Study On Environmental Geochemistry Of Iodine In Chinese Coals

The pyrohydrolysis apparatus system was constructed and the procedure was designed to burn and hydrolyze coal steadily and completely through orthogonal designed experiment,then credible and accuracy method for the determination of iodine was summarized.The limit of detection and quantification of the proposed method was 0.09μg/g and 0.29μg/g,respectively.Nationwide sampling program is designed according to the resources distribution and coal-forming periods as well as coal rank and yield of coal in China, 305 coal samples were collected and determined by catalytic spectrophotometry combined with pyrohydrolysis.The geochemical mechanism of the concentration or depletion of iodine was discussed during the process of coalification,which including peat diagenesis and coal metamorphism.The contents of iodine in Chinese coals fall in the range of 0.04-39.51 mg/kg.The arithmetic mean of iodine in coals is 2.60 mg/kg and the geometry mean is 1.27 mg/kg for the contents of iodine show logarithm normal frequency distributions.The correlation obtained from the statistical evaluation combining the fact of iodine levels increasing with the incraese of coal rank indicates that iodine in coals is of the chalcophile nature and mainly of an inorganic association.When peats developed to lignites through diagenesis,95.1%-99.9%of their original iodine was lost.The difference of assemblage and structure of minerals in coal resulting from the different coal-forming depositional environment lead to the iodine levels increasing with the increase of degree of marine influence.Iodine levels increase from lignite through subbituminous coal and bituminous coal to anthracite,it indicates that coal adsorbed excess iodine from the hydrothermal fluids during the process of metamorphism,including geothermal metamorphism and telemagmatic metamorphism.Telemagmatic metamorphism accounts mainly for the majority of higher-rank Chinese coals,and it resulted from the magmatic activities controlled by the structural systems.House combustion have a high emission factor of 98.24%, which would cause the level of environmental iodine increased,finally give a crucial influence for iodine uptaking.