an assessment of surface mining on water quality, ABA became the preferred method to predict post-mining water quality, and permitting decisions for surface mines are based on the values determined by ABA. In order to predict the post-mining water quality, the amount of acid-producing rock is compared to the amount of alkaline-producing rock, and a prediction of the water quality at the site (whether acid or alkaline) is obtained.

Samples were collected from the coalfields of Jindal Steel and Power Limited, Raigarh. Maximum potential acidity (MPA), net neutralization potential (NNP), neutralization potential (NP), and NP/MPA ratios were determined for each site based on ABA.

Neutralization potential of overburden ranges from 8.1 to 27.0 ppt while in coal it varies from 2.4 to 12.0 ppt. ABA is a good tool to evaluate overburden quality during leaching before mining and to forecast post-mining drainage quality after mining.