Fluoride Adsorption by Illinois Soils

Abstract

ourteen surface and 6 subsurface horizons of' Illinois soils adsorbed significant amounts of 1;-with release of OH -. At low concentrations, adsorption was described by both Langmuir and Freundlich isotherms. The calculated Langmuir adsorption capacities were related to pH, clay, organic carbon, and amorphous aluminum contents.Two soils with different gross chemical properties behaved in essentially the same manner, with adsorption maxima occuring between pH 5.5 and 6.5. The similarity between adsorption at different pH values for the soils and those for bauxite, allophane and synthesized 'soil chlorite', and the lack of adsorption maxima between pH 5.5 and 6.5 for pure kaolinite and montmorillonite, suggest that F -adsorption in the soils is due primarily t o the presence of amorphous aluminum oxyhydroxides which are common weathering products in these soils.

Fluoride sorption and mineral stability in an Alberta soil interacting with phosphogypsum leachate

“…Studies have shown that F adsorption is accompanied by OH release from the mineral surface supporting the theory that the process involves ligand exchange with a coordinated OH group (Bower and Hatcher l96j; Omueti and Jones 1977). The amount of OH released through F adsorption has been positively correlated with the release of Al from various phyllosilicates and amorphous aluminum hydroxides suggesting degradation of the mineral structure (Huang and Jackson 1965;Perrott et al 1976).…”

“…Montmorillonite adsorption of F is highest near pH 6, whereas kaolinite adsorption decreases linearly from pH 3 to 7 (Omueti and Jones 1977).In general, kaolinite tends to adsorb more F than montmorillonite (Bar-yosef et al 1988).…”

“…Some workers suggest that F added to soils may initially undergo a rapid exchange reaction, followed by a slower reaction such as precipitation of fluorite or fluorapatite (Fhihler et al 1982;Peek and Volk 1985;Bar-Yosef et al 1989). Fluoride adsorption has been positively correlated with soil clay and organic C contents (Omueti and Jones 1977) andnegatively correlated with pH and cation exchange capacity (Bar-yosef et al 1989). In some cases F retention was greatest near pH 5.5 and decreased at both lower and higher pH levels (Omueti and Jones 1977;Banow and Ellis 1986).…”

“…Fluoride adsorption has been positively correlated with soil clay and organic C contents (Omueti and Jones 1977) andnegatively correlated with pH and cation exchange capacity (Bar-yosef et al 1989). In some cases F retention was greatest near pH 5.5 and decreased at both lower and higher pH levels (Omueti and Jones 1977;Banow and Ellis 1986). This pH dependency may be related to the soil mineralogy.…”

Effects of aluminium on fluoride uptake by plants

“…This has long been recognized by analysts because aluminium interference has to be avoided or eliminated by various means during determination of fluoride. Fluorine-aluminium complexes have received most attention in relation to soil (Bower & Hatcher, 1967;Omueti & Jones, 1977;Davison, 1983) and, more recently, in connection with acidification of fresh water (Driscoll, et al, 1980;Johnson et al, 1981). Where plants are concerned, Hani (1978) reported that when fluoride was added to an acid sandy loam, both it and aluminium increased in solution and this led to an increase in both elements in the leaves of maize, hi an investigation of species of the Theaceae that accumulate high concentrations of fluoride from 'normal' soils, Davison (1983) and Davison, Takmaz-Nisancioglu & Bailey (1985) found that they also contained high concentrations of aluminium.…”