Innovative and eco-friendly techniques of waste rocks management

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During the last decades, the development of open pit mining worldwide has responded accordingly to a difficult economic context as well as high prices for some strategic and precious metals. This has led to increased interest in many high tonnage/low-grade type deposits, particularly in Canada. Such mining operations generate large footprint and significant amount of waste rocks to be stored generally at the surface of mine site. Some underground mine are also facing similar problems. Since these materials are often sulphide bearing and have coarse and wide particle-size distributions (micrometric to metric sizes) as well as high permeability to water and oxygen, they are likely to be a source of more or less contaminated mine drainages, sometimes highly acid generating. The phenomenon is worldwide known as acid rock drainage (ARD). Sulfide reaction lead to the releases of acid-soluble metals/metalloids, sulfates, and acidity within the drainage waters. The oxygen diffusion within waste rock piles is favoured by the material properties. The available techniques to control ARD are all implemented during waste disposal (roof sealing, co-disposal with tailings, water diversion, etc.), and/or after disposal upon mine site closure and reclamation, thus necessitating the installation of complex but costly cover techniques followed by appropriate revegetalisation.The present project aims to tackle challenges surrounding waste rocks management through the investigation of different steps of a new, innovative, and eco-friendly approach. This approach, which has to be applied upstream immediately after waste rock extraction, integrates optimized waste blasting, reprocessing, and/or valorisation. The main hypotheses of the project are that: (i) sulphides within waste rocks are mainly associated with coarse particles and are not significantly exposed to weathering conditions, and (ii) mineral weathering occurs primarily in the fine fraction (size to be further defined), due to the high available exposed surface area of these particles. Knowing the important needs of research for more innovative and sustainable waste rock management techniques, the main objectives defined for the research program are the following:1- Evaluation of blasting pattern and adaptation for waste extraction and management;2- Suggestion of a rigorous sampling technique which is optimal for waste rocks;3- Fine characterization (physical, chemical and mineralogical properties) and implementation of new predictive tools based on automated mineralogy, microtomography, etc;4- Optimization of an efficient desanding process and desulphurization of the sandy fraction through gravity separation and/or coarse/fine pyrite flotation;5- Technical/economical feasibility of the collective approach, including feasibility of revalorization of the coarse fraction (for use in concrete, road pavement, etc.)