Integrated phosphorus recovery from lake sediment via electrodialysis, capacitive deionization and chemical precipitation

Phosphorus recovery from nutrient- and contaminant-rich lake sediments is crucial for closing nutrient cycles and mitigating environmental risks. This study investigates a multi-stage separation strategy that combines electrodialysis (ED), capacitive deionization (CDI), and calcium-phosphate (CaP) precipitation to selectively extract and recover phosphorus from lake sediment. ED was applied to mobilize bound ions, selectively transporting phosphate and sulphate into the anolyte, while directing heavy metals into the catholyte. Phosphorus from the ED anolyte was recovered as calcium phosphate precipitate (CaP) using three distinct pathways: PA) CaP precipitation by mixing ED anolyte and ED catholyte at different ratios, PB) CaP precipitation from CDI eluate following CDI treatment of the ED anolyte, and PC) CaP precipitation from the ED anolyte via direct addition of CaCl₂ salt. Results showed that mixing anolyte and catholyte enabled efficient precipitation but introduced multivalent metal impurities. Direct CaCl₂ addition to untreated anolyte yielded highly crystalline hydroxyapatite with minor lattice substitution, while the CDI-mediated route produced nanocrystalline CaP with reduced impurity incorporation. This integrated process demonstrates a viable path for selective P separation and recovery from complex matrices, offering practical insights for resource recovery and sediment valorization in line with circular economy goals. Future work should focus on long-term electrode and membrane durability, as well as process optimization to reduce energy demand and evaluate scale-up feasibility.