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Nature of mixed iron and aluminium gels as affected by Fe/Al molar ratio, pH and citrate

Published online by Cambridge University Press:  09 July 2018

A. Violante ,
C. Colombo ,
G. Cinquegrani ,
P. Adamo  and
P. Violante
A. Violante
Affiliation:
Dipartimento di Scienze Chimico-Agrarie, Università di Napoli Federico 11, 80055 Portici, Italy
C. Colombo
Affiliation:
Dipartimento di Scienze Chimico-Agrarie, Università di Napoli Federico 11, 80055 Portici, Italy
G. Cinquegrani
Affiliation:
Dipartimento di Scienze Chimico-Agrarie, Università di Napoli Federico 11, 80055 Portici, Italy
P. Adamo
Affiliation:
Dipartimento di Scienze Chimico-Agrarie, Università di Napoli Federico 11, 80055 Portici, Italy
P. Violante
Affiliation:
Dipartimento di Scienze Chimico-Agrarie, Università di Napoli Federico 11, 80055 Portici, Italy
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Abstract

The nature and mineralogy of mixed Al and Fe(III) gels (initial Fe/Al molar ratios (Ri) of 1.0 and 2.5) formed at pH values ranging from 4.0 to 10.0, both in the presence and absence of citric acid (citrate/Fe + AI molar ratio (Rcit) of 0.01 and 0.1) and aged for a long period at room temperature and at 50°C have been studied. The complexes showed considerable differences in the mineralogy of the precipitation products. The samples formed at Ri = 1.0 contained ferrihydrite at pH 4.0, ferrihydrite + gibbsite at pH 5.0-7.0, and hematite + Al(OH)3 polymorphs + ferrihydrite at pH 9.0-10.0. The samples formed at Ri = 2.5 had greater quantities of poorly crystallized ferrihydrite. Large amounts of Fe+Al (25-82%) were solubilized from the samples aged for 60 days at 50°C by ammonium oxalate. The addition of increasing concentrations of citrate to the gel suspensions containing equimolar amounts of Fe and AI strongly inhibited the formation of Al(OH)3 polymorphs both at pH 5.0 or 8.5 by promoting the formation of short-range ordered materials. Citrate added initially to Fe-Al solutions (R*cit = 0.1) completely inhibited formation of crystals even after 135 days at 50°C.

Type
Research Article
Information
Clay Minerals , Volume 33 , Issue 3 , September 1998 , pp. 511 - 519
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1998

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