Distribution, Occurrence and Enrichment Causes of Sodium in Middle Jurassic Coal from Zhundong Coalfield, Xinjiang

Abstract

The coal found in the Zhundong Coalfield is highly suitable for power generation and gasification. However, the high sodium content within the coal leads to severe boiler slagging and contamination. Additionally, sodium disperses into the gaseous phase to form haze, adversely affecting the local atmospheric environment. This study delved into the distribution and occurrence characteristics and enrichment causes of sodium in the coal, employing sequential extraction experiments and testing methods such as XRF, ICP-OES and SEM-EDS. The findings of this research indicate the following: (1) With the increasing burial depth of coal seams, there is a noticeable decrease in the sodium content within the coal. Sodium is primarily distributed within the coal seam, with higher concentrations observed in the upper portions of the same coal seam. Furthermore, the distribution of sodium within the epipedon, overlying rocks and coal seam also exhibits a decreasing trend. (2) Sodium primarily exists in a water-soluble state within coal seams, with H2O-Na accounting for over 70% of its composition. The ion-exchangeable sodium is higher than that in the roof, floor and gangue. Sodium exists in coal seams in both ionic and hydrated ionic forms. It is worth noting that the minerals within coal are not the primary carriers of sodium. (3) These coal seams were formed in a warm and humid shallow lake peat swamp environment, which is not significantly influenced by terrestrial or marine sources. The enrichment of sodium is primarily influenced by later hydrodynamic conditions.