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- Hällström, Lina, P.B
(författare)
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Geochemical Characterization of Historical W, Cu and F Skarn Tailings at Yxsjöberg, Sweden : With focus on scheelite weathering and tungsten (W) mobility
- 2018
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Little attention has been paid to tailings from skarn ore deposits and their environmental impact, even though they can contain elevated content of elements of potential concern. Historical skarn tailings from a former scheelite mine at Yxsjöberg, Sweden, containing e.g. Be, Bi, Cu, F, Sn, S, W, and Zn were geochemically characterized as a first step to evaluate the potential environmental impact and if re-mining of the tailings can be a remediation option. Beryllium, Bi, F, and W are considered as elements of potential concern, and are at the same time listed by the European Commission (2017) as critical raw materials. Scheelite is considered as a relatively stable mineral but most research has been focused on extraction processes. A few laboratory studies have shown weathering of scheelite by artificial groundwater, where the release of WO42-was hypothesized to be due to anion exchange by CO32-. Thus, the release of W from scheelite should be favorable in skarn tailings due to the presence of carbonates.The tailings at Yxsjöberg were deposited between 1897 and 1963 in the Smaltjärnen Repository without dams or a complete cover, and have been in contact with the atmosphere for more than 30 years. Four vertical cores (P2, P4, P5, and P7) throughout the tailings were taken and divided into 134 subsamples, and analyzed for their total chemical composition and paste pH. Selected samples from different depths were mineralogically characterized using optical microscopy, scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS), Raman vibrational spectroscopy, and X-ray diffraction (XRD). Minerals, hand-picked from drilled rock cores, were analyzed for the element content, and a modified Element to Mineral Conversion (EMC) in combination with a 7-step sequential extraction of the tailings was used to pinpoint the quantitative distribution of elements between the minerals in the tailings. Scheelite weathering and secondary sequestration of W was studied in detail in one representative core. The release of elements to groundwater in the tailings and downstream surface water was measured monthly during 2018 to especially examine the mobility of W.The average concentrations of Be, Bi, Cu, Sn, Zn, W, F and S in the tailings were 280, 490, 950, 560, 300, and 960 ppm, and 1.9 and 1.2 wt.%, respectively. The uppermost tailings have been exposed to the atmosphere for more 30 years, with intensive pyrrhotite oxidation and carbonate dissolution, resulting in low pH (<4) condition, release of elements, and subsequent formations of secondary minerals such as gypsum and hydrous ferric oxides (HFO). Two different deposition periods were identified in one vertical profile. The later period of deposition extended from the ground surface down to 3.5 m, and the older from 3.6 to 6 m. Both periods had unoxidized tailings in the bottom and oxidized sulfides, depletion of calcite and HFO formations upwards.Tungsten was primarily found in scheelite and the abundance was 0.1 wt.% in the tailings at Yxsjöberg. Accumulation peaks of W were found with depth in P2, P4 and P7. In the upper peak of P4, 30% of the total W was associated with secondary HFO. This indicates that weathering of scheelite and secondary capturing of W had occurred in the tailings. At present time, a peak of W in water soluble phases where coinciding with accumulated C in the solid phase at 2.5m depth. Carbonate ions were released when calcite was neutralizing the acid produced in the upper oxidized tailings and the released CO32-was transported downwards to conditions with pH >7. There, it mainly had precipitated as secondary calcite, but small parts are hypothesized to have exchanged WO42-on the surface of scheelite,releasing WO42-to the pore water. In the oxidized tailings of the older and deeper tailing,goethite was found as rims around scheelite grains. This is probably due to Fe ions attracted to the negative surface of scheelite. This is suggested to decrease further weathering of scheelite, and also to some extent decrease the release of WO42-to the groundwater from above lying layers through adsorption.The changes in geochemical conditions in the tailings have decreased the water quality in receiving waters of Smaltjärnens Repository with increased concentrations of Ca, F, Fe,Mn, and SO42-. pH was on average 6.3 in the groundwater in the tailings and 5.7 in the surface water 300 m downstream. EC was on average 2.6 mS/cm in the groundwater and 131 μS/cm in the surface water. Low concentrations of dissolved W was found in the groundwater (max: 20 μg/l) in the tailings and in the downstream surface water the W concentration (max: 0.2 μg/l) was 20 times larger than the reference sample. These results show that scheelite is releasing W to a limited degree to downstream waters and are therefore a potential resource to re-mine to support the supply of critical raw materials in the EU.Beryllium, F, and Zn were released to the downstream surface water from the Smaltjärnen Repository, and to a higher degree than W. The rare and easily-weathered mineral danalite (Fe4Be3(SiO4)3S) contained approximately 40% of the total Be and Zn concentrations in the tailings and is suggested to be the major source to the release of Be and Zn. Fluorine was mainly found in fluorite which showed signs of weathering in the acidic condition in the uppermost oxidized tailings, subsequent with decreased content in the tailings. The mobility of these elements will be further studied.
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| 2. |
- Hällström, Lina P.B.
