Dynamic behavior of trace elements during pyrolysis of coals

Release behavior of sodium and potassium was followed during pyrolysis of coals in a nitrogen stream up to 1200 °C. Sodium and potassium in coal and char were classified into five fractions by a serial dissolution method with H2O, CH3COONH4, HCl, H2SO4 and HF solutions. Distribution of selenium in coal matrix and its release behavior were observed for density-separated samples during pyrolysis. The results showed that lower temperature release of potassium was observed during pyrolysis comparing to the sodium release. Fractions of H2O soluble and CH3COONH4 soluble decreased, and fractions of H2SO4 soluble increased with heat treatments for both alkali metals. Selenium was distributed unevenly in the coal matrix and its content was correlated well with pyritic sulfur content but not with organic sulfur content.