US3539000A - Classification by flotation - Google Patents

Description

United States Patent [72] lnventor Walter Vogel Santiago de Chile, Chile [2| Appl. No. 668,354 [22] Filed Sept. 18, 1967 [45] Patented Nov. 10, 1970 73] Assignee Bergwer Ksverband G.m.h.l'l.

Essen, Germany [3 2] Priority Aug. 5, 1967 [33] Germany I K 46,656

[54] CLASSIFICATION B Y FLOTATION 20 Claims, 15 Drawing Figs.

[52] US. Cl. 209/3, 209/164, 209/ 168 [51] Int. Cl 1303b 1/00, B03d H02 [50] Field ofSearch 209/162- I65:

[56] References Cited U NITED STATES PATENTS 1,240,824 9/l9l7 Clawson 209/169X 6/1920 w11s6n3.... 209/170 1,375,211 4/1921 COIe..... 209 170 1,420,139 6/1922 Peck 209/165x 2,142,207 1/1939 Price...1 209/l68X 2,189,779 2/1940 Daman 209/168 2,226,170 12/1940 Lasseter 209/165 2,628,827 2 1953 Daman 209/169x 2,653.801 9/1953 Fontein 269/79.lX 2,754,963 7/1956 Krijgsman... 209/12 FOREIGN PATENTS 1,158,461 12 1963 Germany 209/168 Primary Examiner-Frank W. Lutter Assistant Examiner-Robert Halper Attorney acobi, Davidson, Lilling and Siegel ABSTRACT: Improvements in flotation apparatus and flotation methods for sulfide ores and other materials are disclosed. The suspension of solid particles and bubbles is caused to pass upwards through zig zag ducts specially dimensioned so as to ensure optimum conditions for adhesion of the hubbles and particles together. Further improvements include the use of a stirrer with replaceable wearing parts and the provision of diffusors associated with the zig zag ducts.

Patented Nov. 10, 1970 3,539,000

Sheet 1 of 12 INFENTOR Ware/C Vo EL Patented Nov. 10, 1 970 0 I 3,539,000

Sheet 1' o! 12 Patented NOV 1970' I 3,539,000

Sheet i 0 l INVENTOR m lz/mmz M 54 Patented Nov. 10, 1970 3,539,000

Sheet B of 12 Patehtd' Nov. 10, 1970 Fly. 8

Sheet 9 of 12 Patented Nov. 10, 1970 Sheet [Q 01'12 uweuron I flaw/"0x v Patented Nov. 10,1970 I 3,539,000

Sheet [1 of 12 Sec/ion 17. I

INPENTOR All, (a A Mk. V I i @652? Patented Nov. 10, 1970 Sheet b 2 of 12 kmtmbxu i m B tmut mu mmkmwmk INVENTOR The present invention relates toclassification of particles by flotation. One object of the invention is to improve the efflciency of previously known flotation methods, whether they are of thestirrer or air bubble type and atthe same time provide the possibility of reducing the complexity and size of plant used for flotation so asto bringabout a corresponding reduction in capital costs.

Flotation methods used at the present time are practically exclusively stirring methods in which the vigorous turbulence caused by the stirring mechanism coacts with the foamer added toproduce a finely divided dispersion of air bubbles-to which theconcentrate. particles adhere and rise with the foam since the actual adhesion is unsatisfactory because it takes placein a turbulence or eddy zone in the suspension in conditions which are largely a matter of chance, the-retreatment or repetition taking placein a number-of scries-connectedlcomparatively small cells and requiring a complicated subsequent treatment of the foam bed form in order to remove the entrained suspensionparticlesfromit. I 7

Also the-use-of larger cells does not provideasolution to these difficulties in known methods or the unsatisfactory working conditions because in the uncontrollableturbulence zone of the stirring or agitating cell and the-steadying space above it there are'only a few random positions which provide really favourable conditions for the attachment of the solid phase to'the bubbles.

