Effect of Gamma Irradiation on the Thermal Decomposition Behaviour and Electrical Resistivity of Some Indian Lignite and Bituminous Coals

It is known that irradiation of coal by high-energy and ionising gamma rays affects the structure of coal, as a result of which its physical and chemical properties are also likely to be and indeed are, affected or modified. Very little work has heen on this aspect of Indian coals, which are quite different from their foreign counterparts. From this point of view. over the past some years, the effect of gamma irradiation on different types of Indian coals and lignites have been extensively investigated at the Central Fuel Research Institute, Dhanbad. The work reported here is a part of those studies. Since thermal decomposition behaviour of coal is quite important for the selection of a suitable type of coal to be used in the coal hydrogenation process and also since the electrical resistivity of coal too is an important property which is imperatively considered in the non-fuel use of coal especially for the manufacture of carbon artifacts (e.g. graphite, electrodes etc.), it prompted us to investigate as to whether the irradiation of coal with gamma rays affects its thermal decomposition behaviour and its electrical resistivity and, if so. to what extent and how will it be useful technologically. Presented in this paper are the results of investigations on the effect of gamma irradiation on the thermal decomposition/transformation of Rajasthan lignite and bituminous coal of Raniganj (West Bengal) coaltield and also on the electrical resistivity of high volatile, non-coking Hariajam (Gopinathpur seam) coal ofRaniganj coaltields. The results of these investigations have evidenced that at a maximum gamma dose of 120 Mrad, the thermal decomposition behaviour of both the Rajasthan lignite and bituminous Raniganj coal is significantly affected and eventually their transformation takes place. A comparison of the differential thermal analysis (DTA) curves of the unirradiated and irradiated coal and lignite samples reveals that in the DTA curves of irrradiated lignite and bituminous coal , additional endothermic and exothermic peaks appear. Whereas exothermic peaks correspond to solidifying temperature, the exothennic peaks connote temperature of maximum tluidity and decomposition and vapourisation of lower molecular weight constituents. Likewise, the results on the ctlect of gamma irradiation on high volatile, non-coking Hariajam coal clearly shows that the electrical resistivity of this coal is greatly affected. It has been found that in the beginning. upto a gamma dose of 150 Mrad, the electrical resistivity decreases. but at doses higher than this. the electrical resistivity gradually increases at all the temperatures studied (viz. 200, 500. and 800 "e) and at 800 'C it shoots up abruptly, attaining maximum value. The results of these investigations have been explained on the basis of degradation and polycondensation as also the cross-linking of molecules that take place in coal under the intluence of gamma rays. In conclusion. it is inferred from these studies that whereas the changes/moditications brought out in the thermal decomposition behaviour of Rajasthan lignite and bituminous Raniganj coal after gamma irradiation can be advantageously exploited in the usc of these coals in the coal hydrogenation process. the increased electrical resistivity of non-coking Hariajam coal will he potentially useful in the manufacture of coke and other carbon artifacts like graphite and carbon electrodes. Metalo-bacterial Interaction: Boon or Curse S N Upadhyay & R S Dube Department of Chemical Engineering and Technology, Institute of Technology, Kashi Hindu Vishwavidyalaya, Varanasi-221 OOS Abstract Eliminating carbon. nitrogen, sulphur and microelements from organic and inorganic material is an important biological activity of bacteria. By means of these bio-chemical activities the cells along with obtaining necessary energy for their development and elements also playa very important role in mineralization, mineral decomposition and biochemical cycles etc. Through meta.lobacterial interactions available in nature separation of metal from minerals, bio-conservation from poorly concentrated solutions or through adsorption the increase in the concentration of metals becomes possible. Such processes possess economic and industrial importance. In this review article a brief scientitic description is available pertaining to the biological processes followed by the interactions of metals and bacteria. 335