Oil Sands Tailings Research Articles

Strategies for Hydrocarbon Removal and Bioleaching-Driven Metal Recovery from Oil Sand Tailings

Oil sand tailings from bitumen extraction contain various contaminants, including polycyclic aromatic hydrocarbons, BTEX, and naphthenic acids, which can leak into surrounding environments, threatening aquatic ecosystems and human health. These tailings also contribute to environmental issues such as habitat disruption and greenhouse gas emissions. Despite these challenges, oil sand tailings hold significant potential for waste-to-resource recovery as they contain valuable minerals like rare earth elements (REEs), titanium, nickel, and vanadium. Traditional metal extraction methods are environmentally damaging, requiring high energy inputs and generating dust and harmful emissions. Furthermore, the coating of hydrocarbons on mineral surfaces presents an additional challenge, as it can inhibit the efficiency of metal extraction processes by blocking access to the minerals. This highlights the need for alternative, eco-friendly approaches. Bioleaching, which uses microorganisms to extract metals, emerges as a sustainable solution to unlock the valuable metals within oil sand tailings. This review discusses the minerals found in oil sand tailings, the challenges associated with their extraction, methods from hydrocarbon removal from minerals, and bioleaching as a potential metal recovery method.

Short‐term survival and growth of 32 native boreal plants on treated oil sands tailings

AbstractThe consolidation of oil sands tailings is a cost‐ and time‐consuming process that requires treatment via active (e.g., centrifugation) and passive (e.g., self‐weight consolidation) methods. The use of plants to dewater tailings is a promising concept and has previously been evaluated using agronomic grass species in greenhouse studies. This greenhouse study evaluated the short‐term survivorship and growth of 32 upland and lowland native plant species (12 forbs, 14 graminoids, and six woody plants) in centrifuged tailings and benchmarked their performance against reclamation soil and undisturbed forest soil. All plant species were propagated from seed and transplanted as seedlings into containers filled with one of the three substrates. After 42 days, the height (woody species only) and total aboveground biomass were determined for all living plants. As expected, the mortality of seedlings in tailings was higher than plants grown in the other two substrates. Graminoid species, regardless of species community type (wetland or upland), had higher survival probabilities and growth compared to forb or woody species across all substrates. Of forbs and woody species evaluated, Geum aleppicum and Populus tremuloides showed the most promise amongst the upland species, and Rumex occidentalis was the wetland equivalent.

Exploring Soil–Water Characteristic Curves in Transitional Oil Sands Tailings

Soil–water characteristics curves (SWCC) have proved useful in estimating parameters used in modeling unsaturated geotechnical properties of soils including permeability and strength. Either saturation, gravimetric, and instantaneous and initial volumetric water content designation can be used to develop SWCCs. Studies have shown that any of the designations will give good estimates for soils that do not undergo volume change with suction change whereas, for soils that undergo substantial volume change, only saturation and instantaneous volumetric water content designation obtained by incorporating shrinkage curves can give correct estimates. Transition oil sands tailings have fines content that cannot be categorized as sandy or fine materials, and research on volume change with suction change in these materials is limited. In this study, HyProps, Tempe cells, and a chilled-mirror water potential meter were used to measure suction and corresponding water contents for samples that were prepared by mixing coarse sand and Fluid Tailing by ratios that mimic transition zone tailings. Shrinkage tests were also performed to observe the extent of volume change with suction increase. Air Entry Values (AEV) estimated from SWCCs based on gravimetric water content were found to be lower than those estimated from saturation-based SWCCs due to substantial volume changes in these materials with suction increase. The use of saturation water content designation is recommended in estimating AEV for transitional oil sands tailings. This is useful information in predicting the long term unsaturated geotechnical behavior of these materials for environmental management and safety purposes.