None of 'the known processes takes into account the recentlyobtainedknowlcdgc conccrning the conditions under which thc adhcsion of whydrophobic particle toan'air bubble occurs, that is-to say thefactuthatthis-adhesion only" occurs under certainprecisely defined'kinetic conditions (see the articleby Spetel and'Dedek .Ncue Erkenntnisse aus der Kinetik des Flotationsprozesses" inthe proceedings of the fifthlnternationaler Aufbereitungskongress). g

A further highly significant disadvantage of known, methods is that the apparatus required-more particularly.the'stirring means and thezspacesin whichthey rotate is subjected to an extremely high degreefwear because'the stirring means exert a comminuting action and the coarser particles of the material accumulatingin the stirring space collect and form fine mudlike substances and continue to' be comminuted until the particles are entrained. Evcn'with the use of a so-called free flow system involving-the use of a number of stirrersor agitators in a continuous trou'gh'in which the sand-sized-partitransported so-as to be carried out-with the suspension after passing all stirrers, doinot solve the difficulties.

One object to the, present invention istto provide amethod which avoids all these d'ifficulties, uses only-a few cells, and

can be carried out, in apreferredembodiment with a single cell of compact construction though it hasa correspondingly greater height.-

The prescnt' invention consists in a flotation method comprising, forminga' finely dispersedmixture of air bubbles with suspended solid concentrate particlesby turbulence. causing the'mixture to flows upwards in ac'ell in a number of generally rising guide walls defining rising zigzag paths at whosebends a braking action is'exerted on the flowing material leading to the establishment attthe bends of a'relative speed between the solidparticles and the bubbles-which is optimum for theadhesion of the concentrateparticles onto the bubbles, the particles travelling between'any two such bendsassurning aspeed distance between the guide walls and the distances from one bend to the next. With the arrangement in accordance with the invention optimal kinetic conditions are created for the adhesion of hydrophobic particles on the air bubbles.

A particular feature of the invention consists in the produc- ;tion of the mixture of liquid suspension and foam bubbles, to be treated in the cell in the manner described, by mixing as intimately as possible the liquid suspension and air in a premixing space of comparatively large capacity andthen in this state of admixture to transfer to the central part of the stirring meansin which the mixture is-dispersed by a vigorous turbulence and is put under sufficient pressure to drive it to the flow sections in the cell.

In acoaxial space arranged around the stirring blades of the stirring means, from which the prepared suspension-passes ing ,a higher precipitation speed in the suspension when .quiescent than the vertical componentsof the lowest flows occuring in the adhesion zone. These coarser particles are removed in a tangential direction from the annular space without coming into the cell, and pass into a downstream hydrocyclonev and. are thenintroduced into the grinding device while the overflowfrom the,hydrocyclone is reintroduced into the premixing space. Theaddition of foamer to the mixing spaceupstream on thestirring means is carried out with the -purpose.of producing air bubbles with the required high cles areraised'from onestirrer to another-and thenfurther degree. ofstabilityin thesubatmosphericpressure zone over the airdraw-inpipe of the mixing chamber and thus ensure the formation of the air bubbles in a foam sheath under subat- 1mospheric pressure protecting them against bursting after reaching the surface.

In a preferred embodiment of the form of the invention as justdes'cribed, the guiding walls to which the flow sections .pass in the 'cellhave a slope, length, distance between adjacent bend points in the flow path, and ,wallrto-wall distance such that onzthe emergence of the dispersion containing the foam 'thebends in the flow with substantially those speeds which they had on'leaving the preceding bends in order to emerge finally from the guide walls with this same speed, which is only a fraction of the speed of bubbles in known cells, and reach the surfaceof thesuspension where, in accordance with a vfurther feature of the invention to be described, below the separation of the suspension from the foam bubbles loaded with concentrate particles occurs.

.A particularly important feature of the method ,in accordance withthe invention residesin the manner of introduction o'fkt-he flow sections emerging from the stirring means under the pressure of the cell through a number ofducts .which define paths leaving the annularspace above the cell, .intothe lower part of the cell so as to be distributed over the whole cross section amongst a numberof diffusorlike devices 1 which. are present-in a number corresponding to the number of guide ducts formed in the cell and into which the correspondtling ofany particles greater than the maximum allowable size,

- entrained inthe suspension flows, are created in the diffusors.

