Kaolin Waste Applied as Support for Photocatalytic Materials

Kaolin is a common mineral resource that is used commercially. However, when processed, it generates a large amount of waste, usually rich in kaolinite, mica and quartz, which gives rise to the need to manage and reuse these mineral residues, in agreement with the SDG 12/UN (ensuring sustainable consumption and production) requirements. Therefore, this work aims to explore how to add value to this residue via its use as a photocatalytic support for TiO2, while also meeting the SDG 6 (clean water and sanitization) requirements. After determination of its chemical and mineralogical composition, the residue underwent mineralogical separation, by mechanical stirring and sieving of its aqueous suspension. After separation, TiO2 was deposited on the quartz fraction of the residue by the modified-Pechini method, using different quartz proportions and at different calcination temperatures. For the deposition of TiO2 on the mica fraction, the conventional hydrothermal synthesis was used, with 20% of the mica. Each material was tested in a photohydroxilation of terephthalic acid under UV-C irradiation to evaluate the formation of hydroxyl radicals. The results of the photocatalytic tests demonstrated that quartz and mica are inert to photocatalysis but provide an interesting support for TiO2. The highest photocatalytic efficiency was obtained for the material synthesized at 600 °C with 20% of the quartz.