Preparation of red mud-based polyferric silicate aluminum-guar gum composite flocculant by constant temperature water bath method and its fluoride removal performance in photovoltaic wastewater.

To achieve red mud resource utilization and efficient treatment of photovoltaic wastewater, this study extracted Fe, Al and Si from red mud, and prepared a red mud-based polyferric silicate aluminum-guar gum (PSAF-Guar) composite flocculant with natural guar gum via a constant temperature water bath method. Its composite mechanism was analyzed by SEM, EDS, XPS, XRD and FT-IR. Guar interacted with PSAF through coordination, hydrogen bonding and covalent bonding, forming a tight organic-inorganic network structure. When the mass ratio of PSAF to Guar was 5:1, the synergistic effect was optimal, allowing efficient fluoride removal over a wide pH range of 3-11. For actual photovoltaic wastewater, under the conditions (dosage 0.45 g/L, rapid mixing 220 r/min, flocculation stirring 50 r/min, sedimentation 30 min), the F- removal efficiency reached 62.8% and turbidity removal efficiency 93.1%. Three-dimensional fluorescence spectroscopy indicated that fluorescent pollutants such as humic-like substances were also removed via charge neutralization, adsorption and macromolecular decomposition. The flocs had a high fractal dimension, and the defluoridation performance was better than pure PSAF and PAC + PAM (Polyaluminum Chloride+Polyacrylamide) system. With simple preparation, green and low-cost raw materials, this composite flocculant shows promising application prospects in photovoltaic wastewater treatment.