Induced oxidation effects on physical and mechanical properties of lignite from Tempoku, Hokkaido, Japan for sustainable mining via subsurface cultivation and gasification method

The lignite resource has been under consideration for the subsurface cultivation and gasification (SCG) method to produce biomethane from lignite in Hokkaido, Japan. The primary phase of the method entails initiating the oxidative transformation of lignite using an H2O2 solution, resulting in the formation of dissolved organic carbon (DOC), a pivotal component. To examine the effects of induced oxidation on lignite's mechanical properties, artificial oxidation tests were conducted to form DOC. While there was a slight decrease in P-wave velocity and density, the uniaxial compression and indirect tensile strengths, as well as stiffness, did not decrease. These results were obtained at room temperature and atmospheric pressure. Therefore, further examination of the results under pore and confining pressures and at a higher temperature is necessary. However, it is expected that a significant strength decrease due to H2O2 oxidation would not need to be considered in the SCG method. This would lead to a reasonable design of the SCG site, saving time and costs. Moreover, DOC, strengths, and Young’s modulus showed positive correlations with P-wave velocity. Its measurement could be an effective tool for designing the site and predicting the performance of the SCG method.