In February 1998, The U.S. Environ-mental Protection Agency (EPA, 1998 - PDF document

In February 1998, The U.S. Environ-mental Protection Agency (EPA, 1998a,b)from electric utilities as the largestcury released to the air. EPA officialscoal-burning powerplants, with lesseramounts coming from oil- and gas-burn-ing units. According to EPA estimates,emissions from coal-fired utilitiesStates. On December 14, 2000, the EPAin mercury emissions from coal-firedpowerplants, with regulations proposedby 2003 and final rules for implementa-tion completed by 2004 (EPA, 2000).from powerplants generally is not consid-ered harmful; however, in the naturalenvironment, mercury can go through aconvert elemental mercury to a highlytoxic form that is concentrated in fish andbirds (fig. 1). The most toxic form ofmercury is methylmercury, an organicform created by a complex bacterial con-version of inorganic mercury. Methyla-availability, bacterial population, nutrientparticularly in aquatic organisms, andenrichment of a substance in an organismand includes bioconcentration from envi-uptake via the food chain. Cases of mer-cury poisoning have been documented inpeople who eat contaminated fish for pro-and abroad. Pregnant women and subsis-tence fishermen are particularly vulnera-ble. Because high levels of mercury havebeen detected in fish, many U.S. Stateshave issued advisories that restrict fishing.U.S. coal-fired powerplants may helpminimize or avoid health problems causedby exposure to excess mercury. There areseveral ways in which this reduction canis to use high-rank coals. Generally, mois-ture in coal decreases and calorific value(thermal energy) increases as coal rank(degree of maturation) increases. There-fore, powerplants that burn high-rank coalgiven thermal output. Thus, for coals hav-higher rank coals will contribute lessmercury to the environment. Additionaloptions include selective mining of coal(avoiding parts of a coal bed that arehigher in mercury content), coal washing U.S. Department of the InteriorU.S. Geological SurveyUSGS Fact Sheet FSÐ095Ð01September 2001 and Modes of Occurrence Local andregionaldeposition Reemittedanthropogenicand natural HgGlobal depositionReemittedanthropogenicand natural HgAtmosphericHgterrestrialmarine Hg Figure 1.Simplified geochemical cycle of mercury (Hg). fs095-01 10/29/01 11:37 AM Page 1 ry values in the COALQUAL databasestandard deviation of 0.11 ppm and 0.17,respectively. About 80 percent of theare less than 0.25 ppm. The maximummercury database value for coal in thehigher value as a statistical outlier.Table 1 shows the median and meanvalues for mercury concentrations (inppm) and calorific values (British thermalproducing regions in the United States,using the COALQUAL database. Themercury data in table 1 have been calcu-lated back to an as-received basis,Northern Appalachian area coal hasthe highest mean and median values formercury, with coal from the southernAppalachian area having the second high-est value and coal from the centralAppalachian area slightly lower. Coalfrom these three areas has extremely highcalorific values. Coal from the Uintaregion has the lowest mean and medianmercury values of all indicated areas.Some western U.S. coals are low in mer-cury but are also low in calorific value,because they are low in rank.also be presented on an equal-energy) Btu to provide a convenientdifferent areas (fig. 3). This is a simplecalculation, dividing as-received mercuryppm values by Btu/lb and expressing thevalue on a 10Btu basis. The data fromCOALQUAL used in this analysis yield adeviation of 15). The calculated inputloads from individual samples were usedto calculate a mean value for each of theselected coal-producing regions listed individed into arbitrary 5-unit intervals andare color-coded in figure 3. According tothe Energy Information Administrationsimilar between coal regions east andwest of the Mississippi River (38 and 48percent, respectively). About 14 percentshown in figure 3, the Gulf Coast lignitemay have the highest potential for mercu-ry emissions, and the Green River coalfrom western Wyoming may have thelowest mercury emissions on an equal-energy basis. Of the two major bitumi-nous coal-producing regions, samplesfrom the Appalachian region containhigher mercury levels than those fromthe Eastern Interior. Samples from thePowder River Basin are slightly higher inmercury levels than the subbituminouscoals of the San Juan River Basin.The COALQUAL data set does nottake into account the potentially substantialcoal as it exists in the ground. The modesaffect the way the element behaves duringcoal cleaning, combustion, and leaching. FREQUENCY, IN PERCENTMERCURY, IN PARTS PER MILLION0.2530.5031.0031.2531.5031.753 Figure 2.Histogram of mercury concentrations (remnant moisture, whole coal basis) for conter-minous U.S. coal from the COALQUAL database. Table 1. Calorific vregion MeanNo.MeanNo. 