Teemu Karlsson & Päivi M. Kauppila, Geological Survey of Finland, P.O. BOX 1237, FI-70211 Kuopio, FINLAND, e-mail: teemu.karlsson(at)gtk.fi
Comprehensive mineralogical analysis is essential is assessing the environmental impacts of mine wastes. The mineralogical characterisation of mine waste is used to determine the mineralogical composition i.e. relative abundances of the minerals and the relative degree of weathering of mineral grains. The objective is to identify acid-generating and neutralizing minerals, minerals which contain potentially harmful substances, harmful fiber forming minerals like asbestos, and easily weathering minerals, e.g. salt minerals. (Kauppila et al. 2013) Microscopic studies also enable more detailed assessment of the suitability of the waste materials for other applications, such as construction material or raw material, through characterisation of properties such as grain size distribution, grain morphology and the nature of grain boundary interfaces (Heikkinen et al. 2005).
The first observation of the minerals in waste material, especially on waste rocks, is usually carried out on-site as a visual description. A commonly used mineralogical investigation is the simplified petrographic description, which consists of a macroscopic description of hand specimen and a more detailed investigation of a thin section with a petrographic microscope i.e. transmitted light microscope or reflected light microscope. Polished thin section studies under reflected light (ore microscopy) are typically needed for waste rocks and tailings from mining activities, since these materials contain opaque minerals i.e. ore minerals that do not transmit light. The mineral abundances (i.e. modal mineralogical composition) of the waste materials are typically determined in the microscopic studies using a standard point-counting method (measuring 600 points), where the general grain size and/or the occurrence of opaque minerals make it possible, or with X-ray diffraction analysis or scanning electron microscope equipped e.g. with MLA (mineral liberation analyser). For more detailed mineralogical analysis recommendable methods include e.g. X-ray diffraction analysis of fine grained rock powder and scanning electron microscopic studies (Kauppila et al. 2013).
The most typically used mineralogical analysis methods include (Technical Committee 2012, Kauppila et al. 2013, INAP 2009, European Commission 2009):
- On-site observations, visual description
- Optical microscopy: transmitted light microscopy (TLM), reflected light microscopy (See Simplified petrographic description)
- X-ray diffraction (XRD)
- Scanning electron microscopy (SEM)
- Infrared (IR), near infrared to infrared (FT-IR method) and Raman spectroscopy
Other mineralogical methods intended for more detailed analysis of certain mineralogical properties include e.g. (Technical Committee 2012, INAP 2009, European Commission 2009):
- Thermal analysis differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) (+ analyser of flue gas)
- High-resolution transmission electron microscopy (HRTEM)
- X-ray photoelectron spectroscopy (XPS) or electron spectroscopy for chemical analysis (ESCA)
- Vertical scanning interferometry (VSI)
- Electron paramagnetic resonance
- Nuclear magnetic resonance
- Mössbauer spectrometry
- Specialized microbeam mineralogical techniques
- Laser ablation ICP-MS
- Proton induced x-ray emission (PIXE)
- Secondary ion mass spectrometry (SIMS). See SIMS-page of SERC (Mueller & Vervoort 2012)
- Extended x-ray absorption fine structure / x-ray absorption near-edge structure (EXAFS/XANES)
European Commission 2009. Reference Document on Best Available Techniques for Management of Tailings and Waste-Rock in Mining Activities. January 2009.
Heikkinen, P.M. (ed.), Noras, P. (ed.), Salminen, R. (ed.), Mroueh, U.-M., Vahanne, P., Wahlström, M., Kaartinen, T., Juvankoski, M., Vestola, E., Mäkelä, E., Leino, T., Kosonen, M., Hatakka, T., Jarva, J., Kauppila, T., Leveinen, J., Lintinen, P., Suomela, P., Pöyry, H., Vallius, P., Nevalainen, J., Tolla, P. & Komppa, V. 2008. Mine closure handbook. Espoo: GTK; VTT; Outokumpu Oyj; Finnish Road Enterprise; Soil and Water Ltd. 169 p.
INAP 2009. The GARD Guide. The Global Acid Rock Drainage Guide. The International Network for Acid Prevention (INAP). http://www.gardguide.com/|http://www.gardguide.com/
Kauppila, P., Räisänen, M.L. & Myllyoja, S. (eds) 2013. Best Environmental Practices in Metal Ore Mining. Finnish Environment Institute 29en / 2011. 219 p. https://helda.helsinki.fi/handle/10138/40006
Mueller, P. and Vervoort, J. 2012. Secondary Ion Mass Spectrometer (SIMS). Retrieved Dec. 3 2014, from http://serc.carleton.edu/research_education/geochemsheets/techniques/SIMS.html
Technical Committee CEN/TC 292 2012. Characterization of waste – Overall guidance document for characterization of wastes from extractive industries. CEN/TR 16376:2012.