US2243302A - Means of treating liquids - Google Patents

Description

INVENTOR. WEj/V/ 6 ATTORNEYS 2 Sheets-Sheet 1 ARTHUR J A J WEINIG MEANS OF TREATING LIQUI DS Filed Aug. 7, 1959 May 27, 1941.

May 27, 1941. A. J. WElNlG 2,243,302

MEANS OF TREATING LIQUIDS Filed Aug. 7, 1959 2 Sheets-Sheet 2 INVENTOR. ARTHUR cf wz/m/s I @i zw/wu W /LL60 i 6402 14X! AT ORNEYS Patented May 27, 1941 UNITED STATES ATENT QFFICE MEANS OF TREATING LIQUIDS Arthur J. Weinig, Golden, Cola, assignor to Morse Bros. Machinery Company, Denver, 0010., a corporation of Colorado 18 Claims.

This invention relates to improvements in agitation and aeration of liquids containing solids in suspension and more particularly relates to improvements in means of agitating and aerating pulps in the well-known froth flotation process.

In the froth flotation treatment, an ore pulp is subjected to the influences of aeration in the presence of certain reagents which act on one or more of the ore constituents to induce a surface reaction by which such particles of matter become attached to bubbles of air in the liquid body and are elevated thereby to the surface where they collect in the froth which may be separated from the pulp as a concentrate.

In most of the flotation processes now in use, the preferred practice is to treat the pulp in one or more flotation cells in which the pulp is agitated by a rotary impeller, the action of which is also utilized in mixing and diffusing air throughout the pulp body. In such operations, the pulp has been entered into the impeller from above or below or both and is thereafter thrown outwardly across the periphery of the impeller by its centrifugal action.

In order to insure thorough and intimate intermixture of air with particles in the pulp acted on by the reagent of the treatment, air has also been introduced into the rotary impeller at or near the point of the pulp introduction and the centrifugal action has been utilized to mix pulp and air within the impeller and to eject the mixture from the impeller for its subsequent movement into a separation zone in which the treated constituents are separated from the untreated constituents of the pulp.

The present invention has particular application to froth flotation treatments in machines of the sub-aeration type, in which the mixing of gas and pulp is induced by the action of rotary impellers.

In my Patent No. 1,998,694, of April 23, 1935, for Impeller, an impeller construction is shown and described in which certain vanes of the impeller are utilized for slicing into the body of the pulp beyond the impeller and by such slicing ac- No. 199,883, filed April 4, 1938 (U. S. Patent 2,198,143, issued April 23, 1940), for Aeration apparatus, and is a continuation-in-part thereof. Theaerating practice as therein disclosed is being claimed in the aforesaid application and will only be claimed in thepresent application in conjunction with the features of improvement as hereinafter set forth.

By utilizing the principle of the slicing action of the aforementioned patent and employing the gas introduction at the periphery of the impeller in conjunction with such slicing action, the present invention provides for a thorough and intimate i-ntermixture of gas and pulp during the interval in which such matter is maintained within the confines of the impeller and thereafter the resulting intermixture is subjected to a novel circulatory movement throughout the flotation cell.

It is an object of the present invention to provide a means for agitation and aerationof a liq uid containing solids in suspension, in which the aerated material is caused to ascend in a zone immediately above a rotary impeller and solids not elevated by the aerating influences and which tend to separate out of suspension are caused to move laterally from the zone of ascension and to descend through another zone separated therefrom for .retreatment by the impeller.

.Another object .of the invention is to provide a mixture of gas and pulp by inducing movement of .pulp and gas through a rotary impeller fro-m the periphery thereof to a'point of discharge centrally of the same.

A'further object of the invention is to induce a direct upward movement of mixed matter through a body of liquid under treatment by a controlled discharge of such matter from a retary impeller inducing the agitation.

Still another object of the invention is the provision of a novel impeller construction productive of a novel type of mixing action which is economical in production and is not subject to excessive wear on its working parts.

A still further object of the invention is the provision of a means for utilizing the rotary movement of an agitator to draw into suspension solids in the liquid body under treatment, which have settled therefrom.

Other objects reside in novel treatments and operations and novel combinations and arrangements of parts, all of which will appear more fully in the course of the following description.

