Electronic Thesis and Dissertation Repository

Degree

Master of Engineering Science

Program

Civil and Environmental Engineering

Supervisor

Julie Shang

Abstract

Oil Sands Mature Fine Tailings (MFT) are generated from extraction of bitumen from oil sands. Fine tailings contain significant fraction of clay minerals, which makes dewatering and consolidation difficult and time-consuming. In this thesis, chemical stabilization of MFT is investigated in an experimental program. Portland cement (PC) and two liquid-based silicate grouts (NS and AAAS) are used for stabilization of MFT. The effectiveness of these stabilizers at different dosages and curing durations is assessed by conducting a series of laboratory tests in terms of the undrained shear strength (Su) and solid content (S%), plasticity and pore fluid chemistry. The gel time and gel syneresis of silicate grouts are studied. Scanning electron microscopy (SEM) observations and X-ray diffraction (XRD) analyses are conducted to understand the microstructural changes in MFT after chemical stabilization.

The results indicate that the inclusion of Portland cement or silicate grouts increases the solid contents and Atterberg limits of MFT. The undrained shear strength of MFT after chemical treatment increases up to 7.65 kPa with 10% PC, 15.5 kPa with 15% PC, 7.55 kPa with 15% NS and 5.5 kPa with 8% AAAS after 28 days of curing period. The pH of MFT paste increases after chemical treatments. Furthermore, SEM analyses indicate that after chemical treatment by Portland cement, fibrous cement hydrates (CS- H gel) formed during stabilization process bind the MFT particles together, while after the treatment of silicate grouts, gelling products with undulating and irregular shapes serve as cementation agent. The XRD analysis of MFT shows that clay minerals’ peak intensities in XRD patterns reduce after chemical stabilization. The results also indicate the additional C-S-H peaks in cement-MFT mixtures but show no new secondary mineral formations in silicate-MFT mixtures.


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