Effects of pressure on the biogeochemical and geotechnical behavior of treated oil sands tailings in a pit lake scenario

Reclamation options for oil sands fluid fine tailings (FFT) are limited due to its challenging geotechnical properties, which include high water and clay contents and low shear strength. A feasible reclamation option for tailings with these properties is water capped FFT deposits (pit lakes). A relatively new proposal is to deposit FFT that has been treated with alum and polyacrylamide in pit lakes. Though over 65 Mm3 of alum/polyacrylamide treated FFT has been deposited to date, there is limited publicly available information on the biogeochemical and geotechnical behavior of this treated FFT. Further, the effects of pressure from overlying tailings on microbial activity and biogeochemical cycling in oil sands tailings has not been previously investigated. Twelve 5.5 L columns were designed to mimic alum/polyacrylamide treated FFT deposited beneath a water cap. A 2x2 factorial design was used to apply pressure and hydrocarbon amendments to the tailings. Pressure (0.3–5.1 kPa) was applied incrementally and columns were monitored for 360 d. Pressure significantly enhanced consolidation and microbial activity in treated FFT. Columns with pressure generated significantly more CH4(g) and CO2(g) and had significant increases in dissolved organic carbon and chemical oxygen demand in the FFT and water caps. The enhanced microbial activity in columns with pressure indicates that pressure increased the solubility of microbial substrates and metabolites in the tailings, thereby increasing the bioavailability of these compounds. Ammonium generation was significantly higher in columns with pressure, suggesting that microorganisms utilized polyacrylamide and/or N2 fixation as a nitrogen source to meet enhanced nutrient demands. Pressure also impacted microbial community structure, shifting methanogenic communities from hydrogenotrophic methanogens to predominately acetoclastic methanogens. This study also revealed the importance of sulfur cycling in treated FFT. Extensive sulfate reduction occurred in all columns, generating dissolved sulfides and H2S(g), and this was accelerated by hydrocarbon amendments.

Effects of size and composition of bitumen drops on intra-oil diffusion and dissolution of hydrocarbon solvents in froth treatment tailings ponds

The rate of mass transfer of lower molecular weight hydrocarbons (naphtha) from bitumen drops in mature fine tailings of oil sand tailings ponds (OSTPs) may control their bioavailability and the associated rate of GHG production. Experiments were conducted using bitumen drops spiked with o-xylene and 1-methylnaphthalene to determine the mass transfer rate of these naphtha components from bitumen drops. The results were compared to simulations using a multi-component numerical model that accounted for transport in the drop and across the oil-water interface. The results demonstrate rate-limited mass transfer, with aqueous concentrations after 60 days of dissolution that were different than those in equilibrium with the initial drop composition (less for o-xylene and greater for 1-methylnaphthalene). The simulations suggest that mole fractions were unchanged at the center of the drop, resulting in concentration gradients out to the oil-water interface. Numerical simulations conducted using different drop sizes and bitumen viscosities also suggest the potential for persistent naphtha dissolution, where the time required to deplete 80% of the o-xylene and 1-methylnaphthalene mass from an oil drop was estimated to be on the order of months to years for mm-sized drops, and years to decades for cm-sized drops assuming instantaneous biodegradation in the aqueous phase surrounding the bitumen.

Effects of Coal Particles on Microbubble-Enhanced Bitumen Separation in the Concentrated Slurry Flow of Oil Sands Tailings

Effects of Coal Particles on Microbubble-Enhanced Bitumen Separation in the Concentrated Slurry Flow of Oil Sands Tailings

Molecular and microbial insights towards anaerobic biodegradation of anionic polyacrylamide in oil sands tailings

