Numerical simulation of reactive particle transport in a randomly-orientated rough fracture with reversible and irreversible surface attachments

A novel and robust methodology has been developed to simulate reactive, dense, and polydisperse particle transport behavior in a randomly-orientated rough fracture by applying particle tracking algorithms and the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. More specifically, particle attachment onto an aperture surface is described by both reversible and irreversible adsorptions, which are respectively controlled by the energy barrier and the dominant forces at the secondary minimum on the DLVO interaction profiles. After the simulation model is validated, a number of simulation scenarios are conducted to examine the effect of dominant factors on the particle transport behavior subject to aperture surface attachment. It is found from the simulated results that a large spreading of particle plume is induced with the presence of particle gravity settling and surface attachment. Particle attachment is positively affected by particle size, fracture heterogeneity (i.e., Sigma 2ln(2b)) and particle density (i.e., pp) but negatively affected by hydraulic gradient (i.e., dh/dx), fracture inclination (i.e., 0), and the ratio (i.e., Ax/ Ay) of the x-directional to the y-directional correlation length scales of an aperture field. The sensitivity of particle attachment follows a strong-to-weak order for the non-DLVO parameters as dh/dx > 0 approximate to pp > Sigma 2ln(2b) > Ax/ Ay. Inconsistencies are also found between mass and number attachments for the associated quantities as well as sensitivities to the dominant factors. Among the non-DLVO factors, reversible attachment is more sensitively affected by dh/dx, Sigma 2ln(2b), and Ax/ Ay as they are capable of influencing the velocity field. An increased Hamaker constant (i.e., A123), particle surface potential (i.e., Wp), and ionic strength (i.e., Is) respectively enhances, reduces, and enhances the overall particle attachment, while the irreversible attachment can be mildly mitigated by the increased A123 and Is when a deep secondary minimum appears on the DLVO profile. This study technically improves the previous work by jointly incorporating fracture orientation, particle gravity settling, and the reversible/irreversible surface attachment into the original particle transport models through a scientific manner. Also, this work further reduces the deviation between the existing theoretical modeling and the real particle transport/filtration behavior in fractured media, while the associated findings in this study provide better understanding and significance on this research topic.