Patent GB-1469292-A (GB)
Title: Froth flotation
IPC: B03D1/22
Filed: 1974-03-22
Abstract: 1469292 Froth flotation NATIONAL RESEARCH DEVELOPMENT CORP 18 March 1975 [22 March 1974 [17 Jan 1975] 12857/74 and 2128/75 Heading B2H In a method of effecting froth flotation in a receptacle divided by separating means to provide two or more flotation cells arranged one above the other, froth is passed upwardly from a first cell into a second cell above it and the thickness of the froth layer in the first cell is controlled to correct variations therein and thereby inhibit coalescence of gas bubbles present in the froth layer. In one embodiment, Figs. I and 2, the receptacle is divided into three cells 3, 4, 5 by plates 6 provided with frusto-conical perforations 7 tapering towards the top. Feed enters the lowest cell 5 through an inlet 11 tailings are removed through an outlet 13 which incorporates a flow control valve 14. The latter is connected to a sensor 15 which records the hydrostatic pressure in the upper cell 3, the valve being adjustable by a control 16 to open automatically when this pressure rises above a set value and vice versa. Froth is produced by compressed air supplied both through an inlet 12 and mixed with the feed in the form of fine bubbles by means of an impeller 24, 25. A baffle is mounted at the bottom of cell 5 and comprises vertical rectangular plates 30 joined by a grid 31 and horizontal square plates 32 located one at each corner of the cell. A leakage pot 33 and a bearing housing 34 are provided beneath the cell 5. An inlet 8 for fresh water and an outlet 9 for froth are provided in cell 3 and sample ports 10 are provided in cells 3, 4. Outlets 17 in cells 3, 4 interconnect with inlets 18 in cells 4, 5 via chambers 19 for transfer of pulp downwardly through the receptacle. Each chamber 19 contains a weir 44 hinged at 45 to the exterior of the receptacle. Low pressure air is introduced into the chamber 19 via an inlet 46 provided with a restrictor 47. An air outlet 48 from the chamber 19 is controlled by a disc 49 attached to the weir 44 by a rod 51 and loaded by a spring 50 associated with a pressure control 52. In operation, the receptacle is first filled with water mixed with a frother. Fresh water is continuously fed in through inlet 8 whilst feed pulp containing the material of interest to be separated is fed batchwise through inlet  11. The tailings from outlet 13 are recirculated as feed through the inlet 11 until they are free of material of interest. Additional frother and other additives e.g. a collector oil, may be included in the feed. Additional frother is also fed in with the fresh water until no further material of interest leaves the upper cell 3 through an outlet 9. The thickness of the froth layer 53 in cells 4, 5 is automatically controlled by the action of weir 44. Thus if the froth layer decreases in thickness, a decrease in the pulp level at the weir 44 occurs leading to a reduction in the outward force exerted against the disc 44 by the weir through the rod 51. The force exerted by the spring 50 on the disc then prevails and causes the latter to close the outlet 48 causing the air pressure in the chamber 19 to rise. This leads to a decreased pulp flow over the weir 44 due to the fall in the liquid level above the lip of the weir and thus the froth thickness is restored to the desired value. An increase in froth thickness results in an opposite sequence of events. The apparatus may be used for cleaning fine coal and treating metalliferous ores, e.g. sulphide ores, or non-metallic ores, e.g. fluorspar. Other embodiments and various modifications are described.