Behaviour of Metals during Bioheap Leaching at the Talvivaara Mine, Finland

The behaviour of base metals Ni, Zn, Cu, Co, Fe, and Mn, potentially toxic metals Pb, Cr, and Cd, and the radioactive elements, U and Th, in the Talvivaara mining process, Finland has been studied by tracing metal concentrations from the black schist ore, through ores subjected to bioheap leaching of varying duration, to pregnant leach solution (PLS), and solid process waste material deposited on site in gypsum waste ponds. It is apparent that Zn, Cu, Co, and Cd are leached from the ore in a similar manner and recovered efficiently in the PLS; however, Ni, though leached, was also found in the gypsum pond at relatively high concentrations. Relatively little Pb is released from the ore, but the small fraction that is mobilised accumulates in the gypsum pond. Of the radioactive constituents, Th is essentially immobile, whereas U is readily leached from the ore, again accumulating in gypsum pond waste. In addition, a laboratory-based sequential leach test was applied to assess the future leaching potential of metals from residual ore and process waste material under different environmental conditions.Peer reviewe

Radionuclide and heavy metal redistribution at the former pilot-scale apatite plant in Sokli, northern Finland

A new phosphate mine is being planned at Sokli in northern Finland. In the late 1970s, pilot-scale mining and mineral processing took place at the site. The mobilisation of radionuclides and heavy metals from the mill tailings was examined in order to assess the potential environmental impact of past and future mining activities. Given the considerable amount of apatite still present, the waste material does not represent true tailings. Variations in abundance probably represent material discharges to the tailings rather than mobilization of the elements from the tailings themselves. No indication of heavy-metal migration was found. Extraction results suggest that only a small proportion of cadmium is in exchangeable form. Elements that are partly soluble under weakly-acidic conditions include copper, zinc, cadmium, uranium and lead. However, most of the elements are tightly bound to the sample matrix and therefore not easily released to the environment.Peer reviewe

Release of radionuclides from waste rock and tailings at a former pilot uranium mine in eastern Finland

The Paukkajanvaara mine in Eno, eastern Finland, started to operate in 1959. The mine was a test site for assessing the feasibility of larger-scale uranium extraction. Pilot-scale mining and milling were carried out between 1958 and 1961, and the mine site was rehabilitated in the early 1990s. The aim of this study was to examine the potential for further mobilization of radionuclides after remediation. There are two primary sources of contamination at the site, the waste-rock pile and the tailings. Our study indicates that 226Ra leached from the waste-rock pile and accumulated in surrounding soil. In run-off sediment samples collected from a dry stream bed near the waste-rock pile, the activity concentrations of 226Ra and 238U were higher than in soil samples. From the tailings, radionuclides can leach directly to the lake and to another small stream, which flows to the east of the waste-rock pile. In the water samples collected from this stream, uranium concentrations increased at the outlet to the lake. The results from the soil samples collected between the tailings area and the stream indicate leaching of 238U and 226Ra with the surface flow. Sediment samples collected from the bottom of the lake displayed pronounced uranium series disequilibrium with fractionations of 210Pb and 226Ra relative to the parent 238U. The results therefore indicate that leaching and accumulation of at least 226Ra from the waste-rock pile and possibly tailings is still ongoing.Peer reviewe

A comparison of analytical methods for determining uranium and thorium in ores and mill tailings

Three different methods for determining uranium and four for determining thorium in an apatite ore, black schist and mill tailings are compared. The aim of the comparative study is to obtain analytical verification of field results so that site characterization could be optimized without compromising reliability of the analysis. The samples were collected from a former pilot scale phosphate mine in Sokli, northern Finland and the Talvivaara nickel mine in Eastern Finland. A non-destructive, portable X-ray fluorescence (XRF) spectrometer was used on site to measure, semi-quantitatively, the composition of major elements, including thorium in each material. The samples were then analyzed by X-ray diffraction (XRD) to identify the main mineral components and electron probe micro-analysis (EPMA) used to identify the uranium and thorium-bearing minerals. Gamma spectrometry was used for direct determination of uranium and thorium isotopes in powdered samples. Thereafter, sample digestion experiments were performed with various acids to optimize the method for microwave digestion allowing determination of uranium and thorium by Inductively Coupled Plasma Mass Spectrometry (ICP-MS) and alpha spectrometry. For the latter method, uranium and thorium were separated using anion exchange resin filled in a column. The results show that overall a sample mass of 0.1–0.5 g with addition of 20 mL concentrated nitric acid is the most efficient means for extracting uranium and thorium simultaneously from apatite ore, black schist and mill tailings. The results for uranium and thorium concentrations determined by gamma spectrometry, alpha spectrometry and ICP-MS were in good agreement. Also the on-site measurements with portable XRF gave comparable results to other methods used in this study for thorium even without prior sample preparation

