Permeability–porosity model considering oxidative precipitation of Fe

What is it about?

Despite decades of research into the interactions between groundwater and seawater, the evolution of permeability produced by iron precipitation has received little attention, resulting in uncertain predictions of permeability in porous media. This study establishes a novel permeability–porosity model for estimating permeability considering the oxidative precipitation of Fe(II) in granular porous media. The accuracy of this model is validated by a series of sand column tests investigating iron precipitation driven by subsurface freshwater–saltwater mixing. The experiments showed a localized pattern of iron precipitation concentrated near the freshwater–saltwater interface in those columns, where a low-permeability zone with intensive precipitation was generated, subsequently leading to a decrease in sand permeability of 45%. Extracted samples analyzed by scanning electron microscopy showed quartz sand particles coated by iron precipitates. With those successful experiments, the newly developed model is validated and fully capable of estimating the sand permeability underlying this geochemical process, providing predictions to within an order of magnitude. The present experimental results and model predictions bring valuable insights into how the pore matrix of a granular porous media evolves during iron precipitation in the subsurface groundwater–seawater mixing zone.

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Photo by Jimmy Ofisia on Unsplash

Photo by Jimmy Ofisia on Unsplash

Why is it important?

Highlights • A novel permeability–porosity model is developed by including iron precipitation. • The model is verified against sand column tests exploring iron precipitation. • Intensive iron precipitates concentrated near the freshwater–saltwater interface. • Iron oxides coat sand particles, leading to a larger surface area than pure quartz. • The new model predicts experimental permeabilities within an order of magnitude.

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