Physicochemical and Mineralogical Characteristics of Sepiolite Deposits of Northeastern Iran

There is no information about the occurrence and characteristics of sepiolite deposits in Iran. Thus, to identify and characterize the physicochemical and mineralogical properties of Eliyato deposits in northeastern Iran, 10 samples from different locations were taken and studied by powder X-ray diffraction, scanning and transmission electron microscopy, X-ray fluorescence, thermal analysis, infrared spectroscopy, specific surface area and cation exchange capacity. The results indicated that these deposits consist of well-crystallized sepiolite (70–80%), with minor amounts of quartz (10–20%) and dolomite (5–10%). The electron micrographs of the samples showed sepiolite as a long interwoven fibrous mat, pore-filling and coating material. This textural evidence suggests direct chemical precipitation of sepiolite from an Mg-rich solution and/ or after the precipitation of dolomite. The chemical composition, determined by X-ray fluorescence, indicated a Mg-rich mineral with the structural formula (Si11.97Al0.03) (Mg7.20Al0.11Fe0.15) O30 (OH)4 (H2O)4.8H2O. This suggests low isomorphic substitutions of Al for Si and Mg in the tetrahedral and octahedral sheets of the mineral, respectively. In addition, thermalanalysis indicated four endothermic reactions at 134, 336, 546 and 818 °C which are associated with the gradual elimination of adsorbed and zeolitic water from the mineral structure. The associated weight losses are 8.69, 3.31, 2.65 and 10.19%, respectively. The high surface area of the material, compared to that of the Vallecas sepiolite deposit in Spain, suggests its suitability for industrial applications.