The apex fraction from the hydrocyclone 52, the shale fraction, is first passed across a draining screen 58 and subsequently across a washing screen 59 having sprayers 60, receiving clarified liquid through the pipeline 42, and sprayers 61 which are fed with water, arranged thereover. The shale is carried off at e and the dilutedsuspension which is collected under the screen 59 is supplied to the magnetic separator 12 through a pipeline 62. The undiluted separating suspension collected under the screens 53 and 58 is fed to a suspension reservoir 64 along a pipeline 63. The reservoir also receives the thickened suspension from the thickener 21 through a pipeline 65, pump 66 and valve 67. From the suspension reservoir 64,gold ball mill the suspension is fed to the mixing tank 5 through a pump 68 and a pipeline 50. Disposed in the mixing tank 5 is an overflow compartment 69 having an ...view middle of the document...
Through a pipeline 74 having a magnetizing coil 75, fresh magnetite is supplied to the thickener 21. The overflow from the thickener 21 is discharged at f.
Usually the overflow fraction 1 is subjected to a further treatment. This is desirable because the overflow consists of a strongly diluted suspension of very fine coal and shale particles which may also contain a small amount of fine magnetite. The fraction 7 may be fed, for example, to a small froth flotation plant in which the fine coal is separated oif. Subsequently, the froth is supplied for example to a (Imperial) filter. The resulting filtrate may then be returned to the thickener 21. The tailings containing water from the froth flotation plant may be flocculated in a thickener, and the tailings then dried in a filter press. The overflow water from the flocculating thickener may be re-used for feeding the sprayers 56 and 61 and/or for grinding fresh magnetite and/ or be returned into the pipeline 16. The water losses may then be made up in the overflow tank of the flocculating thickener. The treatment of the fraction f has not been indicated in the drawing, as this would tend to make the drawing unduly complicated. Moreover, several reservoirs and discharge pipes, which naturally are indispensable in practice, have likewise been omitted from the drawing. For example, the thickener 21, will also serve as a collecting reservoir for the spillage water. Moreover, part of the diluted suspension from the spraying screens 54 and 59 may be fed to the thickener.
The system is controlled as follows. The separating suspension which is supplied to the mixer 15 through pipelines 13 and 73 should have a specific gravity not lower than that necessary for eifecting the separation in the hydrocyclone 8. The exact specific gravity may be obtained by adjusting the valve 17. The level in the reservoir 3 'is kept constant by means of the valve 19.
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