Dry Beneficiation Research Articles

97/02559 Characterizing dry triboelectrostatic beneficiation of coal and fly ash using recovery analysis

Unlike wet beneficiation technologies such as dense media or floatation, dry, triboelectrostatic separation has no counter part to float-sink analysis or release analysis. In an attempt to develop a performance method or procedure for dry, electrostatic processing of coal and fly ash, a recovery analysis technique was developed. It provides data similar to washability or release analyses that are used for wet beneficiation technologies and offers a way to characterize the performance of dry beneficiation technologies. To demonstrate the validity of the method, the data obtained on an analytical laboratory separator were used to generate recovery curves for a suite of coals and fly ashes. The results of these recovery analyses are presented and discussed. A comparison of the dry, separation recovery analyses with release analyses is used to show that the wet-based analysis methods are not appropriate for characterizing dry, triboelectrostatic separation. Dry triboelectrostatic separation can effectively remove minerals from coal, or carbon from fly ash.

The role of an innovation centre

The quantities of coal being beneficiated and the levels of beneficiation required are increasing while the quality of raw coals is decreasing. Although coal is currently cleaned with the minimum of size reduction, fine particle processing, recovery, and tailings disposal are already major problems. Furthermore, adequate water resources are not always available. Dry beneficiation is an alternative approach. The present work is a review and critical assessment of topics relevant to dry processing of coal, comprising comminution, size classification, characterisation and analysis, sorting at coarse sizes, mechanical beneficiation according to density at medium sizes, and electrical and magnetic beneficiation at fine particle sizes.

Clay–coal charge transfer and beneficiation by dry mineral removal

Most coal requires upgrading (beneficiation) prior to burning to reduce the amount of ash left after combustion. Normal washing techniques may produce large amounts of clayey sludge requiring expensive storage behind dykes and dams.Dry coal powder, pulverized to 150 μm for burning, is suitable for dry beneficiation using electrostatic techniques. Such a process would eliminate clay sludge. Agitation of the powdered coal and its mineral wastes results in a charge transfer on contact, the coal becoming positive and the mineral matter negative. Separation in an electrostatic tower produces high quality coal and dry clay mineral waste.Clay minerals form the main component of the ash in most Canadian coals; kaolinite in eastern coals and montmorillonite in western coals. The cumulative amount of charge transfer controls the efficiency of separation. The test results show that the cumulative amount of charge transfer increases with increasing number of contacts, montmorillonite generating four times more charge than kaolinite at a given dry density. Typical values of cumulative charge after 100 contacts on montmorillonite and kaolinite pellets of 1.9 g/cm3 dry density are 0.3 × 10−10 and 0.07 × 10−10 C, respectively.

Magnetic susceptibility of strongly magnetic ores at different magnetic field intensities

1. At a given intensity, the magnetic susceptibility of strongly magnetic ores is directly proportional to the maximum susceptibility, proportional to the fourth root of the magnetic field intensity corresponding to the susceptibility maximum, and inversely proportional to the fourth root of the given magnetic field intensity. 2. The proposed procedure for determining the specific force of magnetic attraction (5) of strongly magnetic particles to the separator poles, which takes account of the dependence of the susceptibility on the field intensity, the textural-structural chracteristics of the ore, and the ferromagnetic phase content of the intergrowth can be used to calculate the operating conditions of the separator and of apparatus for dry magnetic beneficiation of crushed strongly magnetic ores.