Comparison of two cationic polymeric flocculant architectures on the destabilization of negatively charged latex suspensions

Abstract

This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues.Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. Flocculation studies between cationic polymers and oppositely charged colloidal particles are reported in which both flocculation kinetics and floc structures are systematically investigated. The flocculation rate constant, stability ratio and kinetics laws are experimentally determined using particle counting for two polymer architectures; a cationic linear polymer and a two-branched polymer. Comparisons are also made using NaCl at different ionic concentrations for the destabilization of the colloidal particles. Detailed measurements of electrophoretic mobility and kinetics rate constants on varying the polymer dosage are reported. Results suggest that the polymer architecture plays important roles on the polymer dosage for the rapid destabilization of the colloidal suspension. The branched polymer at optimal dosage exhibits the highest flocculation rate constant, whereas on the other hand, the linear polymer concentration range of flocculation is larger. In both cases, polymer flocculation is more efficient by a factor of 5e6 than charge screening effects due to the presence of salt. Analysis of the stability ratio indicates that tele-bridging flocculation and electrostatic forces dictate the stability of the charged latex particle suspension. It is shown that the fractal concepts which are valid for aggregation processes are also applicable here and branched polymers as well as linear polymers yield to the formation of compact flocs in comparison to those obtained with salt.

Salt concentration influence on the efficiency of two cationic polymeric flocculants

“…The presence of sulfate groups at the surface resulted in a constant charge density value equal to 3.9 μC/cm 2 for pH values above 4. The zeta potential determined with a Malvern Zetasizer Nano ZS was found to be equal to −100±3 mV [7]. The Zetasizer Nano Series uses a combination of laser Doppler velocimetry and phase analysis light scattering (PALS) in a patented technique called M3-PALS to measure particle electrophoretic mobility.…”

“…Two solutions of NaCl of 1 and 5 M were prepared as stock solutions. Colloidal particles were flocculated by positively charged linear (BHMW) or two-branched (B1 ++ ) polyacrylamide polymers synthesized, characterized, and supplied by Aqua+Tech Specialities S.A (Switzerland) [7,12,31]. These polymers have charges which are 55 mol%, equivalent to approximately 80 wt%.…”

“…On the one hand, in aquatic systems, algal and bacterial exudates composed of polysaccharide chains are promoting the flocculation of the suspended colloids and adsorbed pollutants [1,2]; on the other hand, in many industrial processes, flocculation is used for rapid water clarification or wastewater treatment [3,4]. For efficient water clarification, flocculation is usually induced by positively charged polyelectrolytes such as organic synthetic polymers to rapidly separate the liquid phase from the solid one and hence obtain a clear filtrate [5][6][7]. Generally, the use of polymeric flocculant versus other inorganic polyelectrolytes, such as poly-aluminum complexes, gives significant advantages when the water has a high concentration of suspended solids since usually, and in the same conditions, the concentration of the polymeric flocculant is lower, the resulting sludge is more compact, and there is less coagulant left in the water after treatment [4,8].…”

“…The polymer branching also plays here a key role since it is largely controlling the polymer interaction behavior with the particles [20][21][22]. Moreover, the branching also induces important differences in the floc structure, compactness, and fractal dimensions, which are affecting the sedimentation rates and floc strength with regards to filtration processes [7].…”

“…However, if flocculant dosage is not properly controlled, an excess of polymers will redisperse the particle suspension by charge inversion or steric stabilization. Usually, from a practical point of view, three different regimes must be considered: (1) when flocculant concentration is too low to induce rapid flocculation, (2) flocculant dosage is optimal for rapid destabilization, and (3) flocculant concentration is too high and results in particle restabilization [7].…”