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Illinois basin coal fly ashes. 2. Equilibria relationships and qualitative modeling of ash-water reactions

Environmental Science and Technology

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Abstract

Alkaline and acidic Illinois Basin coal fly ash samples were each mixed with deionized water and equilibrated for about 140 days to simulate ash ponding environments. Common to both equilibrated solutions, anhydrite solubility dominated Ca2+ activities, and Al3+ activities were in equilibrium with both matrix mullite and insoluble aluminum hydroxide phases. Aqueous silica activities were controlled by both mullite and matrix silicates. The pH of the extract of the acidic fly ash was 4.1 after 24 h but increased to a pH value of 6.4 as the H2SO4, assumed to be adsorbed to the particle surfaces, was exhausted by the dissolution of matrix iron oxides and aluminosilicates. The activities of aqueous Al3+ and iron, initially at high levels during the early stages of equilibration, decreased to below analytical detection limits as the result of the formation of insoluble Fe and Al hydroxide phases. The pH of the extract of the alkaline fly ash remained above a pH value of 10 during the entire equilibration interval as a result of the hydrolysis of matrix oxides. As with the acidic system, Al3+ activities were controlled by amorphous aluminum hydroxide phases that began to form after about 7 days of equilibration. The proposed mechanisms and their interrelations are discussed in addition to the solubility diagrams used to deduce these relationships. ?? 1984 American Chemical Society.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Illinois basin coal fly ashes. 2. Equilibria relationships and qualitative modeling of ash-water reactions
Series title:
Environmental Science and Technology
Volume
18
Issue:
10
Year Published:
1984
Language:
English
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Environmental Science and Technology
First page:
739
Last page:
742