US2259243A - Flotation apparatus and method - Google Patents

Description

0ct.`1'4, 1941. A. c. DAMAN FLOTATION APPARATUS AND.` METHOD Filed Feb. 5, 1938 v 3 Shee'bSf-Sheet l u lll p al E ATTORNEY.

Oct. 14, 1941. A. c. DAMAN FLOTATION APPARATUS AND METHOD Filed Feb. 5, 1938 3 Sheets-Sheet 2 I INVENTOR Af? THU/ C. DAMA/v ATTORNEY.

3 Sheets-Sheet 5 INVENTOR ARTHUR C DAMA/V WORNEY.

A. C. DAMAN Filed Feb. 5, 1938 FLOTATION APPARATUS AND METHOD Oct. 414, 1941.

Patented Oct. 14, 1947.1

FLoTA'rIon APPARATUsAND METHOD Arthur C. Daman, Denver, Colo., assigner to Mining Process and Patent Company, Denver, Colo., a corporation of Colorado Application February 5, 1938, Serial No. 188,872

21 Claims.

This invention relates to apparatus for and methods of froth flotation, and more particularly relates to improvements in agitation and aeration in such a process.

It it a primary object of the invention to inan intimate intermixture of solids, gas and ref agent in a zone of agitation while controlling the discharge of -such intermixture from the agitation zone into a zone of separation.

A further object of the invention is the provision of a novel type of agitation in a otation cell induced by the action of a plurality of impeller elements rotating in opposed relation within a restricted zone.

Still another object is the provision of a novel method of recirculating valuable constituents, suspended in the pulp liquid below the froth body, through the agitation zone of the treatment.

Other objects reside in novel combination-s and arrangements of parts, and novel steps and treatments, all of which will appear more fullyin the course of the following description.

In the froth notation process, ore in finelydivided condition is agitated in, liquid in the presence of air or other suitable gas, while being subjected to the action of a reagent having a selective ainity for one or more ofthe mineral constituents. The finely-divided gas bubbles carry the mineral so treated to the surface where it collects in a froth and. is removed as a concentrate.

Since the gas is the elevating medium'of the tact with the greatest possible mineral surface.

To this end, the mineral and reagent are frequently mixed in advance of the flotation treatment, although in many operations it will be` of a zone of compression in the agitation stage, through which mineral and reagentare circulated in the presence of the gas of the treatment. As a result of such compression, large quantities of gas are entered into solution, and because of the agitation a thorough and intimate intermixture of solids and liquid is obtained.

Thereafter, the compressed material is discharged into a zone of separation maintained underatmospheric pressure, and the pressure differential between the zones ofseparation and compression causes the dissolved and entrapped gases to rise through the liquid of the pulp to the surface.

The mineral to be recovered is surface coated in the compression zone by the gas-reagent liquid and the subsequent pressure release creates a wide diffusion of gas rising as bubbles, many of which form, in surface contact with the mineral, while others during their ascension are in such close association as to exert a sweeping action on substantially all suspended mineral particles in the separation zone, with the result that the notation reaction attains a high degree of efficiency. Y

Some of the mineral particles in suspension will be lacking in suflicient contact with the reagent to be carried into the froth, and provision is made for retreatment of this material by recirculating the same through the compression zone where it is again subjected to the intimate intermixture with the gas and-reagent.

Because of the Widespread diffusion and iine size of the gas bubbles rising through the liquid, the aeration of the present process is relatively gentle, and little, if any, of the mineral being elevated or held in the froth is subjected to any jarring inuence suicient to break the surface tension and permit descent of the mineral.

As a result of the action aforesaid. a high degree of separation will be attained in a relatively short operating interval, thereby increasing the -treatment capacity of a machine of a given size.

While the treatment aforesaid may be incorporated in a variety of apparatus, certain essential features will of necessity be incorporated in any such structure, and to illustrate the operation, as well as to give a better understanding of such essential features, reference will be made to the accompanying drawings, inwhich apparatus adapted for performing the invention has been illustrated. y

In the drawings, in the several views of which like parts have been designated similarly,

Figure "1 is a plan view of two cells of a multicell otation machine embodying features of the present invention;

Figure 2 is a section taken approximately o the line 2-2, Figure 1;

Figure 3 is a plan view of another embodiment of a flotation cell of the type illustrated in Figures 1 and 2; y

Figure 4 is a section taken approximately on the line 4-.I, Figure 3;

