| 1. |
|
|
| 2. |
|
|
| 3. |
- Alakangas, Lena, et al.
(författare)
-
Simulation of pyrite oxidation in fresh mine tailings under near-neutral conditions
- 2012
-
Ingår i: Journal of Environmental Monitoring. - 1464-0325 .- 1464-0333. ; 14:8, s. 2245-2253
-
Tidskriftsartikel (refereegranskat)abstract
- Sulphidic residual products from ore processing may produce acid rock drainage, when exposed to oxygen and water. Predictions of the magnitude of ARD and sulphide oxidation rates are of great importance in mine planning because they can be used to minimize or eliminate ARD and the associated economic and environmental costs. To address the lack of field data of sulphide oxidation rate in fresh sulphide-rich tailings under near-neutral conditions, determination and simulation of the rate was performed in pilot-scale at Kristineberg, northern Sweden. The quality of the drainage water was monitored, along with oxygen and carbon dioxide concentrations. The chemical composition of the solid tailings was also determined. The field data were compared to predictions from simulations of pyrite oxidation using a 1-D numerical model. The simulations' estimates of the amount of Fe and S released over a seven year period (52 kg and 178 kg, respectively) were in reasonably good agreement with those obtained by analysing the tailings (34 kg and 155 kg, respectively). The discrepancy is probably due to the formation of secondary precipitates such as iron hydroxides and gypsum; which are not accounted for in the model. The observed mass transport of Fe and S (0.05 and 1.0 kg per year, respectively) was much lower than expected on the basis of the simulations and the core data. Neutralization reactions involving carbonates in the tailings result in a near-neutral pH at all depths except at the oxidation front (pH < 5), indicating that the dissolution of carbonates was too slow for the acid to be neutralized, which instead neutralized deeper down in the tailings. This was also indicated by the reduced abundance of solid Ca at greater depths and the high levels of carbon dioxide both of which are consistent with the dissolution of carbonates. It could be concluded that the near-neutral pH in the tailings has no decreasing effect on the rate of sulphide oxidation, but does reduce the concentrations of dissolved elements in the drainage water due to the formation of secondary minerals. This means that sulphide oxidation rates may be underestimated if determined from drainage alone.
|
|
| 4. |
- Jia, Yu, et al.
(författare)
-
Degradation of digested sewage sludge residue under anaerobic conditions for mine tailings remediation
- 2014
-
Ingår i: Environmental Earth Sciences. - : Springer Science and Business Media LLC. - 1866-6280 .- 1866-6299. ; 72:9, s. 3643-3654
-
Tidskriftsartikel (refereegranskat)abstract
- Previous studies showed that 85 % of total organic matter (TOM) in digested sewage sludge (biosolids) used as a sealing layer material over sulfide tailings at the Kristineberg Mine, northern Sweden had been degraded 8 years after application, resulting in a TOM reduction from 78 % to 14 %. To achieve a better understanding of the field observations, laboratory studies were performed to evaluate biodegradation rates of the TOM under anaerobic conditions. Results reveal that the original biosolid consisted of ca. 60 % TOM (48.0 % lignin and 11.8 % carbohydrates) that had not been fully degraded. The incubation experiments proved that 27.8 % TOM in the biosolid was further degraded anaerobically at 20-22 C during the 230 d incubation period, and that a plateau to the biodegradation rate was approached. Based on model results, the degradation constant was found to be 0.0125 (day-1). The calculated theoretical gas formation potential was ca. 50 % higher than the modeled results based on the average degradation rate. Cumulated H2S equated to 0.65 µmoL*g-1 of biosolid at 230 d. However, the large sulfurous compounds reservoir (1.76 g SO42- kg-1 biosolid) together with anaerobic conditions, can generate high concentrations of this gas over a long-term perspective. Due to the rate of biodegradability identified via anaerobic processes, the function of the biosolid to serve as an effective barrier to inhibit oxygen migration to underlying tailings, may decrease over time. However, a lack of readily degradable organic fractions in the biosolid and a large fraction of organic matter that was recalcitrant to degradation suggests a longer degradation duration, which would prolong the biosolid material’s function and integrity.
|
|
| 5. |
- Jia, Yu, et al.
