Oil Sands Mature Fine Tailings Research Articles

Enhancing the dewatering of oil sands mature fine tailings by coagulation-flocculation and pressure filtration with tannic acid-mediated polymeric complex network

This study presents a new method to improve the dewatering efficiency of oil sands mature fine tailings (MFT) by pressure filtration using a tannic acid-mediated polymeric complex network as a flocculant. It was found that the prior addition of tannic acid ahead of poly(ethylene oxide) and ferric chloride significantly increased the vacuum filtration rate by improving the permeability of the filter cake and reducing its specific resistance to filtration. The beneficial role of tannic acid was investigated by slurry shear stress, sedimentation, floc morphology and size distribution measurements, and UV–Vis and FTIR spectroscopic characterization. Results indicated that tannic acid acted as a crosslinker to complex with both poly(ethylene oxide) and ferric chloride to develop a tri-component polymeric network. Within the network, numerous hydrogen bonds and coordination bonds enabled a sufficient crosslinking density, resulting in higher floc strength and compression resistance. Flocs generated by the tannic acid-mediated polymeric network were more rigid with an expanded structure, allowing drainage channels to remain open in the filter cake for better permeability. Scale-up experiments on a Millipore pressure filtration unit verified the beneficial role of tannic acid in filtering the mature fine tailings, achieving a much higher net water release rate and cake solid content.

Fused silica as an anti-fouling material for oil sands optical instruments

Optical instruments have application in many chemical industries for use in inline observation, measurement, and process control for product and waste streams. Typically, these instruments are fitted with sapphire windows which offer extreme hardness, optical transparency and inertness but can be susceptible to fouling with hydrocarbons in the streams. This work explored the potential of fused silica as an alternative anti-fouling material for optical instrument windows for use in aqueous streams containing hydrocarbons. The advantage of fused silica is that it offers adequate hardness and transparency while retaining chemically reactive silanol groups on its surface. Closed loop experiments conducted with oil sands mature fine tailings (MFT) containing residual bitumen, a hydrocarbon known to cause severe fouling of optical windows, demonstrated no fouling issue on fused silica. The hydrophilicity of the optical surface increased following exposure to the mildly alkaline MFT. We hypothesized that in alkaline aqueous streams the silanol groups are deprotonated to create a negatively charged surface, thereby introducing a repulsive force between the surface and the negatively charged hydrocarbon droplets and increasing the hydrophilicity of both materials. Contrarily, the relatively inert sapphire is limited in its capacity to form negative surface charges and consistently fouled with bitumen. When silanol groups on the fused silica were removed via fluoro-functionalization, it resulted in complete fouling of the optical surface. Finally, bitumen fouling was observed on both fused silica and sapphire surfaces in neutral aqueous environments compared to none on the fused silica in an alkaline environment.

Flocculating oil sands tailings with dual anionic/cationic polymers: Dose and charge density effects

AbstractA two‐step process, with anionic hydrolyzed polyacrylamide (HPAM) and cationic poly(vinylbenzyl trimethylammonium chloride) (PVBTMAC), was used to flocculate oil sands mature fine tailings (MFT). The charge density of HPAM and the dosages of HPAM and PVBTMAC were varied to maximize the dewatering of MFT and minimize the turbidity of the supernatant. The dual flocculant system performed better at lower doses than when used alone. The best HPAM charge density for fast initial settling rate and high sediment solids content was 32%, but it increased to 38% for best sediment dewatering, as measured by capillary suction time. The clearest supernatants were found when the zeta potential approached 0 mV because the cationic PVBTMAC neutralized the surface charges of the particles suspended in the MFT. More importantly, undiluted MFT was flocculated with the HPAM/PVBTMAC system and then filtered at low‐pressure (69 kPag), resulting in a filter cake with a high solids content of 61 wt.%. This study shows that treating MFT with a combination of anionic and cationic polymer is a flexible way to optimize flocculation performance.

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.