Figure 5 is a plan view of a modified type of a flotation cell;

Figure 6 is a section taken approximately on the line 6-6, Figure 5;

Figure 7 is another embodiment of a flotation cell of the type illustrated in Figures 5 and 6;

. Figure 8 is a fragmentary section, taken along the line 3 8, Figure 7; v

Figure 9-is another embodiment of a flotation cell of the type illustrated in Figures 1 and 2;

Figure 10 is a section taken approximately on the line III-I0,'Figure 9;

Figure 11 is a diagrammatic representation of one form `of impeller operation employed in a .cell of the type illustrated in Figures 5 and 7;

Figure l2,is a diagrammatic representation of another form of impeller operation employed in a cell of the type illustrated in Figures 5 and 7;

Figure 13 is a diagrammatic representation of an arrangement of open-type impellers intended for use in a cell ofthe type illustrated in Figures 5 and 7; and i Figure 14 is a diagrammatic representation of an arrangement of another type of open impellers intended for use ina cell of the type illustrated in Figures 5 and 1. l

Referring rst to the'apparatus illustrated in Figures 1 and'2, the reference numeral I5 indicates a tank, divided by suitable partitions I6 and I6a into a plurality of flotation cells I1.

Each cell has one of its sidesterminating at its The waus or partitions Isa of each of theY cells are slotted as indicated at I9 to provide a Weir discharge for such cell, and a suitably mounted gate-member 26 is slidable along the walls I6 a, `to vary the effective elevation of the discharge outlet I9. Preferably such gates are The structure thus far described is typical of the well-known Denver Sub-A flotation machines, which illustrates the adaptability of the present invention to conventional constructions.

In the present construction, a plurality of impeller-elements 25 are carried on suitable shafts 26 and disposed at a substantially uniform distance from the bottom of `each cell I1, and preferably in 'proximity thereto. of the invention illustrated 'in Figures l and 2, three impellers are so mounted, with their shafts defining a triangle to vposition adjoining peripheral surfaces of the impellers in close proximity.

A cover-element 21 supported on baffles 28 in superposed relation to the respective impellers 25 is preferably of disk-shaped contour of a size slightly greater than the combined spheres of rotation of the impellers 25, and has a iianged rim 29 extending lower in the cell than the bottom edges of the impellers 25.

The upper and lower surfaces of the coverelement 21 are suitably apertured as indicated at 30 and 30a to admit the respective shafts 26, and if desired, rubber or other erosion-resisting sleeves 3| may be mounted on the shafts 26 where they enter the openings 30 to prevent excessive wear.

Interconnecting passages 32 extend laterally in Iconverging relation from the shaft-enclosing portions of cover-element 21, and the upper surface of element 21 is apertured at the point of convergence to admit a hollow column 33, which extends above the liquid level in the cell and is provided at its upper end with a capor closure 34, slidable thereon, and acting as a valve to control air passage therethrough.

The column 33,- intermediate its ends, is apertured as indicated at 35 in this form of cell, and a valve-controlled branch A36 extends from the column upwardly in the cell above the liquid level.

screw-actuated, although any satisfactory means l of level regulation may be employed.

An open-ended casing 2| fixed on each wall I6a extends from an elevation above the maximum froth level to a point well below the same f and defines a discharge passage to the Weir overow through which tailings are removed from the cell while effectively preventing escape of froth other than across overflow lip I9.

A sand relief hole 22 is provided in each wall cell of a multi-cell machine other than the first cell.

A its upper surface a plurality of blades 39, either A feed. i-nlet 31', preferably in the form of a conduit, fittedin an opening 38 in cover-element 21 delivers incoming feed to the impellers 25 in each of the cells I1, the conduit 31 of the first cell of a multi-cell machine, or of a unit cell being connected with a suitable supply conduit for this purpose, while the second and subsequent cells of a multi-cell machine are supplied by the passages 23.'

To distinguish the cells I1. in the machine of Figures 1 and 2, the first cell has been designated A, while the letter B has been used to designate the second cell, which letter maybe used also to designate any subsequent cells.

In cell B of Figures 1 and 2,y a slightly different form of cover-element 21 from that shown in cell A is employed to permit use of a different type of impeller-element. yThe impellers 25a of this cell are formed by a dished plate 40 carrying on upright or disposed at an inclination to elevate matter acted on during their-rotation.

