A.V. Savenko – Ph.D.(Geogr.), Senior Research Scientist,  Lomonosov Moscow State University

E-mail: Alla_Savenko@rambler.ru

V.S. Savenko – Dr.Sc.(Geol.-Mineral.), Professor, Leading Research Scientist,  Lomonosov Moscow State University

Mobilization-immobilization of fluorine during the interaction of clay minerals (montmorillonite, palygorskite) with fluorine-containing aqueous solutions was experimentally studied. It was shown that specific sorption of fluorine ГF, determined by change in the concentration of dissolved fluorides, linearly depends on their equilibrium concentration [F]eq: ГF = k[F]eq − b, and the angular coefficient k decreases with increasing of equilibrium pH. There is a concentration [F]0, at which equality with the equilibrium concentration [F]eq the fluoride content in solution does not change (ГF = 0). At [F]eq < [F]0, the specific sorption takes negative values ГF < 0, which is caused by passing of fluorine, initially contained in the adsorbed complex of minerals, into solution. Total (true) sorption is always positive and can be calculated from the equilibrium concentration of fluorine in solution: ГFtotal   ГF b k[F] .eq The sorption immobilization of fluorides is most effective at pH < 8, while in a more alkaline medium they are desorbed from the absorbed complex of natural minerals. Natural and artificial geochemical barriers based on clay minerals can be used to control the fluorine content in waters. At ГF < 0, passing of fluorine from the adsorbed complex of clay minerals into solution can provide an increase in the concentration of fluorides to optimal level of 0.7…1.5 mg/L, which is most easily carried out in alkaline medium. In a neutral and acidic medium at ГF > 0, the interaction of water with clay minerals leads to decrease in the concentration of fluoride ions, and clay geochemical barriers can be used to immobilization of excess amounts of dissolved fluorides. The necessary conditions for achieving the optimal level of fluorine content in water (0.7 mg/L < [F]0 < 1.5 mg/L) in each case can be experimentally determined by the method described in this work.

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