Dewatering Oil Sands Tailings with Degradable Polymer Flocculants

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.

A review of the roles of constituent minerals and residual bitumen in the solid-liquid separation of oil sands tailings

The efficient dewatering of fluid fine tailings (FFT) generated from warm-water extraction of Canadian oil sands is a major challenge that has limited the timely reclamation of the tailings. It is generally recognized that both chemical amendments and physical/mechanical solid-liquid separation treatments are required to speed up FFT dewatering. Significant efforts have been made to enhance the rate of solid-liquid separation of FFT in the past several decades. The fact that these efforts have met with limited successes calls for a better fundamental understanding of the solid-liquid separation process. In this work, we reviewed and critically analyzed the factors that contribute to the difficult dewatering of FFT, including the role of constituent minerals and residual bitumen. In particular, the effects of mineralogical composition, mineral particle size, and the role of residual bitumen on settling rate, hydraulic conductivity, and filtration rate are reviewed and discussed. This review also points out directions to accelerate the dewatering of FFT, such as reducing the effective volume fraction of swelling clays and releasing bitumen coating from clay surfaces, that may significantly increase the filtration rate of oil sands tailings.

Estimating the bioaccessibility of flocculants in the presence of sediments in model wastewater

The cationic degradable polymer poly(lactic acid) choline iodide ester methacrylate, poly(PLA₄ChMA), can be used to flocculate particles and dewater sediments from tailings ponds and wastewater. A suitable bioaccessibility method is required to characterize the interactions of this novel flocculant in the human gastrointestinal system. To this end, a physiologically based extraction test (PBET) was modified to evaluate the bioaccessibility of flocculants. Bioaccessibility (bioaccessible fraction) is a measure of the solubility of a contaminant in gastrointestinal fluids and that may be available for systemic absorption. The flocculants poly(PLA₄ChMA), SNF C3276, and FLOPAM A3338 were tested at a solid-to-liquid ratio of 1:200 in the absence and presence of kaolin clay, which is used as a model sediment compound. Bioaccessible fractions were characterized by proton nuclear magnetic resonance spectroscopy and estimated by gravimetry. The bioaccessibility of poly(PLA₄ChMA) in gastric and intestinal PBET solutions decreases from 78% to 100%, respectively, in the absence of kaolin to approximately 0% with kaolin, indicating that poly(PLA₄ChMA) remains adsorbed onto the clay surface throughout the PBET, a result confirmed by thermogravimetric analysis. The bioaccessibility of cationic SNF C3276 and anionic FLOPAM A3338 in gastric solution is approximately 76% and 26%, respectively, and is not affected by the presence of kaolin. However, in intestinal solutions, the bioaccessibility of SNF C3276 and FLOPAM A3338 (60-85% in the absence of kaolin) changes to 0% and 100%, respectively, in the presence of kaolin. These results, interpreted in terms of solution pH and surface charge, demonstrate that interactions with kaolin influence the solubility of flocculants and must be considered in the evaluation of bioaccessibility. In future works, such bioaccessibility methods can be applied to assess the human-health safety of using flocculants in wastewater treatments.

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.

Synthesis, Surface Tension, Flocculation and Antibacterial Properties of Cationic Copolymer Methacryloxyethyl Trimethyl Ammonium Chloride-Butyl Acrylate-Acrylamide

Three cationic copolymers methacryloxyethyl trimethyl ammonium chloride-butyl acrylate-acrylamide (MTAC-BA-AM terpolymer) were designed and synthesized by emulsion polymerization. Their structures were confirmed by FT-IR and 1H NMR. The effect of content of hydrophobic monomer butyl acrylate (BA) in MTAC-BA-AM terpolymer on surface activities, flocculation and antibacterial properties were investigated. The study of surface tension shows that MTAC-BA-AM terpolymer has good surface activity due to the introduction of hydrophobic monomer BA. The flocculation experiment showed that the light transmittance of the kaolin suspension supernatant was 98.13% when the dose of MTAC-BA-AM terpolymer in the kaolin suspension was 0.03 mg/L, which was obviously better than the P(MTAC-AM) (91.02%) without hydrophobic modification of BA. The bacteriostatic experiment of MTAC-BA-AM terpolymer showed that as the content of hydrophobic monomer BA in MTAC-BA-AM terpolymer increased the inhibitory rate of MTAC-BA-AM terpolymer aginst Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus)

Perspectives and design considerations of capillary-driven artificial trees for fast dewatering processes

