Ferrada, N, Coene, E, Arcos, D, Alarcón, R & Bouguereau, M 2024, 'Development of a predictive numerical model of water–rock interaction to estimate mine drainage water quality evolution from a waste rock dump located in northern Chile', in AB Fourie, M Tibbett & G Boggs (eds), Mine Closure 2024: Proceedings of the 17th International Conference on Mine Closure, Australian Centre for Geomechanics, Perth, pp. 513-528, https://doi.org/10.36487/ACG_repo/2415_37
(https://papers.acg.uwa.edu.au/p/2415_37_Ferrada/)
Abstract: Waste rock dumps are considered one of the main sources of compromised mine drainage, both due to their geochemical and physical properties, and the large volumes they can reach.
The objective of the study is to evaluate the chemical stability of an extensive waste rock dump located in northern Chile, at a high geographic altitude (over 4,000 m) in extremely arid and high evaporation conditions, and to predict the water quality of its effluents in preparation for the mine closure stage.
The heterogeneous particle size, when considered with the extended geometry of the waste dump, favours water and oxygen circulation through the material. Its internal structure was modelled using a detailed block model and it was characterised by different geoenvironmental units, depending on the area and future growth stages, as determined using detailed geochemical tests. A prediction of effluent water quality was made through numerical modelling carried out with iCP software, which couples unsaturated flow, heat transmission, solute transport and geochemical reactions in the waste dump. Thereafter, the reaction rates of the various minerals were calibrated by performing kinetic geochemical tests.
Reactive materials vary both in location and concentration inside the dump, which leads to a spatially and temporally variable mine drainage generation process. In response, modelling allows for the prediction of mine drainage evolution in time and space, and therefore evaluation of the need for and/or relevance of prevention,control and/or treatment measures. This can be considered according to the risk that they pose as part of an onsite chemical stability management strategy.

Keywords: acid-base accounting, acid mine drainage, acid rock drainage, block model, effluent chemical quality, geochemical characterisation, geoenvironmental units, kinetic tests, metal leaching, predictive numerical modelling, reactive transport, static tests, unsaturated flow, waste dump, water quality