Anionic polyacrylamide (A-PAM) is widely used as a flocculant in the management of oil sands tailings. Nevertheless, apprehensions arise regarding its potential biodegradation and environmental consequences within the context of oil sands tailings. Consequently, it is imperative to delve into the anaerobic biodegradation of A-PAM in oil sands tailings to gain a comprehensive understanding of its influence on tailings water quality. This work explored the dynamics of A-PAM biodegradation across concentrations: 50, 100, 250, 500, 1000, and 2000 mg/kg TS. The results showed a significant decrease in A-PAM concentration and molecular weight at lower concentrations (50 and 100 mg/kg TS) compared to higher ones, suggesting enhanced degradation efficiency. Likewise, the organic transformation and methane production exhibited dependency on A-PAM concentrations. The peak concentrations observed were 20.0 mg/L for volatile fatty acids (VFAs), 0.07 mg/L for acrylamide (AMD), and 8.9 mL for methane yield, with these maxima being recorded at 50 mg/kg TS. The biodegradation efficiency diminishes at higher concentrations of A-PAM, potentially due to the inhibitory effects of polyacrylic acid accumulation. A-PAM biodegradation under anaerobic condition did not contribute to acute toxicity or genotoxicity. SEM-EDS, FT-IR and XRD analyses further revealed that higher concentrations of A-PAM inhibited the biodegradation by altering floc structure and composition, thereby restricting the microbial activity. Major microorganisms, including Smithella, Candidatus_Cloacimonas, W5, XBB1006, and DMER64 were identified, highlighting A-PAM's dual role as a source of carbon and nitrogen under anaerobic conditions. The above findings from this research not only significantly advance understanding of A-PAM's environmental behavior but also contribute to the effective management practices in oil sands tailings.

Low adsorption affinity of athabasca oil sands naphthenic acid fraction compounds to a peat-mineral mixture

Much of the toxicity in oil sands process-affected water in Athabasca oil sands tailings has been attributed to naphthenic acids (NAs) and associated naphthenic acid fraction compounds (NAFCs). Previous work has characterized the environmental behaviour and fate of these compounds, particularly in the context of constructed treatment wetlands. There is evidence that wetlands can attenuate NAFCs in natural and engineered contexts, but relative contributions of chemical, biotic, and physical adsorption with sequestration require deconvolution. In this work, the objective was to evaluate the extent to which prospective wetland substrate material may adsorb NAFCs using a peat-mineral mix (PMM) sourced from the Athabasca Oil Sands Region (AOSR). The PMM and NAFCs were first mixed and then equilibrated across a range of NAFC concentrations (5–500 mg/L) with moderate ionic strength and hardness (∼200 ppm combined Ca2+ and Mg2+) that approximate wetland water chemistry. Under these experimental conditions, low sorption of NAFCs to PMM was observed, where sorbed concentrations of NAFCs were approximately zero mg/kg at equilibrium. When NAFCs and PMM were mixed and equilibrated together at environmentally relevant concentrations, formula diversity increased more than could be explained by combining constituent spectra. The TOC present in this PMM was largely cellulose-derived, with low levels of thermally recalcitrant carbon (e.g., lignin, black carbon). The apparent enhancement of the concentration and diversity of components in PMM/NAFCs mixtures are likely related to aqueous solubility of some PMM-derived organic materials, as post-hoc combination of dissolved components from PMM and NAFCs cannot replicate enhanced complexity observed when the two components are agitated and equilibrated together.

A molecular extraction process for vanadium based on tandem selective complexation and precipitation

Recycling vanadium from alternative sources is essential due to its expanding demand, depletion in natural sources, and environmental issues with terrestrial mining. Here, we present a complexation-precipitation method to selectively recover pentavalent vanadium ions, V(V), from complex metal ion mixtures, using an acid-stable metal binding agent, the cyclic imidedioxime, naphthalimidedioxime (H2CIDIII). H2CIDIII showed high extraction capacity and fast binding towards V(V) with crystal structures showing a 1:1 M:L dimer, [V2(O)3(C12H6N3O2)2]2−, 1, and 1:2 M:L non-oxido, [V(C12H6N3O2)2] ̶ complex, 2. Complexation selectivity studies showed only 1 and 2 were anionic, allowing facile separation of the V(V) complexes by pH-controlled precipitation, removing the need for solid support. The tandem complexation-precipitation technique achieved high recovery selectivity for V(V) with a selectivity coefficient above 3 × 105 from synthetic mixed metal solutions and real oil sand tailings. Zebrafish toxicity assay confirmed the non-toxicity of 1 and 2, highlighting H2CIDIII’s potential for practical and large-scale V(V) recovery.

Uncovering Anaerobic Hydrocarbon Biodegradation Pathways in Oil Sands Tailings from Two Different Tailings Ponds via Metabolite and Functional Gene Analyses.

