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The Selective Adsorption of Sodium by Clay Minerals in Lakes Pontchartrain and Maurepas, Louisiana

Published online by Cambridge University Press:  01 July 2024

Ray E. Ferrell Jr.  and
Robert A. Brooks
Ray E. Ferrell Jr.
Affiliation:
Department of Geology, Louisiana State University, Baton Rouge, La. 70803
Robert A. Brooks*
Affiliation:
Department of Geology, Louisiana State University, Baton Rouge, La. 70803
*
*Present address: Exploration Research Division, Continental Oil Company, Ponca City, Oklahoma
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Abstract

Ion exchange analyses of the clay-sized fraction of sediments in Lakes Pontchartrain and Maurepas suggest the selective adsorption of Na at the expense of Mg. The literature suggests that Mg should be preferentially adsorbed. As the chlorinity of the lake waters increases from 300 mg/l to 3250mg/l, the percentage of exchangeable Na increases from 13·6 to 30·6 while the percentage of exchangeable Mg decreases from 65·6–36·8. The observed exchangeable Na percentages are higher than the ones calculated from the sodium-adsorption-ratios. The difference is attributed to an increase in the Na exchange constant of the sediment and therefore an increased selectivity for Na. With an increase in chlorinity, montmorillonite increases from 47 to 61 per cent and the total of the exchangeable cations (Na, Mg, Ca, K) increases from 36 to 82 m-equiv./100 g.

Résumé

Résumé

L’étude des échanges ioniques concernant la fraction argile granulométrique de sédiments des lacs Pontchartrain et Maurepas, suggère une adsorption sélective de Na aux dépens de Mg. La littérature indique que Mg devrait être adsorbé préférentiellement. Lorsque la teneur en chlorure des eaux des lacs monte de 300 mg/l à 3250 mg/l, le pourcentage de Na échangeable augmente, en passant de 13,5 à 30,6, alors que le pourcentage de Mg échangeable diminue, en passant de 65,5 à 36,8. Les pourcentages de Na échangeable observés sont plus élevés que ceux que l’on calcule à partir des rapports d’adsorption du Na. La différence est attribuée à une augmentation de la constante d’échange du Na dans le sédiment, et donc, à une sélectivité accrue pour Na. Lorsque la teneur en chlorure augmente, la montmorillonite passe de 47 à 61%, et la somme des cations échangeables (Na, Mg, Ca, K) augmente en passant de 36 à 82 m-equil./100 g.

Kurzreferat

Kurzreferat

Ionenaustauschanalysen der Tongrössefraktion von Ablagerungen in den Pontchartrain und Maurepas Seen deuten auf die selektive Adsorption von Na auf Kosten von Mg Hin. Nach der Literatur sollte das Mg vorzugsweise adsorbiert werden. Mit Zunahme der Chlorinität der Seewässer von 300mg/l auf 3250mg/l, steigt der Prozentgehalt an austauschbarem N von 13,6 auf 30,6 während der Prozentgehalt von austauschbarem Mg von 65,5 auf 36,8 absinkt. Die beobachteten Prozentgehalte an austauschbarem Na sind höher als die aus dem Natrium-adsorptionsverhältnissen berechneten. Der Unterschied wird einer Zunahme in der Na-Austauschkonstanten der Ablagerung und damit einer erhöhten Selektivität für Na zugeschrieben. Mit Zunahme der Chlorinität erholt sich der Montmorillonit von 47 auf 61% und die Gesamtmenge der austauschbaren Kationen (Na, Mg, Ca, K) steigt von 36 auf 82 mäq/100 g.

Резюме

Резюме

Определение ионно-обменных свойств глинистых фракций осадков озер Понтчартрейн и Маурепас позволило установить избирательное поглощение Na по сравнению с Mg; литературные данные указывают на предпочтительное поглощение Mg. По мере того, как содержание хлора в озерной воде возрастает от 300 мг/л до 3250 мг/л, содержание обменного Na увеличивается от 13,6 до 30,6%, в то время как содержание обменного Mg падает с 65,5 до 36,8 %. Наблюдаемые количества обменного Na выше, чем вычисленные из отношения натрий — адсорбент. Подобное различие является признаком увеличения константы ионного обмена Na осадка и, следовательно, увеличения избирательной адсорбции Na. С увеличением содержания хлора в воде содержание монтмориллонита возрастает с 47 до 61 %, а общее содержание обменных катионов (Na, Mg, Са, K) увеличивается от 36 до 82 мэкв/100 г.

Type
Research Article
Information
Clays and Clay Minerals , Volume 19 , Issue 2 , June 1971 , pp. 75 - 81
Copyright
Copyright © 1971, The Clay Minerals Society

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