Recent progresses on nanocapillary-driven water transport under metastable conditions have substantiated the potential of artificial trees for dewatering applications in a wide pressure range. This paper presents a comprehensive performance analysis of artificial trees encompassing the principle for negative capillary pressure generation; impacts of structural, compositional, and environmental conditions on dewatering performance; and design considerations. It begins by delineating functionalities of artificial trees for evaporation (leaves), conduction (xylem), and filtration (root) of water, in the analogy to natural trees. The analysis revealed that the magnitude of (negative) capillary pressure in the artificial leaves and xylem must be sufficiently large to overcome the osmotic pressure of feed at the root. The required magnitude can be reduced by increasing the osmotic pressure in the artificial xylem conduits, which reduces the risk of cavitation and subsequent blockage of water transport. However, a severe concentration polarization that can occur in long xylem conduits would negate such compensation effect of xylem osmotic pressure, leading to vapor pressure depression at the artificial leaves and therefore reduced dewatering rates. Enhanced Taylor dispersions by increasing xylem conduit diameters are found to alleviate the concentration polarization, allowing for water flux enhancement directly by increasing leaf-to-root membrane area ratio.

Evaluation of a Novel Polymeric Flocculant for Enhanced Water Recovery of Mature Fine Tailings

The novel cationic flocculant, poly(lactic acid) choline iodide ester methacrylate (poly(PLA4ChMA)), has been shown to provide improved flocculation of 5.0 wt.% mature fine tailings (MFT) diluted in deionized water compared to commercial anionic polymers, with continued dewatering of the sediment occurring as the polymer undergoes partial hydrolytic degradation. However, the elevated dosages (10,000 ppm) required would make the polymer costly to implement on an industrial scale. With this motivation, the impact of MFT loading and the use of process water is explored while comparing the settling performance of poly(PLA4ChMA) to available commercial alternatives such as anionic FLOPAM A3338. Improved consolidation of 5.0 wt.% MFT diluted with process water could be achieved at reduced dosages (500 ppm) with poly(PLA4ChMA). However, the final compaction levels after polymer degradation were similar to those achieved with the nondegradable commercial flocculants. Flocculation-filtration experiments with undiluted MFT are also conducted to compare the performance of the polymers. Significantly faster rates of water release were observed with the cationic flocculants compared to FLOPAM A3338, but no improvement in the overall tailings compaction was found either before or after poly(PLA4ChMA) degradation. Thus, the improved dewatering observed with poly(PLA4ChMA) in dilute MFT suspensions does not extend to conditions that would be encountered in the field.

Rapid Dewatering and Consolidation of Concentrated Colloidal Suspensions: Mature Fine Tailings via Self-Healing Composite Hydrogel

Billions of tonnes of thick waste streams with highly concentrated colloidal suspensions from different origins have accumulated worldwide, exampled as over 220 km² mature fine tailings (MFT) from oil sands production in north Alberta. Current treatment technologies are limited by slow yet insufficient water release and sludge consolidation. Herein, a self-healing composite hydrogel system is designed to convert concentrated aqueous colloidal suspensions (e.g., MFT with colloidal solid content >30 wt %) into a dynamic double cross-linked network for rapid dewatering and consolidation. The resultant composite hydrogel demonstrates an excellent dewatering performance so that over 50% of water could be rapidly released within 30 min by vacuum filtration. Furthermore, the formed infinite cross-linked network with self-healing ability can effectively trap fine particles of all sizes and capture small flocs during mechanical mixing, thereby enabling a low solid content at the ppm level in the released water. This new strategy outperforms all the previously reported treatment methods; under mechanical compression, over 80% of water is removed from the MFT, thereby generating a stackable material with >70 wt % solids within an hour. These results demonstrate a highly effective approach and provide insight into the development of advanced materials to tackle the challenging environmental slurry issues.

Adsorption Characteristics of Carboxymethylated Lignin on Rigid and Soft Surfaces Probed by Quartz Crystal Microbalance

