Integrated recovery of magnesium sulfate from hydrate desalination brine and its conversion into MgO nanoparticles for phosphate removal

Integrated brine valorization produced high-purity MgO nano • 98.4% Mg was recovered by selective precipitation. • MgO reached 1291.7 mg PO₄ 3− g −1 phosphate capacity. • 98.98% phosphate removal was achieved in real wastewater. • A circular desalination–resource recovery process was demonstrated. This study presents an integrated resource recovery strategy that converts magnesium-rich brine from hydrate-based desalination into high-performance MgO nanoparticles for phosphate removal from wastewater. Magnesium was recovered from concentrated brine by pH-controlled precipitation, followed by purification and conversion into MgO nanoparticles via an oxalate-assisted sol–gel process and calcination. The synthesized material was characterized by XRD, FTIR, SEM – EDS, BET, DLS, and pH pzc analyses, and its phosphate adsorption performance was evaluated under different operating conditions using kinetic, equilibrium, and mechanistic analyses. After five enrichment cycles, the brine contained 6734 ± 36 mg L −1  Mg 2+ , and 98.4% of the magnesium was recovered at pH 10.5. The recovered precursor was converted into cubic periclase MgO with a conversion efficiency of 98.1% and a purity of 98.8%. The MgO nanoparticles exhibited a flake-like morphology, an average particle size of 27.4 nm, and a specific surface area of 128.13 m 2  g −1 . Phosphate adsorption followed the pseudo-second-order kinetic model and the Langmuir isotherm, achieving a maximum adsorption capacity of 1291.7 mg PO 4 3− g −1 (approximately 422 mg P g −1 ). The removal mechanism involved electrostatic attraction, inner-sphere Mg–O–P complexation, and magnesium phosphate precipitation. Application to real livestock wastewater containing 94.8 ± 0.3 mg PO 4 3− L −1 achieved in a phosphate removal efficiency of 98.98% ± 0.10%. These findings demonstrate a sustainable pathway for simultaneously valorizing desalination brine and removing phosphorus from wastewater, providing an integrated circular water treatment approach that supports resource recovery and environmental protection. Download: Download high-res image (158KB) Download: Download full-size image