Standard Weathering Procedure for Coal Overburden, Inter-Laboratory Study of Leachate Composition

Abstract

Abstract. Simulated weathering tests are used to estimate leachate quality from rocks containing varying concentrations of pyrite and carbonates at mines. Five rock samples of coal overburden materials were subjected to a standardized column leaching test at eight commercial, university and government laboratories. Splits from sized, homogenized bulk samples were loaded in duplicate columns, incubated under humid air containing 10% CO 2 , and leached every 7 days for a 14 week period. Leachates were analyzed for mine drainage parameters including acidity, alkalinity, metals, sulfate and selected trace elements.Relative percent difference (RPD) and relative standard deviation (RSD) statistics show the variation within individual labs and among the group of labs. Fe, Al, Se, Zn and Acidity exhibited the greatest variability in results across all rock samples and labs. RPD's usually exceeded 30% for these parameters. The variation in Fe and Acidity increased with weathering duration. Ca, Mg, Na, SO 4, and specific conductance were the most consistent parameters. Mass weighting the chemical concentrations to account for differences in sample mass and leachate volumes did not noticeably improve the RPD and RSD statistics. Cumulative quantities leached were, however, consistent among labs for most parameters.About 2 to 6 % of the total sulfur present in the rocks was leached during the test. One rock sample was near saturation for gypsum, and some sulfate may have been retained in the column. Acid neutralizing capacity was depleted at a faster rate than acid producing potential. Carbonate dissolution varied, with 3 of 5 rocks producing solutions that were saturated for calcite, while two rocks produced under-saturated solutions. Four of five rocks had less than 5 % of total Ca and Mg leached, with similar or smaller leaching fractions for other elements. More than 90% of the iron mobilized by pyrite weathering was retained in the column for all samples. One acid forming sample leached elements more aggressively than the rocks producing neutral leachates.The inter-lab results show that the standard column test can yield consistent estimates of mine water composition, and differentiate the behavior of various rock and mineral assemblages. __________________

Geochemical Characterisation of Waste Rock Dump and Its Potential to Predict Acid Mine Drainage

“…Apart from waste rock dumps and tailings, surface runoff from open pit mine faces, pit workings, underground workings, spent heaps, and process waste are a few more types of mine activities that could produce AMD. (Perry et al;Naidoo, 2017). Several developed countries such as USA, China, Australia and South Africa have abandoned mine sites that are struggling to clean up their environments because of issues with acid mine drainage (Morin and Hutt, 1994;Naidoo, 2017).…”