Low head hyperfiltration through intact Burlington Limestone and Jefferson City Dolomite discs |
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| Institution: | 1. Department of Soils, Federal University of Santa Maria, Av. Roraima 1000, Building 42 – Office 3311A, Postal 97105-900, Santa Maria, RS, Brazil;2. Large Lakes Observatory, University of Minnesota Duluth, Research Laboratory Building 109, 55812-3024, Duluth, MN, United States;1. Department of Geography, Environment and Earth Sciences, University of Hull, Cottingham Road, Hull HU6 7RX, UK,;2. School of Geosciences, Meston Building, University of Aberdeen, Old Aberdeen, Scotland AB24 3UE, UK;3. Faculty of Earth and Life Sciences, VU University Amsterdam, De Boelelaan 1085, 1081HV Amsterdam, The Netherlands;4. Department of Chemistry, University of Hull, Cottingham Road, Hull HU6 7RX, UK;5. BP Exploration, Sunbury-on-Thames, United Kingdom;1. Key Laboratory of Orogenic Belts and Crustal Evolution, MOE, School of Earth and Space Sciences, Peking University, Beijing, 100871, PR China;2. Department of Earth and Space Sciences, University of Washington, Seattle, WA, 98195, USA;3. Key Laboratory of Economic Stratigraphy and Palaeogeography, Nanjing Institute of Geology and Paleontology, Chinese Academy of Science, Nanjing, 250038, PR China;4. Department of Geology and Geophysics, Louisiana State University, Baton Rouge, LA 70803, USA |
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| Abstract: | Hyperfiltration is the ability of a membrane to retard the passage of a solute under a hydraulic head in excess of osmotic pressure. Disaggregated and recompacted shales, mudstones, clays and tuff have been shown to exhibit hyperfiltration-induced membrane effects in past experiments. However, limestone and dolomite have not previously been tested. Therefore, eight hyperfiltration experiments were performed on intact Burlington Limestone and Jefferson City Dolomite to assess the membrane properties of these lithologies. Four experiments were conducted on each lithology using 0.0050 and 0.0100 M Cl− solutions at heads of 0.50 and 1.00 m. Reflection coefficients, a measure of osmotic efficiency, ranged from 0.34 to 0.39 for the Burlington Limestone and 0.32 to 0.40 for the Jefferson City Dolomite. At the end of the hyperfiltration experiments, Cl− was concentrated within the cell above input concentrations by 85–95% for the Burlington Limestone and 79–105% for the Jefferson City Dolomite. An additional experiment passed 0.0020 M dissolved silica solution through the Burlington Limestone at a head of 0.965 bar (14 psi). The final concentration of silica within the cell was 0.0043 M dissolved silica at steady-state; a concentration 114% higher than the original input solution concentration. The reflection coefficient for this experiment was calculated to be 0.33. The results of these experiments suggest that membrane properties in these lithologies may be worthy of consideration in some geologic scenarios, including: (1) shallow or perched aquifers bounded by thin limestone or dolomite strata, (2) overpressured aquifers bounded by limestone or dolomite, (3) limestone or dolomite bounded aquifers with significant vertical components of flow, and (4) facies changes with significant lateral component of flow bounded by either lithology. Furthermore, the results suggest that silica cementation may be possible even under relatively low head conditions. Cementation due to hyperfiltration, even at shallow depths and low pressures should be further investigated. Similarly, other low permeability lithologies lacking a charged surface could potentially function as geologic membranes. |
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