MINERALOGICAL AND GEOCHEMICAL INVESTIGATION OF PYRITE-RICH MINE WASTE FROM A KYANITE MINE IN CENTRAL VIRGINIA

A kyanite mine in Central Virginia produces 150,000 metric tons of commercial grade kyanite annually. This operation currently produces an estimated 18,000 metric tons of pyrite waste per year. This is significant as pyrite plays a major role in the environment because it is a source of acid mine drainage (AMD). Acid mine drainage affects the surrounding environment’s water quality, and the surrounding landscape and ecosystem. The dissolution and oxidation of pyrite is the main cause of AMD. The extent of this alteration process is dependent on crystallinity, particle size, and reactivity.

Samples of the kyanite mine pyrite waste stream were investigated to determine environmental risks and assess suitability for recycling. Grain size distribution of this waste stream is variable, being between 2.0 mm and 0.038 mm in diameter. In addition to pyrite, other major minerals of the waste stream are quartz, muscovite, kyanite, pyrophyllite and hematite. These minerals have potential for recycling. Pyrite can be recycled for use in the production of sulfuric acid and can be used as a pigment in glass production. Pyrite is currently sold by the mine or is stored in sealed silos on site depending on market demand. Muscovite found in the waste stream can be recycled and used in industrial applications, including in paint pigment. Pyrophyllite occurs in variable amounts and may be recycled for certain ceramic applications if quantities permit. Minor minerals observed include galena and rare earth element (REE) phosphates. Galena is of environmental concern as lead is a priority pollutant metal. REE phosphates are relatively uncommon and economical reprocessing is not likely to occur. Galena and REE phosphates can be separated by density concentration methods and therefore do not restrict recycling.

The study of the mineralogy of the waste stream indicates some level of viability for recycling. However, further investigation to determine heavy metal content, mineral purity, and precious metal content are needed. Heavy metal content and mineral purity must be assessed to establish the most viable means of recycling. Precious metal content should be assessed to establish economic value and if present may be a driver for recycling. If found viable, recycling of the pyrite waste stream may improve the economy of the local area.