Leaching of Fluoride from Biotite Mica in Soil: Implications for Fluoride in Shallow Groundwater
Leaching of from biotite was investigated at room temperature by performing a series of short-term leach tests. The leaching of from biotite structure strongly depends on its weathering stage. Results of this study suggest that high concentration of is leached from highly weathered biotite, compared to fresh biotite. Results of dissolution experiments confirm that the organic acids in soil promote the leaching of from biotite compared to inorganic acids. Citric acid which is a week organic acid enhances leaching of from biotite structure compared to strong inorganic acid HNO3, independent of the weathering stage of biotite. Strong positive correlation between K+ and Fe2+ with in biotite treated with citric acid suggests that readily leachs into the solution through an ionic exchange and complex formation. Organic acids involve sorption and complex formation processes leading to release of into the solution. Our studies suggest that in the presence of organic acids is leached readily into water percolating through the soil. Therefore, shallow groundwater replenished by the water table may achieve high concentrations by this leaching process.