Production of CO${}_2$-reduced eco-cements using bauxite-mining overburden Belterra Clay and bauxite washing residue from Brazilian Amazon

Calcium sulfoaluminate based cements (CSA) have been quoted as an alternative to reduce CO${}_2$ emissions from the cement sector. In this work, residues of bauxite mining were tested as alumina source to produce CSA. These residues are the Belterra Clays that cover the bauxites in the Amazon and the clay from the bauxite washing beneficiation. Raw meals composed of calcite, gypsum and the clays were modelled using design of experiments and stoichiometry. Up to 38% of the clays could be used by clinkering at 1250°C. The clinkers had up to 45% of ye'elimite and high amounts of belite, besides brownmillerite and Fe-perovskite forming a discontinuous solid solution. At least 30% less CO${}_2$ was generated in the clinkering process compared to ordinary Portland cements (OPC). The main hydrates were ettringite and monosulfoaluminate. The produced mortars developed similar and higher compressive strength than an OPC. Both clay residues are suitable to produce CSA-based eco-cements.