Geology, Characteristics and Possible Industrial Applications of Some Sudanese Kaolins

Abstract

Due to it’s special physical and chemical properties, kaolin has been considered to be one of the most important industrial mineral utilized in many industries such as in ceramics, refractories, paper, paint, rubber, plastics and cement. In Sudan, Sabaloka (North of Khartoum) and Derudeb (Eastern Sudan) primary kaolin occurrences have been investigated. Investigations covered also secondary kaolins which predominantly occur in the Upper Cretaceous sedimentary strata including: Marawi (Northern Sudan), Geraif, Um Ali, Hafyan, Nagaa (Central Sudan), and Merkhieyat (West of Omdurman). One of the most important objectives of this study is to characterize the Sudanese kaolins in terms of mineralogy, geochemistry, geotechnical properties, genesis and their suitability to various industrial uses. In this respect, many analytical techniques were used, these include: X-Ray Diffraction (XRD), X-Ray Fluorescent Spectroscopy (XRF), Scan Electron Microscopy (SEM), grain and particle analysis, Atterberg limits determinations, Hinckley Index crystallinity measurements, drying and firing shrinkage, whiteness, color determination and dilatometric analysis. Based on mineralogical and geochemical characteristics revealed by this study, the sedimentary kaolins had been genetically originated from intermediate to felsic parent rocks under hot humid environment. The Sabaloka kaolin is genetically formed due to in-situ chemical weathering affecting the basement rocks as well as the older granites. The presence of halloysite mineral in the kaolinitic materials of Derudeb suggests hydrothermal alteration together with chemical weathering of metarhyolites. XRD coupled with XRF investigations revealed that the kaolinite contents of Derudeb and Sabaloka are very low (5% and 14% respectively) and the white color is due to none-clay minerals such as quartz and un-altered feldspars. The presence of some evaporite minerals such as halite, calcite and gypsum in some samples of Um Ali kaolinitic deposits suggests lacustrine environment of slightly salt water. Carbonates reported in Sabaloka and Derudeb are presumed to be formed due to hydrothermal alteration (carbonitization). The maximum kaolinite content is reported in Marawi (77.84%), while Nagaa, Merkhieyat, Geraif and Hafyan gave average contents as (57.57%, 49.84%, 49.53%, and 47.75%) respectively. ii