US2684233A - Froth flotation apparatus - Google Patents

Description

July 20, 1954 P. M. PAYNE FROTH FLOTATION APPARATus 4 Sheets-Sheet l Filed Dec. 7, 1951 [W23 I na lJlp. 'a W wm P M. N R

A E P/ (Ittomeg July 20, 1954 P, M, PAYNE 2,684,233

FROTH FLOTATION APPARATUS Filed Dec. 7, 1951 4 Sheets-Sheet 2 L [7mm 23 i l 24/ F ig. 2 '5 lo :Srwentor F'g' 3 PEARsoN M. PA N (Ittomeg July 20, 1954 Filed Dec. '7. 1951 P. ML PAYNE 2,684,233 FROTH FLoTATIoN APPARATUS 4 Sheets-Sheet 3 3nventor PEARSON M. PAYN (Ittorneg July 20, 1954 PM. PAYNE 2,684,233

FRoTH FLoTATIoN APPARATUS Filed Dec. '7l 1951 4 Sheets-Sheet 4 Jnventor PEARSON M PAYNE Gttorneg .cienc' andxfacilitate Patented July 20, 1954 'U N21 TED 'S LS PATENT z-fO'F'FalC'E i` FROTHHYFLO TATIONI ;APPATS Pearson. M.` Payne, Denver, `C'oio.

Application `December 7, 1951, Serial' fNo.'.26 0,480

(Cl. I?61--- 93) `llClairris. .1

This invention relates togapparatus iorthe agtationa'nd iroth fiotative separation of granu'lar -or'comminnted materials, such-as ores, and ;more particuiarly .tog-agitating and. froth ;fiotation-.apparatus of the generaltype vand operativezorgan- .iza-tion disolosecl in my application .for Letters Patent oitheUnited 'Statesfiled .on August1l3, 19.48,' serialrlo. 44,118, Vnow issuecl .under .dateof December ,11, 1951, as v;Patent No.2,577,8)2, :and has asan ohjecttoprovide noveland improved means; in. combination-. and operative association with the apparatus zofz my .said earlier patent effective to extencl. the-Utility, .enhanoe thezeffi- -regulation and .operative control thereof.

lviy eariierxpatent above identifie-(iiscloses the :operativez association with. a flotationeh .or .agitatihg ;compartmentfofiagitating and -air incluc- -tion`` means. inlthe ;formV of a vvertical-ly-axiseoL rotatable "iinpeller :unit characterized by. xedlyassociated, angularly-spaced, ;like ;rods or :stiii ,whip elements ;diverging ;outwardly v.ar-1d:olown- :fvvardiyin ;intersecting relationwith the level of the materia to ibeiagitated and `through 'thelbocly of such ;materialzto terminationin.free ends spacedly adiacent ;the fioorfof the cell; or .compartment, vand ;the improvements-of "theinstant invention relate .to -means Tor; efiectively; applyiinfcfA the agitationszand: air inductions incident to rotation of such an fimpeller to efiicient-nsein ,the conditioning. of materials Iintrorluced within vthe .cell or.V compartrnent, .to the seleetive iroth fiotati-ve. .separ-aticnl of such` materials, .to the recirculatonlof -the cell or cornpartmentV contents toand through the `influenoe of l,theimpellen andto the .regulationand Acontrol of suchoperations.

