Geochemical characterization of sulfide mineral weathering for remediation of acid producing mine wastes

Abstract

The generation of acid mine drainage as a consequence of sulfide mineral oxidation is a widespread source of resource degradation. The objective of this investigation was to evaluate the influence of sulfide mineral weatherability on acid generation processes. In addition to acid generation by pyrite, the weathering characteristics of common sulfide minerals was investigated and correlated to detection by acid-base account (ABA) methodologies. The influence of particle morphology, and not particle size, was found to exert the dominant control on mineral weathering processes. Massive morphology particles generated acid at a significantly greater rate than euhedral morphology samples. Acid generation was a consequence of mineral dissolution which occurred nonuniformly across the surface of minerals during oxidation. Mineral surface weathering occurred at sites of excess energy including grain edges, steps, defects, microcracks and inclusions, resulting in the formation of etch pits. Massive morphology particles exhibited the greatest density of crystalline defect, and had the greatest rate of oxidation. Sulfide minerals found to be acid generating, in addition to pyrite, include marcasite, pyrrhotite, arsenopyrite, chalcopyrite and sphalerite. Minerals containing sulfur in the atomic structure which were not acid producing include barite, anhydrite, gypsum, anglesite, jarosite, chalcocite and galena. Delineation of acid producing and nonacid producing sulfur forms by ABA extraction methods, a standard operating procedure used in the United States, was determined to be ineffective. Effective mineral classification, particle morphology identification and observation of mineral weathering processes were accomplished by scanning electron microscopy. Accurate assessment of sulfur form distribution and sulfide mineral weathering characteristics are required for effective remediation of sites impacted by mining.