Oil Sands Tailings Research Articles

Flocculating and dewatering performance of hydrophobic and hydrophilic solids using a thermal-sensitive copolymer.

Thermal-sensitive polymers have been tested on settling, compacting or dewatering of clays or oil sand tailings. However, not much attention has been paid to explore the effect of temperature on flocculating performance using thermal-sensitive polymers. In this study, poly(NIPAM-co-DMAPMA) was synthesized and employed to investigate the flocculating and re-flocculating performance of hydrophilic and hydrophobic particles at two specific temperatures; meanwhile settling and dewatering behaviors were also investigated. The results demonstrated that good flocculating performances were achieved at both room temperature (∼23 °C) and lower critical solution temperature (45 °C). Furthermore, larger flocs were formed at 45 °C as the copolymer was added. Floc strength and re-flocculating ability of the flocs were also intensified prominently at 45 °C. Additionally, settling and dewatering rates of suspensions were improved, and the moisture of filtered cakes was reduced when suspensions were at 45 °C. The phenomena could be justified by the phase transition of the copolymer from hydrophilicity to hydrophobicity as the temperature increased. There were much stronger adhesion forces between particles and higher adsorption amount of the copolymer onto solid surfaces at 45 °C. Therefore, the copolymer may be promising in solid-liquid separation to improve the floc size, floc strength, and settling and dewatering rate to achieve much lower moisture filtered cake.

Effect of naphtha diluent on greenhouse gases and reduced sulfur compounds emissions from oil sands tailings

The long-term storage of oil sands tailings has resulted in the evolution of greenhouse gases (CH4 and CO2) as a result of residual organics biodegradation. Recent studies have identified black, sulfidic zones below the tailings-water interface, which may be producing toxic sulfur-containing gases. An anaerobic mesocosm study was conducted over an 11-week period to characterize the evolution of CH4, CO2 and reduced sulfur compounds (RSCs) (including H2S) in tailings as it relates to naphtha-containing diluent concentrations (0.2, 0.8, and 1.5% w/v) and microbial activity. Our results showed that RSCs were produced first at 0.12μmol°RSCs/mL MFT (1.5% w/v diluent treatment). RSCs contribution (from highest to lowest) was H2S and 2-methylthiophene>2.5-dimethylthiophene>3-methylthiophene>thiofuran>butyl mercaptan>carbonyl sulfide, where H2S and 2-methylthiophene contributed 81% of the gas produced. CH4 and CO2 production occurred after week 5 at 40.7μmolCH4/mL MFT and 5.9μmolCO2/mL MFT (1.5% w/v diluent treatment). The amount of H2S and CH4 generated is correlated to the amount of diluent present and to microbial activity as shown by corresponding increases in sulfate-reducers' Dissimilatory sulfite reductase (DsrAB) gene and methanogens' methyl-coenzyme M reductase (MCR) gene.

The microbiology of oil sands tailings: past, present, future.

Surface mining of enormous oil sands deposits in northeastern Alberta, Canada since 1967 has contributed greatly to Canada's economy but has also received negative international attention due largely to environmental concerns and challenges. Not only have microbes profoundly affected the composition and behavior of this petroleum resource over geological time, they currently influence the management of semi-solid tailings in oil sands tailings ponds (OSTPs) and tailings reclamation. Historically, microbial impacts on OSTPs were generally discounted, but next-generation sequencing and biogeochemical studies have revealed unexpectedly diverse indigenous communities and expanded our fundamental understanding of anaerobic microbial functions. OSTPs that experienced different processing and management histories have developed distinct microbial communities that influence the behavior and reclamation of the tailings stored therein. In particular, the interactions of Deltaproteobacteria and Firmicutes with methanogenic archaea impact greenhouse gas emissions, sulfur cycling, pore water toxicity, sediment biogeochemistry and densification, water usage and the trajectory of long-term mine waste reclamation. This review summarizes historical data; synthesizes current understanding of microbial diversity and activities in situ and in vitro; predicts microbial effects on tailings remediation and reclamation; and highlights knowledge gaps for future research.

