Industrial Symbiosis and Ash Utilization for Circular Economy Transitions: A Systematic Literature Review and Gap Analysis

Industrial symbiosis (IS) is a well recognised circular economy strategy for improving resource efficiency, reducing waste, and transforming industrial by-products into valuable secondary resources. Ash generated from coal combustion, municipal waste incineration, biomass processing, and other industrial activities has considerable potential for use in cement, concrete, construction materials, carbonation processes, and other industrial applications. However, existing research remains fragmented, with many studies focusing either on specific ash types and technical applications or on industrial symbiosis as a broader circular economy concept. Limited attention has been paid to ash-based industrial symbiosis as an integrated system that combines material flows, treatment technologies, environmental and economic benefits, regulatory conditions, stakeholder coordination, and scalability challenges. This study aims to address this gap by systematically mapping the evolution, thematic structure, applications, innovations, barriers, and enabling factors of ash utilization within industrial symbiosis frameworks. Using data retrieved from Scopus and Web of Science, the study applies VOSviewer and the RStudio Biblioshiny package to analyse publication trends, keyword co-occurrence, conceptual structures, and emerging research themes. In addition, 61 relevant publications are systematically reviewed to classify ash types, industrial sectors, application areas, technological pathways, benefits, and implementation challenges. The review shows that regulatory uncertainty, insufficient data standardisation, limited socio-economic analysis, and difficulties in scaling symbiotic systems remain key barriers. The study contributes to the literature by positioning ash not only as a waste-derived material, but as a strategic resource within circular, inter-organisational, and governance-dependent industrial systems.