Mineralogical and particulate morphological characterization of geophagic clayey soils from Botswana

G-I Ekosse,S Anyangwe

doi:10.4314/bcse.v26i3.6

Abstract

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

Highlights

Geophagia or geophagy, classified as a form of pica [1] is the habitual wilful consumption of earth or soil-like substances such as chalk, by humans and animals [2,3,4]
Quartz was the most dominant mineral ranging from 70 wt% for sample S-69 to 80 wt% for samples S-66 and S-68 identified in the geophagic clayey soil samples (Figure 1)
Being the most dominant in terms of wt %, quartz in the Botswana samples could destroy dental enamel. Another health risk resulting from the angular coarse quartz particles is the possible abrasive tendencies they may cause in the human gastro-intestinal tract

Summary

Introduction

Geophagia or geophagy, classified as a form of pica [1] is the habitual wilful consumption of earth (soils and clays) or soil-like substances such as chalk, by humans (human) and animals (enzootic) [2,3,4]. Geophagic clayey soils are generally composed of kaolin of which kaolinite is the dominant type of mineral [20]. Other clay minerals found in geophagic clayey soils include palygorskite, and montmorillonite (usually from bentonite). Optical microscopy technique was used for descriptive analysis of the non-clay size particles in the clayey soil samples.

Results

Conclusion