The present invention introduces a new principle in the use of rotary agitators for the treat- Such an action is utilized to induce a novel circulatory movement of the solids in the bodya under treatment. The controlled discharge moves the solids either attached or unattached to air bubbles in a direct upward movement toward the surface of the body under treatment and since all particles in this liquid ascending column are traveling in the same direction, there is littleer no tendency for particles attached to air'bubbles to break therefrom and separate by gravitational descent. 7 7

Likewise, solids in suspension only and which tend to separate out of suspension after a certain degree of elevation, move laterally from theascending column upon reduction in velocity and finally descend under gravity in another zone exteriorly of the ascending column forsubsequent return to the zone of influence of the impeller and recirculation therethrough.

In many treatments there will be a considerable portion of the mineral content which it is desired to collect, which is only feebly attached to bubbles of air upon discharge from the impeller. In the usual practice, the peripheral discharge and the provision of bafiles and grids is productive of a countercurrent flow in the cell in which the material being elevated by the aerating influences moves back and forth across the cell in its rise to the surface and similarly, solids separating out of suspension travel back and forth across the cell under the eddying influences until they again reach the suspending influences of the agitation zone.

In such an action, there is ample and repeated opportunity for the descending particles to fall against the rising air bubbles and because of the feeble attachment, any slight jar or impact will usually so disturb the surface tension as to break the attachment and cause the mineral to descend under the gravitational influences.

The utilization of a central zone of ascent is of particular advantage because in that region of the cell there is less turbulence causedby bafiles and corners, and the separation of the collected material from the non-floated constituents is further aided by reason of the fact that the ascending column moves conjointly with the flow of froth at or near the surface instead of moving in opposition thereto.

Inasmuch as the division between the froth bed and surface of the liquid body represents what may be termed a twilight zone with no clear line of demarcation, it obviously is advantageous to move the preformed froth toward its discharge without opposition to the movement of the aerated mass rising out of the ascending column into the froth zone.

Such an arrangement permits utilization of tender froths where separation will be improved thereby or other advantages derived therefrom and in such a treatment no mechanical disadvantage is encountered in the selection of tender frothsin the present operation.

From the foregoing, it is apparent that the circulatory movement of the present process represents a novel advance in the art, productive of many advantages and extends the froth flotation treatment to separations of a type not previously amenable to the treatment by reason of the economic disadvantage inherent in prior practice.

The mixing action of the present treatment is also productive of many advantages. In many treatments and particularly those in which one or more of the constituent minerals is of relatively high specific gravity, a portion of the solids content under treatment will separate out of suspension and collect on the bottom of the tank, particularly in the corners thereof. Impellers of the type now in use exert a sweeping influence on the bottom of the tank and this action is relied upon to move the separated matter into suspension andthus bring it within the influences of the treatment. However, the sweeping action is only partially effective for this purpose and as a result, in almost any treatment, there will be a not inconsequential amount of solids remaining outside the influences of the treatment.

The process of the present invention exerts a pumping or suction influence on the material in the lower portion and on the bottom of the tank with the result that separated solids are drawn toward and into the impeller rather than being impelled therefrom, and due to the circulatory action thus established, the solids descending from the liquid body are not permitted to become inert, but upon reaching the bottom are immediately drawn to the impeller and elevated thereby into and through the same.

In this manner, all the solid content of the body under treatment is subjected to the mixing influences of the impeller. In preferred practice, gas of any suitable composition is introduced into the pulp body adjacent the periphery of the impeller and immediately becomes subject to the suction and slicing influences thereof which serve to bring it into intimate and repeated contact with the solids content of the pulp in the impeller and which also serve to thoroughly diffuse and break up the gas to the end that it is ejected from the impeller into the central ascending column in finely-divided condition thoroughly distributed throughout the liquid of such column.

This method of mixing has the further advantage of condensing the mass of material subjected to'the mixing influences, for by comparison, the zone of introductionto the impeller is relatively large, whereas the discharge therefrom is of a relatively restricted character.

This condition results in a relatively long travel of material through the impeller and due to the circuitous movement thereof, as will be explained hereinafter, the interval of travel also is relatively long compared with the period of treatmentin impellers of the peripheral ejector p I a The restriction of the discharge from the impeller and the treatment" interval provided within the confines of the impeller serve tobring gas, pulp and reagent into repeated and intimate contact during treatment within the impeller and upon discharge therefro-min the elevating movement, the gas and solids of the column are in such. close association that mineral acted on by the reagent quickly attaches to the rising bubbles and, is borne thereby to thesurface. Furthermora'the elevating movement servesto encourage attachment -of particles not initially adhering to 'gas bubbles because of the continued bombardment of the gas bubbles which tend to ascend through the upper portion of the column at a faster rate than solids merely in suspension.

