Patent GB-975655-A (GB)
Title: Concentration apparatus and method
IPC: B03D1/14
Filed: 1961-12-11
Abstract: 975,655. Froth flotation. DENVER EQUIP MENT CO. Dec. 11, 1961 [April 5, 1961], No. 44318/61. Heading B2H. A process for the concentration of minerals, e.g. of copper, in an ore by froth flotation in a cell, in which one constituent of the ore rises and is separated from the upper part of an ore pulp formed of a mixture of ore particles and a liquid, e.g. water, and at least one other constituent settles in the ore pulp to form tailings, is characterized in that at least a fraction of the settled particles are moved into a vortex beneath the flotation cell to separate the lighter from the heavier of said particles, the heavier particles being discharged continuously from the lower end of the vortex. In the flotation cell 60, Fig. 4, the ore pulp, which enters through a conduit 74, is agitated by an impeller 61 driven by a rotary shaft 62. The shaft 62 is enclosed in a casing 64 closed at its upper end by a bonnet 65 to which air is supplied at 66. Air passes down the casing and a froth is formed by the impeller 61, which froth rises to the top of the cell and is removed by a rotating horizontal paddle 71. The tailings and middlings settle in the cell and enter a conical separator 78 fitted directly beneath the impeller 61. As the impeller rotates a vortex of pulp is created in the separator 78 and the heavier middlings leave through an outlet 80 to be reprocessed whilst the tailings and fine middlings leave eventually over a weir 75, adjustable by means of a hand wheel 76. The speed of the vortex may be controlled by vertical adjustment of the impeller 61 using slotted support plates 69, 70 and the impeller may be fitted with adjustable blades on its underside, Fig. 5 (not shown), to increase the speed of the vortex. The separator 78 has a rubber lining 81 to prevent damage, and air may be supplied tangentially to the outlet 80 to prevent a blockage of the heavier particles therein. The invention may be applied to a multi-cell flotation machine 10, as in Fig. 1, which machine has a feed inlet 11, a tailings outlet 12 and the froth concentrate is removed in a launder 13 with an outlet 14. Conical separators 15a, b, c, d and e are fitted to the last five cells of the machine 10. The heavier middlings particles from the separators 15a to e are fed to a classifier 17, where slimes are removed through a line 18, the raked solid product being fed to a ball or rod mill 21 to which fresh feed is also led by a line 20. The discharge from the mill 21 is fed to a screen 22 to remove outsize particles through a line 23, and the feed from the screen 22 is led to a conditioner tank 25 and through a pump 26 to the feed inlet 11 of the machine 10. Thus the heavier middlings particles are reprocessed to recover a proportion of the ore values they contain. The arrangement shown in Fig. 1 is suitable for use with an ore which settles slowly. In the case of an ore in which the heavier particles settle rapidly, the conical separators are fitted below the first few cells of the machine series, with one other separator fitted to a cell towards the tailings discharge end of the machine, Fig. 2 (not shown). The separators may have outlets of decreasing diameters, and thus discharge capacities, and the combined outlet discharge may be fed to a cyclone separator to remove fine particles to waste before feeding the heavier particles back to the ball mill. As a further alternative, the combined outlet discharge from the conical separators may be fed to a concentrating table or jig to remove fines and slimes, the concentrate of this step being removed as a final product whilst the middlings are returned to a classifier as in Fig. 1. In another alternative, where the ores to be concentrated settle very rapidly, the outlets from the first conical separators may be led to waste and only the output from the last separator is reprocessed. Alternative arrangements of impellers and conical separators are shown in Figs. 6, 7 and 9. In Fig. 6, the conical separator has an annular portion 88 with a separate agitator 90 driven from the impeller, and a tangential liquid inlet 91 is provided to increase the speed of the vortex. In Fig. 7, the outlet from the conical separator is fed tangentially to a cyclone separator 95, slimes being removed through an outlet 96, whilst a cleaned and graded concentrate is removed through an outlet 97. The conical separator of the invention may also be employed with the impeller shown in Fig. 9, which has depending fingers 102, or with a squirrelcage rotor, Fig. 10 (not shown), disposed for rotation inside a fixed squirrel-cage enclosure. Specification 456,249 and U.S.A. Specification 2,107,289 are referred to.