A further possibility for separatingsuch oversize particles which happen to have been introduced into the guide channels is provided for by forming intermediate channels between the partitions which delimit the flow sections in the cell and open into the bend positions; any oversize particles present or settling at the bends are led away into the diffusor devices. These possibilities for separating oversize particles are of especial importance if, as is in principle made possible by the new method, the suspension contains intergrown particles.

The favorable kinetic conditions created by the guiding of the suspension flows in the cell and the consequently optimum exploitation of the space available in the cell make it possible to use less cells than in known methods, possibly in a single, correspondingly dimensioned cell in which final concentrate is obtained directly.

For economizing in space it has been found, more particularly in the last-named case, and also for facilitating access to the stirring means which on account of the necessarily high resistance to wear the stirrer is preferably like an armored pump, to arrange the stirring means not in the customary manner within the lower part of the cell, which would lead to the stirring means shaft passing through the cell requiring internal fittings in the. cell, which would be disadvantageous for the formation of flow sections, but instead at a suitable position as regards height in relation to the lower zone of the cell beside the cell.

In accordance with a particular feature of the invention the subsequent treatment of the flows of suspension loaded with foam and emerging from the zigzag-shaped passage channels at the upper end of the cell is carried out in such a manner that all the flow sections are made to flow horizontally in a joint flow whose length is sufficient to ensure the complete separation of the froth or foam bubbles from the suspension and thus the formation ofa foam bed covering the horizontally moving suspension and carried on it. For this purpose the suspension flow is caused to pass over the surface of a Spitzkasten or box classifier, or preferably a row of such chests arranged one behind the other, through which in each case the lower layers of the suspension current flowing over them are drawn off. In order to free the foam, after it has been separated from the greater amount of the suspension, finally from any remaining particles from the suspension between the foam bubbles without adhering to them, the foam or froth bed is caused to flow further on a thin residual suspension layer over an adjoining water Spitzkasten and during this travel is subjected to the action of a fine spray. In this Spitzkasten any concentrate particles which are washed by the spray from the foam bubbles or have been released owing to the bursting of bubbles are caught and conducted away for repeated treatment. At the end of this travel a completely pure foam is obtained which does not require further subsequent treatment and contains the concentrate.

The one or more Spitzkasten communicate with the cell, that is to say the level of the liquid in them is the same as in the cell.

By carrying out the new method in a battery of cells the yields of the first cells of the battery, possibly in circuit with a basic grinding mill, are fed to a subsequent comminuting means grinding to a greater degree of fineness, while the yields of the following cells of the battery are only fed to the comminuting means after thickening and separation of the finest slurries, and both types of yield are then floated in cells whose cyclone outlets after passing through a thickening means are fed back in circuit with the second mill, the foam removed being delivered for subsequent cleaning at a suitable position in the battery, preferably the penultimate cell in it.

Details and further features of the invention will be gathered from the following particular description of a flotation installation for carrying out the new method, with reference to the accompanying drawings.

FIGS. la represent a diagrammatic partial vertical section showing a whole installation with the features of the invention and, in order to simplify the description, with only one cellwhich is more particularly suited for the flotation of sulfide ores, without there being any intention to limit the invention to this particular embodiment.

FIGS. 2a-2b show on a scale larger than that of FIG. I the installation for producing the suspension charged with bubbles and the part of the installation for introducing the suspension into the flotation cell.

FIG. 3 is a partial section in accordance with the broken line A-B of FIG. 2 and shows a construction of the diffusors.

FIG. 4 is a horizontal section in accordance with the line C- D of FIG. 2 showing the removal of the coarse particles from the annular space formed in the stirring means.

FIG. 5 is a perspective view, partially in section, of the premixing arrangement from which the material passes to the stirring means, in order to show the internal fittings, of which only one is shown in the FIG., ofthe premixing arrangement.

FIG. 6 is a horizontal section in accordance with the line E- F of FIG. 2 showing the introduction of the suspension flows into the premixing space.

FIG. 7 is a vertical section on a larger scale showing the construction of the zigzag-shaped partitions guiding the flow sections.

FIG. 8 is a view, partially in section, taken in the direction of the arrow of FIG. 7, of the partitions.

FIG. 9 is a section on the line lI-II of FIG. 7.

