Facile surface-controlled synthesis of phytic acid-facilitated calcium carbonate composites for highly efficient ferric ion adsorption and recovery from rust

This work presents a simple synthesis of calcium carbonate (CaCO 3 )-based composites designed for the efficient adsorption of ferric ions (Fe 3+ ) from solution, and specifically applied for Fe 3+ recovery from rust. The strategy involves coordinating phytic acid (PA) with calcium ions (Ca 2+ ) and coprecipitation with carbonate ions (CO 3 2− ) at room temperature to form phytate-CaCO 3 (Ph-CC) composites. The obtained composites exhibited a robust mesoporous crystal structure with numerous phosphate groups of phytate functionalized on CaCO 3 microparticles. The surface properties of the composites were optimized by adjusting the molar ratio ( x ) of PA:Ca 2+ in synthesis. The Ph-CC 0.10 composite ( x  = 0.10), with the highest specific surface area (99.56 m 2 /g), demonstrated exceptional Fe 3+ adsorption (>99% efficiency in 80 min). The adsorption process followed the pseudo-second-order and Langmuir isotherm models, indicating monolayer coverage. Impressively, the maximum adsorption capacity reached 1385.85 mg/g, surpassing that of previously reported adsorbents. Thermodynamic studies confirmed a spontaneous and exothermic adsorption process. The superior Fe 3+ adsorption of the composite was attributed to electrostatic and chelation interactions, with partial ion exchange. Furthermore, the Ph-CC 0.10 composite effectively captured Fe 3+ from rust dissolution in an acidic solution (pH 3) under sonication at 35 kHz for 60 min. These results highlight the potential use of the developed composites in mitigating environmental pollution and transforming waste materials into valuable sources. Therefore, Ph-CC composites are promising alternatives for wastewater treatment and metallurgical applications.