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

Recycling of mine waste can greatly reduce the on-site environmental impact of mining operations as well as benefit local communities. Kyanite Mining Corporation of Dillwyn, Virginia is the sole producer of the alumino-silicate mineral kyanite in the U.S. and is the largest producer of the mineral in the world. Processing of the kyanite-quartzite ore creates a silicate-rich waste stream of 450,000 to 600,000 tons annually. This study involves the mineralogical, geochemical and bulk physical properties of the silicate-rich waste stream for determination of possible alternative uses such as recycling for secondary industrial minerals or environmental applications including the use in constructive wetlands.

Fifteen representative samples were collected in April of 2008. X-ray diffraction indicates that four minerals are dominant: quartz, muscovite, hematite, and kyanite. Muscovite composes approximately 3 to 5 percent of the waste, is uniform in chemical composition and is Ti-bearing. DCP analysis of major elements resulted in SiO₂ (87.89-90.99 wt %), Al_­2O₃ (6.75-7.74 wt %), Fe₂O₃ (1.13-1.28 wt %), K_2­O (0.36-0.60 wt %). Other major elements such as TiO­₂, P₂O₅, CaO, Na₂O, MgO, and MnO were present at concentrations < 1.0 wt% or were below detection limits. ICP-MS analysis for trace elements of particular concern showed concentrations of Ag (0.05-1.7 ppm), As (0.01-0.36 ppm), Ba (177.28-218.97 ppm), Cr (6.83-8.40 ppm), Cu (12.38-37.61 ppm), Hg (0.02-3.46 ppm), Ni (4.95-14.35 ppm), Pb (18.42-31.51 ppm), Sb (0.06-2.68 ppm), Sn (4.03-6.82 ppm) Tl (0.01-0.73 ppm), V (52.54-57.36 ppm), and Zn (0.57-5.53 ppm). Se and Cd had concentrations below detection. Other trace elements detected but of less concern include Be, Rb, Sr, and Zr.

Mineralogy combined with hydraulic conductivity measurements (0.025 to 0.061 cm/s) suggests the waste is suitable for use in constructed wetlands. Bulk chemical data however indicates there are some elements of concern, although the concentrations of many are relatively low and the solubility of these components has not been determined. Muscovite is of a quality such that it may be recycled. Kyanite is of low concentration and occurs in textures not conducive to recycling. Results of this investigation suggest environmental and economic gains may be achieved by recycling this waste stream.