GB2060439A - Apparatus for separating solids - Google Patents

Abstract

An apparatus for use in separating solids comprises an upright vessel 12 provided at its upper end with an inlet 11 and with an outlet 25 for light solids, at its lower end with an outlet 27 for heavy solids, and at a location intermediate the upper and lower ends of the vessel with an inlet 14 for an aqueous washing medium. The vessel is provided with one or more trays 18 which extend across the vessel and are provided with a perforated, downwardly-inclined surface 21 and with one or more downpipes 22. The aqueous washing medium may be pulsed. <IMAGE>

Description

SPECIFICATION Apparatus for use in separating solids This invention relates to apparatus for use in separating solids and, more particularly, is concerned with an apparatus suitable for use in separating from a crude mineral, such as a clay mineral or an alkaline earth metal mineral, a substantial proportion of the solid impurities associated therewith.

Various impurities exist in crude minerals and are undesirable in the finished product for a number of reasons. For example, mica, tourmaline and titania are often associated with kaolinitic clay minerals and they frequently contain iron atoms in their crystal lattice or iron compounds associated with them, and as a result are dark coloured and impair the whiteness of a kaolinitic clay in which they are present; kaolinitic clay minerals may also contain quartz and feldspar which are relatively hard minerals and a kaolinitic clay containing them tends to be abrasive when used as a filler or coating pigment for paper, thus causing wear of paper making or printing machinery; and kaolinitic clay minerals also contain minerals, such as montmorillonite, which may have the property of expanding their crystal lattice in water and thus influence the overall particle size distribution and the particle packing of a kaolinitic clay in such a way that the viscosity of a concentrated aqueous suspension of the kaolinitic clay is increased.

In our copending Application No. we have described and claimed a process for separating impurities from a crude mineral containing them which process comprises forming a deflocculated aqueous suspension of the crude mineral, selectively flocculating either the desired mineral particles or the impurity particles in the deflocculated aqueous suspension of the crude mineral, and then causing the flocs of desired mineral particles or impurity particles to flow countercurrent to a stream of an aqueous washing medium in order to wash the flocs and separate therefrom entrapped deflocculated particles. An important step in this process is the washing of the flocs to separate therefrom the entrapped deflocculated particles.This step is preferably achieved by suspending the flocs in a continuous rising current of an aqueous washing medium having a velocity which is sufficient to convey all the deflocculated particles present, from the finest to the coarsest, upwards and away from the suspended but gently falling flocs, but not so high that the smallest flocs are conveyed upwards. It is an object of the present invention to provide an apparatus which can be used inter alia to wash thoroughly flocs of mineral particles to separate therefrom deflocculated particles.

Accordingly, the present invention provides an apparatus which comprises an upright vessel provided at its upper end with an upper inlet and an upper outlet, at its lower end with a lower outlet, and at a location intermediate its upper and lower ends with an intermediate inlet, the vessel being further provided with means for controlling the flow of an aqueous washing medium to the intermediate inlet and with a tray, or with a plurality of trays arranged above one another, the or the lowermost of said plurality of trays being disposed above the intermediate inlet and the or each of the trays extending across the vessel and being provided with a perforated, downwardly-inclined surface which at its lower extent communicates with a downpipe.

The apparatus of the present invention can be used to perform a continuous countercurrent washing of flocs of mineral particles in order to separate therefrom deflocculated particles. When used for this purpose, the upper inlet of the apparatus of the invention, is supplied with an aqueous suspension containing a mixture of flocculated mineral particles and deflocculated particles. The lower outlet is used for the discharge of the flocculated mineral particles and the upper outlet is used for the discharge of the deflocculated particles. The intermediate inlet is supplied with an aqueous washing medium which flows upwardly through the tray or trays and entrains therein the deflocculated impurities.The lower part of the vessel, including the lower outlet, is preferably constructed in a manner promoting sedimentation and thickening of the flocculated mineral, and to this end it is preferably tapered towards the bottom thereof, for example it can be conically shaped, in order to promote the thickening of the flocs of mineral particles and to facilitate discharge thereof.

