Determination of Naphthenic Acids in Oil Sands Tailings: Extraction, Cleanup, and Molecular Characterization

This study reports an optimized workflow for the quantitative profiling of naphthenic acids (NAs) in oil sands tailings. Systematic screening of solvent composition and agitation conditions identified two successive leaches with 0.5 M NaOH, each shaken orbitally for 40 min, as the most efficient protocol for liberating NAs from freeze-dried solids. The alkaline extracts were purified on hydrophilic–lipophilic balance cartridges and eluted with formic-acidified methanol, followed by reconstitution of the dried fraction in 1:1 methanol–water, with maximized recovery. Purified samples were resolved by ultraperformance liquid chromatography and interrogated with quadrupole time-of-flight mass spectrometry. With application to three representative waste streams, fluid fine tailings (FFT), mature fine tailings (MFT), and FFT treated in a permanent aquatic storage structure, the method yielded total NA concentrations of 56–112 mg kg–1. Despite these differences in abundance, all tailings shared congruent class distributions (O2–O6) and nearly identical carbon-number and double-bond-equivalent (Z number) patterns for the dominant O2 family, irrespective of the mine source. The protocol affords a robust, high-throughput tool for routine surveillance of NA speciation in oil sands tailings, enabling operators to track compositional evolution during treatment and to inform evidence-based reclamation strategies.