Abstract
Sustained oscillations in pH and redox potential are found in the chlorite−sulfide reaction in a continuous-flow stirred tank reactor (CSTR). Autocatalytic oxidation of HSO3 − by ClO2 − is the major source of positive feedback of hydrogen ions. The reaction between H2S and ClO2 − to form S8, which consumes H+, is an important source of negative feedback. A model consisting of five protonation−deprotonation equilibria and nine redox reactions is proposed for the oscillatory reaction between S2- and ClO2 −. The 10 species included are HS−, H2S, S2O3 2−, SO3 2−, HSO3 −, OCl−, HOCl, ClO2 −, H+, and OH−. In contrast to the H2O2−S2- oscillatory reaction, S2O3 2− is shown here by capillary electrophoresis to be an important intermediate. Simulations give qualitative agreement with the pH oscillatory behavior observed in the CSTR.