Two-dimensional reactive transport modeling of the alteration of a fractured limestone by hyperalkaline solutions at Maqarin (Jordan) |
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| Institution: | 1. Department of Biotechnology, Institute of Geotechnics, Slovak Academy of Sciences, Watsonova 45, 040 01 Košice, Slovakia;2. Department of Physical and Physico-chemical Methods of Mineral Processing, Institute of Geotechnics, Slovak Academy of Sciences, Watsonova 45, 040 01 Košice, Slovakia;3. Department of Applied Technology for Raw Materials, State Geological Institute of Dionýz Štúr, Regional Center Košice, Jesenského 8, 040 01 Košice, Slovakia;4. Department of Solid State Chemistry, University of Chemistry and Technology Prague, Technická 5, 166 28 Prague 6, Czech Republic;5. Institute of Geosciences, Faculty of Mining, Ecology, Process Control and Geotechnologies, Technical University of Košice, Park Komenského 15, 042 00 Košice, Slovakia;1. Mining, Energy and Materials Engineering School, University of Oviedo, Oviedo, Spain;2. Department of Mathematics and Geosciences, University of Trieste, Trieste, Italy;3. IGEA, Biogeochemistry Laboratory of Heavy Metals, University of Castilla La Mancha, Almadén, Ciudad Real, Spain |
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| Abstract: | Two-dimensional reactive transport modeling of the Maqarin Eastern Springs site, a natural analogue for the alteration of a fractured limestone by high-pH Portland cement waters, has been performed using the CrunchFlow code. These 2D calculations included transport by advection–dispersion–diffusion along a single fracture and diffusion in the wall rock. Solute transport was coupled to mineral dissolution and precipitation. A limited sensitivity analysis evaluated the effect of different values of primary mineral surface areas, flow velocity and sulfate concentration of the inflowing high-pH solution.Major secondary minerals include ettringite–thaumasite, C–S–H/C–A–S–H and calcite. C–S–H/C–A–S–H precipitation is controlled by the dissolution of primary silicates. Ettringite precipitation is controlled by diffusion of sulfate and aluminum from the wall rock to the fracture, with aluminum provided by the dissolution of albite. Calcite precipitation is controlled by diffusion of carbonate from the wall rock. Extents of porosity sealing along the fracture and in the fracture-wall rock interface depend on assumptions regarding flow velocity and composition of the high-pH solution. The multiple episodes of fracture sealing and reactivation evidenced in the fracture infills were not included in the simulations. Results can qualitatively reproduce the reported decrease in porosity in the fractures and in the wall rock next to the fractures. Instances of porosity increase next to fractures caused by carbonate dissolution were not reproduced by the calculations. |
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| Keywords: | Maqarin Modeling Fracture Limestone Portland cement Advection Diffusion Porosity |
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