Advances in adsorbent materials for uranium removal from waters and wastewaters

ABSTRACT Uranium contamination of water resources poses severe environmental and human health risks due to its chemical toxicity and radioactivity. Among available remediation techniques, adsorption has emerged as the most promising approach owing to its cost‑effectiveness, operational simplicity, and high removal efficiency. This review provides a critical, comparative analysis of five major adsorbent classes, activated carbon, biosorbents, composite materials, nanoadsorbents, and mesoporous silica, for uranium(VI) sequestration from waters and wastewaters. Unlike previous descriptive compilations, we systematically benchmark performance under standardized conditions (pH 5–6, room temperature), explicitly quantifying trade‑offs between adsorption capacity, selectivity, material cost, regenerability, and technology readiness level (TRL). Our analysis reveals that while composites and nanoadsorbents achieve exceptionally high laboratory capacities (up to 2357 mg/g), their practical applicability is constrained by high precursor costs, impractically low dosages, and limited scale‑up validation (TRL 3–4). In contrast, biosorbents and activated carbon offer superior cost‑performance balance for real‑world applications but suffer from 30–70% capacity reduction in complex water matrices due to competing ions (Ca²⁺, Mg²⁺, carbonate) and anionic uranyl‑carbonate complexes. A mechanistic matrix is presented, linking adsorption behaviour—electrostatic attraction, ion exchange, inner‑sphere complexation, chelation—to functional group chemistry, spectroscopic fingerprints (XPS, EXAFS, FTIR), and thermodynamic parameters (ΔH°, ΔS°). We critically evaluate regeneration performance, finding that robust composites withstand 6–10 cycles with >80% capacity retention, whereas unmodified biosorbents degrade after 4–5 cycles. Engineering challenges including fixed‑bed column dynamics, mass transfer limitations, fouling, and practical issues of handling, storage, and batch consistency are systematically assessed. Finally, we outline future research directions: AI/ML‑driven adsorbent design, molecularly imprinted selective materials, stimuli‑responsive regenerable sorbents, and the urgent need for standardized testing protocols and real‑water validation. This review bridges the gap between laboratory breakthroughs and industrial deployment, providing researchers and engineers with an evidence‑based decision framework for selecting fit‑for‑purpose adsorbents and advancing sustainable uranium remediation technologies.