Experimental study of tailings percolation into waste rock

Nicolas Rey, Isabelle Demers, Bruno Bussière

In the proceedings of: GeoRegina 2014: 67th Canadian Geotechnical Conference

Session: Mining Geotechnics

ABSTRACT: al study of tailings percolation into waste rock Nicolas Rey, Isabelle Demers, Bruno Bussière IRME Œ UQAT, Rouyn-Noranda, Québec, Canada ABSTRACT To reduce the footprint of tailings storage sites, it is more and more common to recycle wastes by using them as construction materials for on-site facilities. In this study, it is proposed to use non contaminant-generating mine waste as part of covers with capillary barrier effects to control the generation of acid mine drainage. The goal is here to estimate, through column tests, the migration of fine particles of tailings within the underlying coarse rocks, and to evaluate the influence that this phenomenon induces on the saturated hydraulic conductivity of waste rocks. The results show that for the tested materials, the migration of fine particles occurs more significantly and deeply in the case of coarser waste rocks and that this effect tends to be amplified when the solid percentage of tailings decreases. However, the migration thus highlighted does not affect much the results of saturated hydraulic conductivity of waste rocks. RESUME Pour réduire l'empreinte des sites d'entreposage de rejets miniers, on propose de plus en plus de valoriser ces rejets dans la construction d'infrastructures minières directement sur site. Dans la présente étude, on suggère d'utiliser des rejets miniers non-générateurs de contaminants dans des recouvrements de type couvertures à effet de barrière capillaire afin de contrôler la génération de drainage minier acide. Le but est ici d'estimer, par le biais d'expériences en colonne, la migration de particules fines de résidus à l'intérieur de stériles grossiers sous-jacents et d'évaluer l'influence que ce phénomène induit sur la conductivité hydraulique saturée des stériles. Les résultats montrent que pour les matériaux testés, la migration des particules fines s'effectue plus abondamment et plus en profondeur dans le cas de stériles plus grossiers et que cet effet s'avère amplifié lorsque le pourcentage solide des résidus diminue. La migration ainsi mise en évidence, n'affecte cependant que peu les résultats de conductivité hydraulique saturée des stériles. 1 INTRODUCTION In a social setting of growing concerns toward environmental issues, the management of wastes and the development of long-term closure plans have become a crucial challenge for the mining industry. Some of the wastes produced by the exploitation of diverse ore deposits contain a significant portion of sulphidic minerals susceptible to generate Acid Mine Drainage (AMD). AMD can trigger the solubilisation of metals present in the host rock (Aubertin et al. 2002a, Bussière, 2006, Lottermoser, 2007), which causes an aggravated contamination of the natural environment (Gray, 1997). These sulphidic mine wastes therefore require a special attention; indeed numerous studies were conducted in order to elaborate and optimize approaches able to prevent AMD generation. In humid climates, the most attractive approach is to insulate the sulphidic minerals of the tailings from atmospheric oxygen, an essential reagent in the production of AMD. To reach this goal, an efficient way is the construction of Covers with Capillary Barrier Effects, or CCBEs (Nicholson et al. 1989; Aubertin et al. 1995). The concept of CCBEs is based on the capacity to maintain high moisture content in one (or more) of the layers, hence reducing significantly the oxygen flux (Mbonimpa et al. 2003, Aachib et al. 2004). More specifically, the CCBE approach consists in layering a fine material (with a relatively high water retention capacity) upon a coarser one (having a low water retention capacity). That water retention contrast limits the percolation of water through the interface, allowing the upper layer to remain nearly saturated, and thus allows the cover to act as a barrier to oxygen (Bussière et al. 2003). However, since such covers generally necessitate the use of significant amounts of natural materials, their construction can imply high costs if the appropriate materials are located far from the site to reclaim. Furthermore, the use of natural material can have a significant impact on disturbed surface areas. To circumvent these constraints, numerous research works were conducted with the aim to find a way to recycle mine wastes as integral parts of a CCBE. In this regard, it has been established that the use of recycled mining materials can be profitable both environmentally and economically (Aubertin et al. 1995, 2002b). Studies performed recently showed that the use of low sulphidic (non AMD-generating) material as moisture retaining layer can reduce the oxygen flux by lowering the oxygen diffusive flux and by consuming part of it (Aubertin et al. 1999; Bussière et al. 2004, 2007; Demers et al. 2008). Recently, it has been suggested to use non AMD generating waste rock as coarse-grained layers in the CCBE. However, before using waste rock into CCBEs, some aspects need to be investigated further, such as the possibility of placing the fine-grained layer hydraulically (by pumping) instead of mechanically, and the level of crushing needed for the waste rock to avoid

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Nicolas Rey; Isabelle Demers; Bruno Bussière (2014) Experimental study of tailings percolation into waste rock in GEO2014. Ottawa, Ontario: Canadian Geotechnical Society.

@article{GeoRegina14Paper218,author = Nicolas Rey; Isabelle Demers; Bruno Bussière,title = Experimental study of tailings percolation into waste rock,year = 2014}