The cover forthis type of impellercomprises three conical hoods 4I joined by --a triangularlyshaped central portion 42 apertured to admit a column 33 and associated parts, but having no openings corresponding to the openings 35 of cell A. InV addition, discharge ports 43 are provided at the peripheries of the hoods 4I adjacent the periphery. of the dished surfaces 40. Unrestricted communication between the impellers 25ais providedby elimination of the passages 32.

In operation, pulp and reagent are fed into cell In the formy A through the inlet 31, and descend onto the impellers 25. At the same time, air or other gas, under pressure, is admitted through valve-controlled jets 44 into the zone of influence of the impellers 25, and the rotation of the impellers causes violent intermixing of air, reagent and pulp dueto impinging the discharge of the several impellers in a common restricted zone under the resulting centrifugal influences.

As a result, a portion of this material rises from the irnpinging streams and enters the passages 32, being returned thereby to the impellers 25. The annular baille 23 so restricts the, discharge of the impellers that the intermixture aforementioned is compressed, causing large quantities of the gas to dissolve in the liquid. The compression forces the intermixturethrouh the passages l! into the column 33 where it finally discharges through the openings 35.

I'he release of pressure on the compressed matter so discharged, permits the dissolved and entrapped gas to rise to the surface in the form of finely diffused bubbles and these 'bubbles by reason of their intimate association with the mineral constituents oi the pulp and the reagent carry the valuable constituents tothe surface where they collect in a froth and are moved across the overflow lip I3 in any suitable manner (not shown).

It will be appreciated that the action of the rotary impellers .withinthe compression zone brings gas, pulp and reagent into frequent and intimate association, and by reason of the delayed passage of material from said zone as a result of the restriction of the discharge and the recirculating influences, the intermixture rising in column 35 contains mineral particles effectively coated by the reagent and intimately associated with the gaseous medium by which they will be elevated after the pressurerelease.

Thenon-floated solids in cll A discharge over Weir I9 or through the sands relief outlet 22, and are subjected to further -mixing in the passage 23 due to the cascading action. The material after mixing enters inlet 31of cell B and passes .under the hoods 4| to be acted onby the impellers 25a.

This material is then subjected to further mixing with air or other gas. By regulating the position of the cap 34 and the valve in branch 36,' the amount of air under pressure admitted to column 33 may be controlled, and this air after passage through the column discharges beneath the hood 42, where it is subjected to the action of impellers 25a.

At the same time, additional reagent may be introduced fo`r mixing, and if desired this reagent also may be fed to the mixing zone through branch 36 and column 33, or otherfise. In any event, reagent carried in the pulp from the preceding cell will be present, and the mixing in thesion results, again causing large quantities of air to enter into solution.

Material thrown out by the impellers 25a passes through the restricted po'rts 43 and is then free to ascend through the separation zone of the cell. The ballles23 restrain the agitation in the lower portion of the cell and counteract any vortex tendency.

Due to the combined action of the reagent and the aeration, the valuable constituents are carried to the surface and collected in a froth for subsequent removal across overw lip I3. The non-floated solids are again discharged from the cell over weir I3 and through outlet 22.

A portion of the mineral is sometimes imperfectly elevated and collects near the surface within the pulp body, requiring treatment with additional reagent to produce the necessary reaction for carrying it into the froth.

This material is recirculated through the opening 24 into passage 23 back to the impellers 25a. where it is again subjected to compression and intimate intermixture with entering pulp, air and reagent to give it additional coating. Thereafter, upon discharge it ascends under the influence of the aeration and collects in the froth.

Inconnection with the foregoing operation, it will be understood that for any given treatment the correct pulp density and gas-reagent ratio will be determined in advance and during treatment according to common practice in the art.

The gas admitted is subject to regulation by control of the valved branch 36 which may be employed for this purpose, or by adjustment of Valve 34 or by regulation of valve-controlled jets 44.- A certain amount of air will also be entrained by the cascading action of material in passage 23, but since this amount is relatively small, the introduction of air by other means will be necessary to give the desired aeration, and being subject to regulation, such means provide a close quantitative control of gas admission.

Further, the gas-regulating means provide a compression control as the operation of valve 34, and the valve in branch 36 affects the resistance developed below the cover-element 21, and since the compression is a factor of the intermixture, this control in turn defines a degree of the intermixture attained.

Thus `it will be understood that the regulations of the operation as herein dened serve to render the apparatus and process amenable to close control at all times and in treatments where 'proportions are critical the process as performed in apparatus of the character described will attain a high degree of efficiency.