,Withuthe foregoing andv other objects in view, my inventionconsists in the. construction,` arrangement, andcombination of elements as hereinafter, setiorth, pointed out ,in myclaims, and illustrated by the .accornpanying .drawings, in whch- .Figure 1 sideelevationpartly in Vertical section, ofV`` a laboratory batch fiotation machine embodying the`l disclosuresA ofmy, earlier application ,as V typically associated .i With the. improvements hereinafter'descrihecl. 'Figurez' is a Vertical section, on a relatively enIaITgBd Scale, taken axi'ally through .the cell and impeller organization of the apparatnsshown irrFigure 1. ,Figura 3 is a cross section. taken substantally on the indicated line 3-;3 of Figure 2. 'lfigure 4 is a cross section' takenl substantiallyon the indicated line 4-4 of Figura, 2. Fg'ure 5 is a'fragmentary, de- .taill Vertical section, on afurther eniarged Scale and withportionsfbroenawayto conserve space, taken "suhstantiallyf;axially-Vf .altitudinallyarijustable-mounting-,and support utilized. in the organizatienaccording tofFigure 1. Figure .6 is-a dettl crQss.section,--on a vrelativelyenlargecl scale, taken-substantia-lly ,'Qn; heindieatecl linel 6-6 'of Eigure 1. Figure'lis atop plan. view ofan alternative embodimentand adaptation of the invention. Figurefisamertical section takensubstantially onthe indicated-linesB-TS of Figure'Y. Figure 9 isza ficross'.section,.on, a relativelyfien- ;largedscale, `taken-snlostant'lallyI on vthe indicated line9-S of fFig1 ire 8. Figure 10 isa fragmentary, detail; section takensubtantiaHy on the indicatediine ,It- .-l' of EigureQ.

vIn the. embodimentzof the invention typified by Figuresl-, inchisve,v of, the'olrawingsa froth fiotation `.cell is conventionally, represented Jas a relatively-;ieep, conveniently-cylindriaL opentoppbowl .iii iormd witha `froth-overfiow lip H cooperatingwith a l.ntch intheupper marginof the bowl.-.wall. :The-bowl .1.0 is shown. as carried by and to upstandr,withj-itsiaxis Vertical from-,a base; i-whichsnpportsas hereinafter more particularly described, an .altitudinally-adjustable driveandzop-erative cmounting' forl animpeller shaft-i3 coax ial .with.said boWl-and .rotatable `aboutits axisin an'operative disposition intersecting thevplane of`1 the bowl top rim. Fixed ,-t0 .and rotatablewith the-lower end of the shaft 1,3,

van .impeller assembly, 4comprising a plurality of like, stiif, rod elements' l 4. fixedlyengagedat-thir .upperends .imandzwith a-collar ,I 5. secured to Vthe shaft. 13 anclfcorrepondingly `cliverging outwardlyand ,downwarlyrromz ,said .collar inaoniform .angular spacing ciefinitye of a hollow frustumof a `cene-is mounted `and disposed for rotation within the bowlglfl with the divergent free lower enclsof the vrods |.4.we11.spaced,from and ,to clear .the bowl bottomrandr-sidezwall areasl andthe'collar -I-labove the,normalg.pulp.1evel ofthebowl 'to dispose said rods in norrnaiintersectingrelation with the=-surf;ace ofthe:,bowl-'charge as indicated atL in Figure 2. Tofoprativelymount and ,adjustablyfsupport; Lthe; shat l 3 v: and its .associated impellerassemhly, na;postf i fixelly Aupstancling fromthe base.` ,I Linaxial parallelism withA and` at one .side ,'-otthe `boizvlf I 0. slidaloly.` .engages within and `reciprooablyftfincmntsl a tubular .memberil'l fixedly .related at its upper end with a rightangulararmflBarranged to overhang the bowl'l andv a'sleeve l9=on"the -free end of saidarm'i-is -arranged torotatably accommodate and to be traversed by' ,thefshaft 13' ina coaxial relationship of saidsleeve, 'shaft,, and the bowl li). A bracket 2i adjustably engaged with the member ll upper end in an extension laterally therefrom opposite to the arm iii projection mounts an electric motor :ii with its shaft paralleling the shaft i3 so that coplanar pulleys 22 and 23 xed respectively to the motor shaft upper end and to the end of the shaft E3 above the sleeve 19 and interlinked by a belt 2d may function as a drive for the shaft SS and its impeller assembly powered by said motor 25. Selective altitudinal adjustment of the member il and the elements carried thereby is provided through the agency of a rack 25 fixed longitudinally of the post Hi interiorly of said member, a gear 2% rotatable in ears 21 outstanding in spaced parallelism from said member and meshing with the rack 25 through an opening in the member wall, a handle 28 for the manual rotation of the gear 26, and a ratchet and detent arrangement 255 effective to hold the gear 25 in any adjusted relationship along the rack 25, the adjusting means shown and described being capable of functioning in an obvious manner to elevate and lower the impeller assembly axially of the bowl iii and to hold said assembly available and in condition for operation at any position in its range of altitudinal adjustment.

