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Competition between kaolinite flocculation and stabilization in divalent cation solutions dosed with anionic polyacrylamides
Lee, B.J.; Schlautman, M.A.; Toorman, E.; Fettweis, M. (2012). Competition between kaolinite flocculation and stabilization in divalent cation solutions dosed with anionic polyacrylamides. Wat. Res. 46(17): 5696-5706. http://dx.doi.org/10.1016/j.watres.2012.07.056
In: Water Research. Elsevier: Oxford; New York. ISSN 0043-1354; e-ISSN 1879-2448
Peer reviewed article  
Available in  Authors 
    Vlaams Instituut voor de Zee: Open Marine Archive 252122 [ download pdf ]
Keywords
    Colloids
    Divalent cations
    Polyelectrolytes
    Separation > Chemical precipitation > Flocculation
    Stabilization
    Marine/Coastal
Author keywords
    Cationic bridge
Authors  Top 
  • Lee, B.J.
  • Schlautman, M.A.
  • Toorman, E.
  • Fettweis, M.
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 Ca2+ and Mg2+ 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.
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