Assessment of Green and Waste-Derived Materials for Heavy Metal Removal from Water: A Review - A Circular-Economy Perspective

Abstract

Heavy metal contamination of water and wastewater represents a persistent environmental challenge due to the toxicity, non-biodegradability, and bioaccumulative nature of metallic pollutants, which pose serious risks to human health and aquatic ecosystems. Conventional treatment technologies, such as chemical precipitation, ion exchange, membrane filtration, and electrochemical processes, are often constrained by high operational costs, energy intensity, limited selectivity, and secondary waste generation. Consequently, increasing research interest has focused on green and waste-derived materials as sustainable alternatives for heavy metal removal. This review critically examines the application of green and waste-derived adsorbents for the removal of heavy metals from aqueous systems. The occurrence, sources, toxicological impacts, and regulatory constraints of priority heavy metals are first outlined to define treatment performance requirements. The fundamental removal mechanisms, including adsorption, ion exchange, surface complexation, electrostatic attraction, and precipitation, are systematically discussed, together with the influence of key operational parameters and adsorption modelling approaches. A comprehensive classification of adsorbent materials is presented, encompassing agro-waste and plant-derived materials, industrial by-products, biochars, biosorbents, biopolymers, and hybrid composite systems. Comparative assessment highlights performance trade-offs relative to commercial activated carbon, while environmental and techno-economic considerations are evaluated within a circular-economy framework. Finally, key challenges related to scale-up, real wastewater application, and future research directions are identified to support the practical implementation of sustainable adsorbents.