Journal
WATER RESEARCH
Volume 46, Issue 17, Pages 5696-5706Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.watres.2012.07.056
Keywords
Flocculation; Stabilization; Polyelectrolyte; Colloid; Divalent cation; Cationic bridge
Funding
- USDA Natural Resources Conservation Service through the Changing Land Use and Environment (CLUE) Project at Clemson University [NRCS-69-4639-1-0010]
- USDA Cooperative State Research, Education, and Extension Service (USDA-CSREES) [SC-1700278, SC-1700395, SC-1700427]
- Clemson University Department of Environmental Engineering and Earth Sciences
- Clemson University Graduate School
- Flemish Science Foundation (FWO) [G.0263.08]
- OMFLOC project (Royal Belgian Institute of Natural Sciences - MUMM)
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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. (C) 2012 Elsevier Ltd. All rights reserved.
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