Article pubs.acs.org/Langmuir
Molecular Weight Dependence of Synthetic Glycopolymers on Flocculation and Dewatering of Fine Particles Han Lu,† Li Xiang,† Xin Cui, Jing Liu, Yinan Wang, Ravin Narain,* and Hongbo Zeng* Department of Chemical and Materials Engineering, University of Alberta, 116 Street and 85 Avenue, Edmonton, Alberta T6G 2G6, Canada ABSTRACT: In this study, poly(2-lactobionamidoethyl methacrylamide) of various molecular weights (MWs) was synthesized using conventional free-radical polymerization. The effect of MW and polymer dosage on the settling rate of kaolin particles, turbidity of the supernatant, mud-line position, and solid content was investigated to determine the flocculation performance. The interaction forces, polymer conformation, particle sizes, and MWs were determined using several techniques, including surface forces apparatus, atomic force microscopy (AFM), dynamic light scattering, and gel permeation chromatography. Our results reveal that the initial settling rate of kaolin particles and the clarity of supernatants increase with increasing MW of the glycopolymers. Surface force measurements and AFM imaging of the adsorbed polymer surfaces show strong polymer−particle adhesion and bridging attraction between the glycopolymers and clay surfaces, which increase with increasing MW of the glycopolymer. The strengthened bridging attraction with the polymer MW is attributed to the formation of stronger adhesion (e.g., via hydrogen bonding) between the fine particles and the abundant hydroxyl groups in the glycopolymers of higher MW, thus contributing to enhanced flocculation behaviors. Our results provide new insights into the development of eco-friendly polymer flocculants based on glycopolymers for an efficient solid−liquid separation in tailing treatment and into the fundamental understanding of associated intermolecular interactions and flocculation mechanisms.
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INTRODUCTION Removing solid particles and recycling water have been critical issues for mineral and oil sands industry for several decades because fine particles suspended in the wastewater can cause potentially serious environmental issues.1−3 Inorganic salts and synthetic high-molecular-weight (MW) polymers are widely applied to coagulate and flocculate the particles in mine tailings and oil sands tailings.2−12 However, inorganic flocculants such as alumina13 and polymers such as poly(N-isopropyl acrylamide) [P(NIPAAm)] are never considered to be eco-friendly because of the potential risk to environment and health. Several natural and synthetic polymers have proved to be more effective and eco-friendly, such as chitosan,14 modified starch derivatives,15−17 poly(vinyl alcohol) (PVA), and poly(ethylene oxide).18−21 A number of studies about the surface interaction of nonionic linear polymers on the particles have been carried out since the 1970s. PVA and poly(ethylene oxide) are the two most widely used examples to help researchers gain a deep insight into the adsorption and flocculation mechanism.22−32 From previous studies, it can be seen that the adsorption of nonionic polymers such as PVA was driven by hydrogen bonding of the hydroxyl groups of PVA to the free silanol groups of silica particles and influenced by the solution pH. At the point of zero charge (pH 2) of silica, the adsorption of PVA was the highest because of the presence of more undissociated silanol groups in silica acting as the adsorption site.33 © XXXX American Chemical Society
Synthetic carbohydrate-based polymers, also known as glycopolymers, are receiving increasing attention for their application in drug/gene delivery carrier and antibacterial/virus because of their high biocompatibility, low or no cytotoxicity, and potential targeted delivery of cargo.34 The synthesis, characterization, and biomedical applications of glycopolymers with different compositions and architectures were investigated in previous studies.35 However, few studies have reported on the application of glycopolymers in solid−liquid separation.36 The carbohydrate−protein interaction was attributed to specific interaction of the protein with the sugar residues mediated by the hydroxyl groups; therefore, these hydroxyl groups can be exploited for enhanced flocculation when a glycopolymer is used as a nonionic flocculant.35 Because of the presence of pendant sugar residues, poly(2-lactobionamidoethyl methacrylamide) (PLAEMA) contains more hydroxyl groups than PVA with the same average number of repeating units (DP), which is expected to contribute to a stronger attraction (hydrogen bonding) to the silanol groups in solid particles. In addition, the wide applications of PLAEMA in the biomedical field have proved its outstanding eco-friendly property. It is expected that PLAEMA would be able to attract solid particles via its Received: August 18, 2016 Revised: October 5, 2016 Published: October 14, 2016 A