Enhanced Settling and Dewatering of Oil Sands Mature Fine Tailings with Titanomagnetite Nanoparticles Grafted with Polyacrylamide and Lauryl Sulfate

In this study, a three-in-one nanoflocculent that consists of nanoparticles of titanomagnetite (NTM) grafted with multiple segments of hydrophobically modified chains of polyacrylamide (PAM) with sodium laurel sulfate (SLS) was developed for enhanced settling and dewatering of oil sands mature fine tailings (MFT). The existence of NTM allowed more than one segment to graft/functionalize (i.e., hydrophobic and hydrophilic) on the same surface. This three-in-one nanoflocculent not only provides better exposure for the functionalized species, but it also increases the nanoflocculant specific gravity and dispersibility for better interactions. The NTM was initially synthesized by the coprecipitation method and subsequently grafted with PAM and SLS at room conditions. The flocculation and dewatering performance of the as-synthesized nanoflocculants was evaluated using the initial settling rate (ISR), supernatant turbidity, sludge volume index, capillary suction time (CST), and specific resistance to filtration (SRF). Flocculation of the MFT suspension using the novel optimized nanoflocculants at 3000 ppm had 15 times faster ISR, and the supernatant turbidity, CST, and SRF had stronger outcomes than the traditionally used 20,000 ppm commercial anionic PAM. This study demonstrates the potential of designing nanoflocculants to effectively enhance settling and dewatering of oil sands tailings, while reducing the required amount of coagulants.

Flocculation Efficiency and Spatial Distribution of Water in Oil Sands Tailings Flocculated with a Partially Hydrophobic Graft Copolymer.

This work investigates the effect of partially hydrophobic grafted polymers on flocculation and dewatering of oil sands mature fine tailings. Here, we combine confocal microscopy and rheology to investigate how the graft density of ethylene-propylene-diene grafted with hydrolyzed poly(methyl acrylate) (EPDM-g-HPMA) affects its dispersion in water and flocculation efficiency in terms of sediment solids content and long-term dewatering of oil sands tailings. Increasing the graft density from 30 to 50% makes the flocculant easier to disperse, increases the rate of initial dewatering, and also enhances the viscoelastic response of the flocculated sediments. Conversely, the long-term rheological properties of the flocculated sediments were similar for all flocculants. Tri-dimensional microscopic details of the spatial distribution of water within the flocculated sludge provide novel insights into the performance of the flocculants. Increasing the graft density in EPDM-g-HPMA traps more water within the individual flocs and, consequently, decreases the post-flocculation dewatering rate. Our systematic approach confirms the importance of the spatial distribution of water in the flocculated sediment, which depends on how the flocculant is dispersed and how it retains water in the flocs.

Flocculation and dewatering of oil sands tailings with a novel functionalized polyolefin flocculant

• Use of novel partially-hydrophobic graft polymer flocculant for mineral tailings treatment. • Grafts of PMA with different molecular weights and densities were attached to EPDM backbones. • Use of a central composite experimental design to assess the effect of polymer architecture on flocculation and dewatering performance. • The performance of the graft copolymers was quantified by initial settling rate (ISR), capillary suction time (CST), supernatant turbidity, and sediment solids content. This work investigates the impact of the molecular weight and grafting density of partially hydrolyzed poly(methyl acrylate) grafted onto ethylene-propylene-diene copolymer backbones (EPDM -g- HPMA) on the flocculation and dewatering of oil sands mature fine tailings through a central composite experimental design by measuring initial settling rate, capillary suction time, supernatant turbidity, and sediment solids content. Flocculants with high molecular weight grafts and low grafting densities reduced the initial settling rates, decreased supernatant turbidities, and increased the solids content of the flocculated sediments. The capillary suction time, however, depended mostly on the charge density and on the hydrophobicity of the grafted copolymer. The effect of the EPDM backbone molecular weight was also investigated. Shorter backbones resulted in flocculants that dispersed more easily in water and settled the sediments faster. In addition, they decreased the supernatant turbidity and increased the solids content in the sediments. EPDM -g- HPMA flocculants with graft molecular weight of 179 kDa and grafting density of 13% are outstanding filtration aids, helping generate sediments with 43% solids content and outperforming a reference commercial polyacrylamide flocculant.

