Facile Conversion of Oil Shale Semicoke and Ferrous Sulfate Byproduct into Yellowish-Red α-Fe2O3 Composite Pigments via Twin Screw Extrusion Strategy

Resource utilization of bulk industrial solid wastes and byproducts has been recognized as a feasible strategy for coping with a sustainable resource supply in the future. Herein, the iron red composite pigments with a yellowish-red color were fabricated by twin screw extrusion mechanochemical technology followed by the calcining process based on oil shale semicoke (OSSC) waste and ferrous sulfate byproduct, which were derived from the retorting of oil shale and the production of titanium white pigment, respectively. The mechanochemical effect during the extrusion process promoted the complex reaction between the active groups of residual organic matter in OSSC and the involved Fe ions and contributed to the shaping formation of the precursor. The thermally diffused Al species derived from OSSC induced the formation of α-Fe₂O₃ nanoparticles on the silicate surface via Al–O–Fe chemical bond and endowed the pigment particles with excellent dispersion and environmental stability. In addition, the doping of the diffused Al species changed the band gap energy of α-Fe₂O₃ crystals, and the composite pigments presented a bright yellowish-red color (L^* = 32.05, a^* = 33.22, b^* = 37.89, C^* = 50.39), while the tinting strength, oil absorption, and hiding power of composite pigments were slightly inferior to those of the commercial iron red pigments due to the lower content of chromogenic iron species and the particle size difference. Based on the synergistic effect of each component in composite pigments, the composite pigments exhibited good application prospects in the high-temperature overglaze ceramic, coloring, and reinforcing of polypropylene and anticorrosion coating.