Abstract:
An evaluation of the effects of calcination temperature and solution pH on the fluoride removal
capacity of Al/Fe oxide-modified diatomaceous earth was carried out. The sorbent was observed to
be most effective and stable within the pH range 6.70–8.12, where the lowest concentrations of Al
and Fe (<1 mg/L) in treated water were recorded. Thus, sorbent loss was minimal at that pH range. It
was observed that the sorbent lost its efficiency and stability at calcination temperatures above
600 WC. Inductively coupled plasma-mass spectrometer analysis of metals in supernatants and
thermogravimetric analysis of the sorbent showed that there was substantive loss of Al and Fe from
the sorbent at temperatures above 600 WC because of evaporation. K2SO4 solution proved to be the
best regenerant for spent sorbent compared to NaOH and Na2CO3, which caused sorbent loss owing
to high solution pH. The CO2
3 from Na2CO3 bound to regenerated sorbent so much that it could not
be displaced by fluoride during subsequent defluoridation experiments. Sorbent regenerated with
0.1 M K2SO4 solution could reduce 10 mg/L fluoride in artificial water at a dosage of 0.8 g/100 mL by
81.8% and 67.2% at the second and third cycles, respectively.
