Assessing the Quality, Mining and Processing Techniques of Bombawuha Kaolin Deposit, Southern Ethiopia
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Date
2018-06-02
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Addis Ababa University
Abstract
Bombawuha kaolin deposit is a residual type deposit formed by weathering and hydrothermal alteration of granite and pegmatite units. The present study was designed to assess the quality, mining and processing techniques of Bombawuha kaolin deposit by physical observations of the site and different analytical methods. For this purpose, samples of the source rock, kaolin deposit, run of mine, and processed kaolin were collected for analyses. Chemical, and mineralogical (thin section) analyses were applied to examine the source rock of the deposit. For kaolin deposit, and processed kaolin chemical, mineralogical (XRD), and physical properties were investigated. A chemical analysis was also carried out to investigate the composition of run of mine. The result of the study revealed that the source rock of the deposit is composed of higher SiO2 (72.1%), coloring impurities (1.88% Fe2O3, and 0.13% TiO2), fluxes (5.765 alkalies, and 0.38% alkali earth oxides), and lower Al2O3 (16.3%) and loss on ignition (3.85%) values compared to its altered product. It is composed of quartz, k-feldspar, plagioclase, biotite, muscovite, and opaque minerals. The kaolin deposit has light gray to white color, higher grits (79.9-96.7%>63μm), pH (6.27-6.37), lower plasticity (<10%), linear shrinkage (0-3), and specific gravity (2.53-2.60) values. The deposit is constituted by higher SiO2 (51.5-70.5%), and lower Al2O3 (18.1-33.4%) comparing to ideal pure kaolin 46.6 and 39.5% respectively. It also has higher Fe2O3 (1.09-1.92%), and lower TiO2 (0.03-0.17%). The XRD result revealed that kaolinite and quartz are the major minerals of the deposit with minor k-feldspars and illite. Specifically, kaolinized granite and kaolinized pegmatite have different physical and chemical characteristics. The kaolinized granite has higher grits, lower plasticity, and linear shrinkage values. It also has higher SiO2 (68%), Fe2O3 (1.65%) and TiO2 (0.13%), and lower Al2O3 (20.19%) and LOI (7.84%) values compared to the kaolinized pegmatite. Mineralogically, it is composed of kaolinite, halloysite, quartz, and k-feldspar. Kaolinized pegmatite contains quartz, mica (illite), and kaolinite minerals. Although these two units have different characteristics, they are mined together by simple open pit mining method. A run of mine having higher SiO2 (71.2%), Fe2O3 (1.88%), and lower Al2O3 (17.95%) is produced for processing. The wet processing method enhanced the quality of kaolin product by producing higher Al2O3 (35.5%), lower SiO2 (45.8%), and Fe2O3 (0.99%). It reduced SiO2 and Fe2O3, and increased Al2O3 by 36%, 47% and 98% respectively from its crude state. The processed kaolin contains major kaolinite, and minor orthoclase and muscovite minerals. Based on findings of this study, it is concluded that Bombawuha kaolin product can be used in ceramics (bricks, pottery, floor and wall tiles), plastics, paint and rubber filer productions after processing.
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Bombawuha, Impurity, Kaolin, Mining, Processing, Quality