Alternative Materials for Dense Medium Separations

Approximately 640 million tons of coal are treated annually in the U. S. to remove impurities that could cause negative environmental effects during combustion and to upgrade heating value. Dense medium processes, which are used to clean approximately 65% of the total processed coal in the U. S., employ ultrafine magnetite suspensions to separate the coal from the mineral matter. As a result of a recent closure of the only domestic magnetite source and a growing demand from the Chinese coal industry that is exhausting supplies on the international market, the U.S. coal industry is facing increased magnetite costs and a lack of confidence in future supplies. The proposed 2-year project will evaluate and develop alternative materials that can be used in the dense medium process. Alternatives to ultrafine magnetite used in dense medium separators include a vast source of coarse magnetite, steel production slag, magnetic material from combustion residue and fine reject material that comprises the feed coal. Coarse magnetite is generally perceived as providing inferior separation performances. However, recent research indicates that coarse magnetite containing greater than 30% + 100 11m particles provides excellent separation performances in dense medium cyclones. Similar performances were also reported from a full-scale study conducted in Australia involving the use of magnetic material from combustion residue. The associated fine mineral matter that exists within the raw coal may also provide a material that can be successfully used in formulating dense medium as a sole source or as a supplement to magnetite. The findings of previous research concluded that the use of fine coal rejects results in inferior separation performance due to an elevated medium viscosity. However, it is proposed to investigate a nominal 150 x 25 11mfraction in the fine reject stream of an operating plant. Varying amounts of -25 11mcoal reject and magnetite will be added to the coarser fraction in an effort to identify an optimum particle size distribution and blend, respectively. The proposal requests funds for a two-year study that will investigate the aforementioned alternatives for dense medium material. The test program will he conducted using a 152-mm (6- in) dense medium cyclone to treat lOx 1 mm coal in a closed loop system that exists in the University of Kentucky processing laboratory. The criteria used to determine adequacy of each alternative include separation performance. efficiency and economics. )