Polyacrylamides revisited: flocculation of kaolin suspensions and mature fine tailings

A series of acrylamide‐based water‐soluble (co)polymers was synthesized and they were investigated as flocculants of model kaolin suspensions and mature fine tailings of oil sands. The effects of molar mass, charge density, and polymer concentration on flocculation efficiency were studied by monitoring the initial settling rate during sedimentation. Hydrolyzed polyacrylamide (HPAM) with high molar mass and intermediate acrylic acid contents (0.14–0.41 mol/mol (14–41 mol%)) performed better in flocculation tests on kaolin suspensions requiring lower dose for maximum initial settling rate than native polyacrylamide (PAM). Surface force measurements showed that at low polymer concentrations (1 ppm), the partially‐adsorbed polymer induced a bridging attraction between the mica surfaces. Increasing the polymer concentration to 10 and 50 ppm caused purely repulsive forces. The presence of anionic groups in HPAM led to stronger repulsion, which was also demonstrated by the higher viscosity and larger hydrodynamic radius of the charged polymer. The charge‐induced increase in the viscosity of polymer solutions was suppressed by the screening effect of salts in a buffer solution and reducing the viscosity is desirable in the injection of flocculants in the industrial process.     

Scaling inline static mixers for flocculation of oil sand mature fine tailings

Operations to reclaim mature fine tailings (MFT) ponds involve flocculation using high‐molecular‐weight polymers, for which inline static mixers are suited. Three different commercial static mixers were utilized to determine mixing parameters corresponding to optimal dewatering performance of flocculated MFT. MFT was treated with polymer solution under different mixing conditions. The dewatering rates passed through a peak with increasing mean velocity, V and Reynolds number, Re of the fluid. The greater the number of mixer elements, the lower the V and Re at which the peak dewatering rate occurred. Mixing parameters such as G‐value, residence time, and mixing energy dissipation rate of the most rapidly dewatering flocculated MFT were dependent on mixer type and setup. In contrast, peak dewatering rates converged when scaled with respect to specific mixing energy, E, demonstrating that E is a suitable scale‐up parameter for inline static mixing to produce optimally dewatering MFT. © 2015 American Institute of Chemical Engineers AIChE J, 61: 4402–4411, 2015     

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

A 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.     

Collapse of house-of-cards clay structures and corresponding tailings dewatering induced by alternating electric fields

Oil sands tailings are composed of charged clay colloidal solutions that are stabilized due to their double layer repulsions. Due to these repulsions, the microstructural arrangement of clay platelets in tailings is observed to be a stable house-of-cards like pattern with dominant edge-to-edge or edge-to-face attractions. The microstructural gaps from this arrangement tend to trap significant amounts of water. Scanning electron microscopy (SEM) was conducted on freeze dried samples to determine these gaps to be around 7?μm in control tailings with 40?wt.% clays and 30?μm in control tailings with 30?wt. % clays. In this study, we investigated the role of alternating current (AC) in inducing dewatering by collapsing this stable house-of-card structure. AC frequency caused localized charge displacements leading to formation of induced dipoles around clay double layers. These dipoles then underwent dielectrophoresis allowing face-to-face aggregation, which reduced microstructural gaps and caused dewatering. Depending on the electrical impedance of tailings-electrode load, decided by electrical properties of tailings and electrode configuration, optimal AC electric fields were identified and applied. AC frequencies between 10?kHz to 1?MHz were tested and a signature electric field between 500 and 1600?V/m was identified that resulted in the most desirable aggregation and dewatering effect. Control tailings with 30 and 40?wt.% solids content were tested and observed, respectively, to transform to 40–55?wt.% solids content on loose aggregation and 50 to 65?wt.% on strong aggregation. The dewatering effect arising from both aggregation cases resulted in about 12% water recovery, observed through gravity settling tests. Structural transformations of tailings post-AC treatment observed by SEM further prove the collapse of the stable house-of-card microstructural arrangement.     

Design of ionic liquids for dewatering stable solid/liquid complex slurries

Exploitation of mineable oil sands in Canada has thus far produced over 50 km² of tailings in ponds where the fine solids remain suspended for years, even decades. These ponds represent a major liability and environmental burden for operating companies, with their dewatering critical to their remediation. In this work, we used the chemistry of the tailing pond constituents to design an ionic liquid (IL) for dewatering the mature fine tailings (MFT), taking advantage of the ability to introduce unique and different functionalities into each ion of the IL. We chose a class of protic ILs whose ions will interact with the solids while rejecting water. As an example, octylammonium oleate can be used to remove more than 70% of the water from MFT. The nature of the ILs makes their use amenable to a variety of large-scale separation techniques allowing engineering versatility in the design of the final process.     