Electrophoresis and its applications in oil sand tailings management

Oil sands mines generate tailings during the extraction process, which are a mixture of water, clay, sand and residual bitumen. When the tailings are released to tailings ponds, the coarse solids settle quickly, whereas fine solids containing clay minerals, namely mature fine tailings (MFT), remain suspended for years, even decades. A study is carried out to assess the suitability of electrokinetic (EK) sedimentation to accelerate sedimentation of MFT. A series of laboratory-scale column experiments are carried out to examine the effects of electrophoresis during settling processes. The investigation focuses on the effects of EK sedimentation as related to the initial solid content of the tailings suspension, applied electric field intensity, water pH, and the use of an optimized coagulant FeCl3. Based on the experimental data, an electric field intensity of 150V/m along with an initial tailings solid content of no >5% are the optimum condition for EK sedimentation of MFT, in terms of reducing the overall sedimentation time and increasing the final solid content. The results show that the current density of EK sedimentation for MFT should not be >20A/m2 to control the bubble effect and reduce power consumption.

Fluidic delivery system for in-situ naphtha detection

A fluidic delivery system that operates, as processing unit for naphtha sensor, has been developed to detect naphtha. It is a mixture of varied hydrocarbons, which constitute less than 1% seepage in the tailings waste that further incorporates into Mature Fine Tailings. Presently, a sample of mature fine tailings is collected and analyzed using Gas Chromatography Mass Spectrometry every 6h to monitor its naphtha content. This conventional method of detecting naphtha is time consuming, expensive and requires trained personnel. Furthermore, it does not allow for real-time detection. To meet the demand of real-time naphtha detection in mature fine tailings, efforts were made to design and develop fluidic delivery line as processing unit for naphtha sensor. This paper presents a portable monitoring system, which would facilitate in-situ naphtha detection, and reduced manual labor, cost, among others. This prototype combines filtration unit, pumping system, heating unit and vapor storage for a compact and portable delivery system of the feed obtained from Oil Sands Tailings. The device runs in continuous mode and bears inlet tubing that can be used to draw feed into the system at any source where naphtha is to be detected.

Electrokinetic thickening of mature fine oil sands tailings

Mature fine oil sands tailings (MFT) are the fine parts of oil sands tailings that remain suspended in tailings disposal pond for decades because of the low sedimentation/consolidation rate. This study applies electrokinetics to thicken, that is, to increase the solid content, of the MFT suspension. The geotechnical properties of MFT solids and chemical analysis of tailings pore water are measured, followed by electrokinetic (EK) tests. The results of this study indicate that EK thickening is very effective for the settling of MFT suspensions under an applied voltage of 219 V/m, the final solid content of the sediment reached 18·75% from an initial 5% after 7 h. The EK treatment is also very effective in clarifying the supernatant. The final turbidity of the supernatant is 30·6 NTU under 219 V/m applied voltage gradient. Regression models are developed using statistical software MINITAB 15 in coded and uncoded units to relate the final solid content of the sediment with the initial solid content and applied voltage gradient. The models and the independent variables are statistically significant at 95% confidence level based on F test and t test results, respectively.

Modeling Effect of Bitumen Extraction Processes on Oil Sands Tailings Ponds

Modeling Effect of Bitumen Extraction Processes on Oil Sands Tailings Ponds

Methanogenic biodegradation of paraffinic solvent hydrocarbons in two different oil sands tailings.

Microbial communities drive many biogeochemical processes in oil sands tailings and cause greenhouse gas emissions from tailings ponds. Paraffinic solvent (primarily C5-C6; n- and iso-alkanes) is used by some oil sands companies to aid bitumen extraction from oil sands ores. Residues of unrecovered solvent escape to tailings ponds during tailings deposition and sustain microbial metabolism. To investigate biodegradation of hydrocarbons in paraffinic solvent, mature fine tailings (MFT) collected from Albian and CNRL ponds were amended with paraffinic solvent at ~0.1wt% (final concentration: ~1000mgL-1) and incubated under methanogenic conditions for ~1600d. Albian and CNRL MFTs exhibited ~400 and ~800d lag phases, respectively after which n-alkanes (n-pentane and n-hexane) in the solvent were preferentially metabolized to methane over iso-alkanes in both MFTs. Among iso-alkanes, only 2-methylpentane was completely biodegraded whereas 2-methylbutane and 3-methylpentane were partially biodegraded probably through cometabolism. 16S rRNA gene pyrosequencing showed dominance of Anaerolineaceae and Methanosaetaceae in Albian MFT and Peptococcaceae and co-domination of "Candidatus Methanoregula" and Methanosaetaceae in CNRL MFT bacterial and archaeal communities, respectively, during active biodegradation of paraffinic solvent. The results are important for developing future strategies for tailings reclamation and management of greenhouse gas emissions.

