Magnetic Field Enhanced Cake-Filtration

摘要

The cake filtration process is a very broad applied solid liquid separation process, which isrnused in many different industries like chemical, pharmaceutical or mineral industry. Therndesign ranges from lab-scale discontinuous nutsche filters to large-scale continuous rotaryrndrum filters. Another common separation device especially in the mineral industry is thernmagnetic separator, which uses magnetic forces to separate magnetic from non-magneticrnmaterials. Even though both processes, the cake filtration and the magnetic separation, arernwell known and understood unit-operations the combination of the two mechanisms describedrnin this paper is a totally new approach and results in positive synergetic effects and anrnextension of the field of application. This work describes the phenomenology of this newrnhybrid process combining pressure forces with magnetic fields or forces and defines potentialrnfields of applications like pigment separation or bio-separation as well as separation ofrnnanostructured magnetic materials in the electronic industry. It also visualises the analogy tornthe existing and at the University of Karlsruhe developed electrofiltration process.rnThe experimental results presented in this work show that the cake filtration process ofrnmagnetic particulate products can be improved significantly by superposing a homogeneousrnas well as an inhomogeneous magnetic field. The reason can be seen in magnetophoreticrneffects as well as magnetic field enhanced structure changes of the particulate system. Thisrnresults in a faster cake formation, a higher permeation rate through an already built filter cakernand therefore an integral improvement of the overall cake filtration process. But thernexperimental results also define a critical magnetic field strength. If this magnetic induction isrnexceeded, there will no longer be a homogeneous cake formation and the cake will berndisrupted by the acting external magnetic forces. This critical field strength is a function ofrnthe applied gas pressure as well as a function of the (magnetic) product properties. Anotherrnreason for the inhomogeneous cake formation can be seen in the dominating attractivernparticle-particle interactions, which are influenced significantly by the magnetic field.