Molecular structure characterization of coal under the water–rock interaction in acid mine drainage (AMD)

Abstract

AMD weakens the compressive strength of coal pillar and threatens the safety of coal mine production. In order to study the effect of AMD on coal, this paper uses X-ray diffraction (XRD) and Fourier transform infrared (FTIR) test techniques to detect the molecular structure of coal samples treated with different immersion acidity and immersion time. The results show that with the increase of soaking acidity and soaking time, the layer spacing (d002) from 0.349 to 0.353 and La from 55.719 to 57.420 nm, showing a positive correlation; Lc from 1.85 to 1.66 nm and N from 5.31 to 4.71, showing a negative correlation. It shows that the original microcrystalline structure in the coal sample changes due to the chemical reaction of organic matter, the spacing and average diameter of the microcrystalline layers increase, the average height and the number of carbon layers decrease, and the degree of order gradually decreases. Aromatic hydrogen(farH), aromatic carbon(farc), the relative abundance of aromatic and aliphatic functional groups(I) and A(CH2)/A(CH3) gradually decrease, degree of condensation (DOC) and oxygen-containing structural(‘C’) gradually increase. The research results show the molecular structure characteristics of coal in AMD water–rock interaction, and provide a reference for studying the macroscopic characteristics of coal under the action of AMD.