Modes of iodine occurrence in bituminous coal and anthracite and their environmental effects

Modes of iodine occurrence in bituminous coal and anthracite were investigated by using inductively coupled plasma-mass spectrometry (ICP-MS) and sequential chemical extraction. The results showed that the iodine in both these coals occurs in a descending order of organic, bound with Fe-Mn oxide, water-soluble, residue, ion exchangeable, and the fraction bound to carbonate. In bituminous coal and anthracite, the mean relative content values are 47.4% ± 3.28% and 43.3% ±2.42% for the iodine bound to organic matter, 36.8% ± 3.70% and 34.6% ± 4.77% for the iodine bound to Fe-Mn oxides, respectively; the amounts of water-soluble and ion-exchangeable iodine are 10.3% ± 3.00% and 14.3% ± 3.37%, respectively; the potential leachable rates of iodine are 10.9% and 16.0%, and the potential leachable iodine contents are 0.9 μg/g and 1.2 μg/g, respectively. These results suggested that iodine leaching from both these coals can lead to an increase of iodine concentration in surface water at the supergene conditions; the effect of iodine in anthracite is more environmentally favorable than that in bituminous coal.