Rheological Properties and Permeability Properties of Cemented and Uncemented High-Density Paste Tailings: Effect of Sulphide Minerals

Abstract

The sustainable management of sulphide-bearing mine tailings remains one of the most pressing environmental and geotechnical challenges in modern mining. This challenge arises from the reactive nature of iron sulphide minerals, particularly pyrite (FeS₂), which oxidizes to produce acid, leading to structural instability and environmental degradation. To curb these impacts, several tailings management strategies have been developed. Among the emerging approaches, paste tailings (PT) technology has emerged as a sustainable solution as it repurposes tailings into a dense, often cemented material that provides structural support for underground excavations, enhances storage stability, and mitigates acid mine drainage risks. Beyond its technical benefits, this approach contributes to environmental protection and supports the mining industry’s transition toward more sustainable waste management practices.

PTs can be used underground as cemented paste backfill (CPB) or on the surface as uncemented (UPT) or lightly cemented paste tailings (LCPT). CPB and LCPT are composed of tailings, binder, and water, while UPT contains no binder. Preparation occurs at surface backfill plants, and the mixtures are transported to deposition sites by pumping or gravity flow. Consequently, flowability (or rheological properties) is a key design parameter. Once placed, PTs must exhibit low permeability to limit the movement of water and air, which can trigger acid generation and contaminant leaching. Therefore, understanding and optimizing both rheology and permeability properties are critical to the safe and sustainable design of PT systems.

However, there is limited knowledge about these properties, particularly when reactive pyrite-bearing tailings are incorporated. Pyrite addition may significantly alter the rheological and permeability behaviour of PTs. To address this knowledge gap, this study conducted a comprehensive laboratory investigation of PTs containing pyrite under various mix conditions (tailings type, binder composition, curing time, and pyrite content) that simulate field environments. Tests included rheological (vane shear, viscosity), hydraulic (permeability), and physicochemical (pH, electrical conductivity, porosity, and void ratio) measurements. Complementary microstructural analyses, including thermogravimetric (TG/DTG), X-ray diffraction (XRD), and scanning electron microscopy (SEM), were performed to interpret the mechanisms governing the behaviour.

Results showed that increasing pyrite content elevated yield stress and viscosity, reducing flowability. Slag Portland cement blends exhibited better flow characteristics than pure Portland cement systems. Permeability increased with higher pyrite and sulphate levels due to ettringite and gypsum formation, which caused microcracking and pore enlargement. Air exposure intensified oxidation and matrix weakening. Overall, binder type, sulphate concentration, and oxidation control were identified as critical factors for ensuring the long-term stability and durability of sulphide-bearing paste tailings.