FIG. 10 is a view similar to that of FIG. 7 showing a different form of the partitions.

FIG. 11 is a view corresponding to that of FIG. 8 showing partitions in accordance with FIG. 10, also in the direction of the arrow in accordance with FIG. 10.

FIG. 12 is a flow diagram of an installation embodying the process in accordance with the invention for the flotation of sulfide ores, operating in two stages of which each comprises two cells connected in series.

The main units of the installation shown in FIG. 2 include the flotation cell, denoted by general reference a, a unit b, which in accordance with the preferred embodiment ofthe invention shown is not below the cell a but beside it, for preparing the finely dispersed mixture of suspension and foam bubbles, and the unit c for subsequent treatment of the foamsuspension mixture.

The installation consisting of these main units will now be described in an order corresponding to the course of the classification process taking place in the installation.

Reference numeral 1 denotes a rod mill which receives a comminuted water-containing material to be treated, of a suitable pregrain size, for example an agglomerated sulfide ore. The outlet of the rod mill is connected with a stirring mixer 2 in which the collector and collector-foamer reagents are applied and in which the material, comminuted in the rod mill to a grain size of for example 0.6 mm. is introduced preferably through a number of ducts 3 into the premixing space or chamber 4 whose construction is similar to that of an air cyclone and which is provided with internal fittings 5 which serve for distributing the air in the suspension and are described in more detail below with reference to FIG. 5.

A supply duct 6 opens centrally into this premixing space or chamber and serves for introduction of air which is to be beaten up with the suspension and which contains a mist of foamer, supplied by a container 8, the mist being formed by an atomizing device 7 which may be automatically controlled by the device 101.

In accordance with a particular feature of the invention the quantity of air introduced into the duct 6 by the action of the vacuum or suction produced by the stirrer is controlled in accordance with pulses delivered by a measuring device automatically in such a manner that the quantity of air is held constant or a particular degree of vacuum is held constant.

In order to prevent an uncontrolled entrainment of air by the flow sections which fall freely into a tubular duct, in accordance with the invention there is an increase in cross section in the relevant tubular duct above and below the level of the surface of the suspension in the duct. This increasing cross section is such that the speed of the sinking suspension has a vertical component which is below the speed of a rising air bubble after the first centimeter in the stationary suspension.

In consequence the entrained air rises again and can escape overflow of one cell into the mixing space of a subsequent cell.

As can be seen from FIG. 1, the means for atomizing the foam er into the air is arranged at the same height as the working platform from which both the flotation cell and the subsequent equipment can be observed.

In a position which is coaxial in relation to the premixing device 4 below the narrowing lower end of the latter there is a stirring device 9 which is driven below and is constructed in a manner similar to an armored pump. This stirring device includes an annular space It) arranged outside the stirring parts and from which the suspension formed can pass through a number of outlet openings two sets each of eight openings being shown inthe'drawing, in an upward direction, while the coarse particles coming against the wall of this annular space owingto'centrifugal force are passed through ducts 10 which leave the annular space in a tangential direction, to a pump cyclone 13 from which they pass via a return pump 14 and a duct 15 back into the rod mill l,while the overflow from the cyclone is passed to the premixing space again for repeated treatment. y

Connected with the outlet openings 11, I provide a corresponding number of flexible single ducts 16 each of which leads to a diffusorlike housing upstream from the cell a. These housings are distributed evenly over the bottom of the cells. The diffusor action of these devices brings about a reduction in the flow speed of the suspension to a value lying below the largest particle-settling speed in the cell. In these diffusors there also occurs a separation of the overlimit particles which are fed through th'e'bottom ends of flexible pipes or hoses 18, whiehopen into a common duct 19, and then, in accordance with the cmbodimcntshown, pass to one or two cyclones 20 for the first or single cell whose'lower outlet passes, as can be seen from the FlG., to the pump 14, while the overflows of these cyclones are fed to the premixing spaces of the cell for repeated treatment.

The obliquearrangement of the diffusors as a whole in a chest-shaped box is necessary in order to obtain the greater cross section required for reducing the flow speed, and also is advantageous as regards the precipitation of the overlimit particles sliding downwards against the lower walls of the diffusors.

