pH-oscillations in a closed chemical system of CaSO3–H2O2–HCO3−

Long-lasting large amplitude periodic change of the pH is measured in an aqueous suspension of CaSO3–H2O2–HCO3− at 2.0–10.0 °C in a closed reactor. The amplitude can be as large as 2 pH units between pH 5 and 7. The observed phenomenon is explained and simulated by taking into account a slow dissolution of CaSO3, which serves as a continuous supply of HSO3− for a H+-producing autocatalytic composite reaction between H2O2 and HSO3−. Protonation of HCO3− to form CO2 in a reversible reaction provides for the necessary negative feedback in [H+].