(författare)
-
Investigation of biosolids degradation under flooded environments for use in underwater cover designs for mine tailing remediation
- 2015
-
Ingår i: Environmental Science and Pollution Research. - : Springer Science and Business Media LLC. - 0944-1344 .- 1614-7499. ; 22:13, s. 10047-10057
-
Tidskriftsartikel (refereegranskat)abstract
- To evaluate the potential suitability of digested sewage sludge (frequently termed biosolids) for use as underwater cover material for mine waste tailings, the degradability of biosolids at 20 − 22 °C under flooded anaerobic conditions was evaluated during incubation for 230 days. Leaching of elements from the flooded anaerobic system was also evaluated. Biosolid degradation was confirmed by the generation and accumulation of CH4 and CO2. Specifically, approximately 1.65 mmoL gas/g biosolids was generated as a result of incubation, corresponding to degradation of 7.68 % of the organic matter, and the residue was stable at the end of the laboratory experiment. Under field conditions in northern Sweden, it is expected that the degradation rate will be much slower than that observed in the present study (Nason et al. Environ Earth Sci 70:30933105, 2013). Although the majority of biosolid fractions (>92 %) were shown to be recalcitrant during the incubation period, long-term monitoring of further degradability of residue is necessary. The leaching results showed that most of the metals and metalloids leached from the biosolids at day 230 were below the limit value for non-hazardous waste, although Ni was the only element approximately three times higher than the limit value for inert material at the landfill site. In conclusion, biosolids have potential for use as covering material for underwater storage of tailings based on their biodegradability and leaching of elements.
|
|
| 6. |
- Nason, Peter
(författare)
-
Advances in using sewage sludge to remediate sulfidic mine tailings : An overview from pilot- and field-scale experiments, northern Sweden
- 2013
-
Ingår i: Reliable Mine Water Technology. - 9781627487757 ; , s. 681-686
-
Konferensbidrag (refereegranskat)abstract
- Sewage sludge can and has been used effectively as an organic-rich cover for sulfidic mine waste remediation. However, the optimum use of the material as a layer in engineered covers remains unconfirmed. Results obtained from four different sewage sludge applications are presented and discussed in context to their success and for their applicability for being used at full-scale sulfidic-mine waste remediation projects. The experiments evaluated sewage sludge when used as a vegetation substrate on bare tailings, a water-saturated cover, a composite cover, and lastly when used as a sealing-layer barrier material, which was deemed the most successful technique.
|
|
| 7. |
- Nason, Peter, et al.
(författare)
-
Alternative Waste Residue Materials for passive in-situ prevention of sulfide-mine tailings oxidation : A Field Evaluation
- 2014
-
Ingår i: Journal of Hazardous Materials. - : Elsevier BV. - 0304-3894 .- 1873-3336. ; 267, s. 245-254
-
Tidskriftsartikel (refereegranskat)abstract
- Novel solutions for sulfide-mine tailings remediation were evaluated in field-scale experiments on a former tailings repository in northern Sweden. Uncovered sulfide-tailings were compared to sewage-sludge biosolid amended tailings over 2 years. An application of a 0.2 m single-layer sewage-sludge amendment was unsuccessful at preventing oxygen ingress to underlying tailings. It merely slowed the sulfide-oxidation rate by 20%. In addition, sludge-derived metals (Cu, Ni, Fe, and Zn) migrated and precipitated at the tailings-to-sludge interface. By using an additional 0.6 m thick fly-ash sealing layer underlying the sewage sludge layer, a solution to mitigate oxygen transport to the underlying tailings and minimize sulfide-oxidation was found. The fly-ash acted as a hardened physical barrier that prevented oxygen diffusion and provided a trap for sludge-borne metals. Nevertheless, the biosolid application hampered the application, despite the advances in the effectiveness of the fly-ash layer, as sludge-borne nitrate leached through the cover system into the underlying tailings, oxidizing pyrite. This created a 0.3 m deep oxidized zone in 6-years. This study highlights that using sewage sludge in unconventional cover systems is not always a practical solution for the remediation of sulfide-bearing mine tailings to mitigate against sulfide weathering and acid rock drainage formation
|
|
| 8. |
- Nason, Peter, et al.
