Immobilization of Pb and Zn leached from waste rock (WR) using shrimp shells, waste concrete, and sea water was investigated in continuous flow column leaching tests. To evaluate dynamic long-term leaching behaviors, leachate was collected at different liquid/solid (L/S) ratios up to 10 L/kg (≈ 12 weeks). The results showed that the leached content of Pb, Zn, Ni, Cu, Cd, and As from the WR control treatments generally decreased over the experimental period. The shrimp shell treatment further decreased the release of Pb (0.4–0.5%), Zn (19%), Cu (140–150%), and Cd (20–24%), possibly caused by a change in pH. In contrast, the concrete treatment increased the release of Pb (110–150%) and Zn (200–250%) in the leachate, while the leaching of Cu and Cd remained basically unaffected, reflecting a weaker pH effect than that of the shrimp shell treatment. Multi-variate data analysis further confirmed the experimental data and suggested that the release of arsenic, and to some extent also Cu, originated from the shrimp shells. The mechanisms behind the immobilization of these elements are likely biological sulfate reduction caused by the shrimp shell amendment raising the pH, which increased the precipitation of secondary minerals. The results suggest that these amendments carry the potential for bringing new elements into the system and any future remediation plans for these mine sites should be tailored with that in mind. The results suggest that this mitigation could be effective and should be further investigated.

Sulfide-rich soils (also called potential acid sulfate soil), with their sulfur content, and potential to generate acidity, pose challenges for construction due to low bearing capacity, shear strength, and their acidification potential. This study compares the effectiveness of Portland cement and Multicem binders in stabilizing these soils by analyzing unconfined compressive strength (UCS), porosity, pH changes, and strain behavior. Four soil samples with varying state of oxidation, pH, sulfur content, and water content were treated with binders at different dosages and analyzed after 28 days of curing. The results demonstrate that binder type and dosage, initial pH, and soil composition together significantly influence stabilization performance. Portland cement achieved higher UCS values across all samples, particularly in soils with low pH, due to its high alkalinity and facilitation of hydration reactions. In contrast, Multicem achieved acceptable UCS in soils with moderate initial pH, as its slower hydration limited its effectiveness in highly acidic conditions. Porosity reduction in stabilized samples correlated with increased binder content. Strain behavior exhibited an inverse relationship with UCS. Higher UCS samples showed reduced strain, indicating increased stiffness. However, in oxidized and highly acidic sulfate soils, such as Sunderbyn, UCS gains were limited, suggesting that extreme pH conditions inhibit binder effectiveness. The study offers practical guidance for optimizing binder selection and application strategies, especially for the treatment of acid sulfate-rich soils in geotechnical engineering. Future research should prioritize the assessment of durability, stability and performance under varied environmental stresses to ensure sustainable solutions.

Multilayer cover systems are commonly used for reclamation of waste rock and tailings facilities to prevent the diffusion of oxygen to underlying mine waste. The construction of this type of cover needs large amounts of soil material. The material needs specific hydraulic properties, e.g. the sealing layer properties that are difficult to reach, such as low hydraulic conductivity and high water-retention capacity. To enable the use of locally available soils that do not meet those requirements, a proposed solution is to include a bentonite mat in the sealing layer. In this study, the performance of a sealing layer composed of a bentonite mat associated with a layer of either compacted or uncompacted till is evaluated. The cover is evaluated using numerical modelling and laboratory columns built as a replicate of a field trial. The cold climatic conditions of boreal areas are characterised by a dry winter period accumulating precipitations that are released during a short and wet snowmelt period. The objective of the research is to simulate and understand the effect of such rapid succession of water regimes, including the effect of snow cover, on the water balance in the cover and its effect on the performance of the cover. Field trial monitoring data obtained from soil moisture sensors were used to calibrate and validate the numerical model, ensuring its accuracy and reliability in predicting the performance of multilayer cover systems under real weather conditions. This approach allows a better understanding of how a multilayer cover will perform during the dry winter, the wet snowmelt, and the humid summer and autumn. Combining laboratory columns and numerical modelling is hypothesised to provide an efficient way to assess the performance of different designs.

In Sweden, the most common remediation measure to stop acid rock drainage (ARD) formation from mine waste is to apply a multi-layer cover on top of the waste deposit. The access to suitable cover-materials is, however, limited, creating a driving force for alternative solutions. The recycling of an industrial residue for this purpose is beneficial for the industry where the residue is generated, the mining industry using the residue, and the society’s strive for end-of-waste. Green liquor dregs (GLD), a residue from pulp production, is an example of an industrial residue that has the potential to improve the sealing properties of a till. The use of a GLD-till mixture for the construction of a sealing layer in mine waste covers is one alternative to the wellused bentonite amendment to a permeable till. A few trials on using GLD-amended till have been made at demonstrational scale, but this study is the first to evaluate a sealing layer of a sulphidic mine waste cover consisting of GLD-amended till, monitored for four years. The results are compared to a traditional bentoniteamended till cover, analysing soil water content and oxygen concentrations. In addition, two methods of instrument installation (pits and monitoring wells) were evaluated. The monitoring of the soil water content in the sealing layers indicate saturation, or close to saturation, in both materials. This implies a successfully functioning sealing layer that minimises oxygen diffusion to the waste rock underneath. More monitoring is needed to conclude on the long-term performance of both types of sealing layers, i.e. bentonite-amended till and GLD-amended till. The findings in this and a previous study suggest that pits are recommended as an installation method if horizontal installation of instruments is possible. However, this study also concludes that the current great variation in GLD, especially its water content, makes it difficult to use compared to commercial, more homogenic, products.

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.

A laboratory investigation was conducted to identify principal variables-initial mixing water content, porosity, and binder content- impacting undrained shear strength (qu) of stabilized sulfur-rich silty soil. An equation for predicting qu of stabilized soil was established based on the experimental data. Initially, samples were prepared with soils sample with different initial water and binder contents. Multicem, a binder consisting of a mix of cement and cement kiln dust, was added to the samples. Three different percentages of Multicem were mixed at five different soil water contents to measure qu of stabilized mixtures to understand how water content and porosity levels in the samples affect the performance of the binder and their combined impact on the strength of the samples. The soil-binder mixtures were compacted and subsequently cured in laboratory-controlled environment. The prepared samples were tested in uniaxial compression test apparatus. The results evidenced that binder content and corresponding porosity affect the strength of specimens at an equal water content. The results showed that at equal initial mixing water content, the qu of a sample increased by increasing binder content. Furthermore, it was observed that increase of binder content has a reverse effect on porosity. It was appeared lowering the soil water content, initially increased the strength until an optimum water content. Further lowering water content increased the porosity and consequently decreased qu of samples. Moreover, a ratio of porosity/volumetric binder content was chosen to evaluate the impact of these two variables on strength of samples. This study showed that qu is an exponential function of porosity/binder volumetric content ratio which depends on initial mixing water content of mixtures. It was shown at water content lower than the optimum, results of stabilization are more effective than in soil at higher water contents. Therefore, reducing the water content and thereby porosity has more significant effect on improving qu than increasing the binder content.

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.

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.