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Leaching Characteristics of Fly Ash after Four Years of Natural Weathering

Published online by Cambridge University Press:  21 February 2011

A. Andrade
Affiliation:
Faculty of Geology and Geophysics, Dept. of Chemical Geology, Utrecht University, 3508 TA Utrecht, The Netherlands.
Y. M. A Coenegracht
Affiliation:
Faculty of Geology and Geophysics, Dept. of Chemical Geology, Utrecht University, 3508 TA Utrecht, The Netherlands.
G. G. Hollman
Affiliation:
Faculty of Geology and Geophysics, Dept. of Chemical Geology, Utrecht University, 3508 TA Utrecht, The Netherlands.
M. Janssen-Jurkovicova
Affiliation:
NV KEMA, 6800 ET Arnhem, The Netherlands
H. S. Pietersen
Affiliation:
Faculty of Civil Engg., Materials Science Section, Delft Tech. Univ., 2628 CN, The Netherlands.
S. P. Vriend
Affiliation:
Faculty of Geology and Geophysics, Dept. of Chemical Geology, Utrecht University, 3508 TA Utrecht, The Netherlands.
R. D. Schuiling
Affiliation:
Faculty of Geology and Geophysics, Dept. of Chemical Geology, Utrecht University, 3508 TA Utrecht, The Netherlands.
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Abstract

The natural weathering process of fly ashes was studied in artificial fly ash beds. The ashes were previously classified according to their total alkali content into acid, neutral and alkaline. After 4 years the effects of weathering are minor. The formation of concretions due to local cementation by calcite is observed in alkaline fly ash. Small brown pellets, highly enriched in some heavy metals, are present in the acid fly ash beds. Under natural conditions leaching is mainly confined to the alkaline fly ash. Elements which are leached most are sulphur and some alkalis as well as minor amounts of some trace elements.

Shake- and column experiments of the weathered fly ashes with acids of pH 1 and 4, the latter also in combination with complexing agents, were carried out in order to check if the natural leaching process may be accelerated artificially. Strong acids (pH= 1) were most effective, but relatively large quantities of major elements were also leached. Experiments with the weak acids, combined with complexing agents, resulted in leaching percentages which did not significantly differ from experiments without these agents. This indicates that a major part of the elements are present in an immobile form; because of the use of sulphuric acid, it is likely that they are in some cases precipitated as sulphates (e.g. barium, calcium).

Type
Research Article
Copyright
Copyright © Materials Research Society 1990

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