Forms of occurrence of fluorine in drinking water

Alum coagulation and fluoridation are common processes in many water treatment plants. Under these conditions, fluorine may be present in treated water as less physiologically active fluoroaluminates. This study reports the results of a mathematical analysis of the corresponding chemical equilibria. The influence of at least two possible side-reactions must be taken into account (protonation and hydrolysis). In neutral and alkaline solutions, fluoroaluminates will be, under given conditions, converted to hydroxoaluminates so that the total fluoride concentration can be considered approximately equal to the free fluoride ions. In acid solutions the presence of fluoroaluminates might be significant.