As a result of such action, a high degree of elevating emciency is attained from the aeration of the treatment and the provision of separate zones of ascension and descent insures the return of non-floated particles to the mixing stage of the treatment without impedance to the material influenced by the flotation reaction.

The present invention is susceptible of embodiment in a variety of forms and to afford a clear understanding of the method of operation and of structure necessary to effect such operation, reference will now be made tothe accompanying drawings, in the several views of which like parts have been designated similarly and in which:

Figure l is a side elevation of a flotation cell embodying features of the present invention;

Figure 2 is a bottom plan view of the impeller illustrated in Figure 1;

Figure 3 is a top plan view of the impeller of Figure 1;

Figure i is a bottom plan view of a modified form of impeller construction embodying features of the present invention;

Figure 5 is a top plan view of the impeller of Figure 4; and

Figure 6 is a section drawn to an enlarged scale, taken along the line 6-6 of Figure 4.

Referring to Figure l, a flotation cell 1 has been illustrated which preferably, although not necessarily, comprises a rectangular tank having along one side thereof a, froth overflow lip 8. The side of the cell opposite the overflow lip preferably is inclined in its upper portion 9 to exert a crowding action on froth collecting on the surface of the pulp body under treatment in the tank. A rotary shaft i9 driven in any suitable manner, such as by a pulley ll connected with prime mover (not shown), is mounted in suitable bearings i2 and extends downwardly in the tank i. An impeller E3, the details of which will be described hereinafter, is mounted upon the shaft H} at its lower end and preferably has its lowermost surface in close proximity to the bottom of the tank 1 for purposes that will be explained hereinafter.

Gas under pressure is introduced into the tank 1 adjacent the impeller it. As here illustrated, the gas enters through a conduit l4 mounted in suitable supports 55 on a wall of the tank and terminates at its lower end in a discharge nozzle to. A conduit id is connected with a suitable header (not shown) carrying gas under pressure from a suitable source of supply (not shown) and a valve i? in conduit I i permits regulation of the amount of gas introduced into the cell 1 from the header.

Figure l is intended to typify a flotation cell, which may be either a single cell, or a given cell of a multi-cell machine. Where the latter construction is employed, provision will be made for maintaining a predetermined liquid level by having the tank subject to oontinous feed and discharge, controlled by suitable devices in a manner well-known in the art.

The present invention is adapted for and intended to utilize different methods of gas introduction and any means for introducing gas to the sphere of influence of the impeller will satisfy operating requirements. However, the method of introduction here illustrated has been found to be highly satisfactory in practice and accordingly is illustrated as the preferred method of gas introduction. 7

Next referring to Figures 2 and 3, it will be seen that while the impeller illustrated embodies features of construction described and illustrated in my prior Patent No. 1,998,694, certain differences in construction have been incorporated in the present impeller, which are productive of the novel operating procedure of the present invention. Thus, the impeller of my patent employs vanes in groups, which have been designated .as pumping, slicing, and striking vanes. In the present construction, the vanes of the impeller are likewise arranged in groups and each group contains a vane 13a corresponding to the pumping vane of my patent, a second vane l3b corresponding to the slicing vane of my patent, and a-third vane I30 corresponding to the striking vane of the patent.

In the form of the invention illustrated in Figure 2, a second slicing blade ltd extends from an end of the striking blade I30 transversely thereto and terminates at the periphery of the impeller. ,An opening l3j through the impeller disc l3 extends between the pumping vane l3a and the striking vane I30 in a lengthwise direction from the slicing vane 5301 to a point of termination at or near the inner end of striking vane 1.30. As a result of such arrangement, pulp is drawn inwardly from beyond the periphery between the slicing vanes l3b and Kid in the zone designated A in Figure 2 and also is drawn in by slicing vane 13b along the opposite side thereof in the zone marked B. At the same time, pulp in the-zone centrally of the impeller is moved by the action of the pumping vane i3a on both sides thereof, as indicated in the zones marked C and D respectively.

The streams B and D converge in the passage between the end of pumping vane [3a and slicing vane to, bringing the material of the streams into thorough and intimate contact by reason of' such impingement. The mixture then passes on toward the striking vane [30 where it impinges upon matter moving through zone C under the influence of the pumping vane l3a. As a result, a second impingement and intermixture results at the convergence of these streams and due to the'fact that both streams are tending to move toward the periphery of the impeller under the impelling influences of the-vanes and the centrifugal movement, the resulting intermixture is brought into opposition with the stream of material traveling through zone A between the slicing vanes l3b and I311.

