Integrating adsorption mechanisms and circular economy principles: A systematic conceptual review of fly ash-based magnetic composites for sustainable dye removal

Abstract

Background: The uncontrolled release of synthetic dyes into aquatic ecosystems presents serious ecological and public health risks due to their persistence, toxicity, and resistance to biodegradation. Conventional treatment methods often lack sustainability and cost efficiency. To address this challenge, integrative strategies are needed that combine adsorption technology with circular economy (CE) principles, particularly through the valorization of industrial waste such as fly ash into functional magnetic composites. Methods: This study employs a PRISMA-guided systematic review of fifty peer-reviewed articles published between 2020 and 2025 and indexed in Scopus and Web of Science. The analysis integrates adsorption theory, materials engineering, and circular economy frameworks. It also incorporates Life Cycle Assessment (LCA) and Techno-Economic Analysis (TEA) perspectives to evaluate environmental and economic performance. Findings: Surface modification of fly ash with Fe₃O₄, TiO₂, or biochar enhances surface heterogeneity, active site density, magnetic recoverability, and regeneration capacity. Dye removal primarily occurs through electrostatic interactions, hydrogen bonding, and π–π stacking. Magnetic properties enable efficient separation and reuse. LCA and TEA analyses indicate that these composites achieve high adsorption efficiency with lower costs and reduced carbon footprints compared to conventional adsorbents. The synthesis demonstrates how waste-derived materials can support both pollution control and resource circularity. Conclusion: Fly ash-based magnetic composites represent an eco-efficient and sustainable solution for dye-contaminated wastewater treatment. Integrating material innovation with circular economy strategies strengthens waste valorization, reduces environmental burdens, and supports sustainable industrial systems. Novelty/Originality of this Article: This study introduces a unified conceptual framework that bridges micro-level adsorption mechanisms with macro-level sustainability transitions. By integrating adsorption science, sustainability assessment, and circular economy theory, it offers a comprehensive interpretive model linking material innovation to systemic environmental transformation and global sustainability goals.