Characterization of Egyptian kaolins for health-care uses

This work aimed to evaluate by first time the suitability of the Egyptian Abu Zenima (Sinai Peninsula) kaolins to be used in pharmaceutical and cosmetic applications. Sixty five kaolin samples were collected from six stratigraphic sections: Wadi Khaboba, Gabal Hazbar and Wadi Abu Natash sections, belonging to the Abu Thora Formation (Carboniferous age), and Gabal El Dehessa, Gabal Farsh El Ghozlan and Wadi Budra sections, belonging to the Malha Formation (Lower Cretaceous), and characterized by mean of X-ray diffraction and fluorescence, electron microscopy, spectrophotometry and rheometry. Most of the samples were dominated by kaolinite, and half of the samples contained > 75% of this mineral, reaching up to 96%. Quartz was the main impurity, with very variables quantities; it was always present except in some parts of the Wadi Abu Natash and Wadi Budra sections. Mica, anatase and hematite were frequently present, but they normally did not exceed 10%. Other detected impurities were carbonates (calcite, dolomite, ankerite), sulfates (gypsum, alunite), smectite, feldspars, magnetite, pyrite, halite and heulandite, but in lesser amounts and only in some samples. Carboniferous kaolinites exhibited a high crystallinity (Hinckley Index > 1), while most of Cretaceous kaolinites were medium to poorly crystallized (Hinckley Index normally < 1). CIELAB colorimetric parameters put into evidence the general grayish color of the samples, some of which showing light tints of redness and yellowness in correlation with their iron content. The rheological characterization of the 31 purest kaolin samples revealed that their dispersion exhibited similar and good pseudoplastic flow behavior at 50% W/W solid concentrations. The apparent viscosity and yield stress values of Carboniferous samples showed a widest range of variations when compared to Cretaceous ones. The observed variations were interpreted to be correlated with both, the kaolinite content as well as microtexture and the dimensions of kaolinite particles. With these premises, some of the studied kaolins are considered to have a very high economic potential, once the detected impurities are removed easily by the appropriate process, and then suitable for pharmaceutical and cosmetic purposes. Even if there were zones rich in kaolinite in all the studied sections, the highest quality for the target purposes is found at the lower part of the Wadi Abu Natash section, where quartz was absent and include the samples with the highest viscosities.