Red mud valorization in stoneware pastes: Technical and environmental assessment

Red mud (RM), resulting from alumina production by Bayer process, is classified as hazardous waste and is, nowadays, one of the most abundant industrial waste worldwide. Currently, over 4 billion tons are stored in ponds/dried mounds and is of utmost importance to tackle this problem. This work aims to recycle RM as colouring agent in stoneware products. For this purpose, several proportions of RM (0-10 wt%) were added to ceramic pastes. The developed products with RM exhibit a reddish/brown colour. Further, the technical characteristics of the specimens with 10 wt% of RM (RM10) are within the industrial limits: firing shrinkage (7.1%), weight loss (6.9%) and water absorption (1.38%). RM10's density and flexural strength are higher than RM0, 2.16 g/cm3 and 2.07 g/cm3, and 416 kgf/cm2 and 388 kgf/cm2 respectively. Leaching tests performed in cups industrially prepared indicated that all the values were below the maximum permitted. Lastly, through a life cycle assessment, it was concluded that the carbon footprint decreases 18% when RM10 is incorporated into the stoneware paste. Therefore, this work provides a viable alternative for the management of considerable amounts of this waste and reduces the carbon footprint associated with the ceramic production process.