A circular-adsorption framework for surface-engineered, waste-derived adsorbents: from contaminant removal to strategic-element recovery

Adsorption effectively removes contaminants from aqueous media and recovers valuable metals from leachates, and the field has expanded substantially over the past two decades. Adsorption research has generated numerous high-capacity, waste-derived materials, but many studies still evaluate them individually, using adsorption capacity as the principal metric, and treat both the spent adsorbent and the captured species as waste. This review proposes a different unit of analysis: a circular-adsorption framework in which feedstock origin, surface engineering, regenerability, and the fate of the captured species are designed and reported as a coupled system rather than as sequential afterthoughts. To develop this framework, we conducted a defined literature search focused on recent waste-derived adsorbents. The reviewed cases indicate that surface charge, functional-group density, and surface heterogeneity are transferable design variables; that statistical-physics modeling can provide comparative descriptors such as site occupancy and fitted adsorption-energy parameters; and that demonstrated regenerability spans approximately three to fifteen cycles depending on the regeneration chemistry, which in turn influences whether the process terminates in contaminant destruction or resource recovery. The review concludes with a research roadmap centered on real-matrix validation, co-designed regeneration and elution, durability of green crosslinks, direct benchmarking against established separations, and life-cycle accounting, so that water purification and resource recovery can be assessed as a single, auditable circular operation.