(författare)
-
Assessing the impact of sewage sludge on a formally remediated tailings impoundment in relation to the transport of metals in groundwater
- 2011
-
Ingår i: Mine Water - managing the Challenges. - Aachen, Germany : RWTH Aachen University, Institute of Hydrogeology. - 9783000355431 ; , s. 429-434
-
Konferensbidrag (refereegranskat)abstract
- In 2009 sewage sludge was applied to an already successfully remediated saturated and dry covered sulphide tailings impoundment in northern Sweden as a vegetation substrate. The aim of this study was to identify the dispersion, magnitude and duration of sludge-borne constituents released. Readily leachable sludge-borne constituents (DOC, Fe, Co, Cr, Ni, Pb and Zn) created a contamination plume which affected the impoundment groundwater within the first year of application. The majority of the plume originated from the water-saturated area of the impoundment that was only covered with a 10% surface area of sludge. The dry-composite covered area of the impoundment, which contained a 70% sludge cover, did not contribute to the contamination plume due to the efficiency of the cover at reducing water infiltration and contamination dispersal. The constituents were transported along the dominant groundwater flow direction, underneath the dry covered area of the impoundment, to the effluent of the impoundment groundwater system due to inflowing uncontaminated groundwater from an adjacent till slope. All metal and DOC concentrations in the impoundment groundwater returned to pre-sludge application concentrations within two years, due to successful plant establishment on the sludge.
|
|
| 9. |
- Nason, Peter, et al.
(författare)
-
Biodegradation of Biosolids Under Aerobic Conditions : Implications for Cover Materials for Sulfide Mine Tailings Remediation
- 2016
-
Ingår i: Mine Water and the Environment. - : Springer Science and Business Media LLC. - 1025-9112 .- 1616-1068. ; 35:3, s. 273-282
-
Tidskriftsartikel (refereegranskat)abstract
- Sewage sludge residue (biosolids) was investigated for its potential as a long-term tailings cover. Biosolids may prevent oxygen diffusion into underlying sulfide tailings through microbial aerobic biodegradation of organic matter. Biosolids were investigated at laboratory-, pilot-, and field-scale using analysis of total organic matter (TOM) mass reduction and O2, CO2, CH4 concentrations to quantify the biodegradation rate. A 156-day, open microcosm experiment, in which the loss of biosolids mass over time at differing temperatures, mimicking ambient (20–22 °C), mesophilic (34 °C), and thermophilic (50 °C) conditions, indicated that TOM biodegradation was best in the mesophilic temperature range, with 14.8, 27.2, and 26.7 % mass depletion at ambient, mesophilic, and thermophilic conditions, respectively. The data was correlated to field-scale data that evaluated biodegradation rates via decreasing O2 and increasing CO2 concentrations. Field biodegradation rates were less than laboratory rates because lower mean annual temperatures (0.6–0.7 °C) diminished microbial activity. A calibrated model indicates that 20 % of a field application of biosolids will degrade within 2 years. However, the rate declines with time due to exhaustion of the most readily degradable organic fraction. If biodegradation cannot be maintained, the long-term effectiveness of biosolids as a covering material for mine tailings remains a concern.