Oil sands tailings, a slurry of alkaline water, silt, clay, unrecovered bitumen, and residual hydrocarbons generated during bitumen extraction, are contained in ponds. Indigenous microbes metabolize hydrocarbons and emit greenhouse gases from the tailings. Metabolism of hydrocarbons in tailings ponds of two operators, namely, Canadian Natural Upgrading Limited (CNUL) and Canadian Natural Resources Limited (CNRL), has not been comprehensively investigated. Previous reports have revealed sequential and preferential hydrocarbon degradation of alkanes in primary cultures established from CNUL and CNRL tailings amended separately with mixtures of hydrocarbons (n-alkanes, iso-alkanes, paraffinic solvent, or naphtha). In this study, activation pathway of hydrocarbon biodegradation in these primary cultures was investigated. The functional gene analysis revealed that fumarate addition was potentially the primary activation pathway of alkanes in all cultures. However, the metabolite analysis only detected transient succinylated 2-methylpentane and 2-methylbutane metabolites during initial methanogenic biodegradation of iso-alkanes and paraffinic solvent in all CNUL and CNRL cultures amended with iso-alkanes and paraffinic solvent. Under sulfidogenic conditions (prepared only with CNUL tailings amended with iso-alkanes), succinylated 2-methylpentane persisted throughout incubation period of ~ 1100days, implying dead-end nature of the metabolite. Though no metabolite was detected in n-alkanes- and naphtha-amended cultures during incubation, assA/masD genes related to Peptococcaceae were amplified in all CNUL and CNRL primary cultures. The findings of this present study suggest that microbial communities in different tailings ponds can biodegrade hydrocarbons through fumarate addition as activation pathway under methanogenic and sulfidogenic conditions.

Effect of flyash addition to flocculation and freezing and thawing treatment on consolidation of oil sands fluid fine tailings

The total volume of fluid fine tailings (FFT), reached 1,270 Mm3 in 2019. Extensive research is underway by a number of operators to develop dewatering technologies for oil sand tailings reclamation to comply with Directive 085 issued by the Alberta Energy Regulator. A promising technology for the disposal of FFT is to add flocculents and then use thickeners or centrifuges to decrease the water content. Following this treatment, freezing/thawing processes can then be utilized to further dewater the tailings. The effect of flocculation/flyash addition and thickening coupled with freezing/thawing treatments on FFT was investigated by performing large-strain consolidation and shear strength tests on the treated flocculated TTs. It was found that flocculation and thickening treatment increases the hydraulic conductivity of the treated TT which will result in the TT consolidating much faster than the untreated TT. The most important benefit of the flyash addition is the increase in shear strength and hydraulic conductivity of the flyash-treated TTs. The benefit of the freezing/thawing treatment processes coupled with flyash treatment is the increase in the compressibility and hydraulic conductivity at effective stresses lower than 100 kPa and void ratios greater than 1.2, respectively. This will facilitate earlier progressive reclamation required to support hydraulic sand capping.

Using machine learning to identify indicators of rare earth element enrichment in sedimentary strata with applications for metal prospectivity

Rare earth elements (REE), classified as critical minerals which are crucial for clean energy technologies, face soaring demand. While economic deposits are found in limited geologic environments including carbonatites and ion-adsorption clays, unconventional, secondary sources such as those from sedimentary basins could hold potential to meet this increased demand. Coal and its associated combustion by-products, phosphorites, oil sands tailings, and formation waters have all garnered interest for REE recovery, yet they remain significantly underexplored. Accordingly, new tools for data analysis and optimization such as machine learning can assist in mineral prospectivity, with these tools being subject to rapid proliferation in the Earth sciences.This work leverages compositional data analysis principles and machine learning to probe geochemical relationships and predict REE abundances in sedimentary lithologies using unsupervised (correlation, principal component, and cluster analysis) and supervised (regression, support vector machine, random forest, and boosting) machine learning models. These three unsupervised models display similar results, with REE typically being associated with incompatible elements (e.g., Th, Nb, and Hf). Gradient boosting, Adaboost, and Random Forest had the highest performance for predicting REE concentrations, with Th and P commonly being the most important predictor variables. Identifying geochemical indicators of REE enrichment that may be used to assist in discovering potentially exploitable REE resources based on existing data, as well as increasing the understanding of metal behaviour in sedimentary systems, is a step forward in understanding novel secondary and unconventional REE sources. Although REE concentrations from these sources are generally lower than primary ore deposits, the amount of available feedstock, potentially simpler, cheaper, and less environmentally taxing extraction processes, and the added benefit of remediating waste streams and contributing to the circular economy make these sources alluring.

