Binding Bauxite Residue to Prepare Porous Alkali-Activated Materials

The aluminum industry is one of the fastest growing metallurgical industries on a global scale. Aluminum is used to design household items, spacecraft parts, building facades, and renewable energy technologies like solar panels. The metal is refined from aluminum oxide, which is obtained from bauxite through the Bayer process. This process releases a red and alkaline material, called bauxite residue (BR), that possesses a mineral-rich composition and a corrosive nature. Due to the industry’s growing nature, the production volume of BR is straining its global storage capacity. Hence, the research to find alternate valorization methods needs to be prioritized. An area of growing research is binding BR in an alkali-activated material (AAM). The major challenge in binding BR is to increase its reactivity to form strong bonds. Generally, BR is thermally or chemically treated before being used in conjunction with other precursors, like fly ash, to prepare the AAM. In this study, raw BR was used as the primary precursor, hence reducing the percentage of other raw materials in composition. Preparation of porous AAMs has been researched due to their applications as adsorbents and insulation materials. BR’s well-documented ability to adsorb impurities from aqueous solutions directed this study to prepare porous AAMs with raw BR as primary precursor to enable future studies on its application as an industrial adsorbent. Porous AAMs were prepared using raw BR as the main precursor and hydrogen peroxide as the pore-forming agent. The varying parameters to optimize porosity in the AAM were the water-to-binder ratio and the percentage of hydrogen peroxide in composition. Resulting samples were analyzed for physical properties and open porosity. Up to 65% open porosity could be attained without compromising structural integrity. This method displays the use of a high percentage of BR without pretreatment to develop a porous material.