DOI: 10.1021/acs.langmuir.6b03072 Langmuir XXXX, XXX, XXX−XXX
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model 250 dual detectors system) using 0.5 M sodium acetate and 0.5 M acetic acid as eluents. The flow rate was set to 1.0 mL/min and pullulan standards (Mw = 5.0 × 102 to 4.0 × 106 g/mol) were used for calibration. The resulting polymers were characterized by a Varian 500 1 H NMR using D2O as the solvent. Settling Tests. The settling tests followed the previously reported procedure.4 For complete dissolution of the polymer flocculant before mixing with the kaolin suspension, a selected amount of polymer (1, 2.5, 5, 10, and 15 mg) was dissolved in 10 mL of distilled deionized water and kept for 24 h. The kaolin suspension (5 wt %) was homogenized using a mechanical stirrer (IKA Digital Stirrer RW20, Fisher Scientific). The kaolin suspension (90 mL) was transferred into a standard 250 mL baffled beaker and was stirred with a 4-blade stainless steel impeller (blade width 3 cm, Fisher Scientific) at 600 rpm for 2 min. The polymer stock solution was then added to the suspension in 1 min with an agitation speed of 200 rpm. The agitation was stopped immediately after complete addition of the polymers with the desired amount. The mixture was transferred to a 100 mL cylinder. The cylinder was inverted for 5 times and then kept standstill for 24 h at room temperature. The height of the so-called mud-line was monitored as a function of time. The mud-line position was determined as % mud-line = hf/H, where hf and H represent the height of the sediment and the original suspension, respectively. The ISR was determined by the initial slope of the plot (normalized height vs time), and the light transmittance of the supernatant at 500 nm wavelength was monitored using a UV−vis spectrometer. Ten milliliter of released water was transferred from the cylinder for a turbidity test after 1 h of settling test. The turbidity of the released water was calculated from the equation nephelometric turbidity units (NTU) ≈ 0.191 + 926.1942 × [−log(%T/100)], where %T represents the value of transmittance of the supernatant. The solid content of the sediment was determined by dividing the mass of the solid particles (ms) by the total mass of the sediment (mf). Polymer Sizes. The hydrodynamic radii of polymers in the bulk solution were determined by DLS using a Malvern Zetasizer Nano ZSP. For a complete dissolution, 100 ppm polymer solutions were prepared by dissolving desired amounts of polymers in distilled deionized water for 24 h in 20 mL glass vials before the experiment. All tests were carried out at 23 °C. Interaction Force Measurements between Polymers and Clay Surfaces and Imaging of Adsorbed Polymers. SFA was used to measure the interaction of the polymer with the model mica clay surface, which has a silicate structure and composition similar to those of kaolin. The morphology of the adsorbed polymer coating was imaged using AFM (MFP-3D, Asylum, Santa Barbara, CA). The polymer films for AFM imaging were prepared by dipping the freshly cleaved mica sheets in a 1000 ppm polymer solution (1 mg/mL in distilled deionized water) to allow adsorption for 1 h, followed by thoroughly rinsing the surfaces with distilled deionized water several times to remove the unbounded polymer chains and then drying in vacuum. Surface topography of the adsorbed polymer layer on mica was characterized using AFM in tapping mode in air. At least three mica substrates and more than three different positions on each surface were measured, and typical AFM images were presented. SFA has been widely used to directly measure the intermolecular and surface forces of various material systems in both vapor and liquid media, with Angstrom distance resolution and nanonewton force precision.38−41 In a typical SFA experiment, two back-silvered mica sheets with the same thickness of 1−5 μm were glued on to two cylindrical silica disks with a radius (R) of 2 cm. If the separation distance D was much smaller than R (D ≪ R), the interaction between two cross-cylindrical mounted mica surfaces is locally equal to the interactions between two spheres of radius 2R or a sphere of radius R near a flat surface.42 The absolute distance between the two mica surfaces was determined using an optical techniquemultiple beam interferometry employing fringes of equal chromatic order (FECO) and the surface forces were derived through Hooke’s law by multiplying the spring constant with the spring deformation.32,35 During the force measurements, the reference distance (D = 0) was measured at the adhesive contact between the two bare mica surfaces