The vanes I30 and It'd confine the resulting intermixture in the zone of convergence and impact against further movement under the centrifugal influence, and the pressure created in the pulp bodyat this stage is provided release by the opening I31 immediately above the impacting bodies. As a consequence, the material of the intermixture is caused to change direction and is ejected forcibly through the opening l3 in an ascending movement. From the foregoing, it will be apparent that the several streams of pulp passing to a given point of discharge I3 originate in separated relation and by the action of the impeller and the control of the movement of such streams are first condensed or compressed before escape through the restricted discharge opening.

The force .thus created in .inducing discharge, has a pronounced impelling ieffect upon the .dis-

charge, with the result that the solids of the pulp move upwardly through the body of material under treatment in a well defined zone immediately above the impeller as illustrated by the arrows in Figure 1.

To further facilitate the impelling action and to avoid undue turbulence by reason of the forceful ejection, blades or vanes l3g are provided on the upper surface of the impeller in contiguous relation to the openings I3 and at a side thereof forwardly with respect to the direction of rotation of the impeller.

These vanes l3g may be either inclined or upright, and as illustrated in Figures 1 and 3 are in an inclined position partially overhanging opening I31.

While these blades may be either attached members or an integral construction, it has been found advantageous in forming the impeller to utilize the material taken from the impeller disc l3 in the formation of the openings I31 as the material of the blades formed integrally therewith in the casting or molding operation.

The provision of the blades 139 at the front side of the openings I3 serves to impart an elevating movement to liquid on the upper surface of the impeller l3, with the result that the discharge through the openings 13 is thrown into a stream of ascending material instead of impinging upon a more or less static body. As a result, the mineral held in air attachments passing through the discharge is not broken therefrom upon entrance into the liquid column to the same degree that it would be if the blades were not provided on the upper surface of the impeller to exert a sweeping action.

However, under certain circumstances, it may be desirable to utilize the static body for further mixing and diffusion of gas at the beginning of the ascending movement. Therefore, while the vanes have been illustrated, it will be understood that under certain conditions they may be omitted and effective mixing and circulation will still be attained.

The form of the impeller illustrated in Figures 4, 5, and 6 has been shown to suggest the various types of modification that may be incorporated in the impeller of Figure 2. Thus, the openings or passages I31 are in non-radial arrangement in contradistinction to the radial arrangement of the passages in the impeller of Figure 2. Similarly, the blades or vanes Hg in Figure are in a substantially upright or vertical position along the front side of the passage I3j with respect to the direction of rotation of the impeller.

Under certain circumstances, one slicing vane will be sufficient for each group and in Figure 4 such an arrangement has been illustrated in which the slicing vane I3d adjoins the striking vane 130 while the second slicing vane l3b has been omitted. With this arrangement, pulp is drawn in across the impeller along the zone A and also pumped from the central portion of the impeller between the vanes !3a and I30 in zone C. The vanes I30 and l3d confine the pulp streams at or near the point of convergence and the opening l3 permits escape of the mixed materials during and after impact.

The foregoing arrangements are not intended to cover all the various structural forms which may be employed for performing the process of the present invention, but will serve to illustrate the operating requirements thereof. Thus, the blades l3g on the upper portion of the plate may be increased in number, reduced in number, or

omitted entirely, and the shape, proportion, and number of blades on the under surface of the impeller also may be changed.

In this connection, it is noted that it is essential to the operating procedure of the present invention that some means be provided for inducing movement of pulp across the periphery of,

the impeller to the interior thereof and that in the interior additional means he provided to induce the ascending discharge of th pulp thus drawn in.

Likewise, the flotation cell illustrated in Figure 1 is only typical of the machines in which the present invention may be embodied and it will be understood that the impellers of the present design may be embodied in the various machines utilizing'rotary impellers for agitation. So long as an adequate gas supply is provided for such impellers, either in the manner herein illustrated, or by other suitable means, the process of this invention can be performed in such machines.

Further, while no grids or baflles have been illustrated in the cell of Figure 1, the present process is adapted for performance in tanks having such structure, and the controlled circulatory movement of pulp through the cell will not be impeded appreciably 'by such means.

Thus, it is apparent that the process is not limited to use with the structure illustrated herein, but variations thereof which adopt the operative features herein described are within the contemplation and scope of the invention.

