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Mechanism of Sulfate Adsorption by Kaolinite

Published online by Cambridge University Press:  02 April 2024

Sudhakar M. Rao  and
A. Sridharan
Sudhakar M. Rao
Affiliation:
Soil Mechanics Laboratory, Department of Civil Engineering, Indian Institute of Science, Bangalore 560 012, India
A. Sridharan
Affiliation:
Soil Mechanics Laboratory, Department of Civil Engineering, Indian Institute of Science, Bangalore 560 012, India
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Abstract

Sulfate adsorption on kaolinite was followed at 0.7 μeq/ml to 99 μeq/ml solution concentrations at 30°C and at pH 6.0, and the amount of OH~ ions released and the change in surface charge were determined. Sulfate was adsorbed at positive and neutral sites by displacing OH2 and OH− groups, respectively. Adsorption of sulfate occurred predominantly at positive sites at low (0.7 μeq/ml to 0.9 /μeq/ml) solution concentrations, whereas at higher solution concentrations, the proportion of the sulfate adsorbed at the neutral sites increased, varying from 51% at 4.9 μeq/ml to 68% at 99 μeq/ml. The form of sulfate bonding was apparently governed by the level of the positive charge on the clay surface. Higher positive charge at low and intermediate levels of sulfate saturation resulted in the adsorption of sulfate as a divalent anion by forming a 6-member ring with surface Al. With a decrease in positive charge at higher levels of adsorption, the sulfate ion formed both monodentate and bidentate complexes.

Резюме

Резюме

Адсорбция сульфата каолинитом исследовалась для концентрации раствора между 0,7 дэкв/ мл и 99 дэкв/мл при 30°С и рН = 6,0; были определены количество выделенных ионов ОН− и из¬менения поверхностного заряда. Сульфат адсорбировался на положительных и нейтральных местах путем вытеснения групп ОН2 и ОН−, соответственно. Адсорбция сульфата происходила в главной мере на положительных местах при низких концентрациях раствора (0,7 μэкв/мл до 0,9 μ экв/мл), тогда как при больших концентрациях, пропорция сульфата адсорбированного на нейтральных местах увеличивалась, принимая значения от 51 % для 4,9 μ экв/мл до 68% для 99 μ экв/мл. Тип связи сульфата зависел, вероятно, от уровня положительного заряда на поверхности глины. Больший положительный заряд при низких и промежуточных уровнях насыщения сульфатом приводил к адсорбции сульфата в виде двухвалентного аниона путем формирования 6-членового кольца с поверхностными атомами А1. При уменьшении положительного заряда на больших уровнях адсорбции, ион сульфата образо¬вывал монозубчатые и двухзубчатые комплексы. [Е.G.]

Resümee

Resümee

Die Sulfatadsorption an Kaolinit wurde von 0,7 μÄquivalent/ml bis 99 μÄquivalent/ml Lösungskonzentration bei 30°C und pH 6,0 verfolgt, wobei die Menge der freigesetzten OH2-Ionen und die Veränderung der Oberflächenlagen bestimmt wurde. Das Sulfat wurde an positiven und neutralen Plätzen adsorbiert, wobei es OH2- und OH−-Gruppen ersetzte. Die Sulfatadsorption erfolgte bei niedrigen Lösungskonzentrationen (0,7 μÄquivalent/ml bis 0,9 μÄquivalent/ml) vor allem an den positiven Plätzen, während bei höheren Lösungskonzentrationen der Anteil des Sulfats, das an neutralen Plätzen adsorbiert wird, zunahm, wobei er von 51% bei 4,9 μÄquivalent/ml bis 68% bei 99 μÄquivalent/ml variierte. Die Art der Sulfatbindung wurde offensichtlich durch die Höhe der positiven Lagen auf der Tonoberfläche reguliert. Eine höhere positive Ladung führte bei niedriger oder mittelmäßiger Sulfatsättigung zu der Adsorption von Sulfat in Form eines divalenten Anions, wobei ein 6-er Ring mit dem Oberflächen-Al gebildet wurde. Wenn die positive Ladung bei höherem Adsorptionsgrad abnahm, dann bildete das Sulfation sowohl einzähnige als auch zweizähnige Komplexe. [U.W.]

Résumé

Résumé

On a suivi l'adsorption sulfate sur la kaolinite à des concentrations de solution de 0,7 μeq/ml à 99 μeq/ml à 30°C et au pH 6,0, et on a déterminé la quantité d'ions OH− relâchés et le changement de charge de surface. La sulfate a été adsorbée à des sites positifs et neutres par déplacement de groupes OH2 et OH−, respectivement. L'adsorption de sulfate s'est passée de façon prédominante à des sites positifs à des concentrations de solution basses (0,7 μeq/ml à 0,9 μeq/ml), tandis qu’à de plus hautes concentrations de solution, la proportion de sulfate adsorbée aux sites neutres a augmenté, variant de 51% à 4,9 μeq/ml à 68% a 99 μeq/ml. La forme de liaison de sulfate était apparemment gouvernée par le niveau de la charge positive sur la surface de l'argile. Une plus haute charge positive à des niveaux de saturation de sulfate bas et intermédiaires a résulté en l'adsorption de sulfate en tant qu'anion divalent par la formation d'un anneau à 6 membres avec l'Ai de surface. Lors d'une diminution de charge positive à des niveaux d'adsorption plus élevés l'ion sulfate a formé à la fois des complexes monodentates et bidentates. [D.J.]

Keywords

AdsorptionBidentateHydroxylKaoliniteMonodentateSulfate
Type
Research Article
Information
Clays and Clay Minerals , Volume 32 , Issue 5 , October 1984 , pp. 414 - 418
Copyright
Copyright © 1984, The Clay Minerals Society

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