Transformation of sodium during Wucaiwan coal pyrolysis

The existing forms of sodium in Wucaiwan coal, a high sodium content coal from Zhundong area in Xinjiang Uygur Autonomous Regions, China, were determined by three-step-extraction method and by the analysis of microwave digestion and inductively coupled plasma atomic emission spectrometry (ICP-AES). The existing forms of sodium in treated samples and the chars were also determined. The transformation of sodium in the raw coal and the treated coals during pyrolysis was investigated. The results show that most of the sodium in Wucaiwan coal exists in the form of water-solution sodium, and the organically bound sodium exists mainly in the form of carboxylate. During pyrolysis, the release of water soluble sodium and ammonium-acetate soluble sodium from the coal samples mainly takes place in the temperature range of 650~850 ℃, and the release of total sodium gets to the largest value at 1 050 ℃ accompanied with the releasing of hydrochloric soluble sodium. However, most of the sodium in the treated coal chars exists in the form of insoluble type. The transformation of a part of water soluble sodium and hydrochloric soluble sodium in all samples into ammonium-acetate soluble sodium during pyrolysis at 450~650 ℃ can be observed.