Synergy between Dual Polymers and Sand-to-Fines Ratio for Enhanced Flocculation of Oil Sand Mature Fine Tailings

The current challenges in dewatering oil sand mature fine tailings (MFTs) by flocculation using a single flocculant include the requirement of very high doses and high cost, inefficient flocculation, and low content of solids in sediment. The obtained flocculated sediment with less than <40 wt % solids is difficult in further consolidation and dewatering for the final disposal. In this work, we examined a new approach for dewatering by dual polymer flocculation in combination with varying sand-to-fines ratios (SFRs) in MFTs. The dual polymers were an anionic polyacrylamide (APAM), and a nanosized cationic hybrid polymer (NHP). Our results confirmed that using single polymers alone was unable to achieve satisfactory flocculation. The solids content in the sediment was <30%, even with increasing flocculant dosages up to 2000 ppm for APAM, and 5000–8000 ppm for NHP, respectively. Although better flocculation was obtained by dual polymers, with reduced total flocculant dosages, the improvement was also limited, in terms of the final sediment solids content (<44%). However, much improved flocculation performance was obtained by increasing the SFR value of the MFT (from 0.1 to 1.5), with significantly reduced total polymer dosages at only 650 ppm. Using different combinations of SFR values and dual polymer dosages, the sediment solids could reach 56 wt % after 24 h of natural settling. It was found that the dual polymer system was less sensitive to the changes in polymer dosages, and that no “overdosing” phenomenon was observed for the tested dual polymers. To rationalize the synergy from dual polymers and SFR, we propose that loose and extended flocs formed by the large anionic polymer and suspended fines were consolidated by the small and cationic polymer through strong electrostatic attraction with fines and the large anionic polymer. Coarse sands were “cores” to carry and condense the loosely structured flocs of fine solids, and they exclude the entrapped water inside the flocs. Our work demonstrates that combining dual polymers and suitable SFRs may be an effective strategy to produce sediment with high solids contents, reduce the required flocculant dose, eliminate overdosing issues, and achieve fast settling rates.

Nonthermoresponsive and Thermoresponsive Cationic Starch for the Flocculation of Oil Sands Mature Fine Tailings

The mature fine tailings (MFT) in the massive tailing ponds created during bitumen extraction from oil sands must be dewatered before the land and water can be reclaimed. Here, we report the first ...

Enhanced dewatering of oil sands tailings by a novel water-soluble cationic polymer

This work investigates how poly(vinylbenzyl trimethylammonium chloride)–poly(VBTMAC)–flocculates oil sands mature fine tailings (MFT). This water-soluble cationic polymer contains pendant benzene rings that make it partially hydrophobic. The positive charges on the poly(VBTMAC) backbone neutralize the negatively-charged MFT clays while the hydrophobic benzene rings help expel the water trapped in the aggregates. Vinylbenzyl trimethylammonium chloride can be polymerized to produce long chains (comparable to anionic polyacrylamide) with fast polymerization rates. Focused beam reflectance measurement (FBRM) experiments showed that larger aggregates were formed using higher molecular weight poly(VBTMAC), which is evidence of the bridging mechanism. The flocculation performance of poly(VBTMAC) was tested against commercially available anionic polyacrylamides for undiluted MFT by measuring the extent of dewatering in filtration tests and the rheological properties of the sediments. Our results showed that poly(VBTMAC) is a better flocculant in terms of ease of production, fast dewatering rate, and formation of sediments with high shear strength, but required substantially higher dosages to perform better than commercially available anionic polyacrylamides.

Thermoresponsive Starch for the Flocculation of Oil Sands Mature Fine Tailings.

