Pristine coals

Many coals contain elemental sulfur. It is clearly a ubiquitous constituent of bituminous coals that have been exposed to the atmosphere. In contrast, three pristine samples obtained from the Premium Sample Program at the Argonne National Laboratory are free of elemental sulfur within the detection limit of four sensitive analytical methods. Exposure of the pristine coals to the atmosphere leads to the production of elemental sulfur. These observations strongly suggest that sulfur is not a natural constituent of coal, but rather is produced after exposure to the atmosphere by chemical or bacteriological action. 

All of the investigators have observed that the amount of sulfur that can be extracted from the pristine coal is below the detection limit. Conservatively, these observations mean that there is less than 0.001% sulfur in the pristine coal samples. 

The results that have been obtained for three pristine coals and six other samples are summarized in Table IV. 

In the course of our work, we exposed several pristine coals to the atmosphere. The results are presented in Table V. 

Table V. Elemental Sulfur Content of Pristine Coals after Intentional Exposure to the Atmosphere...

It is evident that detectable quantities of sulfur form in the pristine coals in less than two months. The rate of formation of sulfur appeared to be enhanced significantly when the coal was suspended above water in a closed desiccator. Clearly, a broad array of factors such as particle size, air currents and so forth will influence the rate of sulfur production, but there is no doubt that it is a facile process. 

The notion that naturally occurring organic polysulfides in coal decompose to form elemental sulfur has also been tested in another way. Buchanan and his associates have shown that the 32S/34S ratios of the elemental sulfur and the pyrite in another Illinois Basin Coal Sample Program coal are similar and different from the 32S/34S ratio for the organic material in the same coal (Buchanan, D., private communication, 1989). This result infers that pyrite is the source of elemental sulfur. Thus, we conclude that oxidative chemical and bacteriological processes convert pyrite to elemental sulfur when pristine coals are exposed to the atmosphere. 

Hicrodilatometer results can also be correlated with a non-pristine coal, Bruceton hvA bituminous (24). As shown in Figure 9. the softening temperature (T,) corresponds to a second minor transition within the high temperature region. Contraction temperature (Tc) occurs at the steepest part of the high temperature transition curve in the IGC. 

A variety of human activities and products may contaminate estuaries with arsenic, including wood preservatives, pesticides, fertilizer manufacturing, mine drainage and wastes, coal utilization, runoff from slags used as road ballast, and arsenical paints from ships (Landrum, 1994 Davis, De Cumou and Eary, 1997), 370 (Pirrie et al., 2002 Mirlean et al., 2003). In some cases, specific arsenic sources cannot be identified (O Reilly Wiese, Bubb and Lester, 1995). Nevertheless, the cycling of arsenic between water and sediments in contaminated estuaries is often similar to cycles in pristine estuaries, open marine environments, and lakes. 

Elemental Sulfur. In 1942, Chatterjee (44) reported the presence of elemental sulfur in weathered Indian coal but not in fresh samples. He suggested that, during weathering, pyrite is first oxidized to ferrous and ferric sulfates, and that then ferric sulfate oxidizes pyrite to elemental sulfur. The presence of elemental sulfur in U.S. coals was confirmed recently by Richard et al. (45) and White and Lee (46). Duran et al. (47) used extraction and gas chromatographic analysis to determine elemental sulfur in a suite of U.S. coals. They found that elemental sulfur (0.03-0.17%) is present in coal that has been exposed to the atmosphere, but is absent in pristine samples that have been processed and sealed under a nitrogen atmosphere. These data support Chatteijee s discovery that elemental sulfur in coal is a weathering product. 

Sulfur is a reactive oxidizing agent. Hence, some precautions need to be observed in its removal from coal and in its quantitative measurement. Recent contributions have discussed several different methods for its quantitative analysis (4-9). The results for two coal samples, one a pristine sample of Illinois No. 6 coal, APCSP-3, and the other an exposed sample of Illinois No. 6 coal, IBCSP-1, are summarized in Table III. 

A variety of solvents including hexane, acetone, tetrahydrofuran, toluene and perchloroethylene have been used in these studies together with four analytical strategies. No sulfur has been detected. This feature is well illustrated in Figure 1, which displays the contrasting results for the pristine Wyodak sample, APCSP-2, and another exposed sample of this low sulfur coal. Elemental sulfur at the 0.002% level is easily detected in the exposed sample, none is observed in the pristine sample. 

Figure 1. Chromatographic observations for pristine and exposed samples of low sulfur Wyodak coal. Elemental sulfur emerges at 38.3 minutes under the conditions of the analysis. A. Unconcentrated extract of APCSP-2. B. The extract of APCSP-2 after 20-fold concentration. C. Unconcentrated extract of exposed Wyodak coal. D. The same extract after 20-fold concentration. (Adapted with permission from ref. 6. Copyright 1985 Fuel.)...

The compositions of each coal used in this study is shown in Table I. The conditions under which these pristine samples were collected and prepared have been reported previously (12). The weathered Upper Freeport sample was exposed to air and sunlight at room temperature for four weeks, while the oxidized coal was heated... 

Impacts of particulate emissions from coal fly-ash pollution have been seen close to emission sources in and around the cities of Vorkuta and Inta where there are examples of environmental damage due to acidification, reduced air quality and eutrophication (Getsen et al. 1994 Virtanen et al. 2002 Walker et al. 2003b). However, it should be emphasised that vast areas of the Russian Arctic appear close to pristine condition (Rovinsky et al. 1995). 

Producing and processing the sustainable energy supplies needed to satisfy future needs are not always clean, pristine, or non-intrusive activities. The truth is that the processes used for mining coal or drilling for oil and natural gas can cause or release toxic byproducts. These chemicals and waste products can contaminate the air, soil, and water. 

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