Bitumen is highly viscous and metal-rich, requiring upgrading prior to refinery processing and pipeline transport. In this study, bitumen was treated in a batch autoclave reactor under base-case thermal, supercritical water (SCW, >= 374 degrees C), and combined supercritical carbon dioxide-supercritical water (SCCO2-SCW) conditions to evaluate viscosity reduction and trace-metal redistribution. Product phases were characterized for viscosity, density, American Petroleum Institute (API) gravity, coke yield, trace-metal partitioning, and phase-specific elemental mass distributions among upgraded bitumen, coke, and aqueous phases. Transition into the SCW regime (>= 375 degrees C) reduced viscosity from 5.7 & times; 10(5) cP to < 20 cP and increased API gravity from 9 degrees to > 23 degrees, achieving substantial viscosity reduction and API gravity values commonly associated with pipeline transport conditions without diluent addition. Coke yield decreased from similar to 40 wt% in thermal experiments to 18-30 wt% under optimized supercritical conditions. Trace-metal partitioning analyses indicated that V, Ni, and Mo were preferentially removed from the upgraded bitumen and concentrated predominantly in coke, with negligible aqueous transfer. Phase-specific elemental mass calculations provide quantitative support for the partitioning trends observed across the experimental conditions and the interpretation of metal redistribution during upgrading. This study provides one of the first systematic evaluations of trace-metal redistribution among upgraded bitumen, coke, and aqueous phases during SCW and SCCO2-SCW upgrading of Athabasca bitumen. These results demonstrate that SCCO2-assisted SCW upgrading intrinsically functions as a demetallization process, partially decoupling viscosity improvement from carbon rejection while concentrating trace metals into a solid residue for subsequent management, with implications for sustainable partial upgrading of heavy oil.

This work investigates a method for stabilizing bio-oil by increasing its pH through treatment with sodium hydroxide and ammonia. It was shown, that alkaline treatment significantly improves the thermal stability of bio-oil and provide the possibility of its involvement in the process of catalytic cracking of vacuum gas oil was demonstrated. The stabilized samples were subjected to catalytic cracking in order to study the effect of the processing stage on the yield of the main products. An increase in the pH level of bio-oil contributes the intensification of the cracking process. Sodium hydroxide treatment leads to an increase in the conversion of vacuum gas oil from 78.6 to 82.2 % wt. and the yield of the gasoline fraction (IBP-200ºC) increased from 44.7 to 47.3 % wt. Ammonia treatment leads to an increase the yield of the gasoline fraction from 50 to 54.2 % wt. However, the cracking of bio-oil treated with sodium hydroxide led to irreversible catalyst deactivation due to the presence of sodium, whereas no such deactivation was observed for bio-oil treated with ammonia.

Oligochaete worms enhance dewatering of mature fine tailings. In this context, the research team has investigated the beneficial effects of Oligochaete worms in dewatering and strengthening of fresh samples of fluid fine tailings (FFTs) and thickened tailings (TTs), including cold temperatures. Applying Oligochaete worms to FFT and TT resulted in enhanced permeability leading to faster solid content ( S c ) increases that are twice as large as in controls, up to final S c of 37% for FFT and 61% for TT, and shear strengths that are twice as large in their absolute value as in controls too.

In this study, we proposed mitigation strategies to reduce methane emissions from oil sands tailings ponds and determined the extent to which certain chemicals (Na2MoO4·2H2O, Fe2(SO4)3, Na2SO4, and Na3C6H5O7·2H2O) could affect the methanogenesis process. Lab-scale mesocosms were used to compare the amount of fugitive emissions between paraffinic and naphthenic producer tailings. The inter-relationships among different parameters, such as methane, water chemistry, residual bitumen content in tailings, and microbial community, were investigated before and after the methane inhibition process. It was found that under different chemical treatment regimens, methanogenic populations were either suppressed or stimulated, demonstrating that functionally similar disturbances in natural systems may result in distinct responses of the microbial populations involved. The 16S RNA gene sequencing data revealed that both solvents and chemical treatments significantly impacted microbial diversity and communities in tailings, leading to notable shifts in dominant microbial families and a decrease in diversity in the treated samples. These treatments affected methanogenic families, reducing the abundance of archaeal methanogens (e.g., Methanegulaceae) while increasing the presence of microbial families involved in hydrocarbon degradation, such as Spirochaetaceae and Thermovirgaceae. This study lays the groundwork for potential economically viable approaches to reduce methane emissions from oil sands tailings ponds.

