Magnetic separation of water suspensions containing TiO2 photocatalytic nanoparticles

Abstract

The dynamics of magnetic separation of TiO2 nanoparticles (25 nm) from water by adding composite magnetic Fe-C-COOH nanoparticles (15 nm) and subsequent magnetic sedimentation or magnetic filtration has been studied. Magnetic sedimentation was carried out in a gradient magnetic field (Hmax = 0.3 T, (gradH)max = 0.13 T / m), and magnetic filtration (Hmax = 0.5 T, (gradH)max ~ 105T / m) was carried out in a column bench filter with a steel wool magnetic matrix. The applied methods of spectrophotometry using the PLS algorithm and nuclear relaxometry made it possible to determine the partial concentrations of the target TiO2 particles and of the magnetic seeds in water. Oppositely charged target TiO2 nanoparticles and magnetic Fe-C-COOH nanoparticles formed heteroaggregates in water, the size of which depended on the pH of the aqueous medium, on the ratio of their concentrations, and on the concentration of the solid phase in water. The maximum efficiency of TiO2 separation from water by both methods was observed at pH = 6, at which the electric charge of the aggregates was minimal. The largest heteroaggregates (with dh ~ 3 μm) are formed at initial concentrations of TiO2 nanoparticles of 0.1–0.5 g / l and at the 2:1 mass ratio of the nonmagnetic and magnetic components. Magnetic filtration is a more efficient separation process than magnetic sedimentation due to higher magnetic field gradients applied.It was found that by adding Fe-C-COOH magnetic nanoseeds, the magnetic filtration at a flow rate of 7 * 10-3 m / s through a filter of the 50 cm length, leads to the reduction of the TiO2 concentration in water from 0.5 g / l to 3 * 10-4 g / l for 10 min. The results obtained can serve as a basis for designing a magnetic separation unit in photocatalytic reactors for water purification.