Patent GB-547102-A (GB)
Title: Improvements in or relating to the separation of solid materials of different specific gravities
IPC: B03B5/44
Filed: 1941-02-10
Abstract: 547,102. Wet-separating. TROSTLER, F., and HUNTINGTON, HEBERLEIN & CO., Ltd. Feb. 10, 1941, No. 1808. [Class 82 (ii)] In the preparation, for use in sink-and-foat separating processes, of a heavy suspension medium comprising a disoersion in liquid of insoluble solid particles having sizes within a range extending from comparatively coarse to very fine, the medium having a prescribed density and a viscosity and settling rate, within prescribed maximum and minimum working values, the aggregate surface area required of the insoluble particles per unit of volume of the desired medium to enable them, when suspended in the liquid in ratio appropriate for giving the medium the desired density, to produce the stated settling rate and viscosity is ascertained and the means for producing such particles, such as a grinder classifier combination, are adjusted so that it will provide particles of the said aggregate surface area within the prescribed size range and without regard to the oresence or absence of any particular size groups within the range and without regulation of the proportions of different size fractions except such as may be necessary to produce premature segregation and then operated to produce such particles. The operating means may also be adjusted in such a manner as to ensure in the medium during use a sufficient balance of the size groups of the particles to prevent objectionable segregation while maintaining the aggregate surface area of said particles per unit of volume of the medium substantially the same. In an example a heavy suspension is used having 68-81 per cent. of solid particles by weight, a viscosity of 1.1-1.4, an undisturbed settling rate, in the absence of a dispersing agent of not more than approximately 5 minutes per cm. over a period of 20 minutes and absence of segregation of, comparatively large particles in 20 minutes, the particles containing some or all of the size groups, 300-500 mesh (average 400 mesh or 44.48 microns), 500-800 (average 650 mesh or 26 microns), 800-1500 (average 1250 mesh or 14 microns) and about 1500 (10 microns) or smaller mesh the particles of the last group comprising about 22 per cent. and upwards of the total solids and the aggregate surface area of that group per unit of volume being in excess of 70-75 per cent. of the total surface area per unit of volume of the groups 300-500 mesh, 500-800 and the 1500 or over. When galena is the substance used for the suspension, the aggregate surface area is not less than 4 square metres per 100 grammes of the medium. In using a suspension prepared as above in a sink- and-float separating process the medium is used in circuit and is treated as required to prevent the aggregate surface area of the solids per unit of volume from increasing more than the ascertained area, e.g. by withdrawing continuously used medium from the separating vessel, periodically ascertaining which of the size groups have in creased and the rate of increase, withdrawing continuously from the withdrawn medium a percentage of the total flow, returning the remainder to the medium feed for the separator and adding fresh medium compound of a plurality of the size groups and having a decreased proportion of size groups which have been increased in the separating operation and increased proportions of size groups which have not been increased. The maintenance or rejuvenation of the medium is adjusted by recleaning, carried out by known flotation means to remove slimes and gangue produced by attrition and reconditioning, i.e. adjusting the characteristics of the medium, particularly viscosity and/or segregation to correct changes due to the attrition of the ores to be treated and disintegration of the solid particles in the medium. One method of carrying out the process is shown in Fig. 2, in which medium from the ball-mill classifier combination 1 passes to a repulper 2 and thence as indicated at 4 to a separating vessel 3. The float particles are removed over the boom 5, and the sunk particles removed by the elevator 6 fall on to draining screens 7, 8, the medium discharged being returned to the circuit. Overflow from the weir 10 is usually passed to and joins the tailings on the screen 7. The sink- and-float particles are passed independently to cencentrators 9, 9a medium which overflows therefrom passing back into the circuit and the preconcentrated pulp passing by connection 12 either directly by connection 13 to a filter .14 or partly by this path to the filter and partly by the connection 15 to flotation cells 16 for recleaning. The refloated solids from the cells 16 pass by a connection 17 to the filter 14, the cake from which passes by connection 18 to the repulper 2 where comparatively dilute pulp from the apparatus 1 is utilised to repulp the filter cake into medium of the desired density. If reconditioning is required part of the medium is withdrawn at 19 and can be discharged, the resulting deficit being made up by pulp from the apparatus 1. In general, the proportion of the refloated solids from the cells 16 withdrawn at 19 to the refloated particles returned at 18 would be S 2 /S where S 2  is the aggregate surface of the solids after flotation and S that of the solids of the initial,medium per unit of volume in each case. If the quantity of solids which must be taken away is to be kept as low as possible, the dilute medium for the apparatus 9. 9a is divided, part going to a two-compartment filter 14 and the rest to flotation cell 16, from which part of the liquid passes by connection 17 to the filter 14 and the rest to a reservoir 21 which is allowed to fill up. The medium therein is then examined and the aggregate surface area per unit of volume adjusted either by removal or addition of fractions thus producing a medium which can be returned to the circuit. If the correction was by way of addition only, all the material from the reservoir 21 passes by connection 22 to the filter 14 the cake from which passes to the repulper 2; if the correction was by removal the remainder passes by the connection 22 to the filter and the rejected sizes pass by connection 23 through a compartment of the filter and are then discharged. If an open circuit is used in which only recleaning is required part of the dilute medium for the concentrators 9, 9a passes partly to the filter 14 and partly to the cell 16 from which the solids pass to a filter and then to discharge. Each concentrator 9, 9a, Fig. 2, comprises a pan 24, Fig. 5, with an horizontal portion 25 and inclined portion 26 mounted on a jigging screen 27. The feed is introduced at 28 and water sprays 29 wash the solids which passes into the pool 30. The tails or sunk particles passing over the end of the part 26 on to the screens 27. The dilute medium overflows through a slot 31 into the circuit to the filter and back to the repulper 2. Specifications 507,661 and 547,099 are referred to.