Each of the diffusors opens into zigzag-shaped ducts, formed by correspondingly shaped internal fittings 21 in the flotation cell, to a cross section range corresponding to the crosssection of the diffusors and, if required, widening at a small angle so as to reach a highercross section than the cross section of the diffusors.

The parts of the cells lying to thesides of the outermost internal fittings 21 do not carry any flow and are only necessary for reasons of mechanical rigidity.

The internal fittings and the channels they form end in the upper part of the cell a at a sequence of different levels corresponding with an oblique plane so that the foam-suspension mixture flows emerging from the channels lie one above the other in the jointflow formed when, as can be seen, they are diverted at right angles. This common flow moves in a horizontal direction, as shown in FIG. I, over Spitzkasten 22, of which inthe example only one is visible, and whose tapering outlet'ducts 23 pass around the cell and are connected by means of flexible pipes 24 in an overflow whose height can be adjusted by means of a handwheel 26. This overflow 25 runs to repeated treatment. The settled coarse material in the lower part of the Spitzkasten is introduced into the duct passing from the diffusor devices 17 to the cyclone 20 or conveyed in any other suitable manner for repeated treatment.

The Spitzkasten 22 is connected in the direction of flow of the foam-suspension mixture, which during passing through the liquid level of the Spitzkasten is decomposed into foam and suspension, with a pure water Spitzkasten 28.

Above the foam bed formed above the suspension flow and extending from the outermost zone of the cell, there runs an endless chain band provided with entraining blades which extends as far as the end of the Spitzkasten or thesubsequent foam removal trough or gutter 29 from which the foam passes through the concentrate thickener 31. The band 30 moves with a speed which in the case of a sulfide or similar flotation operation amounts to about 50 to 60 percent of the speed of the suspension flow and brakes the foam bed on the suspen sion flow. In the zone of action of this band I provide at a convenient position for spraying of the foam bed with water for the purpose of washing away suspension held between foam bubbles. This spraying operation is not shown in the drawings.

Witha speed of the flow or stream of 13 cm./sec., 72 seconds are available for the cleaning of the foam in accordance with the embodiment illustrated, this being quite sufficient to wash a foam layer 20 cm. thick.

In the caseof flotation operations in which the greater part of the material comes into the froth or foam, for example in the case of the flotation of coal or in an oxide flotation, it is convenient to arrange for the speed of the chain band to be somewhat greater than that of the horizontal flow in order to prevent an excessively thick froth or foam bed being formed. In such cases, however, the length of the foam bed must be increased by the arrangement of two or more Spitzkasten.

It can also be advantageous to construct the guiding rails of the chain hand with the blades in such a manner that the blades move upwards and downwards somewhat so that there is a certain mechanical action on the foam bed in order to 1 favor separation of suspension from the foam.

' ever, from known armor pumps in that the header space 10 into a funnel 27 from which the suspension is either removed i from the installation entirely or, if required, is supplied to a subsequent further cell. If required, the adjustment of the height of the overflow can be controlled automatically in accordance with the level of the suspension above the outflow.

The oblique internal fittings visible in the drawing in the upper part of the Spitzkasten serve to facilitate the removal of any intergrown particles still present which are to be subjected formed outsidethe stirring parts is shaped to form a widened annular space and the external generally upright wall is arranged so as to define apassage of upwardly decreasing cross section. Connected with this space, I provide a number of flexible ducts joined up by means of elbow connections 32 whose number corresponds to the number of connecting ducts 16 leading to the cell.

With this construction of the stirring device the initially mentioned preseparation of the coarsest particles of the suspension occurs at the outer lower wall of the annular space 10 and this coarsest part is then led away to the cyclone 13 by means of the tubular duct 12 leaving the annular space tangentially, as can be seen in FIG. 4.

As shown in FIG.- 5, the premixing space 4, which is basically of cyclonelike shape, and which serves to supply the stirring device, is provided with an intermediate funnel part 34, in

addition to the internal fittings 5 in its lower funnel-shaped.

meral 36 in FIG. 5. Of these hollow bodies three are supplied from the overflows of the three cyclones provided a further one is supplied from the water Spitzkasten and the remaining two are provided from the stirrer mixer.

