Review on algae-derived biopolymers to remove radionuclides from aquatic systems: sorption mechanisms, kinetics and stability

The carboxyl, sulfate, phosphate and hydroxyl groups on algal biomass and its polysaccharides bind uranium, caesium, strontium and radium. The reported uranium capacities for brown macroalgae vary greatly depending on pH and pretreatment, ranging from roughly 150 to 560 mg/g. Green macroalgae and immobilized microalgae report much smaller uranium capacities, typically in the range of 75-290 mg/g. Certain microalgae remove 88-95% of dissolved 137 Cs within 48 h. However, these values mostly stem from acidic, single-solute batch experiments. When the same material is used to test actual effluents, removal rates drop, often dramatically. This review evaluates algae as a feedstock for functional polymers, combines capture mechanisms with the aqueous chemistry that governs them, and re-evaluates how isotherm, kinetic, and thermodynamic models are interpreted. The review then compares the quantitative and qualitative data regarding engineered hydrogels and composites, including their stability, regeneration, and response to competition from other ions. Finally, the loaded sorbent is viewed as secondary radioactive waste, and column operation, life-cycle burden, and traditional alternative options are placed within this context. Maximum capacity is less important than selectivity in real water and safe end-of-life management as critical evaluation criteria.