Environmental and economic assessment of coal fly ash flotation for sustainable unburned carbon recovery

Incorporating coal fly ash (CFA), a byproduct of coal combustion, into cementitious materials is a promising strategy for reducing the consumption of natural resources and mitigating environmental burdens. Although flotation effectively lowers the unburned carbon content in CFA to enhance its recyclability, the associated carbon emissions and economic costs necessitate rigorous sustainability evaluations. This study evaluates the environmental-economic trade-offs of CFA flotation at a Technology Readiness Level (TRL) 6 (pilot scale), utilizing integrated life cycle assessment (LCA) and life cycle cost analysis (LCCA). Instead of static modeling, a Calorific-Based Economic Valuation (CBEV) framework is introduced to optimize process parameters by coupling market pricing mechanisms with flotation grade-recovery. The results revealed that kerosene and turpentine oil dosages critically influenced system performance: overuse caused economic losses, whereas optimal conditions (1% kerosene + 0.1% turpentine oil per ton of CFA ) achieved a carbon benefit of 94.29 kg CO 2 -eq (247.70% improvement) and a net benefit of 0.986 USD/t (4.69% return). Sensitivity analysis reveals that the adoption of electric vehicles yields synergistic environmental and economic benefits. In contrast, a 50% increase in transport distance reduces economic returns by 3.6%, despite a marginal variation in carbon footprint (<5%), highlighting the importance of logistics optimization. Based on industrial scale-up principles, these results represent a conservative baseline for informing future industrial applications. This study establishes a dual-perspective framework for assessing the feasibility of CFA flotation and provides quantitative insights to support sustainable process intensification.