Kinetic model for sulfate/hydroxyl radical oxidation of methylene blue in a thermally-activated persulfate system at various pH and temperatures
Sustain. Environ. Res., 22(4), 199-208 (2012)
Chen-Ju Liang and Shun-Chin Huang
Sodium persulfate, chemical oxidation, groundwater, remediation
Sulfate and hydroxyl radicals (SO4-· and ·OH) can be generated in the thermally activated persulfate oxidation system depending upon pH conditions. The objective of this study was to derive a kinetic model for the reaction of SO4-· and ·OH with a model compound, methylene blue (MB), and to determine the reaction rate constant, radical concentrations and activation energies under various temperatures (60, 70 and 80 °C ) and pH levels (pH 3, 7, and 11). Experiments performed and data analyzed using the developed kinetic model exhibited second-order rate constants for the reaction of MB with the predominant SO4-· at pH 3 of 0.34 × 108, 1.01 × 108, and 2.20 × 108 M-1 s-1 at 60, 70, and 4 80 °C, respectively. Average steady state concentrations of SO4-· and ·OH were determined: 4.36 × 4 10-6 M for predominant SO4-· at acidic pH; 6.68 × 10-11 and 1.18 × 10-10 M, respectively, for simultaneous presence of SO4-· and ·OH at neutral pH; 2.68 × 10-12 and 1.15 × 10-6 M, respectively, for SO4-· and ·OH at basic pH. Furthermore, activation energies were determined over the temperature range 60-80 °C: 87, 109, and 90 kJ mol-1 at pH 3, 7, and 11, respectively. This study successfully derived a kinetic model which can be used in a thermally-activated persulfate oxidation system for treating different compounds.