The other forms of three-impeller type cells illustrated herein are similar in 'essential features to the cells A and B of Figures 1 and 2, and it will be understood that as each of these cells is best suited for particular treatments, a given form will be selected according to treatment requirements, and in some instances certain cells will be of one form While other cells are ofva different form, as illustrated in Figures 1 element 21 has been omitted, and each of the shafts 26 is encased in a column 33, provided The open- Y with a. valve-controlled branch 36. ings 35 are also omitted in the columns 33 and the closure 34 is apertured forpassage of the shaft 26 therethrough. The impellers 2.5Y areprovided on their lower surface with vanes 45 to suck in material from a feed inlet 31a, suitably connected with a source of supply (not shown), and also for sweeping the cell Abottom to prevent any accumulation of sands thereon.

There is provided also a feed tube 46 extending into the cell from an elevation above the liquid level and terminatingin an opening in the cover-element 21. This tube may be used to supply reagent, gas or even pulp, but is usually employed as a reagent feeder.

The operation of this cell is similar to that hereinbefore described. Material is agitated, mixed and forced upwardly into passages 32 and columns33, the resistance therein being regulated by the valved branches 36 and valves 34. The admission of pulp, gas and reagent is controlled as desired to effect proper mixing and dissolution of gas in the agitation zone.

Inasmuch as there is less restriction to discharge of material by the impellers, 'it may be preferable to increase the number of bailles 28 in order to avoid undue turbulence in the separation zone. The recirculation opening 24 while not illustrated may be employed in this cell, if

, desired, in which case, a portion of the solids previously treated would return through inlet 21 and again be subjected to the agitation and compression inuences. 1

The form of cell illustrated in Figures 9 and 10 is generally similar to cell A of Figures 1 and 2. A feed tube 46 is also shown in this form of cell structure, and it will be understood that these tubes may be incorporated wherever desired in the several forms.

Aprtures 43a in the annular baille or rim 29 permit restricted discharge of matter from the impellers, but because of such restriction an effective compression zone is created beneath cover-element 21.

In this connection, the passages 32 may be of sufficient cross-sectional area tocirculate all the matter elevated by the impellers without restriction, in which case compression will be confined to the lower portion of the agitation compartment.

The free circulation of the 'intermixture through passages 32 exerts a suction or pumping influence' on column 33, as a result of which large quantities of air will be drawn down, whenever the upper end of the column is left open by proper adjustment of closure 34.

Therefore, whenever it is desired to eliminate the expense ofv supplying gas under pressure, aeration can be effected in this manner, and while the feature is illustrated withspeciflc r`eference to Figure 10, it will beunderstood that it may be used in the various cell constructions illustrated, so long as the column 3,3 is not used as a conveying medium for the compressed body.

Further, it should be noted that by extending a portion of each baille 28 to the cell bottom, any

centrifugal movement of the discharged matter;

is effectively converted into an upward linearmovement, further aiding in the diffusion'of -the ascending gas bubbles rising to the surface.

In operation, the material in the cell of Figure 10 is agitated, compressed, and recirculated in the manner hereinbefore described, and it will be understood that the compressed matter will notk rise in column 33 because of the capacity of passages 32 and also because there is less restrict1on to discharge laterally of impellers 25.

this cell as will be apparent by reference to Figures 9 and l0. The baffles in this form are shown as vextending over the cover 21 (Figure 9) to a greater degree than the baiiles illustrated in the other forms.

It will be understood that in any of the threeimpeller type cells, all impellers may rotate in the same direction, or one impeller may rotate in a direction opposite to the others.

From the foregoing, it will be apparent that in the various forms of three-impeller type cells described and illustrated.. the process performed is essentially the same, and except for slight operating differences and variations in structure to modify the action in minor respects, the arrangey ment is basically uniform.

is defined-by the open-ended casing 2|. Feed in-4 In the modied form of the linvention illustrated in the other views, the chief distinction resides in the employment of two impellers in place of three to'produce an action similar in its basic features to that already described.

Referring first to Figures 5 and 6, the cell |5a preferably is oblong and provided with a froth overiiow lip I8 of the type previously described. A weir overflow I9 is provided in the wall I6a of this cell and the discharge passage thereto lets 31 and 31a deliver pulp .to the cell and this pulp may be a previously conditioned pulp mixedwith reagent, if desi-red.