|
|
| 10. |
- Nason, Peter
(författare)
-
Field and pilot-scale geochemical investigations into using sewage sludge for sulphidic mine waste remediation
- 2012
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Successful mine waste reclamation is a fundamental aspect in mine plan development and is legislated through the European Parliament’s ‘Management of Waste from Extractive Industries Directive (2006/21/EC)’. Field and pilot-scale trials were utilised to evaluate different applications of an alternative cover material, sewage sludge, in its ability to remediate and prevent acid rock drainage formation from sulphidic mine tailings derived from the Kristineberg Zn-Cu mine, northern Sweden. Sewage sludge is an organically-rich waste material generated from the treatment of domestic waste water. It may function suitably as a low permeable barrier against oxygen ingress when compacted or as a surface vegetation substrate. The first study focused on evaluating the effectiveness of a sewage sludge sealing layer, part of a composite dry cover design system. Data on tailings, leachate water and pore gas geochemistry during eight years from two experimental pilot-scale test cells revealed that the sludge was an effective barrier to oxygen influx, which prevented sulphide oxidation and acid rock drainage formation. Sludge-borne metals (Cd, Co, Cu, Fe, Pb, Zn) precipitated and were retained in the underlying tailings due to the reduced conditions produced, resulting in low concentrations of dissolved metals (<10μg/L Cd, Co, Cu, Ni, Pb, Zn) in the drainage, several orders of magnitude lower than that from an uncovered tailings reference cell. However, a 19.6% mass reduction of the sludge due to organic matter degradation may compromise the effectiveness of the cover in the long-term. The second study evaluated the geochemical impact of a field-scale surface application of sewage sludge on the groundwater quality of a formally-remediated sulphidic-tailings impoundment. Thirteen years after initial remediation, 12 000 tonnes of sludge were applied to a depth of 0.3m to re-vegetate and stabilise the pre-existing water-saturated and composite dry cover design systems. After two years, a 17% reduction of the sludge volume occurred due largely to aerobic degradation of the organic matter fraction, leaching of the constituents Ca and S, and partially due to the leaching of Cu, Ni, Pb and Zn. Groundwater data indicated that sludge-borne constituents derived from the dry covered areas were prevented from infiltrating through the low permeable sealing layer. Instead they drained laterally through the protective layer to the impoundment toe and did not reach nor have a negative impact on the tailings groundwater. Oppositely, a major plume of sludge-borne constituents derived from the water-saturated area entered the tailings groundwater vertically unhindered, then dispersed laterally through the tailings due to the dominating hydrogeological regime. The plume migrated underneath the dry composite covered area after 2.2 years, where concentrations of Cu (188µg/L), Fe (254mg/L), Ni (263µg/L), Pb (95µg/L) and Zn (1.55mg/L) peaked. The plume included elevated nitrate concentrations (167mg/L) released from nitrification of ammonium in the sludge, which oxidised pyrite in the tailings. However, the effects were temporary due to declining sludge-borne nitrate and metal release from the sludge due to vegetation establishment after 2 years. The expected duration of the plume to disperse and exit the tailings impoundment is estimated to take another 4 years. In conclusion, these studies have found that sewage sludge can be effectively utilised as a suitable alternative cover material within the study periods observed as a sealing layer and as a final vegetation substrate on composite dry covers, but not water-saturated covered systems for the remediation of sulphidic mine tailings. Further investigations will have to verify the effectiveness of these applications in the long-term.
|
|
| 11. |
- Nason, Peter, et al.
(författare)
-
Impact of Sewage Sludge on Groundwater Quality at a Formerly Remediated Tailings Impoundment
- 2014
-
Ingår i: Mine Water and the Environment. - : Springer Science and Business Media LLC. - 1025-9112 .- 1616-1068. ; 33:1, s. 66-78
-
Tidskriftsartikel (refereegranskat)abstract
- Sewage sludge can be a suitable, organic-rich substrate to promote vegetation ofsulfide-mine tailings, but it may contain contaminants, that, when oxidized, canadversely affect underlying groundwater systems. The geochemical impact of asurface application of 12,000 metric tons of anaerobically-digested sewage sludge on the groundwater quality of a remediated sulfide-tailings impoundment in northern Sweden was evaluated to determine if sludge-borne metals and nitrate were released to the underlying groundwater system. Two years of data from a field-scale groundwater monitoring programme initiated just before the sludge application was compared to groundwater data from 1998-2006. Grass was successfully established within two years. However, until that occurred, elevated concentrations of sludge-borne metals (Cu, Ni, Pb, Zn) were released to the underlying groundwater. In addition, the release of nitrate likely exacerbated metal concentrations by providing an oxidant for pyrite in the underlying tailings. The release was periodic due to the establishment of the grass, which immobilized metals and nitrate in the sludge. Metals bound asorgano-metallic complexes, due to dissolved organic carbon released from the sludge, migrated across the tailings impoundment. Model simulations indicate that the plume will take six years to exit the groundwater environment. Though the impacts are relatively short-term, this type of application should be reconsidered in the future.
