Improved magnetite recovery in coal cleaning by HGMS

A research program at this Laboratory has demonstrated successful recovery of magnetite at high throughput rates from mixtures of magnetite and coal-like those found in a coal-washing circuit-by High Gradient Magnetic Separation (HGMS). Improving the rate of magnetite recovery with HGMS over that found with conventional magnetic separators is an achievement important to the coal cleaning industry. A single-stage separator was used at rates up to 4.4 tons per hour per square foot of matrix cross-section. At this rate more than 99% of the magnetite was trapped along with less than 5% of the coal, an improvement over drum separators working in the particle size range of the feeds used in this study. Data is presented on the effect of loading on magnetite recovery and on non-magnetic material entrainment in the magnetic fraction. This fraction increases with increased loading indicating non-magnetics trapping but the effect is least at the highest material throughput values. Dispersants help to reduce entrainment, also. Some magnetic agglomeration appears to occur as the separation is performed but there seems to be little difference in separator performance on the basis of particle size.