Abstract
Passive systems that utilize a natural power such as a pond, plant, or microorganisms, is expected to be a cost-effective method for acid mine drainage (AMD) treatment. The Ningyo-toge mine, a non-operational uranium mine located in Okayama Prefecture, Japan, generates AMD containing arsenic and iron. To quantitatively study arsenic and iron ion removal in an artificial wetland and pond, chemical reactions were modeled and incorporated into the GETFLOWS (general-purpose terrestrial fluid-flow simulator) software. The chemical reaction models consisted of arsenite and ferrous oxidation equations and arsenic adsorption on ferrihydrite. The X-ray diffraction analysis of sediment samples showed ferrihydrite patterns. These results were consistent with the model for arsenite/ferrous oxidation and arsenic adsorption on ferrihydrite. Geofluid simulation was conducted to simulate mass transfer with the utilized topographic model, inlet flow rate, precipitation, and evaporation. The measured arsenic and iron ions concentrations in solution samples from the wetland and pond, fitted well with the model. This indicated that the main removal mechanism was the oxidation of arsenite/ferrous ions and that arsenic was removed by adsorption rather than dilution.
Highlights
Acid mine drainage (AMD) from abandoned or closed mines is an environmental problem associated with mining [1,2,3]
Since point A was near the inlet and the surrounding area was an artificial wetland, it was directly affected by the raw water in the mine, which had a stable temperature of around 15 ◦ C regardless of the season
Since point H had a long residence time and the surrounding area was a pond, it was affected by the outside temperature
Summary
Acid mine drainage (AMD) from abandoned or closed mines is an environmental problem associated with mining [1,2,3]. It often contains toxic ions, such as iron (Fe(II). To avoid contamination around mines, AMD has mainly been treated by a neutralization process to add a neutralizer, such as calcite (CaCO3 ) and slaked lime (Ca(OH)2 ) [4]. This process can effectively remove toxic ions from AMD through precipitation as hydroxide or adsorption of hydroxides, such as ferrihydrite (Fe(OH)3 ) and aluminum hydroxide (Al(OH)3 ) [5,6,7].
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