Magnetite-coal separation by continuous HGMS

Magnetite, slurried in water, is used to create an apparent heavy medium in which fine coal (0.1 to 2.4 mm) is cleaned of its mineral impurities. The magnetite is much finer in size (1 to 44 μm) than the coal and is usually recovered from the coal and refuse by magnetic drum separators. Their performance suffers from changes in feed conditions and a number of them are needed for the average coal cleaning plant. We have adapted HGMS for magnetite recovery because of its insensitivity to coal/magnetite ratio and slurry density and its ability to capture fine magnetite at high velocity. An open vertical matrix able to capture 10 μm (avg. size) magnetite without entraining 2 mm coal has been incorporated in a 1.85 m diameter continuous separator. Three-quarter ton samples of magnetite (in 1000 gallons of water) have been recovered with the matrix ring turning at 40 cm/s through a field of 6 kOe. A laminated core demagnetizing coil followed by water sprays removes the recovered magnetite. In preparation for this continuous program, tests of slurry densities from 20 to 35% solids and coal/magnetite ratios´from 3:1 to 1:4 showed almost no variation in recovery or entrainment. A 4.8 m diameter separator, the largest currently available, with multiple heads, should be able to treat 350 tons of magnetite and coal per hour.