EFFECT OF TEMPERATURE ON THE STRUCTURE, MORPHOLOGY, TEXTURE AND ADSORBENT PROPERTIES OF A BIOGENIC SILICA

Among natural ceramic materials, diatomaceous earth is of special interest due to its low toxicity, high porosity and permeability, with good mechanical and chemical stability, which have allowed it to be used as an adsorbent and filter bed, among other applications. In this research, the effect of the calcination temperature between 200 and 1000 °C, for 6 h in an air atmosphere, on the crystalline phases, morphology, texture and adsorbent properties, in the removal of methylene blue dye (MA), from a representative sample of biogenic silica from the municipality of Chivatá (Boyacá) in Colombia, was evaluated. The results of the adsorption-desorption isotherms of N2 at 77 K correspond to type IV, typical of mesoporous materials, with surface area development from 45.2 m2g-1 to 53.8 m2 g-1 at 500 °C. X-ray diffraction analysis indicates that it is an amorphous silica with the presence of crystalline phases such as quartz, kaolinite and muscovite. The reflections of the quartz are maintained during calcination, while the reflections of the clays disappear. Micrographs show the predominance of porous cylindrical frustules that are preserved even after calcination. The maximum adsorption capacity of the AM dye was 58.5; 51.5 and 6.81 mg g-1 for crude diatomaceous earth, and calcined at 500 and 1000 °C, respectively; with a satisfactory fit of the experimental data to the Langmuir isotherm model. The Bed Height Service Time (BDST) model applied to the column study fits satisfactorily to all bed heights in the column. In conclusion, the persistence of mesoporosity and the conservation of the fustules show the high thermal stability of the diatomaceous earth, but calcination decreases its adsorbent capacity in the removal of the methylene blue dye in aqueous solution.