Geochemical Factors Controlling the Mobilization of Inorganic Constituents from Fossil Fuel Combustion Residues: I. Review of the Major Elements

Abstract

Large quantities of fossil fuel combustion (FFC) wastes, such fly ash, bottom ash, flue gas desulfurization (FGD) sludge, and oil ash are being disposed of on land. There is a need to accurately assess the mobilization of elements that results from the weathering of these wastes. To help meet this need, available data on physical, chemical, mineralogical, extract, and leachate characteristics have been compiled and reviewed, and a comprehensive approach to understanding how major elements are mobilized from fossil fuel wastes is described. Many of the physical properties of fly ashes overlap those of bottom ashes; similar data for FGD sludge and oil ashes are sparse. One taxonomic and three utilitarian classification schemes have been proposed for fly ashes. However, no taxonomic system is applicable to all FFC wastes. The ranges of concentrations of AI, Ca, and Fe found in these wastes were within the ranges of their concentrations in soils. Concentrations of K, Na, Mg, and S in some FFC wastes may exceed their highest concentrations in soils. The matrix of fly ashes consists principally of quartz, glass, and mullite. As minor components in fly ashes, anhydrite, lime, periclase, hematite, and magnetite are reported frequently. A minor fraction of many of the major elements may also be present in a glassy phase. The principal compounds in FGD sludges are sulfites, sulfates, carbonates, and hydroxides of Ca. The oil ashes contain mainly sulfates and oxides of AI, Na, Fe, and Mg. Water extracts of FFC wastes contain significant fractions of Ca, Mg, K, and Na, a fact that confirms the presence of these elements in highly soluble forms. Leaching studies conducted using fly ash columns have shown that initial leachates contain high concentrations of Ca, Na, K, and S and that as leaching continues these concentrations decline and reach steady states. Usually only negligible fractions of Si, AI, Fe, and Mg are leached from fly ash columns. In this article, a comprehensive approach is suggested, one that combines thermochemical principles with chemical and mineralogical data to predict the upper limits of elemental concentrations that can be attained in leachates from weathering FFC wastes. This thermochemical approach has shown that secondary solid phases may control concentrations of AI, Ca, and S measured in extracts of fly ashes and FGD sludges and in pore waters from fly ash lysimeters at a field site. Characterization of weathered wastes and improved thermochemical data for secondary solid phases in these wastes will be useful for understanding and predicting the chemistry of leachates.All authors, Environ. Sci. Dep., Battelle, Pacific Northwest Lab.,

Extraction Characteristics of Selenium as Affected by Coal Fly Ash Type, Water Extractant, and Extraction Time

“…Previous studies [53] [54] investigating eastern bituminous, western sub-bituminous, low-sulfur bituminous, sub-bituminous, lignite, and subbituminous PRB fly ash reported that the most alkaline (pH = 11.05 to 12.57) ash suspension was from sub-bituminous PRB ash. Environmental weathering and leaching of Ca, Fe, and S may have contributed to the lower pH of the weathered ash, which is supported by previous findings that fly ash with a Fe/Ca ratio > 3 produces acidic suspensions, while ratios < 3 generate alkaline suspensions [55]. The fresh and weathered ash had Fe/Ca ratios of 0.21 and 0.20, respectively.…”

Fate of sulphate removed during the treatment of circumneutral mine water and acid mine drainage with coal fly ash: Modelling and experimental approach

“…Class F fly ash is formed during the combustion of either bituminous or anthracitic type of coal (Mattigod et al, 1990).…”

Single-crystal elastic constants of natural ettringite

“…It is both a primary crystalline product during cement paste consolidation and a secondary phase which crystallizes in hardened concrete and it plays an important role in concrete deterioration in humid environments. In addition, ettringite, effectively absorbs in its structure poisonous oxoanions from alkaline solutions produced by drainage of mining and industrial by-products, and from leachate from cement-based waste matrices with serious implications in terms of environmental impact [4][5][6][7]. In this study we determine the complete elastic tensor of ettringite and we highlight the relationship between crystal structure and elastic anisotropy in comparison with Ca(OH) 2 .…”