- Ca–Al–CO3 layered double hydroxides showed affinity for F– at 2–12 mg/L.
- A higher F– removal capacity at lower pH and lower temperature was observed.
- Only marginal defluorination improvements by calcination/microwave treatment.
- Fast F– uptake during the initial 20?min and little anions competition was observed.
- F– removal capacity is not necessarily reflected in specific surface area.
In this study, F– removal by Ca–Al–CO3 layered double hydroxides (LDHs) was investigated at environmentally-relevant concentration ranges (2–12 mg/L) to below the WHO guideline, with an emphasis on the effect of LDHs’ modification, as well as the effects of initial F– concentration, adsorbent dose, pH, temperature and co-existing ions. Ca–Al–CO3 LDHs, either untreated, calcined or microwave treated, showed affinity for the removal of F– from synthetic groundwater with capacities of 6.7–8.4 mg F–/g LDHs at groundwater-relevant pH, with a higher F– removal capacity at lower pH (<8) and lower temperature (12 °C, as compared to 25 °C & 35?°C). Since calcination and microwave treatment resulted in only marginal defluorination improvements, using untreated LDHs appears the practically most feasible option. For the untreated LDHs, competition with Cl– and NO3– was not observed, whereas at higher HCO3– and SO42- concentrations (>250 mg/L) a slight reduction in F– removal was observed. This study indicates the potential of Ca–Al–CO3 LDHs as a cost-effective F– removal technology, particularly when locally sourced and in combination with low-cost pH correction.
*Original article online at https://www.sciencedirect.com/science/article/pii/S0045653519325470