Sustainable mine waste management: from microscale hydrogeochemical processes to macroscale prediction models

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*INTRODUCTION* Mine wastes can negatively impact the environment through the release of poor-quality drainage with harmful levels of acidity, metal(loid)s or other contaminants. Effective long-term management of mine waste storage facilities is predicated on the ability to forecast seepage rates and the chemical composition of these effluents for decades beyond mine closure. For this, a wide range of geochemical weathering reactions and coupled physical transport processes needs to be quantitatively understood. Mineralogical dynamics, effluent composition and solute speciation vary greatly across storage conditions and waste rock types but lack systematic characterization to date. Furthermore, our ability to integrate such microscale hydrogeochemical phenomena with practical, macroscale prediction models is still limited: effective waste management remains a costly technical challenge for the mining industry. *OBJECTIVES* The objectives of this research program are to advance our understanding of critical hydrogeochemical processes in mine wastes and to improve the application of this knowledge in prediction models for mine waste effluent quality. The proposed research occurs along two major themes: microscale processes and macroscale prediction models. These themes, respectively, have the objectives to i) experimentally constrain the controls of mineralogical dynamics and aqueous solute speciation on weathering rates and contaminant mobility, and ii) to create and evaluate long-term macroscale prediction models using reactive-transport modeling and dimensionless numbers analyses. *METHODS* Using controlled laboratory experiments, we will study the weathering rates, mineralogical surface dynamics and generated effluent qualities from different waste rock materials under contrasting exposure conditions. By analyzing the aqueous speciation of thiolated metalloids in effluent, we will determine the conditions in which these contaminant species are formed and degraded and thereby shed light on their environmental persistence. Second, we will monitor and quantify the evolution of the mineral assemblages and derive kinetic parameters and indicator proxies for bulk waste rock reactivity that can ultimately be used in prediction models. Finally, we will perform reactive-transport simulations to assess the importance of distinct hydrogeochemical, mineralogical, and physical transport processes towards overall drainage quality as a function of waste rock type and storage conditions. *IMPACT* This research program will train several graduate and undergraduate students in advanced analytical, experimental, and simulation techniques, using world-class infrastructure and extensive collaboration with (international) mining practitioners. Our results will produce fundamental knowledge on mine waste hydrogeochemistry as well as practical insights for improved mine waste management, helping Canadian companies to remain global frontrunners in sustainable mining.