It may be advantageous to provide a pulsed rising current of an aqueous washing medium as the pulsing action helps the washing process. The pulsing action can be introduced by using a reciprocating pump to supply and control the flow of the aqueous washing medium to the intermdiate inlet. Most preferably, the apparatus comprises a plurality of stages so that, in use the flocs fall from a higher stage to the next lower stage countercurrent to a rising current of the aqueous washing medium. The aqueous washing medium can be water, an aqueous solution or a dilute aqueous suspension containing particulate solid material.

The apparatus of the invention is preferably constructed so that large flocs of mineral particles are subjected to a thorough washing action and at the same time there can be passed through the apparatus a sufficiently rapid current of an aqueous washing medium to elutriate relatively coarse, but deflocculated, particles.

The upper outlet for the deflocculated particles conveniently comprises an overflow weir which discharges into a collecting trough.

It will usually not be necessary for the apparatus to include more than five trays and for most purposes three are ali that are required. Each tray is provided with perforated inclined surfaces down which the flocs of mineral particles can slide gently without being broken, the number and diameter of the perforations being such that the washing medium is distributed substantially uniformly over the whole cross-section of the upright vessel, or tower, without causing excessive local turbulence which would break-up the flocs. At the lowest region of the inclined surfaces there are provided down-pipes of a diameter such that the flocs can pass freely down them but the rising stream of the aqueous washing medium is unable to ascend through them. Conveniently, each tray comprises a plurality of funnel-shaped members supported in an apertured plate of water-impermeable sheet material.The funnel-shaped members are set in the apertured plate with their widest portions opening upwards and with the upper rim of the widest portions substantially flush with the upper surface of the apertured plate. Each funnel-shaped member preferably includes a conical portion perforated with a plurality of holes of diameter in the range from about 1 mm to about 5 mm. It has been found that it is convenient to provide from about 80 to about 90 holes, each having a diameter of about 3 mm in the conical portion of each funnel-shaped member. Each funnel-shaped member has a downpipe which should have an internal diameter such that an adequate passage is provided for descending flocculated mineral but not so great that the rising washing medium is able to ascend therethrough.The length of the downpipes is such that the hydrostatic head of flocculated material in the downpipes exceeds the pressure drop experienced by the washing medium as it ascends through the perforations.

The length of the downpipe is conveniently in the range of from about 100 mm to about 150 mm.

The internal diameter of the downpipe is conveniently in the range of from about 10 mm to about 35 mm, most preferably from 20 mm to 25 mm. The sloping surface of the funnel-shaped members preferably makes an angle in the range of from 450 to 750 to the horizontal, most preferably about 600. Conveniently, each tray has nine funnel-shaped members each having a conical portion of maximum diameter in the range of from 150 mm to 175 mm. Advantageously, the trays are spaced apart by a minimum vertical distance which allows for uniform distribution of the flocs on each tray. In the case of a tray containing nine funnel shaped members the vertical spacing of the trays should be at least 300 mm.The apparatus described above makes it possible to provide good contact between the flocs and the washing medium without exposing the flocs to any high velocity currents or turbulence which would reduce the size of the flocs.

For a better understanding of the invention, and to show more clearly how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings in which Figure 1 shows a flow diagram of a plant, for carrying out a process for separating impurities from a crude mineral, including an apparatus according to the invention; and Figure 2 shows in cross-section a detail of part of the apparatus shown in Figure 1.

Referring to the drawings, an aqueous suspension of crude kaolin from a previous processing plant containing not more than 0.1% by weight, based on the weight of dry crude kaolin, of a sodium polyacrylate dispersing agent is supplied through a conduit 1 to a mixing tank 2.

There is also supplied to mixing tank 2 through a conduit 3, a solution of a sodium silicate dispersing agent. A stirrer 4 is provided in tank 2 to enable there to be dissipated in the suspension from 5 to 50 horsepower hours of energy per ton of dry crude kaolin (13 to 130 kJ kg-1). The resulting deflocculated suspension is drawn through a conduit 5 by a variable-speed centrifugal pump 6 to the inlet port of which there is also supplied, through a conduit 7, by means of a peristaltic dosing pump 8, a solution of an anionic polyelectrolyte floccuiant which is prepared in a stirred tank 9. The mixture of flocculated kaolin and deflocculated impurities which is thereby formed is passed by the pump 6 through a conduit 10 to an inlet 11 at the top of an apparatus in accordance with the invention.

