Abdelkabir Maqsoud

Natural lateral particle segregation commonly occurs during the hydraulic deposition of slurry and thickened tailings in surface tailings storage facilities (TSFs), producing spatial heterogeneity in physical, hydrogeotechnical, and mineralogical properties, as well as in the water table. In sulfide-rich tailings, such heterogeneity complicates the design of reclamation cover systems, which are themselves affected by it. This study investigates the impact of physical and rheological properties of hard-rock mine tailings slurries on their segregation under hydrodynamic conditions. It proposes a multiparametric equation for the segregation index (SI) based on Buckingham’s π theorem. For this purpose, six flume experiments were conducted using tailings with initial solid mass concentrations of 63%, 66%, and 69% at slopes of 0.5% and 1%. Results revealed strong exponential correlations (R² > 0.95) between SI and tailings’ physical properties (solid concentration, bulk density) as well as rheological parameters (Herschel–Bulkley yield stress and flow index, Cross infinite dynamic viscosity). The SI equation was developed using MATLAB R2025b nonlinear least-squares optimization with a trust-region reflective algorithm. Using an SI threshold of 0.05 to define non-segregating behavior, the proposed model can predict segregation tendencies as a function of tailings properties and slope conditions. Further laboratory and field investigations are needed to validate and generalize the criterion.

Natural lateral particle segregation commonly occurs during the hydraulic deposition of slurry and thickened tailings in surface tailings storage facilities (TSFs), producing spatial heterogeneity in physical, hydrogeotechnical, and mineralogical properties, as well as in the water table. In sulfide-rich tailings, such heterogeneity complicates the design of reclamation cover systems, which are themselves affected by it. This study investigates the impact of physical and rheological properties of hard-rock mine tailings slurries on their segregation under hydrodynamic conditions. It proposes a multiparametric equation for the segregation index (SI) based on Buckingham's π-theorem. For this purpose, six flume experiments were conducted using tailings with initial solids mass concentrations of 63%, 66%, and 69% at slopes of 0.5% and 1%. Results revealed strong exponential correlations (R² > 0.95) between SI and tailings' physical properties (solids concentration, bulk density) as well as rheological parameters (Herschel–Bulkley yield stress and flow index, Cross infinite dynamic viscosity). The SI equation was developed using MATLAB nonlinear least-squares optimization with a trust-region reflective algorithm. Using an SI threshold of 0.05 to define non-segregating behavior, the proposed model can predict segregation tendencies as a function of tailings properties and slope conditions. Further laboratory and field investigations are needed to validate and generalize the criterion.

Low-saturated hydraulic conductivity covers (LSHCC) or hydraulic barriers are one of the reclamation techniques used to control the acid mine drainage generation (AMD). These covers are intended to limit the infiltration of water into reactive tailings. Compacted clays are among the materials used as LSHCC. The performance of clay-based hydraulic barriers can be affected by their geotechnical and hydrogeological properties. Freeze–thaw cycles can increase their saturated hydraulic conductivity (k_sat). However, these effects can be minimized by adding amendments. To evaluate the performance of these clay-based covers, four field experimental cells were built. The first one simulates a cover composed entirely of clay, the second a clay–silt mixture, the third a clay–sand mixture and the last two layers of clay with an intermediate layer of silt. Each cell has been equipped with a monitoring station with continuous measurements of volumetric water content, suction and temperature. In situ permeability tests were also conducted to assess field hydraulic conductivity. Numerical simulations were also conducted to evaluate the water balance for each cover scenario. The laboratory results showed low-saturated hydraulic conductivity values meeting waterproofing criteria, whereas field measurements and calibrated model values were consistently higher and exceeded the waterproofing criteria. Infiltration monitoring indicated that 15 to 40% of precipitation infiltrated the covers, with possible overestimation due to preferential flow. Discrepancies between laboratory and field-saturated hydraulic conductivity values were mainly attributed to inadequate compaction, unfavorable weather conditions, and excessive water content during cover installation. Variations in saturated hydraulic conductivity over time were generally within statistical variability, although differences among cells and responses to wetting–drying cycles highlight the influence of construction conditions on field performance.

Many countries employ mining and ore processing techniques to concentrate and extract precious natural resources. However, the slow leaching of numerous dissolved elements and compounds from large quantities of waste rock and mine tailings can significantly threaten groundwater quality in the affected region. When exposed to oxygen and water, sulfide minerals in mine tailing oxidize, potentially forming acid mine drainage (AMD). Various reclamation techniques can inhibit AMD generation, including monolayer cover combined with an elevated water table (EWT), hydraulic barrier, and cover with capillary barrier effect (CCBE). Selecting the most suitable technique requires consideration of site-specific hydrogeological conditions (e.g., water table depth) and available cover materials. Numerical modeling tools such as PHT3D and MT3D can help identify optimal reclamation methods during preliminary planning stages. The 119-hectare Quémont 2 mine site near Rouyn-Noranda city will undergo reclamation following the closure of its tailings storage facilities (TSF). A three-dimensional numerical groundwater and solute-transport model were constructed and calibrated to simulate the site’s hydrogeological behavior post-closure, enabling selection of the most effective AMD control technique. Subsequently, a three-dimensional multicomponent reactive transport model incorporating various cover designs was developed, with simulations considering climate change impacts. The PHT3D model code, which integrates the PHREEQC geochemical model with the MT3D three-dimensional transport simulator, was employed to evaluate cover performance on the Quémont 2 TSF. Four reclamation configurations were tested: Cell #1 (80 cm single-layer clay cover), Cell #2 (60 cm single-layer clay-sand cover), Cell #3 (60 cm single-layer clay-silt cover), and Cell #4 (120 cm multilayer clay-sand-clay sequence). Simulations were conducted under various climate change scenarios (Representative Concentration Pathways—RCPs 2.6, 4.5, and 8.5). This paper describes the numerical model, cover materials, and modeling results both with and without covers. Results indicate that Cells #1 and #4, completely reduced sulfate in groundwater, suggesting these configurations would provide the most effective reclamation solutions for the Quémont 2 mine site.

