Application of magnetic forces to disk vacuum filtration in the laboratory and plant

Abstract

The use of magnetic forces to enhance solid/liquid separation of magnetic pulps in a laboratory drum vacuum filter has previously been demonstrated to have potential, especially for steel industry waste materials and iron ore industry pulps. However, the novel process has been used to date in only limited applications, and has only been demonstrated on a bench top scale. This paper details the extension of magnetic vacuum filtration to a laboratory disk filter, and subsequently to an industrial vacuum disk filter. The design of the laboratory disk filter and the evaluation of magnetic field strengths and gradients is described, and results presented for the treatment of steelmaking and magnetite pulps. The modification of an industrial disk filter is then detailed and results presented for tests on the dewatering of pulps containing finely ground magnetite. The research results indicate that magnetic forces can be successfully applied to a disk filter with capacity enhancements of 30–50% being found for the treatment of steelmaking sludges containing approximately 20% magnetics, and for 50/50 magnetite/quartz mixtures. The filter cake was found to discharge easily from the disk despite the magnetic field, but cake moistures did increase due to the formation of magnetic flocs entrapping water. The magnetically modified industrial disk filter gave increased cake rates of over 100%, and the air pressure discharge had no difficulties removing the filter cake in the presence of the magnetic field. Cake moisture contents were slightly higher in the presence of a magnetic field.