Experimental investigation into the application of a magnetic dense medium cyclone in a production environment

Abstract

The magnetic dense medium cyclone project was undertaken at Koingnaas Mine on a 250 mm diameter cyclone during 1998 and a 510 mm cyclone during 2000. The aim of the project was to evaluate the performance of a magnetic DM cyclone in a production environment. Previous test work on magnetic DM cyclones were conducted during 1995 and 1996 on small (100 mm) cyclones in a laboratory environment, with medium feed only. Solenoid position, magnetic field strength and medium inlet density were varied, while operational parameters such as medium grade, cyclone configuration and inlet pressure were kept constant. Two feed conditions were simulated, namely with medium feed only and with ore feed. The magnetic field had a similar affect on medium passing through a large and a small DM cyclone. The effect of the magnetic field on the medium of a DM cyclone fed with a medium-ore mixture was found similar to one fed with medium only. The magnetic field stabilised the medium for all tests conducted, reducing medium segregation. This was observed by a reduction in the underflow medium density. The reduction in underflow density was approximately linearly related to the magnetic field strength, up to a point, after which magnetic flocculation and a disruption in the flow pattern inside the cyclone occurred. It was discovered that the underflow density primarily determines the cut point. Thus the application of the magnetic field allows direct control over the cut point as well as improved separation efficiency due to increased medium stability. The direct stabilisation of the medium and manipulation of the underflow density with the magnetic field brings metallurgists one step closer to on-line control of all relevant DM cyclone parameters.