Abstract:
Consumption of drinking water with a high concentration of fluoride (>1.5 mg/L) causes
detrimental health problems and is a challenging issue in various regions around the globe. In this
study, a continuous fixed-bed column adsorption system was employed for defluoridation of water
using volcanic rocks, virgin pumice (VPum) and virgin scoria (VSco), as adsorbents. The XRD, SEM,
FTIR, BET, XRF, ICP-OES, and pH Point of Zero Charges (pHPZC) analysis were performed for both
adsorbents to elucidate the adsorption mechanisms and the suitability for fluoride removal. The
effects of particle size of adsorbents, solution pH, and flow rate on the adsorption performance
of the column were assessed at room temperature, constant initial concentration, and bed depth.
The maximum removal capacity of 110 mg/kg for VPum and 22 mg/kg for VSco were achieved at
particle sizes of 0.075–0.425 mm and <0.075 mm, respectively, at a low solution pH (2.00) and flow
rate (1.25 mL/min). The fluoride breakthrough occurred late and the treated water volume was
higher at a low pH and flow rate for both adsorbents. The Thomas and Adams–Bohart models were
utilized and fitted well with the experimental kinetic data and the entire breakthrough curves for
both adsorbents. Overall, the results revealed that the developed column is effective in handling
water containing excess fluoride. Additional testing of the adsorbents including regeneration options
is, however, required to confirm that the defluoridation of groundwater employing volcanic rocks is
a safe and sustainable method
