Developments in Acid Mine Drainage Prediction

The earliest observations to understand AMD formation and its impacts date back to the 16th century when Diego Delgado recognised that the oxidation of pyrite at Rio Tinto mine generated acidic drainage that poisoned fish, and that the use of simple tests to indicate the formation of AMD provided evidence for the ecotoxicity of AMD (Lottermoser, 2015). Since then, the chemistry of acid generation (see Chapter 3) has been studied extensively and is fairly well understood. Following the introduction of laboratory tests to predict AMD, a lot of progress has been made in developing and improving the testing tools to identify and accurately predict AMD formation. Historically, the prediction approach has evolved from merely making qualitative observations and correlations between mineralogical characteristics and leachate composition, to the introduction of geochemical static and kinetic tests. These geochemical tests have formed the basis of the AMD prediction procedures still being utilised today (Lottermoser, 2015).

The Mine Environment Neutral Drainage (MEND) (2000) defined prediction as a set of integrated approaches that are followed in order to assess, in advance, the geochemical behaviour of mineral wastes at all phases of the mine life cycle. The geochemical reactions, described in detail in Chapter 3, that lead to AMD formation depend primarily on the mineralogical composition of mineral wastes and the presence of water and oxygen. Various prediction methods aim to determine whether mineral wastes at mine sites will react and oxidise to generate acid and to predict the drainage quality. However, due to high variations in the mineralogy of different waste materials from different mine sites, it may be a difficult and costly task to accurately predict the potential for AMD formation, and sometimes the reliability of data may be questioned (USEPA, 1994). Price, (2009) proposes a site-specific approach in predicting the drainage chemistry and suggests that all waste materials should be considered in the AMD prediction process.

The purpose of a prediction study is to evaluate the characteristics of the present and future drainage chemistry, and to determine the potential environmental impacts and the required remediation measures to address the problems (Price, 2009). Depending on the stage of a mining project in its life cycle, the specific prediction objectives may be to address the quality problems of existing drainage chemistry or to determine if any of the mineral waste materials will potentially form acidic drainage and estimate the timing of acid generation (MEND, 2000).

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