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Minerals 2018, 8(4), 130; doi:10.3390/min8040130

Understanding Cationic Polymer Adsorption on Mineral Surfaces: Kaolinite in Cement Aggregates

1
Lafarge—Centre de Recherche, 95 Rue du Montmurier, BP 15, 38291 Saint Quentin Fallavier, France
2
Department of Physics, Durham University, Lower Mountjoy Site, Stockton Road, Durham DH1 3LE, UK
3
Department of Earth Sciences, Durham University, Lower Mountjoy Site, Stockton Road, Durham DH1 3LE, UK
*
Authors to whom correspondence should be addressed.
Received: 15 February 2018 / Revised: 6 March 2018 / Accepted: 16 March 2018 / Published: 23 March 2018
(This article belongs to the Special Issue Organo-Mineral Interactions)
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Abstract

We present a joint experimental and theoretical investigation into the adsorption of polycationic quaternary ammonium polymers on the clay mineral kaolinite. Within the cement and concrete manufacturing industries such polymers are used to improve the final product by inerting the adsorption capacity of the clay minerals for more expensive additives. The adsorption of the presently used polymer (FL22) was compared with both a similar variant, but without a hydroxyl group (Fl22mod) and uncharged polyvinyl alcohol (PVA). Experimental results show that adsorption of FL22 is higher than that of FL22mod at both pH 6 and at pH > 10 and that the adsorption of PVA is the highest. Theoretical density functional theory (DFT) results and simplified models consisting of the basal surfaces of kaolinite, with monomers of FL22, FL22mod and PVA gave monomer coverage per unit surface area of kaolinite, a comparison of the configurations of the relaxed models, formation energies and Mulliken charges. These results show that the polycationic polymers interact with the basal surfaces of kaolinite electrostatically, explaining the high affinity of these polymers for kaolinite surfaces in the experimental results. The hydroxyl groups of FL22 and PVA form hydrogen bonds with the basal surfaces of kaolinite in conditions of pH 6. The joint experimental and theoretical results suggest that, due to the presence of the hydroxyl group, the conformation of FL22 changes under pH, where at neutral pH it lies relatively flat to the kaolinite surfaces, but at higher pH, conformational changes of the polymer occur, thereby increasing the adsorbed quantity of FL22. View Full-Text
Keywords: clay mineral; kaolinite; cement; polymer; simulation; density functional theory clay mineral; kaolinite; cement; polymer; simulation; density functional theory
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Jacquet, A.; Geatches, D.L.; Clark, S.J.; Greenwell, H.C. Understanding Cationic Polymer Adsorption on Mineral Surfaces: Kaolinite in Cement Aggregates. Minerals 2018, 8, 130.

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