Long term hydro-geochemical behaviour of surface paste disposal in field experimental cells

Gilles Barast, Mostafa Benzaazoua, Abdelkabir Maqsoud, Bruno Bussière

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

Session: Mining Geotechnics

ABSTRACT: hydro-geochemical behaviour of surface paste disposal in field experimental cells Gilles Barast, Mostafa Benzaazoua, Abdelkabir Maqsoud & Bruno Bussière Institut de recherche en mines et en environnement Œ University of Quebec in Abitibi-Témiscamingue, 445 Boulevard de l'Université, J9X5E4, Rouyn Noranda, Québec, Canada ABSTRACT The effectiveness of the Surface Paste Disposal (SPD), combined with cement amendments, to limit mine drainage production was evaluated on a three year hydro-geochemical investigation. Two field cells were constructed in 2010 at the LaRonde mine site (Quebec, Canada): (UC) un-cemented and (CC) cemented at 2 wt.% Portland cement in the first 10 cm layer. The results showed that the degree of saturation remained between 85 and 95% in the bottom layers. The pH (around 6) and As, Cu, Ni and Pb concentrations remained below the standard values accepted by the environmental regulations. However, some metals (Fe and Zn) were leached at high concentrations. Finally, the cemented layer improved the effectiveness of the cover SPD, allowing the reduction of released metals concentration, water content variation in the cell and cracks intensity on the top surface. RÉSUMÉ L'efficacité des Dépots de Pâtes en Surface (SPD) avec amendement cimentaire utilisés pour limiter la production du drainage minier a été évalué en utlisant les résultats relatifs aux suivis hydro-géochimique durant trois années sur deux cellules de terrain construites en 2010 à la mine Laronde (Québec, Canada) : (UC) non cimentée et (CC) amendée à 2% de ciment Portland en première couche de 10 cm. Les résultats de mesures ont montré le maintien du degré de saturation entre 85 et 95% dans les couches inférieures. Les concentrations en As, Cu, Ni et Pb ainsi que pH (autour de 6) des lixiviats demeurent dans la plage des valeurs acceptées par la réglementation environnementale. Cependant certains métaux (Fe et Zn) ont été léxiviés avec de fortes concentrations. Finalement, on peut conclure que la couche cimentée améliore l'efficacité de la couverture SPD permettant ainsi de réduire les concentration en métaux relargués, les variations des teneurs en eau au sein de la cellule et l'intensité de fissuration en surface. 1 INTRODUCTION The mining activity generates large amounts of tailings from the plant ore processing. These tailings are ground rock particles from which the valuable minerals or metals have been extracted. They often contain high volume of water (20-50%) due to the separation process at humid state. The mine tailings are well-known for the possible risk of Acid Mine Drainage (AMD) production (Aubertin et al., 2002). The AMD occurs when sulphide minerals such as pyrite and pyrrhotite contained in mine waste are exposed to ambient air and water. Chemical reactions occur between the sulphide minerals, water and atmospheric oxygen. These induce a decrease of pH of in-contact water and dissolution of metals within minerals. For low or inexistent content of alkaline minerals in the tailings, the acidity of the water cannot be fully neutralized. The resulting leachate will eventually remain at acid pH by favoring the release of soluble metals, which will be above environment regulatory requirements (Bussière, 2007). The Surface Paste Deposit (SPD) is a promising alternative to the conventional tailings disposal (Newman et al., 2001; Deschamps et al., 2009). The SPD technique is similar to the CPB technique used in underground mines (Belem and Benzaazoua, 2008). The tailings are filtered then re-watered to the desired solid content (75-85%). After that, the mixture can be blended with cement to the required concentration, before pond disposal. There are numerous advantages for the geotechnical design offered by the SPD technique (Theriault et al., 2003) and the cement addition (Deschamps et al., 2009). Among these benefits, the increasing of solid tailings stored volume and the reduction of the water pressure on the embankments are usually expected. The environmental impact is also reduced due to the fact that the thickened amended materials control the production of AMD. When cement is added, SPD has lower porosity, lower permeability and higher capacity of water retention than conventional tailings. These properties allow maintaining tailings at high degree of saturation Sr. Therefore, the flow of water and diffusion of oxygen become limited and the AMD is less likely to occur (Nicholson et al., 1989). In addition, the alkaline minerals in the cement addition immobilize the bearing heavy metals with secondary precipitations and neutralize any acidity in the water, preventing the dissolution of metals (Benzaazoua et al., 2004b). The application of SPD on tailings ponds is more recent and the general issue focuses on its chemo-environmental impacts under the influence of oxygen and water. Although, the SPD technique benefits from the researches devoted to the interactions between the tailings and the binding agent in CPB (Benzaazoua et al., 2004a), a few studies have investigated the evaluation of the cemented SPD efficiency. Most of these investigations are dedicated to the laboratory testing of a few kilograms SPD specimens under forced kinetic conditions (Benzaazoua et al., 2004a; DeVos and Verburg, 2006; Simms et al., 2007; Deschamps et al., 2009; Hadimi,

