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

Liangfu Wei,Frederik Zietzschmann,Luuk C Rietveld,Doris Van Halem

doi:10.1016/j.chemosphere.2019.125307

Liangfu Wei, Frederik Zietzschmann + Show 2 more

Open Access

https://doi.org/10.1016/j.chemosphere.2019.125307

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Journal: Chemosphere	Publication Date: Nov 6, 2019
Citations: 37	License type: cc-by

Affiliation: Delft University of Technology

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.

Highlights

Fluoride (FÀ) is essential for the growth of teeth and bones, but FÀ removal and some of them showed promising FÀ removal capacities, many of them indulge in high installation and maintenance costs, complex treatment processes, and by-product pollutants (Ayoob et al, 2008; Osterwalder et al, 2014; Bhatnagar et al, 2011)
This study indicates the potential of CaeAleCO3 Layered double hydroxides (LDHs) as a cost-effective FÀ removal technology, when locally sourced and in combination with low-cost pH correction
The general formula of LDHs is [M2þ1-xM3þx (OH)2]xþ [AmÀx/m ∙nH2O], where M2þ corresponds to a divalent metal, such as Mg2þ, Zn2þ or Ni2þ, M3þ corresponds to a trivalent metal, such as Al3þ, Fe3þ or Cr3þ, x is the ratio of M3þ/(M2þþM3þ), and AmÀ corresponds to an exchangeable anion such as CO32À, ClÀ, NO3À (Cavani et al, 1991; Ingram and Taylor, 1967)

Summary

Introduction

Fluoride (FÀ) is essential for the growth of teeth and bones, but FÀ removal and some of them showed promising FÀ removal capacities, many of them indulge in high installation and maintenance costs, complex treatment processes, and by-product pollutants (Ayoob et al, 2008; Osterwalder et al, 2014; Bhatnagar et al, 2011). The presence of a large number of exchangeable anions and sizable interlayer spaces makes LDHs attractive for the removal of dissolved contaminants from water (Mandal and Mayadevi, 2008a), including FÀ, ClÀ, NO3À, BrO3À, PO43À, As(III), Pb(II), Cr(VI), Cu(II) and Cd(II) (Batistella et al, 2011; Chitrakar et al, 2011; Halajnia et al, 2012; Das et al, 2006; Lazaridis et al, 2004; Perez et al, 2006; Caporale et al, 2013; Lv et al, 2009). Microwave radiation heating is an alternative method that heats the material from inside out (Bhatnagar et al, 2013), and has been applied for activated carbons (Yuen and Hameed, 2009). Microwave treatment has been applied for synthesis and construction research (Benito et al, 2009), but not for LDHs’ modification

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