A field trial demonstrating CO2 removal through enhanced weathering in mine tailings: design, commissioning and early performance of a European Union-funded pilot

Authors: Shiimi, R; Savage, W; Mouchos, E; Brussee, O; Ronne, E; Pearce, S

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DOI https://doi.org/10.36487/ACG_repo/2655_49

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Shiimi, R, Savage, W, Mouchos, E, Brussee, O, Ronne, E & Pearce, S 2026, 'A field trial demonstrating CO2 removal through enhanced weathering in mine tailings: design, commissioning and early performance of a European Union-funded pilot', in AB Fourie, M Horta, M Oliveira & S Wilson (eds), Paste 2026: Proceedings of the 28th International Conference on Paste, Thickened and Filtered Tailings, Australian Centre for Geomechanics, Perth, pp. 1-12, https://doi.org/10.36487/ACG_repo/2655_49

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Abstract:
Tailings from mafic and ultramafic mines can be utilised to neutralise acids, and capture and store carbon dioxide (CO2) via enhanced rock weathering (ERW). As part of the European Union (EU)-funded C-SINK project, Boliden’s active Kevitsa Mine, Finland, hosts a field trial to develop scalable monitoring, reporting and verification (MRV) for carbon dioxide removal (CDR). At Kevitsa, a 2 m deep, 25 m2 filtered tailings test cell was installed in August 2025 to quantify ERW-driven CDR and establish a mine-ready MRV approach. Filled with filtered tailings, the cell is equipped with 3 vertical stations, with ports at various depths. Each port includes CO2 and oxygen (O2) sensors plus temperature, water content and electrical conductivity (EC) probes, for continuous, depth-controlled pore/void monitoring. A pH probe tracks near-surface changes. To capture reaction products and quantify carbon flux, a drainage well with an autosampler collects leachate for laboratory analysis of pH, EC, alkalinity, dissolved inorganic carbon, major cations/anions and trace elements. Determination of CDR is carried out using these sensor and leachate chemistry data, coupled with periodic solid-phase sampling of tailings for in situ carbonate formation evidence. This paper reports: This study assesses how these data streams can estimate CO2 drawdown and support sustainable upscaling of ERW deployment at tailings storage facilities (TSF) during mine operation and closure. To our knowledge, this is the first EU pilot testing MRV for ERW of tailings at an active mine, combining continuous multi-depth flux monitoring with systematic leachate and solid-phase chemistry data to provide a scalable pathway for long-term sustainable CDR at a TSF.

Keywords: enhanced weathering, mineral carbonation, mine tailings, carbon dioxide removal, MRV methodology

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