Mining operations generate large volumes of sulfidic waste rock and tailings that, upon exposure to oxygen and water, initiate oxidation reactions producing acid mine drainage with the potential to acidify soils and waterways for extended periods. Dry cover systems using compacted till as a sealing layer represent an established technical solution to prevent this process. Conventionally, the till is mixed with bentonite, an imported clay mineral with documented low hydraulic conductivity. Green liquor dregs (GLD), a residual material from the pulp and paper industry, has been shown in field studies to achieve comparable geotechnical properties and has been identified as a potentially circular alternative. Despite this, a quantitative comparison of the two materials from a life cycle perspective has been lacking.

The aim of this study is to quantify and compare the environmental impact of two sealing layer systems at the Garpenberg mine in Dalarna, Sweden: till mixed with bentonite and till mixed with GLD.The study was conducted as a comparative life cycle assessment in accordance with ISO 14040 and ISO 14044, with a cradle-to- installation system boundary. The functional unit was defined as 1 m2 of completed sealing layer with a thickness of 0.5 m. Three impact categories were assessed: global warming potential (GWP), acidification potential (AP), and eutrophication potential (EP), using the CML-IA baseline V3.10 characterisation method in SimaPro 9.6 with Ecoinvent 3 as the background database. A sensitivity analysis was conducted using the one-at-a-time (OAT) method across four scenarios, varying the transport distance for bentonite and GLD, layer thickness, and compaction productivity .

The results show that bentonite–till exhibited a climate impact of 28.60 kg CO2-eq per m2, compared with 7.46 kg CO2-eq per m2 for GLD–till. The acidification

potential was 7.7 times higher for bentonite–till and the eutrophication potential 4.1 times higher. Bentonite transport from India to Garpenberg was identified as the dominant contributing process across all impact categories. The sensitivity analysis showed that GLD–till remained the environmentally preferable alternative across all analysed scenarios. Within the studied system boundary, the results demonstrate that GLD as an industrial residue substantially reduces the environmental impact of sealing layer construction compared with imported bentonite, while further research regarding long-term performance and alternative allocation methods is still needed.

Keywords: Life cycle assessment (LCA), industrial symbiosis, green liquor dregs (GLD), bentonite, sealing layer, global warming potential (GWP), acidification potential (AP), eutrophication potential (EP)