Assessing the long-term carbon balance in mine waste storage facilities and implications for mine closure

Authors: Shiimi, R; Pearce, S; Barnes, A

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DOI https://doi.org/10.36487/ACG_repo/2515_60

Cite As:
Shiimi, R, Pearce, S & Barnes, A 2025, 'Assessing the long-term carbon balance in mine waste storage facilities and implications for mine closure', 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. 1-12, https://doi.org/10.36487/ACG_repo/2515_60

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Abstract:
The mining industry excavates and processes billions of tonnes of mine wastes per year and has the potential to leverage its infrastructure and capabilities to use suitable mine wastes for carbon dioxide removal (CDR), by enhanced rock weathering (ERW) as part of mine closure planning to offset mine emissions and mitigate climate change. However, before this opportunity can be realised, further development of key methodologies to measure and predict CO2 flux (uptake and release) from mine waste over the long timescales related to closure is required. While there is an increasing amount of research on the potential for mine wastes to sequester CO2 through the mineral carbonation of Mg-rich and Ca-rich silicates, less research into the determination of net CO2 mass flux/balance is being carried out, which also considers the potential of mine waste to emit CO2 due to cooccurrence of reactive sulphides; organic carbon; and carbonate minerals. This study expands on prior research into mine waste CDR, using novel laboratory and field methods to calculate and estimate the relative balance between sulphide oxidation (oxygen consumption and acidity production), carbonate dissolution (acid neutralisation and CO2 release) and silicate-related carbonation (CO2 sequestration) rates within mine waste. The study describes development of both closed and open system experimental design and utilises data collected to evaluate the carbon balance of various types of mine waste. Findings from the closed-system experiments are used to demonstrate validation of potential testing protocols to estimate site mine waste net CO2 flux. While ERW shows great potential in small-scale laboratory tests, several challenges arise when implementing it on a larger scale. ERW large-scale field trials and improved scaler laboratory-based methods can provide valuable tools for mine closure planning, specifically for designing waste storage facilities and assessing opportunities and risks related to CO2 net flux.

Keywords: carbon sequestration, carbon balance, mineral carbonation, mine wastes, mine closure planning

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