Short-term dewatering of treated oil sand fine tailings

Background The appropriate management of oil sand tailings requires a reduced environmental footprint of the waste containment facilities. This study models the short-term dewatering behavior of a 10 m deep deposit.ResultsResults indicated that inherent material properties along with hydraulic boundary conditions govern the rate and amount of consolidation.ConclusionsThe process alone is not sufficient for meaningful tailings dewatering in one year and must be augmented by other methods to further improve the tailings disposal scheme.

Microstructural, hydraulic conductivity and geochemical changes of drying mature fine oil sand tailings in column experiments

This study offers new insights into two-lift deposition of mature fine tailings under atmospheric drying. The interaction of newly added lift and former lift(s) was evaluated using column experiments in terms of volumetric water content, electrical conductivity (EC), hydraulic conductivity, geochemistry and microstructure. Water content and EC followed the same trend and decreasing of water content appears to be responsible for significant reduction in EC. Evaporation on top of the column reduced the water content to almost zero. The obtained results support the coupling between the hydraulic and chemical processes that should be considered by active operators.

Sequential biodegradation of complex naphtha hydrocarbons under methanogenic conditions in two different oil sands tailings

Methane emissions in oil sands tailings ponds are sustained by anaerobic biodegradation of unrecovered hydrocarbons. Naphtha (primarily C6–C10; n- iso- and cycloalkanes) is commonly used as a solvent during bitumen extraction process and its residue escapes to tailings ponds during tailings deposition. To investigate biodegradability of hydrocarbons in naphtha, mature fine tailings (MFT) collected from Albian and CNRL tailings ponds were amended with CNRL naphtha at ∼0.2 wt% (∼2000 mg L−1) and incubated under methanogenic conditions for ∼1600 d. Microbial communities in both MFTs started metabolizing naphtha after a lag phase of ∼100 d. Complete biodegradation/biotransformation of all n-alkanes (except partial biodegradation of n-octane in CNRL MFT) followed by major iso-alkanes (2-methylpentane, 3-methylhexane, 2- and 4-methylheptane, iso-nonanes and 2-methylnonane) and a few cycloalkanes (derivatives of cyclopentane and cyclohexane) was observed during the incubation. 16S rRNA gene pyrosequencing showed dominance of Peptococcaceae and Anaerolineaceae in Albian MFT and Anaerolineaceae and Syntrophaceae in CNRL MFT bacterial communities with co-domination of Methanosaetaceae and “Candidatus Methanoregula” in archaeal populations during active biodegradation of hydrocarbons. The findings extend the known range of hydrocarbons susceptible to methanogenic biodegradation in petroleum-impacted anaerobic environments and help refine existing kinetic model to predict greenhouse gas emissions from tailings ponds.

Addition of Tubifex accelerates dewatering of oil sands tailings

Accelerating dewatering of fluid fine tailings (FFT) to facilitate land reclamation is a major challenge to the oil sands industry in Canada. A new method was tested, addition of Tubifex to FFT. Tubifex is an indigenous earthworm in Canada. The survival rate tests showed that Tubifex can survive in oil sands tailings and penetrate to 42 cm depth (maximum depth tested). Columns (5 L of FFT) were set-up with tailings alone, Tubifex treated tailings and polymer-Tubifex treated tailings. Test results showed that (a) the final mud–water interface of tailings alone was 26% higher than that of Tubifex treated tailings; (b) solids content of Tubifex treated tailings was 21% more than that of tailings alone; (c) Tubifex was capable to accelerate the dewatering process of both cationic and anionic polymer treated tailings; (d) anionic polymer was superior in facilitating long-term dewatering and its coupled effects with Tubifex were better than the cationic polymer.

Cationic Hydrolytically Degradable Flocculants with Enhanced Water Recovery for Oil Sands Tailings Remediation

Micellar radical polymerization of a short‐chain polyester macromonomer, polycaprolactone choline iodide ester methacrylate (PCLnChMA), is used to produce a new cationic flocculant that becomes more hydrophobic in response to hydrolytic degradation. The cationic tips of the comb‐like poly(PCL3ChMA) accelerate the settling rate of oil sands tailings, while partial hydrolysis of the polyester grafts reveals the hydrophobic segments that reduce capillary suction time by 30%. This technology combines the material properties of polyesters with the productivity of radical polymerization to make dual functional flocculants with characteristics that can be easily tuned to control flocculation performance, such as polymeric cation density, hydrophobic content, and polymer architecture. image

Estimation of methylene blue index in oil sands tailings using hyperspectral data