This apparatus comprises an upright vessel 12 which is constructed in the form of a tower of square cross-section and internal dimension 520 mm x 520 mm with a bottom portion 13 in the shape of an inverted pyramid in order to promote sedimentation and thickening of the flocculated material. Washing water is introduced into the separating vessel 12 through an intermediate inlet 14 which is positioned intermediate the upper and lower ends of the separating vessel 12 just above the top of the bottom portion 13. She washing water is supplied via a conduit 1 5 and its flow rate is controlled by a valve 16 and monitored by a rotameter-type flowmeter 1 7. Four trays 18 are mounted in the separating vessel 12 above the washing water inlet 14.Each tray comprises a square of marine plywood 19 (Figure 2) in which are formed nine circular holes 20 each of which accommodates a polyethylene funnel 21. Each funnel 21 has a diameter at its mouth of 1 65 mm and a straightsided downpipe 22 of internal diameter 22 mm and length 125 mm. The frustoconical portion 23 of the funnel has sides inclined at an angle of 600 to the horizontal and is provided with eighty four evenly spaced holes 24 of diameter 3.5 mm through which the upcurrent of washing water passes. The washing water with entrained deflocculated impurity particles rises to the top of the separating vessel and overflows an upper outlet, in the form of a veir 25, into a collecting trough and then through a conduit 26 to a tailings dam. The flocculated product, consisting of substantially pure kaolin, is discharged through a lower outlet 27 and a conduit 28 at the bottom of the separating vessel 12, the flow being regulated by valve 29.

Claims (10)

1. An apparatus which comprises an upright vessel provided at its upper end with an upper inlet and with an upper outlet, at its lower end with a lower outlet, and at a location intermediate the upper and lower ends of the vessel with an intermediate inlet, the vessel being further provided with means for controlling the flow of an aqueous washing medium supplied to the intermediate inlet and with a tray, or with a plurality of trays arranged above one another, the or the lowermost of said plurality of trays being disposed above the intermediate inlet and the or each of the trays extending across the vessel and being provided with a perforated downwardlyinclined surface to permit the upward passage of a rising current of an aqueous washing medium therethrough from the lower side of said tray to the upper side thereof and with one or more downpipes to enable flocs of solid particles which have passed downwardly over said inclined surface to pass from the upper side of said tray to the lower side thereof.

2. An apparatus as claimed in claim 1, wherein the lower part of the said vessel is tapered towards the bottom thereof and wherein said lower outlet is located at the bottom thereof.

3. An apparatus as claimed in claim 1 or 2 wherein said vessel has from two to five trays.

4. An apparatus as claimed in claim 1,2 or 3, wherein each tray comprises a plurality of funnelshaped members supported in an apertured plate of water-impermeable sheet material.

5. An apparatus as claimed in claim 4, wherein each funnel-shaped member includes a conical portion perforated with a plurality of holes having a diameter in the range of from about 1 mm to about 5 mm.

6. An apparatus as claimed in claim 5, wherein there are from 80 to 90 holes in the conical portion of each funnel-shaped member.

7. An apparatus as claimed in claim 4, 5 or 6 wherein each funnel-shaped member has a downpipe which has an internal diameter large enough for descending flocculated material to pass therethrough but not large enough for a washing medium to be able to ascend therethrough.

8. An apparatus as claimed in claim 7, wherein the internal diameter of the downpipe is in the range of from 10 mm to 35 mm.

9. An apparatus as claimed in claim 7 or 8, wherein each downpipe has a length such that, in use, the hydrostatic head of flocculated material in the downpipe exceeds the pressure drop experienced by the washing medium as it ascends through the holes in the funnel-shaped members.

10. An apparatus according to claim 1, substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.