Add time:08/15/2019         Source:sciencedirect.com

The iron disulfide minerals, pyrite and marcasite, are assumed to be the principal cause of acid mine drainage. Although research has shown a correlation between total sulfur content and the total acidload, it is quite clear that there is no one single compositional parameter which controls both the rate and amount of acid production from the weathering of toxic mine wastes. The objective of this research is to evaluate the relationships which may exist between the amount and rate of acid production and the size, morphology, type and immediately associated mineralogy of iron disulfide minerals contained within the toxic rock materials.To this end, 116 samples were collected from the various potentially toxic rock units associated with coal for five different coal beds from twenty mines over an area of five counties in West Virginia in the northern Appalachian Basin. Each sample was subjected to the soxhlet leaching technique to evaluate the acid-producing potential. Of the samples thus characterized, 56 were chosen for petrographic analysis by both reflected and transmitted light microscopy. The reflected light analysis provided: (1) the volume percentage of each iron disulfide morphological type present, calculated as a portion of the whole rock, (2) the average dimension of each morphological type, and (3) the volume percentage of marcasite present. The immediate mineralogical associations of the individual disulfide grains were determined by transmitted light microscopy.It is shown that both the total amount of acid and sulfate ion produced by the artificial weathering of the rock materials correlated with an increase in the percentage of the massive iron disulfide morphology. There also appears to be a positive correlation between the abundance of euhedral aggregates and both acidload and sulfate ion production. The study indicated, that contrary to reports in the literature, framboids are not major contributors to either acidload, sulfate ion production or acid production rate. The percentage of marcasite was not significantly correlated with acidload, sulfate production or acid production rate. The rate of acid production did appear to be somewhat influenced by the size of the massive iron disulfide morphology. However, the relationship is not strong and additional research suggests that other factors such as the porosity and permeability of the rock may be more important.

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