STRONTIUM ISOTOPE SYSTEMATICS OF COAL UTILIZATION BYPRODUCTS AND THEIR INTERACTION WITH ENVIRONMENTAL WATERS

摘要

The major element and strontium isotope systematics and geochemistry of coal utilization byproducts (CUB) and their interactions with environmental waters were investigated using laboratory leaching experiments with water, sodium carbonate, acetic acid, nitric acid, and hydrochloric acid. Analysis of elemental data from both column and sequential leaching procedures shows rapid release of most major elements early in the leaching procedure, excluding silicon and iron, suggesting association with soluble and surface bound phases. Possible sulfate mineral phases can be inferred due to the high proportions of S leached with sodium carbonate solution, effective at dissolving sulfates such as anhydrite (CaSO3). For all elements except sulfur, highly acidic leachates were most effective in extracting elements from the CUB. In both the column and sequential leaching procedures silicon was leached most effectively by stronger acidic solutions later in the experiment, suggesting the presence of a more resistant silicate phase, possibly residual biotite, feldspar, or clays, or an amorphous glass phase formed during combustion.Isotopic results from the column leaching experiment show a marked increase in 87Sr/86Sr ratio with continued leaching. This general trend is also seen in the sequential leaching data, showing an increase in 87Sr/86Sr ratio with continued leaching in increasingly acidic solutions. These data show that there are isotopically distinct phases within the CUB, suggesting the presence of a more resistant, highly radiogenic phase that survives the combustion process and is leached after the more soluble minerals are removed. The Sr isotope systematics and leaching behavior of the Class F CUB samples demonstrate that isotopic homogenization of minerals in coal does not always occur during the combustion process, despite the high temperatures encountered in the boiler. A key factor in accessing more resistant phases within CUB appears to be the extent of leaching, rather than the particular leaching procedure or acid used. Early-released Sr tends to be isotopically uniform; thus the Sr isotopic composition of CUB could be distinguishable from other sources and a useful tool for quantifying the possible contribution of fly ash leaching to the total dissolved load in natural surface and groundwaters.