Prediction of acid mine drainage: Where we are

The mining and ore processing of sulfide-bearing deposits generates large volumes of waste rock (WR) and tailings, which often contain barren and residual iron sulfides (e.g., pyrite and pyrrhotite). Sulfide oxidation under atmospheric conditions can generate acidic leachates loaded with high concentrations of dissolved metal(oid)s when the carbonate content is insufficient to buffer the produced acidity. The acid generation potential of mine waste is defined by its sulfide and carbonate occurrences. Nowadays, the environmental behavior of mine waste is a key factor for the economical and technical feasibility of mining projects from exploration to mine closure. Consequently, the prediction of mine drainage formation is crucial for the mining industry to identify the costs related to mine site reclamation. Prediction is often based on multiscale laboratory and/or field tests such as static tests, column-leach tests, humidity cells, and/or field-testing. The geochemical behavior of mine waste and its prediction are controlled by many intrinsic characteristics (e.g., particle size, mineralogy, chemical composition) and extrinsic factors related to the applied tests (e.g., test dimension, flushing frequency, liquid–solid ratio, climatic conditions). The prediction of mine drainage can be conducted using chemical and/or mineralogical static tests and/or kinetic tests. Static tests provide a simple and rapid overview of the type of mine drainage by comparing the neutralization and acidification potentials. However, static tests may show contradictory results for the same sample. For this reason, static tests can be used as a preliminary indicator. Kinetic tests are used to provide information about mineral reactivity and chemical species release rates. The accurate prediction of acid mine drainage and contamination generation must further consider the following aspects: i) an accurate sampling strategy, ii) the textural properties (mineral liberation and association) of the mine waste, and iii) the scale effect during kinetic tests. Finally, from a circular economy perspective, mine waste valorization is superior to conventional management.