Method fo sepg. particular solids consists of applying a shock to the particles, pref. first reduced in size to 1 1/2". The amplitude of the shock is sufficient to break the bonds between the particles and to reduce the size of the softer particles, but insufficient to reduce the size of the harder particles, so that the particles are sepd. with a min. of attrition by friction between one another. Appts. for breaking up minerals of different hardness, of size 1/2", incorporates means of creating a high speed fluidising flow and of introducing the minerals into this flow. The flow is contained in an elongated chamber, pref. of rectangular cross-section, in which are a number of adjustable rigid plates arranged along a wall of the chamber. The plates have a surface hardness between that of the substance to broken up and that of the harder particles which do not have to be broken up. The chamber leads to a separatory section. A part of the gaseous flow is recycled. The appts. includes a dehumidifier. Coal of small particle size is obtd. with a reduced humidity and ash content. Secondary coals of poor quality, which would otherwise be rejected, can be used economically. The particles of coal can be reduced to sizes as small as 0.1 mu. The redn. of coal particles to 20 mu will reduce ash content from 6-60% to 1%.
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