Leaching characteristics of iodine in coal

The dynamic leaching experiments were carried out by different pH solutions in order to investigate the leaching behaviour of iodine in coal. Based on the contents of iodine in coal, residual and different leachates measured by inductively coupled plasma spectrometry (ICP-MS), the leaching rate (η) of coal and concentration of iodine (c) in leachate were calculated. The results show that the modes of occurrence and sites of iodine in coal, leaching time, and pH play important roles in controlling the leaching behavior of iodine. In limited time, the released iodine from coal increases with the rise of acidity of leaching solution, with leaching rates (η) of iodine from coal leached by pH 2.0 and pH 4.0 are 7.22% and 6.20%, respectively. However, the leaching rate of iodine in leachate (w_x) leached by solution of pH 2.0 (1.92%) is less than that of pH 4.0 (5.42%). The average iodine concentration in leachate leached by pH 2.0 and pH 4.0 solution are 10.9μg/L in the first 40h and 10.6μg/L in the first 110h, respectively; there is little iodine in the leachates leached by pH 6.0 and pH 7.5 solution. Leached by acidic solution, the iodine occurred in little water-soluble and exchangeable, part of carbonate and Fe-Mn oxide forms which are on the surface of coal particles may be released firstly; and then the part of water-soluble and exchangeable iodine which are inside coal matrix come to be released.