Water purification with magnetic micro and nanoparticles
Résumé
Water pollution is an important problem for the environment. The presence of inorganic and organic pollutants, like metallic cations or polyaromatic hydrocarbons (PAHs), causes environmental damage and provokes different health diseases. Many techniques are currently used to extract these pollutants from water but most of them do not allow elimination of pollutants at trace concentrations. To solve this problem, we propose to use functionalized magnetic particles of two different sizes. The small nanoparticles will be used to adsorb pollutants on their surface and these nanoparticles will be removed from water with the help of magnetic micron-sized particles which exhibit a higher response to the applied magnetic field. First, we present experimental results on the magnetic separation of the magnetic iron oxide nanoparticles by magnetic microparticles under an external magnetic field. In the absence of flow, we see the attraction of nanoparticles around the microparticle and formation of thick nanoparticle clouds in the direction of the magnetic field. We compare these results with a theoretical model based on the equilibrium of chemical potentials of the captured and un-captured nanopartciles. Under flow, the size and the shape of the nanoparticle clouds strongly decreases with the Mason number (defined as a ratio of hydrodynamic -to magnetic forces). The range of Mason numbers within which the nanoparticle capture still takes place is determined. Finally we study adsorption of metallic cations on the iron oxide nanoparticles. The influence of various parameters (pollutant concentration, pH ...)will be discussed.