Fluoride removal by Ca-Al-CO&lt;sub&gt;3&lt;/sub&gt; layered double hydroxides at environmentally-relevant concentrations

Wei, L.; Zietzschmann, F.E.; Rietveld, L.C.; van Halem, D.

doi:10.1016/j.chemosphere.2019.125307

Fluoride removal by Ca-Al-CO₃ layered double hydroxides at environmentally-relevant concentrations

Title

Fluoride removal by Ca-Al-CO₃ layered double hydroxides at environmentally-relevant concentrations

Author

Wei, L. (TU Delft Sanitary Engineering)
Zietzschmann, F.E. (TU Delft Sanitary Engineering)
Rietveld, L.C. (TU Delft Sanitary Engineering)
van Halem, D. (TU Delft Sanitary Engineering)

Date

2020

Abstract

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.