Bayer-geopolymers: An exploration of synergy between the alumina and geopolymer industries

Previously, caustic residues such as red mud and sodium oxalate have been used to provide filler and as a supplementary source of alkali for geopolymers. However, rather than incorporation of dilute alkali residues within geopolymer precursors, a significant counter-intuitive approach is to synthesise geopolymers using Bayer process liquors as a primary source of caustic sodium aluminate and to add locally available fly ash as a source of reactive silica and additional alumina. In addition to the potential for using significant quantities of industrial residues to manufacture geopolymers, these relatively new cements have the ability to bind a range of contaminants. As the Bayer process could achieve significant process impurity removal by utilisation of plant liquor, synergy between the alumina and geopolymer industries could be achieved. Geopolymers with a Si/Al ratio of 2.3 and a Na/Al ratio of 0.8 were targeted. With only synthetic plant liquor as the alkali activator, geopolymers with a mean compressive strength of 33 MPa were synthesised, while use of processed plant liquor resulted in compressive strengths of 43 MPa.