Aquatic Oliogochaete worms (Lumbriculus variegatus) combined with straw led to improved geotechnical properties of fluid fine tailings (FFT) and thickened tailings (TT) in large-scale column studies. Gravity settling caused 19.9% and 20.6% consolidation of FFT and TT over 125 and 127 days, while the addition of straw and worms increased consolidation to 22.0%-24.3% for FFT and 28.1%-28.9% for TT. Solids content and yield stress were up to 1.1x and 6.6x higher in straw and worm columns, with greatest improvements seen in the top tailings layers where worm tunnels were visually observed. Surviving worms were only found in one column, suggesting the worms provide benefits extending past their depth of penetration and lifespan. The addition of straw stimulated methanogenic activity, decreasing pH, increasing alkalinity, and creating strictly anaerobic conditions (-300 mV), which may have impacted the survivability of the worms but provided another bioconsolidation pathway.

Ebullition of biogenic gases, primarily methane (CH4), might affect the trajectory of end pit lake (EPL) reclamation. We investigated the influence of nutrients (N with or without P) on methanogenesis and the resulting chemical flux from underlying fluid fine tailings (FFT) to cap water. Anaerobic 10 L columns were filled with FFT amended with a mixture of hydrocarbons (n-alkanes, iso-alkanes, and monoaromatics from C-6-C-10 ; HC columns) and capped with process water. Some amended FFT were further amended with N (HCN columns) or N and P (HCNP columns). A microbial community dominated by Desulfobacterota and Desulfotomaculales plus acetoclastic and hydrogenotrophic methanogens depleted hydrocarbons at different rates concomitant with CH4 production in the order HCN > HC > HCPN, indicating stimulation of methanogenesis by N and inhibition by P amendments. Microbial processes transformed FFT minerals (Fe-III to Fe-II minerals and dissolution of carbonates), mobilized ions, and trace elements (Ca2+, Mg2+, K+, HCO3-, Sr, and Ba) in FFT porewater and densified FFT and induced chemical flux to cap water. Other dissolved trace elements (As, Sb, and Mo) decreased in porewater and cap water during methanogenesis. The results provide novel information about nutrients' effect on methanogenesis and associated chemical flux to inform predictions about sustainable management of EPL.

Engineering strategies to reduce greenhouse gases (GHGs) emissions by inhibiting methanogenesis in oil sands tailings have rarely been examined. In this study, we explored the potential impact of chemical treatment (lime) and biological treatment using enzymes (lysozyme and protease) on inhibiting methane emissions from tailings. Overall, treatment with protease 3%, lysozyme 3%, and lime 5000 ppm reduced CH4 production (by 52%, 28%, and 25%, respectively) and were weakly associated with the archaeal abundance. Enzymes treatment resulted in a higher reduction in CH4 production compared with lime treatment. A 3% lysozyme treatment suppressed CH4 production (the change in methane was 0.48 mmol) and reduced the degradation of hexane throughout the experiment. Similarly, 3% protease suppressed CH4 production throughout the experiment (the change in methane was 0.78 mmol), which could be attributed to the pH reduction to pH 4.9 at week 23 resulting from the formation of volatile fatty acids. Another possible mechanism could be the formation of toxic compounds, such as high nitrogen content, after protease treatment that inhibited the microbial community. The toxicity effect to Vibrio fischeri was greater with lysozyme 3% and protease 3% treatment than with lime treatment (124 TU and 76 TU, respectively). Lime treatment resulted in the highest reduction in 16S rRNA gene copies from 5.7 x 106 cells g-1 (control) to 2.7 x 105, 1.71 x 105, and 1.4 x 105 cells g-1 for 1600, 3500, and 5000 ppm treatments, respectively. This study supports further work to examine and determine the optimum conditions (e.g., enzyme and lime dosages) for CH4 inhibition.

