Carboxylic ligands to enhance material recovery from construction waste to produce CaCO3 for carbon utilization

Abstract

The decarbonization of the built environment is a pressing issue to achieve CO₂ reduction targets in the concrete industry. Carbon mineralization of construction and demolition waste (C&DW) is an attractive pathway to capture of CO₂ as stable carbonates which can be re-utilized and upcycled in a circularized fashion through the creation of new building blocks. Material recovery from the C&DW is often performed in hydrometallurgical leaching using acidic media; however, this process is often hindered by solubility issues and passivation. To ensure high recoveries of these elements, ligands can be used to enhance dissolution. Carboxylic acids are used in conventional hydrometallurgical mineral processing, such as leaching, floatation, and solvent extraction, and are desired due to their affordability and stability. In this study, we explore the dissolution of waste cement pastes in acidic conditions under the presence of four carboxylic acid ligands: formate, acetate, glutamate, and citrate. The leaching kinetics are categorized and the pseudo-rate constants are established, demonstrating the advantages of these agents to enhance reaction rates in the general order of citrate ⋙ formate > acetate > glutamate > control. The characterization of the post-extraction reactor residue (PERR) revealed a significant increase in Si-content. Finally, the leachate was carbonated to produce calcium carbonate, which was characterized for its use based on morphology and size. Glutamate demonstrated distinct advantages compared to other ligands, with a dual function of not only improving leachability of cement but promoting and stabilizing vaterite during crystallization. Overall, this study motivates the use of sustainable ligands to enhance material recovery during the dissolution of alkaline wastes for carbon mineralization.