In order to demonstrate the change of coal structure and the effect of mineral

Yangquan anthracite

Northeast lean coal and Xiaolongtan lignite were used in this study

and the samples were prepared by washing with water and acid.Low-temperature ashing and X-ray fluorescence(XRF) were used to analyze the ash compositions

and coal structure was analyzed by Fourier infrared spectrum(FTIR）.Introducing infrared parameters provided additional information of the molecular structure of coal which was not reflected by FTIR.It was shown that the effect of water-washing for demineralization was not remarkable

and the main removed minerals were soluble substances

but the main removed minerals during acid-washing were crystalline SiO2.With the increase of coal rank

minerals and coal molecular structure integrated more closely.The lower the coal rank

the more complex the groups in coal structure

but the IR spectrum indicated a regular pattern in high rank coal.The aliphatic degree in lean coal and anthracite were very low and there was aromatic carbon skeleton mainly

but there was a lot of branched-chain structure in lignite.