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.
Department of Environmental Engineering and Earth Sciences, Clemson University, 342 Computer Court, Anderson, SC 29625-6510, USA.
Water Res. 2012 Nov 1;46(17):5696-5706. doi: 10.1016/j.watres.2012.07.056. Epub 2012 Aug 11.
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.
二价阳离子已被报道在阴离子聚电解质和带负电荷的胶体颗粒之间形成桥，从而增强颗粒絮凝。然而，本研究用各种阴离子聚丙烯酰胺（PAMs）处理高岭石悬浮液的结果表明，在某些条件下，Ca（2+）和 Mg（2+）可导致胶体稳定。为了解释与二价阳离子共存的相反的絮凝和稳定过程，提出了一种带有（1）PAM 分子与高岭石颗粒之间的颗粒结合二价阳离子桥，和（2）PAM 分子之间的聚合物结合二价阳离子桥的絮凝概念模型。颗粒结合桥增强了絮凝，将高岭石颗粒聚集在大的、易于沉降的絮体中，而聚合物结合桥通过在高岭石表面形成聚合物层来增加空间稳定化作用。带负电荷的 PAM 和高岭石悬浮液中同时存在颗粒结合和聚合物结合的二价阳离子桥，从而诱导颗粒絮凝和稳定的相反过程。因此，由于聚合物结合的二价阳离子桥的存在，富含二价阳离子的水溶液中的阴离子聚电解质有时会导致胶体颗粒的稳定。
