FLUORIDE SORPTION AND DESORPTION INDEXES IN QUEBEC SOILS

Sorption and desorption of fluoride (F) were measured on 24 samples fr om the A, B, and C horizons from the most representative soil series o f the aluminium smeltering areas of the province of Quebec, Canada. Th e sorption was estimated by 48 h contact with 0.005M NaClO4 solutions of increasing F concentration and described with the van Bemmelen-Freu ndlich equation, Desorption (Qdes) was measured with two 48 h contact periods in the same electrolyte. The affinity parameter (K) was most c losely correlated with ammonium oxalate extractable aluminum (Al) (AlO X, r = 0. 78) and iron (Fe) (FeOX, r = 0.59**), and organic carbon (C ) (OC, r = 0.59*) contents and to the soil pH (r = 0.56**), whereas t he peak sharpness of the distribution of affinity terms parameter (n) was most closely related to AlOX (r = 0.63*). The K parameter was bes t predicted by a combination of AlOX, FeOX, and OC. A combination of e xchangeable magnesium (Mg) and potassium (K) and FeOX predicted 75% of the variation in Qdes suggesting that cation-rich Aqueptic soils reta in F less strongly than Spodosols. The results of this study indicate that Spodosols which have much larger AlOX contents than Aqueptic soil s should preferably be selected as sites for Al smeltering operations.