Naphthenic acid fraction compounds, produced by the extraction of bitumen from oil sands, alter survival and behaviour of juvenile yellow perch (Perca flavescens)

We evaluated whether naphthenic acid fraction compounds (NAFCs) extracted from oil sand tailings adversely affect fish survival and behaviour. Following a before–after-control-impact design, we housed wild-caught juvenile yellow perch ( Perca flavescens) in outdoor mesocosms to assess survival and behaviour under baseline conditions, then exposed fish to one of three treatments: negative control, 2 mg/L NAFC, or 15 mg/L NAFC. We performed behavioural assays (no-stimulus activity, food stimulus, and predator stimulus using a model bird) and assessed a comprehensive suite of endpoints (equilibrium losses, activity, shoaling, burst swimming, freezing, and space use). We found that exposure to 15 mg/L NAFCs substantially reduced fish survival and impaired fish equilibrium in all three behavioural tests. Furthermore, exposure to NAFCs impaired anti-predator behaviour: while the activity of control fish increased by two-fold in response to a predator stimulus, fish exposed to 2 or 15 mg/L NAFC did not change their activity levels after stimulation. No significant changes were observed in other behavioural endpoints. Overall, our findings suggest that a week-long exposure to NAFCs at concentrations commonly found in tailings ponds, constructed wetlands, and other mining-impacted waters may affect multiple facets of fish behaviour that could ultimately lead to reduced fitness in fish populations.

Aerobic biodegradation of cycloalkanes in non-aqueous extracted oil sands tailings

Management of growing volumes of fluid fine tailings (FFT) is a significant challenge for oil sands industry. A potential alternative non-aqueous solvent extraction (NAE) process uses cycloalkane solvent such as cyclohexane or cyclopentane with very little water and generates smaller volumes of ‘dry’ solids (NAES) with residual solvent. Here we investigate remediation of NAES in a simulated bench-scale upland reclamation scenario. In the first study, microcosms with nutrient medium plus FFT as inoculum were amended with cyclohexane and incubated for ∼1 year, monitoring for cyclohexane biodegradation under aerobic conditions. Biodegradation of cyclohexane occurred under aerobic conditions with no metabolic intermediates detected. A second study using NAES mixed with FFT spiked with cyclohexane and cyclopentane, with or without additional nutrients (nitrogen and phosphorus), showed complete and rapid aerobic biodegradation of both cycloalkanes in NAES inoculated with FFT and supplemented with nutrients. 16S rRNA gene sequencing revealed dominance of Rhodoferax and members of Burkholderiaceae during aerobic cyclohexane biodegradation in FFT, and Hydrogenophaga, Acidovorax, Defluviimonas and members of Porticoccaceae during aerobic biodegradation of cyclohexane and cyclopentane in NAES inoculated with FFT and supplemented with nutrients. The findings indicate that biodegradation of cycloalkanes from NAES is possible under aerobic condition, which will contribute to the successful reclamation of oil sands tailings for land closure.

Numerical Insights from a Population Balance Model into the Distribution of Bitumen Residues in Industrial Horizontal Pipes During the Hydrotransport of Oil Sands Tailings

Numerical Insights from a Population Balance Model into the Distribution of Bitumen Residues in Industrial Horizontal Pipes During the Hydrotransport of Oil Sands Tailings

Inhibition of methanogenesis through redox processes in oil sands tailings

Inhibition of methanogenesis through redox processes in oil sands tailings

Drained instability of coarse oil sand tailings

Lateral stress relief and effective stress reduction have been recognised as the culprits in flow failures of several mine tailings dams. This research examines the instability of coarse oil sand tailings (CSTs) subjected to such a stress path through a series of monotonic direct simple shear tests. To investigate the impact of tailings fabric, laboratory specimens were reconstituted by moist-tamping, air pluviation and slurry deposition techniques. Loose, medium-dense and dense specimens were prepared and consolidated to target vertical and initial shear stresses. The vertical stress was subsequently unloaded while maintaining a constant initial shear stress under a drained condition. The occurrence of instability coincided with the volumetric collapse of the specimens followed by a sharp rise in shear strain. The effects of consolidation stress, bitumen, void ratio, initial shear stress and unloading rate on the drained instability of CST specimens were also investigated.

