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.

Mining of sulfidic ore generates acidic waste which often leads to the generation of acid rock drainage (ARD) having an adverse impact on aquatic flora and fauna. Engineered multilayer cover is one of the commonly used methods to prevent oxygen from being transported to mine waste. The sealing layer has a key function in the cover, thanks to its high water retention capacity and a low hydraulic conductivity, which enable the layer to remain near water saturation, effectively hindering oxygen diffusion. When adequate material is not available improvement of local soil material with a sealing agent is principally the only option to produce sealing layer material. Apart from bentonite clay, Green Liquor Dregs (GLD), a waste from the pulp and paper industry, have the ability to reduce the oxygen diffusion when mixed to granular soil, improving the water retention capacity of the blend. Experience from the development of Till/GLD-blends for the construction of sealing layers is compiled to address issue related to soil amelioration using waste with focus on material variation and quality control. The presentation focuses on the opportunities and challenges for the establishment of a circular system based on reutilization of a waste, herein GLD for improvement of soil’s geotechnical property.

In Sweden, the common method to stop sulfide oxidation and the production of acid rock drainage (ARD) from unattended sulfidic mine waste is the application of a dry cover solution on the waste. Recycling a non-hazardous industrial residue, such as green liquor dregs (GLD), in this cover solution is beneficial for both the mining industry where there is a great need for alternative materials and the providing industry by minimizing the waste deposited. The objectives of this field study were to install and evaluate the instrumentation of a sealing layer made of GLD- and bentonite amended till (respectively), and to evaluate two different methods of installation: monitoring wells and pits. Experiences from this study demonstrate that it is difficult to properly seal the drill holes after installation of the probes and suggest that the best alternative for future installation of instruments in a sealing layer might be to excavate a pit in the protection layer after installation of the soil cover and then drill the probes into the sealing layer from that pit.

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.