Two rotary impellers 25, here shown provided with sweeping vanes 45, are located in the cell on shafts 26 and acover element 21a defines a com'- pression zone in association with the impellers 25. 'Iwo columns 33 rise from openings in cover 21a, above the liquid level and are provided above the froth body with closures 34 and valve-oontrolled branches 36y of the type hereinbefore described.

The cover-element comprises disk portions 41 above the impellers 25 and an intermediate portion 48 projecting from opposite sides of the disk portions 41. A anged rim 49 on the projections of portion 48 provides a closure for the compression zone and a plurality of ports 50 in the rim 49 are providedfor the restricted discharge of the mixture from such zone. In addition, bailies 5| are provided inside the closure defined by rim 49 to restrain'agitation of material discharged through the ports 58.

Feed tubes 46 extend into openings in the cover-element 21a and the openings 30 provided therein to admit the shafts 26 are of a sufficient size to provide recirculation passages therethrough. Erosion-resistant sleeves 3l are carried on shafts 26 at the openings 30.

The form of the invention illustrated in Figures '1 and 8 differs from the form of Figures 5 and 6 chiey in the omission of the disk portions 41 of the cover-element 21a, and the use of covered-type impellers 25h in place of the impellers The controls of gas-admission, reagent and pulp The operationof a single cell of this type has been diagrammatically illustrated in Figures 11 and l2. In Figure 11, both impellers 25 rotate in the same direction with the result that the confluence of the discharge of the respective impellers results in-violent collision, throwing gas, pulp` and reagent into intimate intermixture and creating expansive tendencies in the intermixture.

The restriction imposed by the cover 21a induces a compression of the intermixed body causing the 'gas to dissolve and giving the mineral an effective surface coating of gas andreagent. The

provision of rim 49 and bailies 5| cooperative with the restricted discharge ports 50 aids in this compression and the process as performed in such cells is substantially that previously described.

When one impeller is rotated in a clockwise direction and the other in a counter-clockwise direction as illustrated in Figure 12, the violent impingement is eliminated and a mixing of a different type occurs. The streams travel at their confluence in substantially tangential relation and matter in each is impinged upon matter in the other, while at the same time a vortex is created in the area marked S due to the pumping influence ofthe impellers, While a high pressure zone develops on the discharge side as indicated at P, in which a high degree of mixing prevails because of the opposed forces imparted thereto by the impellers.

The mixing as aforesaid in zone P creates expansive forces causing much gas to enter into solution and giving an eective surface coating to mineral particles in such zone. In this operation also, the rim 49, ports 50 and baffles 5I cooperate with the hood 48 in restricting such expansive forces to develop the compression zone as aforesaid.

In Figures 13 and 14 another arrangement of impellers for cells of the two-impeller type has been illustrated diagrammatically. The impellers in this instance are the open-type having freely 'projecting blades and are mounted for rotation with the spheres of rotation of the respective impellers lapping. In order for such an arrangement to be effective one of the impellers rotates in a clockwise direction and another in a counterclockwise direction.

With such an arrangement, the rotation of the impellers preferably is synchronized to keep the blades of the respective impellers from striking one another. But if for any reason, the movement of one impeller is faster than the other, no damage will be apt to occur because the blades travel in the same direction during engagement. As illustrated, the blades of the impellers in Figure 13 are straight and disposed radially, while `the blades of Figure 14 are curved, and radially disposed as well.

Impellers of this type will be operated under v hoods of the type hereinbefore described, which divide the cells into intercommunicating agitation and separation compartments, and it will be apparent that a high degree of mixing and an effective compression in the agitation compartment will result from this arrangement.

From the foregoing description, it will be apparent that the process carried on in all the cells illustrated herein is essentially the same, and except for variations in control features and minor phases of the operation, the results attained are substantially uniform.

It should be noted further that the variations in operating detail, while described with reference to a given cell are intended for general application to flotation apparatus and may be incorporated in the several cells, wherever such cells are adapted therefor.

In the operation of the various cells illustrated, a mixture of pulp, reagent and gas is subjected to compression by the agitative action of the impellers, causing gas to enter into solution, and giving an effective surface coating of gas and reagent to the minerals therein.

Frothing is induced by a pressure differential between the separation and compression zones,

inducing gas to rise to the surface, carrying with it mineral constituents of the pulp which respond to the flotation reaction. Undue agitation is prevented in the separation zone, and the entrapped minerals are free to pass into the froth without settling occasioned by disturbance of surface tension.

