Novel mature fine tailings treatment using colloidal silica particles

Abstract

The oil sands tailings industry currently employs a vast array of technologies ranging from flocculation/coagulation to traditional mechanical techniques such as filtration or centrifugation. The performance of the treatment options, alone or in combination, have proven to be challenging for practical implementation with reliable results in terms of sediment compactness levels, water release, and strength development due to unpredictable tailings composition, solids content, and clay activity levels. As a new and promising treatment route, the application of silica particles for tailings clay densification has not been studied in depth and governing treatment mechanisms are unknown. The study presented here focused on understanding the effects of addition of monodisperse bare colloidal silica particles on the structural and rheological properties of highly stable mature fine tailings (MFT) with the end goal of colloidal suspension destabilization and subsequent water release. A simple mixing regime involving addition of CSPs and NaOH to the MFT at different stages was developed. Controlled experiments showed synergistic effect of CSPs and NaOH in the destabilization and flocculation of MFT over the course of a day whereas the addition of CSPs or NaOH alone did not cause the same effect. Final pH of the suspension was fixed at 10 which triggered the dissolution of ionic species from the CSPs and clay particles thereby causing polycondensation reaction and produced strong aggregates. The characterization by confocal microscopy and SEM as well as rheometry confirmed the presence of three different layers having varying compaction levels and strength with the bottom layer being the strongest and readily reclaimable. Higher dosage of CSPs in the MFT resulted in the formation of a bi-layered structure in the sediment sludge. The specific way in which the destabilization was induced and its governing mechanisms resulted in the liberation of residual bitumen from the MFT which can potentially minimize the GHG emissions from the tailings ponds. The results reported in this thesis give significant new insights into the mechanism and efficiency of MFT flocculation using CSPs that applied alone or in combination with other techniques could lead to better tailings management.