Utilization of ferroalumina as raw material in the production of Ordinary Portland Cement

Red mud (RM), the digestion by-product of bauxite processing from “Aluminum Hellas”, was dewatered by means of a filter press. The filtrand with water content from 28 to 32 wt% was named ferroalumina (FA). In order to utilize it as a raw material in the production of Ordinary Portland Cement (OPC), mixtures were prepared with limestone, sandstone and 1, 3 and 5 wt% FA addition, respectively. The design of the mixtures was based on the cement's compositional indexes LSF, AM and SM. Burnability tests showed that less than 1 wt% free lime can be obtained in all cases for firing at 1450 °C, except for the mixture with 1 wt% FA addition, which requires 1550 °C. XRD analysis and optical microscopy examination showed that FA addition did not affect the mineralogical phases of the produced clinkers. The characterisation of the produced Portland cements indicated that differences on surface area, water requirement and setting time are negligible. Compressive strength results after 28 days of curing varies from 55 to 63 MPa, which ranks the produced cements in CEM I 42.5N category. More specifically, the cements with FA addition due to their relatively high 2-day strengths (>20 MPa) can be ranked in CEM I 52.5N category. Addition of FA increases the amount of water-soluble chromium proportionally to the amount of total chromium to the mixture; however, conversion of total Cr to hexavalent Cr remains practically constant, in the range of 32-35 wt%. The results indicate that FA can be used as raw material in the production of OPC up to 5 wt% according to the chemical composition of the other raw materials.