Valorization of FGD and Bauxite Residue in Sulfobelite Cement Production

Cement, the most used building material amounts to an annual world production of 3.5 Gt. Sulfobelite cements, SB, require lower kiln temperature and emit less CO2, compared to Ordinary Portland cement, OPC. The main difference of SB from OPC is the reduction of alite (CaO)3SiO2, the increase of belite (CaO)2SiO2 and the formation of yeelimite (CaO)4(Al2O3)3SO3, also called “Klein’s salt”. Industrial byproducts, such as Flue Gas Desulphurization gypsum, FGD and dry Red Mud, the so–called bauxite residue, BR can also be used as raw materials, decreasing the CO2 footprint. In the present study, SB cements were prepared in laboratory scale from FGD and BR, as well as, conventional raw materials. All compositions were characterized by XRD, Q–XRD, optical microscopy, SEM and were tested for their compressive strength, soundness, coagulation, etc. The main result of this work is that the studied industrial byproducts, FGD and BR, can be used as alternative raw materials for the raw meals of SB cements, accomplishing low–temperature clinkering at 1330 °C and lower quantities of conventional raw materials. Conclusions suggest that SB cements can be a promising eco–friendly building material and can be used in other applications such as 3-D printed building, rapid-setting mortars, rapid sealants, etc. Moreover, this is an attempt to apply circular economy in cement production utilizing the established production route of cement industries.