Eight Argonne Premium Coal samples and two other coal samples were used to observe the effects of combustion and leaching on 30 elements. The results were used to infer the modes of occurrence of these elements. Instrumental neutron activation analysis indicates that the effects of combustion and leaching on many elements varied markedly among the samples. As much as 90% of the selenium and bromine is volatilized from the bituminous coal samples, but substantially less is volatilized from the low-rank coals. We interpret the combustion and leaching behavior of these elements to indicate that they are associated with the organic fraction. Sodium, although nonvolatile, is ion-exchangeable in most samples, particularly in the low-rank coal samples where it is likely to be associated with the organic constituents. Potassium is primarily in an ion-exchangeable form in the Wyodak coal but is in HF-soluble phases (probably silicates) in most other samples. Cesium is in an unidentified HN03-soluble phase in most samples. Virtually all the strontium and barium in the low-rank coal samples is removed by NH4OAc followed by HC1, indicating that these elements probably occur in both organic and inorganic phases. Most tungsten and tantalum are in insoluble phases, perhaps as oxides or in organic association. Hafnium is generally insoluble, but as much as 65% is HF soluble, perhaps due to the presence of very fine grained or metamict zircon. We interpret the leaching behavior of uranium to indicate its occurrence in chelates and its association with silicates and with zircon. Most of the rare-earth elements (REE) and thorium appear to be associated with phosphates. Differences in textural relationships may account for some of the differences in leaching behavior of the REE among samples. Zinc occurs predominantly in sphalerite. Either the remaining elements occur in several different modes of occurrence (scandium, iron), or the leaching data are equivocal (arsenic, antimony, chromium, cobalt, and nickel). The results of these combustion and leaching experiments indicate that some previously held assumptions concerning modes of occurrence of elements in coal should be reconsidered.

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Forty-one samples of low-temperature ash from bituminous coal were leached with hot (80° C) distilled water, to determine the teachability of elements in the low-temperature ash of coal. The leachates were analyzed by inductively-coupled atomic emission spectroscopy and by ion chromatography. In general, only small amounts (<20 percent) of Al, Ba, Mn, Na, Ti, P, and F were leached from the low-temperature ash. These elements are probably predominantly associated with stable inorganic phases in the coal or they formed water insoluble phases during the low-temperature ashing process. Moderate amounts (10-59 percent) of Fe were leached from most low-temperature ash (LTA) samples. Leachable sulfur (as sulfate) in the LTA is equivalent to more than 75 percent of the sum of the organic sulfur + sulfate sulfur as determined in the coal. It is inferred that some of the leachable Fe and S is attributable to pyrite which was oxidized during the low-temperature ashing process. Modest amounts (25-75 percent) of Mg were leached from most LTA samples. The leachable Mg is possibly derived from organically-bound Mg and from ion-exchangeable Mg in clays. Water-soluble Sr appears to be uniformly high. The leachable Sr may have been derived from organically-bound Sr or from water-soluble Sr-sulfates in the coal. There are only small amounts of leachable Cl and N, perhaps because these elements were volatilized during low-temperature ashing.

A series of heating and leaching experiments were conducted on a split taken from the coal used to create the U. S. Geological Survey's CLB-1 coal standard. The behaviors of approximately 30 elements were monitored by a variety of analytical procedures, including instrumental neutron activation analysis, inductively coupled plasma optical emission specroscopy, atomic absorption spectroscopy, and ion chromatography. Br, Se, and Hg were the only elements to exhibit volatilization at temperatures up to 1000 C. At this temperature virtually all of these elements had been volatilized. Leaching of the coal with hot (80 C) distilled water generally removed no more than a few percent of the elements monitored. Hot water leaching of the low-temperature ash was more effective, removing from 10 to 50 percent of many elements. A split of the coal was subjected to sequential leaching by ammonium acetate, hydrochloric acid (HC1), hydrofluric acid (HF), and nitric acid. Ammonium acetate, which was used to remove ion-exchangeable cations, removed 40 to 50 percent of the Ca. HCl (1:3) was effective in removing 20 to 40 percent of the chalcophile elements (As, Sb, Zn, and Fe); elements that are generally acid soluble when associated with monosulfides. HF (48%) removed 20 to more than 80 percent of the elements (K, Na, Cs, Sc, Hf, U, and Mg) commonly associated with silicate and oxide minerals. Nitric acid (10%) was generally ineffective in leaching elements from this coal sample. The responses of the various elements in the Lower Bakerstown coal during the combustion and leaching experiments were similar to the behavior reported for the elements in other Appalachian basin coals.