Bitumen extraction from oil sands ore in Alberta, Canada, has generated > 1.3 billion m3 of tailings comprised of slurry of fine silt, clay, residual bitumen, and diluent hydrocarbons, deposited in ponds. Key environmental issues associated with oil sands tailings include biogenic greenhouse gas emissions (methane and carbon dioxide), water toxicity and its potential seepage, water reuse, and solids consolidation. Methane produced during anaerobic microbial metabolism of hydrocarbons is emitted from tailings ponds and end-pit lakes where tailings are reclaimed. This study tests one of the strategies to minimize methane emissions using iron minerals and other terminal electron acceptors for the biodegradation of residual hydrocarbons under alternative, non-methanogenic redox conditions. Preliminary data exhibited biodegradation of a higher number of hydrocarbons (heptane, octane and decane, and toluene) under sulfate-reducing conditions compared to toluene biodegradation only under nitrate- and iron-reducing conditions. Amorphous iron mineral suppressed methanogenesis, whereas iron crystalline mineral enhanced methane production. Our overall results reveal the potential of indigenous microbes to biodegrade hydrocarbons in the tailings under different redox conditions, and thereby channel carbon flow from hydrocarbons to carbon dioxide.

Reclamation of fluid fine tailings (FFT) produced by mined oil sands ore processing is an environmental and technical challenge. End-pit lakes (EPLs) are a prospective reclamation strategy needing comprehensive evaluation. We investigated biogeochemical changes in water quality and sediments by using 140 L columns containing 50 L of FFT, either unamended or amended with hydrocarbons, and capped with 20 L of process water to simulate an EPL. The columns were incubated up to 3 years anaerobically at 10, 20, or 30 degrees C. Microbial metabolism of hydrocarbons in FFT produced methane (CH4) and carbon dioxide (CO2), accelerated FFT settling by expressing more porewater to the surface, and increased turbidity in cap water. Gas ebullition caused bitumen release and chemical flux from the underlying FFT to cap water. Dissolution and biotransformation of carbonate and Fe bearing minerals in FFT during incubation led to the positive flux of major cations (Ca2+ and Mg2+), anions (HCO3-), and some trace elements (primarily Ba and Sr), thereby influencing the chemistry of overlying cap water. No discernible trend in flux of dissolved organic carbon and naphthenic acids was observed. The results suggest that microbial anaerobic activity stimulated by residual hydrocarbons in FFT may influence the progression of EPLs into viable aquatic ecosystems.

Remediation of oil sands tailings is a crucial environmental aspect of the Canadian oil sands industry. Because of the poor released water quality and slow consolidation of tailings, engineered non-natural strategies to improve the consolidation of tailings are warranted. Here, we investigated enzymatic treatment (using cellulase, protease, and lysozyme) to accelerate the dewatering of fluid fine tailings (FFT). Our findings illustrated that lysozyme (0.5% and 1%) significantly improved FFT dewatering by increasing the water recovery (WR) up to 20% compared with the other enzymes (up to 12%) or the control (2%). Moreover, lysozyme treatment resulted in the highest increase in ionic strength (0.038 to 0.1 mol L-1), decrease in diffuse double layer (DDL) thickness (1.54 x 10(-7) to 9.40 x 10(-8) cm), and increase in zeta potential (-34.7 to-14.8 mV). Increased methane production was observed for cellulase (0.5% and 1%), lysozyme (0.5% and 1%), and protease (0.5%). The enhanced dewatering could be linked to the ebullition of methane gas resulting from the methanogenic activity, which created pathways for the trapped water release. In addition, the dissolution of carbonate minerals during the release of methane gas increased ionic strength and decreased the DDL of the FFT. Lysozyme 1% treatment was also the most effective in reducing naphthenic acid fractions (1934.6 to 243 ng mL(-1)); however, the released water had high toxicity toward Vibrio fischeri and had a slight decrease in microbial populations. This study provides a fundamental insight into enzymatic treatment for oil sand tailings.

