Titanium xerogel as a potential alternative for polymeric ferric sulfate in coagulation removal of antimony from reverse osmosis concentrate

• TXC was more effective than PFS for Sb(V) removal from RO concentrates. • Electrostatic interaction played a major role in Sb(V) removal by PFS. • Sweep flocculation was the dominant mechanism in Sb(V) removal by TXC. • TXC was less sensitive to pH and organic matter than PFS. • TXC coagulation is a robust approach for treatment of RO concentrates. Reverse osmosis (RO) is a useful process for water purification or water reuse. Nevertheless, the generated RO concentrate may adversely affect the environment if not properly treated. Coagulation with polymeric ferric sulfate (PFS) is a widely used method for the treatment of antimony (Sb)-containing RO concentrate. However, the PFS coagulation is still suffering from high residual metal and turbidity. Herein, a titanium xerogel coagulant (TXC) was evaluated as an alternative for PFS to remove Sb from RO concentrate. The RO concentrate collected from a local textile factory had an initial Sb concentration of 806 μg/L, a turbidity <1 NTU, and a high conductivity (5.3 mS/cm). With TXC as the coagulant, the residual Sb concentrations met the direct discharge limit (50 μg/L) at all the tested conditions (pH: 3.0–9.0, dosage: 40–100 mg/L). Based on the analyses with potentiometric titrations, X-ray photoelectron spectroscopy, and X-ray diffraction pattern, the binding states between Sb and the flocs of TXC and PFS were investigated. The results reveal that sweep flocculation dominated in the removal of Sb by TXC, whereas charge neutralization played a major role in Sb removal by PFS. As a result, TXC coagulation was robust in a wide pH range and was less sensitive to organic matter. The work here provides a promising approach for the treatment of RO concentrate.