| 1. |
- Dublet-Adli, Gabrielle, et al.
(author)
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A trade-off in activated biochar capping of complex sediment contamination: reduced PAH transport at the cost of potential As mobilisation
- 2024
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In: Journal of Soils and Sediments. - : Springer Nature. - 1439-0108 .- 1614-7480. ; 24:1, s. 497-508
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Journal article (peer-reviewed)abstract
- Purpose: The effect of thin-layer capping with activated biochar on sediment-to-water flux was investigated. For the first time, the diffusion of both polycyclic aromatic hydrocarbons (PAHs) and arsenic (As) were studied simultaneously. The fate of As was investigated, under successive dysoxic and oxic conditions, in order to assess and discuss potential trade-off effects when using biochar as an active sorbent for capping of multi-contaminated sediments.Methods: Sediments from the Bureå bay (Sweden), contaminated with PAH and metal elements including As and Hg, were capped with activated biochar and/or bentonite in simple microcosm test systems in the laboratory. The contaminant transport from sediment through the capping to water body was studied by sampling metals in the water phase above the cap over time, or PAH in a heptane layer over water, at regular time intervals.Results: Consistently with the limited previous studies, reductions were observed (e.g., 60–65% for 15-PAH, 100% for chrysene) in sediment-to-water PAH fluxes upon biochar-based thin-layer capping. However, the most important novel finding revealed ambiguous effects of biochar capping on redox-sensitive elements, in particular As. Under the microcosm conditions of the experiment, where pH was affected by the capping material, biochar treatments favoured As mobility under oxic conditions, directly and/or via effects on Fe speciation. While capping limited the diffusion of As under dysoxic conditions, this also favoured greater As mobility under oxic water conditions compared to no capping.Conclusion: Design and monitoring of capping of PAH contaminated sediments should account for potential negative effects on co-occurring contaminants.
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| 2. |
- Jia, Yu, et al.
(author)
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Using shrimp shells and concrete to mitigate leaching for metals from waste rock
- 2023
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In: Environmental Science and Pollution Research. - : Springer. - 0944-1344 .- 1614-7499. ; 30, s. 40825-40845
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Journal article (peer-reviewed)abstract
- The capability of shrimp shells or construction demolition concrete as amendments to immobilize elements, primarily Pb and Zn, generated from mine waste weathering, was investigated via standard batch leaching test (L/S 10 cm3/g, 24 h). The effect of the amendment was tested at waste rock-to-residue ratios 9:1, 9.5:0.5, and 9.8:0.2 (weight:weight, w/w), with seawater as leachant. The effect of freshwater vs. seawater on the leaching pattern was investigated. The elemental contents of rock varied largely. Elemental levels in shells and concrete had much lower values than waste rock. Leaching results showed that amendment in both cases had high capacity to immobilize Pb and Zn. A decrease of concrete-to-rock ratio from 1:9 to 0.2:9.8 (w/w) led to more leaching of Pb but less of Zn. Similarly, decreasing shrimp-to-rock ratio increased and decreased leaching of Pb and Zn, respectively. Increasing experimental time to 5 and 10 d in a shrimp-amended batch caused less leaching of Pb and more of Zn. Both Pb and Zn immobilization in the concrete amendment was considered due to the increase of pH by concrete amending. The Pb leaching in the present study was considered controlled primarily by a sorption process, whilst the leaching for Zn might have been influenced by other factors such as pH and DO. Pb leaching from rock was much higher in seawater than in freshwater, with same range for Zn leaching, irrespective of leachant. It showed consistence between the laboratory data and the field conditions. Calculation procedures were established for amendment to mitigate mine drainage.
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| 3. |
- Malmi, Teemu, et al.
