Phosphate mining byproduct-derived PHI-type zeolite with intrinsic Mg2+ ions for enhanced Cd2+ removal from water

Synthesizing functional zeolites from industrial residues advances circular materials chemistry, but controlling framework composition is challenging. In this study, PHI-type zeolite was synthesized from a phosphate mining byproduct containing SiO 2 , Al 2 O 3 , CaO, MgO, and Fe 2 O 3 . The PHI zeolite retains waste-derived Mg within its cationic environment, setting it apart from PHI made from conventional precursors. Similar syntheses using conventional precursors, with/without MgO, yielded phase-pure PHI without MgO addition, whereas MgO introduced secondary impurities or competing zeolites. The influence of precursor-dependent cation chemistry on functional performance was studied using Cd 2+ adsorption as a model water-treatment application. The waste-derived PHI zeolite exhibited superior adsorption capacity compared with its commercial counterpart, highlighting the combined effects of intrinsically incorporated Mg 2+ and enhanced pore accessibility on Cd 2+ adsorption. Comprehensive characterization (XRD, FTIR, TGA, SEM-EDX, and N 2 sorption) elucidated the structural and textural properties underlying this enhanced behavior. Adsorption kinetics followed a pseudo-second-order model, and equilibrium data fit the Langmuir isotherm, indicating chemisorption on homogeneous sites with a maximum uptake of 99.8 mg g −1 . The material shows excellent stability and recyclability, maintaining > 95% capacity after five cycles. These findings highlight industrial waste as more than a feedstock for zeolite synthesis, revealing its potential to shape composition and functional performance.