Indian Journal of Chemical Technology VoLI,July 1994,pp. 237-240 Mercury in Indian coals S B Ghosh, M C Das, B Ghosh, R R P Roy & N N Banerjee Central Fuel Research Institute, Dhanbad 828 108, India Mercury in Indian coals belonging to different geological period and in some fly ash and bottom ash samples obtained from thermal power stations has been determined. A wide range of variations in mercury content from the value as low as 0.01 to as high as 1.5 ppm in coal samples have been observed. The fly ash and bottom ash samples mostly contain less than 0.005 ppm of mercury. The concentrations of mercury in different specific gravity fractions of four coal samples show that the metal is concentrated mostly in the fractions 1.6-1.7 and asbove 1.7 indicates its inorganic associa- tion in the fossil fuel. Mercury is known to have practically no benefi- Experimental Procedure cial effect on human body and is highly toxic ex- In order to .retain mercury in the samples and hibiting a special propensity for cellulex deposi- to avoid volatilisation losses of mercury during LT tion and retention disrupting the function of cen- ashing procedure, dissolution of coal and lignite tral nervous system and other organs of human samples was done in oxygen bomb calorimeter in body. Its study is of paramount importance from presence of 5% HN03 solution. The method for the point of view of its dissipative nature causing bottom ash and fly ash sample preparation was environmental hazards from burning huge quantit- followed as reported earlier", ies of coal and lignites in thermal power stations. A Philips PU-9360 continuous hydride vapour Air is contaminated through the emission of mer- generation system linked with a Pye Unicam cury vapours, and dust containing mercury. The SP2900 atomic absorption spectrophotometer, emission and distribution of this metal is different was used for mercury estimation. Sodium borohy- from other trace metals due to its low melting and dride was used as reducing agent in all cases as it boiling point with monoatomic nature in vapour was found more effective in terms of speed and phase. This enhances its fallout in the nearby area efficiency of reduction of the metal in the sample of the power plant from its subsequent emission solution. Concentration of mercury was deter- from the stack. The deposited mercury at the vi- mined from the calibration curve drawn for the cinity of power plant leads to rapid vaporisation metal in appropriate ranges. due to its volatile nature. The rate of vaporisa- tion also depends on the local condition of the Results and Discussion fallout site. The effluent water may contain mer- Results for mercury in coals belonging to differ- cury in various forms. The toxic severity becomes ent geological period alongwith their origin and more when mercury is converted by bacteria in ash content are given in Table 1. It is apparent the muddy sediment into organic mercurials The from the samples analysed in the present study fish and other aquatic forms of life grown in such (Table 1) that the lignites are covered by the contaminated water, in turn, affect human beings range 0.01-0.21 ppm mercury, mean value 0.06 when they eat them CiS a food 1.2. (as ppm mercury). Tertiary coals from Assam by Mercury content in foreign coals are well docu- 0.02-0.30 ppm (mean value 0.16), coals from mented. However, information on Indian coals Jammu & Kashmir by 0.72-0.87 ppm (mean value are not available. Mercury was found in some 0.80), coals from Damodar Valley coalfields by Russian coals ' in quite high concentrations of up 0.01-1.0 ppm, (mean value 0.52) and the coals to 20 ppm. It is reported in the range of U.Ol- from Son Mahanadi coalfields are covered by the 0.40 ppm in Australian coals">. Belgean coals" range 0.10-1.10 ppm with mean value of 0.56 contain mercury in the range 0.2-2.0 ppm. Cana- ppm mercury. dian coals 7 have been found to contain mercury The largest user of coal and lignite in India is in the range less than 0.03-1.3 ppm. Extensive the power sector consuming about fifty per cent studies on mercury in American coals (0.01-2.0 of the present production. The coals from Damo- ppm) have been reported", dar Valley coalfield (S1. Nos. 16-20 and 22-31) 238 INDIAN J. CHEM. TECHNOL., JULY 1994 Table I-Mercury content of some