AbstractClay minerals constitute a significant fraction of oil sands tailings; and clay mineralogy, abundance, and morphology can dramatically affect the strength of the tailings during consolidation. The ability of clays to expand or swell in the presence of water is of importance in establishing the post‐depositional strength and the geotechnical stability of a tailings deposit for reclamation purposes. The surface activity of oil sands tailings solids is typically determined using the methylene blue index (MBI), an analytical technique that quantifies the ionic absorption capacity of a sample. The present work explores the use of short‐wave infrared (SWIR) and long‐wave infrared (LWIR) hyperspectral observations for the estimation of the swelling potential or activity of oil sands tailings indicated by MBI. Spectral features in reflectance spectra were characterized in the SWIR and LWIR, in particular those attributed to the presence of quartz and clays. These features were employed to assess the correlation between MBI and remote sensing reflectance measurements collected in the laboratory from air‐dried tailings. In the SWIR, a band ratio of reflectance at 2.111 and 1.992 μm was highly correlated with MBI. For the potential estimation of MBI in outdoor settings, where the intervening atmosphere can impact the spectral measurements, a band ratio of reflectance at 1.773 and 1.307 μm provided an estimation of MBI when moisture of tailings did not exceed 0.20 g/g (20 wt%). The best predictions of MBI were obtained in the LWIR using the reflectance peaks at 9.67 µm and 11 µm attributable to clay minerals.

Total Internal Reflection Fluorescence Microscopy To Investigate the Distribution of Residual Bitumen in Oil Sands Tailings

A major waste byproduct of oil sands in situ extraction is oil sands tailings, which are a mixture of water, clay, and residual bitumen. These tailings represent a huge ecological footprint in the form of tailings ponds, which not only render large land areas unusable but also prevent reuse of water. The slow dewatering of the tailings ponds poses a major challenge to the industry. The presence of complex inorganic–organic bitumen–clay mixtures in these tailings contributes to this problem. Hence, understanding the nature of the bitumen–clay association and the effect of bitumen on clay particle–particle interactions is important for the development of more effective chemicals or processes to accelerate particle aggregation and sedimentation during dewatering. Previous studies that investigate these interactions used techniques that are sensitive only toward inorganic clay but not sensitive towards organic bitumen. Here, we use a high-resolution total internal reflection fluorescence (TIRF) microscopy to ...

Enriching acid rock drainage related microbial communities from surface-deposited oil sands tailings.

Little is known about the microbial communities native to surface-deposited pyritic oil sands tailings, an environment where acid rock drainage (ARD) could occur. The goal of this study was to enrich sulfur-oxidizing organisms from these tailings and determine whether different populations exist at pH levels 7, 4.5, and 2.5. Using growth-based methods provides model organisms for use in the future to predict potential activities and limitations of these organisms and to develop possible control methods. Thiosulfate-fed enrichment cultures were monitored for approximately 1 year. The results showed that the enrichments at pH 4.5 and 7 were established quicker than at pH 2.5. Different microbial community structures were found among the 3 pH environments. The sulfur-oxidizing microorganisms identified were most closely related to Halothiobacillus neapolitanus, Achromobacter spp., and Curtobacterium spp. While microorganisms related to Chitinophagaceae and Acidocella spp. were identified as the only possible iron-oxidizing and -reducing microbes. These results contribute to the general knowledge of the relatively understudied microbial communities that exist in pyritic oil sands tailings and indicate these communities may have a potential role in ARD generation, which may have implications for future tailings management.

A two-step flocculation process on oil sands tailings treatment using oppositely charged polymer flocculants

Water management and treatment of mineral tailings and oil sands tailings are becoming critical challenges for the sustainable development of natural resources. Polymeric flocculants have been widely employed to facilitate the flocculation and settling of suspended fine solid particles in tailings, resulting in the separation of released water and solid sediments. In this study, a new flocculation process was developed for the treatment of oil sands tailings by using two oppositely charged polymers, i.e. an anionic polyacrylamide and a natural cationic biopolymer, chitosan. The new process was able to not only improve the clarity of supernatant after settling but also achieve a high settling efficiency. Treatment of the oil sands tailings using pure anionic polyacrylamide showed relatively high initial settling rate (ISR) of ~10.3m/h but with poor supernatant clarity (>1000NTU); while the treatment using pure cationic polymer resulted in clear supernatant (turbidity as low as 22NTU) but relatively low ISR of >2m/h. In the new flocculation process, the addition of anionic polyacrylamide to the tailings was followed by a cationic polymer, which showed both a high ISR (~7.7m/h) and a low turbidity (71NTU) of the supernatant. The flocculation mechanism was further investigated via the measurements of floc size, zeta potential and surface forces. The new flocculation process was revealed to include two steps: (1) bridging of fine solids by anionic polyacrylamide, and (2) further aggregation and flocculation mediated by charge neutralisation of the cationic polymer, which significantly eliminated the fine solids in the supernatants as well as increases floc size. Our results provide insights into the basic understanding of the interactions between polymer flocculants and solid particles in tailings treatment, as well as the development of novel tailings treatment technologies.

