Geochemical Behaviour of Nickel Contained in Tio Mine Waste Rocks Benoit Plante a) , Mostafa Benzaazoua a) , Bruno Bussière a) , Geneviève Pepin a) , Donald Laflamme b) a) Université du Québec en Abitibi-Témiscamingue (UQAT), 445 boul. de l’Université, Rouyn-Noranda, Québec, Canada, J9X 5E4, e-mail : benoit.plante@uqat.ca b) QIT-Fer et Titane Inc., 1625, route Marie-Victorin, Sorel-Tracy, Québec, Canada, J3R 1M6 Abstract In this study, humidity cells (ASTM D5744-96) were used for contaminated neutral drainage (CND) prediction from waste rock piles of an ilmenite deposit known to occasionally release above-level nickel loadings. The influence of mineralogy and in-situ alteration degree of waste rock on its geochemical behaviour are investigated, using samples of waste rocks having various mineral compositions and which underwent different alteration times in the waste rock piles (fresh to approximately 25 years old waste). The nickel adsorption potential of the studied waste rocks appears to play a significant role on the nickel geochemical behaviour. Introduction Acid mine drainage (AMD) is often characterized by low pH, high acidity, and high metal loadings. The phenomenon received much attention in the past decades in terms of prediction, control, and remediation. However, many toxic metals such as nickel, zinc, cobalt, arsenic, and antimony are soluble at near-neutral pH, and can potentially lead to the contamination of mine effluents without the presence of acidic conditions; this phenomenon is called contaminated neutral drainage (CND) (Nicholson, 2004). Since many Canadian mines can potentially face nickel release from waste rock, and nickel geochemistry received much less attention than other CND-related elements (ex. As) in the past years, this work focuses on nickel geochemistry at near-neutral conditions. The present study is performed on waste rock from the Lac Tio mine, an ilmenite deposit near Havre- Saint-Pierre, Québec, Canada, exploited through an open pit operation by QIT-Fer et Titane Inc. since the early 1950’s. Waste rock piles from Lac Tio mine, estimated at over 70 Mt, cover approximately 92 ha and are between 20 and 80 meters high. Water draining from waste rock piles are near-neutral and sporadically show nickel concentrations slightly higher than those allowed by local regulations. Preliminary studies on this waste rock showed that nickel is generated mainly from the dissolution of nickel-bearing pyrite and pentlandite, sulphides that seem to be associated with ilmenite in the Lac Tio deposit, and that the waste rock beneficiate from an important metal retention potential most probably occurring via surface adsorption (Bussière et al., 2005). Materials and methods In this work, 6 Lac Tio waste rock samples are investigated: 3 samples of freshly blasted waste rock and 3 “altered” samples from an old waste rock pile (approximately 25 years old) which underwent significant natural alteration. Table 1 lists the names and ilmenite content of the waste rock samples studied. Nickel content ranges from 0.028 to 0.043 wt% and sulphur content ranges from 0.142 to 0.384 wt% in the studied samples; altered samples have significantly lower sulphur values (<0.172 wt%) than fresh samples(>0.345 wt%), probably due to alteration. Such a sample configuration enables the evaluation of the alteration degree and ilmenite content effects on geochemical behaviour of the wastes, which was evaluated through the use of humidity cell tests (ASTM D5744-96). This procedure consists of weekly drying-wetting cycles ending with flushing of the studied material with deionized water, which is then analyzed for various geochemical parameters. Table 1 General description of the Lac Tio waste rock samples studied C1 C2 C3 C4 C5 C6 Sample age Freshly blasted Freshly blasted Freshly blasted 25 years 25 years 25 years Ilmenite content low intermediate high low intermediate high S (wt%) 0.384 0.345 0.472 0.142 0.164 0.172 Ni (wt%) 0.028 0.032 0.043 0.031 0.033 0.037