title: Competition between kaolinite flocculation and stabilization in divalent cation solutions dosed with anionic polyacrylamides.
abstract: Divalent cations have been reported to develop bridges between anionic polyelectrolytes and negatively-charged colloidal particles, thereby enhancing particle flocculation. However, results from this study of kaolinite suspensions dosed with various anionic polyacrylamides (PAMs) reveal that Ca(2+) and Mg(2+) can lead to colloid stabilization under some conditions. To explain the opposite but coexisting processes of flocculation and stabilization with divalent cations, a conceptual flocculation model with (1) particle-binding divalent cationic bridges between PAM molecules and kaolinite particles and (2) polymer-binding divalent cationic bridges between PAM molecules is proposed. The particle-binding bridges enhanced flocculation and aggregated kaolinite particles in large, easily-settleable flocs whereas the polymer-binding bridges increased steric stabilization by developing polymer layers covering the kaolinite surface. Both the particle-binding and polymer-binding divalent cationic bridges coexist in anionic PAM- and kaolinite-containing suspensions and thus induce the counteracting processes of particle flocculation and stabilization. Therefore, anionic polyelectrolytes in divalent cation-enriched aqueous solutions can sometimes lead to the stabilization of colloidal particles due to the polymer-binding divalent cationic bridges.
authors.affiliation: Hydraulics Laboratory, Department of Civil Engineering, Katholieke University of Leuven, Kasteelpark Arenberg 40, B-3001 Heverlee, Belgium; Management Unit of the North Sea Mathematical Models (MUMM), Royal Belgian Institute of Natural Sciences, Gulledelle 100, 1200 Brussels, Belgium.
authors.forename: Byung Joon
authors.initials: BJ
authors.lastname: Lee
authors.affiliation: Department of Environmental Engineering and Earth Sciences, Clemson University, 342 Computer Court, Anderson, SC 29625-6510, USA. Electronic address: mschlau@clemson.edu.
authors.forename: Mark A
authors.initials: MA
authors.lastname: Schlautman
authors.affiliation: Hydraulics Laboratory, Department of Civil Engineering, Katholieke University of Leuven, Kasteelpark Arenberg 40, B-3001 Heverlee, Belgium.
authors.forename: Erik
authors.initials: E
authors.lastname: Toorman
authors.affiliation: Management Unit of the North Sea Mathematical Models (MUMM), Royal Belgian Institute of Natural Sciences, Gulledelle 100, 1200 Brussels, Belgium.
authors.forename: Michael
authors.initials: M
authors.lastname: Fettweis
mesh_terms: D000180:Acrylic Resins / Q000737:chemistry*; D000838:Anions / Q000737:chemistry*; D002413:Cations, Divalent / Q000737:chemistry*; D005427:Flocculation; D007616:Kaolin / Q000737:chemistry*; D000099166:Polyacrylamides
chemical_list: D000180:Acrylic Resins; D000838:Anions; D002413:Cations, Divalent; D007616:Kaolin; D000099166:Polyacrylamides