화학공학소재연구정보센터
Energy & Fuels, Vol.19, No.3, 882-891, 2005
Trace elements in high-sulfur Assam coals from the makum coalfield in the northeastern region of India
The trace-element contents in several high-sulfur Assam coal samples from the Baragolai colliery of the Makum coalfield were estimated using inductively coupled plasma-atomic emission spectroscopy (ICP-AES). The coals are relatively rich in gallium (8-122 ppm) and poor in arsenic (0.04-0.24 ppm), boron (0.02-0.11 ppm), selenium (0.04-0.24 ppm), germanium (0.19-1.19 ppm), and barium (0.38-2.39 ppm), relative to most of the world coal. The contents of copper (9.86-30.35 ppm), manganese (15.27-63.81 ppm), antimony (0.22-1.19 ppm), tin (0.18-1.43 ppm), lead (5.06-24.13 ppm), and vanadium (5.92-64.29 ppm) are in the same range as those for world coal. The mode of occurrence of all the aforementioned trace elements present in these coals have been determined. Assam coals have the following trace elements: arsenic, boron, lead, and selenium of great concern; copper and vanadium of moderate concern; barium, germanium, and manganese of minor concern; and tin of concern but present in negligible concentration in coal. The trace elements in Assam coals are harmful because of several reasons: (i) the presence of quartz (respirable a-quartz during mining and sample preparation leading to the disease silicosis); (ii) leaching of arsenic, boron, lead, selenium, copper, vanadium, barium, germanium, and manganese from fly ash/bottom ash due to regular rains, contaminating the water table; (iii) pyrite oxidation, ultimately leading to hydrated ferric oxide, which is an undesirable addition to surface water; and (iv) SO2 emission from thermal power plants, brickmaking, the cement industry, etc. The problem in the near future will be alarming with the growth of heat- and power-generating industries in and around the northeastern region of India, based on these coals. In this study on Assam coals, some trace elements such as gallium, germanium, and tin, which are generally less common, were observed; however, some trace elements, such as beryllium, cadmium, chromium, cobalt, fluorine, and nickel, that are present in most of the world coals were not observed. There seems to be no relation between the region of rank of coal on trace-element concentration. The concentration of trace elements in Assam coals have been found to be less than that in the Earth's crust.