All of the foregoin'g is but typical of organizations and arrangements utilizing the novel impeller asseinbly and operative relationships disclosed in inv earlier Patent No. 2,577,802, and is herein illustrated and described as representative of known means and particular combinations -wherewith and wherein my further improvements are of especial advantage, it being readily apparent that power rotation of the shaft IS and its impeller assembly with the rods ifi'i of the latter penetrating the body and intersecting the surface of a pulp charge within the bowl w will function to whip and agitate the pulp charge and to entrain air from above the charge surface along and iinmediately behind the moving rods ifi for dissemination as bubbles within and throughout the agitated charge and for jet-like delivery from the rod free ends at appropriate sp-eeds of rod translation.

` Apparatus characterized by impellers of the type shown in my earlier Patent No. 2,577,802, and hereinabove described has successfully operated to effectively agitate and to thoroughly and satisfactorily aerate pulps of Various natures and consistencies for selective froth fiotation and for conditioning thereof, but factors pertinent to v'pulp reoirculation, to the development of circulatory currents Within the pulp, to scourng of the sediments from the cell bottoni, to maintenance of a quiescent zone adjacent the froth bed, to the depth and location of the impeller Vortex, and to regulation of the induced air volume, are significant to the Operating eflicency of the particular impeller assembly shown and desoribed and give practical occasion for the further improvernents of the present invention.

Primary to the organization and operation of the features characteriz-ing the present invention, a hollow, frusto-conical shroud il is provided in a size and form to spacedly engage about and to house the major length of the impeller assembly and the orbit of impeller rod Ill revolution. As associated with the apparatus according to Figures 1-4, inclusive, of the drawings, the shroud is provided with a coaxial, fiXedly-related, tubular neci Si extending from its lesser end for telescopic engagement With and about the lower end of the sleeve 19 in a tight frictional fit on, or other attachment to, the latter effective to mount the shroud 353 on and for altitudinal adjustment with said sl'eeve in coaxial relation with the shaft E3 and associated impeller assembly and in a doWnwardly-fiaring extension through the surface of the pulp charge within the bowl and into the body of the pulp charge such as will position the lower open end of the shroud somewhat above the plane common to the lower or free ends of the rods l'l and dispose the shroud conical Wall in clearing relation about and outwardly from the impeller assembly rods Ill and their operative orbit, thus to permit free rotation of the impeller assembly interioriy of the shroud. Since the shroud 3B and its necl 3! fully house and enclose the impeller assembly elements extending above the surface of the pulp charge in the bowl, it is clear that rotation of the impeller assembly as so housed will be ineffectual to establish induction of air within and through the pulp charge unless provision is made for supply of air, or analogous gases, to said necl: and the shroud lesser end, for which purpose a suitable ow line 32 equipped with a valve 33 leads from atmosphere, or from a supply of desred particular gas, to and opens at its delivery end through the n-eck iii. Thus, when the impeller assembly is rotating interiorly of the shroud (it, the amount of air, or other gas, consequently introduced and disseminated Within the pulp charge may be controlled and regulated by means of valve 33 adjustment and the position of the Vortex in the pulp surface incident to such impeller assembly rotation may be correspondingly lowered or elevated within the shroud relative to the normal pulp level in reaction to such valve manipulation.

