The applicability of X-ray microtomography for mineral liberation determination

In mineral processing, a detailed characterization of multiphase particulate systems is fundamental to guarantee an efficient separation of the valuable minerals. A precise analysis allows the process engineer, for instance, to evaluate the optimum concentration route and to achieve the best metallurgical recovery possible. One of the most important aspects of the ore is mineral liberation, as it defines the maximum possible grade for subsequent mineral concentration processes. Scanning electron microscope-based (SEM-based) automated image analysis systems have been used to obtain information concerning mineral liberation. One of the limitations of SEM-based techniques for mineral liberation assessment is the unavoidable loss of 3D information, leading to significant stereological errors. In this regard, X-ray microtomography emerges as a solution that allows three-dimensional imaging and direct measurement of spatial characteristics of mineral ores, eliminating stereological issues. In this thesis, high-resolution X-ray microtomography was used to evaluate the characteristics of liberation of a metallurgical bauxite ore and of an iron ore tailing. Mineralogical characterization showed that the bauxite ore was composed by 54.5% of gibbsite as the aluminum-bearing mineral, 39.8% of kaolinite as silicate gangue, and 5.7% of hematite, whereas the iron ore tailing was constituted by 88.8% of quartz, 10.4% of hematite, and 0.8% of goethite. The liberation analyses were carried out with respect to compositional liberation (grade) and textural liberation (surface exposure), in both 2D and 3D perspectives to assess the degree of stereological bias. For the bauxite ore, grade distributions in 2D and 3D were correspondent when all possible cross-sections were considered in 2D. However, 2D surface exposure did not converge accurately to the 3D fashion due to the loss of 3D information. In the case of the iron ore tailing, the stereological effect was more pronounced in surface exposure quantification. There was a linear relationship between grade and surface exposure and also between particle size and surface exposure. A comparison of the results of SEM-based and X-ray microtomography for the iron ore tailing evidenced the fact that only a 3D technique would be able to represent the real characteristics of particulate systems. (author)