Correlation between firing temperature and defluoridation capacity of brick clay

The amount of fluoride ions adsorbed on laboratory fired brick clay varies with the initial concentration according to Type I adsorption isotherm for firing temperatures up to 700 °C, forming inner-sphere complexes between fluoride and mineral surfaces of brick clay. Type II isotherm is valid above this firing temperature forming outer sphere complexes. The turbidity of suspensions of low fluoride concentrations is negligible with brick clay fired at 300°C to 600°C. Moreover, the removal of fluoride by brick clay fired at intermediate temperatures is high followed by a decrease at high firing temperatures.