The reclamation of land and recovery of water from tailing ponds created during bitumen extraction from oil sands is a major technical and environmental challenge. In the current study, thermoresponsive hydroxybutylated (HB) corn starch (HB-CS) and potato starch (HB-PS), with lower critical solution temperatures (LCSTs) ranging from 36 to 45 °C, were examined as flocculants for oil sands mature fine tailings (MFT). The ability of different doses of the HB-CS and HB-PS to flocculate 2 and 10 wt % MFT, prepared by diluting 35 wt % MFT in tap water, in terms of the initial settling rate (ISR), supernatant turbidity (ST), sediment solids content (SSC), and water recovery (WR), was examined at temperatures below and above their LCSTs. The thermoresponsive HB-CS and HB-PS were good flocculants of MFT, and their thermoresponsive behavior was essential for optimal results in that they were considerably more effective in several aspects at temperatures above their LCSTs than below. In terms of ISRs, the HB-PS was a considerably better flocculant than the HB-CS, and this was especially so with the 10 wt % MFT. With the HB-PS, the ISR was lower when using diluted MFT prepared with tap water as opposed to simulated oil sands process water.

Electrokinetic and chemical treatment of oil sands mature fine tailings: dewatering and strengthening

Oil sands tailings have become a major challenge in Canada due to various geotechnical and environmental concerns. Mature fine tailings (MFT) typically contain 70% water and 30% silt- and clay-sized solids and have low hydraulic conductivities, which lead to difficulties in consolidation by nature. Electrokinetics (EK) has been proved to be effective at dewatering and strengthening oil sands tailings, but is only limited to the anode area. Further treatment is needed to improve the tailings around the cathode. Chemical stabilisation is a mature technique for ground improvement. However, there is limited information for the combined effects of EK and chemical treatment on high water content geomaterials such as MFT, slurry, sludge and so forth. This research study was carried out to evaluate the effects of combined EK and chemical treatment of MFT. Quicklime and Portland cement were selected as the chemical additives. The changes in water content, undrained shear strength, plasticity, pore-water pH and electrical conductivity and particle zeta potential after treatment were studied. It was found that the chemical treatment reduced the material property difference between the anode and cathode, whereas it reduced EK-induced water flow. Combined EK and chemical treatment of MFT may be beneficial at a low chemical dosage.

Microbially-mediated de-watering and consolidation (“Biodensification”) of oil sands mature fine tailings, amended with agri-business by-products

Oil sands surface mining operations in northeastern, Alberta, Canada produce enormous volumes of fluid fine tailings, an aqueous suspension of fine clays, sand, unrecovered bitumen, and diluent hydrocarbons. The tailings are deposited and retained on-site in large settling basins where the colloidal solids sediment and consolidate very slowly by gravity and pore water collects at the surface for re-use. Tailings ‘biodensification’, mediated by indigenous microbes that produce methane and/or carbon dioxide, is a phenomenon observed in situ and in vitro whereby tailings with active anaerobic microbial communities consolidate and de-water faster than predicted by gravitational (self-weighted) consolidation alone. To exploit this phenomenon, we used organic amendments to stimulate endogenous anaerobic tailings microorganisms. Tailings from three different operators were amended with agri-business by-products, placed in 100-mL microcosms and 1.5-L settling columns, and monitored for methanogenesis, pore water recovery, and solids densification. Several amendments increased methane production and accelerated biodensification compared to unamended and negative controls. Hydrolyzed canola, blood meal, bone meal and glycerol generally accelerated biodensification, stimulated methane production and supported growth of methanogens and fermentative microbes. Amendment altered the chemistry of the tailings, generally decreasing pH, increasing conductivity and magnesium, potassium, sodium, and bicarbonate concentrations. Biodensification is a potential engineered technology for accelerating water recovery and reducing the volume of stored oil sands tailings.

