Reactive transport modelling to investigate multi-scale waste rock weathering processes

Prediction of drainage quantity and quality is critical to reduce the environmental risks associated with weathering mine waste rock. Reactive transport models can be effective tools to understand and disentangle the processes underlying waste-rock weathering and drainage, but their validity and applicability can be impaired by poor parametrization and the non-uniqueness conundrum. Here, a process-based multicomponent reactive transport model is presented to interpret and quantify the processes affecting drainage quantity and quality from 15 waste- rock experiments from the Antamina mine, Peru. The deployed uniform flow formulation and consistent set of geochemical rate equations could be calibrated almost exclusively with measured bulk waste-rock properties in experiments ranging from 2 kg to 6500 tons in size. The quantitative agreement between simulated dynamics and the observed drainage records, for systems with a variety of rock lithologies and over a wide range of pH, supports the proposed selection of processes. The controls of important physicochemical processes and feedbacks such as secondary mineral precipitation, surface passivation, oxygen limitations, were confirmed through sensitivity analyses. Our work shows that reactive transport models with a consistent formulation and evidence-based parametrization can be used to explain waste-rock drainage dynamics across laboratory to field scales.