|
|
| 12. |
- Nason, Peter
(författare)
-
Novel advances using sewage sludge in engineered dry covers for sulphide mine tailings remediation
- 2013
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Effective remediation of sulphide-bearing mine tailings is a fundamental aspect in mine plan development. Novel solutions to replace virgin materials in engineered dry cover amendments using sewage sludge biosolids (SS) were evaluated in laboratory-, pilot-, and field-scale experiments. The aim of this thesis is to be able to identify the applicability of SS as a long-term (10 000 year) dry cover amendment for sulphide mine tailings remediation. The utilisation of SS could provide a low-cost approach to mitigate sulphide mine tailings oxidation, acid rock drainage (ARD) formation, and offer a solution towards the co-disposal of two wastes simultaneously. Three experiments evaluated five different SS applications at pilot- and field-scales. The experiments were innovative as they stepped outside of the laboratory domain, and evaluated time periods spanning 0-8 years. The first study addressed a novel solution to replace common sealing layer barrier materials within a composite dry cover with SS. In the 8-year experimental period, it was found that the SS acted as an effective physical and organic reactive barrier to oxygen diffusion. This created a reductive, high alkalinity, near-neutral pH environment in the underlying tailings. Sludge-derived Cd, Cu, Pb, and Zn accumulated in the sludge-to-tailings interface, and the effluent drainage exhibited low (<10 µg L-1) dissolved Cd, Cu, Pb, and Zn concentrations. However, aerobic and anaerobic degradation processes exhausted 85 % of the organic fraction of the SS, and combined with the leaching of metals, exhibited a 19.6 % sludge mass reduction. The second study focused upon using a field-scale application of SS as a vegetation substrate applied onto a formerly remediated tailings impoundment. The objective delineated the magnitude, duration and fate of sludge-borne constituents by groundwater well monitoring methods and geochemical modelling. The findings indicated that ~ 17 % of the SS was degraded after 2 years of surface weathering, due to nitrification, aerobic degradation, and the leaching of Cu, Ni, Pb, and Zn. The metals formed highly mobile organo-metallic complexes that were readily transported though the groundwater. Stoichiometric ratios indicated that nitrate acted as an oxidant to pyrite in the underlying tailings. The effects were temporary due to vegetation establishment, which suppressed nitrate release within 2 years. The third field-scale study investigated the use of a single SS layer onto bare sulphide mine tailings, and when combined with a fly-ash layer. The aim of the study was to identify if a single layer would mitigate oxygen diffusion, and if not, if a combined sludge/fly-ash cover would be more effective. The findings of this study indicated that a single layer of SS above the tailings was ineffective at preventing oxygen diffusion and ARD formation, and merely slowed the process by 20 % in 2 years. In addition, sludge-derived metals (Cu, Fe, Ni, Zn) accumulated in the underlying tailings. The combined sludge/fly-ash cover was effective at immobilising the sludge-derived metals, and acted as an effective barrier to oxygen. Nevertheless, the SS continued to perpetuate the application, as high concentrations of nitrate provided an oxidant to pyrite. Two laboratory experiments were set-up to quantify aerobic and anaerobic biodegradation rates of the organic fraction of the SS and to calibrate them with the field data to provide a model for estimating the life-time of the cover. Within 156 and 230 day experiments at 20-22°C, aerobic and anaerobic degradation rates each resulted in a 14.8 % and 27.8 % loss of the organic fraction respectively. Field biodegradation rates were modelled to be slower, due to colder field temperatures and a high degree of water-saturation. Predictions indicate aerobic biodegradation rates will result in a 20 % loss of total organic matter degradation in 2 years of field conditions. Anaerobic biodegradation prediction rates indicate an exhaustion of readily-degradable organic fractions within 2 years. However, a large residual organic fraction left is more recalcitrant to biodegradation. The findings of this thesis indicate that SS may be effective in limited application types for sulphide mine tailings remediation. However, long-term engineered cover applications may be compromised by high rates of biodegradation in both surface and sub-surface amendments.
|
|
| 13. |
- Nason, Peter, et al.
