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Effect of Selective Dissolution on Charge and Surface Properties of an Acid Soil Clay

Published online by Cambridge University Press:  02 April 2024

Nancy Cavallaro*
Affiliation:
Department of Agronomy, Cornell University, Ithaca, New York 14853
M. B. McBride
Affiliation:
Department of Agronomy, Cornell University, Ithaca, New York 14853
*
1Present address: Centro de Edafologia, Chapingo, Mexico.
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Abstract

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To evaluate the importance of oxides to the surface chemistry of acid mineral soils, clay fractions were separated from a surface and subsurface horizon of an Inceptisol representative of many of the acid soils of the Southern Tier of New York state. Portions of the clays were treated to remove selectively noncrystalline and microcrystalline Fe and A1 oxides (acid ammonium oxalate extraction), total free iron oxides (dithionite reduction in buffered citrate solution), and organic matter (hypochlorite oxidation). Charge and ion-adsorption characteristics of the treated and untreated clays were investigated by means of Ca2+- and Cl-exchange capacities, potentiometric titrations, and electrophoretic mobility (zeta potential) measurements of the CaCl2-treated clays.

Based upon surface area and anion- and cation-exchange measurements, the Fe and A1 oxides or oxideorganic matter complexes were found to contribute a large part of the surface area and pH-dependent charge of these clays. Oxide removal increased the cation-exchange capacity (CEC) and virtually eliminated the anion-exchange capacity (AEC) at pH 3 and 5.5 while shifting the positive zeta potential (ZPC) of the B-horizon clay toward negative values. Organic matter oxidation increased the AEC at pH 3 and the CEC at pH 5.5 and markedly shifted the ZPCs of both A- and B-horizon clays toward more positive values, probably by the removal of adsorbed organics from oxide surfaces. Estimates of the ZPCs of the clays varied among the three methods used, Ca2+- and Cl-exchange capacities giving the lowest, and electrophoresis giving the highest values.

Резюме

Резюме

Фракции глин сепарировались из почвенных и подпочвенных ярусов характерных для большинства кислотных почв Южного Яруса в Штате Нью-Йорка, для оценки значения окисей в химии поверхностей почв, содержащих кислотные минералы. Порции глин обрабатывались для селективного отделения некристаллических и микрокристаллических окисей Fe и Al (экстракция при использовании щавелевокислого аммония), всех свободных окисей железа (редуцирование дитионитом в содержащем буфер растворе цитрата), и органической материи (окисление гипохлоритом). Зарядо- и ионо-адсорбционные характеристики обработанных и необработанных глин исследовались путем изменений Са2+- и Сl-обменных способностей, потенциометрического титрования и электрофорезной подвижности (потенциал зета) на глинах, обработанных СаСl2.

На основании измерений площади поверхности и анионо- и катионо-обмена, окиси Fe и Al или комплексы окисей с органической материей вносили большой вклад в величину площади поверхности и pH-зависимый заряд этих глин. Удаление окиси увеличивало катионо-обменную способность (КОС) и фактически исключало анионо-обменную способность (АОС) при pH = 3 и 5,5 в то время, как положительный потенциал зета (ПЗ) глины из яруса В перемещался в сторону отрицательных величин. Окисление органической материи увеличивало АОС при pH = 3 и КОС при pH = 5,5 и значительно перемещало величины ПЗ глин из обоих, А- и В-ярусов к более положительным значениям, вероятно, путем удаления адсорбированных органических веществ с поверхности окисей. Оценки величин ПЗ глин были различны при использовании этих трех методов; Са2+- и Сl-обменные способности давали наиболее низкие величины, а электрофорез—наибольшие величины. [E.G.]

