CO2 mineralization into waste-valorized lightweight artificial aggregate

Abstract

The construction industry faces a notable scarcity in the supply of aggregates. This study investigated the upcycling of red mud (also known as bauxite residue), a hazardous waste from alumina production, into porous and lightweight (lighter than water) red mud artificial aggregates (RMAA) for CO2 sequestration. Calcite is identified as the main carbonation product, with two hydration modes at low and high water to solid (w/s) ratios. A low w/s ratio inhibited formation of calcium carbonate, implying water is indispensable in CO2 sequestration. A high w/s ratio increased carbonate crystallinity and boosted the amount of carbonation products and calcium conversion. The highest CO2 sequestration ability (16.4 %) and calcium conversion degree (59.3 %) for red mud powder, as well as the highest strength (∼8 MPa) of carbonated RMAA, occur to the highest investigated w/s ratio. The CO2 sequestration effectively stabilized the heavy metals in RMAA. The CO2 sequestration mechanism and strength gain of RMAA are explored considering the key factors of CO2 diffusion rate and the quantity and crystallinity of carbonation products. This study advances carbon capture, utilization, and storage by transforming solid waste to energy to combat climate change.