Synthesis of Bimetal Al/Fe-Oxide Infused Diatomaceous Earth and Its Application for Defluoridation of Groundwater
A bimetal Al/Fe-oxide modified diatomaceous earth was synthesis through co-precipitation of the metal oxides
on the diatomaceous earth’s surface. In an attempt to improve the stability and adsorptive capacity of the adsorbent, it was
subjected to thermal treatment and the impact thereof on the fluoride adsorption. Another important factor in adsorption is
pH of medium, the adsorbent was evaluated for its fluoride adsorption potential with variation of pH. These experiments
were carried out at batch scale. The adsorbent was observed to be most effective and chemically 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. This indicated adsorbent
loss was minimal at that pH range. It was observed that the adsorbent lost its efficiency and thermal stability at calcination
temperature above 600ᵒC. ICP-MS analysis of chemical species supernatants and thermogravimetric analysis of the
adsorbent showed substantive loss of Al and Fe from the sorbent at temperatures above 600ᵒC. K2SO4 solution was observed
to be the best regenerant for spent adsorbent compared to NaOH and Na2CO3 which caused adsorbent loss. The
2- formed strong bonds with the adsorbent active sites thus reducing adsorbent fluoride adsorbent capacity in subsequent
cycles. The adsorbent regenerated with 0.1 M K2SO4 solution could reduce 10 mg/L fluoride in fluoride spiked water
at a dosage of 0.8 g/100 mL by 81.8% and 67.2% at the second and third cycles respectively. The results demonstrate potential
of the application of the adsorbent in defluoridation for household devices since no pH adjustment will be required.
Keywords- calcination; solution pH; diatomaceous earth; defluoridation; metal leaching; reuse.