Numerical Modeling of a Laboratory-Scale Waste Rock Pile Featuring an Engineered Cover System

Katherine E Raymond,Bissé Poaty,Danyang Su,Bruno Bussière,Nicolas Seigneur,K Ulrich Mayer,Benoît Plante

doi:10.3390/min10080652

Katherine E Raymond, Bissé Poaty + Show 5 more

Open Access

https://doi.org/10.3390/min10080652

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Journal: Minerals	Publication Date: Jul 23, 2020
Citations: 13	License type: CC BY 4.0

Affiliation: Université du Québec en Abitibi-Témiscamingue

Abstract

Improved design to reduce contaminant mass loadings from waste rock piles is an increasingly important consideration. In certain cases, an engineered cover system containing a flow control layer (FCL) may be used to mitigate the release of metals out of a pile using capillary barrier effects (CBEs), diverting water away from reactive materials below. In this study, a reactive transport model was calibrated to observational data from a laboratory experiment designed to evaluate a cover system. The results show that the numerical model is capable of capturing flow rates out of multiple drainage ports and matching key effluent concentrations by including the spatial distribution of hydraulic parameters and mineral weathering rates. Simulations were also useful for characterizing the internal flow pathways within the laboratory experiment, showing the effectiveness of the cover in diverting the flow away from the reactive waste rock and identifying secondary CBEs between different rock types. The numerical model proved beneficial in building an improved understanding of the processes controlling the metal release and conceptualizing the system. The model was expanded to investigate the robustness of the cover system as a function of the applied infiltration rate, supporting that water diversion will occur with infiltration rates representative of field conditions.

Highlights

The long-term storage of waste rock—material considered not economically viable, which must be removed from the subsurface to access valuable resources during the mining process—is an increasingly important consideration for mine operations globally
frequency domain (FD) probe sensor measurements showed that stable volumetric water contents were reached within the laboratory experiment after 2 days, while the measured flow rates reached a quasi-steady state after approximately 8 days
Based on examining the drainage rates alone, it is unclear whether a higher volume of water leaving reservoir 3 is caused by water leaking through the flow control layer (FCL) into the HI material, or whether water is being diverted by the FCL, as intended, and rerouted to reservoir 3

Summary

Introduction

The long-term storage of waste rock—material considered not economically viable, which must be removed from the subsurface to access valuable resources during the mining process—is an increasingly important consideration for mine operations globally. To mitigate the release of metals and contaminants from ARD and CND, engineered design structures such as cover systems, subaqueous disposal, blending and layering, or co-disposal techniques may be applied as a means of prevention [7,8,9,10,11,12]. In addition to the laboratory- and field-scale tests required to assess these techniques, reactive transport modeling (RTM) may be used as a tool to investigate the processes involved in the release and attenuation of metals from waste rock piles through scenario analyses. The reactive transport code MIN3P-HPC [23] was used to create a numerical model to supplement the ongoing research for an engineered cover system applied at the Lac Tio RTM has been used in the context of mine waste management to compare outcomes under multiple scenarios, investigate the effect of material heterogeneity, contrast different storage techniques, and bracket expected behaviour for forecasting in a number of previous studies e.g., [13,14,15,16,17,18,19,20,21,22].

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