Assessing the environmental risk and toxicity of cementitious composites incorporating coal bottom ash: A hierarchical analysis framework

Sustainable practices increasingly explore the valorization of industrial by-products, while addressing potential toxicity implications associated with the practice. Coal bottom ash (CBA), a coal combustion by-product, is gaining attention for use in cementitious composites, though concerns remain regarding its long-term environmental safety. This study presents a hierarchical toxicity analysis using the Toxicity Characteristics Leaching Procedure (TCLP) to assess the leaching behavior across raw CBA, coal fly ash (CFA), optimized ground CBA, and two cementitious paste variations incorporating optimized ground CBA. Physico-chemical characterization was conducted through ICP-MS, quantifying eleven trace elements (As, Ba, Cd, Co, Cr, Mn, Ni, Pb, Se, V, Zn). In comparison, CFA exhibited higher leaching of non-compliant elements (As, Cr, Mn, Se) compared to CBA (exceeding limits only for Mn). While grinding increased Mn and Ni leachability in optimized ground CBA, their integration into cementitious binder systems significantly reduced overall trace element concentrations. Minor Ba leaching was observed. These findings demonstrate that optimized ground CBA is viable for incorporation into cementitious pastes, as evidenced by the consistently low trace element concentrations in the leachates. Overall leachability across all assessed trace elements remained minimal, with a maximum of only 1.13 %, highlighting the environmental safety of the investigated material. These outcomes support the potential transformation of CBA from waste into a viable resource, aligning with sustainable practices and public health considerations. This study provides critical insights to guide more informed scientific decision-making among stakeholders in the cement and concrete sectors, as well as policymakers, particularly in sustainable waste management and resource recovery. • Investigation of hierarchical leaching characteristics of CBA using TCLP. • Analysis of all states of CBA, including raw form, cementitious binder, and paste. • Quantification of multiple trace element concentrations using ICP-MS. • Cementitious paste with ground CBA reduces leachability, enhancing CBA’s viability. • Minimal barium leaching requires monitoring to ensure regulatory compliance.