FLUORINE SPECIATION AND MOBILITY IN F-CONTAMINATED SOILS

Fluorine speciation and mobility were investigated in Luvisols and Regosols, contaminated during 50 years by an aluminum smelter. Fluorine solubility shows a minimum at pH 6.0-6.5 and is increasing at pH < 6 as well as at pH > 6.5. The high solubility of fluorine under acid conditions can be explained by the occurrence of cationic [AlF]2+- and [AlF2]+- complexes, the increase of fluorine solubility at pH > 6.5 by desorption of free fluoride due to repulsion by more negatively charged surfaces. Therefore, a contamination risk for the food chain and groundwater is low in slightly acid soils, but increases under strong acid as well as under alkaline conditions.