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 temperature above 600 °C. 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 °C 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 CO32− 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.
- diatomaceous earth
- metal leaching
- solution pH
- First received 11 January 2016.
- Accepted in revised form 15 August 2016.
- © IWA Publishing 2016