Correlating macroscopic rheological behaviour to microstructure of polymer flocculated Mature Fine Tailings (MFT)
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2021-01-28
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Abstract
Northern Alberta holds over 178 million barrels of proven oil reserves in the form of oil sands. However, these deposits require extensive processing to extract the bitumen and result in generation of vast amount of tailings waste. The growing inventory of tailings represents a huge oil sands industry liability and an enormous environmental issue due to the associated GHG emissions and potential pollution of water bodies in their vicinity. Treatment of tailings with polymers (combined with other processes such as thin-lift drying, atmospheric fines drying) is one of the preferred methods for capturing the suspended solids and releasing the trapped water. However, the fundamental understanding of microstructure of the sludge formed after polymer treatment (i.e. flocculation) is still lacking. The microstructural information is vital for designing enhanced flocculation procedures. In this study, the microstructural and rheological parameters were utilized to understand the effect of processing conditions on the polymer flocculation of mature fine tailings (MFT). Laser scanning confocal microscope (LSCM) was used to capture 3-D images of sludge fabric and microstructural parameters (i.e. porosity and fractal dimension). Oscillatory amplitude sweep tests were performed to acquire rheological signature of the flocculated samples. The effect of overshearing as well as ionic strength of the polymer solution was investigated. It was shown that as the over-shearing time increased from 30 sec to 210 sec, the porosity of flocculated MFT increased from 18.77% to 31.26% and the fractal dimension decreased from ~2.903 to ~2.869. An explicit link between microstructural and rheological parameters was established, wherein bond breakage was quantified both at micro and macro scales. This information can be used to optimize energy input, increase water release and improve sediment strength in MFT flocculation procedures. Flocculation experiments done with process water showed that ionic strength of the process water utilized for polymer dissolution by itself does not change polymer configuration significantly (as compared to model process water) to change the strength of sludge appreciably. However, dilution of MFT resulted in lower sludge strength post flocculation, but these differences became negligible after aging the samples for 30 days due to consolidation effects.
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Nagial, R. (2020). Correlating macroscopic rheological behaviour to microstructure of polymer flocculated Mature Fine Tailings (MFT) (Master's thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.