(author)
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Culture and management control interdependence: An analysis of complementary control choices to delegation in Western cultural regions
- 2020
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In: Accounting, Organizations and Society. - : Elsevier BV. - 0361-3682. ; 86
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Journal article (peer-reviewed)abstract
- This study examines the influence of cultural regions on the interdependence between delegation of decision rights and other management control (MC) practices. In particular, we assess whether one of the central contentions of agency theory, that incentive contracting and delegation are jointly determined, holds in different cultural regions. We argue that the MC practices that operate as a complement to delegation vary depending on societal values and preferences, and that MC practices other than incentive contracting will complement delegation in firms in non-Anglo cultural regions. Using data collected from 584 strategic business units across three Western cultural regions (Anglo, Germanic, Nordic), our results show that the interdependence between delegation and incentive contracting is confined to Anglo firms. In the Nordic and Germanic regions, we find that strategic and action planning participation operate as a complement to delegation, while delegation is also complemented by manager selection in Nordic firms. Overall, our study demonstrates that cultural values and preferences significantly influence MC interdependence, and suggests that caution needs to be taken in making cross-cultural generalizations about the complementarity of MC practices.
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| 4. |
- Nigéus, Susanne, et al.
(author)
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Dimensioning and Construction of a Sealing Layer Made of Green Liquor Dregs Amended Till—Remediation of Sulfidic Mine Waste
- 2023
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In: Mining, Metallurgy & Exploration. - : Springer Nature. - 2524-3462 .- 2524-3470. ; 40:6, s. 2281-2292
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Journal article (peer-reviewed)abstract
- Using non-hazardous industrial residues in mine waste remediation is beneficial not only for the mining industry where substantial amounts of the waste generated have potential to produce acid rock drainage and pollute the environment, but also the providing industry, minimizing the waste landfilled. In this study green liquor dregs (GLD), residue from 15 different paper mills were characterized to valorize it as a potential product as a cover material. In another part of the study, one of the GLDs and a local till were characterized to determine the optimal mixture of GLD amended till to be used in a field application at the closed Näsliden Mine in northern Sweden. The study concluded 10% GLD-amended till to be the optimal recipe and was successfully applied at the Näsliden mine waste dump. However, the great variability in the characteristics of GLD creates challenges if it is to be valorized as a product.
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| 5. |
- Nigéus, Susanne, et al.
(author)
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Hydrogeological Properties of Till Amended with Green Liquor Dregs (GLD): Recycling of an Industrial Residue for Reclamation of Acid Generating Mine Sites
- 2023
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In: Geotechnical and Geological Engineering. - : Springer. - 0960-3182 .- 1573-1529. ; 41, s. 3625-3639
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Journal article (peer-reviewed)abstract
- The oxidation of sulfide minerals in mine wastes is a possible threat to the environment as it might have potential to generate acid rock drainage (ARD). A common method to reduce ARD is to apply a dry cover on the mine waste deposit. Considering the massive amounts of mine waste produced in Sweden (104-million-ton in year 2018) there is a great need for suitable dry cover materials. Using non-hazardous industrial residues in the dry cover would be beneficial for both the mining industry and the providing industry as stricter waste management legislation incentivizes them to develop their waste management strategies. The objective of this study was to investigate if an addition of Green Liquor Dregs (GLD), a residue from pulp production, can decrease the hydraulic conductivity and increase the water retention capacity (WRC) of three different tills, with the purpose of improving the performance of a dry cover material on a mine waste deposit. Another objective was to investigate how the hydraulic conductivity and WRC are affected by the contents of fines and clays in the tills. The study concludes that the water retention capacity of the tills improves with GLD addition, however, the hydraulic conductivity did not decrease enough to reach the in Sweden required < 10−8 m/s. Even though, GLD could still successfully be used in the reclamation of mine sites as the high WRC can be seen as the most important factor in deterring acid rock drainage by keeping the sealing layer close to saturation. This study further indicates that there are other factors than the particle size distribution of the materials that controls the hydraulic conductivity of the mixtures, such as initial water content, dry density, and compaction effort.
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| 6. |
- Nigéus, Susanne, et al.
