The adsorption isotherm of fluoride from actual drinking
water is graphed in Figure 11 together with the adsorption
isotherms at pH 7 and 10. The adsorption isotherm of fluoride
from the actual drinking water was slightly lower than theadsorption isotherm of fluoride from a water solution at pH 7.
This can be explained by recalling that increasing the solution
pH caused a decrease in the fluoride adsorption capacity of bone
char. The initial pH of the drinking water sample was 8.42,
and the final pH ranged between 8.04 and 8.41. The final pH
of the actual drinking water always decreased during adsorption
as was explained in section 3.5.
The percentage of fluoride removal, % R, was estimated using
the following equation