X-ray diffraction measurement of stress and strain induced in magnetite and chromite by ultrafine grinding

This paper presents the results of grinding tests performed on magnetite from Kiruna (Sweden) and on chromite from Skoumtza (Macedonia, Greece). Stresses were measured by XRD, which determined the variations in the characteristic structural spacings of the minerals both before and after grinding in a HSM/250 Herzog laboratory ring mill. Analysis of the magnetite and chromite crystallinity was performed by measuring the broadening of the strongest diffraction peak (311). Also, structural analysis on chromite was carried out using the Mikheev model. Ultrafine-grinding tests on the magnetite and chromite demonstrated that this type of treatment can induce profound variations in the surface-stress state. These included plastic variations of the cell followed by “chemical” stress with oxidation from the structure to form hydroxide or carbonate films. This can have a great influence on the minerals reactivity to flotation reagents.