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Geochemistry of Acid Mine Waste
Published in William J. Deutsch, Groundwater Geochemistry, 2020
The precipitation of secondary minerals at different “fronts” in a tailings pile can affect the movement of porewater by forming horizontal banners to vertical flow. Blowes et al.22 discuss the occurrence of a discontinuous, cemented layer (hardpan) at the Quebec tailings pile described above. This layer is 1 to 5 cm thick and occurs at the depth of active sulfide mineral oxidation. Cementation is produced by Fe(III) minerals, principally goethite, lepidocrocite, ferrihydrite, and jarosite. At a separate, inactive, sulfide tailings site in New Brunswick, they describe another type of hardpan that is 10 to 15 cm thick and continuous and occurs 20 to 30 cm below the depth of active oxidation at the first appearance of calcite. In this case cementation is caused by the precipitation of gypsum and Fe(II) solid phases, principally, melanterite (FeSO4·7H2O). The lack of precipitation of the Fe(III) oxide and sulfate minerals at this site is attributed to a higher sulfide content in the tailings and a lower pH, which increases the solubility of the Fe(III) minerals, minimizing their formation. Concentrations of Fe(II) and sulfate increase until melanterite becomes supersaturated. Gypsum also precipitates when calcite is encountered because the dissolution of calcite releases calcium that can combine with sulfate to form gypsum. The presence of these hardpan layers in the tailings piles are viewed as a benefit because they limit the movement of solution and gases through the reactive tailings material.
Analysis on Spontaneous Combustion Characteristics of Adding Associated Sulfur Minerals in Coal
Published in Combustion Science and Technology, 2019
Hailin Jia, Hedi Shen, Chenguang Zhai
Melanterite and copiapite are one of the hydrates formed by the reaction of iron sulfate with oxygen in a humid environment (Ackermann et al., 2009; Majzlan et al., 2006). Melanterite and copiapite can be co-existed with pyrite, elemental sulfur, and other substances in the coal seam or coal seam roof rock. Melanterite, copiapite, pyrite, and elemental sulfur will undergo a series of chemical reactions in a humid environment with sufficient oxygen: