Removal of fluoride from aqueous solutions through Fe(III) modified water treatment residues

The extensive presence of fluoride (F−) in ground and surface water poses a potential threat to human health. Water treatment residues (WTR) are potential absorbents that can remove F−, but this removal capacity needs to be enhanced further for its optimal utilization. In this study, we have proposed a method of Fe-modified WTR (Fe-WTR) to ameliorate removal efficiency and investigated the associated mechanism. The physicochemical properties of Fe-WTR were characterized using X-ray fluorescence spectrometry (XRF), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). The maximum adsorption capacities of WTR and Fe-WTR for F− reached 6.09 and 16.09 mg/g under natural pH (pH = 6.5). The F− adsorption kinetics most suitable model was the pseudo-second-order model, indicating that the chemical adsorption may play a primary role in the F− removal process. A probable mechanism for F− adsorption by Fe-WTR was proposed, where the complexation reaction of F− with Al3+ and Fe3+ and ion exchange of F− with OH− were the main processes. The excellent resistance to interference from coexisting anions and the change in pH value clearly demonstrates that Fe-WTR can be efficiently applied for various environments. To conclude, owing to its high adsorption capacity, economy, and environmental friendliness, Fe-WTR is a potentially efficient adsorbent for F− removal from polluted waters. Moreover, this study presents a deeper understanding of the mechanism of F- removal by WTR, which may pave way for future appropriate modifications of WTR for future applications. [Display omitted] •The Fe-modified WTR are used for the first time to remove fluoride from water.•The F− adsorption capacity of Fe-WTR exceeds that of most reported adsorbents.•Fe-WTR performs stably for extensive pH and coexisting anions environments.•Complexation reaction and ion exchange are dominated the F− adsorption on the Fe-WTR.•Al–F and Fe–F are responsible for the formation of new complex on the Fe-WTR surface.