Anoxic alkaline oxidation of bisulfide by Fe/Ce oxides: Reaction pathway



The kinetics of the anoxic reaction between bisulfide and iron/cerium oxide–hydroxide was studied for alkaline pH [8.0–11.0] at 0.1 MPa and 298 K in a batch slurry reactor as a part and parcel of the surface chemistry in action in the oxidation of the total reduced sulfur pollutants in the pulp and paper atmospheric emissions. Bisulfide was converted into thiosulfate and polysulfides; while the leached divalent iron and thiosulfate dovetailed equimolarly for pH ≥ 9.5 which was attributed to the breaking of sulfur–oxygen surface intermediates initiated by iron-disulfide FeII(SS) complexes. X-ray photoelectron spectroscopy of S 2p and Fe 2p of the material revealed iron sulfide, polysulfides/elemental sulfur and thiosulfate signatures along with Fe(III) oxide–hydroxide, Fe(II) sulfide and some Fe(II) connected to sulfoxy species. A detailed reaction pathway of the anoxic oxidation of bisulfide by Fe/Ce oxide–hydroxide based on FeII(SS) complex was proposed for explaining the formation of zerovalent sulfur, thiosulfate, and leached ferrous iron, and whereof a kinetic model was derived to depict the Fe(II) leaching and bisulfide consumption rates. The model rate constants were analyzed in terms of sensitivity to pH, and initial concentrations of bisulfide and surface Fe(III). © 2007 American Institute of Chemical Engineers AIChE J, 2007