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Colloids Interfaces 2018, 2(1), 12; doi:https://doi.org/10.3390/colloids2010012

Comparison of the Critical Coagulation Concentrations of Allophane and Smectites

1
Bundesanstalt für Geowissenschaften und Rohstoffe (BGR), Stilleweg 2, D-30655 Hannover, Germany
2
Landesamt für Bergbau, Energie und Geologie (LBEG), Stilleweg 2, D-30655 Hannover, Germany
Present Address: Bundesamt für Kerntechnische Entsorgungssicherheit (BfE), Willy-Brandt-Straße 5, 38226 Salzgitter, Germany.
*
Author to whom correspondence should be addressed.
Received: 5 March 2018 / Revised: 16 March 2018 / Accepted: 19 March 2018 / Published: 21 March 2018
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Abstract

Clays consist of fine particles (clay minerals) which under certain conditions can be dispersed in water, forming a fairly stable dispersion. The stability of the clay mineral dispersions depends on the pH, solid/liquid ratio, and most of all on the type and concentration of dissolved ions. The difference between the dispersibility of different clays is not yet understood. In the present study allophane and smectite (main constituent of bentonite) are compared. Allophane surfaces are dominated by aluminol groups. Therefore, they can be used to investigate the properties of the edges of platy dioctahedral clay minerals. Dispersion and coagulation of allophane was understood based on the charge of the surface functional groups. Dispersion of allophane was only possible at pH < 5 where the aluminol groups became positive and at low ionic strength (critical coagulation concentrations (CCC) < 10 mmol/L NaCl). Dispersion at high pH may also be possible but this was not tested in the present study. In contrast to allophane, bentonite dispersions coagulated when the edges of the smectites became positive. This is probably caused by heterocoagulation leading to edge (+)/face (−) aggregation. CCC values of different bentonite dispersions ranged from 10 to 750 mmol/L. Most of the Wyoming bentonite dispersions were more stable and even above the CCC, sedimented much slower compared to other bentonites. The reason for this phenomenon could not be identified and needs further research. View Full-Text
Keywords: allophane; smectite; bentonite; dispersion; critical coagulation concentration allophane; smectite; bentonite; dispersion; critical coagulation concentration
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Kaufhold, S.; Kaufhold, A.; Dohrmann, R. Comparison of the Critical Coagulation Concentrations of Allophane and Smectites. Colloids Interfaces 2018, 2, 12.

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Colloids Interfaces EISSN 2504-5377 Published by MDPI AG, Basel, Switzerland RSS E-Mail Table of Contents Alert
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