Water defluorination using granular composite synthesized via hydrothermal treatment of polyaluminum chloride (PAC) sludge

Abstract

In this work, we newly synthesized granular composite (GASA) via hydrothermal treatment of polyaluminum chloride (PAC) and subsequently granulation pelleting with starch gel as an organic binder. The resulting composite was characterized with analytic instruments, and the feasibility of utilizing GASA as adsorbent for the removal of fluoride (F−) was tested in the batch and column experiments. The characterization results revealed that GASA possessed a spherical/porous framework consisting of aluminosilicate (i.e., ordered albite, NaAlSiO3O8). The results of final pH effect experiments and XRD/XPS analyses showed the dominant adsorption mechanisms of F− on GASA were electrostatic attraction by protonated surface Al–OH, ligand exchange between surface hydroxyl groups and F ions, and surface precipitation (i.e., cryolite formation). Based on the results of adsorption kinetics and adsorption isotherm, granulation resulted in the relatively slow kinetics of F adsorption compared to the powder type, but was preferred to retain good adsorption capacity. The regeneration possibility of GASA was also proven with the adsorption/desorption cyclic test. In the column study, 15-cm length of the GASA layer and the flow rate less than 0.85 mL min−1 were proposed to keep the satisfactory level of F in water. The experimental results offer a potential of PAC sludge-derived composite as adsorbent for the removal of F from water.