Mineralogical and particulate morphological characterization of geophagic clayey soils from Botswana

This study focused on determining the minerals composition and particle morphology of geophagic clayey soils from Botswana in order to infer on how they could influence human health. Six representative geophagic clayey soils from Botswana were mineralogically characterized using X-ray powder diffractometry (XRPD), optical microscopy, and environmental scanning electron microscopy (ESEM). Results of identified mineral phases revealed quartz (SiO2) as the most dominant in all samples constituting close to 70 wt %; followed by goethite (FeO.OH) having a mean concentration of 9 wt%, and kaolinite (Al2Si2O5(OH)4) with a mean concentration of 8 wt%. Other minerals present were smectite ((Na,Ca)(Al,Mg)6(Si4O10)3(OH)6-n(H2O)), mica (AB2-3(Al,Si)Si3O10)(F,OH)2), feldspar (Na/K(AlSi3O8)) and hematite (Fe2O3). The quartz particles were generally coarse; and angular to very angular in morphology. Due to ions present in goethite, kaolinite, and smectite, these minerals impact positively on properties of geophagic clayey soils and could possibly influence human health when consumed. The quartz particles could negatively affect dental enamel as a result of mastication; and cause abrasion of the walls of the gastro-intestinal tract which may lead to rupturing. Although the studied clayey soils could have potential to provide medicinal benefits to the consumer, there is need for beneficiation exercise to be conducted to reduce the coarse angular particles contained in them. It is therefore necessary for constructive efforts to be directed at beneficiating geophagic materials which will render them safe for human consumption. KEY WORDS: Beneficiation, Geophagia, Kaolinite, Quartz, X-Ray powder diffractometry Bull. Chem. Soc. Ethiop. 2012, 26(3), 373-382. DOI: http://dx.doi.org/10.4314/bcse.v26i3.6