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Apparent Charge Heterogeneity in Kaolins in Relation to Their 2:1 Phyllosilicate Content

Published online by Cambridge University Press:  02 April 2024

Oscar Talibudeen  and
Keith W. T. Goulding
Oscar Talibudeen
Affiliation:
Rothamsted Experimental Station, Harpenden, Herts., AL5 2JQ, United Kingdom
Keith W. T. Goulding
Affiliation:
Rothamsted Experimental Station, Harpenden, Herts., AL5 2JQ, United Kingdom
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Abstract

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Measurements of the differential heats of K-Ca exchange are used to show that 6 groups of sites (ranging from −13.8 to −5.1 kJ/eq and with as many as 4 in any one sample) exist in kaolins that range from 0 to 15% in their 2:1 phyllosillicate content. These heat values, coupled with entropies of exchange, suggest that 0.1−10% vermiculitic, micaceous, and smectitic layers are present, presumably interstratified with kaolinitic layers which are assumed to have no permanent charge. Changes in the activity coefficients of adsorbed K with K saturation confirm these conclusions qualitatively. Thus, fK values at x ↑ 0 correlate inversely (r2 = 0.655) with the content of vermiculite + partially expanding micas, and x values at maximum fK indicate the content of vermiculite + nonexpanding mica + partially expanding micas (r2 = 0.732).

Резюме

Резюме

Использовались измерения величин дифференциальной теплоты обмена К-Са для показания, что в каолинах, содержающих от 0 до 15% 2:1 филлосиликатов, находится 6 различных групп мест (от −13,8 до −5,1 кдж/экв и в количестве до 4 в одном образце). Эти величины, связанные с энтропией обмена, указывают на присутствие 0,1 до 10% вермикулитовых, слюдовых и смектитовых слоев переслаивающихся, вероятно, с каолинитовыми слоями, которые не имеют постоянного заряда. Изменения коэффициентов активности адсорбированного К в зависимости от насыщения К подтверждают кочественно эти выводы. В таком случае, величины fк при х → 0 обратно пропорциональны (r2 = 0,655) содержанию вермикулита + частично-расширяемых слюд. Величины х при максимальном fк указывают на содержание вермикулита + нерасширяемые слюды + частично-расширяемые слюды (г2 = 0,732). [Е.С.]

Resümee

Resümee

Messungen der differentiellen Wärme des K-Ca-Austausches zeigten gewöhnlich, daß 6 Arten von Plätzen (von -13,8 bis -5,1 kJ/Äqu und mit bis zu 4 Arten in einer Probe) in Kaolinen vorkommen, die von 0–15% ihres 2:1 Phyllosilikatgehaltes ausmachen. Diese Wärmewerte zusammen mit den Austauschentropien deuten darauf hin, daß 0,1–10% vermiculitische, glimmerartige und smektitische Lagen vorhanden sind, wahrscheinlich in Wechsellagerung mit kaolinitischen Lagen, von denen man annimmt, daß sie keine permanente Ladung haben. Veränderungen in den Aktivitätskoeffizienten fK von adsorbiertem Kalium bei K-Sättigung bestätigen qualitativ diese Schlußfolgerungen. Daher sind die fK-Grenzwerte für Molenbruch x → 0 umgekehrt proportional (r2 = 0,655) dem Gehalt an Vermiculit + teilweise expandierbaren Glimmer, und die x-Werte bei maximalem fK zeigen den Gehalt an Vermiculit + nicht expandierbarem Glimmer + teilweise expandierbarem Glimmer (r2 = 0,732) an. [U.W.]

Résumé

Résumé

Des mesures des chaleurs différentielles de l’échange K-Ca sont employées pour montrer que 6 groupes de sites (s’étageant de -13,8 à -5,1 kJ/eq et avec jusqu’à 4 dans un échantillon donné) existent dans des kaolins qui s’étagent de 0 à 15% quant à leur contenu 2:1 en phyllosilicate. Ces valeurs de chaleur, accouplées avec des entropies d’échange, suggèrent que 0,1–10% de couches vermiculitiques, micacées et smectitiques sont présentes, que l'on présume être interstratifiées avec des couches kaolinitiques suposées être sans charge permanente. Des changements dans les coéfficients d'activité de K adsorbé avec saturation de K confirment qualitivement ces conclusions. Ainsi, les valeurs fK à x → 0 sont inversément apparentées (r2 = 0,655) au contenu en vermiculite + micas à expansion partielle, et les valeurs x à fK maximum indiquent le contenu en vermiculite + mica non-expansible + micas à expansion partielle (r2 = 0,732). (D.J.]

Keywords

Cation exchangeEnthalpyHeatKaolinSmectiteSurface charge
Type
Research Article
Information
Clays and Clay Minerals , Volume 31 , Issue 2 , April 1983 , pp. 137 - 142
Copyright
Copyright © 1983, The Clay Minerals Society

References

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