Eii'ectlve recirculation of valuable constituents not carried or held in the froth, through the compression zone serves to accelerate the otation reaction in a given quantity of pulp to the end that the time required for completing a. given separation is reduced materially over the time required in treating the same material by the methods heretofore in use.

As a consequence, a machine of a given size receives an increased treatment capacity when the features of the present invention are incorporated therein.

Where the expression "flotation reagent occurs throughout the specification, it is used to designate various types of reagents, such as co1- lectors, frothers, inhibitors, agglomerating agents, dispersing agents, and the like, since the present process deals generally with a flotation separation, rather than a specific treatment.

Changes and modifications may be availed of within the spirit and scope of the invention as defined in the hereunto appended claims.

What I claim and desire to secure by Letters Patent is:

1. In froth flotation apparatus inclusive of a tank, a plurality of impellers disposed for rotation in a horizontal plane in the lower portion of the tank, an element enclosing the impellers and dividing the tank into an upper separation compartment and an agitation compartment therebelow, and means for feeding a pulp, gas and a flotation reagent onto impellers in the agitation compartment, there being communicating enclosed passages, in the enclosing element over the impellers, having a peripheral intake and a central discharge outlet relative to the respective impellers for establishing intercommunication between the respective impellers for the circulation of matter therethrough and there being a discharge passage from the agitation compartment to the separation compartment of less capacity than said pulp feeding means whereby to induce compression of a body of pulp, gas and reagent intermixed by the action of the impellers, prior to its discharge therethrough.

2. In froth notation apparatus inclusive of a trai discharge outlet relative to the respective impellers for establishing intercommunication between the respective impellers for the circulation i of -matter therethrough and there being a discharge passage through said element from the agitation compartment to the separation compartment of less capacity than said pulp feeding means whereby to induce compression of a body of pulp, gas and reagent intermixed by the action of the impellers, prior to its discharge therethrough.

3. In froth notation apparatus inclusive of a tank, a plurality of impellers disposed for rotation in a horizontal plane in the lower portion of the tank, an element enclosing the impellers and dividing the tank into an upper separation compartment and an agitation compartment therebelow, and valve-controlled means for forcibly feeding a pulp, gas and a flotation reagent onto impellers in the agitation compartment, there being enclosed communicating passages, in the enclosing element over the impellers, having Va peripheral intake and a central discharge outlet relative to the respective impellers for establishing intercommunication between the respective impellers for the circulation of matter therethrough and there being a discharge passage from the agitation compartment to the separation compartment of less capacity than said pulp feeding means whereby to induce compression of a body of pulp, gas and reagent intermixed by the action of the impellers, prior to its discharge therethrough.

4. In froth flotation apparatus inclusive of a tank, a plurality of impellers disposed for rotation in a horizontal plane in the lower portion of the tank, an element enclosing the impellers and dividing the tank intoan upperY separation compartment and an agitation compartment therebelow, and means for feeding a pulp, gas and a notation reagent onto the impellers in the agitation compartment, there being communicating passages in the enclosing element having a peripheral intake and a central discharge outlet relative to the respective impellers for establishing intercommunication between the respective impellers for the circulation of matter therethrough and of less capacity than said pulp feeding means whereby to induce compression of the intermixture therein.

v 5. In flotation apparatus inclusive of a tank, a A plurality of impellers disposed for rotation in a horizontal plane in the lower portion of the tank, a cover-element overhanging the impellers and dividing the tank into an upper separation compartment and an agitation compartment therebelow, and means for feeding a pulp, gas and a flotation reagent under pressure onto the impellers in the agitation compartment, the cover- A element having passages providing a peripheral intake and a discharge outlet centrally of each impeller for establishing intercommunication between the respective impellers for the recirculation of matter therethrough and of less capacity than said pulp feeding means whereby to induce compression of the'intermixture therein.

