Pilot scale high gradient magnetic filtration of steel mill wastewater

High gradient magnetic separators have been pilot tested for the removal of fine suspended solids from wastewaters of two Swedish steel mills. The first research into the use of these magnetic separators for wastewater treatment in the steel industry was conducted at the Massachusetts Institute of Technology under the sponsorship of the American Iron and Steel Institute [1] and Sala[2]. The results generated interest in exploring this technology further in certain Swedish and U.S. steel manufacturing companies. More extensive laboratory tests in Sweden led to on-site pilot testing at two mills in Sweden, NJA and Granges Nyby Bruk. The SALA-HGMS TM Model 10-15-20 Automatic High Gradient Magnetic Separator was operated on feed to and overflow from scale pits fed by hot rolling mill cooling and scarfing waters. These waters contained up to 150 mg/l of suspended solids. Tests were conducted at magnetic field strengths from 0.1 to 0.9 T (1 to 9kG) and at flow velocities between 145 and 800 m/h. The results show that filtration efficiencies of over 90% are achieved with the Sala high gradient magnetic separator at process velocities many times higher than those in conventional treatment processes.