Water soluble polymer flocculants are important constituents of solid–liquid separation units for the treatment of a variety of process‐affected effluents. The systematic development of a flocculant relies on a good understanding of flocculation process, polymer synthesis, polymer characterization, and, not the least, flocculation performance assessment as desired for a particular treatment process, all of which are essential to establish meaningful relationships between flocculant microstructure and flocculation efficiency. The aim of this article is to communicate the bigger picture of this research area to the readers. The recent advances in the application of bio/natural, synthetic, and stimuli‐responsive flocculants are reviewed. Then, the basic polymer reaction engineering tools to control the microstructure of flocculants are provided and the techniques for the quantification of flocculant microstructure are concisely discussed. This is followed by a review of the methods used for the characterization of particle‐polymer force measurement, and flocculation/dewatering assessment with attention to the characterization of aggregate structures.

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Copolymers of acrylamide and cationic comonomers such as diallyldimethylammonium chloride can effectively dewater solid suspensions containing negatively charged fine particles. A good example of such suspensions is oil sands mature fine tailings (MFTs). However, little is known about the impact of the microstructure of copolymers in dewatering performance. In this study, we used a surface response methodology to systematically assess the impact of chemical composition and average molecular weight of poly(acrylamide-codiallyldimethylammonium chloride) in dewatering MFTs. We controlled the chemical composition and average molecular weight of the copolymers by manipulating feed monomer/comonomer ratios and initiator concentration. We found both the copolymer composition and the molecular weight averages were statistically significant variables for initial settling rates and supernatant turbidities of flocculated MFTs. However, capillary suction time and resistance to filtration depended only on copolymer composition and polymer dosage, not on average molecular weight. Depending on the polymer dosage, we found the optimum chemical composition to vary between 0 and 60 mol % acrylamide. The results of this study are important for the oil sands and polymer flocculation industry trying to use/produce flocculants at minimum cost and maximum performance.

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.

volume of tailings is projected to reach two billion cubic meters in 2034 if tailings management procedures remain the same. [3] When fresh tailings consolidate for a few years after their transfer to tailings ponds, gravitational forces cause the coarse components (sands) to settle, releasing a limited amount of the water to the surface. The bottom part of the remaining suspension is called mature fine tailings (MFT). Typically, MFT contains negatively charged clays (≈30-35 wt%), water (≈65 wt%), and residual bitumen (3-5 wt%). [4] Compared to fresh tailings, which still contain coarse particles that consolidate over time, MFT is a gel-like suspension that consolidates extremely slowly. Clays in MFT contain mainly kaolinite, illite, and mixedlayer clays such as interstratified illitesmectite and kaolinite-smectite. [5] Fine clays are mostly responsible for the water retained in MFT due to their high surface area. Additionally, fugitive bitumen binds clay particles, constricting interparticle pathways and trapping water. Colloidal Stability of Tailings and Challenges in DewateringSince MFT contains a mixture of negatively charged clays, it shows strong negative zeta potential that causes colloidal stabilization. Generally, clays contain hydroxyl and oxide functional groups that make their particles negatively charged at neutral pH (pH = 7) and even more negative as pH increases. Thus, the stability of clays in MFT increases with increase in pH. Current bitumen extraction processes use caustic additives to liberate bitumen from oil sands, generating alkaline tailings with pH of approximately 8.5. This alkaline medium increases the electrostatic repulsive forces between clays and significantly increases MFT stability. Surface charges also arise when ions from the neighboring solution adsorb on an initially neutral solid surface. Another source of surface charges is the dissociation of surface groups. The silica surface of clays can react with water to form silicic acid, which can then dissociate to form a silicic anion, as shown below. SiOHO HSiO (HSiO ) H 2 S 2 2 3 S 3 S ( ) ( ) + ↔ ↔ + − +(1) Multifunctional FlocculantsThe 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. Th...