Separation of mineral particles in cyclones under the influence of a magnetic field

The separation of mineral particles in a cyclone under the influence of a magnetic field was investigated using an electromagnetic - cyclone arrangement. Feed pulps of dolomite and magnetite were used in the study. Two different cyclone types were investigated: An air-type cyclone arrangement and a conventional cyclone arrangement. Magnetic field strengths of 0 to 3000 gauss (0 - 0.3 Tesla) were used in the study by varying the current through the coils of the electromagnet . The parameters evaluated in the study were the grades and recoveries of the magnetic concentrates produced, the enrichment ratios, the improvement in recoveries achieved and the selectivity indices of the processes. The air-type cyclones operating without the magnetic field (ie as a classifier) produced 50% recoveries of the magnetic fraction of the feed with an enrichment ratio of 1.0. The use of the magnetic field resulted in enrichment ratios as high as 1.8 and up to 25% improvement in recoveries. Using a conventional cyclone (as distinct from the air-type cyclones) resulted in higher concentrate grades and recoveries when operated in the magnetic field. Recoveries of 88% or better were achieved with enrichment ratios as high as 2.35. Cast iron pieces were used to alter the magnetic field distribution around the cyclone yielding recoveries well above 90%. The effects of pressure and percent solids in the feed were also investigated. The recovery and grade were observed to decrease at pressures above 8 psi. The grade increased with increasing percent solids in the feed whilst the recovery decreased at the same time. However, the changes in both pressure and percent solids had to be large for these to be significant. Initially, the study investigated feed pulps containing 10% magnetite. Use of feed pulps containing 20 to 30%. magnetite showed that the higher the percent magnetite in the feed, the less the field intensity required to achieve high recoveries under similar conditions. To increase the concentrate grades, the feed to the cyclone should have particles with sizes just below the d50 of the cyclone. The cyclone operating under the influence of the magnetic field would then recover mostly magnetic materials to the underflow resulting in higher grades --Abstract, pages ii-iii