The aqueous oxidation of sulphide minerals leads to the generation of acid mine drainage (AMD), one of the main causes of water pollution worldwide. Mineral reactivity is greatly enhanced as a result of extraction and processes such as blasting, crushing, and grinding that increase rock surface area. The exposition of sulphide mine wastes to atmospheric conditions enhances AMD generation. However, a large number of processes and factors (e.g., pH, redox conditions, aqueous and surface complexation reactions) may control the mobility of elements in solution. In particular, the formation of soluble secondary minerals may act as transient storage of metals and acidity during AMD generation, leading however to their release upon rainfalls. To study the influence of mineralogy and grain size on the metal release from a variety of sulphide mine wastes collected in the Iberian Pyrite Belt, different grain size samples were treated with distilled water (S:L ratio 1:10) for 24 h simulating rainfall weathering. Results reveal that grain size plays a major role on metal mobility from sulphide mine wastes. However, mineralogical and geochemical evidence points at the partitioning of highly soluble secondary minerals among grain size fractions as the key factor controlling the metal release rate from these wastes. The results obtained show the importance of grain size on the reliability of the different leaching test procedures, and thus encourage standardizing these procedures worldwide.

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