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- Hällström, Lina P.B., et al.
(author)
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The geochemical behaviour of Be and F in historical mine tailings of Yxsjöberg, Sweden
- 2020
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In: Journal of Geochemical Exploration. - : Elsevier. - 0375-6742 .- 1879-1689. ; 218
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Journal article (peer-reviewed)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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| 2. |
- Hällström, Lina, et al.
(author)
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Scheelite weathering and tungsten (W) mobility in historical oxidic-sulfidic skarn tailings at Yxsjöberg, Sweden
- 2020
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In: Environmental Science and Pollution Research. - : Springer. - 0944-1344 .- 1614-7499. ; 27:6, s. 6180-6192
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Journal article (peer-reviewed)abstract
- More knowledge of the geochemical behavior of tungsten (W) and associated contamination risks is needed. Therefore, weathering of scheelite (CaWO4) and secondary sequestration and transport of W to groundwater in historical skarn tailings and surface water downstream of the tailings were studied. The tailings contained 920 mg/kg W, primarily in scheelite. Mineralogical and geochemical analyses were combined to elucidate the geochemical behavior of W in the tailings, and water samples were taken monthly during 2018 to monitor its mobility. In the tailings, a large peak of W was found at 1.5 m depth. There, 30 wt%. of W was present in easily reducible phases, indicating former scheelite weathering. Currently, W is being released from scheelite to water-soluble phases at 2.5 m depth. The release of WO42− is hypothetically attributed to anion exchange with CO32− released from calcite neutralizing acid produced from pyrrhotite oxidation in the upper tailings and transported downwards to pH conditions > 7. Higher concentrations of dissolved W were found in the groundwater and particulate W in downstream surface water than in reference water, but they were lower than current contamination thresholds. Tungsten showed correlations with hydrous ferric oxides (HFO) in both the tailings and surface water.
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