Comparative Mineralogical and Chemical Characterization of Kombelcha and Bombowha Kaolin Deposits, Ethiopia

The investigation into the mineralogical and chemical properties of Ethiopian kaolin deposits is essential for transitioning the national manufacturing sector from a reliance on imported raw materials to domestic resource utilization. This study provides an exhaustive comparative characterization of the Kombelcha and Bombowha kaolin deposits, representing two distinct geological and environmental origins. Analytical techniques, including X-ray Diffraction (XRD), Differential Thermal Analysis (DTA), Scanning Electron Microscopy (SEM), and wet chemical analysis, were employed to delineate the characteristics of the raw materials and their behavior during high-temperature treatment. Kaolinite is the primary mineral phase in both deposits, yet the Bombowha occurrence is uniquely distinguished by the presence of halloysite and gibbsite, which are absent in Kombelcha. Chemically, the Bombowha kaolin exhibits higher purity, with Al<sub>2</sub>O<sub>3</sub> content exceeding 35% and total iron and alkali impurities below 3%. In contrast, the Kombelcha kaolin averages 32% Al<sub>2</sub>O<sub>3 </sub>with significantly higher Fe<sub>2</sub>O<sub>3</sub> (2.75%) and total alkalis (1.50%). Firing tests reveal that the Kombelcha deposit vitrifies at 1150°C, whereas the Bombowha deposit maintains refractoriness up to 1250°C. The study further evaluates the efficacy of kyanite additions (5–15%) in controlling firing shrinkage. Genetic evidence suggests that Kombelcha is a product of in-situ weathering of granite, while Bombowha originates from a complex interplay of hydrothermal alteration and subsequent weathering of pegmatitic and granitic dikes. These findings provide a scientific framework for the industrial application of these clays in ceramics, refractories, and paper manufacturing.