Oscillations and Mechanistic Analysis of the Chlorite−Sulfide Reaction in a Continuous-Flow Stirred Tank Reactor

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 HSO(3)(-) by ClO(2)(-) is the major source of positive feedback of hydrogen ions. The reaction between H(2)S and ClO(2)(-) to form S(8), 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 S(2-) and ClO(2)(-). The 10 species included are HS(-), H(2)S, S(2)O(3)(2-), SO(3)(2-), HSO(3)(-), OCl(-), HOCl, ClO(2)(-), H(+), and OH(-). In contrast to the H(2)O(2)-S(2-) oscillatory reaction, S(2)O(3)(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.