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Amorphous ferri-aluminosilicates in some tropical ferruginous soils

Published online by Cambridge University Press:  09 July 2018

G. S. R. Krishna Murti ,
V. A. K. Sarma  and
P. Rengasamy
G. S. R. Krishna Murti
Affiliation:
Indian Agricultural Research Institute, New Delhi, India
V. A. K. Sarma
Affiliation:
Indian Agricultural Research Institute, New Delhi, India
P. Rengasamy
Affiliation:
Indian Agricultural Research Institute, New Delhi, India
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Abstract

The amorphous mineral selectively dissolved from the clay (<2 μm) fractions of twenty-six ferruginous soils contains considerable iron in addition to silicon and aluminium. SiO2/Al2O3 and SiO2/R2O3 molar ratios are between 2·03-3·52 and 1·72-2·95 respectively. The model of the amorphous ferri-aluminosilicate (AFAS) consists mainly of negatively charged tetrahedrally coordinated silica-alumina phase Si3AlO6(OH)4 containing domains of neutral FeOOH, with an outer positively charged hydroxyaluminium polymeric component [Al(OH)2.5]n.The calculated hydroxyl water content of the AFAS averages 17·8%; cation exchange capacity varies from 48·6 to 112·0 mEq/100 g and shows a negative correlation with the outer hydroxyaluminium octahedral component and a positive correlation with the ratio of the tetrahedral Si-Al component to the octahedral hydroxyaluminium component. The K-fixation capacity (1·9-6·1 mEq/100 g) of the AFAS does not appear to be related to the chemical composition. The genesis of the amorphous mineral is discussed.

Sommaire

Sommaire

La sélectivité su mineral amorphe dissout à partir de fractions d'argiles (<2 μm) contenue dans vingt six sols ferrugineux contient une proportion de fer considerable en plus du silicium et de l'aluminium. Les coefficients molaires de SiO2/Al2O3 et SiO2/R2O3 se situent respectivement entre 2·03-3·52 et 1·72-2·95. Le ferri-alluminosilicate étalon (AFS) consiste principalement de la phase silica-alumina Si3A106(OH)4 tétrahiquement égale at négativement chargée, laquelle contient des ensembles de FeOOH neutres possédant une positivité extérieure chargée du composant polymérique d'hydroxya-aluminium [Al(OH)2.5]n. La teneur en eau de l'hydroxyle dans AFAS est en moyenne de 17,8%; la capacitò d'échange de cations varie de 48,6 à 112 mEq/lOOg et révèle une correlation negative avec le composant extérieur octahédrique d'aluminium ainsi qu'une correlation positive avec le taux du composant tétrahédrique Si-Ai en fonction du composant octahéyaluminium. La capacitò à K-fixé (1,9-6,1 mEq/lOOg) de AFS n'apparait pas avoir de rapport avec la composition chimique. On peut alors discuter de la genèse du minerai amorphe.

Kurzreferat

Kurzreferat

Das amorphe Minerai, das aus den Tonfraktionen (<2 μm) von 26 eisenhaltigen Erden durch selektive Lòsung gewonnen wurde, enthàlt zusàtzlich zu Silizium und Aluminium erhebliche Eisenanteile. SiO2/Al2O3 und SiO2/R2O3 weisen Molekularverhàltnisse zwischen 2·03-3·52 unf 1·72-2·95 auf. Das Modell des amorphen Ferri- Aluminiumsilikats (AFAS) besteht hauptsachlich aus negativ geladener tetraedrisch koordinierter Tonerde-Silikatphase Si3A106(OH)4, die Bereiche von neutralem FeOOH mit einem auBeren positiv geladenen polymerem Bestandteil von Hydroxyalurninium [Al(OH)2.5]n enthàlt. Der errechnete Hydroxylwassergehalt des AFAS enthàlt mittlere Anteile von 17,8%; die Kationenaustauschfàhigkeit schwankt zwischen 48,6 und 112,0 mEq/100 g und steht in negativer Beziehung zu dem àusseren oktaedrischen Bestandteilen und in positiver Beziehung zu dem Verhàltnis zwischen den tetraedrischen Si-Al und Oktahexyaluminium-Bestandteilen. Die K-Fixierfahigkeit (1,9- 6,1 mEq/100 g) des AFAS scheint von der chemischen Zusammensetzung unabhangig zu sein. Es wird das Entstehen des amorphen Minerals eròrtert.

Referata

Referata

La selectividad del mineral-amorfo disuelto a partir de fracciones (<2 μm) arcillosas de veintiséis suelos ferruginosos contiene considerable hierro, ademàs de silicio y aluminio. Las proporciones molares de SSiO2/Al2O3 y SiO2/R2O3 son de entre el 2·03-3·52 y el 1·72-2·95 respectivamente. El modelo del ferri-aluminosilicato amorfo (FASA) consiste principalmente de coordenada de silice-alùmina, fase Si3A106- (OH)4 tetraèdricamente con carga negativa, conteniendo dominios de FeOOH neutro con un componente mas externo polimèrico de hidroxi-aluminio con carga positiva [Al(OH)2.5]n. El contenido calculado de hidroxil-agua de los FASA tiene promedios del 17,8%; la capacidad de intercambio catiónico vario desde 48,6 a 112,0 mEq/100 g. y muestra una correlación negativa con el componente externo octaédrico de hidroxialumino y una correlación positiva con el indice proporcional del componente Si-Al tetraèdrico al componente octahey-aluminio. La capacidad de fijación-K (1,9-6,1 mEq/100 g.) de las FASA no parece estar relacionada con la composición quimica. Se comenta la genesis del mineral amorfo.

Type
Research Article
Information
Clay Minerals , Volume 11 , Issue 2 , June 1976 , pp. 137 - 146
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1976

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