Analysis of iron-bearing phase components in Shenhua coal and their combustion transformation products by acid separation and mossbauer spectroscopy methods

Abstract

The study on iron-bearing minerals in coal is important because these iron-bearing substances often cause boiler slagging. Mossbauer spectroscopy is very useful to analyze the distribution of iron-bearing substances in coal and coal ash. However, there are some uncertainties when only Mossbauer spectrum is used to determine iron-bearing substances in coal and coal ash. A Shenhua coal was separated using a hydrochloric acid, and the low temperature ash (LTA) samples were prepared using the coal samples before and after the chemical separation. Mossbauer spectroscopy and X-ray diffraction were used to analyze the iron-bearing minerals in these LTA samples. Also, these two analysis methods were used to measure the product components of iron-bearing minerals in the ash samples derived from this coal prepared in a drop tube furnace (DTF) system at 1050 and 1250 °C. The results showed that there were no iron-bearing clay minerals in the coal, and the iron element in the coal had two existing forms: pyrite and ferrous sulfate. Moreover, the pyrite in the coal could dissolve partly into the hydrochloric acid. It should be cautious when the acid solubility of iron of coal is used to determine the distribution of iron-bearing minerals in coal. The iron-bearing phrases in the DTF ash of the Shenhua coal were aluminosilicate glass and oxide. The content of the aluminosilicate glass was influenced less by the DTF temperatures although these products came from the combination reactions of the clay minerals with the pyrite and ferrous sulfate. The components of oxide products were complex, and they were affected more by the DTF temperatures. These results provide a new insight into the formation mechanism of easily slagging substances in coal ash.