Defluoridation of Water Using Aerosil-Modified Lignocellulosic Membranes

Abstract

The country’s first tubular microfiltration membranes for water purification from various contaminants, made from an alternative natural material—wood,—was developed at the Dumansky Institute of Colloid and Water Chemistry of the National Academy of Sciences of Ukraine. The proposed procedure cuts significantly the costs of manufacturing membranes. They studied the main patterns of the defluoridation process of water using these lignocellulosic (wooden) membranes, which were modified with a dynamic layer of hydrophilic A-300 aerosil. The modification of the lignocellulosic membranes involved the preliminary formation of an additional retentive layer on their surface, due to the steric mechanism, in the form of a dynamic membrane. The research demonstrated the high efficiency of the water defluoridation process using a dynamic membrane made of SiO₂ particles, which retained fluoride ions (F^–) ions due to the electrostatic mechanism of their interaction. Specific conditions for forming the dynamic membrane included concentrations of modifying and membrane-supporting aerosil additives at 500 and 100 mg/dm³, respectively, with an operating pressure of 1.0 MPa and a formation duration of 120 min. The concentration of suspended SiO₂ particles in the permeate (turbidity) did not exceed the maximum permissible concentration (0.3 mg/dm³) in water. The modified lignocellulosic membrane could decrease the fluoride concentration in water to the permissible level for drinking water (0.7–1.5 mg/dm³) from an initial concentration of up to 7.5 mg/dm³ and a neutral pH at an operating pressure of 1.0 MPa. The membrane’s specific productivity was 0.024 m³/(m² h), due to significant pore blockage by SiO₂ particles.