Influence of grading in compacted tailings behaviour: towards resilient design

The inherent variability of tailings is the main challenge in compacted filtered tailings stacks (CFTS) operation. Despite the advances in dewatering technologies, the filtration efficiency depends on the tailings’ gradation and mineralogy. A usual process is to filter materials separately, which can later be mixed and compacted. In this paper, two iron ore tailings (flotation and slime) from a unique mine and three mixtures (80/20, 70/30 and 60/40) produced from them are studied, to investigate the influence of grading on tailings’ compressibility, strength, stiffness and state measures. The materials were thoroughly characterised and submitted to triaxial tests under low (50 kPa) and high (1000 kPa) confinement levels and different moulding conditions (loose and dense). The results showed that the behaviour of the range of gradings investigated was similar in terms of compressibility, strength mobilisation (peak and M value), dilatancy and stiffness for similar compaction efforts. The packings produced seem to be affected mainly by the mineral composition and grading, while the mechanical procedures only change the magnitude of the state achieved, maintaining the proportion between them. Understanding how grading and mineralogy affect different geomechanical aspects of tailings is the first step towards resilient projects, which are essential to the future of the mining industry.