Sustainable utilization of natural sands for cleaner preparation of high-performance nanostructured cobalt blue composite pigments by dolomite-induced mechanochemistry

Abstract

The strategic concept of green and sustainable development has given birth to a series of technologies for cleaner conversion and value-added utilization of natural mineral resources. In this study, a cleaner route of dolomite (CaMg(CO₃)₂)-induced mechanochemical preparation of cobalt blue composite pigments with lower cobalt consumption and high blue intensity derived from the abundant natural sands (sea sand and desert sand) was developed. The characterization results revealed that mechanical forces realized the ingenious activation of natural sands and dolomite. The activated natural sands provided the silicon source for the formation of anorthite (CaAl₂Si₂O₈) to improve the lightness of the composite pigments. The Ca and Mg species derived from dolomite transformed into CaAl₂O₄ and MgAl₂O₄ accompanied by the formation of CoAl₂O₄, which was favorable for the distortion of the crystal structure of CoAl₂O₄ and the improvement of reflectance to blue light. The lamellar dolomite served as a benign substrate to induce the formation of CoAl₂O₄ nanoparticles on its surface and improve the dispersion. The as-prepared composite pigments exhibited more excellent color performances than those of the commercial and house-made pure cobalt blue pigments due to the above-mentioned synergistic effect, and the b* value of cobalt blue composite pigments prepared with sea sand reached −50.30. In addition, composite pigments exhibited excellent environmental stability and high temperature resistance to be applied as promising outdoor coatings. Therefore, this study is expected to provide a cleaner strategy for the construction of high-performance cobalt blue pigments with low cobalt content and high blue intensity, as well as direct value-added and sustainable utilization of huge amounts of natural sands.