interaction with surface silanol groups, improving the flocculation performance of solid particles and water recycling. In this work, 2-lactobionamidoethyl methacrylamide (LAEMA) homopolymer with various MWs has been synthesized for the solid−liquid separation, viz. flocculation and enhanced dewatering of fine solid suspensions. To the best of our knowledge, this is the first report of using glycopolymers containing galactose residues for solid−liquid separation in tailing water treatment. Kaolin particles were used as model clay solids in the study, which is a major component of oil sands tailing solids, consisting of alternating layers of silica tetrahedra and alumina octahedra, which are broken at the edge of the crystal to expose silanol and aluminol groups, resulting in pH-dependent charge property. Kim et al. have found that the zeta potential of kaolin is negative at around pH = 5−8,19 which was used as the standard condition in this study. The initial settling rate (ISR), supernatant turbidity, sediment solid content, and mud-line position were investigated. Dynamic light scattering (DLS), surface forces apparatus (SFA), and atomic force microscopy (AFM) were also used to characterize the intermolecular and surface interactions between the polymers and the solid particles, providing insights into the flocculation mechanism.
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MATERIALS AND METHODS
Materials. An LAEMA monomer was prepared in-house according to a previously reported procedure.37 Ammonium persulfate was purchased from Sigma-Aldrich Chemicals (Oakville, ON, Canada). N,N,N′,N′-Tetramethylenediamine (TEMED) was purchased from Fisher Scientific. All organic solvents were purchased from Caledon Laboratories Ltd. (Georgetown, ON, Canada). The particle size distribution of kaolin (Acros Organics) was determined using laser diffraction (Mastersizer 2000, Malvern) and is shown in Figure 1.
Figure 1. Particle size distribution of the kaolin sample used in this study. Synthesis of PLAEMA. Linear PLAEMA homopolymer was prepared according to previously reported procedures.34 Typically, LAEMA (650 mg; 1.39 mM) was dissolved in 5 mL of distilled deionized water in the presence of ammonium persulfate (5 mg; 0.02 mM) and TEMED (20 μL; 0.063 mM) as the initiator and catalyst, respectively. The mixture was purged with nitrogen for 30 min in a sealed 10 mL Schlenk tube, and the reaction was conducted at room temperature for 24 h. The polymer was purified by dialysis against double-distilled deionized water for 4 days. Then the solution was frozen using liquid nitrogen for 10 min and freeze-dried for 2 days. The number-average MW (Mn) and MW dispersity (Mw/Mn) were determined using gel permeation chromatography (GPC) (Viscotek B
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Figure 2. (a) Synthesis of the LAEMA homopolymer via conventional free radical polymerization. (b) Proposed mechanism of the adhesion of the polymer to the particle surface. in air. Then, the prepared 10 ppm polymer solution was introduced into the gap between the two mica surfaces and incubated for 30 min. All experiments were conducted at room temperature (∼23 °C). For each sample, the surface forces measurements were repeated at least three times for two different pairs of surfaces to ensure reproducibility.
residues. As expected, the synthesized polymers have broad MW distributions, and PLAEMA with the highest MW has the broadest polydispersity index (PDI) as shown in Figure 3.
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RESULTS AND DISCUSSION LAEMA homopolymers with various MWs were synthesized via conventional free radical polymerization, and their performances on aggregating particles were evaluated, as shown in Figure 2. Table 1 shows Mn, polydispersity (Mw/Mn), and compositions of the glycopolymers. Table 1. Synthetic Parameters, MWs, and MW Distributions of the Glycopolymers, PLAEMA Prepared through Conventional Free Radical Polymerization polymer compositions
LAEMA (mg)
ammonium persulfate (mg)
TEMED (μL)
Mn (kDa)
Mw/ Mn
P(LAEMA)177 P(LAEMA)397 P(LAEMA)975
650 650 650
5 2.5 1.25
20 20 20
83 186 456
2.61 3.67 3.35
Figure 3. MW and polydispersity of synthesized PLAEMA measured using gel permeation chromatography (GPC) (black solid line, 83 kDa; red solid line, 186 kDa; and blue solid line, 456 kDa).
