ABSTRACT
This chapter examines the effects of pH and carbonate on defluoridation using calcium salts. An ion that competes with fluoride for calcium, namely carbonate, was introduced into the calcium fluoride equilibrium system to study its effect on precipitation at various pH levels. Samples were collected and divided for comparison purposes. Analytical results indicated only very slight differences between distilled and undistilled samples; therefore, the study was continued without distillation. Calcium concentrations were determined by atomic absorption spectrophotometry using the same instrument and analyst. Residual carbonate ion appeared at pH values higher than those minimum pH readings where fluoride residuals increased. Consequently, analysis of the solid precipitates is considered essential to thoroughly analyze the calcium fluoride-calcium carbonate equilibria system. Therefore, in order to predict more realistic target residual fluoride concentrations, efforts must be directed toward approximating activity coefficients. To obtain the most precise fluoride predictions using theoretical solubility product relationships, activity coefficients must be considered.
