Some frequently overlooked aspects of reactive flow through permeable media

Solid dissolution and precipitation are major reactions that occur in reactive flow through permeable media. Precipitated reaction products, in particular, can clog pore space and cause flow impairment, which is one of the reasons their simulation is important. Many calculations assume local equilibrium, ideal solutions, no aqueous reactions, and no supersaturation, but depending on the flow conditions, these assumptions can lead to a misrepresentation of the effects of the reactive flow. This paper evaluates the effects of these simplifying assumptions. We applied a method of characteristics model to run generic reactive flow cases consisting of a single mineral initially present and one possible precipitate. Results show that, under the conditions studied, the amount of precipitation predicted is less than that calculated by assuming equilibrium conditions; however, this precipitate can, nevertheless,cause flow impairment. The same conclusion-reduced precipitation- appears to be true for the assumptions of no super-saturation, ideal solutions, and negligible flowing-phase reactions. Including these effects leads to no precipitation at all in some cases. It seems clear that including these effects is important for accurate geochemical modeling. This work is one of the many tangible consequences of Dr. R. S. Schechter's distinguished work in geochemical flow modeling. This work has ranged from laboratory experiment to fieldwork to theoretical analysis to numerical simulation. The second author on this paper attributes much of his success to this diversity and to Bob's unwavering devotion to scientific principles. We are pleased to be able to continue the pursuit of knowledge begun by Dr. Schechter and to honor him and his career at the same time.