Characteristics and potential environmental consequence of weathered materials in the surface layer of a spontaneously combusting mine spoil stockpile

Investigation was carried out to characterize the sulfidic mine spoils in the surface layer of a spontaneously combusting waste rock stockpile. The objective was to assess its potential impacts on acid mine drainage generation. The results show that there were substantial amounts of elemental S and various sulfate minerals in the weathered materials, indicating the occurrence of significant sulfide mineral oxidation in the investigated spontaneously combusting mine spoils (SCMS). It is likely that the surfacially-occurring elemental S was derived from the deeper waste rock layers experiencing spontaneous combustion under limited aeration conditions. The significantly higher acidity, EC and SO42- concentration in the SCMS, relative to the Non-SCMS suggest that spontaneous combustion is a much faster and more powerful process driving sulfide-derived acid generation, compared to microbially-catalyzed oxidation of sulfide minerals. The export of acid sulfate materials from the spontaneously combusting waste rock stockpile not only generates severe acid mine drainage but could also act as an inducer for biologically-catalyzed oxidation of newly exposed sulfide minerals in the areas surrounding the stockpile.