Microscale fracture studies in geological materials with implications for mineral liberation

The comminution of mineral ores to separate valuable minerals from waste rock is both energy intensive and relatively inefficient. A lack of fundamental understanding of the relationships between material fracture properties and rock fragmentation is an obstacle to developing process improvements.; The indentation fracture technique was used to estimate properties of materials studied in this dissertation. A new formulation for a simplified indent crack geometry was derived and used as a prototype for some quasi-3D finite element analyses of irregular indentation crack geometries. It was found that the stress intensity factor at the intersection of an indent crack with the material surface is essentially dependent only on the indenter load and the radial distance of the crack tip from the indent center; this conclusion was supported by experimental data.; A simple model for differential breakage in binary material ores was developed and the comminution behavior of five binary ore materials was investigated. Image analysis measurements showed that differential breakage takes place in some ores; however, model predictions did not agree with these data, which was attributed to microstructural reasons in two of the materials. At the current level understanding, it appears unlikely that differential breakage of ore systems could be predicted by a simple model that does not account for more complex phenomena.; Phase boundary fracture occurred to different degrees in the ores during comminution and a qualitative correlation was found between the fraction of indents causing phase boundary fracture and the amount of phase boundary fracture occurring during comminution. A number of materials showed evidence of weaker grain boundary regions and developed higher indentation crack densities than within the grain interiors which has implications for their liberation characteristics.; The effects of mechanically induced surface damage on breakage was investigated and found to be material specific. Materials with prior low levels of damage experienced significant drops in fracture energy and particle strength; those with a high levels of preexisting damage showed little change. Increasing levels of surface damage also causes a coarsening in the progeny size distribution. In some materials particle strength increased for low levels of damage intensity.