Study on Mercury Species in Coal and Pyrolysis-Based Mercury Removal before Utilization

Coal-fired mercury (Hg) pollution control is an important global environmental context. Eight coal samples from different coal fields in China were used to investigate Hg species and the Hg removal effects under different pyrolysis conditions in the presence of nitrogen. These conditions included temperature, particle size, and residence time. The study concludes that the temperature is the most important factor affecting Hg removal from coal, and the mercury release activity at specific temperatures depends on the species and content of Hg present. Large particle size limits the removal rate of Hg, and coal particles smaller than 40 mesh are more favorable for the rapid removal of Hg. For most coal types, pyrolysis of 10-15 min can achieve the ultimate Hg removal effect. Rapid pyrolysis at 600 °C in nitrogen is feasible to remove Hg from coal. Consequently, the Hg removal rate reaches 88-100%, the loss rate of coal calorific value is 2-12%, and approximately 17-58% of S is removed synergistically. HgS, HgSe, HgSO₄, organic matter Hg, and HgO are the main types of Hg species detected in coal, whose thermal decomposition characteristics are the essential criteria for determining the type of Hg removal process. This research will facilitate the improvement of pollution control methods for coal-source Hg pollution.