Characterization, quantification and distribution assessment of naphtha-range compounds in oil sands-related samples

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Residual naphtha from oil sands bitumen extraction persists in fluid fine tailings (FFT) within tailings reclamation sites including Syncrude’s Base Mine Lake Demonstration (BML), the first full-scale pit lake in the Alberta oil sands region. Understanding the composition and distribution of residual naphtha is essential for evaluating its persistence, mobility, and potential to influence the biogeochemical processes, especially methanogenesis occurring within aquatic tailings reclamation systems. Here we characterized naphtha samples by comprehensive two-dimensional gas chromatography (GC×GC) and optimized an analytical protocol to extract and analyze naphtha-range compounds from FFT. Using this method, we assessed bitumen-water partitioning coefficients (K BW ) of naphtha as well as the spatial distribution of naphtha-range compounds within BML FFT. The predominant constituents in the naphtha were C7-C10 n- , iso- , cycloalkanes, and BTEX compounds. The log KBW of total naphtha-range compounds was 2.81 ± 0.08 in ultrapure water and 3.46 ± 0.01 in oil sands process-affected water (OSPW). Thus, naphtha will be adsorbed/ partitioned into the bitumen phase in the presence of OSPW within FFT or in the presence of freshwater that may develop within the lake in future. Residual naphtha concentrations in BML FFT varied from 17 to 3200 µg/g of FFT within and between sites. The weak correlation between naphtha and bitumen contents within BML FFT indicates varying naphtha contents within FFT bitumen, but such bitumen still represents a long-term source of naphtha-range compounds that can participate in degradation and transport processes within the system. • Diluent naphtha mainly contains C7–C10 n- alkanes and BTEX, with minor iso- and cycloalkanes. • Adding ultrapure water and vigorous mixing improved extraction of naphtha-range compounds from tailings. • Residual naphtha is strongly adsorbed to bitumen in oil sands tailings based on partitioning assessment. • Residual naphtha occurs at variable concentrations within the upper 4 m of Base Mine Lake tailings. • Naphtha concentrations are decoupled from bitumen content due to heterogeneity and weathering processes.