Degradation of kaolinite clay added with Al2O3-Ta2O5 in H2SO4

Abstract

This study focuses on the degradation of kaolinite clay added with Al2O3 and Ta2O5, also known as tantite, to increase its resistance to an acid solution (H2SO4) at 300 °C. The samples tested for degradation were previously crushed, sieved, mixed, formed under cold isostatic pressing and sintered at 1150 °C. X-ray fluorescence (XRF) and X-ray diffraction (XRD) techniques were used to determine the composition and reveal the phases present in the samples. Degradation by static immersion (98 wt% H2SO4) was evaluated by the ASTM C267 mass loss technique. Predominant oxides of SiO2, Al2O3 and Fe2O3 were found within the kaolinite clay, as well as other oxides in proportions lower than 2.39 wt%. The immersion of natural clay in sulfuric acid (at 300 °C) caused an increase in SO3 content as well as in the mass of all samples. The X-ray diffractograms revealed the presence of quartz, cristobalite, curundum and tantite, as well as a significant reduction in their peak intensities after the interaction with H2SO4. The results showed that adding 20 wt% (sample M3C) and 40 wt% (sample M4C) of Ta2O5 to the kaolinite clay (sample M1C), produces a more stable structure and greater resistance to attack by H2SO4,.