Fixed to and outstanding laterally from and about the lower end of the shroud 313, a series of like, flat vanes 34 is arranged in a uniform angular spacing of the individual vane elements to dispose the latter as fixed bafiies within and substantially across the space between the shroud lower end and the adjacent bowl Wall. The vanes 35 are approximately rectangular in plan, are similarly fixed at their corresponding inner margins to the shroud lower end in a generally radial projection therewith so as to position their outer margins substantially parallel with the bowl side wall, extend vertically across the plane of the shroud open lower end to dispose their parallel upper and lower margins respectively above and below said plane and to position their said lower margins adjacent and in clearing relation above the floor of the bowl and in a common plane below that of the impeller rod [4 free ends, and are preferably, though not necessarily, similarly inclined to the Vertical, substantially as shown. It is the function of the vanes 34 to modify and direct pulp currents and agitations developed by impeller assembly rotation in a manner and to a degree susceptible of regulation through Variation in the numberrelative size, particular disposition, and inclination of the said vanes in a given installation, the vane arrangement illustrated being obviously effective upon impellergenerated pulp outfiow from the shroud lower end to interrupt and inhibit the development of pulp currents tending to swirl With the impeller circularly of the bowl, to direct pulp currents against and with scourng effect upon the bowl floor, to stimulate pulp agitation through the generation of uprise currents along the bowl Walls and between the vanes, and to thoroughly commingle the agitated pulp with air or gas bubbles introduced along and delivered from the free ends of the rods Ill. Enhancing the pulp-agitating and bubble'-disseminating'A effect of the vanes 34, holes may beformed in and through said vanes in any number, particularV size, and pattern deemed to' be appropriate in a givenpractical application of/the apparatus, andV interruption and deflection of' radially-directed pulp currents may be effectively had, whendesired, through the provision of an annularband 36, of appropriate width,- engaging and fixed to the outer margins of the vanes 34.

For maintenance of a pulp charge interiorly of the shroud 3d lower portion subject to action of the 'impeller assembly and to accommodate circulation and'recirculation of the pulpthrough the' influence-of the impeller, the length'of said shroud is' interrupted'well below the normal pulp level of lthe cell, and preferably a short distance above the upper margins of the vanes 34, by-an annular throat 31 of operatively-suitable"width axially of the shroud which extends entirely about the shroud in an orbit perpendicular" to the shroud axis and clivides said-shroud into an upper portion carried by the neck 3i and a separate, lower shirt portion attached to and supported from said upper portion by suitable means, such as struts 38 bridging said throat 31 in angularly-spaced relation and fixedly end-engaged with the separated shroud portions, the upper end of the shroud lower shirt portion expediently being formed as a radialy and outwau'dlyl directed annular fiange 3i effective to stiffen the tubular shroud skirt and to direct infiow of pulp through the throat 31. With the impeller and shroud arrangement shown and described, rotation of the impeller assembly operates to exhaust pulp and intermingled air bub-bles from the shroud interior through the open lower end of the shroud for agitationand uprise within the cell under the influence and direction of the vanes i'and band 36', the material so exhausted from the` shroudv interior being continuously replaced by` infiow of pulp` through the throat 3'i with consequent most thorough recirculation of the pulp andagitation thereof in intimate and` repetitious exposure to the air or gas bubbles generated within the pulp byV the impeller action.

In accordance with the principles of froth flotation, the'air or gas bubbles generated within the cell rise through the'pulp charge'with thepulp part'icles to which they have become attached and colle'ct on and above the pulp level of the cell as a froth `ced removable over the lip H'for segregation of the material levitated thereby, such uprise of the bubbles and the'efiicient collection thereof in and as a froth bed on the pulpsurface being facilitated with advantage-of separatory,7 efiiciency through damping out of turbulence and eddy currents'in the upper levelsiof the pulp charge and the consequent provision of a qui'escent pulp zone underlying the froth'bed. For the purposes and to develop the effects just above noted, it .ispractical and'convenient-l to provide a diffusing bafile dil'zion and about the shroud 30 above the throat 3 `l"in a Vgenerally horizontal disposition across the space-between the shroud and the cell: side wall,

saidfbaffle llpreferably being in the form of a somewhat fiattened frustoconicalplate conform'ed in-plan with the bowl l and of a size to slidably engage within said bowl, an opening centrally'and through the lesser end of said plate sized andv conformed to embracethe shroucl 30 upper portionand to marginally engage said shroud portion immeoliatelyV abovethe throat 3'1 for positioned supportof the battle thereon, holes 4-I intersectingl thebafl'ie conical' area'in such size, number, and pattern as willV adequatelyaccommodatel uprse3 of. air and gas'bubbl'es therethroug'h, andanupturned lip;4Zfperipherallyvofthe bafile-plate facilitative of baiile plate introduction'within, .and ad- J'ustment'. thereof altitudinally of,V the bowl Ill.