Settling Test. The flocculation performance of PLAEMA with different MWs as a function of dosage was investigated, as shown in Figure 4. As shown in Figure 4a, in the case of P(LAEMA)975 (with an MW of 456 kDa), the ISR reached a maximum value (1.26 m/h) at the dosage of 10 ppm. However, PLAEMA with lower MWs (186 and 83 kDa) showed negligible ISR because of relatively lower adhesion of polymers to the particle surface. P(LAEMA)397 (with an MW of 186 kDa) showed a maximum settling rate (0.52 m/h) at the dosage of 25 ppm. In the case of P(LAEMA)177 (with an MW of 83 kDa), the settling rate kept increasing up to 0.49 m/h at the dosage of 150 ppm. Comparatively, in the cases of P(LAEMA)975 and P(LAEMA)397, the settling rate reduced nearly to zero at 150 ppm, which is even lower than the settling rate of the kaolin suspension without any polymer treatment.
Characterization of the Tailings and Polymers. Particle size distribution is a critical factor that influences the flocculation and settling performance. As shown in Figure 1, the D10, D50, and D90 of the kaolin particles are 1.94, 6.67, and 27.2 μm, respectively. The size distribution parameter Dm represents MW % of the particle sample and was smaller than the corresponding value of Dm (μm). In this study, 10 wt % of the kaolin particles were smaller than 1.94 μm. Similarly, 90 and 50 wt % of the particles were smaller than 27.2 and 6.67 μm, respectively. The adhesion of PLAEMA to the surface of kaolin particles was mainly caused by bridging interactions, such as van der Waals force and hydrogen bonding as a result of a large number of hydroxyl groups from the pendant sugar C
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Figure 4. (a) ISR and (b) supernatant turbidity of the PLAEMA-treated model tailing (kaolin suspension) at 25 °C (black squares, 83 kDa; red circles, 186 kDa, and blue triangles, 456 kDa).
The gel-like formation of the kaolin suspension was observed at an extremely high polymer dosage, which was the result of overdose of the polymer flocculant. The extra polymer chains covered on the particle surface left less bare surface for the interaction and bridging of polymers adsorbed on other particles, leading to poor bridging and linkage of multiple particles and flocculation. The significance of controlling the dosage of flocculants also lies in the fact that strong attraction is necessary to overcome the steric force that arises from the adsorbed polymer chains on particle surfaces.45 PLAEMA with high MW induced a higher settling rate with less dosage as compared with that of low MW, suggesting stronger attraction (van der Waals force and hydrogen bonding) to bridge and flocculate the solid particles. The longer polymer chains are capable of forming more hydrogen bonds on the particle surface and bridging more particles, as compared with the shorter ones. The clearance of the released water was determined by testing the turbidity of the supernatant after 1 h of settling test. As shown in Figure 4b, the turbidity of the kaolin suspension with polymer treatment was reduced from 3179 to 2510, 1526, and 750 NTU at 10 ppm in the cases of P(LAEMA)177, P(LAEMA)397, and P(LAEMA)975, respectively. As the dosage increased up to 25 ppm, the turbidity of P(LAEMA)975 (456 kDa) was reduced to 95 NTU. By contrast, in the case of P(LAEMA)177 (83 kDa), the reduction of turbidity was not obvious. At a polymer dosage of 150 ppm, the turbidity of all cases was reduced to an extremely low value (∼20 NTU), showing a negligible amount of kaolin particles left in the supernatant. For the high MW polymer, the attraction between the polymer and the solid surfaces was sufficiently strong at a relatively low dosage, which also suggests a stronger ability of providing more hydroxyl groups for flocculation. Figure 5a−c are the photographs taken after 24 h of settling at room temperature, directly showing supernatant clarity for different cases with varying MWs and dosages. The cylinders from left to right represent polymer dosages of 10, 25, 50, 100, and 150 ppm, respectively. In the case of P(LAEMA)975, all samples showed the clearest supernatant. However, in the cases of P(LAEMA)177 and P(LAEMA)397, higher dosage induced clearer supernatants. The clarity phenomena of the supernatant observed in Figure 5 are in good agreement with the settling results of Figure 4. Consolidation of Sediment. The normalized height of the liquid−solid interface (mud-line) and the solid content of the sediment reflect the ratio of the released water and the water trapped in the sediment. As shown in Figure 6a, the mud-line of the sediment treated with P(LAEMA)177 was the lowest among
Figure 5. Photographs showing the effect of dosage and MW on the turbidity of the supernatant: (a) 83 kDa, (b) 186 kDa, and (c) 456 kDa. The dosages are 10, 25, 50, 100, and 150 ppm (from left to right), respectively.
