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Coal fly ash and volcanic ash both contain a high level of aluminosilicate glass; however, coal fly ash rapidly forms clay and dissolutes glass, suggesting its negative environmental impact may be less than supposed.

An applied surface complexation/precipitation modeling effectively described the leaching of contaminants from weathered municipal solid waste incinerator (MWSI) bottom ash. Results revealed that sorbent mineral and sorbate concentrations can be obtained by utilizing a combination of selective chemical extractions and leaching at pH values not ideal for sorption. Most model calculations were based on the Diffuse Layer Model and a database of sorption constants for hydrous ferric oxide.

Arsenic and Se sorption on amorphous iron (hydr)oxide in acidic fly ash is investigated to determine if this process can be used to control the leaching of these contaminants. The results showed that sorption on hydroxylamine-extractable iron (hydr)oxide controls the partitioning of arsenic and Se between acidic fly ash and leachate. The amount of arsenic and Se decreases at lower pH and oxyanions coprecipitate in this range.

Carbonation of industrial alkaline residues can be used as a C02 sequestration technology to reduce carbon dioxide emissions. In this study, steel slag samples were carbonated to a varying extent. Leaching experiments and geochemical modeling were used to identify solubility-controlling processes of major and trace elements, both with regard to carbonation mechanisms and the environmental properties of the (carbonated) steel slag. Carbonation was shown to reduce the leaching of alkaline earth metals (except Mg) by conversion of Ca-phases, such as portlandite, ettringite, and Ca-(Fe)-silicates into calcite, possibly containing traces of Ba and Sr. The leaching of vanadium increased substantially upon carbonation, probably due to the dissolution of a Ca-vanadate. The reactive surface area of Al- and Fe-(hydr)oxides increased with the carbonation degree, which tends to reduce the leaching of sorption-controlled trace elements. Sorption on Mn-(hydr)oxides was found to be required to adequately model the leaching of divalent cations, but was not influenced by carbonation. Consideration of these three distinct reactive surfaces and possible (surface) precipitation reactions resulted in adequate modeling predictions of oxyanion and trace metal leaching from (carbonated) steel slag. Hence, these surfaces exert a major influence on the environmental properties of both fresh and carbonated steel slag. [ABSTRACT FROM AUTHOR]