The presence of free muscovite in tailings can negatively affect the mechanical strength and rheological properties of cemented paste backfill, as has been observed for several cementitious materials. The aim of this study is to evaluate the influence of free muscovite content in tailings on the consistency and rheology of cemented paste backfill. For this purpose, cemented paste backfill mixtures were prepared from two different tailings. The mixtures were prepared at solids contents between 70% and 74% and with the addition of 5% GU (general use Portland cement)/slag binder. In addition, the influence of muscovite was studied by varying the muscovite content of the tailings from about 14% to 25%. Abrams cone slump tests and rheological analyses were carried out for each recipe. The results show a decrease in slump height and an increase in yield stress, Herschel–Bulkley flow index, and infinite shear rate Cross viscosity with increasing muscovite content for a given solids content. Therefore, water should be added to maintain the required flowability of cemented paste backfill, which increases the water/binder ratio and may affect the mechanical strength. A method is presented for determining the amount of binder to be incorporated to maintain the water/binder ratio of the original cemented paste backfill recipe.

The reclamation of waste rock piles (WRPs) is complex, requiring adaptation of existing mine site reclamation techniques. An alternative approach has been developed for waste rock piles reclamation which involves installing finer materials on the top of waste rock piles. These finer layers (flow control layers—FCLs) redirect water flowing inside the pile toward its slope and limits water infiltration into reactive waste rocks. In the context of sustainable development, a mixture material made with sludge and slag can be used as an FCL in the reclamation of a waste rock pile. To assess the effectiveness of this material, a physical model was used and instrumented with sensors for monitoring volumetric water content and suction and equipped with the following components: (1) a rain simulator; and (2) drains that allow the recovery of water that infiltrates through the system. The physical model was tested with various cover layer thicknesses, inclinations, and precipitation rates. Investigation results showed that the water infiltration across the system was very low, leading to the conclusion that the sludge and slug mixture performed well as a flow control layer in the reclamation of waste rock piles.

Studies have indicated the potential of mixtures of silty soil and sludge produced by active treatment of acid mine drainage for use in covers with capillary barrier effects for mine site reclamation. Very high water contents of sludge in the settling pond could negatively affect the required hydrogeotechnical properties of soil sludge mixtures with high sludge contents. The challenge is then to determine the optimum wet sludge content of soil-sludge mixtures with air entry values (AEV) and/or saturated hydraulic conductivity (k_sat) required for use in mine site reclamation covers. This paper presents a method to determine the optimum wet sludge content β_opt for obtaining the maximum dry density of compacted soil-sludge mixtures. Two types of soil (S1 and S2) and two types of sludge (A and W) were tested. It was observed that β_opt can be determined when the initial water content of the soil used in the mixture is lower than the optimum water content determined from the Proctor curve of the soil alone (10 wt% and 6 wt% for soils S1 and S2, respectively) and that β_opt does not change with increasing initial soil water content. Optimum wet sludge contents found were low (≈15 wt% and ≈7 wt% for mixtures containing soils S1 and S2, respectively) for the test conditions, indicting a limited quantity of reusable sludge in the mixtures. For all mixtures, the water content corresponding to β_opt was close to the optimum water content of the soil alone. Results of soil water retention and saturated hydraulic conductivity (k_sat) tests conducted on selected optimized mixtures indicated that the mixtures based on soils S1 and S2 have air entry values higher than 20 kPa and would be suitable for use in the moisture retention layer of covers with capillary barrier effects, while soil S2 and the derived mixtures exhibited k_sat < 10⁻⁷ cm/s and would be potential materials for the low permeability layer in low saturated hydraulic conductivity covers.

Compacted clay covers have been the most commonly used materials for hydraulic barrier layers. During their construction, the control of some parameters such as compactive effort and molding water content is required. These last parameters affect the hydraulic conductivity, which is considered as one of the important key parameters for cover design. To reach the target in terms of hydraulic conductivity, the cover must be compacted to a pre-determined dry unit weight that usually corresponds to a certain percentage of the maximum dry unit weight (γ_dmax). During the prefeasibility stage of a project (before conducting the required tests), γ_dmax and the optimum water content (w_Opt) can be estimated to obtain an early overview of the conditions that can be anticipated. In this regard, a new approach was proposed to estimate these parameters using the liquid limit (w_L) and the plastic limit (w_P). The proposed equations were developed using data from 56 compacted clay liners and validated using 44 others taken from published data. Results presented in this paper indicate how the proposed equations can successfully estimate parameters of the optimum compacted point.

Until 2008, the Aldermac mine was considered one of the most problematic abandoned mines sites in Québec due to the high production of acid mine drainage caused by mine tailings spread over a large area. The site was reclaimed between 2008 and 2009 to reduce the ecological footprint and to minimize any further tailings oxidation (production of acid mine drainage). For this purpose, a monolayer cover with an elevated water table was used as an oxygen barrier on the north zone of the site. To assess the performance of the monolayer with an elevated water table cover, a network of observation wells was set up to monitor the water table level and collect groundwater samples for the analysis of physical and chemical parameters. Results of water table level measurements show that the cover successfully maintains the tailings within the water table at all times, thus preventing further tailings oxidation. Hydrogeochemical results, interpreted with principal component analysis, show that the quality of water is improving, thus indicating that reclamation is helping to reduce groundwater contamination at the site.