'Ihese spiral-shaped internal fittings are each provided with a through longitudinal slot 33 whose lips or borders overlap. The cross section of these slots narrows in a downward direction so that it causes an increase in pressure in a downward direction in the suspension flows they carry and there is a jetting or spraying of the suspension through the slots 32 into the air introduced through the central duct 6 into the space. As a result there is an atomization of the suspension in the air and a simultaneous entrainment of air into the lower part of the premixing contained, whose middle part, as is shown both by FIGS. 2 and 5, at first only contains air. Owing to the construction of the outlet slots so that their borders overlap, as is more particularly indicated by reference numeral 38 in the bottom part of FIG. 5, the suspension emerges from the top surfaces of the internal fittings into the air filling the premixing container in the form ofa thin veil. The ribs 37 shown in FIG. 5 inside the overlapping part serve to give the suspension emerging from the slots a tangential component of movement in the premixing device itself, this movement being in the same direction as the direction of rotation of the stirrer.

From the openings of the tapering spiral bodies there therefore emerges only a comparatively small part of the suspension flow entering.

The manner of supply of the suspension by the stirring device at a suitable pressure into the Cell a and the Construction of the diffusors leading to the cell is shown in detail in FIGS. 2 and 3.

The diffusors which as a whole form a box-shaped body which is oblique in relation to the cell for the above mentioned reasons, are connected in accordance with the particular embodiment shown with l6 flexible ducts 16 coming from the stirring device, and are each provided with a passage 39 placed in accordance with the upper side of the diffusor in accordance with the oblique setting and separated by a partition from the remainder of the diffusor, each such passage broadening out in an upward direction to the full breadth of the channels formed in the cell by the guide walls 21.

These passages open at a level about half way up the diffusor body into the free upper space of the latter, the upper wall of the latter preferably being provided with internal bulges which maintain the rising speed of bubbles in the suspension within the desired limits. To the side of each of the passages 39 I provide thickening spaces 41 in which the overlimit particles settle so that they can pass through the previously described flexible ducts 18 into the common collecting duct 19 leading overlimit suspension particles away for retrcatment, regulating nozzles 42 being arranged upstream from the openings ol the ducts 18 into the collecting duct 19 to make possible an adjustment in the amount of suspension returned with overlimit particles.

The construction of the two sets of eight zigzag guiding channels provided in the embodiment of the invention described is shown in FIGS. 8 and 9 and FIGS. 10 and 11 in two different forms.

The zigzag-shaped walls 21 delimiting the channels are provided with a slope of approximately 60 in the case of a construction using only one cell, as is required also in the connection ofa stepwise connection for the first flotation stage.

In the case of a number of cells connected in series this slope can be decreased to 50 so that with the same height of the construction of the cell a greater number of bends is obtained. The drawings show this latter construction with a slope of50.

As is shown in detail in FIGS. 7 and 8, the partitions 21 are made up of sheet metal sections 43 welded together at the bends and having ribs 44 at their ends serving for holding plate-shaped specially profiled guiding bodies 45 preferably made of a plastic which is both oil repellant and is completely impermeable, for example of plexiglass. The sides of these plastic plates facing the guiding channel can be seen from FIG. 7 to be flattened in an arcuate manner from 50 to about l5 and have pronounced grooves as shown in FIG. 8 in order to exert a braking action on the bubbles passing along them. The flattening and the grooving together result in a reduction in the cross-sectional area. A particularly profiled bulge on the lower edge of the next higher plate reinforces this action. FIG. 7 shows how the limited eddying is produced in the dispersion by the widening 47 to the full width of the guiding channels. The rising bubbles have to pass through this eddying and as a result the air bubbles are provided with every opportunity providing for favorable conditions for adhesion on the solid phase since the whole zone is maintained within optimum kinetic parameters.

To provide for improved guiding of the flow it is possible to provide the guide bodies 49 and 50, both made of the same plastic as the plates, on the groove of formations at narrow position 46. The guiding body 50 has the purpose of producing a return eddy downwards about itself in order to keep the lower end of the partition 2] clean.

