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| 2. |
- Holmström, Henning, et al.
(författare)
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Oxygen penetration and subsequent reactions in flooded sulphidic mine tailings: a study at Stekenjokk, northern Sweden
- 1999
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Ingår i: Applied Geochemistry. - 0883-2927 .- 1872-9134. ; 14:6, s. 747-759
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Tidskriftsartikel (refereegranskat)abstract
- A study of O2 penetration and pore water geochemistry of the flooded tailings at Stekenjokk has been performed. The results show that there is a diffusion of elements from the tailings pore water to the overlying water. The presence of elements such as Ca, Mg, S, Si, Ba and Sr are likely the result of diffusion of older process water trapped in the tailings. Oxygen concentrations in the tailings measured with microelectrodes show that there is O2 available down to 16 to 17 mm depth in the tailings. Pore water analyses show that there are subsurface maxima for the elements Cu, Zn, Ni, Co and Cd at depths of 0.25 to 2.75 cm. The highest concentrations of almost all elements were found where previously oxidised material was deposited before the flooding. Lower pH is measured in the uppermost part of the tailings compared with the pond water and the tailings pore water at depth. Oxidation of sulphides in the uppermost part of the tailings is probably occurring. A decrease in oxidation rate can be expected in the future due to deposition of organic material at the tailings surface. Flooding seems to be an efficient remediation method at Stekenjokk.
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| 3. |
- Holmström, Henning, et al.
(författare)
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Role of carbonates in mitigation of metal release from mining waste. Evidence from humidity cells tests
- 1999
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Ingår i: Environmental Geology. - : Springer Science and Business Media LLC. - 0943-0105 .- 1432-0495. ; 37:4, s. 267-280
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Tidskriftsartikel (refereegranskat)abstract
- Leaching of two contrasting types of sulphidic tailings in humidity cells has been performed. The release of heavy metals and the oxidation rate have been studied. Tailings from the Laver mine contain a few percent sulphides and lack carbonates, whereas tailings from the Stekenjokk mine are both sulphide- and carbonate-rich. The results showed that in the leachates from the Laver samples, the metal concentrations increased and pH decreased with time, indicating an increased oxidation rate. In the Stekenjokk samples, pH remained high during the experiment, thereby keeping the metal concentrations low in the leachates. The oxidation rate also decreased with time, probably due to Fe-hydroxide coatings on sulphide surfaces. The results show that addition of carbonates and the maintenance of a high pH not only reduce the solubility of heavy metals, but also decrease the oxidation rate of sulphides.
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| 4. |
- Holmström, Henning, et al.
(författare)
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Secondary copper enrichment in tailings at the Laver mine, northern Sweden
- 1999
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Ingår i: Environmental Geology. - : Springer Science and Business Media LLC. - 0943-0105 .- 1432-0495. ; 38:4, s. 327-342
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Tidskriftsartikel (refereegranskat)abstract
- Field and laboratory studies of the sulphide-bearing tailings at Laver, northern Sweden, show that the present release of metals from the tailings is low, especially with regard to Cu. A large part of the Cu released by sulphide oxidation is enriched in a distinct zone just below the oxidation front. The enrichment zone occurs almost all over the tailings area except in areas with a shallow groundwater table. The Cu enrichment is caused by formation of covellite and adsorption onto mineral surfaces. The transport of Zn, Co, Cd, Ni and S seems to be controlled mainly by adsorption. No secondary zone or secondary minerals containing these metals have been found. Just below the groundwater table, metals are released into solution when the enrichment zone reaches the groundwater due to the low pH. An increased release of metals, especially Cu, can be expected in the future, since the enrichment zone is moving towards the groundwater table.
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| 7. |
- Land, Magnus, et al.
(författare)
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Past and present weathering rates in northern Sweden
- 1999
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Ingår i: Applied Geochemistry. - 0883-2927 .- 1872-9134. ; 14:6, s. 761-774
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Tidskriftsartikel (refereegranskat)abstract
- Past and present chemical weathering rates in granitic till have been estimated. The Kalix River watershed in northern Sweden was used as a study area in which 17 evenly distributed soil profiles were investigated. The two estimations are based on elemental depletion trends in soil profiles and input/output budgets for the elements in the watershed, respectively. In the calculations of the past weathering rate it was assumed that zircon is resistant, and thus Zr was considered to be immobile during weathering. The long-term average chemical erosion rate since the area was deglaciated 8700 a ago, expressed as the sum of major element oxides (SiO2, Al2O3, CaO, Fe2O3, K2O, MgO, MnO, Na2O), was estimated to be 5.8 g·m−2·a−1. In terms of base cation (Ca2+, Mg2+, Na+, K+) depletion this corresponds to 0.36 keq·ha−2·a−1. All elements analysed have been depleted from the E-horizon, and the most affected elements are P with an average mass loss of 86% (as P2O5), La 81%, Co 78%, Cu 77% and Ni 76%. The present-day weathering rate was calculated as the difference between outputs and inputs in the Kalix River watershed. The input was considered as the contribution from precipitation, while the output was calculated as the sum of (1) the river-transported dissolved fraction, (2) the river-transported suspended non-detrital fraction (chemically precipitated Fe- and Mn-oxy-hydroxides and matter sorbed on these particles), and (3) the biotic nutrient net uptake. River-transported outputs were measured for an annual cycle starting in September 1991 and ending in August 1992. The present-day chemical erosion rate of the till was estimated to be 6.3 g·m−2·a−1 (sum of major element oxides), or a base cation flux of 1.42 keq·ha−2·a−1. Part of this present-day rate is related to carbonate weathering in the Caledonian mountain range which makes it difficult to compare the present weathering rate with the historical weathering rate. After correction for carbonate weathering the resulting present-day weathering rate of granitic till in terms of base cation flux was estimated to be 0.65–0.75 keq·ha−2·a−1. This result indicates that the present cation flux has increased by a factor of 1.8–2.1 compared to the long-term average. However, given the uncertainties introduced by the carbonates in the Caledonian mountain range it is not possible to prove any significant difference between the mean post-glacial and the present-day weathering rate with the methods used in this study.
