TECHNOGENIC MINERALS IN THE WASTE ROCK HEAPS OF ESTONIAN OIL SHALE MINES
AND THEIR USE TO PREDICT THE ENVIRONMENTAL IMPACT OF THE WASTE
E. PUURA
Department of Chemical Engineering and Technology
Royal Institute of Technology
Stockholm, S-10044 Sweden
and
Institute of Geology
University of Tartu
46 Vanemuise, Tartu
51014, Estonia
| The newly formed minerals inside the waste rock heaps of Estonian oil shale mines
were studied using X-ray diffraction analysis and scanning electron microscopy. In the unburnt heaps, the only
detectable new solid phases were ferric oxyhydroxide and gypsum. In the burnt heaps, however, a large number of
technogenic minerals were found, including lime, periclase, portlandite, brussite, calcite, aragonite, leucite,
diopside, gehlenite, wollastonite, anhydrite, ettringite, hematite, tobermorite, larnite and spurrite. The reasons for spontaneous combustion include heap size and shape, but importantly also the heterogeneities, especially gravitational fractionation of the rocks during the disposal. The areas where the shale remains not fully oxidised were found, characterised by the presence of oil in the surface layer and layers of amorphous carbon on the waste rock lumps. The negative environmental impacts of the burnt heaps, including leachate with high alkalinity and sulfate content, as well as oil plumes, may become evident after decades after burning only, because the temperature inside the heaps decreases very slowly. |