Résumé - Abstract:

Fluid fine tailings (FFT) generated during bitumen extraction are eventually incorporated into aquatic and terrestrial reclamation landforms. The FFT contains inorganic solids, oil sands process-affected water (OSPW) and residual bitumen. The solids contents, which range from 25% to 35 % (w/w), are dominated by clay minerals (i.e., kaolinite, illite, and illite-smectite mixed layer) and quartz with minor carbonates, trace sulfides and oxides. Associated OSPW contains elevated concentrations of Na⁺, Cl^-, HCO₃^-, and NH₄⁺, plus trace elements, naphthenic acid (NAs), and residual hydrocarbons. The elevated concentrations of Na⁺ relative to other cations hinder clay minerals from aggregating. The resulting slow settlement and dewatering behaviour impede progressive reclamation. Consequently, FFT inventories in tailings ponds roughly doubled to 1.27 billion m³ from 2009 to 2019. Regulators have issued directives intended to curtail these growing inventories and promote progressive mine reclamation. These directives, coupled with slow settlement behaviour, prompted oil sands operators to develop various dewatering technologies to manage fluid tailings inventories in active tailings ponds and promote progressive reclamation. These technologies often utilize chemical coagulants and flocculants, yet their impacts on water chemistry and gas production are poorly understood. This research uses batch experiments to examine how different coagulants (i.e., alum [Al₂(SO₄)₃.nH₂O], ferric sulfate [Fe₂(SO₄)₃.nH₂O], and gypsum [CaSO₄.2H₂O]) and doses (i.e., 0, 500, 1000, and 1500 ppm) affect FFT geochemistry, mineralogy and microbiology over time. We found that protons contributed by initial acidic solutions and hydrolysis of Al³⁺ and Fe³⁺ promote carbonate-mineral dissolution and associated increases in dissolved Ca²⁺, Mg²⁺ and Fe²⁺ concentrations. For the 1000 and 1500 ppm alum batches, the addition and generation of protons consume the acid neutralization potential of the carbonates, and pH consistently decreases below 6. For all other batches, pH remains above 6 and sulfate reduction and sulfide-mineral precipitation influence water chemistry. Sulfate reduction inhibited methanogenesis in batches where SO₄ concentrations remained above ~60 mg L⁻¹. Additionally, H₂S concentrations decrease in all alum and ferric sulfate batches with elevated Fe²⁺ concentrations and increase with gypsum batches where Fe²⁺ concentrations are limited. These results improve our understanding of the biogeochemical implications of chemical coagulants used by the oil sands industry and offer opportunities for improving geochemical outcomes of FFT dewatering technologies.

Biographie du présentateur - Biography of the presenter: Philip Adene is a Ph.D. candidate in Geology at the University of Saskatchewan, Canada, with a research interest in Environmental Geochemistry. He is a member of the NSERC TERRE-NET program; project id: 5d. Working with Dr. Mathew Lindsay, Philip’s research focuses on the impact of chemical coagulation on water chemistry in oil sands fluid fine tailings deposits. He obtained a Master of Science degree in Geological Sciences from Queen’s University, Canada and a Bachelor of Technology in Applied Geology from the Federal University of Technology, Akure, Nigeria. Philip did his master’s research project in exploration geochemistry under the supervision of Dr. Kurt Kyser. During this time, he used techniques like basin analysis, isotope geochemistry and the geochemical analysis of organic matter to evaluate the possibility of Uranium deposits at Hawk Rapids, Athabasca Basin, Saskatchewan, Canada. Philip aspires to work in Research and Development with the hopes to uncover innovative solutions to environmental issues.

Language: English

Menu

Mr. Philip Adene