Bromate reduction and reaction-enhanced perchlorate adsorption by FeCl₃-impregnated granular activated carbon

This work studied simultaneous bromate (BrO₃^-) reduction and adsorption of perchlorate (ClO₄^-) by FeCl₃-impregnated granular activated carbon (Fe-GAC) and the mutual co-solute effects. We report that BrO₃^- reduction by Fe-GAC was coupled with enhanced adsorption of ClO₄^- by the material. The Langmuir maximum adsorption capacity for ClO₄^- by Fe-GAC was increased from 0.179 mmol g^-1 (without BrO₃^-) to 0.256 mmol g^-1 in the presence of 0.2 mmol L^-1 of BrO₃^- (a 43% increase) at pH 6.0. While the activated carbon alone was able simultaneously remove both BrO₃^- and ClO₄^-, Fe-GAC offered much greater removal efficacy and synergistic effect, likely because the immobilized Fe³⁺ acted as a catalyst and provided a local acidic environment, both being in favor of accelerated BrO₃^- reduction. Mechanistic analyses revealed that BrO₃^- removal was through a two-step process: ion exchange with OH^- and Cl^- on Fe-GAC, and then Fe-catalyzed reduction of BrO₃^- to Br^- by carbon. The carbon-BrO₃^- redox reaction generated more Fe-O and C-O groups on the material surface, which can bind with ClO₄^- by surface complexation and electrostatic interactions. To our knowledge, this is the first report that metal modified activated carbon may facilitate synergistic removal of both BrO₃^- and ClO₄^-, which are common co-solutes in contaminated waters.