title: Behaviour of radionuclides during microbially-induced mining of nickel at Talvivaara, Eastern Finland.
abstract: The Talvivaara mine in Eastern Finland utilizes microbe-induced heap leaching to recover nickel and other valuable metals (Zn, Cu, Co) from a black schist ore. In addition to the target metals, the ore contains uranium at a concentration of 17 mg/kg, incorporated as uraninite (UO2). Uranium oxidizes from the U(IV) to U(VI) state during leaching and dissolves as the uranyl ion (UO2(2+)) in the acidic pregnant leach solution. Mobilisation of uranium has caused sufficient concern that plans have been developed for uranium recovery. The aim of this study is to generate new data leading to a better understanding of the fate of its radiotoxic daughter nuclides, primarily (226)Ra, (210)Pb and (210)Po, in the mining process. It is shown that uranium daughters mostly remain in the heaps during the leaching process and are associated with secondary minerals, including jarosite, goethite and gypsum. Thorium and progeny ((232)Th plus (228)Th, (228)Ra) are also mainly retained. High sulphate concentrations in the acidic solutions limit the solubility of radium by incorporation in the crystal lattices of precipitated secondary sulphates. Electron probe microanalysis shows that goethite in the heaps is uraniferous, resulting from the adsorption of U(VI). After recovery of target metals, the pregnant leach solution is neutralized to further remove metal contaminants and the resulting slurries stored in a bunded tailings pond. The activity concentrations of thorium, radium, lead and polonium isotopes are generally low in the pond owing to prior retention by secondary minerals in the heaps. However, (238)U activity concentrations range up to 3375 Bq/kg, which exceeds the permitted value (1000 Bq/kg) for natural radionuclides of the (238)U series.
authors.affiliation: Laboratory of Radiochemistry, Department of Chemistry, University of Helsinki, P.O. Box 55, FI-00014, Finland. Electronic address: hanna.p.tuovinen@helsinki.fi.
authors.forename: Hanna
authors.initials: H
authors.lastname: Tuovinen
authors.affiliation: Geological Survey of Finland, Espoo, Finland.
authors.forename: Esa
authors.initials: E
authors.lastname: Pohjolainen
authors.affiliation: Laboratory of Radiochemistry, Department of Chemistry, University of Helsinki, P.O. Box 55, FI-00014, Finland.
authors.forename: Janne
authors.initials: J
authors.lastname: Lempinen
authors.affiliation: Laboratory of Radiochemistry, Department of Chemistry, University of Helsinki, P.O. Box 55, FI-00014, Finland.
authors.forename: Daniela
authors.initials: D
authors.lastname: Vesterbacka
authors.affiliation: Department of Chemistry Loughborough University, Leics., UK.
authors.forename: David
authors.initials: D
authors.lastname: Read
authors.affiliation: The Finnish Radiation and Nuclear Safety Authority, Finland.
authors.forename: Dina
authors.initials: D
authors.lastname: Solatie
authors.affiliation: Laboratory of Radiochemistry, Department of Chemistry, University of Helsinki, P.O. Box 55, FI-00014, Finland.
authors.forename: Jukka
authors.initials: J
authors.lastname: Lehto
mesh_terms: D005387:Finland; D008906:Mining; D009532:Nickel; D011834:Radiation Monitoring; D012990:Soil Pollutants, Radioactive / Q000032:analysis*
chemical_list: D012990:Soil Pollutants, Radioactive; D009532:Nickel
keywords: Heap leaching; Metals recovery; Mobilization; Radionuclides; Talvivaara