Determination of radiometric characterization and elemental distributions of sepiolite samples used as industrial materials in Turkey

Sepiolite is a naturally occurring clay mineral of sedimentary origin and belongs to the phyllosilicate group and is a magnesium hydrosilicate (Si12O30Mg8(OH)4(H2O)4•8H2O). Due to its absorption (or adsorption), rheological and catalytic properties depending on physicochemical properties such as porosity, surface area, fibrous structure, crystal morphology and composition, sepioilite have been widely used as additive raw material in pharmaceutical, cleaning-detergent, paper, paint, cosmetic agriculture, fertilizer, livestock, ceramics and cement industry. In this study, 30 different sepiolite example collected from open sepiolite quarries of Polatlı (Ankara), Beylikova (Eskişehir) ve Sirvihisar (Eskişehir) in Turkey were was subjected to analysis of porosity volume, radiometric, elemental and particle size. The total porosity volume and surface areas of the Polatlı, Beylikova and Sivrihisar sepiolite samples were found 0,142 cm3/g and 0,479 cm3/g, 0,168 cm3/g and 41 m2/g, 224 m2/g and 50 m2/g, respectively. The average activity concentrations of the 238U, 232Th and 40K radionuclides naturally contained in sepiolite samples were measured as 29.2 ± 3.7 Bq/kg (range: 8.5-120.6 Bq/kg), 4.8 ± 1.0 Bq/kg (range: 0.4-29.2 Bq/kg) and 56.5 ± 8.3 Bq/kg (range: 7.2-140.1 Bq/kg) respectively, by gamma-ray spectrometry with a high purity germanium detector. The average gamma dose rates from the earth crust and cosmic radiation in Polatlı, Beylikova and Sivrihisar sepiolite quarries were found as 20 nGy/h, 16 nGy/h and 22 nGy/h and 45 nGy/h, 43 nGy/h and 42 nGy/h, respectively. In addition to radiological parameters (outdoor absorbed gamma dose rate, annual effective dose rate, radium equivalent activity index, activity concentration index, alpha internal and lifetime cancer risk) were estimated to evaluate the use of sepiolite samples as additive raw materials from a radiological point of view. The elemental distribution of each sepiolite quarry was determined using X-ray fluorescence (XRF) and X-ray diffractometer (XRD) spectrometry. Approximately 94% of the analyzed sepiolite samples are SiO2 (60%), MgO (30%) and CaO (4%). Particle size and morphology of sepiolite samples were analyzed by scanning electron microscope (SEM), and particle sizes of the quarries were compared with each other.