End pit lakes (EPLs) have been proposed as a method of reclaiming oil sands fluid fine tailings (FFT), which consist primarily of process-affected water and clay- and silt-sized particles. Base Mine Lake (BML) is the first full-scale demonstration EPL and contains thick deposits of FFT capped with water. Because of the fine-grained nature of FFT, turbidity generation and mitigation in BML are issues that may be detrimental to the development of an aquatic ecosystem in the water cap. Laboratory mixing experiments were conducted to investigate the effect of mudline biofilms made up of microbial communities indigenous to FFT on mitigating turbidity in EPLs. Four mixing speeds were tested (80, 120, 160, and 200 rpm), all of which are above the threshold velocity required to initiate erosion of FFT in BML. These mixing speeds were selected to evaluate (i) the effectiveness of biofilms in mitigating turbidity and (ii) the mixing speed required to ‘break’ the biofilms. The impact of biofilm age (10 weeks versus 20 weeks old) on turbidity mitigation was also evaluated. Diverse microbial communities in the biofilms included photoautotrophs, namely cyanobacteria and Chlorophyta (green algae), as well as a number of heterotrophs such as Gammaproteobacteria, Desulfobulbia, and Anaerolineae. Biofilms reduced surface water turbidity by up to 99%, depending on the biofilm age and mixing speed. Lifting and layering in the older biofilms resulted in weaker attachment to the FFT; as such, younger biofilms performed better than older biofilms. However, older biofilms still reduced turbidity by 69% to 95%, depending on the mixing speed. These results indicate that biostabilization is a promising mechanism for turbidity mitigation in EPLs.

Tailings produced from surface-mined oil sands ores are retained in ponds on-site, pending water recovery for reuse and reclamation of solids. To enhance dewatering of tailings, we previously demonstrated that incubation of mature fine tailings (MFT) amended with an agricultural byproduct as a substrate in an anaerobic stirred tank reactor (STR) stimulated microbial activity and accelerated porewater expression (water recovery) and MFT consolidation by >50 %. Here, we report how microbial activity stimulated by STR treatment transformed MFT minerals and affected the quality of recovered porewater during subsequent MFT consolidation. STR treatment (methanogenesis) created strong reducing conditions with slight decrease in pH that induced transformation of the tailings solid phase. The concentrations of major ions (Ca2+, Mg2+, and HCO3-) increased in the recovered porewater presumably due to dissolution/precipitation of carbonate minerals. Iron (Fe) fractionation of solids revealed that Fe-III-bearing minerals in STR-treated MFT were transformed into Fe-II minerals, predominantly amorphous in nature, such as iron sulfides (FeS). The concentrations of trace elements (V, As, Co, Ni, and Sr) also increased in the recovered porewater, potentially released from ionically-bound and strongly adsorbed fractions of metal(oid)s determined through sequential extraction. Zn, Cu and Cd were not detected in porewater after STR treatment; these metals might have precipitated as sulfide minerals. MFT biodensification is a promising approach for tailings management, however, the quality of recovered porewater warrants optimization of substrate and STR retention time. These results also inform environmental monitoring of submerged tailings reclamation sites, particularly end-pit lakes.

Bitumen extraction from oil sands ores generates enormous volumes of fluid tailings in on-site repositories where slow consolidation of suspended solids and porewater recovery hamper tailings reclamation. Here, we demonstrate proof-of-concept where mature fine tailings (MFT) amended with hydrolyzed canola meal incubated in an anaerobic stirred tank reactor (STR) for 8 weeks stimulated indigenous microbes and subsequently accelerated consolidation and porewater recovery in columns and methane (CH4) production in sealed microcosms. Compared to untreated MFT, 5 weeks of STR treatment enhanced consolidation (solids increased from 23.2 to 39.4 wt%) and expression of porewater (four-fold more porewater in one-third the time), and up to 30-fold more CH4. The microbial community shifted towards diverse fermentative taxa and different methanogens. This approach suggests a potential technology to reduce tailings pond volumes and increase water use efficiency, decreasing freshwater demand in the bitumen extraction process while converting low-value substrate to CH4 for on-site utilization.

