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Dissolution Kinetics of Phlogopite. I. Closed System

Published online by Cambridge University Press:  01 July 2024

Feng-Chih Lin  and
Charles V. Clemency
Feng-Chih Lin
Affiliation:
Department of Geological Sciences, State University of New York at Buffalo, 4240 Ridge Lea Road, Amherst, New York 14226
Charles V. Clemency
Affiliation:
Department of Geological Sciences, State University of New York at Buffalo, 4240 Ridge Lea Road, Amherst, New York 14226
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Abstract

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Dry ground phlogopite was placed in deionized water saturated with CO2 at room temperature and pressure. The bulk solution was buffered between a pH of 5 and 6 which is close to the pH of natural weathering systems. The conditions simulated a closed system. After 1010 hr, 2.0% of the total K, 0.95% of the Mg, 0.54% of the Si, and 0.74% of the F had been released, indicating that the dissolution was incongruent. Most of the K was released within 3 min, apparently by a rapid surface exchange with hydrogen ion. One-third of the cation-exchange capacity of this phlogopite arises from cations released from the outer surfaces, while two-thirds arises from the release of more deeply seated cations. All cations exhibited decreasing release with time, the slowest being Si. The rate-controlling “factor” in the later stages is related to the release of Si. It is difficult to distinguish linear from parabolic kinetics in the later stages because of the slow rate of dissolution; however, linear kinetics is most likely. If linear kinetics is applicable, the dissolution rate of Si was 3.8 × 10−17 mole/cm2/sec. Conclusions may be affected by the length of the experimental run.

Резюме

Резюме

Сухой, перемеленый флогопит был помещен в деионизированную воду, насыщенную СO2 при комнатной температуре и давлении. Основной раствор был буферован между рН 5 и 6, эти величины близки к рН в системе природной эрозии. Условия симулировали замкнутую систему. После 1010 часов 2% из всего К, 0,95% из Mg, 0,54% из 81 и 0,74% из Р были освобождены, что указывает на инконгруэнтное растворение. Большая часть К была освобождена во время 3 минут, очевидно, при помощи быстрого поверхностного обмена с водородными ионами. Одна треть катионообменной емксти этого флогопвта является результатом освобождения катионов из внешних поверхностей, а две трети—резюльтатом освобождения катионов, находящихся внутри. Для всех катионов наблюдалась уменьшающаяся способность освобождения со временем, самая медленная для 81. “Фактор,” регулирующий скорость обмена на более поздних этапах реакции, связан с освобождением 81. На этих поздних этапах трудно отличить линейную кинетику от параболической вследствие медленной скорости растворения. Тем не менее, линейная кинетика является более вероятной. При предположении линейной кинетики, скорость растворения Si была 3, 8 х 10−17 моль/cm2/сек. Время проведения экспериментов может влиять на эти выводы. [Е.С.]

Resümee

Resümee

Trocken gemahlener Phlogopit wurde in deionisiertes Wasser gegeben, das bei Zimmertemperatur und Atmosphärendruck mit CO2 gesättigt war. Die Gesamtlösung wurde auf pH 5–6 gepuffert, was dem pH-Wert der natürlichen Verwitterung nahekommt. Die Bedingungen simulierten ein geschlossenes System. Nach 1010 Stunden Reaktionszeit waren 2,0% des Gesamt-Kalium, 0,95% des Mg, 0,54% des Si, und 0,74% des F in Lösung gegangen. Das deutet darauf hin, daß die Auflösung inkongruent verlief. Das meiste Kalium ging innerhalb von 3 Minuten in Lösung, offensichtlich durch einen schnellen Austausch gegen Wasserstoffionen an den Oberflächen. Ein Drittel der Ionenaustauschkapazität dieses Phlogopit rührt von den Kationen her, die von den äußeren Oberflächen in Lösung gehen, während zwei Drittel von tiefer gelegenen Kationen herrühren. Alle Kationen gingen mit zunehmender Zeit in abnehmenden Mengen in Lösung, wobei Silicium am langsamsten in Lösung ging. Der geschwindigkeitsbestimmende Faktor in den letzten Stadien hängt mit dem Inlösunggehen des Siliciums zusammen. In den späten Stadien ist, wegen der geringen Lösungsgeschwindigkeit, schwer zwischen linearer und parabolischer Kinetik zu unterscheiden; jedoch ist eine lineare Kinetik am wahrscheinlichsten. Wenn eine lineare Kinetik angewendet werden kann, dann betrug die Lösungsgeschwindigkeit für Silicium 3,8 × 10− 17 Mol/cm2/sec. Diese Schlußfolgerungen könnten dutch die Länge der Versuchszeit beeinflußt sein. [U.W.]

Résumé

Résumé

De la phlogopite sèche moulue a été placée dans de l'eau déionisée saturée de CO2 à température et pression ambiantes. La solution en masse a été tamponée entre un pH de 5 et de 6, ce qui est proche du pH de systèmes d'altération naturels. Après 1010 heures, 2,0% du K total, 0,95% du Mg, 0,54% du Si, et 0,74% du F avaient été relâchés, indiquant que la dissolution était inconforme. La plupart du K a été relâché endéans 3 min, apparemment par un échange de surface rapide avec l'ion hydrogène. Un tiers de la capacité d’échange de cations de cette phlogopite provient de cations relâchés des surfaces externes, tandis que deux tiers proviennent du relâchement de cations situés plus profondément. Tous les cations ont exhibé un relâchement décroissant à mesure que le temps augmentait, le plus lent étant Si. Le “facteur” contrôllant l'allure dans les derniers stages est apparenté au relâchement de Si. Il est difficile de différencier la kinétique linéaire de la kinétique parabolique dans les derniers stages à cause du taux de dissolution lent, cependant, la kinétique linéaire est la plus probable. Si la kinétique linéaire peut êire appliquée, le taux de dissolution de Si était 3,8 × 10−17 mole/cm2/sec. Les conclusions peuvent être affectées par la longueur de l'expérience. [D.J.]

Keywords

Closed systemDissolutionKineticsMicaPhlogopite
Type
Research Article
Information
Clays and Clay Minerals , Volume 29 , Issue 2 , April 1981 , pp. 101 - 106
Copyright
Copyright © 1981, The Clay Minerals Society

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