INFLUENCE OF SPACE VELOCITY ON FLUORINE REMOVAL ABILITY BY USING GRANULAR Si–Al–Mg MIXED HYDROUS OXIDES

Abstract

A Si–Al–Mg mixed hydrous oxide sample was synthesized with a metal composition ratio of Si : Al : Mg=0.1 : 0.1 : 0.8, hereafter referred to as SAM118. The main components of SAM118 are amorphous Mg (OH)₂ and hydrotalcite (Mg/Al double hydroxide) as observed by XRD. Granulated SAM118 was investigated for its adsorption capacity using batch and column tests. The fluoride adsorption capacity of granular SAM118 (<1.0 cm) was demonstrated in batch adsorption tests and compared with that of powder SAM118 (<150 µm). The adsorption capacity was 11.0 mg/g for the powder SAM118, and the granular SAM118 exhibited a similar performance. Column tests of granular SAM118 were conducted at various space velocities (SVs) to investigate the breakthrough curves (adsorption performance). The breakthrough point, defined as the moment when the fluoride concentration in the effluent reaches 8.0 mg/L, was observed. The through-flow capacity was measured at SVs ranging from 0.31 to 0.82/h for aqueous solutions and 1.09/h for Matsue Shinjiko Onsen hot spring water. The fluoride breakthrough capacity of granular SAM118 was consistent with the SV effect. SAM118 demonstrated a high fluoride adsorption performance, achieving an adsorption amount of 5.27 mg/g at an SV of 0.31/h in NaF aqueous solution. Therefore, it can help meet the Japanese standard of fluoride concentration of 8.0 mg/L in wastewater.