Determination of mercury in various coals from different countries by heat-vaporization atomic absorption spectrometry: Influence of particle size distribution of coal

Fifty-one kinds of coals, which are practically used in Japanese power plants and industries, were analyzed for Hg by an automatic mercury analyzer (AMA) based on an official method (heat vaporization atomic absorption spectrometry). Almost all coals were imported coals from various countries. These coals are supplied in a powdery form as standard samples by a Japanese organization and called “SS-coals”. Since the sample amount of coal used in the AMA measurement is usually small, the particle size of coal may greatly affect the measurement, however there have been no systematic studies on the matter. Some of the SS-coals, which were much finer than frequently-used certified reference materials (NIST SRM coals), showed a great deviation in data (relative standard deviation (RSD) is high) in the determination of Hg. The SS-coals were ground further into fine powder, and the resulting coals (ground SS-coals) gave lower RSD values. The mean values of Hg content when the as-received SS-coals were measured many times (more than six runs) became about the same as those for the ground SS-coals. The deviation in data in the Hg determination was discussed with the possibility of localization of Hg in coal body at a microscopic level. The content of Hg in coal (bituminous coals) correlated not with that of sulfur (or pyritic sulfur) but with that of ash. Also, it was found that the coals of high inherent moisture exclusively had low Hg contents.