The plates 45 exposed to wear are constructed so that they can easily be replaced. This is due to the fact that the cells can easily be inserted from the side after one or both side walls have been removed. This can be carried out without difficulty because each cell can stand alone at a distance from the following cell. In the case of narrow cell constructions the plates used for stiffening the cell chests are inserted from one side over the whole breadth of the cells. The other side of the cell chests can then be constructed in a reinforced manner. In the case of broader cells on the other hand a correspondingly strongly constructed central partition wall must be used for stiffening the chest, possibly with the use of a removable cover.

In the case of the construction shown in FIGS. I0 and II, the plates forming the restricted or narrowed zones is the same as in the arrangement shown in FIGS. 7 and 8 but between the individual channels double partitions 21', 21" are provided which are spaced apart so as to leave passages between them which, as shown in FIGS. 10 and II, are provided with guiding ribs 51 and are connected by openings 52 with the interior of the guiding channels. Overlimit particles settling in the region of the bends are separated and slide down in the channels between the partitions 21, 21" so that they pass into the coarse section of the associated diffusor from which they pass away for repeated treatment. These ribs run obliquely downwards so as to diverge from the center and as a result the settling material is diverted to the side so that it comes into the region of the lateral walls of the diffusor.

The flow diagram ofa flotation installation as shown in FIG. 12 operating in accordance with the method of the invention should only require a short description in view ofthc explanations already given. The diagram is of an installation for the flotation ol'materiul dealt with in steps and therefore operates in two steps. Each of the steps or stages comprises, as can be seen from the diagram, two cells connected in series, as opposed to the embodiment of the invention described above. Each of the cells has the same features though the rate of removal of materials is varied and in the second flotation stage all the discharged material from the first stage requiring repeated treatment, or appearing to be worth subjecting to repeated treatment, is treated as an intermediate step.

The main advantages of the method in accordance with the invention, which have been in part emphasized above, include not only the construction of the cells so as to provide for con ditions for the optimum adhesion of a hydrophobic particle on an air bubble, but also that in each case, even in the case of finely or closelyagglomerated ores as a consequence of the fulfillment of these requirements, it is possible to use a small number of cells and there is a concomitant reduction in the number of mills or other apparatus for comminuting the material finely. The constructional measurements of the whole installation brings with it in every case more economy in space than with known installations and there is a substannecessary to change some dimensions of the cell, to make adaptations to the relationship between the foam or froth and the parts of the material discharged. Moreover, in the case of installations with several cells several different types of circuits can be provided. This feature and the ease of adaptations as regards dimensioning, especially as regards the subsequent Spitzkasten for the suspension, particularly as regards the length and speed of the chain band, open up many versatile possibilities of application of the new method in accordance with the invention,

lclaim:

1. In a method for separating particulate material, comprising'forming a finely dispersed mixture of air bubbles with suspended solid concentrate of particles by turbulence, causing the mixture to flow upwards in a cell in a number of generally rising guide walls defining rising zigzag paths having spatially limited'eddy zones at whose bends a braking action is exerted on the flowing material leading to the establishment at the bends of a relative speed between the solid particles and the bubbles which is optimum for the adhesion of the concentrate particles onto the bubbles, the particles travelling between any two such bends assuming a speed before they reach the upper of the two bends equal to that speed which they had at the lower of the two bends, and the bubbles crossing spatially limited eddy zones at the bends owing to their upthrust, said spatially limited eddy zones being defined by said guide walls bearing profiled bodies which are equipped with arcuate surfaces at their sides facing the suspension.

2. A method according to claim 1 in which the relative speed between the air bubbles and the solid particles in the suspension on leaving the bends is maintained at a value of from about 3 to l5 cm./see., independently of the height of the cell.

3. Ina flotation cell for the classification of solid particles a structure which comprises: zigzag-shaped radial guide walls connected with walls of the cell and arranged at an equal distance between them so as to form guide channels for upwardly flowing currents of suspension and air bubbles, said channels'being. formed by internal fittings, the distance between bends of the zigzag walls, the slope of the zigzags and the distance from one partition to another being such that flows which are braked at one bend to a relative speed between air bubbles and the particles contained in the suspension which is optimum for the attachment of concentrate particles to the air bubbles, assume that'speed on their travel to nular space, means defining a space outside the zone of these outlets, duct means leading to a hydrocyclonetangentially, directed towards the annular space and leaving the second mentioned space tangentially; and a flexible duct connection with the premixing space of the cell, this flexible duct serving to supply the overflow of the hydrocyclone'of the cell for the purpose of repeated treatment, while the lower flow from the cyclone is returned by means of a pump associated with the cell and pump ducts to grinding means.

