Determination of Magnetite in Dense-Medium Coal Cleaning Plants by the Use of a Davis Tube

Abstract Magnetite losses are generally significant in commercial coal cleaning plants using high-density medium techniques. It is common practice to monitor the cleaned coal, slurries, and refuse using a Davis Tube method in order to isolate and correct unnecessary losses. To ensure the Davis Tube yields correct results, tests were made by comparison with the magnetization determined with a Faraday balance and a vibrating sample magnetometer. The results showed the Davis Tube gives reasonably correct percentage composition of magnetic and non-magnetic fractions, but was not reliable to determine the magnetite concentration in a sample. Further tests showed that commercial heavy-media magnetite has up to a 20 percent lower magnetization than bulk magnetite. Commercial magnetite often contains significant amounts of α- and γ-Fe2O3, in addition to magnetite. As α-Fe2O3 is non-magnetic, it is not removed in the magnetic separator and is discharged in the refuse. It is believed that this is the cause for much...