The significance of fluorine traces in natural waters and a proposed method to effect their removal

Abstract

1. Methods are described whereby the concentration of solute fluorides in water can be reduced to a safe level for human consumption, at a very low cost. 2. The active defluorinizing agent is derived from commercial superphosphate. The sulphate and fluorine compounds present in superphosphates are precluded from passing into solution. 3. By adopting the concentrate method of fluorine removal, it is estimated that 1 Kilogram of double superphosphate can remove from 9 to 10 grams of fluorine from solution. The figure obtained by Klein, Adler and Lindsay (1938), for tri-calcium phosphate in filter beds, amounts to 1.8 grams of fluorine per Kilogram tricalcium phosphate, for ten consecutive cycles. 4. The reaction between the defluorinizing agent and the fluorine in solution is apparently accelerated by heat. Suspensions boiled for 5 to 10 minutes leave a lower residual fluorine content than cold agitations over a 24 hour period. That the process of defluorinization is however a time reaction, culminating in a quantitative adsorption or precipitation of solute fluorides is proved by the fact that prolonged cold agitations result in an almost complete removal of the fluorine in solution. 5. The process of fluorine removal is concomitant with an improvement in the general nature of the water subjected to treatment. A reduction in total solids including a reduction in the concentration of metals forming insoluble secondary and tertiary phosphates, is encountered. 6. The chemical combination in which the fluorine compound is present in the water is of no importance as far as its removal is concerned, NaF, CaF₂ and silicofluorides being reduced with equal ease. 7. In significant traces of selenium, boron and arsenic were found in the concentrates, adopted in this investigation. 8. The possibility of utilizing the naturally occurring wavelite as defluorinizing agent, is indicated.