Sedimentary and residual clays from Santiago, Boavista e Fogo (Cape Verde): assessment of their properties as geophagic materials

• DOI: 10.1007/s12517-019-4668-6
• Publication Date: 2019-08-08T17:02:39Z
• Authors: Ângela Cerqueira; Cristiana Costa; Fernando Rocha; Cristina Sequeira; Denise Terroso
• Keywords: 01 natural sciences; 0105 earth and related environmental sciences

Geophagy is common in Cape Verde, mainly to prevent or reduce digestive problems. The aim of this study is to understand if clays from three different islands of Cape Verde archipelago (Santiago, Boavista e Fogo) have suitable properties for geophagy. For that, seven samples (one from Santiago, four from Boavista and two from Fogo) were tested in terms of mineralogy, chemistry and physical properties. Performed tests were as follows: X-ray diffraction and fluorescence, scanning electron microscopy with energy dispersive spectroscopy, cation exchange capacity, cooling kinetics, Atterberg limits, viscosity, expandability, pH, abrasivity, specific surface area, thermogravimetric analysis, specific heat and oil absorption. Santiago sample is pure smectite, while Fogo and Boavista samples show high proportions of phyllosilicates (mainly illite-smectite with some kaolinite) and iron oxides. This mineralogical composition explains why Santiago shows higher values for major properties, such as expandability, plasticity and cation exchange capacity. Boavista and Fogo samples show similar chemical composition, whereas Santiago revealed higher percentages of Fe, Ti and Mg. All studied samples have the potential to be applied in geophagy, Santiago sample being the most appropriate one.