Effect of molecular weight of poly(N-isopropyl acrylamide) temperature-sensitive flocculants on dewatering

Residue-Free and Recyclable Starch-Based Flocculants for Dye Wastewater Flocculation

Flocculants are crucial agents in wastewater treatment because they can remove oppositely charged impurities effectively and swiftly. However, flocculation also inevitably causes secondary contamination due to the residual properties, nonreusability, and nondegradability of traditional flocculant molecules. Herein, an ecofriendly starch-based flocculant, i.e., 2,4-bis(dimethylamino)-[1,3,5]-triazine-6-starch, was synthesized via a preactivation-etherification strategy. The large molecular weight property of the flocculant produced by this method enhances the intermolecular hydrophobic association, achieving complete phase separation of all flocculant molecules from water and residue-free flocculation for the first time. Importantly, a large molecular weight tertiary amine starch-based flocculant (LMTS) exhibits a remarkable flocculation capacity of over 1800 mg·g-1 for dye wastewater, which is significantly higher than that of traditional polyacrylamide and polyaluminum chloride flocculants. Furthermore, the LMTS flocculant could be recycled by pH adjustment, and its structural stability ensured sustained reusability. This high-performance residue-free biomass-based flocculant offers a green advance for wastewater treatment.

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.

Stimuli-Responsive Hybrid Polymer for Enhanced Solid-Liquid Separation of Industrial Effluents

In the current study, a novel stimuli-responsive hybrid polymer with aluminum hydroxide colloids incorporated into a cationic copolymer of N-isopropylacrylamide and N-[3-(dimethylamino)propyl]methacrylamide was synthesized to enhance the settling and filtration performance of fine clay suspensions. The conformation of the synthesized hybrid copolymer was shown to respond to changes in both temperature and pH. Compared with a cationic copolymer of similar structure without aluminum hydroxide colloids, settling and filtration rates were significantly enhanced using the hybrid copolymer, which is attributed to the synergy between the inorganic aluminum hydroxide cores and organic copolymer. While the ideal treatment protocol for the hybrid polymer involved the addition of the polymer at room temperature, followed by heating to 45 °C for enhanced settling and dewatering, the synergistic effect between colloidal cores and polymer also allowed the hybrid polymer to perform well when added at temperatures above the LCST, demonstrating the robustness of the hybrid polymer to the process environment. The ideal treatment protocol resulted in an optimal adsorption of polymer on clays before inducing a coil-globule transition to form large and dense flocs, resulting in a more porous filter cake.

Quantitative determination of the spring entropy effect and its indication of the conformational change of polymer coils with varying concentration in aqueous poly(N-isopropylamide) solutions

The lower critical solution temperature (LCST) phase separation behaviors of thermosensitive poly(N-isopropylacrylamide) (PNIPAM) aqueous solutions were investigated by power-compensation differential scanning calorimetry (DSC). The entropic effect and hence the change of swelling state of PNIPAM polymer coils in homogeneous concentrated aqueous solutions with varied solution composition was elucidated by the isothermal enthalpy demixing recovery behaviors in distinct concentration regions.

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.

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 PCL_nChMA 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.

Flocculation of flotation tailings using thermosensitive polymers

The key feature of thermosensitive polymers is the reversible transition between the hydrophilic and hydrophopic forms depending on the temperature. Although the main research efforts are focused on their application in different kinds of drug delivery systems, this phenomenon also allows one to precisely control the stability of solid-liquid dispersions. In this paper research on the application of poly(N-isopropylacrylamide) copolymers in processing of minerals is presented. In the experiments tailings from flotation plant of one of the coal mines of Jastrzębska Spółka Węglowa S.A. (Poland) were used. A laser particle sizer Fritsch Analysette 22 was used in order to determine the Particle Size Distribution (PSD). It was proved that there are some substantial issues associated with the application of thermosensitive polymers in industrial practice which may exclude them from the common application. High salinity of suspension altered the value of Lower Critical Solution Temperature (LCST). Moreover, the co-polymers used in research proved to be efficient flocculating agents without any temperature rise. Finally, the dosage needed to achieve steric stabilization of suspension was greatly beyond economic justification.

