Preparation of Calcined kaolinite/TiO2 composites by titanyl sulfate (TiOSO4) hydrolysis precipitation

Calcined kaolinite (CK)/TiO₂ composites were synthesized through hydrolysis precipitation of titanyl sulfate (TiOSO₄) and calcination. Under optimized hydrolysis conditions (pH 2.5, duration 2.0 h, temperature 90 °C, and mass ratio (TiO₂/CK) = 1.0), a precipitation efficiency of 81.4 % was achieved. The phase composition remained consistent under varying hydrolysis conditions after significant TiO₂ formation. Furthermore, the oil absorption (mass ratio = 2.0) and hiding power (mass ratio = 1.4) of the composites were determined to be 38.8 g/100 g and 88.4 %, respectively. The composites exhibited high good chemical stability as a pigment, maintaining resistance to strong acid erosion, with only 4.0 % dissolution observed after a 15-day immersion in a pH 2.0 solution. H₂TiO₃ underwent the dehydration and desulfurization more rapidly in an oxygen-rich environment, and anatase formation was well-developed at a calcination temperature of 750 °C for 1 h. Further analysis revealed that phase transition process of TiO₂ was influenced by TiO₂ content, disordered structure of CK and calcination conditions. TiO₂ particles formed single- or multi-layered chemical coatings on the active CK surface, although the presence of exposed mullite impeded coating formation. This study successfully developed cost-effective CK/TiO₂ composites with favorable pigment properties, providing a certain reference for CK selection. The composites have potential applications in coatings, pigments and related fields.