Synthesis of iron red hybrid pigments from oil shale semi-coke waste

Abstract

Oil shale semi-coke (SC) is a bulk solid waste produced after shale oil being extracted from oil shale. It is abundant on the earth, but most of them are discarded or piled up as solid waste, and their reuse as resources is very limited. In this paper, adhering to the concept of “waste to materials“, the α-Fe2O3/SC hybrid pigments with the red color (a* = 29.68) better than commercial iron red pigments (a* = 26.92) were synthesized by an one-pot hydrothermal reaction of pretreated SC with Fe(III), using SC as a cheap starting material. The microscopic structure, chemical composition and color of the hybrid pigments were studied, and the reaction parameters for synthesizing the best hybrid pigments from SC were optimized. The results indicate that the hybrid pigments are mainly composed of SiO2 and Fe2O3, where α-Fe2O3 particles grow on the surface of SC-derived silicate substrate with a better dispersion. The hybrid pigments showed a good stability, especially an outstanding high temperature-resistant stability. The secondary heat treatment induced the further improvement of red color value of the hybrid pigments. This work provides a new way and solution for the rational disposal and functional application of SC waste.