Exploring Alternatives to Polyacrylamide: A Comparative Study of Novel Polymers in the Flocculation and Dewatering of Iron Ore Tailings.

Despite being widely used in tailings treatment, polyacrylamide continues to face performance challenges. In this study, two commercial polyacrylamides with different molecular weights were used to flocculate iron ore tailings and their performance was compared with two polymers designed to treat oil sand tailings: poly(vinylbenzyl)trimethylammonium chloride and partially hydrolyzed poly(methyl acrylate) grafted onto ethylene-propylene-diene copolymer backbones. The polyacrylamide with the highest molecular weight performed better than the one with the lowest molecular weight, but its efficiency was still considerably lower than what would be desired for good solid-liquid separation. The new polymer flocculants performed better than the commercially available polyacrylamides but retained high amounts of water in the sediments. This comparison shows that polymers other than polyacrylamide may be used to treat iron ore tailings.

Microbial community structural and functional differentiation in capped thickened oil sands tailings planted with native boreal species.

The oil sands mining operations in Alberta have produced billions of m3 of tailings which must be reclaimed and integrated into various mine closure landforms, including terrestrial landforms. Microorganisms play a central role in nutrient cycling during the reclamation of disturbed landscapes, contributing to successful vegetation restoration and long-term sustainability. However, microbial community succession and response in reconstructed and revegetated tailings remain largely unexplored. This study aimed to monitor the structural and functional responses of microbial communities in tailings subjected to different capping and vegetation strategies over two growing seasons (GS). To achieve this, a column-based greenhouse experiment was conducted to investigate microbial communities in tailings that were capped with a layer (10 or 30 cm) of peat-mineral mix (PMM) and planted with either upland or wetland communities. DNA metabarcoding analysis of the bacterial 16S rRNA gene and fungal ITS2 region as well as shotgun metagenomics were used to asses the impact of treatments on microbial taxonomy and functions, respectively. Results showed that tailings microbial diversity and community composition changed considerably after two GS compared to baseline samples, while communities in the PMM capping layer were much more stable. Likewise, several microbial functions were significantly enriched in tailings after two GS. Interestingly, the impact of capping on bacterial communities in tailings varied depending on the plant community, leading to a higher number of differentially abundant taxa and to a decrease in Shannon diversity and evenness in the upland treatment but not in the wetland treatment. Moreover, while capping in the presence of wetland vegetation increased the energy-related metabolic functions (carbon, nitrogen, and sulfur), these functions were depleted by capping in the upland treatment. Fungi represented a small proportion of the microbial community in tailings, but the relative abundance of several taxa changed over time, while the capping treatments favored the growth of some beneficial taxa, notably the root endophyte Serendipita, in both upland and wetland columns. The results suggest that selecting the right combination of capping material and vegetation type may contribute to improve below-ground microbial processes and sustain plant growth in harsh environments such as oil sands tailings.

Using polymer adsorption data and a population balance model to estimate how polymer dosage affects the flocculation of oil sands tailings

AbstractPopulation balance models can describe how particles aggregate and fragment during the flocculation of mineral tailings. We used a new method to estimate some of the parameters in a population balance model describing the flocculation of oil sands mature fine tailings with poly(vinyl benzyl trimethylammonium chloride). Differently from previous population balance models, the polymer adsorption data onto the particles suspended in the tailings were used to estimate a fundamental parameter relating polymer dosage to the mean diameter of the aggregates formed during flocculation. The model could predict the flocculation behaviour of three polymer samples with different molecular weights. This model is another step toward a quantitative understanding of how polymer properties affect the flocculation of mineral tailings.