Determination of the optimum polymer dose for dewatering of oil sands tailings using UV–vis spectrophotometry

The slow settling of fine clays in oil sands residuals results in the generation of very large amounts of fine tailings that must be stored in dammed impoundments. Dewaterability and settling of oil sands residuals can be greatly improved by adding synthetic polymers, which would help to minimize the volume of tailings. Adding polymers at the optimum dose is extremely important in terms of process efficiency as well as cost-effectiveness. The optimum dose, however, varies based on the changes in the composition and characteristics of the tailings and ideally should be adjusted on a continuous basis. This study evaluated the potential of a UV–vis absorbance based analytical method to measure the polymer concentration and determine the optimum polymer dose for achieving the best thickening and dewatering performance from oil sands tailings. At 190nm, sample absorbance was found linearly correlated with the polymer concentration. The detection limit of the method for polymer A3338 (SNF) was established as 0.37mg/L in reclaimed water, which showed the method has the sensitivity to detect very low polymer concentrations. Furthermore, the method was also used to determine the optimum polymer dose by monitoring the residual polymer concentration in tailings water. Any potential interference from fines, salinity and pH were also investigated and were shown not to have an impact on the detection of the polymers. The results of the research indicate that thickening and dewatering optimization of oil sands tailings can be achieved by directly measuring the polymer concentration using an in-line UV–vis spectrophotometer that can generate real-time information.

Co-occurrence of methanogenesis and N2 fixation in oil sands tailings

Oil sands tailings ponds in northern Alberta, Canada have been producing biogenic gases via microbial metabolism of hydrocarbons for decades. Persistent methanogenic activity in tailings ponds without any known replenishment of nutrients such as fixed nitrogen (N) persuaded us to investigate whether N2 fixation or polyacrylamide (PAM; used as a tailings flocculant) could serve as N sources. Cultures comprising mature fine tailings (MFT) plus methanogenic medium supplemented with or deficient in fixed N were incubated under an N2 headspace. Some cultures were further amended with citrate, which is used in oil sands processing, as a relevant carbon source, and/or with PAM. After an initial delay, N-deficient cultures with or without PAM produced methane (CH4) at the same rate as N-containing cultures, indicating a mechanism of overcoming apparent N-deficiency. Acetylene reduction and 15N2 incorporation in all N-deficient cultures (with or without PAM) suggested active N2 fixation concurrently with methanogenesis but inability to use PAM as a N source. 16S rRNA gene pyrosequencing revealed little difference between archaeal populations regardless of N content. However, bacterial sequences in N-deficient cultures showed enrichment of Hyphomicrobiaceae and Clostridium members that might contain N2-fixing species. The results are important in understanding long-term production of biogenic greenhouse gases in oil sands tailings.

Next-Generation Sequencing Assessment of Eukaryotic Diversity in Oil Sands Tailings Ponds Sediments and SurfaceWater.

Tailings ponds in the Athabasca oil sands (Canada) contain fluid wastes, generated by the extraction of bitumen from oil sands ores. Although the autochthonous prokaryotic communities have been relatively well characterized, almost nothing is known about microbial eukaryotes living in the anoxic soft sediments of tailings ponds or in the thin oxic layer of water that covers them. We carried out the first next-generation sequencing study of microbial eukaryotic diversity in oil sands tailings ponds. In metagenomes prepared from tailings sediment and surface water, we detected very low numbers of sequences encoding eukaryotic small subunit ribosomal RNA representing seven major taxonomic groups of protists. We also produced and analysed three amplicon-based 18S rRNA libraries prepared from sediment samples. These revealed a more diverse set of taxa, 169 different OTUs encompassing up to eleven higher order groups of eukaryotes, according to detailed classification using homology searching and phylogenetic methods. The 10 most abundant OTUs accounted for >90% of the total of reads, vs. large numbers of rare OTUs (<1% abundance). Despite the anoxic and hydrocarbon-enriched nature of the environment, the tailings ponds harbour complex communities of microbial eukaryotes indicating that these organisms should be taken into account when studying the microbiology of the oil sands.