Froth treatment thickened tailings (TT) are a waste product of bitumen extraction from surface-mined oil sands ores. When incubated in a laboratory under simulated moist oxic environmental conditions for ~450d, two different types of TT (TT1 and TT2) exhibited the potential to generate acid rock drainage (ARD) by producing acid leachate after 250 and 50d, respectively. We report here the release of toxic metals from TT via ARD, which could pose an environmental threat if oil sands TT deposits are not properly managed. Trace metal concentrations in leachate samples collected periodically revealed that Mn and Sr were released immediately even before the onset of ARD. Spikes in Co and Ni concentrations were observed both pre-ARD and during active ARD, particularly in TT1. For most elements measured (Fe, Cr, V, As, Cu, Pb, Zn, Cd, and Se), leaching was associated with ARD production. Though equivalent acidification (pH2) was achieved in leachate from both TT types, greater metal release was observed from TT2 where concentrations reached 10,000ppb for Ni, 5000ppb for Co, 3000ppb for As, 2000ppb for V, and 1000ppb for Cr. Generally, metal concentrations decreased in leachate with time during ARD and became negligible by the end of incubation (~450d) despite appreciable metals remaining in the leached TT. These results suggest that using TT for land reclamation purposes or surface deposition for volume reduction may unfavorably impact the environment, and warrants application of appropriate strategies for management of pyrite-enriched oil sands tailings streams.

Tailings produced during bitumen extraction from surface-mined oil sands ores (tar sands) comprise an aqueous suspension of clay particles that remain dispersed for decades in tailings ponds. Slow consolidation of the clays hinders water recovery for reuse and retards volume reduction, thereby increasing the environmental footprint of tailings ponds. We investigated mechanisms of tailings consolidation and revealed that indigenous anaerobic microorganisms altered porewater chemistry by producing CO and CH during metabolism of acetate added as a labile carbon amendment. Entrapped biogenic CO decreased tailings pH, thereby increasing calcium (Ca) and magnesium (Mg) cations and bicarbonate (HCO) concentrations in the porewater through dissolution of carbonate minerals. Soluble ions increased the porewater ionic strength, which, with higher exchangeable Ca and Mg, decreased the diffuse double layer of clays and increased consolidation of tailings compared with unamended tailings in which little microbial activity was observed. These results are relevant to effective tailings pond management strategies.

Consolidation of clay particles in aqueous tailings suspensions is a major obstacle to effective management of oil sands tailings ponds in northern Alberta, Canada. We have observed that microorganisms indigenous to the tailings ponds accelerate consolidation of mature fine tailings (MFT) during active metabolism by using two biogeochemical pathways. In Pathway I, microbes alter porewater chemistry to indirectly increase consolidation of MFT. Here, we describe Pathway II comprising significant, direct and complementary biogeochemical reactions with MFT mineral surfaces. An anaerobic microbial community comprising Bacteria (predominantly Clostridiales, Synergistaceae, and Desulfobulbaceae) and Archaea (Methanolinea/Methanoregula and Methanosaeta) transformed Fe(III) minerals in MFT to amorphous Fe(II) minerals during methanogenic metabolism of an added organic substrate. Synchrotron analyses suggested that ferrihydrite (5Fe2O3. 9H2O) and goethite (α-FeOOH) were the dominant Fe(III) minerals in MFT. The formation of amorphous iron sulfide (FeS) and possibly green rust entrapped and masked electronegative clay surfaces in amended MFT. Both Pathways I and II reduced the surface charge potential (repulsive forces) of the clay particles in MFT, which aided aggregation of clays and formation of networks of pores, as visualized using cryo-scanning electron microscopy (SEM). These reactions facilitated the egress of porewater from MFT and increased consolidation of tailings solids. These results have large-scale implications for management and reclamation of oil sands tailings ponds, a burgeoning environmental issue for the public and government regulators.

