High gradient magnetic separation of micro-pollutant from wastewaters

Recent scientific guidelines and regulation frameworks determine the necessity of improving the effectiveness of the processes for the removal of micro-pollutant from wastewaters. This paper reports the study of a HGMS (High Gradient Magnetic Separation) process for the treatment of industrial wastewaters that considers an assisted chemical-physical pre-treatment for the removal of heavy metals through the bound with added iron-oxide particulate matter (magnetite). Reducing the dimension of iron oxide particles, thanks to the increase in the specific surface, improves the adsorbing property, while worsens the magnetic property, i.e. susceptibility. The filter is constituted by ferromagnetic stainless steel wool that, saturating in presence of an external magnetic field provides the necessary magnetic field gradient, which interacting with the magnetic dipole of the particles can overcome the drag and withhold them and the adsorbed heavy metals. Since the holes of the wool are several orders of magnitude lower than the filter length and of unknown geometry, the magnetic field and the fluid-dynamic regime has been determined in an elementary "mean" cell, using an integral model with spatially periodic conditions. The particles' trajectories have been statistically studied in order to obtain capture parameters. Experimental activities on a laboratory device have been carried out in order to test the model.