6. In notation apparatus inclusive of a tank, a plurality of impellers disposed for rotation in a common plane in the lower portion of the tank, a cover-element overhanging the impellers and dividing the tank into an upperseparation compartment and an agitation compartment therebelow, means for feeding a pulp, gas and a flotation reagent under pressure onto the impellers inthe agitation compartment, the cover-element having passages establishingintercommunication between the respective impellers for the recirculation of matter therethrough and restricted to a degree sufficient to induce tending from above the separation compartment into a recirculating passage in the cover-element, and a valve controlling ingress and egress of matter at the upper `end of the column to thereby regulate the pressure within the column.

compression of the intermixture therein,.a hollow column ex' ent and a gas to a plurality of streams rotating' in opposed relation to each other within the agitation zone, compressing the resulting intermixture in a common zone of impingement of the discharges from the respective streams, discharging the compressed intermixture from the agitation zone through a restricted passage circumferentially of the plurality of rotating streams, and moving gas out of the compressed body so discharged directly to the surface of the separation zone throughout the superficial area of the cell.

8. In a froth notation process having superposed separation and agitation zones within a flotation cell exposed to the atmosphere, the improvement which comprises feeding pulp, reagent and a gas to a plurality of streams rotating disposed in opposed relation to each other within the agitation zone, compressing the resulting intermixture in a common zone of impingement of the discharges from the respective streams, returning portions of the impinging matter centrally of the respective rotating streamsfor recirculation through the zone of compression, discharging the compressed intermixture from the agitation zone through a restricted passage circumferentially of the plurality of rotating streams, and moving gas out of the compressed body so discharged directly to the surface of the separation zone throughout the superficial area ofthe cell.

9. In froth flotation apparatus inclusive of a tank, a plurality of impellers disposed for rotation in a horizontal plane in the lower portion of the tank, a cover element overhanging the im` respective impellers for the recirculation of matter therethrough and of less capacity than said pulp feeding means whereby to induce compression of the intermixture therein, and said cover element being spaced from the tank .to provide a restricted passage from the agitation compartment to the separation compartment circumferentially of the plurality of impellers.

10, In froth iiotation apparatus inclusive of a tank, a plurality of impellers/disposed for rotation in a common plane in the lower portion of the tank,l a cover element overhanging the impellers-and dividing the tank into an upper separation compartment and an agitation conipartment therebelow, means for feeding a pulp. gas and a flotation reagent onto the impellers in the agitation compartment, the cover element having passages providing a peripheral intake and a discharge outlet centrally of each impeller for establishing intercommunication between the respective impellers for the recirculation of matter therethrough and of less caapcity than said pulp feeding means whereby to induce compression of the intermixture therein, and said cover element being spaced from the tank to provide a restricted passage from the agitation compartment to the separation compartment circumferentially of the plurality of impellers, and a plurality of bailies located at intervals aboutthe restricted passage within the separation compartment.

1l. In froth flotation apparatus-inclusive of a tank, a plurality of impellersl disposed for rotation in a common plane in theV lower portion of the tank, a cover element overhanging the impellers and dividing the tank into an upper sep-,

aration compartment and an agitation compartment therebelow, means for feeding a pulp, gas

and a flotation reagent onto the impellers in the agitation compartment, the cover element hav-A ing passages providing a peripheral intake 'and a discharge outlet centrally of each other for estion and separation zones, compressing a mixture of pulp, gas and notation reagent in the agitation zone, releasing a portion of the compressed intermixture into the separation zone at a restricted velocity, moving the portion so released directly to the surface of the quiescent zone exposed to atmosphere in an action in which dissolved gases resume their gaseous state upon entrance into the separation zone, moving another portion of compressed pulp from the agitation zone through a confined zone separate from the separation zone for retreatment at the agitation zone, and removing froth forming atthe surface of the pulp body.

13. The froth flotation process which comprises the treatment of a pulp body in superposed agitation and separation zones, compressing a mixture of pulp, gas and flotation reagent in the agitation zone, releasing a portion of the-compressed intermlxture into the separation zone at a restricted velocity, moving the portion so released directly to the surface of the quiescent zone exposed to atmosphere in an action in which dissolved gases resume their gaseous state upon entrance into the separation zone, restricting another portion of compressed pulp 'while subject to expansive tendencies, and returning the portion' v so restricted through a confined zone separate from the separation zone into the agitation zone before release into the separation zone.

