Hydrothermal treatment of typical combustion and incineration residues: State-of-the-art technologies and future perspectives.

Coal combustion and waste incineration processes generate massive solid residues, posing severe environmental risks and resource waste. Effective valorization of typical combustion and incineration residues, including coal fly ash (CFA), coal bottom ash (CBA), municipal solid waste incineration bottom ash (IBA), and incineration fly ash (IFA), is crucial for achieving circular economy goals and environmental sustainability. As a mild and efficient thermochemical technology, hydrothermal (HT) treatment improves the reactivity of solid residues and enables synthesis of high-value functional products under controllable temperature and pressure, offering unique advantages in detoxification and resource utilization. This review systematically examines current research progress on HT treatment for combustion and incineration residues, identifies key unresolved knowledge gaps, and discusses inherent technical limitations of relevant routes. The work also evaluates the two primary HT technologies (HT synthesis and HT curing) and analyzes critical challenges in process efficiency, energy use, environmental impacts, and economic costs. Targeted future directions are proposed, covering wastewater management, energy-economic balance optimization, scale-up equipment development, and diversified product applications. This review provides theoretical support and practical guidance for advancing large-scale industrial implementation of HT technologies for combustion and incineration residue valorization.