(författare)
-
Sewage sludge as a sealing layer for the remediation of sulphide-bearing mine tailings : ageing and degradation of the barrier material
- 2011
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Using sewage sludge as an organic barrier to mitigate oxygen diffusion to underlying sulphidic tailings was performed in experimental pilot-scale test cells, northern Sweden and was proved to be successful over an 8 year period (Nason et al., 2010). However, degradation and ageing of the sewage sludge may limit its function in the long-term as indicated by surface applications of sewage sludge, as the exposure of the material to atmospheric oxygen may cause aerobic degradation of the organic matter fraction (Peppas et al., 2000), nitrification (Cravotta, 1998) and subsequent structural disintegration (Ahlberg, 2006). A pilot-scale test cell with a 0.3m sewage sludge sealing layer capped by a 1.2m protective layer of glacial till was used to cover tailings. Quantification of the changing properties of the sewage sludge after an 8 year period occurred using temperature data and solid sludge and leachate geochemistry. It was found that all layers were frozen between December to April and that a perched water table formed above the sealing layer from April to August (Shcherbakova, 2006). The subsequent lack of contact of the sludge with oxygen minimised aerobic degradation of the organic fraction, prevented nitrification and created an anoxic environment in the sludge. Nitrate in the leachate was <1mg/l and the subsequent lack of acidification created a neutral pH in the sludge and underlying tailings. Elevated alkalinity (360-600 mg/l) and low sulphate (9-67 mg/l) in the leachate indicated that sulphate reduction by anaerobic degradation of the organic matter had occurred in the sludge. On average, the organic fraction was reduced by 80%, but was most prevalent at the sludge to tailings interface where 92% of the organic matter had been lost since deposition. Mass balance calculations of the sludge revealed a 19.6% total loss of volume due to the organic matter degradation and leaching of Cd, Cu, Hg, Zn and P that were elevated in the original sludge material. No structural degradation as experienced by surface applications such as shrinkage or cracking occurred as the barrier was not exposed to oxygen. The integrity and function of the sub-surface sewage sludge layer was less compromised compared to a surface layer as degradation was dominated by anaerobic processes. However, organic degradation rates were high and it is recommended that this type of application is effective only as a medium-term solution for mitigating oxygen diffusion to underlying sulphidic tailings and for preventing acid rock drainage. Ahlberg, G. (2006). Göteborg University. Doctoral Thesis: 20. Cravotta, C. A. 1998. Ground Water 36(1): 9-19. Nason et al., 2010. IMWA 2010: Nova Scotia, Canada, Cape Breton University Press. Peppas et al., 2000. Minerals Engineering 13(5): 563-574. Shcherbakova, E. 2006. Luleå University of Technology. Doctoral Thesis
|
|
| 14. |
- Nason, Peter, et al.
(författare)
-
The effectiveness of using sewage sludge as a sealing layer on sulphide-rich mine tailings : a pilot-scale experiment, northern Sweden
- 2010
-
Ingår i: Mine Water in Innovative Thinking. - Sydney, Nova Scotia : Cape Breton Univ. Press. - 9781897009475 ; , s. 155-158
-
Konferensbidrag (refereegranskat)abstract
- En utvärdering av effektiviteten av att använda avloppsslam som tätskikt för att hindra syre spridning till underliggande avfall genomfördes under perioden 2001-2009 med pilotskala celler i norra Sverige. Lakvattnet dränering av ett oskyddat bearbetningsavfall kontroll cell och en cell med en 0.25m tätskikt av avloppsslam analyserades utifrån 2003-2009. En första hög koncentration spola av lösta element förekom i båda cellerna. Svavel och kraftiga koncentrationer metal gradvis minskat i både celler men skillnaderna i halter var flera storleksordningar lägre för slammet saneras cellen. Cd-Fe-Zn koncentrationer i kontrollen ökat över tid på grund av svaveloxidering. Konsumtionen av syre i avloppsslam som skapats minskas förhållanden på de underliggande bearbetningsavfall. Förhöjda metallhalter lakas ur slammet i bearbetningsavfall därefter kvar i den anrikningssand och var inte förhöjda i utflödet lakvattnet lösningen.
|
|
| 15. |
- Nason, Peter, et al.
