Vortex magnetic separation

Vortex magnetic separation (VMS) is a new technique (1-3) which can not only greatly increase selectivity of high gradient magnetic separation but can also provide a much higher material throughput because high slurry velocity is used. This technique will have a wide range of applications in fields as diverse as mineral processing, biochemical engineering, sewage and wastewater treatment and industrial effluent treatment. At present in high gradient magnetic separation (HGMS) low Reynolds numbers (with respect to the wire diameter) are usually used and the magnetic product is captured on the upstream side of the wire matrix which results in a serious mechanical entrainment problem that is very detrimental to the purity of the magnetic fraction and to the reduction of the quantity of non-magnetic fraction (4). Vortex magnetic separation runs at moderate Reynolds number ( Re = 6–40) which leads to the formation of vortex flow in the neighbourhood of the matrix. Magnetic particles in the slurry are first concentrated in the boundary layer flow around the matrix and then brought into the magnetically attractive area on the matrix downstream side. The magnetic deposit on the downstream side of the matrix does not suffer the direct collisions with non-magnetic particles in the slurry, so the quality of the magnetic product is drastically improved. As will be described below, a new invention has been made with regard to the VMS matrix which allows capture to take place on both the upstream and downstream sides of the matrix without mechanical entrainment. This paper reviews experimental and theoretical work on the mechanisms involved in vortex magnetic separation.