Persulfate persistence under thermal activation conditions

Contaminant destruction with in situ chemical oxidation (ISCO) using persulfate (peroxydisulfate, S₂O₈^2-) can be enhanced by activation, which increases the rate of persulfate decomposition to sulfate radicals (SO₄^•-). This step initiates a chain of radical reactions involving species (including SO₄ ^•- and OH^•) that oxidize contaminants more rapidly than persulfate does directly. Among current activation methods, thermal activation is the least well studied. Combining new data for environmentally relevant conditions with previously published data, we have computed three sets of Arrhenius parameters (In A and E_act) that describe the rate of persulfate decomposition in homogeneous solutions over a wide range of temperature and pH. The addition of soil increases the decomposition rate of persulfate due to reactions with organic matter and possibly mineral surfaces, but the kinetics are still pseudo-first-order in persulfate and conform to the Arrhenius model. A series of respike experiments with soil at 70°C demonstrate that once the oxidant demand is met, reaction rates return to values near those observed in the homogeneous solution case. However, even after the oxidant demand is met, the relatively short lifetime of the persulfate at elevated temperatures (e.g., >50°C) will limit the delivery time over which persulfate can be effective.