Withthe baiiie-li positioned as shown and described, the turbulence and eddy: currents generated byfimpeller assembly rotation are largely confined-to thervlower area: of 'the pulp=charge below-said bafiie andldeflected away from' disturbing effectuponthepulp chargearea` above the baflle'.

the air or gas'ibubbles approaching. and imping-ingagainstV the baifle passingv through the holes M' thereofV by Virtue 'of their tendencyto uprise vertically through the pulpv andl completing such uprise tothe pulp surface through the relatively quiet Aupper areaiof the-pulp: charge with a minimunrof collapse andloss of their partiole charges;

thecomparatively undisturbed sur-face :of the pulp charge* facilitating development of the desired.

froth bed' in fioatingrelation therewith.

In a structural arrangement and operativeor'- ganization analogous' to that hereinabove described, the improvementsofrz the-present invention are-'shown inlF'igures 7-10; inclusive, asassociated -for practical'use in and with a cell'adapted to accomplishieither froth'fiotative or conditioning treatment of 'a pulp. In the-views last above noted, the ce1l2 iii! is-shown as rectangular inl plan, asformed with a-fioor inwardlyl and down- Wardly-sloped fromf each'sicle of 'the cell to a horizontal iioor area centrally and longitudinally of the cell, andasassoci'ated for 'continuous flow operation with'a pulp feed box'f43\ arranged for input z of pulp'to theV cellat and to oneend'of thecell floor centralarea-andfor delivery of' treated pulpthroughiahoodedioutfiow orifice M to a -succeeding cell IG, all'in-accord'ance with known and conventional' practice.

top wli'ereon the'tubular sleeve i9'ispositioned and supportedfwith itslaxis verticaland centrally offthe cellto dispose the shaftv l3 with its associated impeller assemblyof'rods) 14' and-collar i d in for rotatioirrelative to the cell'inl theimanner and for the purposes of pulp agitation and air induction'previouslx'r described. The motor isf adjustably carried by the bridge 45 with its shaft Vertical so-thatthe pulleys 22 and 23 may engage the belt''tfor completion of a power drive to the shaft iandimpeller assembly as previously set forth. Structurally and'functionally analogousto'the'shroud 3d, a frusto-conical shroud 351' cornprised of upper and lower portions separated by an annular1 throat 31' is supplied with fixedly-re-- lated'stem members 46 engaging its exterior surface and bridging'the throat 37' to interconnect the otherwise separate shroud 36 portions, and extensions of said members 46 beyond the lesser end ofthe'shroud are arranged to parallel the shroud axis and threaded for a'distance adjacent their free ends, so that when said member extensions-are engaged through holes in elements of.

the'bridge 45 supportingthe sleeve l'and with nuts'adjusted to bearagainst said'bridge elements.

pose the'collar l5 and rod l4` upper endsabove its lesser end' plane and to establishprojection ofithe ro'd-l 4 free ends below its greater end plane,

the saidlesser and greater endsV of the shroud'? The cell'| Hi! is furnished with a-rigid bridge 45fixedly' spanning its open'v being preferably stiifened and reinforced by means of annular fianges 39' outstanding radially therefrom and the shroud lesser end preferably being formed as an axially-short cylindrical band Ill upstanding in coaxial relation therefrom. At its lower end the shroud 30' carries fixedlyrelated vanes 34', each preferably intersected by a plurality of holes 35', in a radially-outstanding, angularly-spaced, preferably inclined arrangement structurally and functionally the same as that of the vanes 34 of the embodiment rst described, and outer ends of the said vanes 34' close against and are encircled by an annular band 36' which may be operatively associated with and for altitudinal adjustment relative to the vanes by means of slotted ears 48 fixed to and extending inwardly from the band inner surface to conformably overlie certain of the vane outer ends in clampable association with bolts 49 engaged through the said vane ends and the slots of said ears.

