Separation of particles of different densities by means of liquids

331,841. Holmes, C. W. H., and Birtley Iron Co., Ltd. March 8, 1929. Wet-separating.-In gravity separation by immersion in liquid of density intermediate between the density of the coal or other material to be concentrated and that of the associated refuse, the crude coal, ore &c. is pretreated by spraying with oil or other substance, e.g. crude varnish, which will minimize the wetting of the mineral by the separating liquid. Coal may be sprayed with paraffin oil while passing over a bar screen prior to immersion for separation in a tank containing calcium chloride solution, or the oil may be floated on the calcium chloride solution so that the coal passes through the oil before it reaches the calcium chloride. The solution may be of specific gravity approximately 1.4, the heavier fraction separated in this tank being further treated in a solution of specific gravity 1.7, with or without a further treatment with oil. Zinc chloride may be used as the separating liquid and the process is particularly advantageous with large particles of coal and shale.