Dispersed clay particles in mine tailings and soft sediments remain suspended for decades, hindering consolidation and challenging effective management of these aqueous slurries. Current geotechnical engineering models of self-weight consolidation of tailings do not consider microbial contribution to sediment behavior, however, here we show that microorganisms indigenous to oil sands tailings change the porewater chemistry and accelerate consolidation of oil sands tailings. A companion paper describes the role of microbes in alteration of clay chemistry in tailings. Microbial metabolism in mature fine tailings (MFT) amended with an organic substrate (hydrolyzed canola meal) produced methane (CH4) and carbon dioxide (CO2). Dissolution of biogenic CO2 lowered the pH of amended MFT to pH 6.4 vs. unamended MFT (pH 7.7). About 12% more porewater was recovered from amended than unamended MFT during 2 months of active microbial metabolism, concomitant with consolidation of tailings. The lower pH in amended MFT dissolved carbonate minerals, thereby releasing divalent cations including calcium (Ca(2+)) and magnesium (Mg(2+)) and increasing bicarbonate (HCO(-) 3) in porewater. The higher concentrations increased the ionic strength of the porewater, in turn reducing the thickness of the diffuse double layer (DDL) of clay particles by reducing the surface charge potential (repulsive forces) of the clay particles. The combination of these processes accelerated consolidation of oil sands tailings. In addition, ebullition of biogenic gases created transient physical channels for release of porewater. In contrast, saturating the MFT with non-biogenic CO2 had little effect on consolidation. These results have significant implications for management and reclamation of oil sands tailings ponds and broad importance in anaerobic environments such as contaminated harbors and estuaries containing soft sediments rich in clays and organics.

Bitumen extraction from oil sands ores after surface mining produces different tailings waste streams: ‘froth treatment tailings’ are enriched in pyrite relative to other streams. Tailings treatment can include addition of organic polymers to produce thickened tailings (TT). TT may be further de-watered by deposition into geotechnical cells for evaporative drying to increase shear strength prior to reclamation. To examine the acid rock drainage (ARD) potential of TT, we performed predictive analyses and laboratory experiments on material from field trials of two types of thickened froth treatment tailings (TT1 and TT2). Acid–base accounting (ABA) of initial samples showed that both TT1 and TT2 initially had net acid-producing potential, with ABA values of −141 and −230t CaCO3 equiv. 1000t−1 of TT, respectively. In long-term kinetic experiments, duplicate ~2-kg samples of TT were incubated in shallow trays and intermittently irrigated under air flow for 459days to simulate evaporative field drying. Leachates collected from both TT samples initially had pH~6.8 that began decreasing after ~50days (TT2) or ~250days (TT1), stabilizing at pH~2. Correspondingly, the redox potential of leachates increased from 100–200mV to 500–580mV and electrical conductivity increased from 2–5dSm−1 to 26dSm−1, indicating dissolution of minerals during ARD. The rapid onset and prolonged ARD observed with TT2 is attributed to its greater pyrite (13.4%) and lower carbonate (1.4%) contents versus the slower onset of ARD in TT1 (initially 6.0% pyrite and 2.5% carbonates). 16S rRNA gene pyrosequencing analysis revealed rapid shift in microbial community when conditions became strongly acidic (pH~2) favoring the enrichment of Acidithiobacillus and Sulfobacillus bacteria in TT. This is the first report showing ARD potential of TT and the results have significant implications for effective management of pyrite-enriched oil sands tailings streams/deposits.

The different intensity of feldspar grains weathering in eluvial horizons of Al-Fe-humus podzols was recorded in a chronosequence. The use of a scanning electron microscope makes it possible to reveal initial stages of selective dissolution of mineral grains: formation of shallow cavities on the surface; shearing of corroded surface, along with outcropping of unweathered layers. Analysis of morphological and physicochemical properties of soils in the chronosequence and of the surface morphostructure of feldspar grains has made it possible to reconstruct paleoclimatic conditions and to reveal tendencies in soil evolution in the valley of Lake Tapperiok.