When utilized for froth flotation purposes, the organization represented in Figures 7, 8, 9 and 10 operates to agtate, aerate, and recirculate the pulp in an obvious manner closely similar, except for regulation of air infiow to the impeller, to that charactcrizing operation of the first-described embodiment of the improvements. For such froth flotative operation of the apparatus,

the level L of the cell pulp charge is established,

through altitudinal adjustment of the shroud 30' or through regulation of pulp flow to and through the cell, or both, at a plane below that of the band 47 upper end, thereby to inhibt inflow of pulp to the shroud through its open upper end and to dispose said band M as a bafiie upstanding through the froth bed to dam the latter` away from entrainment within the pulp body, thus constituting the open throat 37' as the means accommodating inflow of pulp from the cell and to the shroud interior as the impeller acts to exhaust pulp from and through the lower end of the shroud, whereby to effectively recirculate the pulp in the lower area of the cell and to minimize the development of eddies and currents within the progressively more quiet pulp zones above said throat.

For thorough and repetitious agitation of the entire pulp charge, as in the conditioning of ore pulps in the presence of reagents, and the like, the apparatus represented in Figures 7, 8, 9 and 10 may be efciently and advantageously utilized simply by closing the throat 31' of the shroud 30' and adjusting the level of the cell pulp charge, through regulation of pulp flow to and through the cell or by varying the altitudinal disposition of the shroud, to a relation with the shroud open upper end indicated at L" such as will submerge the shroud wholly within the pulp charge and establish a continuous feed of pulp to the shroud interior through the open collar 41 when and as the impeller is Operating. Various expedients may be availed of for selectively closing the shroud throat 31", a convenient arrangement for such purpose being illustrated as comprising segmental skirt plates B adapted to close over the throat areas between the stem members 46 in engagernent with positioning and supporting means, such as hooks 55 and latch studs 52, carried by the shroud.

Obviously, the balfle Lit may be utilized with the shroud 3i`i' in the manner and for the purposes to which it is applied in association with the shroud 30, the shroud 36 may be open to atmosphere at its lesser end and provided with closures for its throat 31, whereby to adapt it for use in the conditioning of the pulp, and the shoud 3B' may be provided with a chamber at its upper end closed to atmosphere and furnished with a valved inlet, in the manner and for the purposes characterizing the like means associated with the shroud 3%, all such relationships and reorganizations of the elements shown and described being clearly Within the manifest scope and contemplation of the invention.

Since changes, variations, and modifications in the form, construction, and arrangement of the elements shown and described may be had without departing from the spirit of my invention, I wish to be understood as being limited solely by the scope of the appended claims, rather than by any details of the illustrative showing and foregoing description.

I claim as my invention:

l. The combination with an open-top cell adapted to contain ore pulp and a verticallyaxised, frusto-conical impeller assembly of angularly-spaced, divergent rods rotatable about its axis in agitating and aerating relation with the cell pulp charge with its lesser end uppermost, of a frusto-conical shroud non-rotatably fixed coaxially with and spacedly about the major length of said impeller with the shroud lower end upwardly adjacent the lower end of the imfpeller, vanes fixedly outstanding radially from and in angularly-spaced relation about the lower end of said shroud with their outer ends inwardly clearing the cell walls and their lower margins in a plane above the cell floor and below the lower end of the impeller assembly, and a throat circumferentially interrupting said shroud above said vanes for the circulation of pulp therethrough.

2. The combination with an open-top cell adapted to contain ore pulp and a verticallyaxised, frusto-conical impeller assembly of angularly-spaced, divergent rods rotatable about its axis in agitating and aerating relation with the cell pulp charge with its lesser end uppermost, of a frusto-conical shroud non-rotatably and in angularly-spaced relation about the lower end of said shroud with their outer ends inwardly clearing the Cell walls and their lower margins in a plane above the cell fioor and below the lower end of the impeller assembly, a throat circum- -ferentially interrupting said shroud above said vanes for the circulation of pulp therethrough, a neck extension of the shroud upper end defining a Chamber closed to atmosphere, and a valve- Controlled inlet to said chamber above the pulp charge level.

