The influence of parent rock, mining and processing technologies on the industrial quality of kaolin concentrate –case study from Bombowha kaolin, Ethiopia

Abstract

Bombowha kaolin deposit is a primary deposit formed mainly through weathering of granite and pegmatite. This research was designed to evaluate the influence of parent material, mining practices and processing technology on the quality of processed kaolin. Geochemical, mineralogical, and technological properties of kaolin were analyzed and field observations conducted to evaluate the influence. Samples of the parent rocks, kaolin deposit, Run-Of-Mine, and processed kaolin were analyzed for their geochemistry, mineralogy and physical properties. Results show that the kaolin derived from pegmatite has better quality (high alumina, low silica, better plasticity, low coloring elements and others) than the granite-derived one. The poor quality of the granite-derived kaolin is ascribed to its incomplete kaolinization as evidenced by the presence of minor halloysite. The geochemical analysis of the Run-Of-Mine shows close similarity to that of the parent granite demonstrating severe dilution during mining, hauling and storage of kaolin ore. The high pit-wall angle (80-85°), the rheologically weak overburden, old excavation machinery and unsystematic delineation of mineable portion of the deposit contributed to high level of dilution. The properties of processed kaolin show the wet processing method brought substantial improvement in the quality of the kaolin (Al2O3 increased by nearly 98% and SiO2 decreased by 36% with respect to the Run-Of-Mine). Had the feed kaolin ore not been diluted, the kaolin concentrate would have been better than what is achieved through the adopted processing method. Systematic mine design, selective mining, and graded stockpiling of kaolin ore are advised for better quality kaolin concentrate.