Enhanced fluoride removal by loading Al/Zr onto carboxymethyl starch sodium: synergistic interactions between Al and Zr

In this paper, a novel type of adsorbent was prepared by loading Al/Zr onto carboxymethyl starch sodium to generate CMS–Al, CMS–Zr or CMS–Al–Zr. The adsorbents were tested for removal of fluoride by batch adsorption experiments under various conditions. It was found that CMS–Al–Zr performed well over a considerably wide pH range of 4–10. The adsorption process could be described by a Langmuir isotherm model and Lagergren pseudo-second-order kinetic model. The maximum adsorption capacity for CMS–Al–Zr (60.61 mg g−1) was higher than CMS–Al (51.44 mg g−1) and CMS–Zr (40.23 mg g−1) due to synergistic interactions between Al and Zr. SEM, EDS, XRD, FTIR and XPS studies revealed the Al/Zr loading process and mechanism of fluoride adsorption. The results showed that the metal complex was coordinated to the –COO group of CMS through ion exchange of sodium during the loading process.