Kinetics of Autocatalytic Oxidation of Mn(II) Ions by Periodate in Relation to Manganese Oscillations
The kinetics of the autocatalytic oxidation of Mn(II) ions by periodate was investigated in unbuffered phosphoric acid solutions and in buffered solutions; the process was studied in a bath reactor in relation to the chemical oscillations in a continuously flow stirred tank reactor (CSTR), which are based on the chemistry of manganese. The rate constants k 1 and k' 2 corresponding to the noncatalyzed and catalyzed reaction course were determined by the Schwartz method. While MnO 4 - ions are the reaction product in the unbuffered phosphoric acid medium, in a CH 3 COOH-NaOH buffer the Mn 2+ ions are only oxidized to Mn(IV). For this case, a reaction pathway is discussed where the key step encompasses dimerization of MnO(OH) + ions followed by the formation of (MnO 2 ) col colloids, stabilized by adsorption of H 2 PO 4 - ions on their surface. This reaction pathway is also of importance with respect to the new manganese oscillator which is based on the autocatalytic oxidation of Mn(II) ions by periodate in a CSTR.