Methane and ethane adsorption on calcite surfaces: effects of surface morphology from molecular dynamics and 3D-RISM

Understanding the adsorption of alkanes on mineral surfaces is important for industrial processes such as oil and gas recovery from shale reservoirs. Previous studies have examined the adsorption of functionalized and non-functionalized alkanes on calcite, as well as adsorption under confinement. However, real surfaces commonly exhibit defects that can influence adsorption behavior. In this work, molecular dynamics (MD) simulations and the three-dimensional reference interaction site model (3D-RISM) are used to investigate the adsorption of methane and ethane on calcite surfaces with step defects. MD simulations were carried out with and without positional restraints to investigate the effects of carbonate reorientation. 3D-RISM calculations were performed on these structures and on energy-minimized configurations of the relaxed crystal. Both methods show adsorption enhanced at step defects relative to flat regions, with methane exhibiting higher excess adsorption than ethane. Carbonate reorientation at the relaxed step edges reduces the local density peaks at specific step sites in both methods, while the integrated excess adsorption from MD remains comparable to that of the restrained surface. 3D-RISM predicts lower maxima for the highest density peaks and larger excess adsorption than MD, but reproduces the spatial organization and overall adsorption trends at a fraction of the computational cost. These results highlight the importance of surface heterogeneity in fluid-mineral interactions and demonstrate that 3D-RISM is an efficient tool for semi-quantitative screening of adsorption across complex surface geometries

Source: arXiv:2610.30030v1 - http://arxiv.org/abs/2610.30030v1 PDF: https://arxiv.org/pdf/2610.30030v1 Original Link: http://arxiv.org/abs/2610.30030v1