In describing the performance of the process, reference has been made to the treatment of pulps, which is intended to designate solids in a liquid suspending medium which usually comprise some form of mineralized matter. However, it will be understood that the process is amenable to any form of aeration treatment such as liquids only, mixtures of solids and liquids such as the treatments of ores, paper pulps and the like.

While no means has been shown for the introduction of reagent into the tank I of Figure 1, it will be understood that such tank is adapted forthe treatment of materials previously conditioned by mixing with reagent or by introducing reagent directly into the tank in any suitable manner for mixing with the materials under treatment therein by the agitative action of the process.

The means illustrated herein are the best arrangements at present known to applicant for attaining these ends, but changes and modifications may be availed of within the spirit and scope of the hereunto appended claims.

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

l. Flotation apparatus comprising a tank for fluent pulps, a rotary impeller in the tank for the treatment of matter therein, means for introducing gas into the body of material passing to the impeller for treatment, means on the impeller for drawing pulp and gas from beyond its periphery into the interior thereof, there being a discharge opening in the upper surface of the impeller and means disposed on the impeller cooperative with said first-named means to mix and force matter so drawn in upwardly through the discharge opening.

2. Flotation apparatus comprising a tank for fluent pulps, a rotary impeller in the tank for the treatment of matter therein, a conduit for gas under pressure extending into the tank and having a discharge outlet disposed at the pe-' riphery of the impeller, means on the impeller for drawing pulp and gas from beyond its periphery into the interior thereof, there being a discharge opening in the upper surface of the impellerand means disposed on the impeller cooperative with said first-named means to mix and force matter sodrawn in upwardly through the discharge opening.

3. Flotation apparatus comprising a tank for fluent pulps, a rotary impeller in the tank for the treatment of matter therein, means for introducing gas into the body of material passing to the impeller for treatment, means on the impeller for drawing pulp and gas from beyond its periphery into the interior thereof, there being a discharge opening in the upper surface of the impeller, means disposed on the impeller cooperative with said first-named means to mix and force matter so drawn in upwardly through the discharge opening, and elevating blades disposed on the upper surface of the impeller to impart an upward movement to liquid descending thereagainst.

4. An impeller comprising a body capable of rotation about a central axis, and vanes projecting from a surface of the body in different groups, those of one group projecting outwardly from the axis of rotation in the middle portion of the body to produce a pumping action upon material under treatment, those of a second group extending adjacent and at an acute angle to the periphery of the body to produce a slicing action upon the material, and those of a third group extending toward the periphery of the body in adjoining relation to the vanes of the second group to effect a striking action upon the material, there being an opening through the impeller between the vanes of the first and third groups to permit discharge of the material acted on by the vanes.

5. An impeller comprising a body capable of rotation about a central axis, and vanes projecting from a surface of the body in different groups, those of one group projecting outwardly from the axis of rotation in the middle portion of the body to produce a pumping action upon material under treatment, those of a second group extending adjacent and at an acuteangle to the periphery of the body to produce a slicing action upon the material, and those of a third group extending toward the periphery of the body in adjoining relation to the vanes of the second group to efiect a striking action upon the material, there being an opening of restricted capacity through the impeller between the vanes of the first and third groups to permit discharge of the material acted on by the vanes.

6. An impeller comprising a body capable of rotation about a central axis, vanes projecting from a surface of the body in different groups, those of one group projecting outwardly from the axis of rotation in the middle portion of the body to produce a pumping action upon material under treatment, those of a second group extending adjacent and at an acute angle to the periphery of the body to produce a slicing action upon the material, those of a third group extending toward the periphery of the body in adjoining relation to the vanes of the second group to effect a striking action upon the material, there being an opening through the impeller between the vanes of the first and third groups to permit discharge of the material acted on by the vanes, and a blade projecting from the surface of the impeller opposite the group of vanes in contiguous relation to the opening and forwardly thereof with respect to the direction of rotation of the impeller.

7. An impeller comprising a body capable of rotation about a central axis, vanes projecting from a surface of the body in different groups, those of one group projecting outwardly from the axis of rotation in the middle portion of the body to produce a pumping action upon material under treatment, those of a second group extending adjacent and at an acute angle to the periphery of the body to produce a slicing action upon the material, those of a third group extending toward the periphery of the body in adjoining relation to the vanes of the second group to effect a striking action upon the material, there being an opening through the impeller between the vanes of the first and third groups to permit discharge of the material acted on by the vanes, and a blade projecting from the surface of the impeller opposite the group of vanes in contiguous overhanging relation to the opening and forwardly thereof with respect to the direction of rotation of the impeller.

