Influence of Fluoride Addition on the Composition of Solutions in Equilibrium with Acid Soils

Atmospheric emissions of fluoride from an aluminium smelter-alumina refinery located on the northern coast of Galicia, NW Spain, increase the content of fluorine in soils and vegetation in the vicinity of the complex. The effects of the addition of fluoride solutions on the chemical properties of soil samples from the area surrounding the complex were investigated in laboratory experiments. Addition of fluoride to soils resulted in increases in pH and concentrations of Fe, Al, and organic matter in the equilibrium solutions and decreases in concentrations of Ca, Mg, and K. No consistent effects were observed on the Cu, Mn, or Zn concentrations. Most of the Al in solution was bound to organic matter. Within the fraction "labile aluminium", the concentration of Al-OH complexes decreased and the Al-F complexes increased, especially AlF3 and AlF4 , which are less toxic than Al3+ and Al-OH species.