Performance de recouvrements isolants partiels pour contrôler l'oxydation de résidus miniers sulfureux

RESUME Un defi environnemental important de l’industrie miniere est la restauration des parcs a residus miniers, particulierement lorsque les residus ont un potentiel de generation de drainage minier acide (DMA). Le DMA est cause par l’oxydation naturelle de mineraux sulfureux au contact de l’oxygene de l’air et de l’eau, phenomene pouvant mener a une contamination des eaux de drainage. Le recouvrement isolant est une methode de restauration specialement concue pour les conditions nordiques. Cette methode vise a integrer les residus miniers dans le pergelisol afin de les maintenir dans un etat constamment gele et ainsi eviter la generation de DMA. L’objectif principal du projet est d’evaluer la performance a limiter l’oxydation des residus miniers sulfureux de deux configurations de recouvrements isolants partiels (0,4 m et 1,2 m) installes sur le parc a residus de Mine Raglan. Pour ce faire, une approche basee sur la mesure directe de la reactivite des residus sous les recouvrements isolants partiels avec le test de consommation d’oxygene est utilisee. De plus, la temperature, la teneur en eau volumique et la succion a la surface des residus et dans les recouvrements isolants partiels sont mesures afin d’evaluer l’effet du comportement thermo-hydrique sur la reactivite des residus miniers pour ce site en particulier. ----------ABSTRACT An important challenge for the mining industry is the reclamation of tailings storage area, especially when tailings can generate acid mine drainage (called AMD). AMD is caused by the reaction of sulfide minerals in tailings exposed to air and water. Integrating tailings within the permafrost by the use of an insulation cover is a reclaiming method designed and used especially for Nordic conditions. The main objective of this project is to evaluate the performance of partial insulation covers (0.4 m and 1.2 m thick) built on the Raglan Mine tailings storage facility. The method used to assess the performance of the partial insulation covers includes oxygen consumption tests (OC tests) for measuring tailings reactivity under the partial insulation covers. Moreover, temperature, volumetric water content and suction measurements at various depths in the cover material and in sulfide tailings allow to study the effect of the partial covers’ hydro-thermal behavior on tailings reactivity for this particularly site. Cover and tailings materials were characterized for their mineralogical, physical, hydrogeological and thermal properties. Results show that the tailings hydrogeological properties are typical for that kind of material (saturated hydraulic conductivity around 1x10-5 cm/s and air entry value around 20-30 kPa). Tailings have a good potential for acid generation with their high sulfide content (10 to 20% wt) and low neutralization potential. Tailings reactivity at different degrees of saturation was evaluated in laboratory, and oxygen consumption test variability was assessed in situ in the Raglan Mine tailings storage facility. Cover material (0-20 mm) has a saturated hydraulic conductivity near 1x10-1 cm/s and an air entry value around 1 kPa; its geochemical behavior is not considered problematic. In situ characteristic soil freezing curves for tailings and cover material agree well with water retention curves obtain in laboratory for suction greater than 1x103 cm. In situ water retention curves agree well with the laboratory water retention curve for cover material but underestimate water retention for tailings.