Application of Compound Flocculant for Oil Sand Mature Fine Tailings Two-Stage Treatment

The flocculation method had a good effect in treating oil sands tailings, and polyacrylamide (PAM) was commonly used as an effective flocculant. In this paper, poly diallyl dimethyl ammonium chloride (PDADMAC) combined with PAM and several supplementary materials into three compound flocculants were used to treat oil-sand tailings for the first time. The compound flocculants were applied for two-stage treatment to compare their performance with that of PAM. The first stage flocculation results showed that mature fine tailings (MFT) treated by compound flocculants had faster initial settling rate, higher clarity of supernatant and higher solid content of sediment than PAM, especially Flocculant A. The second stage dewatering of the mud layer indicated that the water release ability of sediment treated with compound flocculants was better than that of PAM, the yield stress was more appropriate and the capillary suction time (CST) was shorter. The deposits treated with the same flocculant for the two stages had great strength gain so reclaimation became much easier, which provided a new and efficient flocculation solution for the treatment of oil sands mature fine tailings.

Multifunctional CO2‐switchable polymers for the flocculation of oil sands tailings

ABSTRACTA series of multifunctional homopolymer and copolymer of 2‐dimethylamino ethyl methacrylate (DMAEMA) and N‐isopropyl acrylamide (NIPAM) were designed and used to flocculate oil sands mature fine tailings (MFTs). Carbon dioxide (CO2) protonated the tertiary amine groups of P(DMAEMA) and P(DMAEMA–NIPAM) making their chains positively charged. The pH sensitivity of these polymers favored the flocculation of the negatively charged clays in MFT due to charge neutralization. Three different polymers, P(DMAEMA), P(NIPAM33–DMAEMA67), and P(NIPAM67–DMAEMA33) were synthesized via aqueous free‐radical polymerization and used to flocculate MFT in the presence of CO2. Experimentally, CO2 was introduced in the system in three different ways: (1) CO2 was first bubbled into polymer solution, then the polymer solution was added to MFT, (2) CO2 was first bubbled into MFT and then the CO2‐free polymer solution was added to MFT, and (3) both polymers and MFT were bubbled with CO2 separately, then mixed together. We compared the effects of the method of CO2 addition, copolymer composition, and polymer molecular weight on MFT flocculation performance. Our results indicate that CO2‐switchable polymers can be employed to enhance the dewatering of challenging wastewaters such as oil sands tailings. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47578.

Polymer reaction engineering tools to design multifunctional polymer flocculants

A series of multifunctional terpolymers, poly(N-isopropyl acrylamide/2-(methacryloyloxy) ethyl trimethyl ammonium chloride/N-tert-butylacrylamide) [P(NIPAM-MATMAC-BAAM)], were designed to flocculate and dewater oil sands mature fine tailings (MFT). The hydrophobic BAAM comonomer helped in expelling water from the sediments, while the cationic MATMAC comonomer promoted the charge neutralization of negatively charged particles suspended in MFT. The chemical composition distributions of these terpolymers were designed based on the knowledge of the reactivity ratios of all comonomers, instead of by trial and error, as usually done for most polymer flocculants. The binary reactivity ratios of the comonomers were estimated by synthesizing the binary copolymers with various mole fractions of each comonomer in the feed and experimentally measuring the corresponding fraction of comonomer in the copolymers. Polymer reaction engineering tools were used to minimize compositional drift and guarantee the synthesis of terpolymers with narrow chemical composition distributions suitable for MFT dewatering. Focused beam reflectance measurement (FBRM) experiments showed that terpolymers promoted the formation of large MFT flocs (120 μm). The initial settling rate decreased with the increase in flocculant hydrophobicity, likely because the hydrophobic terpolymer segments did not take part in the bridging of the MFT particles. In contrast, the sediment dewaterability increased with the increase in terpolymer hydrophobicity. This study provides guidelines to design a polymer flocculant from first principles and demonstrates the potential of using hydrophobically modified cationic polymers to flocculate MFT effectively.

