Effects of thermal and chemical treatments on physical properties of kaolinite

Kaolinite clay from a natural deposit was processed to remove impurities and submitted to thermal and chemical treatments. Based on thermogravimetry/differential thermal analysis data, the samples were submitted to a thermal treatment at 500 °C, for 8 h, to remove organic components and turn the clay color lighter. The chemical treatment was conducted first using hydrogen peroxide and then, an acid attack using nitric acid and sulfuric acid. Chemical compositions of the nanoclay after the chemical treatment indicated that the hydrogen peroxide treatment removed part of the organic matter without any other significant effect on the chemical composition of the clay, while the acid attack reduced significantly the contents of MgO, CaO and Fe2O3 turning the clay color lighter. A small increment in cation exchange capacity was also observed after hydrogen peroxide treatment and acid attack. BET surface area measurements indicated an increment in surface area after the thermal and chemical treatments. The thermal treatment produced only a slight increase in surface area, from about 35.3 to 37.8 m2/g, while the chemical treatment using hydrogen peroxide promoted an increase in specific surface area from 35.3 to 53.0 m2/g. The acid attack did not produce any further increment in surface area. X-ray diffraction patterns of the clay corresponding to various treatments proved that the chemical treatment did not affect the clay structure, while the thermal treatment favored the formation of an amorphous material. Thus, the chemical treatment of kaolinite proposed in this work may be a promising approach to process this clay for the production of advanced materials.