Performance characteristics of coal-washing equipment: air tables. Report of investigations

Four air table tests were conducted in two different preparation plants to determine the performance characteristics that might be anticipated in commercial operation. The air tables provided rough separations at high specific gravities of separation between 1.78 and 2.67; one test was unusually low at 1.56. Air tables are ideally suited to perform a rough black-and-white separation producing a clean coal and a refuse product, or to scalp the heavy impurities and clean coal while retreating the middlings in a subsequent cleaning circuit employing a device which usually produces a sharper separation. Air tables provide an inexpensive method of removing ash and pyrite, but at the cost of poor sharpness of separation. Error area values were above 251 and probable error values were above 0.296. The air table only does an effective cleaning job down to 28 mesh. Virtually all of the feed finer than 28 mesh reports to the clean coal or the dust collection system.