Leaching of Fluoride from Biotite Mica in Soil : Implications for Fluoride in Shallow Groundwater

Abstract EN

Leaching of F- from biotite was investigated at room temperature by performing a series of short-term leach tests.

The leaching of F- from biotite structure strongly depends on its weathering stage.

Results of this study suggest that high concentration of F- 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 F- from biotite compared to inorganic acids.

Citric acid which is a week organic acid enhances leaching of F- from biotite structure compared to strong inorganic acid HNO3, independent of the weathering stage of biotite.

Strong positive correlation between K+ and Fe2+ with F- in biotite treated with citric acid suggests that F- readily leachs into the solution through an ionic exchange and complex formation.

Organic acids involve sorption and complex formation processes leading to release of F- into the solution.

Our studies suggest that in the presence of organic acids F- is leached readily into water percolating through the soil.

Therefore, shallow groundwater replenished by the water table may achieve high F- concentrations by this leaching process.