3. The combination with an open-top cell adapted to contain ore pulp and a verticallyaxised, frusto-conical impeller assembly of angularly-spaced, divergent rods rotatable about its aXis in agitating and aerating relation with the cell pulp charge with its lesser end uppermost, of a frusto-conical shroud non-rotatably fixed coaxially with and spacedly about the major length of said impeller with the shroud lower end upwardly adjacent the lower end of the impeller, vanes fixedly outstanding radially from and in angularly-spaced relation about the lower end of the shroud with their outer ends inwardly clearing the cell walls and their lower margins in a plane above the cell floor and below the lower end of the impeller assembly,` a throat circumferentially interrupting said shroud above said vanes for the circulation of pulp. therethrough, and a baflie engaged with and exteriorly about said shroud immediately above said throat in spacedly-overhanging relation with said vanes.

4. The combination with an open-top cell adapted to contain ore pulp and a verticallyaxised, frusto-con'ical impeller assembly of angularly-spaced, divergent rods rotatable about its axis in agitating and aerating relation with the cell pulp charge with its lesser end uppermost, of a frusto-conical shroud non-rotatably fixed coaxially with and spacedly about the major length of said impeller with the shroud lower end upwardly adjacentthe lower end of the impeller, vanes fixedly outstanding radially from and in angularly-spaced relation about' the lower end of said shroud with their outer ends inwardly clearing the cell walls and their lower margins in a plane above the cell floor and below the lower end of the impeller assembly, a throat circumferentially interrupting said shroud above said vanes for the circulation of pulp therethrough, a neck extension of the shroud upper end defining a chamber closed to atmosphere, a valve-controlled inlet to said chamber above the pulp charge level, and a baffle engaged with an exteriorly about said shroud immediately above said throat in spacedly-overhanging relation with said vanes.

5. The combination with an open-top cell adapted to contain ore pulp and a verticallyaxised, frusto-conical impeller assembly of angularly-spaced, divergent rods rotatable about its axis in agitating and aerating relation with the cell pulp charge with its lesser end uppermost, of a frusto-conical shroud non-rotatably fixed and mounted for altitudinal adjustment e coaxially with and spacedly about the major length of said impeller with the shroud lower end at all times upwardly adjacent the lower end of the impeller, vanes fixedly outstanding radially from and in angularly-spaced relation about the lower end of said shroud with their outer ends inwardly clearing the cell walls and their lower margins in a plane above the cell floor and below the lower end of the impeller assembly, a throat circumferentially interrupting said shroud above said vanes for the circulation of pulp therethrough, an annular collar concentrically upstanding from the shroud lesser end and altitudinally adjustable with the shroud between extension above and submergence below the pulp charge level, and means for selectively closing said throat.

6. In apparatus of the character described having an open-top cell adapted to contain ore pulp and a vertically-axised impeller assembly of angu1arly-spaced, divergent rods rotatable about its axis in agitating and aerating relation with the cell pulp charge with its lesser end uppermost, a frusto-conical shroud non-rotatably fixed coaxially with and spacedly about the major length of said impeller with the shroud lower end upwardly adjacent the lower end of the impeller, vanes fixedly outstanding from and in angularly-spaced relation about the lower end of the shroud with their outer ends inwardly clearing the cell walls and their lower margins in a plane above the cell fioor and below the lower end of the impeller assembly, and a throat circumferentially interrupting said shroud above 10 the vanes to. provide a pulp recirculation passage to the shroud interior.

7. In apparatus of the character described having an open-top cell adapted to contain ore pulp and a vertically-axised impeller assernbly of angularly-spaced, divergent rods rotatable about its axis in agitating and aerating relation with the cell pulp charge with its lesser' end uppermost, a frusto-con-ical shroud non-rotatably fixed defining a Chamber closed to atmosphere, and a valve-Controlled inlet communicating with said chamber above the cell pulp charge level.

