Experimental Investigation on the Migration of Contaminant Generated in the Dry Distillation Channel to Overburden during Underground Coal Gasification

Underground coal gasification (UCG) is a promising technique to develop coal resources efficiently and environmentally. However, contaminants generated from pyrolysis in the dry distillation channels during the UCG process have the risk of migration to the overburden, resulting in the potential contamination of groundwater. In this study, a new experiment was designed and carried out using overlying rock samples. By combining Fourier transform infrared spectrometry (FTIR) and X-ray diffraction (XRD) analysis, the composition of contaminants, including organic and inorganic contaminants, was identified. The migration behavior of contaminants in the overburden was revealed. The results showed that the overburden has a strong adsorption of heavy metals and porosity is an important factor affecting the migration of heavy metals. The adsorption capacity of the overburden for benzene and oxygen-containing functional group contaminants is weak, and the migration abilities of benzene and oxygen-containing functional group contaminants are approximately the same in short-range migration. The main form of benzene contaminants is pentasubstituted benzene, and changes in its relative content are negatively correlated to trisubstituted and disubstituted benzene. Oxygen-containing functional group contaminants mainly consist of alcohols, phenols, and ethers, which have strong mobility in the overburden and are the main substances in contaminants. The migration ability of Mn is the greatest among inorganic heavy-metal contaminants, followed by those of Pb, Cu, and Cd. The research provides a theoretical basis for the prevention and control of contaminants during industrial application of UCG.