Release of bitumen from mature fine tailings in the presence of a polymeric dispersant

The effect of the addition of a polymeric dispersant, sodium lignosulphonate (LS), on the dispersion of mature fine tailings (MFT) was studied using zeta potential and total organic carbon measurements. Three different types of LSs were investigated to determine the importance of molecular weight and level of anionicity of LSs on the treatment of MFT. The presence of two fractions of bitumen was identified in the tested MFT sample. A small portion of bitumen was found to occur in the form of weakly held aggregates between bitumen and fine solids. This fraction was easily dispersed by small dosages of LS, resulting in bitumen liberation to the tailings surface. A much larger amount of bitumen was found to be strongly attached to the solids, and only very high dosages of LS were capable of partly liberating this fraction. The zeta potential promoted an understanding of the mechanism of adsorption of LS on the particles and liberation of bitumen from MFT. Carbon measurements facilitated determination of the adsorption density of the selected types of LS on solid particles.     

Can We Make Better Polyurethane Composite Foams with Oil Sands Mature Fine Tailing?

This study explains how to make rigid polyurethane/mature fine tailings (PU/MFT) foam composites with good mechanical and thermal properties by in situ polymerization. Compared to PU/Cloisite Na⁺ and PU/Cloisite 30B composites, the novel PU/MFT composites have similar tensile properties, but better thermal properties. Adding 2 parts per hundred parts (pphp of polyol by weight) of MFT particles decreases the thermal conductivity of polyurethane foam by 10%, while adding Cloisite Na⁺ or Cloisite 30B decreases it by only 6% and 5%, respectively, resulting in considerable energy savings in large‐scale insulation applications. PU/MFT foams also sustain about the same compressive strength and modulus even when loaded up to 20 pphp MFT. These results are important for oil sands industries trying to decrease the environmental footprint of their operations and for polyurethane‐producing companies attempting to improve properties of their products and contribute to environmental cleanup.

     

Calcined oil sands fine tailings as a supplementary cementing material for concrete

In recent years, metakaolin (MK) has received considerable attention, as a high-performance pozzolanic supplementary cementing material for use in concrete. MK is produced by calcining kaolinite at temperatures between 600 and 1000 °C. In the province of Alberta, Canada, the oil sand mining industry produces millions of cubic metres of oil sand tailings that could become a major source of MK. This paper summarizes the behaviour of calcined fine tailings (CFT) as a supplementary cementing material in high-performance concrete and compares its performance to that of MK and silica fume (SF). It was found that CFT has excellent pozzolanic activity in concrete, making it an environmentally friendly and potentially cost effective supplement.     

Preparation and performance of slag-based binders for the cementation of fine tailings

To achieve effective cementation of fine tailings, slag-based binders were prepared using Portland cement clinker stimulation, early strength activator (ESA, mixture of anhydrite and triethanolamine at 97:3 (w/w)) activation and slag pulverization methods. The compressive strength, hydration products, slag reaction degree and non-evaporable water content of the consolidated samples under different curing times were analyzed to clarify the application performance and early strength action mechanisms of this slag-based binder. The results showed that clinker alone was able to effectively stimulate the slag’s cementitious property, but the cementation strength was relatively low. The addition of ESA in the clinker activated slag promoted the conversion of C₄AH₁₃ into ettringite (AFt) and accelerated the consumption of Ca(OH)₂, all of which significantly improved the early cementation strength of fine tailings. Slag pulverization promoted the slag reaction degree and increased the yield of hydrated products, which led to a further increase in the early strength of the slag-based binder. Eventually, a more efficient and higher early strength slag-based binder was prepared with the composition of 27% clinker, 10% ESA and 63% pulverized slag, and the cementation strength at 3 curing days for the fine tailings sample was 231% more than that of P.O 42.5 Portland cement.     

Process development studies on recovery of clean coal from ultra fine hardcoal tailings using enhanced gravity separator

In this study, we report the experimental results with respect to the beneficiation of fine hardcoal from the Çatala?z? Coal Preparation site tailings containing about 90% (by weight) of ?600 µm size particles. These tailings contain 28.41% ash. The coal sample was subjected to a two‐stage concentration process. The underflow product of hydrocyclone under optimized conditions was further processed in Mozley Multi‐Gravity Separator to reduce the ash content of the coal. The results showed that a coal product containing 6.98% ash was obtainable with recovery of 61.73% by this two‐stage concentration process.     

高分子絮凝剂特性对污泥调理和脱水效果的影响及在线絮凝检测技术应用研究

高分子絮凝剂品种及特性对污泥调理及脱水效果有很大影响,试验结果表明絮凝剂的相对分子质量是决定性因素,电荷特性影响较小。利用一种在线絮凝检测技术可连续检测污泥调理工艺中污泥颗粒絮凝过程,从而形成了一种全新的污泥絮凝检测方法,为污泥调理和脱水工艺的过程控制提供了可能性。