8. In apparatus of .the character described having an open-top cell adapted to contain ore pulp and a vertically-axised impeller assembly' of an'- gularly-spaced, divergent rods rotatable about its axis in agitating and aerating relation with the cell pulp charge with its lesser end uppermost, a frusto-conical shroud non-rotatably fixed coaxially with and spacedly about the major length of said impeller with the shroud lower end upwardly adjacent the lower end of the impeller, vanes fixedly outstanding from and in angularlyspaced relation about the lower end of the shroud with their outer ends inwardly clearing the cell walls and their lower margins in a plane above the cell fioor and below the lower end of the impeller assembly, a throat circumferentially intersecting said shroud above the vanes to provide a pulp recirculation passage to the shroud interior, and a baifle engaging with and exteriorly about said shroud immediately above said throat in spacedly-overhanging relation with said vanes.

9. In apparatus of the character described having an open-top cell adapted to contain ore pulp and a vertically-axised impeller assembly of angularly-spaced, divergent rods rotatable about its axis in agitating and aerating relation with the cell pulp charge with its lesser end uppermost, a frust-o-conical shroud non-rotatably fixed coaxially with and spaced about the major length of said impeller with the shroud lower end upwardly adjacent the lower end of the impeller, vanes fixedly outstanding from and in angularlyspaced relation about the lower end of the shroud with their outer ends inwardly clearing the cell walls and their lower margins in a plane above the cell fioor and below the lower end of the impeller assembly, a throat circumferentially intersecting said shroud above the vanes to provide a pulp recirculation passage to the shroud interior, a bafile engaging with and exteriorly about said shroud immediately above said throat in spacedly-overhanging relation with said vanes, and apertures extensively interrupting said baii'le and said vanes for pulpcirculation therethrough.

10. In apparatus of the Character described having an open-top cell adapted to contain ore pulp and a vertically-axised impeller assembly of angularly-spaced, divergent rods rotatable about its axis in agitating and aerating relation with the cell pulp charge with its lesser end uppermost, a frusto-conical shroud non-rotatably fixed coaxially with and spacedly about the major length of said impeller with the shroud lower end upwardly adjacent the lower end of the impeller, vanes xedly outstanding from and in angularly-spaced relation about the lower end of the shroud with their outer ends inwardly clearing the cell walls and their lower margins in a plane above the cell fioor and below the lower end of the impeller assembly, a throat circumferentially intersecting said shroud above the vanes to provide a pulp recirculation passage to the shroud interior, a neck extension of the shroud upper end defining a Chamber closed to atmosphere, a valve-Controlled inlet communicating with said Chamber above the cell pulp charge level, and a baflle engaging with and exteriorly about said shroud immediately above said throat in spacedly-overhanging relation with said vanes.

11. In apparatus of the character described having an open-top cell adapted to contain ore pulp and a vertically-axised impeller assembly of angularly-spaced, divergent rods rotatable about its axis in agitating and aerating relation with the cell pulp charge with its lesser end uppermost, a frusto-conical shroud non-rotatably fixed coaxially with and spacedly about the major length of said impeller with the shroud lower end upwardly adjacent the lower end of the impeller, vanes fixedly outstanding from and in angularly-spaced relation about the lower end of the shroud with their outer ends inwardly clearing the cell walls and their lower margins in a pl'ane above the cell fioor and below the lower end of the impeller assembly, and an annular band coaxial with said shroud embracing and engaging the outer ends of said vanes in clearing relation with and above the cell floor.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,597,316 Hutchings Aug. 24, 1926 1,796,2'78 Bakewell Mar. 17, 1931 1,976,956 MacLean Oct. 16, 1934 2,031,590 Daman Feb. 25, 1936 2,190,852 Tucker Feb. 20, 1940 2,433,592 Booth Dec. 20, 1947 2,578,805 Johnson Dec. 18, 1951 FOREIGN PATENTS Number Country Date 15,292 Great Britain June 30, 1911

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