The sustainable management of industrial byproducts represents a critical challenge for the aluminum industry. This study developed a cost-effective adsorbent (SA@RM) derived from sodium alginate and red mud for fluoride removal, addressing both solid waste utilization and water purification needs. Systematic adsorption experiments revealed optimal performance under conditions of 15 g/L dosage and pH 5, achieving adsorption equilibrium within 40 min for initial fluoride concentrations of 11.7 mg/L. Notably, the adsorbent demonstrated exceptional cyclic stability, maintaining 54.8% adsorption capacity through three regeneration cycles. The adsorption process followed the Langmuir isotherm model (R² = 0.994) and pseudo-second-order kinetics (R² = 0.975), indicating monolayer chemisorption as the dominant mechanism. Advanced characterization techniques (SEM-EDS, FT-IR, XPS) elucidated three main mechanisms: fluoride complexation with aluminum oxides, ligand exchange with surface hydroxyl groups, and ion exchange with chloride species. This material achieves 92% fluoride removal while valorizing industrial waste, reducing adsorbent production costs by 60–70% compared to conventional materials. The detailed mechanism analysis provides fundamental insights for designing waste-derived adsorbents, offering a practical solution for sustainable industrial development and water treatment applications.

Phosphogypsum (PG) is a major solid by-product generated during wet-process phosphoric acid production. Its stockpiling poses significant environmental risks due to the potential leaching of harmful substances. Therefore, conversion of PG into high-value-added products is urgent. In this work, nano-calcium carbonate (Nano-CaCO₃) was synthesized from PG via a phase-transfer precipitation method. The surface of the as-prepared product was then modified for Hg²⁺ detection. Initially, the nanoparticle surface was functionalized with (3-aminopropyl)triethoxysilane (APTES), followed by grafting with a synthesized rhodamine B-based derivative (RhoB-NCS). The acquired product was denoted as CaCO₃@RhoB-NCS. Physical characterization demonstrated its successful fabrication. The product is an effective sensor for Hg²⁺ detection, exhibiting enhanced fluorescence emission at 600 nm with a detection limit as low as 1.0 × 10⁻⁶ M. Moreover, the CaCO₃@RhoB-NCS was used as a filler for Hg²⁺ test paper. This work demonstrates a promising approach for valorizing solid waste into high-value-added product.