(författare)
-
Using sewage sludge as a sealing layer to remediate sulphidic mine tailings : a pilot-scale experiment, northern Sweden
- 2013
-
Ingår i: Environmental Earth Sciences. - : Springer Science and Business Media LLC. - 1866-6280 .- 1866-6299. ; 70:7, s. 3093-3105
-
Tidskriftsartikel (refereegranskat)abstract
- At the Kristineberg mine, northern Sweden, sulphidic mine tailings were remediated in an 8-year pilot-scale experiment using sewage sludge to evaluate its applicability as a sealing layer in a composite dry cover. Sediment, leachate water, and pore gas geochemistry were collected in the aim of determining if the sludge was an effective barrier material to mitigate acid rock drainage (ARD) formation. The sludge was an effective barrier to oxygen influx as it formed both a physical obstruction and functioned as an organic reactive barrier to prevent oxygen to the underlying tailings. Sulphide oxidation and consequential ARD formation did not occur. Sludge-borne trace elements accumulated in a reductive, alkaline environment in the underlying tailings, resulting in an effluent drainage geochemistry of Cd, Cu, Pb and Zn below 10 μg/L, high alkalinity (810 mg/L) and low sulphate (38 mg/L). In contrast, the uncovered reference tailings received a 0.35-m deep oxidation front and typical ARD, with dissolved concentrations of Cd, Zn and sulphate, 20.8 μg/L, 16,100 μg/L and 1,390 mg/L, respectively. Organic matter degradation in the sludge may be a limiting factor to the function of the sealing layer over time as 85 % loss of the organic fraction occurred over the 8-year experimental period due to aerobic and anaerobic degradation. Though the cover may function in the short to medium term (100 years), it is unlikely to meet the demands of a long-term remedial solution
|
|
| 16. |
- Rodríguez, Nathalie Pérez, et al.
(författare)
-
Copper and iron isotope fractionation in mine tailings at the Laver and Kristineberg mines, northern Sweden
- 2013
-
Ingår i: Applied Geochemistry. - : Elsevier BV. - 0883-2927 .- 1872-9134. ; 32, s. 204-215
-
Tidskriftsartikel (refereegranskat)abstract
- Previous research has shown that Cu and Fe isotopes are fractionated by dissolution and precipitation reactions driven by changing redox conditions. In this study, Cu isotope composition (65Cu/63Cu ratios) was studied in profiles through sulfide-bearing tailings at the former Cu mine at Laver and in a pilot-scale test cell at the Kristineberg mine, both in northern Sweden. The profile at Kristineberg was also analysed for Fe isotope composition (56Fe/54Fe ratios). At both sites sulfide oxidation resulted in an enrichment of the lighter Cu isotope in the oxidised zone of the tailings compared to the original isotope ratio, probably due to preferential losses of the heavier Cu isotope into the liquid phase during oxidation of sulfides. In a zone with secondary enrichment of Cu, located just below the oxidation front at Laver, δ65Cu (compared to ERM-AE633) was as low as -4.35 ± 0.02‰, which can be compared to the original value of 1.31 ± 0.03‰ in the unoxidised tailings. Precipitation of covellite in the secondary Cu enrichment zone explains this fractionation. The Fe isotopic composition in the Kristineberg profile is similar in the oxidised zone and in the unoxidised zone, with average δ56Fe values (relative to the IRMM-014) of -0.58± 0.06‰ and -0.49 ± 0.05‰, respectively. At the well-defined oxidation front, δ56Fe was less negative, -0.24 ± 0.01 ‰. Processes such as Fe(II)-Fe(III) equilibrium and precipitation of Fe-(oxy)hydroxides at the oxidation front are assumed to cause this Fe isotope fractionation. This field study provides additional support for the importance of redox processes for the isotopic composition of Cu and Fe in natural systems.
|
|
| 17. |
|
|
| 18. |
|
|
| 19. |
- Swietlicki, Erik, et al.
(författare)
-
Source identification during the Great Dun Fell Cloud Experiment 1993
- 1997
-
Ingår i: Atmospheric Environment. - 1352-2310. ; 31:16, s. 2441-2451
-
Tidskriftsartikel (refereegranskat)abstract
- A characterisation of the sources influencing the site for the final field campaign of the EUROTRAC subproject GCE (Ground-based Cloud Experiment) at Great Dun Fell, Cumbria, Great Britain in April-May 1993 is presented. The sources were characterised mainly by means of aerosol filter and cascade impactor data, single particle analysis, gas data, data on aromatic organic compounds, cloud water ionic composition, measurements of aerosol size distributions and hygroscopic properties and various meteorological information. Receptor models applied on the aerosol filter and impactor data sets separately revealed two major source types being a marine sea spray source and a long-range transported anthropogenic pollution source. The results of the receptor models were largely consistent with the other observations used in the source identification. Periods of considerable anthropogenic pollution as well as almost pure marine air masses were clearly identified during the course of the experiment.
|
|