RÉSUMÉ: term hydro-geochemical behaviour of surface paste disposal in field experimental cells Gilles Barast, Mostafa Benzaazoua, Abdelkabir Maqsoud & Bruno Bussière Institut de recherche en mines et en environnement Œ University of Quebec in Abitibi-Témiscamingue, 445 Boulevard de l'Université, J9X5E4, Rouyn Noranda, Québec, Canada ABSTRACT The effectiveness of the Surface Paste Disposal (SPD), combined with cement amendments, to limit mine drainage production was evaluated on a three year hydro-geochemical investigation. Two field cells were constructed in 2010 at the LaRonde mine site (Quebec, Canada): (UC) un-cemented and (CC) cemented at 2 wt.% Portland cement in the first 10 cm layer. The results showed that the degree of saturation remained between 85 and 95% in the bottom layers. The pH (around 6) and As, Cu, Ni and Pb concentrations remained below the standard values accepted by the environmental regulations. However, some metals (Fe and Zn) were leached at high concentrations. Finally, the cemented layer improved the effectiveness of the cover SPD, allowing the reduction of released metals concentration, water content variation in the cell and cracks intensity on the top surface. RÉSUMÉ L'efficacité des Dépots de Pâtes en Surface (SPD) avec amendement cimentaire utilisés pour limiter la production du drainage minier a été évalué en utlisant les résultats relatifs aux suivis hydro-géochimique durant trois années sur deux cellules de terrain construites en 2010 à la mine Laronde (Québec, Canada) : (UC) non cimentée et (CC) amendée à 2% de ciment Portland en première couche de 10 cm. Les résultats de mesures ont montré le maintien du degré de saturation entre 85 et 95% dans les couches inférieures. Les concentrations en As, Cu, Ni et Pb ainsi que pH (autour de 6) des lixiviats demeurent dans la plage des valeurs acceptées par la réglementation environnementale. Cependant certains métaux (Fe et Zn) ont été léxiviés avec de fortes concentrations. Finalement, on peut conclure que la couche cimentée améliore l'efficacité de la couverture SPD permettant ainsi de réduire les concentration en métaux relargués, les variations des teneurs en eau au sein de la cellule et l'intensité de fissuration en surface. 1 INTRODUCTION The mining activity generates large amounts of tailings from the plant ore processing. These tailings are ground rock particles from which the valuable minerals or metals have been extracted. They often contain high volume of water (20-50%) due to the separation process at humid

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Gilles Barast; Mostafa Benzaazoua; Abdelkabir Maqsoud; Bruno Bussière (2014) Long term hydro-geochemical behaviour of surface paste disposal in field experimental cells in GEO2014. Ottawa, Ontario: Canadian Geotechnical Society.

@article{GeoRegina14Paper368,author = Gilles Barast; Mostafa Benzaazoua; Abdelkabir Maqsoud; Bruno Bussière,title = Long term hydro-geochemical behaviour of surface paste disposal in field experimental cells ,year = 2014}