Managing phosphogypsum as ecological functional granules: A review of multi-scale immobilization, long-term environmental stability, and application prospects

Phosphogypsum (PG) is a high-volume calcium sulfate byproduct generated during wet-process phosphoric acid production. Its reuse is limited by the need to combine large-scale consumption with long-term environmental safety. Conventional use of PG in construction materials often focuses on strength and bulk utilization, while the release of phosphorus, fluorine, radionuclides and source-dependent trace metals under changing environmental conditions remains insufficiently addressed. This review examines PG-based functional granules as engineered granular waste forms for potential use in ecological and environmental applications. The review summarizes recent progress in three aspects: preparation routes using PG and other solid wastes, reported immobilization pathways involving precipitation, adsorption, gel encapsulation, lattice incorporation and physical blocking, and environmental behavior under acidic, saline and weathering conditions. Application scenarios including constructed wetlands, acid mine drainage treatment, ecological concrete, sediment remediation and marine substrates are discussed with emphasis on technical limitations and environmental risk control. Current studies remain dominated by short-term laboratory tests, while field-scale data, long-term leaching models, radionuclide dose assessment, ecotoxicological evaluation and life cycle assessment are still limited. Future work should develop scenario-based testing protocols and pilot-scale monitoring to support safer and more acceptable PG reuse.