The environmental effect of underground coal gasification semi‐coke on confined groundwater

Abstract

From the health and environmental point of view, the control of soluble metal elements and organic compounds in underground coal gasification (UCG) by‐product is of great importance for groundwater protection. Unlike the leaching of gasification ash as well as leaching in normal pressure, the leaching of trace elements and organics from UCG semi‐coke into confined groundwater has received little concern. In this research, UCG model test of Inner Mongolia lignite was performed, the obtained UCG semi‐coke was then soaked by applying stainless steel leaching column at 0.5, 1.0, 1.5 and 2.0 MPa with nitrogen as pressurizing agent, the concentrations of trace element and total organic carbons (TOC values) in lixiviums were finally determined by applying ICP‐MS and TOC analyzer to investigate the slight leaching in confined groundwater. The results indicate that Cd, Co, Cr, Ni, Pb and V are undetected in all lixivium samples, and compared with soaking under normal pressure, the concentrations of As, Ba, Mn and Sr are lower in confined water. TOC values in lixivium samples approximately approach to the background value of groundwater, indicating that no extra organic compounds could be leached and TOC values also show the similar changing trend as As, Ba, Mn and Sr behave under normal and high pressures. © 2016 American Institute of Chemical Engineers Environ Prog, 35: 1584–1589, 2016