Flocculation of Semidilute Calcite Dispersions Induced by Anionic Sodium Polyacrylate−Cationic Starch Complexes

Abstract

Polyelectrolyte complexes (PECs) formed by mixing oppositely charged polyelectrolytes are widely used as flocculation agents of aqueous solid/liquid dispersions. The complexes have been found superior to single polyelectrolytes in showing a substantially wider optimum concentration range for flocculation. In this work the flocculation performance and mechanisms induced by premixed complexes of cationic starch and anionic sodium polyacrylate (NaPA) on semidilute calcite dispersions were investigated by measuring the particle size and the dynamic mobility. The flocculation performance was studied as a function of the ratio of NaPA to starch, and the total amount of polyelectrolyte added. The influence of pretreatment of the calcite dispersions on the complex-induced flocculation was also investigated. The investigation clearly shows that, by using appropriate amounts of premixed NaPA and starch, the flocculation of the calcite dispersions was strongly enhanced compared to the case of using single NaPA or starch, respectively. Several mechanisms are involved in the enhanced flocculation induced by the two oppositely charged polyelectrolytes. These mechanisms are strongly dependent on the ratio of NaPA to starch, and the total amount of polyelectrolytes added. However, interparticle bridging by the polyelectrolyte complexes, and charge neutralization, induced by the deposition of the complexes, were found as the main reasons for the enhanced flocculation. Pretreating the bare calcite with anionic sodium polyacrylate changed the charge characteristics of the calcite from cationic to anionic. Despite the change in charge characteristics, the pretreatment did not drastically change the flocculation behavior of the semidilute calcite dispersions induced by the subsequent addition of premixed polyelectrolyte complexes. However, the pretreatment resulted in a slight shift in the ratio of NaPA to starch required for optimum flocculation.

Polyelectrolyte complexes. VI. Polycation structure, polyanion molar mass, and polyion concentration effects on complex nanoparticles based on poly(sodium 2‐acrylamido‐2‐methylpropanesulfonate)

“…However, NIPECs as colloidal dispersions bearing positive or negative charges in excess are also of great interest. Such NIPECs have been used as flocculants for cellulose and clay dispersions, organic compounds (dyes and surfactants) from wastewaters, and surface modification of different solid substrates 31–38. The numerous practical applications of such reactive nanoparticles have stimulated further investigations on their formation and stability.…”

“…Such NIPECs have been used as flocculants for cellulose and clay dispersions, organic compounds (dyes and surfactants) from wastewaters, and surface modification of different solid substrates. [31][32][33][34][35][36][37][38] The numerous practical applications of such reactive nanoparticles have stimulated further investigations on their formation and stability. The stoichiometry of IPECs, which also corresponds to the isoelectric point of the complex, (n Ϫ /n ϩ ) iso , is a very important characteristic of a certain polyion pair and must be well known to prepare NIPECs as colloidal particles with a high storage stability and a concentration in the macromolecular components as high as possible.…”

New polyelectrolyte complex particles as colloidal dispersions based on weak synthetic and/or natural polyelectrolytes

“…Examples include controlled drug delivery systems, enzyme and DNA carriers, surface modification of medical implants, membranes for cell culture and growth, biosensors, and nanostructured materials [2][3][4][5]. At relatively low concentrations and when one of the components is taken in excess, PEC formation can lead to stable colloidal dispersions [6][7][8][9][10][11][12]. The characteristics of the polyelectrolyte components (molecular weight, nature of ionic groups, charge density, and architecture) and the solvent (ionic strength, pH) determine the internal structure of the particles.…”

Applying LDS to Monitor Flocculation in Papermaking

“…Light-scattering techniques can also be used to follow flocculation processes, namely laser diffraction spectroscopy (LDS), a common, robust particle size analysis technique (Biggs et al, 2000;Nystrom et al, 2003). Moreover, LDS allows one to extract information about the fractal dimension of the flocs under some basic assumptions (Rayleigh-Gans-Debye regime) as described by Schmidt (1989).…”