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.

In situ investigation of aggregate sizes formed using thermo-responsive polymers: Effect of temperature and shear

Temperature-responsive flocculants, such as poly(N-isopropylacrylamide) (PNIPAM), induce reversible particle aggregation upon heating above a lower critical solution temperature (LCST). The aim of this work is to investigate the aggregation of ground iron ore using PNIPAM and conventional polyacrylamide (PAM) flocculants in a continuously-sheared suspension, through in situ chord length measurements using Focused Beam Reflectance Measurement techniques and real-time imaging of the particle aggregates. In the presence of uncharged PNIPAM, particle aggregation occurs only upon heating to the LCST, and the aggregates continue to grow with further heating. Subsequent cooling re-disperses the aggregates, and repeated heating causes reformation. Unlike uncharged PNIPAM, anionic PNIPAM produces aggregates at temperatures below the LCST due to the polymer chains binding to two different particles via attractive interactions between the acrylic acid groups and the hematite surfaces, and can be added at temperatures above the LCST due to the formation of charge-stabilised micelles. Under continuous shear, the flocculant most able to resist aggregate size reduction was anionic PAM, followed by PAM, anionic PNIPAM, PNIPAM (6MDa), and PNIPAM (122kDa). Reversible aggregate breakage was found with all samples, except with PNIPAM (6MDa) after being subjected to shear rates above 550s^-1. Furthermore, heating of the PNIPAM-dosed suspensions at shear rates below 200s^-1 produced larger and more breakage-resistant aggregates.

Molecular Weight Dependence of Synthetic Glycopolymers on Flocculation and Dewatering of Fine Particles

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.

Xanthate-Functional Temperature-Responsive Polymers: Effect on Lower Critical Solution Temperature Behavior and Affinity toward Sulfide Surfaces

Xanthate-functional polymers represent an exciting opportunity to provide temperature-responsive materials with the ability to selectively attach to specific metals, while also modifying the lower critical solution temperature (LCST) behavior. To investigate this, random copolymers of poly(N-isopropylacrylamide) (PNIPAM) with xanthate incorporations ranging from 2 to 32% were prepared via free radical polymerization. Functionalization with 2% xanthate increased the LCST by 5 °C relative to the same polymer without xanthate. With increasing xanthate composition, the transition temperature increased and the transition range broadened until a critical composition of the hydrophilic xanthate groups (≥18%) where the transition disappeared completely. The adsorption of the polymers at room temperature onto chalcopyrite (CuFeS2) surfaces increased with xanthate composition, while adsorption onto quartz (SiO2) was negligible. These findings demonstrate the affinity of these functional smart polymers toward copper iron sulfide relative to quartz surfaces, presumably due to the interactions between xanthate and specific metal centers.

Temperature- and pH-Responsive Benzoboroxole-Based Polymers for Flocculation and Enhanced Dewatering of Fine Particle Suspensions

Random copolymers based on N-isopropylacrylamide (NIPAAm) containing 2-aminoethyl methacrylamide hydrochloride (AEMA) and 5-methacrylamido-1,2-benzoboroxole (MAAmBo) were synthesized and subsequently evaluated for their performance in solid-liquid separation at various pH and temperatures. The strong interactions between benzoboroxole residues and kaolin hydroxyl groups were evaluated for the first time in the flocculation of fine particle suspensions. The lower critical solution temperatures (LCSTs) of PAMN decreases because of the hydrophobic nature of the benzoboroxole moieties, resulting in strong hydrophobic interaction at temperatures higher than the LCSTs. Temperature and pH responsive polymer, P(AEMA51-st-MAAmBo76-st-NIPAM381) (denoted as PAMN) shows the ability to induce fastest settling at a low dosage of 25 ppm and under the condition of pH 9 and 50 °C. The accelerated settling rate is considered to be due to the strong adhesion of benzoboroxole residues to the kaolin hydroxyl groups, the electrical double layer force, and the hydrophobic force. During condensation phase, increasing the pH of sediment to pH 11 could attain the most compact structure. Random copolymers containing benzoboroxole groups act as dispersants (due to pH-responsive character) rather than flocculants at pH 11, providing repulsive force that enables particles to rearrange their position and consolidate well. Through a two-step solid-liquid separation including settling phase and consolidation phase, rapid settling and compact sediment are feasible simultaneously.

