Exploring Direct and Indirect Carbon Mineralization of Industrial Solid Wastes: Complementary Approaches for Sustainable CO2 Reduction, Waste Management, and Resource Recovery

Abstract

The power and industrial sectors are major contributors to global CO2 emissions with significant by-products generated. These by-products, including coal fly ash (CFA) from coal-fired power plant (CFPP) and steelmaking slags from iron and steel industry, have garnered attention as potential feedstocks for carbon mineralization technology. This dissertation explores both direct and indirect methods of carbon mineralization as complementary approaches on turning the challenges associated with using these industrial by-products into opportunities for sustainable CO2 reduction, waste management, and resource recovery. In Chapter 2, this dissertation investigates the enhancement of carbonation efficiency using CFA through the application of an alkali activator. Carbonation efficiency was significantly improved by breaking down the alumino-silicate bond to provide more reactive calcium (Ca), enabling the formation of a more carbonate layer on the CFA’s particle surface. This study also explored the implications of carbonation for heavy metals and hazardous metalloid stabilization. Carbonation reduced the leaching of heavy metals and hazardous metalloid such as chromium (Cr), copper (Cu), cadmium (Cd), lead (Pb), mercury (Hg), and arsenic (As), making CFA safer for environmental use. The results highlighted the importance of optimizing carbonation conditions to not only increase CO2 storage but also mitigate the risks posed by heavy metals and hazardous metalloid in CFA, thus improving the material’s suitability for reuse in various applications. In Chapter 3, the detailed mechanism of pH swing-based indirect carbon mineralization was investigated, focusing on steelmaking slags as a feedstock. This study examined the elemental precipitation behavior in Kanbara reactor (KR) and basic oxygen furnace (BOF) slags towards sequential pH adjustments. From this basic understanding, ligands (chelating agents) such as nitrilotriacetic acid (NTA), ethylenediaminetetraacetic acid (EDTA), and diethylenetriaminepentaacetic acid (DTPA) were employed in the pH swing process to optimize the selectivity of critical elements recovery, particularly manganese (Mn), from electric arc furnace (EAF) slags. The results revealed that ligands effectively stabilized Mn in solution and preventing its premature precipitation. The recovered Mn achieved high concentration while its Ca content was utilized for CO2 storage through the precipitation of calcium carbonate (CaCO3). Overall, the results of this research provide valuable insights into enhancing carbonation efficiency and stabilizing heavy metals and hazardous metalloid in CFA, as well as recovering critical elements such as Mn and obtaining CO2 storage through CaCO3 precipitation using steelmaking slags. The findings in this dissertation demonstrates the feasibility of applying both direct and indirect carbon mineralization methods to industrial solid wastes and contribute to the development of CO2 sequestration, while simultaneously promoting the circular economy by transforming industrial by-products into valuable materials.