0.190.241,61312,57012,4401,5061,74713,36013,2101,648Appalachian, southern .18 .2197512,85012,760969Eastern Interior .07 .1028911,51011,450255Fort Union .08 .103006,2806,360277Green River .06 .093889,9409,560264Gulf Coast .13 .161416,4406,470110Pennsylvania Anthracite .10 .105112,86012,52039Powder River .06 .086128,0508,090489Raton Mesa .05 .094012,50012,30034San Juan River .04 .081929,3409,610173Uinta .04 .0725311,28010,810226Western Interior .14 .1828611,32011,420261Wind River .08 .15429,5809,56042 fs095-01 10/29/01 11:37 AM Page 2 Thus, the elementÕs mode of occurrencehas an important influence on its environ-of the low concentrations (commonly lessthan 0.2 ppm) of mercury and its volatility,it is particularly difficult to determine themercury in coal is associated with pyrite,compacted (fig. 4). Other forms of mercu-ry that have been reported in coal areorganically bound, elemental, and in sul-fide and selenide minerals (fig. 5).The U.S. Geological Survey is col-species during the combustion processand thus the likelihood of mercury capturefrom the gas. The USGS has also collabo-the removability of mercury from coal byconventional physical coal-cleaning tech-niques. The results of these studies indi-cate that, on the average, 37 percent of themercury is removed by coal cleaning(Toole-OÕNeil and others, 1999). Theon mercury distribution and modes ofoccurrence is also relevant to mercuryreduction by fuel switching, selectiveare also being evaluated by researchorganizations as possible economic solu-veyÕs COALQUAL database averagesterminous United States. Mean valuesfrom the Uinta region to 0.24 ppm forsamples from the northern Appalachiancoal-producing region. On an equal-ener-gy basis, Gulf Coast coal samples havethe highest input load values (27.0 lbBtu), and the Green River regionsamples have the lowest values (6.5 lbThe COALQUAL database is anextremely valuable source of informationfor raw or in-ground trace-element con-for the effect of coal cleaning in appropri-ate coals, can provide a first estimate ofwhere data are not available. Physical coalmercury that enters the combustion sys-enters the atmosphere. The mean mercuryÑBy Susan J. Tewalt,Linda J. Bragg, andRobert B. Finkelman Figure 3.Mercury input loadings (in pounds of mercury per 1012British thermal units (lb Hg/1012Btu)) of in-ground coal for selected U.S.coal-producing regions. fs095-01 10/29/01 11:37 AM Page 3 Bragg, L.J., Oman, J.K., Tewalt, S.J.,Oman, C.L., Rega, N.H., Washing-ton, P.M., and Finkelman, R.B.,1998, The U.S. Geological SurveyCoal Quality (COALQUAL) Data-baseÑVersion 2.0: U.S. GeologicalSurvey Open-File Report 97Ð134,one CD-ROM.Energy Information Adminstration, 2001,Weekly coal production: EIA website at http://www.eia.doe.gov/cneaf/National Research Council, 1978, Anassessment of mercury in the envi-ronment: National Academy of Sci-ences, 192 p.Palmer, C.A., Finkelman, R.B.,Mroczkowski, S.J., Willett, J.C., Tay-lor, K.C., and Bullock, Jr., J.H., 1998[abs.], Arsenic and mercury modes offrom coal-fired powerplants, ceedings of the Air Quality Confer-ence, McLean, Va.: Energy and Envi-ronmental Research Center, Universi-ty of North Dakota, unpaginated.Toole-OÕNeil, B., Tewalt, S.J., Finkel-man, R.B., and Akers, D.J., 1999,Unraveling the puzzle: Fuel, v. 78,U.S. Environmental Protection Agency,tric utilities: EPA fact sheet availableonline at http://www.epa.gov/ttncaaa1/t3/fact_sheets/hg17th.html.(Accessed April 2001.)Congress: EPG white paper availableonline at http://www.epa.gov/oar/merwhite.html. (Accessed AprilÑÑÑ 2000, EPA to regulate mercurycoal- and oil-fired powerplants: EPAfact sheet available online at http://www.epa.gov/ttncaaa1/t3/fact_sheets/fs_util.pdf. (Accessed April 2001.)For more information on the following Susan J. Tewalt (E-mail: stewalt@usgs.gov) ALQ AL database (E-mail: lbragg@usgs.gov) Robert B. Finkelman (E-mail: rbf@usgs.gov)U.S. Geological SurveyNational Center, MS 956Reston, VA 20192 MERCURYWarrior BasinGascoigne Wood #2 AmmoniumacetateHydrochloricacidHydrofluoricacidNitric acid Figure 4e the proportionof mercury leached by nitric acid. This mercury is believed to be associated with the sulfide minerals, such as pyrite. Direct analysis of pyrite grainsby a laser ablation mass analyzer indicated mercury concentrations consistent with selective leaching data. The green bars indicate the mercuryleached by hydrochloric acid; much of this mercury may have come from oxidized pyrite. Arrows indicate minimum values. Scanning electron photomicrographof a polished block of lignite from California. fs095-01 10/29/01 11:37 AM Page 4