Identifying the mechanism of tailings dewatering by lime using surface vibrational spectroscopy

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The Athabasca oil sands are one of the largest oil reserves in the world. Yet one challenge in the oil sands**extraction process is how to deal with the large quantities of waste material. This waste, referred to as fine**tailings, consists of fine sand and clay particles as well as water, residual oil, and additives and salts used in**extraction. After the extraction process, a large fraction of water remains strongly bound to the sand and clay**particles, leading to a sludge consistency, which makes reclamation of tailings ponds difficult. Indeed, the**amount of water needs to be reduced to <20% by mass for the tailings solids to be able to bear the weight**required for land reclamation (i.e. ability to sustain top soil, vegetation, roads, etc.). There are currently no**commercial solutions to reliably achieve this target for oil sands fine tailings. However, recently researchers of**Graymont Western Canada Inc. (Graymont), a Canadian-owned company that specializes in the use of lime,**found that lime addition followed by pressure treatment led to facile dewatering of tailings, yielding tailings**solids with low water content and high strength. To understand this remarkable phenomenon, we will utilize**the surface-specific spectroscopic technique in our lab: vibrational sum frequency generation (SFG). SFG is**sensitive to the amount of water ordered at interfaces, and we hypothesize that it is the ideal tool to monitor**dewatering, which is water released from clay and sand surfaces. We will explore the amount of surface**associated water on silica and clay-particle coated silica as a function of lime concentration in the presence and**absence of bicarbonate. Furthermore, we will look for signatures of salts directly interacting at the clay/water**interface and correlate these results with tailings settling and dewatering measurements and surface potential**analysis. The ultimate goal is to facilitate the expansion of Graymont into tailings treatment based on our**ability to characterize the mechanism of tailings dewatering by lime. This collaboration will benefit Canada by**demonstrating a solution that accelerates the reclamation of oil sands tailing ponds, minimizing the**environmental impact on the Wood Buffalo region.