Characterization and Dynamics of Residual Organics in Oil Sands Fluid Fine Tailings

Fluid fine tailings (FFTs) generated by the surface mining of oil sand ore bodies are high-water-content, clay-rich materials that contain unrecovered bitumen and additional residual organics, including solvents used during bitumen extraction. Despite a large accumulated inventory of these tailings and despite the environmental implications and challenges that the presence of organics poses, little is known about the differences in the residual organics generated by different bitumen extraction processes and about the effects of polymeric flocculation on mineral-organic interactions. This study investigated residual organics in two compositionally different FFTs both before and after flocculation with a commercially available polyacrylamide polymer. Thermogravimetric (TG) analysis, Fourier transform infrared (FTIR) spectroscopy, and evolved gas analysis (EGA-TG-FTIR) were used to characterize the makeup of total organics, free bitumen, and mineral-associated organics. These observations highlighted distinct differences between the FFTs. Relative to the sample receiving waste only from the bitumen extraction process (FFT-1), the FFT sample that received waste from both the extraction and the froth treatment processes (FFT-2) exhibited a higher residual organic content and a larger fraction of lower-molecular-mass organic substances and showed a proportionally smaller release of free bitumen as a result of the washing process, evidence of a higher fraction of mineral-associated organics. Moreover, TG and FTIR analyses showed that the free bitumen released from both FFTs contained a higher fraction of lighter organics and was characterized by a more ordered molecular structure compared to the remaining organics. Finally, the study also found that the bitumen release characteristics of FFT-1 were fundamentally different from those of FFT-2. Bitumen release continued to be observed from both FFTs after polymeric flocculation.