the three cases. With increasing polymer dosage, the mud-line of the sediment became gradually higher in all three cases. The solid content of the sediment was defined by the weight D
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Figure 6. (a) Mud-line position percentage and (b) solid content of the sediment of the PLAEMA-treated model tailing (kaolin suspension) at 25 °C (black squares, 83 kDa; red circles, 186 kDa; and blue triangles, 456 kDa).
values of all glycopolymers studied are close to zero and the zeta potential of kaolin is measured to be −30.67 ± 1.81 mV. Surface Force Measurement. To understand the effect of MW on the interaction of polymers on the kaolin particle surface, surface force measurements were carried out between two model clay surfaces (i.e., mica) in a 10 ppm PLAEMA water solution. The typical force−distance curves measured using SFA shown in Figure 8a−c represent the force results of P(LAEMA)177, P(LAEMA)397, and P(LAEMA)975, respectively. When two mica surfaces approached, repulsion was measured in all three cases, mainly resulting from the steric interaction of the opposing and approaching polymer chains adsorbed on mica substrates. Adhesion (Fad/R) ≈ 3, 8, and 11 mN/m was measured during the separation of the two surfaces in P(LAEMA) 177, P(LAEMA) 397, and P(LAEMA)975 water solutions, as shown in the red curves of Figure 8a, b, and 8c, respectively. Stronger hydrogen bonding could be provided by P(LAEMA)975 absorbed on kaolin particle surfaces because of more hydroxyl groups, resulting in an enhanced flocculation performance of the polymer on the kaolin particle suspension.43 Topography of the Polymer Adsorbed Mica Surface. To monitor the topographical changes with MWs of glycopolymers, P(LAEMA) 177 , P(LAEMA) 397 , and P(LAEMA)975 adsorbed on mica surfaces in distilled deionized water were imaged using AFM, and the typical images are shown in Figure 9a−c, respectively. The root-mean-square roughness determined using AFM was 0.1, 0.15, 0.23 nm for the cases of P(LAEMA)177, P(LAEMA)397, and P(LAEMA)975, respectively. The increased roughness and large aggregates as shown in the AFM images manifest the adsorption of PLAEMA on the mica surface, which is more pronounced for the higher MW case. The polymer−polymer and polymer−particle adhesions mainly result from hydrogen bonding and van der Waals forces, as previously reported.44,45 The dominant hydrogen bonding interaction was due to a large number of hydroxyl groups on the pendant sugars and the hydroxyl groups on the particle surface. Because the high MW P(LAEMA)975 contains more functional sugar residues with longer polymer chains, strong hydrogen bonding interaction could be formed between the polymer and the model clay surface, hence leading to efficient and strong flocculation of the solid particles. The AFM results in Figure 9 are in good agreement with the settling results (Figure 4) and surface force measurements (Figure 8): the higher MW PLAEMA contributed to a stronger adhesion to kaolin particles and a higher settling rate.