A comparison of analytical methods for determining uranium and thorium in ores and mill tailings

Three different methods for determining uranium and four for determining thorium in an apatite ore, black schist and mill tailings are compared. The aim of the comparative study is to obtain analytical verification of field results so that site characterization could be optimized without compromising reliability of the analysis. The samples were collected from a former pilot scale phosphate mine in Sokli, northern Finland and the Talvivaara nickel mine in Eastern Finland. A non-destructive, portable X-ray fluorescence (XRF) spectrometer was used on site to measure, semi-quantitatively, the composition of major elements, including thorium in each material. The samples were then analyzed by X-ray diffraction (XRD) to identify the main mineral components and electron probe micro-analysis (EPMA) used to identify the uranium and thorium-bearing minerals. Gamma spectrometry was used for direct determination of uranium and thorium isotopes in powdered samples. Thereafter, sample digestion experiments were performed with various acids to optimize the method for microwave digestion allowing determination of uranium and thorium by Inductively Coupled Plasma Mass Spectrometry (ICP-MS) and alpha spectrometry. For the latter method, uranium and thorium were separated using anion exchange resin filled in a column. The results show that overall a sample mass of 0.1–0.5 g with addition of 20 mL concentrated nitric acid is the most efficient means for extracting uranium and thorium simultaneously from apatite ore, black schist and mill tailings. The results for uranium and thorium concentrations determined by gamma spectrometry, alpha spectrometry and ICP-MS were in good agreement. Also the on-site measurements with portable XRF gave comparable results to other methods used in this study for thorium even without prior sample preparation

Radionuclide and heavy metal redistribution at the former pilot-scale apatite plant in Sokli, northern Finland

A new phosphate mine is being planned at Sokli in northern Finland. In the late 1970s, pilot-scale mining and mineral processing took place at the site. The mobilisation of radionuclides and heavy metals from the mill tailings was examined in order to assess the potential environmental impact of past and future mining activities. Given the considerable amount of apatite still present, the waste material does not represent true tailings. Variations in abundance probably represent material discharges to the tailings rather than mobilization of the elements from the tailings themselves. No indication of heavy-metal migration was found. Extraction results suggest that only a small proportion of cadmium is in exchangeable form. Elements that are partly soluble under weakly-acidic conditions include copper, zinc, cadmium, uranium and lead. However, most of the elements are tightly bound to the sample matrix and therefore not easily released to the environment

Behaviour of radionuclides during microbially-induced mining of nickel at Talvivaara, Eastern Finland

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 (UO22+) 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 226Ra, 210Pb and 210Po, 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 (232Th plus 228Th, 228Ra) 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, 238U activity concentrations range up to 3375 Bq/kg, which exceeds the permitted value (1000 Bq/kg) for natural radionuclides of the 238U series

Uraniferous bitumen nodules in the Talvivaara Ni-Zn-Cu-Co deposit (Finland): influence of metamorphism on uranium mineralization in black shales

International audienceIn the central part of the Fennoscandian Shield, the Talvivaara Ni-Zn-Cu-Co deposit, hosted by Palaeoproterozoic metamorphosed black schists, contains low uranium concentrations ranging from 10 to 30 ppm. The Talvivaara black schists were deposited 2.0-1.9 Ga ago and underwent subsequent metamorphism during the 1.9-1.79 Ga Svecofennian orogeny. Anhedral uraninite crystals rimmed by bitumen constitute the main host of uranium. U-Pb secondary ion mass spectrometry dating indicates that uraninite crystals were formed between 1,878 +/- 17 and 1,871 +/- 43 Ma, during peak metamorphism. Rare earth element patterns and high Th content (average 6.38 wt%) in disseminated uraninite crystals indicate that U was concentrated during high temperature metamorphism (> 400 A degrees C). The formation of bitumen rims around uraninite may be explained by two distinct scenarios: (a) a transport of U coincident with the migration of hydrocarbons or (b) post-metamorphic formation of bitumen rims, through radiolytic polymerization of gaseous hydrocarbons at the contact with uraninite