Measurement of Hydroxyl Radical Activity in a Soil Slurry Using the Spin Trap α-(4-Pyridyl-1-oxide)- N-tert-butylnitrone

The spin trap compound α-(4-pyridyl-1-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 × 10-15 and 6.5 × 10-16 M, when 4-POBN was initially present at 700 and 1440 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 ...