14. The froth notation process which cdmprises the treatment of a pulp body in superposed agitation and separation zones, compressing a mixture of pulp, gas and flotation reagent in 'the agitation zone by rotating a plurality ofv streams in opposed relation within a restricted zone, releasing a portion of the compressed intermixture into the separation zone at a restricted velocity, moving the portion so released directly to the surface of the quiescent zone exposed to atmosphere in an action in which dissolved gases retreatment at the agitation zone, and removing froth forming at the surface of the pulp body.

l5. The froth flotation process which comprises the treatment of a pulp body in superposed agitation and separation zones, compressing a mixture of pulp, gas and flotation reagent in the agitation zone by rotating two streams in opposed relation within a restricted zone, releasing a portion of the compressed intermlxture into the separation` zone at a restricted velocity moving the portion so released directly to the surface of the quiescent zone exposed to atmosphere in an action in which dissolved gases resume their gaseous state upon entrance into the separation zone, moving another portion of compressed pulp from the agitation zone through a confined zone separate from the rseparation zone for retreatment at the agitation zone, and removing froth forming at the surface of the pulp body.

16. The froth flotation process which comprises the treatment ofL a pulp body ln superposed agitation and separation zones, compressing a mixture of pulp, gas and flotation reagent in the agitation zone by rotating three streams in opposed relation within a restricted zone, releasing a portion of the .compressed intermlxture into the separation zone at a restricted velocity, moving the portion so released directly to the surface of the quiescent zone exposed to atmosphere in an action in which dissolved gases resume their gaseous state upon entrance into the separation zone, restricting another portion of compressed pulp while subject to expansive tendencies, and returning the portion so restricted through a confined zone separate from the separation zone into the agitation zone before release into the separation zone.

17. The froth notation process which comprises the treatment of a pulp body in superposed agitation and separation zones, compressing a mixture of pulp, gas and flotation reagent in the agitation zone, releasing a portion of the compressed intermlxture into the separation zone at a restricted velocity, moving the portion so released directly to the surface of the quiescent zone exposed to atmosphere in an action in which dissolved gases resume their gaseous state upon entrance into the separation zone, moving another portion of compressed pulp from the agitation zone through a confined zone separate from the separation zone for retreatment at the agitation zone and mixing unoated mineral from the separation zone with the portion so returning for retreatment, and removing froth forming at the surface of the pulp body.

18,.' In froth flotation apparatus, a tank divided into superposed agitation and separation corn- -partments, means for feeding a pulp, gas and a flotation reagent into the agitation compartment, a rotary impeller disposed in the pulp in the agitation compartment acting on matter fed thereto for its intermlxture, and a closure for the impeller defining the agitation compartment and having a recirculation passage spaced from the' vvimpeller and with a discharge outlet centrally thereof, said closure cooperating with the tank resume their gaseous state upon entrance into the separation zone, moving another portion of compressed pulp from the agitation zone through a to provide a passage into the separation compartment of less capacity than said pulp feeding means whereby toinduce compression of the intermixture prior to its discharge therethrough'.

19.In froth flotation apparatus, a tank divided into superposed agitationand separation compartments, means for feeding a pulp, gas and a flotation reagent into the agitation compartment, a plurality o f rotary impellers disposed in the pulp in the agitation compartmentacting on matter fed thereto for its intermixture, and a closure for the impellers defining the agitation compartment and having a recirculation passage spaced from the feed means with its intake at the peripheiy of the impeller and with a discharge outlet centrally thereof, said closure cooperating with the tank to provide a passage into the separation compartment of less capacity than said pulp feeding means whereby to induce compression of the intermixture prior to its discharge therethrough. g

20. In froth flotation apparatus, a tank divided into superposed agitation and separation compartments, means for feeding a pulp, gas and a otation reagent into the agitation compartment, three rotary impellers disposed in the pulp in the agitation compartment acting on matter fed thereto for its intermixture, and aclosure for the impellers defining the agitation compartment and having 'a recirculation passage spaced from the feed means with its intake at` the periphery of the impellers and with a discharge outlet centrally of one of the impellers cooperating with the tank to provide a passage into the separation compartment of less capacity than said pulp feeding means whereby to induce compression of the intermixture prior to its discharge therethrough.

21. In froth otation apparatus, a tank divided into superposed agitation and separation compartments, means for feeding a pulp, gas and a flotation reagent into the agitation compartment, two rotary impellers disposed in the pulp in the agitation compartment acting on matter fed thereto for its intermixture, and a closure for the impellers defining the agitation compartment and having a recirculation passage spaced from the feed means with its intake at the periphery of the impellers and with a discharge outlet centrally of one of the impellers cooperating with the tankto provide a passage into the separation compartment of less capacity than said pulp feeding means whereby to induce compression of the intermixture prior to its discharge therethrough.

ARTHUR C. DAMAN.

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