Long-term monitoring of sealing layers consisting of amended (green liquor dregs and bentonite) till: remediation of sulphidic mine waste

Authors: Nigéus, S; Laue, J; Lindblom, J; Maurice, C

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DOI https://doi.org/10.36487/ACG_repo/2515_75

Cite As:
Nigéus, S, Laue, J, Lindblom, J & Maurice, C 2025, 'Long-term monitoring of sealing layers consisting of amended (green liquor dregs and bentonite) till: remediation of sulphidic mine waste', in S Knutsson, AB Fourie & M Tibbett (eds), Mine Closure 2025: Proceedings of the 18th International Conference on Mine Closure, Australian Centre for Geomechanics, Perth, pp. 1-11, https://doi.org/10.36487/ACG_repo/2515_75

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Abstract:
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.

Keywords: mine waste, ARD, cover system, green liquor dregs, end-of-waste, field application

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