Synthesis of low-cost kaolinite-based cobalt blue composite pigments by eco-friendly mechanochemical method

Cobalt blue (CoAl₂O₄) pigment is widely used in various fields such as coatings, glass, ceramics, and plastics due to its brilliant blue color and excellent stability. However, the high energy consumption and the pollution of conventional preparation methods of cobalt blue pigments, as well as the gradual depletion of cobalt resources, lead to high production costs and hinder its further adoption. In this study, we prepared novel kaolinite-based CoAl₂O₄ composite pigments through a mechanochemical method followed by a calcination process, significantly reducing cobalt consumption. The experimental results showed that, with the addition of sodium carbonate at 450 %, addition of kaolinite at 40 wt%, molar ratio of added Co to Al at 0.14, and calcination temperature at 1100 °C, the prepared composite pigment exhibited optimal blue color (L^⁎ = 56.62, a^⁎ = 4.50, b^⁎ = −49.92, and C^⁎ = 50.12) coupled with good chemical stability (∆E^⁎ ≤ 1.15). Further characterization analysis revealed that the enhanced color performance was mainly attributed to the uniformly dispersed CoAl₂O₄ particles with high crystallinity on the surface of kaolinite, which led to a strong reflectance of blue visible light. Therefore, this study is expected to serve as a reference for the cost-effective and eco-friendly preparation of cobalt blue composite pigments.