8. An impeller comprising a body capable of rotation about a central axis, and vanes projecting from a surface of the body in different groups, those of one group projecting outwardly from the axis of rotation in the middle portion of the body to produce a pumping action upon material under treatment, those of a second group extending adjacent and at an acute angle to the periphery of the body to produce a slicing action upon the material, and those of a third group extending toward the periphery of the body in adjoining relation to the vanes of the second group to effect a striking action upon the material, there being a radially disposed opening through the impeller between the vanes of the first and third groups to permit discharge of the material acted on by the vanes.

9. An impeller comprising a body capable of rotation about a central axis, and vanes projecting from a surface of the body in different groups, those of one group projecting outwardly from the axis of rotation in the middle portion of the body to produce a pumping action upon ma terial under treatment, those of a second group extending adjacent and at an acute angle to the periphery of the body to produce a slicing action upon the material, and those of a third group extending toward the periphery of the body in adjoining relation to the vanes of the second group to effect a striking action upon the material, there being a nonradially disposed opening through the impeller between the vanes of the first and third groups to permit discharge of the material acted on by the vanes.

10. An impeller comprising a body capable of rotation about a central axis, and vanes projecting from the surface of the body in difierent groups, those of one group projecting outwardly from the axis of rotation in the middle portion of the body to produce a pumping actionupon material under treatment, those of a second group extending adjacent and at an acute angle to the periphery of the body to produce a slicing action upon the material, those of a third group extending from adjacent an end of those of the first group to the periphery in spaced parallel group and adjoining those of the second group to efiect a striking action upon the material, there being an opening through the impeller between the vanes of the first and fourth groups to permit discharge of the material acted on by the vanes.

11. A closed type impeller for agitating an ore pulp, comprising means for drawing pulp radially inward intothe impeller from beyond its periphery, means centrally of the impeller for moving pulp countercurrent to the pulp acted on by said first-mentioned means, and means on the impeller for discharging the impinging matter upwardly through the top of the impeller.

12. A closed type impeller for agitating an ore pulp, comprising means for drawing pulp interiorly of the impeller from beyond its periphery, means centrally of the impeller for moving pulp countercurrent to the pulp acted on by said first-mentioned means, means on the impeller for discharging the impinging matter upwardly through the top of the impeller, and means on the top of the impeller for imparting an elevating component to matter discharged therethrough.

13. A closed type impeller for agitating an ore pulp, comprising means for drawing pulp radially inward into the impeller from beyond its periphery, means centrally of the impeller for compressing pulp within the confines of the impeller, and means on the impeller for discharging the compressed pulp upwardly through the top of the impeller.

14. A closed type impeller for agitating an ore pulp, comprising means for drawing pulp radially inward into the impeller from beyond its periphery, means centrally of the impeller for retaining pulp within the confines of the impeller in opposition to the centrifugal influence thereof, and means on the impeller for discharging the matter so retained upwardly through the top of the impeller.

15. Apparatus of the character described, comprising a tank for pulp, a rotary impeller submerged in the pulp, means for introducing gas into the pulp at the periphery of the impeller, means for drawing pulp and gas radially inward into the impeller from beyond its periphery, means centrally of the impeller for moving pulp countercurrent to the pulp acted on by said first mentioned means, and means on the impeller for discharging the impinging matter upwardly through the top of the impeller in a rising column separate from descending streams of recirculating pulp laterally of the impeller.

16. Apparatus of the character described, comprising a tank for pulp, a rotary impeller submerged in the pulp, means for introducing gas into the pulp at the periphery of the impeller,

means for drawing pulp and gas radially inward into the impeller from beyond its periphery, means centrally of the impeller for moving pulp countercurrent to the pulp acted on by said first mentioned means, said means also drawing solids collecting on the bottom of the tank into the impeller, and means on the impeller for discharging the impinging matter upwardly through the top of the impeller.

17. An impeller for treating ore pulps, comprising means for drawing pulp radially inward into the impeller from beyond its periphery, means centrally of the impeller for moving pulp countercurrent to the pulp acted on by said first mentioned means, and means for discharging the resulting intermixture upwardly through restricted passages centrally of the impeller.

18. An impeller for treating ore pulps, comprising means for drawing pulp radially inward into the impeller from beyond its periphery,

ARTHUR J. WEINIG.

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