Upgrading and characterization of smectite from selected volcanic sediments of Eastern Uganda

Abstract

Natural clays occur as mixtures of many clay minerals and remains of the rocks that underwent diagenesis to yield the clays. As weathering of clay soils never ceases it may not be possible to mine single clay minerals. The purity of the mineral may increase through hydrocycloning and sedimentation as different clay minerals have different densities, wetting behavior and solubility in water. In this study, information has been accumulated on clays mined from Budadiri, Chelel, Mutufu and Sirron in eastern Uganda which were sedimented to upgrade the content of smectites. The raw clays and fraction the settled from sedimentation mixture after six days were subjected to chemical analysis, differential thermal analysis, Infra-red radiation and X-ray diffraction studies. The data acquired from the various experiments revealed presence of Fe-montmorillonite, illite, kaolinite, K-feldspars, plagioclase and quartz in raw clays. Although smectites and kaolinites may appear similar in color, the alkalinity of aqueous slurries of clay sediments from Budadiri, Chelel and Mutufu showed they were smectites containing nontronite. The clays and clay fractions were made of 40-50% smectite, 20-30% K-feldspars and plagioclase showing they formed from alkaline intrusive granitoids in basic medium. The presence of iron, aluminium, and silicon in approximate percentages of 11, 18 and 60% respectively indicated that sedimentation yielded nontronite and montmorillonite fractions. The IR spectrum absorption peaks at 3600, 3454, 526 and 466cm-1 among others were due to Al-Al-OH, Mg-OH-Al, Si-O-Al and Si-O-Si bond deformations respectively indicated presence of smectites in the clay fractions obtained. DTA showed peaks at temperatures of 100, 250 and 650oC due to presence of smectites.