percentage of solids in the sediment. As shown in Figure 6b, 10 ppm is the optimal dosage to obtain the most compact sediment, and the solid content of the sediment decreases with increasing polymer dosage, which suggests that high dosage and MW would lead to a large amount of trapped water in the sediment. Although a high MW polymer is beneficial for the aggregation of polymer and increasing the settling rate (Figure 4a), the stronger adhesion of the polymer to the particle surface induces stronger sediment, which did not consolidate well.8 In the high dosage case, the gel-like formation of the suspension hindered the consolidation of particles because of steric forces, which also led to a higher mud-line, in good agreement with the settling rate results. At low dosage, much more water was released from the sediment because more interval gaps were occupied by particles, which also contributed to a more compact structure. Polymer Aggregation. The hydrodynamic radii of PLAEMA of various average MWs were investigated at pH 6.5, as shown in Figure 7. The size of the glycopolymer in
Figure 7. Hydrodynamic radii (RH) distribution of polymers with various average MWs (black solid line, 83 kDa; red solid line, 186 kDa; and blue solid line, 456 kDa).
distilled deionized water increased from 5 to 28 nm with increasing MW. The increased hydrodynamic radius with increasing MW of the polymer in distilled deionized water suggests longer polymer chains or large aggregates of PLAEMA, which would have stronger capability to form hydrogen bonding with particle surfaces as compared with those of the lower MW cases, and these results also agree well with the settling rate and consolidation results (Figures 4a and 6a,b). It should be noted that at a solution pH 6.5, the zeta potential E
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Figure 8. Force vs distance profiles between the two mica surfaces in 10 ppm of (a) P(LAEMA)177, (b) P(LAEMA)397, and (c) P(LAEMA)975 water solutions.
Figure 9. Topographic AFM images of (a) P(LAEMA)177, (b) P(LAEMA)397, and (c) P(LAEMA)975 coating absorbed on mica surfaces.
F
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(8) O’Shea, J.-P.; Qiao, G. G.; Franks, G. V. Temperature-Responsive Solid−Liquid Separations with Charged Block-Copolymers of Poly(Nisopropyl acryamide). Langmuir 2012, 28, 905−913. (9) Burdukova, E.; Ishida, N.; Shaddick, T.; Franks, G. V. The Size of Particle Aggregates Produced by Flocculation with PNIPAM, as a Function of Temperature. J. Colloid Interface Sci. 2011, 354, 82−88. (10) Franks, G. V. Stimulant Sensitive Flocculation and Consolidation for Improved Solid/Liquid Separation. J. Colloid Interface Sci. 2005, 292, 598−603. (11) Sakohara, S.; Kimura, T.; Nishikawa, K. Flocculation Mechanism of Suspended Particles Utilizing Hydrophilic/Hydrophobic Transition of Thermosensitive Polymer. Kagaku Kogaku Ronbunshu 2000, 26, 734−737. (12) Li, H.; Long, J.; Xu, Z.; Masliyah, J. H. Flocculation of Kaolinite Clay Suspensions Using a Temperature-Sensitive Polymer. AIChE J. 2007, 53, 479−488. (13) Flaten, T. P. Aluminium as a risk factor in Alzheimer’s disease, with emphasis on drinking water. Brain Res. Bull. 2001, 55, 187−196. (14) Yang, Z.; Shang, Y.; Lu, Y.; Chen, Y.; Huang, X.; Chen, A.; Jiang, Y.; Gu, W.; Qian, X.; Yang, H.; et al. Flocculation Properties of Biodegradable Amphoteric Chitosan-Based Flocculants. Chem. Eng. J. 2011, 172, 287−295. (15) Chen, Y.; Liu, S.; Wang, G. A Kinetic Investigation of Cationic Starch Adsorption and Flocculation in Kaolin Suspension. Chem. Eng. J. 2007, 133, 325−333. (16) Järnström, L.; Lason, L.; Rigdahl, M. Flocculation in Kaolin Suspensions Induced by Modified Starches 1. Cationically Modified StarchEffects of Temperature and Ionic Strength. Colloids Surf., A 1995, 104, 191−205. (17) Bratskaya, S.; Schwarz, S.; Liebert, T.; Heinze, T. Starch Derivatives of High Degree of Functionalization: 10. Flocculation of Kaolin Dispersions. Colloids Surf., A 2005, 254, 75−80. (18) Tadros, T. F. Adsorption of Polyvinyl Alcohol on Silica at Various pH Values and Its Effect on the Flocculation of the Dispersion. J. Colloid Interface Sci. 1978, 64, 36−47. (19) Kim, H.