Resümee

Resümee

Um die Bedeutung von Oxiden für die Oberbflächenchemie von sauren Mineralböden abzuschätzen, wurden die Tonfraktionen von einem Oberflächenhorizont und einem Unterbodenhorizont eines Inceptisols abgetrennt, der für viele saure Böden von Southern Tier, New York Staat, repräsentative ist. Teile der Tone wurden behandelt, um nichtkristalline und mikrokristalline Fe- and Al-Oxide (mittels saurer Ammoniumoxalat-Extraktion), die gesamten freien Eisenoxide (mittels Reduktion durch Dithionit in gepufferten Citratlösungen) und organische Substanzen (mittels Oxidation durch Hypochlorit) selektiv zu entfernen. Ladungs- und Ionenadsorptions-Charakteristika der behandelten und unbehandelten Tone wurden mittels Ca2+- und Cl-Austauschkapazitätsmessungen, potentiometrischen Titrationen und elek-trophoretischen Beweglichkeitsmessungen (Zeta-Potential) der CaCl2-behandelten Tone untersucht.

Aufgrund von Oberflächen- und Anionen- sowie Kationenaustauschmessungen zeigte sich, daß Fe- und Al-Oxide sowie Komplexe aus Oxiden und organischen Substanzen einen großen Anteil der Oberfläche und der pH-abhängigen Ladung dieser Tone ausmachen. Senn die Oxide entfernt wurden, nahm die Kationenaustauschkapazität (CEC) zu und wurde die Anionenaustauschkapazität (AEC) bei pH 3 und 5,5 praktisch zerstört, während das positive Zeta-Potential (ZPC) des B-Horizonttons gegen negative Werte verschoben wird. Die Oxidation organischer Substanzen vergrößert die AEC bei pH 3 und die CEC bei pH 5,5. Außerdem vershiebt sie die ZPCs sowohl des A- als auch des B-Horizonttons in Richtung höherer Werte, was wahrscheinlich auf dem Entfernen von adsorbierten organischen Substanzen von den Oxidoberflächen beruht. Die Schätzwerte der ZPCs der Tone variiert zwischen den drei verwendeten Methoden, wobei Ca2+- und Cl-Austauschkapazität die niedrigsten und Elektrophorese die höchsten Werte ergibt. [U.W.]

Résumé

Résumé

Pour évaluer l'importance d'oxides à la chimie de surface de sols minéraux acides, des fractions d'argile ont été separées d'un horizon de surface et sousterrain d'un représentant d'un Inceptisol d'un des nombreux sols acides de l’état de New York. On a traité des portions des argiles pour enlever sélectivement les oxides Fe et Al non-cristallins et microcristallins (extraction d'oxalate d'ammonium acide), les oxides à fer totalement libre (réduction dithionite dans une solution citrate tempérée) et la matière organique (oxidation hypochlorite). Les caractéristiques d'adsorption de charge et d'ions des argiles traités et non-traités ont été investiguées au moyen des capacités d’échange de Ca2+ et Cl, des titrations potentiomé-triques, et des mesures de mobilité électrophorétiques (potentiel zeta) des argiles traités au CaCl2.

Basé sur l'aire de surface et sur des mesures d’échange d'anions et de cations, on a trouvé que les oxides Fe et Al ou les complexes oxide-matière organique contribuaient une grande partie de l'aire de surface et de la charge dépendante du pH de ces argiles. L'enlèvement de l'oxide a augmenté la capacité d’échange de cations (CEC) et a de fait éliminé la capacité d’échange d'anions (AEC) aux pH 3 et 5,5, tandis que le potentiel zeta positif (ZPC) de l'argile de l'horizon B a été déplacé vers les valeurs négatives. L'oxidation par matière organique a augmenté l'AEC au pH 3 et la CEC au pH 5,5, et a déplacé de manière marqueé les ZPCs des argiles des horizons A et V vers des valeurs plus positives, sans doute par l'enlèvement de la matière organique adsorbée des surfaces oxides. Les estimations des ZPCs des argiles étaient variées parmi les trois méthodes utilisées, les capacités d'echange de Ca2+ et de Cl donnant les valeurs les plus basses, et l’électrophorèse donnant les plus élevées. [D. J.]

Type
Research Article
Copyright
Copyright © 1984, The Clay Minerals Society

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