Valorization of unmodified, filter-pressed bauxite residue as a precursor for alkali activated inorganic polymers in a one-part mixing process

Abstract

The valorization of bauxite residue faces severe challenges arising from its unreactive chemistry and ecotoxicity. The construction sector is widely considered the most viable option for the large-scale consumption of bauxite residue to mitiate its continued global accumulation. However, the use of bauxite residue as a supplemetary cementitious material in concrete is limited by its chemical composition and the degradation it causes in the structural properties. Alkali activation of bauxite residue is an alternative technique to produce construction materials, but conventional methods require either high-temperature calcination of the bauxite residue or the use of large proportions of other precursors to form strong alkali activated materials, adding significant cost. This has stymied commercial efforts to valorize bauxite residue. In this study, an alternative methodology is showcased to alkali activate bauxite residue in its filter-pressed form, eliminating the need for drying and calcination. This is the first alkali activation process to utilize high content of bauxite residue (>70%) without drying and milling, offering a substantial reduction in valorization costs and complexity. Alkali activated materials composed of 80% bauxite residue were produced that exceed 11 MPa in strength, meeting the ASTM requirements for interior bricks. The microstructure was characterized by mercury intrusion porosimetry and isothermal nitrogen adsorption. The alkali activation pacified the trace metallic pollutants in the bauxite residue and the leachate meets surface water standards. This methodology presents a unique avenue to valorize bauxite residue at a large scale as a construction material without cost-prohibiting pretreatment steps.