The spin trap-compound α-(4-pyridy-M-oxide)N-tert-butylnitrone (4- POBN) served as a probe to estimate the activity of Fenton-derived hydroxyl radicals (·OH) in a batch suspension comprised of silica sand and crushed goethite ore. The rate of probe disappearance was used to analyze system kinetics and oxidation efficiency under heterogeneous, Fenton-driven conditions. The ·OH-(4-POBN) adduct produced by the reaction of 4-POBN with ·OH was observed via electron paramagnetic resonance to confirm the mechanism of 4-POBN transformation. The disappearance of 4-POBN with ·OH in the sand/goethite slurry amended with H2O2 (150 mM) was first-order in 4- POBN. Under the conditions of this experiments, the effective steady-state ·OH concentration ([·OH](ss)) was estimated at 1.2 x 10-15 and 6.5 x 10- 16 M, when 4-POBN was initially present at 700 and 144 μM, respectively. Observed kinetics were in qualitative agreement with a conceptual model in which H2O2 is consumed in both Fenton and non-Fenton reactions and 4-POBN competes with other slurry constituents for ·OH. Reaction of H2O2 with ·OH was an appreciable sink for ·OH, but the reaction did not contribute significantly to H2O2 depletion. Nonproductive reactions involving H2O2 (those that did not contribute to ·OH production) represented a significant source of overall reaction inefficiency, as defined.
ASJC Scopus subject areas
- Environmental Chemistry