Dry stacking of iron ore tailings: Possible particle breakage during compaction

The disposal of iron ore tailings in dry stacks has become increasingly common in Brazil. In these structures, the iron ore tailings are compacted in layers using drum rollers that cause compaction and vibration efforts on the ground. Particle breakage is usually observed in granular materials when subjected to static loads of great magnitude, as can occur depending on the stacking height achieved. However, particle breakage also may occur during the layers’ compaction. This study investigates the breakage behaviour of iron ore tailings simulating load conditions that may occur during dry stacks construction. Two usual iron ore tailings with different amounts of clay size particles, but similar mineralogy (about 77% quartz and 19% iron oxide – the usual composition of iron ore tailings in Brazil) were subject to cyclic oedometer tests. Particle size distribution analyses were performed before and after testing all specimens. Both iron ore tailings, representing typical physical and mineralogical characteristics of the Quadrilátero Ferrífero (southeast Brazil), only suffered particle breakage (Relative Breakage between 0.12 and 0.14 for tailings A and between 0.14 and 0.16 for tailings B) under extremely high pressures (σ’v = 85 MPa) applied by oedometer testing, above those usually found in the field. For usual pressures applied in the field, the frequency of load and number of cycles were of no significance in particle breakage.