Mobilization of radionuclides and trace metals in tailings at the Rautuvaara mining site

• Main Author: Pelkonen, Mila Kristiina
• Other Authors: Helsingin yliopisto, Matemaattis-luonnontieteellinen tiedekunta, Kemian laitos, University of Helsinki, Faculty of Science, Department of Chemistry, Helsingfors universitet, Matematisk-naturvetenskapliga fakulteten, Kemiska institutionen
• Format: Master Thesis
• Language: English
• Published: Helsingin yliopisto 2018
• Subjects: Radiochemistry; Radiokemia; Radiokemi; Kolari; Rautuvaara; Niesajoki
• Online Access: http://hdl.handle.net/10138/273579

The old Rautuvaara mining area is located in North-West Finland, in the municipality of Kolari. Rautuvaara mine was operational between the years of 1962 and 1988 and the tailings field, located in the Niesajoki valley, was used to dispose of mine tailings from several different mines until 1995. Currently there are no mining activities at the Rautuvaara mining area, but it has become an object of interest, since an on-going mining prospect in Hannukainen is planning on transporting their produced tailings to Rautuvaara and depositing them above the existing ones. Sulphide-bearing ores and mine waste are known to form acid mine drainage (AMD) when sulphuric acid forms in the oxidative dissolution of sulphide minerals. The decreased pH in the area affected by AMD can further dissolve and mobilize harmful elements from the surroundings minerals, which may contaminate the natural water systems. The aim of this study was to evaluate the occurrence and possible mobilization of the base metals Ni, Zn, Cu, Co, Fe, and Mn, potentially toxic metals As, Pb, Cr, and Cd, as well as the radioactive elements U-238 and Th-232, in samples collected from the Rautuvaara mining area. The collected samples included water samples from the mining area and its surroundings and four types of solid samples: enrichment sand samples from the tailings, sediment samples from the old settling pond, waste rock samples from the old mining area and acidic pond sand samples from the area of the tailings affected by AMD. Measuring the total concentrations of metals and radionuclides in solid sample materials is not enough to understand the mobility and bioavailability of different elements and for this purpose a six-step sequential extraction procedure, with progressively increasing leaching reagents, was applied for all the solid samples. This was done in order to access the geochemical association of metals and radionuclides in the solid samples. The studied fractions were the exchangeable fraction I (pH 7,8), exchangeable fraction II (pH 5,0), ...