Mining operations produce large volumes of waste rocks to access economically valuable mineralized zones. These waste rocks are usually stored in surface piles, and their construction and reclamation are often a challenge. A flow control layer (FCL) made of crushed waste rocks or sand, installed at the surface of the pile, could control infiltration, thus improving geotechnical stability and limiting water contamination. An experimental pile was built and instrumented at the Tio mine (Rio Tinto Fer et Titane, Quebec) to validate the concept of FCL at large scale. Large infiltration tests were carried out and rainfall was monitored to evaluate the performance of the technique in situ. Measured outflow and water contents were also used to calibrate numerical simulations. However, data were noisy, difficult to calibrate, and sometimes incomplete. A new calibration approach based on the determination of the parameters describing the hydrogeological response to water infiltration (such as water content variation amplitude, arrival time and damping), was therefore proposed. An algorithm was developed to automate the numerical simulation calibration, using a black box optimization method to minimize the error between simulated and measured data. Hydrogeological properties of the waste rocks and flow control layer materials were calibrated and the models were then used to optimize the flow control layer design. The proposed method reduces the bias induced by a manual calibration and allows for a rapid and automatic multi-variable calibration. This paper presents the optimization process and discusses the reliability of the results obtained.

Large amounts of waste rocks are usually produced during mining operations and are often disposed of in large piles on the surface. Waste rock segregation can occur during deposition because of waste rock particle size distribution and deposition method. Segregation usually causes complex heterogenous structures within the piles, increasing the risk for instabilities and preferential flow paths. The optimization of waste rock disposal (e.g. bench height, deposition technique) could improve the geotechnical and hydrogeochemical stability of piles but are difficult to test at field scale. The discrete element program Particle Flow Code (PFC) was therefore used in this study to investigate the behavior of waste rock during disposal. Laboratory tests were used to determine repose angle of samples up to 38 mm diameters and to calibrate numerical simulations. Main input parameters included friction coefficient, rolling resistance coefficient and Young’s modulus. Segregation tests were also conducted in the laboratory to validate and calibrate simulations. The effect of maximum particle size was specifically investigated. Once calibrated, large scale numerical simulations were carried out and field observations were used to validate the results. Relationships between calibrated parameters and particle sizes were used to extrapolate the simulations to field scale. Results show that friction coefficient and rolling resistance coefficient can significantly affect the macro-properties of waste rock and are highly related to the particle size. A relationship between these numerical parameters and waste rock particle size was proposed. Main experimental and numerical results will be presented and discussed in this paper.

Tailings consolidation properties are critical parameters to estimate storage capacity of tailings storage facilities (TSF) and plan mine waste integrated management. In this study, consolidation parameters of tailings from different mine sites were experimentally evaluated using various consolidation tests, including column tests, constant rate of strain (CRS) tests and conventional oedometer tests. Column tests with an internal diameter of 10 cm and a height of 45 cm were used to determine the compressibility of the saturated tailings under incremental loadings and to estimate compression index, Cc, coefficient of consolidation, Cv, and saturated hydraulic conductivity, ksat. Pore water pressure at three different elevations along the column and the displacement of the sample were continuously measured during the tests. Several CRS tests and conventional oedometer tests were also conducted to determine the compression behavior of the tailings. Results obtained from these different approaches were compared (also their reproducibility and precision). The effect of initial water content, sample size and loading steps was assessed. Experiment procedures and representative results will be compared, analysed and discussed in this paper. Recommendations will also be proposed regarding choice of experimental approach depending on the application and field conditions

Fluid Fine Tailings (FFTs) produced during bitumen extraction from oil-sands ore is often treated with synthetic polymer to enhance binding of colloidal fine particles into larger flocs. This process is known as flocculation and aimed at improving the dewatering, settling, and strength behaviors of the FFTs. The flocculation quality, however, is influenced by the several in-put parameters into the process including the mineral composition of the FFTs, feed rate of polymer solution, shear rate and shear time during mixing. In this study, in-real time assessment of the effects of the in-put parameters on the flocculation quality was conducted. The study employed FFTs with various solid contents ranged between 30 and 40% (w/w) treated with a synthetic polymer at feed rates ranged between 5 and 36 ml/min. The flocculation process was conducted in an Advanced Couette Rheometer and controlled via the Torque Force-based Technique (TFT). The preliminary results showed that the faster the feed rate the larger the exerted torque force. This coincided with better immediate dewatering and better longer-term dewatering and settling behaviors.

Filtered tailings are often considered a promising alternative to conventional deposition methods and may contribute to improve the geotechnical stability of tailings storage facilities. However, the risk of generation of acid mine drainage (AMD) or contaminated neutral drainage (CND) can be increased by desaturation if the tailings are reactive. The purpose of this study was to evaluate the impact of the climatic and deposition conditions on reactive filtered tailings facilities on AMD/CND generation. Cell tests (an adaptation of kinetic tests) and laboratory column tests were carried out to determine the critical degree of saturation at which AMD generation starts. The influence of layer thickness and compaction on the hydrogeological behaviour of filtered tailings was also investigated to propose recommendations to optimize deposition and improve their geochemical stability.
Mine tailings were received from a partner mining company and compacted in 4 columns (70 cm in height, 36 cm in diameter) in successive layers of 7.5 cm for final thicknesses of 15 cm, 30 cm, 45 cm and 60 cm. The void ratio was similar to the one expected in the field. Each column was instrumented with water content and suction probes installed every 15 cm. Columns were placed on scales to continuously monitor their mass to estimate the evolution of water balance with time. The top of the columns was left open and evaporation was controlled by a fan. An outlet was installed at the base of the columns to allow drainage and to sample leachate. Several wetting and draining cycles were applied to the columns.
Numerical hydrogeological and geochemical simulations completed the study. Models were calibrated and validated using the laboratory test results. Results indicate that the thickness of the tailings layers upon disposal and compaction, and the disposal rate can be optimized to minimize the risk for AMD generation.

De nouvelles équations ont été développées pour interpréter des essais de traceurs, en prenant en compte la déformation d’un champ de vitesse initialement rectiligne uniforme par la présence du puits d’injection, phénomène souvent négligé par les méthodes déjà existantes. Le potentiel complexe d’un aquifère plan dans lequel une injection est effectuée a été calculé par superposition du potentiel complexe d’un écoulement rectiligne uniforme déformé par un cercle de conductivité infinie, et du potentiel complexe d’un écoulement radial uniforme correspondant à une injection ponctuelle seule. Le potentiel complexe a ensuite été dérivé en champ de vitesse, puis une relation entre la position du front d’avancée du panache de traceur et le temps depuis le début de l’injection a pu être établie, en ne considérant que la partie advective du transport. Ces nouvelles équations ont été testées par simulations numériques avec un modèle permettant de faire des écoulements, du traçage de particules et de l’advection-dispersion. Les résultats ont montré que les nouvelles équations sont significativement plus précises que d’anciennes équations ne prenant pas en compte la déformation du champ de vitesse par le puits, notamment lorsque la vitesse d’injection est suffisamment faible devant la vitesse naturelle d’écoulement, pour un puits de diamètre assez grand et au voisinage du puits. Les nouvelles équations ont également mis en évidence un paramètre liant le rapport entre la vitesse d’injection et la vitesse naturelle d’écoulement, et le diamètre du puits. La valeur de ce paramètre permet de distinguer trois formes de panaches observées numériquement.