Granulation of Fe–Al–Ce hydroxide nano-adsorbent by immobilization in porous polyvinyl alcohol for fluoride removal in drinking water

Nano-adsorbents of Fe–Al–Ce trimetal hydroxide (FAC) were immobilized in porous polyvinyl alcohol (PVA) via cross-linking with boric acid. Spherical composite granules of 3–5 mm in size that would not cause a large pressure drop in a packed bed were obtained. SEM images showed that the FAC particles were embedded in holes of about 10 μm in the PVA granules, while the surface pores of the granules were only nano-scale in size. Thermal analysis showed that the FAC and PVA in the granules combined tightly by forming a chemical bond. The mechanical stability of the granules decreased with increased FAC concentration, and increased with increased PVA concentration. The fluoride adsorption capacity of the granules increased with FAC concentration and decreased with PVA concentration. For acceptable mechanical stability and adsorption capacity, a FAC concentration of 12% and PVA concentration of 7.5% were suggested. The adsorption capacity of the granules prepared under suggested concentrations was 4.46 mg/g at an initial fluoride concentration of 19 mg/L and pH 6.5. Immobilization of the nano-adsorbent in porous polyvinyl alcohol granules is a promising granulation method for water treatment in packed beds.

Graphical AbstractNano-adsorbents of Fe–Al–Ce trimetal hydroxide were immobilized in porous polyvinyl alcohol via cross-linking with boric acid. The adsorbent particles were embedded in holes of about 10 μm in the PVA granules. Spherical composite granules of 3–5 mm in size were obtained, which is a promising adsorbent granules for water treatment in packed beds.Figure optionsDownload as PowerPoint slideResearch highlights
► Proposes a new adsorbent-substrate combination for nano-adsorbent granulation to be used for water treatment. Nano-adsorbents of Fe–Al–Ce trimetal hydroxide was granulated into spherical shapes of 3–5 mm in size by immobilizing it in a porous polyvinyl alcohol matrix via cross-linking with boric acid.
► Fe–Al–Ce trimetal hydroxide were embedded in a porous PVA matrix with holes of about 10 μm, while the surface pores of the granules were only on the nano-scale. This structure is promising for adsorption of fluoride ions.
► With spherical granules prepared in the research, satisfactory adsorption capacity and stability in water treatment were achieved.