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| 8. |
- Land, Magnus, et al.
(författare)
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Seasonal variations in the geochemistry of shallow groundwater hosted in granitic till
- 1997
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Ingår i: Chemical Geology. - 0009-2541 .- 1872-6836. ; 143:3-4, s. 205-216
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Tidskriftsartikel (refereegranskat)abstract
- The groundwater chemistry in a small catchment in northern Sweden has been studied for a period of 15 months, including two snowmelt events. The groundwater was sampled from two wells in a slope facing a small stream. One well was placed at the top of the slope (28 m from the stream), and the other was placed closer to the stream (13 m from the stream). Both wells were completed to approximately the same elevation (1.5 m below the stream bed). In addition to groundwater compositions, the chemical composition of precipitation, soil water and stream water was investigated. The chemical composition of the groundwater in the well farther from the stream was fairly constant during the studied period. In the closer well the concentrations of Ca, Mg, Na, Sr, Si, and alkalinity decreased by approximately 10% during snowmelt in May. In contrast, the concentrations of Fe, Al, Ce and Cu increased. After the snowmelt, during June and July, the concentrations of Ca, Mg, Na, Sr, Si, and alkalinity in the closer well increased by a factor of 2–5 compared with the concentrations prior to the snowmelt. By August, the concentrations had decreased to the same levels as before the snowmelt and remained constant until next snowmelt. To explain these variations the Ca/Sr ratio was used as a natural chemical tracer for different water masses. It was found that the increased concentrations of Ca, Mg, Na, Sr, Si, and alkalinity during summer was caused by changes in the groundwater flow direction, which resulted in upwelling of deeper groundwater. At this time the area at the closer well acted as an unsaturated discharge area. The concentrations of Fe, Al, Ce and Cu decreased rapidly after the snowmelt and then remained constant except for two peaks in July and August. These variations were due to mixing with rapidly percolating soil water from the E-horizon and melt water or rain water, which is supported by increased content of dissolved oxygen.
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| 9. |
- Land, Magnus, et al.
(författare)
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Solid speciation and fractionation of rare earth elements in a Spodosol profile from northern Sweden as revealed by sequential extraction
- 1999
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Ingår i: Chemical Geology. - 0009-2541 .- 1872-6836. ; 160:1-2, s. 121-138
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Tidskriftsartikel (refereegranskat)abstract
- A sequential extraction has been carried out on seven soil samples from a spodosol profile in till with granitic composition. The soil profile was sampled in northern Sweden. Five fractions were selected for extraction: (A) CH3COONa-extractable (exchangeable/adsorbed/carbonate); (B) Na4P2O7-extractable (labile organics); (C) 0.25 M NH2OH⋅HCl-extractable (amorphous Fe-oxyhydroxides/Mn-oxides); (D) 1 M NH2OH⋅HCl-extractable (crystalline Fe-oxides); and (E) KClO3/HCl-extractable (organics and sulphides). Extracted rare earth elements (REE) were determined with High Resolution ICP-MS. In addition to the soil, stream water suspended particulate matter was also analysed for REE. Total concentrations in the soil samples show that the REE have been fractionated during weathering. In the acidic (pH 4.28) E-horizon all REE are depleted relative to the unweathered till. The depletion decreases with increasing atomic number. Also in the B-horizon (pH 5.86) the REE are depleted, although to a lesser extent compared to the E-horizon. Secondary phases in the B-horizon fractionate the REE in different ways. Rare earth elements extracted in extractions A and C were enriched in the intermediate REE relative to heavy and light REE if normalized to local till. In extractions B and D, the heavy REE were enriched relative to the light REE, and in extraction E a large enrichment of light REE relative to heavy REE was found. Stream water suspended particulate matter is enriched in all REE relative to local till. The light REE are more enriched than the heavy REE. Normalized La/Lu ratios in the suspended matter ranged from 1.5 to 2.4, and were negatively correlated with stream water discharge as well as with content of detrital inorganic matter in the suspended load. The only extracted phase that potentially can explain the high normalized La/Lu ratio in the suspended matter is the phase extracted in extraction E, which has a ratio of 2.0–4.2. The normalized La/Lu ratio for the rest of the extractions ranged from 0.5 to 1.2. It is concluded that organic matter seems to be important for the particulate transport of REE in northern coniferous areas.
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