Abstract:
Many people worldwide are exposed to extreme levels of fluoride in drinking water. It is,
therefore, critical to develop inexpensive, locally available, and environmentally friendly adsorbents
for fluoride-laden water defluoridation. In the current study, virgin scoria (volcanic rock) from
Ethiopia, was modified with zirconium oxide and used as an adsorbent in a fixed-bed column aiming
at the removal of fluoride from water. The adsorption capability of zirconium oxide-coated scoria
(ZrOCSc) was compared with unmodified virgin scoria (VSco). XRD, FTIR, XRF, SEM, ICP-OES, and
the pHPZC tests were evaluated to explore the adsorption mechanisms. Thermal analysis of VSco
and ZrOCSc revealed lower total weight losses of 2.3 and 3.2 percent, respectively, owing to the
removal of water molecules and OH species linked to metal oxides contained in the material. The
effect of test conditions such as the pH of the solution and the influent flow rate on the adsorption
capacity of the adsorbent was carefully studied. ZrOCSc exhibited the maximum removal capacity of
58 mg/kg, which was 4.46 times higher than the observations for VSco (13 mg/kg) at pH 2, and an
initial flow rate of 1.25 mL/min. Breakthrough time increased with decreasing initial pH and flow
rate. The adsorption experimental data under various test conditions were examined by the Thomas
and Adams–Bohart models. Both models were found very effective in describing the experimental
data with a correlation coefficient (R2
) of ≥0.976 (ZrOCSc) and ≥0.967 (VSco). Generally, coating
VSco with zirconium oxide improved the adsorption performance of VSco; hence, a ZrOCSc-packed
fixed bed could be employed for the decontamination of high levels of fluoride from groundwater.
However, further examination of the adsorbent using natural groundwater is advisable to produce a
definitive conclusion.