(author)
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Instrumentation of Sealing Layers Made of Two Different Amendments (Green Liquor Dregs and Bentonite) to Till for Reclamation of Sulfidic Mine Waste
- 2023
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In: Mine Water and the Environment. - : Springer Nature. - 1025-9112 .- 1616-1068. ; 42:3, s. 441-448
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Journal article (peer-reviewed)abstract
- In Sweden, a dry cover solution is commonly used to stop sulfide oxidation and the production of acid rock drainage from unattended sulfidic mine waste. Recycling a non-hazardous industrial residue, such as green liquor dregs (GLD) generated during pulp production, in this cover solution is beneficial for both the mining industry where there is a great need for cover materials and the pulp production industry. The objectives of this field study were to install and evaluate the instrumentation of sealing layers made of GLD- and bentonite-amended till, and to evaluate the practical aspects of two different methods of installation: monitoring wells and pits. This practical field study demonstrated that it is difficult to properly seal the drill holes after installing the probes in observation wells and suggests that a better (easier and less costly) alternative for future instrument installation in a sealing layer might be to excavate a pit in the protective layer after installation of the soil cover and then drill the probes into the sealing layer from that pit.
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| 7. |
- Nigéus, Susanne
(author)
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Recycling of green liquor dregs in cover application on acid generating mine waste
- 2023
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Doctoral thesis (other academic/artistic)abstract
- The mining industry generates massive amounts of waste that without treatment and in contact with atmospheric oxygen can cause the formation of acid rock drainage (ARD). In Sweden, the most common reclamation measure for mine waste is to apply a multi-layer cover on top of the waste deposit. The access to suitable cover-materials is, however, limited and can lead to extensive costs for the mining companies. This creates a driving force for alternative solutions, e.g., bentonite amendment to till. As bentonite production is costly both economically and environmentally, recycling of industrial residues to produce sealing layer material is an attractive option. The recycling is beneficial for the industry generating the residue, the mining industry using the residue and the society in its strive for zero waste. An industrial residue that has potential to improve the sealing properties of local till is green liquor dregs (GLD), a residue from pulp production. The main objective of this study was to, by laboratory studies and field application and evaluations, investigate if green liquor dregs amended till can be used as a sealing layer material on top of acid generating mine waste. The conclusion from the laboratory study is that the hydraulic conductivity does not decrease significantly with GLD addition to the silty till. However, the water retention capacity, which can be seen as the major important feature of a sealing layer to be used on top of sulfidic mine waste by keeping the layer close to saturation, shows significant improvements with GLD addition. In the field study the GLD amended till was applied successfully from a soil mechanical point of view (e.g., the compaction degree after application). The early results from the monitoring of the sealing layer indicate results comparable to the more frequently used bentonite amendment in a sealing layer, with soil moisture values reaching close to saturation. However, this study also concludes that the great variation in GLD, especially regarding its soil mechanical properties such as water content, makes it difficult to use compared to commercial products. The material used in the laboratory investigations in the planning phase of a project might behave differently than the one that is delivered to the minesite for reclamation.
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| 8. |
- Nigéus, Susanne, et al.
(author)
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The Drivers of Hydraulic Conductivity in Green Liquor Dregs Amended Till: Application to Reclamation of Acid Generating Mine Sites
- 2023
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In: Mine Water and the Environment. - : Springer. - 1025-9112 .- 1616-1068. ; 42, s. 59-69
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Journal article (peer-reviewed)abstract
- The mining industry produces massive amounts of waste that in contact with oxygen can result in leaching of metals. Access to a suitable cover-material for the mine waste is sometimes limited, creating a driving force for recycling industrial residues for these purposes. Green liquor dregs (GLD), an industrial residue from paper and pulp production, has the potential to be used in a sealing layer as an amendment to till. Though hydraulic conductivity is commonly used to evaluate the quality of the sealing layer, field application from laboratory investigations is challenging as many factors, apart from vast variations in the physical properties of both the till and the GLD, control hydraulic conductivity. In this study, 5–20 wt.% of GLD from two different paper mills, with different total solid contents and particle size distributions, were mixed with a silty till with varying total solid contents to investigate how the materials’ dry density, initial water content, and compaction affects the hydraulic conductivity. We found that the initial water content of the materials was the most important factor. With a drier till and GLD, more GLD should be added to attain the lowest hydraulic conductivity possible. The compaction was not found to notably affect the mixtures’ hydraulic conductivity.
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| 9. |
- Nigéus, Susanne, et al.
