Flower-clustered calcium sulfate dihydrate from salt gypsum: Synergistic templating for enhanced Cd2+ adsorption

We synthesized FC-CSD from salt gypsum using a green ternary template and applied it for efficient Cd 2+ adsorption. • A novel flower-clustered CaSO 4 ·2H 2 O was synthesized from industrial salt gypsum. • A ternary template system (PEG, TSC, PAA) guided nanosheet self-assembly. • The FC-CSD shows a 3D porous structure with 16.32 m 2 /g surface area. • Cd 2+ removal involves ion exchange, surface complexation, and physical adsorption. To address the high cost of conventional adsorbents and low surface area/porosity of traditional gypsum for aqueous Cd 2+ remediation, novel flower-clustered calcium sulfate dihydrate (FC-CSD) was synthesized from industrial salt gypsum using a polyethylene glycol (PEG)/sodium citrate (TSC)/polyacrylic acid (PAA) ternary synergistic template system. The influences of templating agent ratio, reaction temperature, reaction time and stirring rate on the morphological structure and adsorption properties of the materials were systematically investigated by one-factor experiments. The FC-CSD synthesized under the optimal process parameters (15.00 g PEG, 1.18 g TSC, 0.33 g PAA, 85 °C, 2.0 h, and 600 rpm) was a porous, three-dimensional flower-cluster structure formed by self-assembly of nanosheets, which achieved a specific surface area of 16.32 m 2 /g. The adsorption performance of FCCSD on Cd was analyzed by batch experiments. The results showed that the adsorption process of Cd 2+ was consistent with the pseudo-second-order kinetics and Langmuir model, and the theoretical maximum adsorption capacity was 20.38 mg/g. The adsorption mechanism involved ion exchange between Ca 2+ and Cd 2+ , complexation of surface functional groups and physical adsorption. FC-CSD demonstrates significant potential for heavy metal wastewater treatment and offers new strategies for solid-waste valorization and environmental remediation.