Indian coals and lignites Table 2-Distribution of mercury in different specific gravity fractions of some coals and lignite Sample details Ash, Hg content in % wt ppm in coal Specific Float, % Ash,% Hg content of gravity bywt. wt coalinppm 1 Nicham Lignite, Kashmir 55.6 0.21 2 Palana lignite, Rajasthan 12.7 0.01 Kalakot coal <1.3 0.4 2.2 3 Kutch lignite, Gujarat 19.5 0.03 1.3-1.4 44.7 8.9 0.42 4 Mehsona lignite, Gujarat 7.2 0.02 1.4-1.5 32.9 16.1 0.61 5 Neyveli lignite, Tamil Nadu 3.2 0.03 1.5-1.6 9.4 20.5 0.65 6 Makum coal, Assam 4.1 0.50 1.6-1.7 0.9 25.4 1.14 7 Baragolai coal, Assam 10.1 0.06 >1.7 11.7 73.5 3.21 8 Baragolai coal, 20ft seam (OV), Overall 100 19.9 0.87 Assam 4.4 0.02 Metkacoal 9 Baragolai coal, 60ft seam IV, Assam 3.5 0.09 <1.3 5.2 3.4 0.95 10 Baragolai coal, 60ft seam V, Assam 4.0 0.02 1.3-1.4 43.0 3.8 1.02 11 Baragolai coal, 60ft seam VI, Assam 4.3 0.03 1.4-1.5 20.5 17.2 1.12 12 West Dharangiri coal, Assam 6.7 0.31 1.5-1.6 9.5 24.2 2.13 13 Talcher coal, Orissa 42.2 0.15 1.6-1.7 4.4 30.6 1.03 14 Metka coal, J&K 21.2 0.72 > 1.7 17.4 57.5 1.50 15 Kalakot coal, J&K 19.9 0.87 Overall 100 21.2 0.72 16 Bazna colly (OCP), Raniganj 17.5 0.49 Ta1cher coal 17 Lakhimata colly, Raniganj 24.8 0.04 <1.5 53.9 18.9 0.08 18 Nabakajora colly, Raniganj 35.9 0.39 1.5-1.6 7.2 35.9 0.12 19 Kapasara colly, Raniganj 30.9 0.80 1.6-1.7 16.0 43.1 0.05 20 North Tisra colly, Raniganj 42.4 9.80 1.7-1.8 4.9 53.7 0.32 21 Lalmatia colly, Rajmahal 37.0 0.55 > 1.8 18.0 71.0 0.63 !2 Chasnala colly, Jharia ~9.5 0.60 Overall 100 42.2 0.15 23 Bhowrah colly, Jharia 26.7 0.25 Nichham lignite 24 Nudkhurkee colly, Jharia 47.6 0.59 <1.4 0.1 25 Sudamdih colly, Jharia 21.2 0.09 1.4-1.5 1.5 19.6 0.05 26 Muraidih colly 45.2 0.65 1.5-1.6 23.6 44.1 0.12 27 Dakra colly, Dakra 35.0 0'80 1.6-1.7 14.5 51.6 0.13 28 Central Sounda colly 32.5 0.75 >1.7 60.3 62.2 0.31 29 Kerketta colly 30.0 1.00 Overall 100 55.6 0.21 30 Karo Spl. East Bokaro 37.1 0.63 31 Dhori colly, East Bokaro 32.4 0.27 32 Jayant Mine, Tura Seam, Singrauli 25.7 0.10 cent ration and their use in thermal power stations 33 Purewa, Top Seam, Khadia Block, may cause contamination; or poisoning of soils, Singrauli 23.0 0.50 water and vegetations from its fallout. 34 Kotma Seam, Sohagpur 31.3 0.33 Mercury contents of different gravity fractions 35 Charcha colly, Sohagpur 14.0 0.89 of Kalakot and Metka coals from Jammu & 36 West Chirimiri colly, Chirimiri 12.5 0.38 Kashmir, Talcher coal from Orissa and one lignite 37 Upper Patphari Seam, Bhatgaon sample from Nicham, are given in Table 2. It is Mine, Bisrampur 30.7 0.62 observed from the table that mercury is mainly 38 Upper Kusmunda Block, Korba 33.8 0.50 associated with the inorganic fractions of the coal 39 Belphar Block, 1b river CF 22.1 1.10 mass. The study of coals from Iowa (USA)9 and 40 Patherdih washery (middlings). 35.2 0.27 Donet basin (USSR)IO suggested that mercury is 41 Dugdha washery (middlings) 34.8 0.52 mostly associated with pyrite in coal mass. Being a toxic element it is suggested that beneficiation and Sone-Mahanadi coalfield (Sl. Nos. 32-39) are of the coals should be carried out prior to their mostly used for power generation in major ther- uses in industries to reduce mercury contents II. mal power stations situated in the states of West By washing coals by different coal cleaning proce- Bengal, Bihar, Uttar Pradesh and Madhya Pra- dures mercury alongwith other toxic trace desh. The mean values, 0.52 and 0.56 ppm mer- metals'<':' especially those of environmental sig- cury respectively, may be considered a high con- nificance", could be removed but this in turn may GHOSH etal: MERCURY IN INDIAN COALS 239 Table 3-Mercury content in feed coal, fly ash and bottom ash samples from (a) Chandrapura, (b) Patratu, (c) Bokaro, (d) Ban- del, (e) Durgapur (DVC), (fJ Farakka, thermal power stations NameofTPS Sample Type Source Hg content in ppm (a) Chandrapura Feed coal Nudkharkee colly 0.22 Muraidih colly 0.65 Pipradih colly 2.00 Dhori Group 0.55 Dugda washery (middling) 0.52 Bottom ash Boiler, Unit I <0.005 Boiler, Unit II <0.005 Fly ash ESP, Unit I 0.01 Mechanical Separator Unit I 0.03 (b) Patratu Feed coal Kerketta colly 1.00 Dakracolly 0.80 Bottom ash Boiler Unit I <0.005 Boiler Unit II <0.005 Fly ash ESP, Unit I 0.008 (c) Bokaro Feed coal Dhori colly 0.27 Karo BpI.