Evaluating fluorspar for fluoridation

Abstract

Data from this study indicate that fluoridation with natural fluorspar could be practical if the raw water is of an appropriate quality. There has been concern about the availability of commercial fluoride chemicals for publicly fluoridated water, coupled with potential problems of overdosing. Fluorspar, a mineral form of CaF2, may provide a more publicly acceptable approach with many advantages over other widely used fluoridation chemicals. This article describes work aimed at gaining insight into the dissolution equilibrium behavior of fluorspar under various conditions for its use in water fluoridation. By treating fluorspar as a blend of CaF2 and CaCO3, the dissolution equilibria were accurately predicted by a theoretical model that accounted for the effects of temperature, background calcium ion concentration, and initial pH. Experimental results and calculations both showed that the ultimate fluoride concentration was approximately 6.0 mg/L at room temperature. Effects of temperature and background calcium ion concentration were much more significant than initial pH. Fluoridation with natural fluorspar could be a practical process with influents of the appropriate quality.