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Influence of pH, Concentration, and Chelating Power of Organic Anions on the Synthesis of Aluminum Hydroxides and Oxyhydroxides

Published online by Cambridge University Press:  01 July 2024

A. Violante
Affiliation:
Istituto di Chimica Agraria dell’ Università di Napoli, 80055, Portici, Italy
P. Violante
Affiliation:
Istituto di Chimica Agraria dell’ Università di Napoli, 80055, Portici, Italy

Abstract

Chelating organic acids hampered the hydrolytic reactions of Al and affected the nature of the crystalline aluminum hydroxides. Chemical composition, structure, size, nature of functional groups, and concentration of each organic anion, as well as the pH of the system, controlled the rate of Al(OH)3 crystallization. The order of effectiveness of the various acids was: glutaric < succinic = phthalic < glycine < malonic < glutamic < aspartic < oxalic < salicylic = malic < citric < tartaric. An increase in the stability of complexes formed between the organic ligands and Al decreased the rate of crystallization and changed the final aluminous products from bayerite to nordstrandite and/or gibbsite and then to pseudoboehmite and/or amorphous material. In the presence of anions with a great affinity for Al, particularly at pH equal to or less than 9.0, the reaction products were commonly poorly crystalline or structurally distorted. In the range of pH 8.0 to 10.0 moderately or strongly chelating anions acted to retard or prevent olation and facilitated the formation of stable pseudoboehmite or X-ray-amorphous products. The stronger the chelating power or the higher the concentration of organic anions, the easier was the formation of pseudoboehmite or amorphous material.

Резюме

Резюме

Хелатообразующие органические кислоты препятствовали гидролитическим реакциям А1 и влияли на природу кристаллических гидроокисей алюминия. Скорость кристаллизации контролировалась химическим составом, структурой, размером, природой функциональных групп и концентрацией каждого органического аниона, а также рН системы. Порядок эффективности различных кислот был следующий: глутаровоя < янтарная = фталевая < аминоуксусная < малоновая < глутаминовая < аминоянтарная < щавелевая < салициловая = оксиянтарная < лимонная < винная. Увеличение стабильности комплексов, формированных между органическими аддендами и А1, уменьшало скорость кристаллизации и изменяло конечные алюминиевые продукты от байерита до нордстрандита и/или гиббсита потом до псевдобемита и/или аморфного материала. В присутствии анионов, которые имеют большое химическое сродстве с А1, особенно для рН равного или меньшего чем 9,0, продукты реакции были обычно плохо выкристаллизированы или структурно искаженные. В диапазоне рН от 8,0 до 10,0 умеренно или сильно хелатообразующие анионы задерживали или предупреждали олацию и облегчали образование стабильного псевдобемита или рентгеновско-аморфных продуктов. Чем сильнее была хелатообразующая способность или чем большая была концентрация органических анионов, тем легче была образование псевдобемита или аморфных материалов. [Е.С.]

Resümee

Resümee

Chelatkomplex-bildende organische Säuren verhindern die hydrolytischen Reaktionen von aluminium und beeinflussen die Art der kristallinen Aluminiumhydroxide. Die chemische Zusammensetzung, die Struktur, die Größe, die Art der funktionellen Gruppen, und die Konzentration jedes einzelnen organischen Anions sowie der pH-Wert des Systems bestimmen die Kristallisationsgeschwindigkeit von Al(OH)3. Die Reihenfolge der Wirksamkeit der verschiedenen Säuren war: Glutarsäure < Bernsteinsäure = Phthalsäure < Glycinsäure < Malonsäure < Glutaminsäure < Asparaginsäure < Oxalsäure < Salicylsäure = Monohydroxibernsteinsäure < Zitronensäure < Weinsäure. Eine Stabilitätszunahme der Komplexe aus den organischen Liganden mit dem Aluminium verringerte die Kristallisationsgeschwindigkeit und veränderte die Aluminium-Endprodukte von Bayerit nach Nordstrandit und/oder Gibbsit und danach zu Pseudoboehmit und/oder amorphe Substanz. In der Gegenwart von Anionen mit einer großen Affinität für Aluminium waren die Reaktionsprodukte, vor allem bei pH-Werten gleich oder kleiner 9,0, im allgemeinen schlecht kristallisiert oder hatten eine verzerrte Struktur. Im pH-Bereich von 8,0 bis 10,0 wirkten mässig oder stark Chelatkomplex-bildende Anion verzögernd oder verhindernd auf die Olation und begünstigten die Bildung von stabilem Pseudoboehmit oder von röntgenamorphen Substanzen. Je größer die Komplexierungsfähigkeit oder je höher die Konzentration an organischen Anionen war, umso leichter war die Bildung von Pseudoboehmit oder amorphem Material. [U.W.]

Résumé

Résumé

Des acides organiques chélatants ont rendu plus difficiles les réactions hydrolitiques d'Al et affecté la nature des hydroxides d'aluminium cristallins. La composition chimique, la structure, la taille, la nature des groupes fonctionnels, et la concentration de chaque anion organique, ainsi que le pH du système ont contrôlé l'allure de la cristallisation d'Al(OH)3. L'ordre d'efficacité des acides variés était le suivant: glutarique < succinique = phthalique < glycine < malonique < glutamique < aspartique < oxalique < salicylique = malique < citrique < tartarique. Un accroissement de la stabilité des complexes formés par les liants organiques et Al a diminué l'allure de cristallisation et changé les produits alumineux finaux de bayerite en nordstrandite et/ou gibbsite et ensuite en pseudobohémite et/ou matériel amorphe. En présence d'anions ayant une grande affinité pour Al, particulièrement à un pH égal à ou inférieur à 9, les produits de réaction étaient souvent pauvrement cristallins ou structuralement dérangés. Dans la gamme de pH de 8 à 10, des anions modérément ou très chélatants ont agi de façon à retarder ou empêcher l'olation et ont facilité la formation de pseudobohémite stable ou de produits amorphes aux rayons-X. Plus le pouvoir de chélation des anions organiques était grand, ou plus leur concentration était haute, plus la formation de pseudobohémite ou de matériel amorphe était facile. [D.J.]

Type
Research Article
Copyright
Copyright © Clay Minerals Society 1980

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Footnotes

1

This work was supported in part by the CNR research grant CT79.01978.06.

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