In situ particle film ATR FTIR spectroscopy of poly (N-isopropyl acrylamide) (PNIPAM) adsorption onto talc

The adsorption of poly(N-isopropyl acrylamide) (PNIPAM) onto talc from aqueous solutions has been studied using the in situ methodology of particle film attenuated total reflection (ATR) Fourier transform infrared (FTIR) spectroscopy. PNIPAM was observed to adsorb significantly onto the talc particle film at a temperature below its lower critical solution temperature (LCST). Peak shifts were seen in the adsorbed layer FTIR spectrum that match those observed when PNIPAM solution is heated above its LCST. This observation indicates that adsorption causes a conformational re-arrangement similar to that seen when PNIPAM undergoes a coil-to-globule transition, in this case presumably induced by hydrophobic interactions between PNIPAM and the talc basal plane surface. The kinetics of adsorption are seen to be complex, with potential influences of conformational rearrangement and differential adsorption kinetics for the two dominant surface regions of talc particles. The adsorbed PNIPAM was seen to be exceptionally resistant to removal, with no desorption occurring when a background electrolyte solution was flowed over the adsorbed layer. Spectra acquired of the adsorbed polymer layer heated above the LCST reveal that a further conformational rearrangement takes place for the adsorbed layer, finalizing the transition from coil-to-globule that was initiated by the interaction with the mineral surface.

Temperature-responsive hyperbranched amine-based polymers for solid-liquid separation

Temperature-responsive hyperbranched polymers containing primary amines as pendent groups have been synthesized for solid-liquid separation of kaolinite clay suspension. The effects of temperature, polymer charge density, and polymer architecture on particle flocculation have been investigated. Suspensions treated with the temperature-responsive amine-based hyperbranched polymers showed remarkable separation of the fine particles at a low polymer dosage of 10 ppm and at testing temperatures of 40 °C. In comparison to other polymers studied (linear and hyperbranched homopolymers and copolymers), the temperature-responsive amine-based hyperbranched copolymers showed better particle flocculation at 40 °C, as evidenced by the formation of a thinner sediment bed without compromising the amount of clay particles being flocculated. This superior solid-liquid separation performance can be explained by the hydrophobic interaction of PNIPAM segments on particle surfaces or the capture of additional free particles or small floc due to the exposure of buried positive charges (because of the phase separation of the hydrophilic amines and hydrophobic PNIPAM part) at temperatures above the lower critical solution temperature (LCST).

Novel thermosensitive flocculanting agent based on pullulan

New thermosensitive polysaccharide (P-g-pNIPAAm) was synthesized by graft-polymerization of p(N-isopropylacrylamide) (pNIPAAm) onto pullulan (P) using Ce(IV) ion as initiator. The grafted polysaccharide was characterized by FT-IR and (1)H NMR spectroscopy and elemental analysis. Its flocculation efficiency was studied in a clay suspension, in comparison with p(NIPAAm) homopolymer, as a function of the polymer dose, temperature and settling time. The thermosensitive polysaccharide could induce clay particle flocculation both below and above the lower critical solution temperature (LCST), but the process was more effective above the LCST. A lower value of the residual turbidity at the optimum polymer dose and a wider flocculation window were recorded at temperature above the LCST. The floc size distribution and surface morphology revealed bigger size flocs when the flocculation was performed above the LCST. The re-dispersion effect was negligible for the flocs obtained in the presence of P-g-pNIPAAm.