Patterns in the Organic-Acid Leaching of Fluorine from Rocks

摘要

Experiments were carried out on fluorine leaching from rocks (alkaline agpaitic granite, dacite, and feldspar-quartz aleurite with 0.005 M solutions of acetic, tartaric, citric, and oxalic acids. The previously revealed decrease of fluorine leaching with organic acids compared to distilled water under an acidity increase within the 6.3-3.5 range of pH values was confirmed. In terms of leaching ability related to distilled water, the organic acids constitute a series: oxalic > citric > acetic similar to tartaric. It has been proposed that a decrease of pH values causes the sorption of fluorides resulting from the substitution of adsorbed hydroxyl ions. In view of this, the less intense fluorine leaching in acids compared to distilled water might be ascribed to sorption immobilization of fluoride ions on a solid phase. A positive correlation between the levels of leached fluorine and magnesium points to the existence of some general but undetermined mechanism of the transition of these elements from minerals into aquatic solutions.