Stability of hydrogen peroxide in sodium carbonate solutions

The rate of decomposition of hydrogen peroxide has been measured in aqueous, concentrated (0.1–1M) reagent-grade sodium carbonate liquors and compared with that in sodium hydroxide liquors at the same pH, temperature, and ionic strength. Over the ranges of temperature (303–323 K), pH (10.0–10.6), and ionic strength (1.5–3.0M), and without peroxide-stabilizing additives, hydrogen peroxide decomposes about nine times faster in the carbonate liquor than in caustic liquor. In the absence of stabilizing additives, the average first-order reaction rate constant for peroxide decomposition in carbonate liquors was 60 E–5 ± 10 E–5 s. Peroxide decomposition in carbonate liquor, which is probably caused by catalytic metal ions, is slowed by conventional alkaline peroxide-stabilizing agents (MgSO4, Na2SiO3, and DTPA). However, the carbonate (or bicarbonate) anion per se also appears to have a role in this system, which differentiates carbonate from caustic liquors in pulp brightening and bleaching systems. The fast decomposition of peroxide in carbonate liquor is suppressed by addition of high concentrations of magnesium, such that the addition of 400 ppm Mg (313 K, pH = 10.3, ionic strength = 2.25M) reduces the estimated first-order rate constant for peroxide decomposition at 313 K from about 50 E–5 to 0.05 E–5 s.