Safe and sustainable use of residue from a vanadium recovery process as alternative to limestone in Portland cement: clinker production and cement performance

There are increasing concerns on both sustainability of natural resources and the management of industrial residues. This study investigates the potential for recycling calcite rich residue from a vanadium recovery process, as a raw material in Portland cement. This type of residue has limited information as feedstock material in cement production. The produced clinkers were characterized by several techniques including X-Ray diffraction with Rietveld refinement, X-Ray fluorescence, isothermal calorimetry, and scanning electron microscopy. The results showed that up to 11 wt.% of the new residue can be incorporated in the clinker raw mix, accounting for a 9 wt.% limestone substitution in the reference clinker, without a significant change in cement composition and properties. Both clinkers were mainly made of alite, belite, aluminate and ferrite/brownmillerite, alite being the major phase at 46 %, followed by belite at 17 %, in the stream-based clinker. Thermal and microstructural analyses of 28-day hydrated cements showed the presence of approximately 20% portlandite, along with a substantial amount of C–S–H gel and remnants of unreacted belite. The leaching of V and Cr in the prepared mortar based on residue was negligible, considering the recommended safe limit by the World Health Organization for wastewater and soil, indicating the potential safe recycling of the side stream in clinker for reduced limestone consumption and sustainability of the cement industry.