6. An apparatus according to claim 5 further comprising: a premixing device having free internal space in the form of an air cyclone whose output is connected with the stirring device; and tubular longitudinally slotted bodies having internal fittings forming tapering spirals, arranged evenly in a peripheral direction and mounted in the premixing space, each such internal fitting being connected with a suspension supply duct and said premixing device further including an air supply duct, said air supply duct having an opening centrally into said premixing device wherein a quantity of air containing foamcr mist is introduced.

7. An apparatus according to claim 6 in which the borders of the slots of said tubular longitudinally slotted bodies provided with tubular internal fittings, open into the free internal space of the premixing device and are so shaped that the suspension from them flows in a direction tangential to the tubular internal fittings in the form of veils into the free internal space of said premixing device.

8. An apparatus according to claim 6 further comprising,

' adjacent to the opening of the air supply duct to the premixing device, an automatically controlled atomizing device for foam introduced into the air stream.

9. An apparatus according to claim 6 further comprising a device for automatically controlling the quantity of the air introduced into the mixer by the subatmospheric pressure produced by the mixer for the purpose of achieving a is widened in a zone which includes a sufficient length above as well as below the corresponding suspension level in the tuthe next higher bend which they assumed at the preceding bend; diffusorlike means arranged below the bottom of the cell evenly and associated with the radial guide walls which bear guiding channels, the diffusorlike means being arranged to conduct the air suspensionmixture to the guide channels and to reducethe entry speed of the air-suspension mixture fed to them incorresponding flow sections to a speed which is less than the lowest speed existing in the cell; and said radial guide walls arranged to maintain an even air bubble distribution in the cell.

4. An apparatus according 'to claim 3, wherein guiding bodies are present in the guide channels for the agitation of the partial suspension flows. t

5. An agitation flotation apparatus comprising: a cell according to claim 3; a stirring means from which flow sections in a number corresponding to the number of guide channels are supplied to thediffusorlike devices; means defining an annular space outside stirring blades of the stirring means, outbular body, to such a cross section that reduction in the vertical component of the downward speed of the flow section is brought about below the upward speed reached by an air bubble after the first centimeter of travel in quiescent suspension.

11. An apparatus according to claim 6 in which said internal fittings of the cell forming the guide channels are so staggered as to height in the top of the cell that the individual flow sections of suspension and foam bubbles are caused to flow horizontally forming a joint flow, and Spitzkasten means communicating with the cell are joined with the cell, the joint flow being arranged to pass over the Spitzkasten means said Spitzkasten defining means by which the settled coarse material of the suspension flow are drawn off and subjected to repeated treatment in said premixing device.

12. An apparatus according to claim 11 further comprising an endless foam transport band provided with blades and arranged to move at a different speed to the speed of the suspension of flow.

13. An apparatus according to claim 12 comprising rising and falling rail guide means for causing blades of the band to move upwards and downwards in the foam.

14. An apparatus according to claim 6 in which the diffusorlike devices arranged to deliver material to the cell each have a Spitzkasten compartment for the separation of overlimit particles and these compartments are connected via a regulating nozzle and a common duct with a joint supply duct for conveying the suspension containing overlimit particles back to the premixing space for repeated treatment.

15. An apparatus according to claim 14 in which the joint supply duct for conveying material for repeated treatment is connected with a hydrocyclone whose overflow is connected 18. An apparatus according to claim 17. wherein the arcuate surfaces are serrated.

19. An apparatus according to claim 18 wherein the passage ducts' for receiving and removing the overlimit particles are formed by doubling the guide walls.

20. An apparatus according to claim 19, wherein the passage ducts are equipped with guide ribs which extend obliquely downwardly and which deflect laterally the overlimit particles.

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