Integration of Two Waste Streams for Carbon Storage and Utilization: Enhanced Metal Extraction from Steel Slag Using Biogenic Volatile Organic Acids

Abstract

Among CO2 fixation technologies, ex situ carbon mineralization using steel slag is a promising option since it produces thermodynamically stable solid carbonates. The utilization of carbonates produced using captured CO2 can allow a new circular economy of carbon. Volatile organic acids (VOAs), which are produced in the anaerobic digestion of biogenic wastes, have recently received significant attention as promising intermediates in biorefinery and another circular economy of a waste stream. This study explored the integration of two circular economies of wastes by investigating the leaching behaviors of steel slag in the presence of biogenic waste-originated organic acids-acetic acid, propionic acid, butyric acid, valeric acid, and their mixtures. The organic acids were more efficient in the elemental extraction from steel slag than strong acids. Furthermore, their mixture showed the highest extraction efficiency for all elements, illustrating the synergetic effect of ligands with different sizes and stability constants. These findings demonstrate that organic acids obtained from the biogenic wastes can be directly employed for the extraction step of an ex situ carbon mineralization process without separation or purification steps. The direct use of both steel slag and waste organic acids will significantly improve the overall sustainability of the ex situ carbon mineralization technology.