Analysis of Naphthenic Acid-Salt Interactions in Simulated Oil Sands Process Water

The extraction of bitumen from oil sands involves the use and reuse of large volumes of water. When water reaches a point where it can no longer be recycled, it is termed oil sands process-affected water (OSPW). OSPW contains a mixture of residual hydrocarbons, including naphthenic acids, and has elevated salinity. This work presents new insights based on a laboratory-based study of how salinity influences the naphthenic acid compounds observed in water. Laboratory bench-scale simulations were set up to measure how water chemistry changes, with both time and under different salt conditions, using Milli-Q water and a simulated OSPW water matrix. Samples were analyzed for basic water chemistry and by high-resolution Orbitrap mass spectrometry. Data are discussed with regard to overall quantification of organic species and naphthenic acid fraction compounds (NAFCs) in the water, as well as by hydrocarbon class, double-bond equivalent, and carbon number. Mass spectral quantitation and characterization showed that the presence of salts and ions in the simulated OSPW (i) increases the concentration of measured species and (ii) changed the relative distribution of oxygenated polar hydrocarbons. For example, a depletion of the aqueous O2-NAFCs occurred over time with a corresponding increase in the levels of the aqueous O3-NAFCs in saline waters. These findings on temporal changes in concentration and molecular level distributions of NAFCs may have implications for the clean-up and remediation of saline OSPW.