The effect of arctic conditions on the geochemical behavior of sulfidic mine wastes

Please join us for a graduate student seminar this Friday October 4 at 3:30 pm in rm 155 Geology presented by visiting PhD student Gary Schudel:

“The effect of arctic conditions on the geochemical behavior of sulfidic mine wastes”

Abstract: Acid mine drainage (AMD), which occurs when sulfide minerals are exposed to atmospheric oxygen and water, is one of the most significant environmental challenges in the mining industry. Given that the costs of reclaiming acid-generating wastes can be up to 100 times greater than for those of non-acid-generating wastes, it is critical to accurately predict the acid-generating potential of wastes as early as possible in the development of a mine. In mineralogical terms, the acid-generating potential is controlled by the balance between the (temperature-dependent) rates of sulfide oxidation (i.e., acid production) and the rates of carbonate dissolution (i.e., acid neutralization).

Using laboratory-scale column tests, this project seeks to assess the influence of arctic conditions (i.e., low temperatures and high salinity) on the mineral weathering processes that affect the long-term geochemical behavior of sulfidic mine wastes. Eight column tests were mounted, with four testing the effects of freeze/thaw cycles and four operated under ambient laboratory conditions. Within each set of four, two columns are rinsed with deionized water and two with a KCl and NaCl solution (5 g/L each). The tailings used in this study were characterized before kinetic testing using various physical (grain-size distribution, specific surface area, relative density), mineralogical (XRD, SEM), chemical (ICP-AES and -MS following acid digestion), and microbiological (MPN, plate counting, high-throughput 16S rRNA gene sequencing) analyses. Oxygen consumption tests were performed each month prior to flushing the columns in order to estimate rates of sulfide oxidation. Following each flush, leachates were collected and analyzed for pH, Eh, electrical conductivity, acidity, alkalinity, and metal concentrations, as well as concentrations of sulfate, thiosulfate, and tetrathionate. The results of this study will be used to better understand the long-term evolution of tailings in impoundments at Arctic mine sites.