Abstract
Clay samples from Tharaka-Nithi County in Kenya were characterized by hydrometer, X-ray fluorescence spectroscopy (XRF), atomic absorption spectroscopy (AAS), TGA, scanning electron microscopy (SEM) and powder diffraction (XRD) methods. The F-test and t-test were used to interpret the results. The major oxides present were Al2O3, SiO2 and the minor ones were CaO, TiO2, MnO, Fe2O3, K2O, MgO and Na2O. The values of SiO2 were greater than those of Al2O3, indicating that the samples were of clay minerals. The clay minerals with low cation exchange capacity (CEC) were present in the samples. The Atterberg limits showed that the inorganic clays of either low or intermediate plasticity having low contents of organic matter were present in the samples. The analysis further showed the availability of essential elements necessary for plant growth. The TGA analysis indicated that the decomposition of clay samples occurred in four steps. The scanning electron microscope photographs revealed that the samples contained a mixture of minerals of morphologies with crystallinity, high porosity and unstable under the electron beam. The major impurity in the clay is quartz, ranging from 22.6-31.9%. Albite is the most dominant component in the clay minerals contributing to 30.3 to 44.1%. The clay from the study area can be used as agro mineral additive to enhance soil fertility for crop production, a fluxing agent in ceramics and glass applications and also as functional fillers in the paint, plastic, rubber and adhesive industries after beneficiation. Key words: Scanning electron microscopy, X-ray diffraction, clay minerals, Atterberg limits, atomic absorption spectroscopy (AAS), Fourier transform infrared spectroscopy (FTIR), TGA, quartz.
Highlights
Clay is a term used to describe either the size of the individual particles present in a deposit or specific minerals of a small size of less than 0.002 mm in dimension (Fabio et al, 2009; Nwosu et al, 2013; Obase et al, 2013; Abuh et al, 2014)
Different clay minerals will exhibit different physical, chemical and mechanical behaviors depending on the structure developed in the course of mineral formation
The chemical and physical properties of clay minerals are of great importance to industry, agriculture and the environment owing to their abundance, high specific surface area, high layer charge, laminar morphology and chemical reactivity with both neutral and charge species (Murray, 1999; Hoidy et al, 2009)
Summary
Clay is a term used to describe either the size of the individual particles present in a deposit (clay size fraction) or specific minerals (clay minerals) of a small size of less than 0.002 mm in dimension (Fabio et al, 2009; Nwosu et al, 2013; Obase et al, 2013; Abuh et al, 2014).Understanding of the distinction between clay size and clay minerals in the assessment of clay minerals is important because two samples of clay having identical particle size can have very different behaviors based on the clay minerals present (Gray et al, 2013). The chemical and physical properties of clay minerals are of great importance to industry, agriculture and the environment owing to their abundance, high specific surface area, high layer charge, laminar morphology and chemical reactivity with both neutral and charge species (Murray, 1999; Hoidy et al., 2009). The presence of iron in the crystal structures of the clay minerals infuses an exceptionally important additional facet into their importance because its oxidation state can be rather modified in situ and such changes evoke profound differences in the surface chemical and structural behaviour of the clay mineral. Example of clay mineral properties that are greatly affected by changes in iron oxidation state are swelling in water, cation exchange capacity (CEC), cation fixation capacity, surface area, clay-organic interactions, surface pH, reduction potential, ability to transform chlorinated organic compounds and ability to degrade pesticides and thereby alter their toxicity. Clay was implicated in the prebiotic synthesis of biomolecules at the very origin of life on earth and has become indispensable to modern living (Bergaya et al, 2012)
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