Limited information is available on the interaction of anionically charged lignin and cationic particles, despite the promising use of anionic lignin as a coagulant and dispersant for suspension systems. The main objective of this study was to discover the fate of lignin on its interaction with rigid and soft surfaces. In this work, carboxymethylated lignin (CML) with two different charge densities were produced, and their adsorption performance on gold and poly(diallydimethylammonium chloride) (PDADMAC)-coated gold surfaces was comprehensively studied. The viscoelastic properties of adsorbed CML on the gold surface were investigated by means of quartz crystal microbalance with dissipation. A higher adsorbed amount and compact layer were observed for the adsorption of CML with a lower charge density of -1.16 meq/g (CML1). CML with a higher charge density (-2.92 meq/g), CML2, yielded a lower surface excess density of 2.31 × 10^-6 mol/m² and a higher occupied area per molecule (71.84 Ų) at the interface of water and gold sensor. Below and at equilibrium, CML2 generated a bulkier adsorption layer than did CML1 on the gold sensor and on the PDADMAC-coated sensor. Studies on the layer-by-layer (LBL) assembly of CML and PDADMAC revealed that CML1 adsorbed more greatly than CML2 on PDADMAC, and it generated a thicker but less viscoelastic layer. In this system, the greater loss to storage modulus ( G″/ G') value was achieved for CML2, indicating its looser structure in the LBL system. Studies on the LBL assembly of carboxymethylated xylan/PDADMAC and CML/PDADMAC provided concrete evidence for the fate of three-dimensional structure of CML on its adsorption performance.

Advanced Polymer Flocculants for Solid-Liquid Separation in Oil Sands Tailings

The generation of tailings as a by product of the bitumen extraction process is one of the largest environmental footprints of oil sands operations. Most of the tailings treatment technologies use polymer flocculants to induce solid-liquid separation. However, due to the complex composition of tailings, conventional flocculants cannot reach the same performance achieved in other wastewater treatments. Over the last couple of decades, the oil sands industry has used acrylamide-based flocculants to treat tailings, achieving major progress in process optimization and integration with mechanical operations, but they still could not reach the required land reclamation targets. Over the last 5 years, the group designed, synthesized, and tested several novel polymer flocculants tailored for oil sands tailings treatment. This feature article communicates recent developments in these innovative polymers. The article first provides a background on tailings generation and treatment, followed by the description of advanced polymer flocculants categorized according to their microstructures such as linear, branched, and graft. The other tailings remediation technologies and one of the initial works on modeling of tailings flocculation is discussed.

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.

Production of Flocculants, Adsorbents, and Dispersants from Lignin

Currently, lignin is mainly produced in pulping processes, but it is considered as an under-utilized chemical since it is being mainly used as a fuel source. Lignin contains many hydroxyl groups that can participate in chemical reactions to produce value-added products. Flocculants, adsorbents, and dispersants have a wide range of applications in industry, but they are mainly oil-based chemicals and expensive. This paper reviews the pathways to produce water soluble lignin-based flocculants, adsorbents, and dispersants. It provides information on the recent progress in the possible use of these lignin-based flocculants, adsorbents, and dispersants. It also critically discusses the advantages and disadvantages of various approaches to produce such products. The challenges present in the production of lignin-based flocculants, adsorbents, and dispersants and possible scenarios to overcome these challenges for commercial use of these products in industry are discussed.

A novel hydrophobically-modified polyelectrolyte for enhanced dewatering of clay suspension

This work investigates the effect of multifunctional poly (N-isopropyl acrylamide/acrylic acid/N-tert-butylacrylamide) [p(NIPAM-AA-NTBA)] ternary polymer on the sedimentation of kaolin clay - a major fraction of oil sands tailings. A series of linear, uncross-linked p(NIPAM), p(NIPAM/AA), and p(NIPAM/AA/NTBM) were synthesized as random copolymers, where all monomer units were randomly arranged along the polymer backbone and connected by covalent bonds. The ternary copolymer, used as a flocculant, exhibited thermo-sensitivity, anionic nature, and hydrophobic association due to NIPAM, AA, and NTBM, respectively. As the ternary polymer is thermosensitive, it undergoes extended to coil-like conformation, i.e. hydrophilic to hydrophobic transition, above its lower critical solution temperature (LCST). The comonomers NIPAM (above LCST) and NTBM help expel water out of sediments due to their hydrophobicity, while AA promotes charge neutralization of the kaolin clay particles. The effect of number average molecular weight, charge density, and concentration of NTBM on settling behavior of kaolin suspension was examined. Settling test at 50 °C resulted in significantly higher settling rates compared to that at room temperature. Further, the quality of water recovered in each experiment was tested in terms of its turbidity. These results indicate that this novel ternary polymer can be employed to enhance the recovery of water from oil sands tailings containing clays.

Strategies to combine ROP with ATRP or RAFT polymerization for the synthesis of biodegradable polymeric nanoparticles for biomedical applications

The available strategies to combine CRPs and ROP in the synthesis of highly engineered polymer nanoparticles are here critically discussed.