Monitoring polymer flocculation in oil sands tailings: A population balance model approach

Oil sands mature fine tailings are stable suspensions of clay particles and residual bitumen in an alkaline aqueous medium. They are formed when bitumen is extracted from oil sands using the Clark hot water process. Polymer flocculants are widely used to flocculate and subsequently dewater these tailings, but our knowledge is limited to empirical observations on how they work. A fundamental mathematical model would help monitor and design flocculation and dewatering processes more efficiently. In this study, we used a population balance model to describe the flocculation of mature fine tailings (MFT) with poly(vinylbenzyl trimethylammonium chloride). A time varying function was defined to account for the aggregate size evolution during MFT flocculation induced by polymer chains relaxation and rearrangement on the particle surfaces. The validity of the model was tested by varying the shear rate, mixing time and flocculant dosage using focused beam reflectance measurements (FBRM). The proposed model is a first step towards a more rational and quantitative approach to monitor and control treatment processes for oil sands tailings.

Dewatering of Oil Sands Tailings with Novel Chitosan-Based Flocculants

Mature fine tailings need to be dewatered to reduce the environmental impact caused by oil sands extraction. Polymer flocculants are commonly used to accelerate this process. In this work, we modified chitosan, a naturally occurring biopolymer, with 3-chloro-2-hydroxypropyltrimethylammonium chloride (Chito-CTA) and also grafted polyacrylamide to chitosan (Chito-g-PAM). We compared the dewatering performance of these two flocculants with that of a commercial cationic polyacrylamide (C-PAM). Chito-CTA and Chito-g-PAM dewatered tailings at rates of 18.27 and 20.72 m/h, respectively. The dewatering ability of Chito-CTA and Chito-g-PAM, measured in terms of capillary suction time (CST), was below 10 s, whereas the value for C-PAM was 82.3 s at optimum dosage. The turbidity of the supernatant obtained after flocculation with Chito-CTA or Chito-g-PAM was below 10 NTU, while C-PAM produced turbid supernatants. We studied the effect of flocculant microstructure on the specific resistance to filtration of the sediments. Chito-g-PAM produced sediments with the lowest resistance, 2.99 × 1012 m/kg, while C-PAM’s sediments had a much higher resistance of 40.26 × 1012 m/kg. We also used the focused beam reflectance measurement technique to determine floc size evolution, floc stability, and time required to induce floc formation. Our results indicate that chitosan-based polymers may be successfully used to treat oil sands mature fine tailings.

Enhanced Flocculation of Oil Sands Mature Fine Tailings Using Hydrophobically Modified Polyacrylamide Copolymers.

Hydrophobically modified acrylamide copolymers dewater oil sands tailings more effectively than anionic polyacrylamide, but the root causes for this enhanced performance have not been investigated systematically. Polyacrylamide‐poly(ethylene oxide methyl ether methacrylate) copolymers with different comonomer compositions, hydrophobic chain lengths, and molecular weights to map out these effects systematically are synthetized. Through a statistical design of experiments, it is found out that all three variables above significantly affected flocculation performance and that certain combinations achieve optimal results. The effect of centrifugation on the flocculation and dewatering performance of these polymers is also investigated.

Dewatering Oil Sands Tailings with Degradable Polymer Flocculants.

We synthesized hydrolytically degradable cationic polymers by micellar radical polymerization of a short-chain polyester macromonomer, polycaprolactone choline iodide ester methacrylate (PCL2ChMA) with two polyester units, and used them to flocculate oil sands mature fine tailings (MFT). We evaluated the flocculation performance of the homopolymer and copolymers with 30 mol % acrylamide (AM) by measuring initial settling rate (ISR), supernatant turbidity, and capillary suction time (CST) of the sediments. Flocculants made with trimethylaminoethyl methacrylate chloride (TMAEMC), the monomer corresponding to PCLnChMA with n = 0, have improved performance over poly(PCL2ChMA) at equivalent loadings due to their higher charge density per gram of polymer. However, MFT sediments flocculated using the PCL2ChMA-based polymers are easier to dewater (up to an 85% reduction in CST) after accelerated hydrolytic degradation of the polyester side chains. This study demonstrates the potential of designing cationic polymers that effectively flocculate oil sands tailings ponds, and also further dewater the resulting solids through polymer degradation.