Ferrate oxidation of distinct naphthenic acids species isolated from process water of unconventional petroleum production.

Distinct naphthenic acid (NA) species were isolated from oil sands process water (OSPW) into 20 fractions via silver-ion solid phase extraction, prior to treatment using potassium ferrate(VI). Untreated and treated fractions F1-F20 were characterized using ultra performance liquid chromatography traveling-wave ion mobility time-of-flight mass spectrometry to identify classical NAs (aliphatic O ₂ -NAs mainly found in fractions F1-F4), aromatic NAs (aromatic O ₂ -NAs in F6-F9), oxidized NAs (O ₃ -, O ₄ -, and O ₅ -NAs in F14-F17), and sulfur-containing NAs (F16-F19). The Fe(VI) oxidation reactivity of individual NA species was studied with minimized confounding effects from the complicated OSPW matrix. Aliphatic and aromatic O ₂ -NAs were found to have different reactivity towards Fe(VI) oxidation, with removals ranging from <50% up to 90% at 200 mg/L ferrate dose. The O ₃ -NAs and O ₄ -NAs from raw OSPW were recalcitrant species with slight degradation under Fe(VI) oxidation conditions. The Fe(VI) oxidation of O ₂ -NAs generated new O ₃ -NAs as byproducts or intermediate byproducts which finally resulted in more oxygen-rich O _x -NAs as the final byproducts depending on the Fe(VI) doses. Besides the obtained knowledge on chemical reactivity, current methodology (i.e., treatment of Ag-ion fractions of OSPW versus raw OSPW) could be applied to evaluate other treatment approaches as well as toxicity of distinct NA species for environmental applications.
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