-J.; Phenrat, T.; Tilton, R. D.; Lowry, G. V. Effect of kaolinite, silica fines and pH on transport of polymer-modified zero valent iron nano-particles in heterogeneous porous media. J. Colloid Interface Sci. 2012, 370, 1−10. (20) Sakthivelu, S.; Vidyavathy, S. M.; Manohar, P. Effect of Polyvinyl Alcohol on Stability and Rheology of Nano Kaolinite Suspensions. Trans. Indian Ceram. Soc. 2012, 71, 175−180. (21) Rubio, J.; Kitchener, J. A. The Mechanism of Adsorption of Poly(ethylene oxide) Flocculant on Silica. J. Colloid Interface Sci. 1976, 57, 132−142. (22) Carasso, M. L.; Rowlands, W. N.; O’brien, R. W. The Effect of Neutral Polymer and Nonionic Surfactant Adsorption on the Electroacoustic Signals of Colloidal Silica. J. Colloid Interface Sci. 1997, 193, 200−214. (23) Garvey, M. J.; Tadros, T. F.; Vincent, B. A Comparison of the Adsorbed Layer Thickness Obtained by Several Techniques of Various Molecular Weight Fractions of Poly(vinyl alcohol) on Aqueous Polystyrene Latex Particles. J. Colloid Interface Sci. 1976, 55, 440−453. (24) Koopal, L. K.; Lyklema, J. Characterization of Adsorbed Polymers from Double Layer Experiments: The Effect of Acetate Groups in Polyvinyl Alcohol on Its Adsorption on Silver Iodide. J. Electroanal. Chem. Interfacial Electrochem. 1979, 100, 895−912. (25) Garvey, M. J.; Tadros, T. F.; Vincent, B. A Comparison of the Volume Occupied by Macromolecules in the Adsorbed State and in Bulk Solution: Adsorption of Narrow Molecular Weight Fractions of Poly(vinyl alcohol) at the Polystyrene/Water Interface. J. Colloid Interface Sci. 1974, 49, 57−68. (26) Joppien, G. R. Characterization of Adsorbed Polymers at the Charged Silica Aqueous Electrolyte Interface. J. Phys. Chem. 1978, 82, 2210−2215. (27) Brooks, D. E.; Seaman, G. V. F. The Effect of Neutral Polymers on the Electrokinetic Potential of Cells and Other Charged Particles: I. Models for the Zeta Potential Increase. J. Colloid Interface Sci. 1973, 43, 670−686.
CONCLUSIONS PLAEMA with varying MWs was synthesized via conventional free radical polymerization. The flocculation performance and adhesion of the polymers to clay surfaces were investigated through the settling test, surface force measurements, and AFM imaging. The impact of the MWs of PLAEMA on the settling rate, released water clarity, solid content, and adhesive interaction was investigated. Glycopolymers of high MW were shown to contribute significantly to rapid particle settling at low dosages. The surface force measurements and AFM imaging of the adsorbed polymer surfaces manifest strong polymer−particle adhesion and bridging attraction between the glycopolymers and the particles, which increases with increasing MW of the glycopolymer. The strengthened bridging interaction with increasing MW of the polymer is attributed to the formation of stronger attraction (e.g., via hydrogen bonding) between the fine particles and the abundant hydroxyl groups on the glycopolymers, thus contributing to enhanced flocculation behaviors. Our results provide new insights into the development of eco-friendly polymer flocculants based on glycopolymers for efficient solid−liquid separation in oil sands tailing treatment and into the fundamental understanding of associated intermolecular interactions and flocculation mechanisms.
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AUTHOR INFORMATION
Corresponding Authors
*E-mail:
[email protected] (R.N.). *E-mail:
[email protected] (H.Z.). Author Contributions †
H.L. and L.X. contributed equally to this work.
Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS The authors would like to thank the generous financial support from the Natural Resources Canada ecoENERGY Innovation Initiative (ecoEII) and Natural Sciences and Engineering Research Council of Canada (NSERC) for this work.
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REFERENCES
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DOI: 10.1021/acs.langmuir.6b03072 Langmuir XXXX, XXX, XXX−XXX
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DOI: 10.1021/acs.langmuir.6b03072 Langmuir XXXX, XXX, XXX−XXX
