The influence of PEO/poly(vinyl phenol-co-styrene sulfonate) aqueous complex structure on flocculation

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.

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.

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).

Controlling the assembly of nanoparticle mixtures with two orthogonal polymer complexation reactions

Self-assembly from mixed dispersions of three sizes of monodisperse polystyrene nanoparticles, large (L), medium (M), and small (S), was controlled by coating each particle type with either a monofunctional or bifunctional polymer capable of participating in specific complexation reactions. The complexation reactions were (1) complexation between phenolic polymers and polyethylene glycol (PEG) containing polymers and (2) condensation of phenylboronic acid containing polymers with polyols. These complexation reactions function independently and can be "turned off" independently; phenylboronic acid complexation was reversed by lowering the pH, whereas the interactions of phenolic copolymers with PEG copolymers could be reversed by adding excess PEG homopolymer. The specificity and reversibility of the interactions was demonstrated by the formation of simple binary aggregates from mixtures. The bifunctional copolymers were poly(vinyl phenol-co-diallyldimethyl ammonium chloride), Ph-DADMAC, and poly(3-acrylamide phenylboronic acid-co-PEG methacrylate), PBA-PEG. The monofunctional polymer was polyvinylalcohol, PVA. Ph-DADMAC forms complexes with PBA-PEG (H-bonding) and with anionic surfaces or polymers (electrostatic/polyelectrolyte complexation). PBA-PEG complexes with Ph-DADMAC (H-bonding) and with PVA (boronate ester formation). PVA does not interact with Ph-DADMAC; therefore, PVA coated particles do not deposit onto Ph-DADMAC coated particles.

Flocculation with poly(ethylene oxide)/tyrosine-rich polypeptide complexes

New insights into the mechanism for the flocculation of aqueous colloids by the sequential addition of a water-borne phenolic polymer, called cofactor, followed by very high molecular poly(ethylene oxide) (PEO) are presented. It is proposed that PEO/cofactor complexes form in the aqueous phase and adsorb onto the surfaces of the target colloidal particles. Flocculation will occur if PEO/cofactor complex on one particle will bind to adsorbed complex on a second particle; i.e., if the complexes are sticky. The proposed mechanism was illustrated by flocculation experiments with precipitated calcium carbonate, very high molecular weight PEO, and a polypeptide cofactor called PEY1 which was a 1:1 random copolymer of l-glycine and l-tyrosine. Independent measurements of the PEO/PEY1 complex properties, in the absence of calcium carbonate, were used to support the mechanism. In order for PEO/PEY1 complexes to be sticky, they must simultaneously have unbound PEY1 and polymer segments. With time the complexes deactivate (i.e., lose their stickiness) by a reconfiguration process which results in elimination of either unbound PEY1 or PEO segments.

The influence of PEO/poly(vinyl phenol-co-styrene sulfonate) aqueous complex structure on flocculation

Colloidal suspensions were flocculated with complexes formed from high molecular weight polyethylene oxide (PEO) and a cofactor. Poly(vinyl phenol-co-potassium styrene sulfate) (PKS) or poly(styrene-co-styrene sulfonate) (PS-co-SSS) copolymers were used as the cofactors for this work. The larger the PEO/cofactor complex species, the better the initial flocculation. Factors such as increasing temperature or ionic strength that gave smaller complexes also gave poorer flocculation. Cofactor performance was sensitive to the balance of hydrophobic phenolic groups and hydrophilic styrene sulfonates. If there are too few phenolic groups, the PEO/PSK complexes are large but are too weak to give shear-resistant flocs, whereas complexes formed with high phenolic content PSK are relatively small, giving poorer flocculation but more shear-resistant flocs. Both phenyl and phenol groups are effective as the hydrophobic component in the cofactor. The hydrogen-bonding potential of phenolic cofactors does not seem to offer much advantage relative to phenyl groups. A crucial step in the flocculation is the adsorption of PEO/cofactor complex onto the target colloids. Thus, flocculation is sensitive to the target colloid surface chemistry. Positively charged precipitated calcium carbonate and surfactant-free polystyrene latex are particularly easy to flocculate because adsorption is driven by electrostatic and hydrophobic interactions, respectively. By contrast, the latex coated with hydrophilic poly(N-isopropylacrylamide) (PNIPAM) does not flocculate because the PEO/cofactor complex does not bind to PNIPAM. Finally, the flocculation of highly negatively charged, dextran sulfate coated calcium carbonate seems to be stimulated by the presence of soluble calcium ions that make the complex less soluble and more likely to adsorb.