(author)
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Water Retention Capacity as a Measure to Evaluate the Effectiveness of a Green Liquor Dregs-Amended Till to Cover Sulfidic Mine Waste
- 2022
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In: IMWA 2022 Conference - "Reconnect". - : International Mine Water Association 2023. - 9783982529301 ; , s. 337-344
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Conference paper (peer-reviewed)abstract
- Hydraulic conductivity is often used as a measure to evaluate the effectiveness of a sealing layer material on top of mine waste. However, the most important soil parameter minimizing the oxygen diffusion to the mine waste is the water retention capacity (WRC) of the sealing layer, as a high saturation corresponds to a low oxygen diffusion rate. This study shows that an amendment of Green Liquor Dregs (GLD), an industrial residue, to a till increases its WRC and has therefore potential to be a more accurate method to evaluate the effectiveness of a sealing layer than hydraulic conductivity.
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| 10. |
- Nyström, Elsa
(author)
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Preventing Acid Rock Drainage Formation from Sulfidic Waste Rock Using Secondary Raw Materials
- 2021
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Doctoral thesis (other academic/artistic)abstract
- One of the central and most challenging environmental problems related to mining is acid rock drainage (ARD) formation. The drainage is characterized by low pH and elevated concentrations of sulfate, metals, and metalloids formed when sulfide-bearing minerals are subjected to oxygen and water. Current remediation solutions, including active and passive techniques, have been developed to reduce ARD's negative impact. However, these treatments require continuous maintenance with an incessant addon of chemicals, energy consumption, not to mention long-term monitoring, until sulfide oxidation has ceased. Once it has been initiated, ARD formation could last for hundreds to thousands of years, making these approaches costly and unsustainable. A more strategic and environmentally sustainable approach would focus on preventing sulfide oxidation rather than treating its symptoms. This thesis explores five different secondary raw materials (SRM) (denoted below) for their use as amendments to prevent pyrite oxidation during storage. A combination of several mineralogical and geochemical methods was used to assess the materials' ability to maintain circumneutral pH when leaching pyritic waste rock (> 60% pyrite) in small-scale test cells (10L) to promote HFO precipitation on the pyrite surfaces. The oxidation of waste rock resulted in a drainage characterized by low pH (<2) and extensive element mobilization of up to 80% of the original content during the first two years. The results highlight the importance of trace element characterization and the need for early preventive measures to hinder or reduce the risk of acid drainage formation that requires active and costly long-term treatment. Conversely, adding 1-5 wt.% SRM to the waste rock created drainages with circumneutral pH and substantially lower sulfate and metal concentrations. However, not all materials could maintain circumneutral pH for an extended time, such as blast furnace slag (air-cooled and granulated) and cement kiln dust. These materials either require larger volumes of water to dissolve or contain minerals that allowed the material to harden upon water contact, inhibiting its neutralization capacity. Biomass bark ash showed a similar but less extensive, hardening effect resulting in a better ability to maintain circumneutral pH for more than two years despite its small addition (1-2.5wt.%). A similar ability was observed for lime kiln dust (5 wt.%). Conversely to lime kiln dust, the ash contained high soluble elements of potential concern, and its usage should be questioned despite only a temporary increase of elements through wash-out. However, the correlation between the amount of bark ash added and the timespan of circumneutral pH was not linear, resulting in the risk of prematurely declining pH if too little is added. Conversely, adding too much bark ash increases the risk of material hardening. One major concern with this treatment method is that it can inflate secondary minerals formation, leading to latent acidity and element release through their dissolution in changing geochemical conditions, such as wet or dry coverage measures. However, the addition of small amounts of SRM (1-4% of the waste rock's net neutralizing potential) to the waste rock dramatically improves the overall drainage quality without increasing the total amount of secondary minerals formed compared to no addition. In general, the type of secondary minerals formed on the waste rock without SRM treatment was considered less stable in an oxidizing environment than those formed through SRM treatment, suggesting that not treating the waste rock is inferior to SRM treatment both before and after covering measures.In conclusion, this thesis's results show that using small amounts of SRM can prevent oxidation during at least two years, likely due to HFO formation on the reactive surfaces. Consequently, it can substantially limit the need for treatment measures, both before and after remediation, decreasing the overall need and cost for chemicals, energy, and long-term monitoring, stressing the need for applying preventive measures during the storage time from mining to remediation. However, secondary minerals' long-term stability needs further evaluation and understanding before this method can be applied on a larger scale.
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