Uranium in coals

This circular reviews the occurrence of 34 trace elements in coal and the occurrence and distribution of chlorine, phosphorus, titanium, and manganese, which are not considered rare in coal. Separate chapters are devoted to germanium, gallium, and uranium in coal. 

Spark source (SSMS) and thermal emission (TEMS) mass spectrometry are used to determine ppb to ppm quantities of elements in energy sources such as coal, fuel oil, and gasoline. Toxic metals—cadmium, mercury, lead, and zinc— may be determined by SSMS with an estimated precision of 5%, and metals which ionize thermally may be determined by TEMS with an estimated precision of 1% using the isotope dilution technique. An environmental study of the trace element balance from a coal-fired steam plant was done by SSMS using isotope dilution to determine the toxic metals and a general scan technique for 15 other elements using chemically determined iron as an internal standard. In addition, isotope dilution procedures for the analysis of lead in gasoline and uranium in coal and fly ash by TEMS are presented. 

Isotope Dilution By Thermal Emission Mass Spectrometry. A three-stage thermal emission mass spectrometer (TEMS) was used for quantitatively measuring lead and uranium in coal and fly ash and lead in gasoline (Figure 3). The basic design of the instrument is modeled on that developed by White and Collins, 1954 ( 6) and modified at ORNL. The addition of an electrostatic third stage increased the abundance sensitivity to 108 as described by Smith et al. (7). 

Kamata E, Nakashima R, Furukawa M. 1987. Determination of trace amounts of thorium and uranium in coal ash by inductively coupled plasma atomic emission spectrometry after extraction with 2-thenoyltrifluoroacetone and back-extraction with dilute nitric acid. J Anal At Spectrom 2 321-324. 

Noble E. A. (1973) Uranium in coal. In Mineral and Water Resources of North Dakota, North Dakota Geological Survey Bulletin 63, pp. 80-83. 

Not all of the interest in mineral matter in coals is stimulated by its detrimental effects during coal use. In several instances coal is a source of desired elements and materials. Uranium has been produced from lignite germanium and sulfur could be produced from coal and coal ash has been used for construction materials such as brick, lightweight aggregate, and road paving material. 

Preparation of Coal and Fly Ash for Isotope Dilution Analysis. Separate aliquots of coal and fly ash are weighed out and spiked with 204Pb and 233U, respectively. The chemical treatment and extraction of lead and uranium from coal and fly ash are identical, except coal is ashed at 450 °C before chemical treatment. The samples are dissolved with a mixture of hydrofluoric, nitric, and perchloric acids in Teflon beakers. The lead is separated by dithizone extraction, evaporated to dryness, redissolved in dilute nitric acid, and 10 ng are loaded on filaments with silica gel for mass analysis. 

Uranium. Perricos and Belkas (25) have determined uranium in six coals by neutron activation followed by separation of the uranium daughter neptunium-239 by carrier-free extraction chromatography. The coals, from mines in northern Greece, had very high uranium concentrations (0.012-0.037%). However, uranium at the few parts per million level found in most coals could no doubt be determined by a modification of this method. 

Dr. Jedwab. The syngenetic origin of uranium in the Dorenaz coal is inferred from the following arguments ... 

Radium may be transported in the atmosphere by the movement of particulate matter derived from uranium and coal utilization (see Section 5.2.1). These fugitive emissions would be subject to atmospheric dispersion, gravitational settling and wash-out by rain. 

This provides some insight into the fact that hydrogen, nitrogen, and methane uranium and coal nitrites in food, DDT, saccharine, and cyclamates, etc. have political as well as chemical and physical properties. 

Combustion of coal is a significant source of enhanced natural radioactivity (especially combustion of coal from the western United States, which contains significantly more uranium than coal from the eastern United States). When coal is burned, some of the radioactivity is released directly to the atmosphere, but a significant fraction is retained in the bottom ash. Enhanced concentrations of uranium have been found on the ground around coal-fired power plants (UNSCEAR 1982). 

There have been numerous attempts to use trace-element concentrations in coal as indicators of depositional environments. Most commonly, these studies have sought evidence of a marine influence on the coal (Goodarzi, 1987, 1988 Swaine, 1983 Chou, 1984 Hart and Leahy, 1983). The elements cited as indicators of marine influence include molybdenum, magnesium, boron, chlorine, bromine, sodium, yttrium, and uranium. However, problems such as mixing in brackish environments, the reworking of sediments, and postdepositional enrichment or leaching, make the data equivocal, and there is no consensus regarding reliable indicators. 

Vine, J.D., 1956. Uranium-bearing coal in the United States. U.S. Geol. Surv. Prof. Pap., 300 405-411. 

Treatment of many materials results in the liberation of the trace elements into the environment, which can have an impact on health. Coal is a particularly useful example of a major source of trace elements poured into the environment from coal combustion. Coal contains an alphabet soup of trace elements, including arsenic, mercury, uranium, selenium, and chromium. Pyrite is a ubiquitous mineral found in coal, but coal can also contain a variety of other mineral phases. West Virginia coal, for example, includes clay minerals such as kaolinite (35%) and illite (35%i), quartz (18%i), pyrite (7%), and calcite (3%). A number of projects that utilize coal for power generation while minimizing the impact on the environment have been described. An excellent example is the SNOX (trademark owner Haldor Topsoe) demonstration project, which utilizes high-sulfur coal (2.8%). The demonstration project of this technology, equally funded by the U.S. Department of Energy and participants at a total cost... 

For those interested in mineral matter in coal, an awareness that some partings may be of volcanic origin may be useful in explaining the distribution of some of these layers and the occurrences of some unusual components, such as strontium, phosphate, or uranium. Volcanic ash partings are likely to be more widespread and uniform in texture, composition and thickness than the more common partings of fluvial origin. They are also more likely to show marked differences from layer to layer, and to contain exotic mineral or chemical components. 

The two most common objections to nuclear energy are easily disposed of. The radioactivity released by most nuclear plants is smaller than the radioactivity released by a coal fired plant with the same energy output. The amounts of radioactive materials contained in coal are very small but 2.5 million times more coal has to be burned than uranium consumed to produce the same amount of energy. The sulphur dioxide problem of coal-fired plants was mentioned before. The second often heard objection is that nuclear plants may explode as bombs do. The enrichment in the uranium used in our plants is far too small to render an explosion possible. 

Uranium existing in coal as silicate mineral coffinite and uraninite (UOj) poses a potential environmental hazard. Following combustion of coal, the refractory coffinite remains in the bottom ash and slag while the uraninite is vaporized and is later condensed on the fly-ash particles as the flue gases cool (Chadwick et aL, 1987). Comparative radiation exposure assessment studies on coal and nuclear-based electricity generation reveal that emissions from both are very low, but dose levels from coal-fired plants are equal to or slightly lower than from a nuclear power plant (UNGA, 1980 Chadwick et al., 1987). 

As most of the excavated uranium is subsequently used as nuclear fuel, the price of conversion of the ore (yellow cake) to UFg, the price of enrichment (separative work units—SWU), the cost of deconversion of the enriched UF to uranium oxide (or other chemical forms), and the production of fuel elements determine economic factors. In addition, the cost of electric power production by nuclear power plants in comparison with other plants (gas, coal, and oil) and the overall cost of disposal of the waste from all these processes will influence the worthiness of uranium extraction. In view of the rapid changes in the prices of these processes, it is difficult to assess the threshold concentration of uranium in the ore that will make mining viable economically. Furthermore, nations or organizations that cannot purchase uranium... 

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