| Description |
Clay minerals, for example kaolinite, have many important applications while at the same time existing as common gangue minerals in the tailings from mineral processing plants during the recovery of valuable resources. To develop improved technology for the processing of kaolinite particles, the surface charging properties of kaolinite are studied in this dissertation. In addition, the dissertation objectives include the investigation of kaolinite particle interactions and the analysis of the reverse flotation mechanism of kaolinite from bauxite ore. To prepare ordered edge surfaces of kaolinite particles, a novel protocol was developed. A sandwich sample with kaolinite edge surfaces in between two resin substrates was prepared by ultramicrotome. The charge of the edge surfaces was found to be negative above pH 4 using atomic force microscopy. In addition, the ionic strength effect on the charge of selected phyllosilicates was investigated. It is found that the magnitude of the charge of the silica faces is dependent on the degree of isomorphous substitution and is not so dependent on the ionic strength. However, the charges of the alumina face and the edge surfaces of kaolinite particles are related to the ionic strength. The kaolinite particle interactions were investigated by Brownian dynamics simulation using a coarse-grained model. At low pH, aggregated particle structures/clusters are found to be formed by the electrostatic interactions of silica face to alumina face and alumina face to edge surface. In contrast, the particles are well dispersed and no clusters are formed at higher pH. The structure of kaolinite clusters was validated by SEM and Micro Computed Tomography. The nature of the reverse flotation of kaolinite particles from bauxite was analyzed based on the surface properties of kaolinite particles and on particle cluster formation. It is concluded that the cluster size and the exposed silica faces account for effective reverse flotation of kaolinite from bauxite ores at low pH. It is expected that the findings in this dissertation will provide fundamental understanding for the development of new technologies and reagent schedules to more efficiently process clay minerals, including both flotation and flocculation processes. |
