Sandstone filters water through its tiny pores, acting like a natural sponge to trap pollutants.
Here's a breakdown of how this filtration process works:
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Pore Size and Permeability: Sandstone is a sedimentary rock composed of sand-sized grains. The spaces between these grains create pores. These pores are small, allowing water to pass through while trapping larger particles. The interconnectedness of these pores determines the sandstone's permeability – its ability to transmit water.
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Physical Filtration: As water percolates through sandstone, suspended solids like silt, clay, and organic matter are physically trapped within the pores. This is similar to how a coffee filter works, albeit on a much grander scale. The smaller the pore size, the more effective the physical filtration.
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Adsorption: The mineral surfaces within the sandstone can also adsorb certain dissolved pollutants. Adsorption is the process where molecules adhere to a surface. Depending on the sandstone's mineral composition (e.g., presence of iron oxides), it may be able to remove specific contaminants.
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Biofiltration (Sometimes): In some cases, microorganisms can colonize the sandstone and contribute to biofiltration. These microbes can break down organic pollutants in the water, further improving its quality. However, the extent of biofiltration varies depending on the environmental conditions and the type of microorganisms present.
In summary, sandstone filters water primarily through physical straining due to its porous structure. It can also offer some level of filtration through adsorption and, to a lesser extent, biofiltration.
