A multifunctional Ce(IV)-based coagulant with integrated oxidation and adsorption for efficient removal of diverse arsenic species

CAN possessed three functions: oxidation, adsorption, and coagulation. • CAN removed anionic arsenic mainly through inner-sphere complexation and reducing steric hindrance. • Ce(IV) in-situ oxidized As(III) to As(V), which was then immobilized and coagulated. • Pre-hydrolyzed CAN B (B>0) resisted pH fluctuations and achieved low residual cerium. • CAN flocs were large and produced a loose cake layer with less pore blocking, reducing membrane fouling. Arsenic contamination is widespread in groundwater and surface water, with species including As(V), As(III), and organic arsenic. This study developed a Ce(IV)-based coagulant, CAN, with dual adsorption and oxidation capabilities for arsenic removal. For organic arsenic, CAN outperformed PAC in removing p-arsanilic acid (p-ASA) and disodium methylarsonate (DSMA); for roxarsone (ROX), CAN achieved > 99% removal at only 1/8 of the PAC dosage. The large ionic radius and high coordination number of Ce(IV) enable stronger binding to organic arsenic ligands via inner-sphere As-O-Ce complexation, overcoming steric hindrance that limits Al(III). For As(III), Ce(IV) exhibits oxidation-adsorption-coagulation synergy, converting As(III) to As(V) and immobilizing it in situ. To further optimize As(III) removal, pre-hydrolyzed CAN B (B>0) was synthesized; with pre-ozonation, it reached > 96% efficiency and residual Ce of 0.006–0.024 mg/L, due to flower-like nanocrystal clusters. CAN hydrolysates are mainly Ce 4 and Ce 6 species, forming large flocs (D 50 > 160–200 μm) and a loose, porous cake layer in the coagulation-ultrafiltration, sustaining ∼70% membrane flux (J/J₀). In real groundwater, CAN resisted competing ions and maintained high removal. Overall, the combined oxidation, adsorption, and coagulation functions of Ce(IV) salts broaden their applications and provide new strategies for treating water containing heavy metal oxyanions. Download: Download high-res image (212KB) Download: Download full-size image