(författare)
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Mobility of Be, Bi, F, Ga, Ge and W in Surface Water and the Water Quality Impact on Epilithic Diatoms Downstream of the Historical Yxsjoberg Mine Site, Sweden
- 2022
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Ingår i: Mine Water and the Environment. - : Springer Nature. - 1025-9112 .- 1616-1068. ; 41:3, s. 731-747
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Tidskriftsartikel (refereegranskat)abstract
- There is a potential risk that the geochemical cycles of several critical metals will be affected when mining of these metals increases to meet the demand of green technology. The geochemistry of Be, Bi, Ga, Ge, and W, herewith called CM5, is lacking, yet is necessary to ensure responsible mine waste and water management. Beryllium, Bi, and W are all considered immobile, but in previous studies of skarn tailings in Yxsjoberg, Sweden, all three elements were mobilized. The tailings are enriched in CM5, together with pyrrhotite, calcite, and fluorite. The mobility and environmental impact of CM5 and F in surface waters downstream of the Yxsjoberg mine site, Sweden, were studied using monthly water samples from seven locations and analysis of diatoms at five of these locations. Bismuth, Ge, and W were present at low concentrations, transported in the particulate phase, and likely settled in the sediments hundreds of meters from the tailings. Beryllium and F were present at high concentrations and dominantly transported in the dissolved phase. At these pH conditions (5.6), Be should form insoluble hydroxides; however, elevated concentrations of dissolved Be were observed more than 5 km from the mine site. Diatoms downstream of the mine site were negatively affected by the mine drainage. The release of low quality neutral mine drainage will continue for hundreds of years if remediation actions are not undertaken since only a small portion of the tailings have weathered during 50-100 years of storage.
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| 3. |
- Hällström, Lina P.B., et al.
(författare)
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The geochemical behaviour of Be and F in historical mine tailings of Yxsjöberg, Sweden
- 2020
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Ingår i: Journal of Geochemical Exploration. - : Elsevier. - 0375-6742 .- 1879-1689. ; 218
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Tidskriftsartikel (refereegranskat)abstract
- The speciation, mobility, transport, and fate of beryllium (Be) in the terrestrial environment is poorly studied even though it is considered to be one of the most hazardous elements in the periodic table. Historical tailings containing the unusual mineral danalite [Be3(Fe4.4Mn0.95Zn0.4)(SiO4)3.2S1.4] together with Fe-sulfides and fluorite has been stored open to the atmosphere for more than 50y. Environmental mineralogy, which combines geochemical and mineralogical techniques, was used to elucidate the weathering of danalite and fluorite. Danalite is unstable in oxic conditions due to the occurrence of Fe(II) and S-(II) in the crystal lattice and has oxidized at the same pace as pyrrhotite in the tailings. The acidic conditions generated from sulfide oxidation and the release of F from fluorite weathering have most likely enhanced Be mobility in the tailings. Secondary gypsum, hydrous ferric oxides and Al-oxyhydroxides are hypothesized to have played an important role regarding the mobility of Be in the tailings. The results indicate that Be released from danalite was first scavenged by these secondary minerals through co-precipitation. However, the dissolution of secondary gypsum due to changing geochemical conditions has also released Be to the groundwater. The groundwater at the shore of the tailings revealed the highest Be concentrations measured anywhere in the world (average: 4.5 mg/L) even though the water has a circumneutral pH. This extraordinary finding can be explained by high concentrations of F (73 mg/L), as F and Be have been shown to form strong complexes. The weathering of danalite and fluorite will continue for hundreds of years if remediation measures are not taken. Re-mining the tailings could be an appropriate remediation method.
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| 4. |
- Hällström, Lina P. B., et al.
(författare)
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The Source, Mobility and Fate of Bismuth (Bi) in Legacy Mine Waste, Yxsjöberg, Sweden
- 2024
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Ingår i: Minerals. - : Mdpi. - 2075-163X. ; 14:2
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Tidskriftsartikel (refereegranskat)abstract
- The usage of bismuth (Bi), a critical and strategic raw material, has increased in the last 10 years. At present, the knowledge of Bi geochemistry is too limited to develop accurate mine waste and water management strategies to prevent environmental impact. Therefore, its geochemistry was studied in historical tailings in Yxsjoberg, Sweden. Intact tailings cores and shore samples were geochemically and mineralogically analyzed. Groundwater was sampled between 2016 and 2021 and analyzed for 71 elements and (SO4, F, Cl). The results were correlated with metals and dissolved organic matter (DOC), which have been previously published. The total concentrations, sequential extraction and scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDS) mapping indicated that Bi had been mobilized from the primary mineral bismuthinite (Bi2S3). In the oxidized tailings from both the cores and shore, Bi was hypothesized to have adsorbed to iron (Fe) (hydr)oxides, which prohibited high concentrations of Bi leaching into the groundwater and surface water. Dissolved Bi in groundwater was significantly correlated with DOC. In surface water, dissolved Bi was transported more than 5 km from the tailings. This study indicates that Bi can become mobile from legacy mine waste due to the oxidation of bismuthinite and either be scavenged by adsorption of Fe (hydr)oxides or kept mobile in groundwater and surface water due to complexation with DOC.
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