Occurrence modes of sodium species in sodium-rich coals

The occurrence modes of sodium species and corresponding content distributions in sodium-rich coals were investigated through a series of analytical methods. The results indicate that for the vast majority of coals sodium are mainly in the form of water-soluble form, then organic form, and the content of insoluble form is negligible. Among them, the water-soluble sodium is mainly presented as nitratine (NaNO₃), halite (NaCl) and hydrated ion (Na·xH₂O). The organic sodium is mainly presented as carboxyl sodium (-COONa), while the insoluble sodium mainly occurs as albite (NaAlSi₃O₈).