US2928543A - Froth flotation separation - Google Patents

Description

March l5, 1960 H. LoGUE 2,928,543

FRo'rH FLoTATIoN SEPARATION Filed Nov. 1o, 1955 2 sheets-sheet 1 ATTORNEYS March 15, 1960 L. H. LOGUE 2,928,543

FROTH FLOTATION SEPARATION Filed Nov. l0, 1955 2 Sheets-Sheet 2 IN V EN TOR.

l5 43 42 Leland H. Logue .ATIQRNEYS FROTH FLTATIN SEPARATION Leland H. Logue, Denver, Colo., assignor, by mesne assignments, to Denver Equipment Company, Denver, Colo., a corporation of Colorado Application November 10, 1955, Serial No. 546,123

5 Claims. (Cl. 269-169) This invention relates to the froth o'tation art and more particularly relates to improved methods and means for performing froth flotation separations.

Mechanical type froth flotation apparatus has come into general acceptance by most flotation operators and many advantages over the pneumatic or air lift machines. There has been a tendency to go to larger sized equipment in ore milling and this has required the production of larger flotation cells. ln almost all pulps, there will be a considerable portion of the solids in liner size ranges and another considerable portion in substantially coarser sizes.

There is a tendency toward size segregation or stratication in the modern machines with a substantial amount of the finer sizes remaining in the upper portion of the pulp body and another substantial amount of coarser sizes remaining in the lowermost portion of the pulp body. These conditions do not favor good dotation as the intermediate sizes tend to float more readily while the line sizes near the top and the coarse sizes near the bottom cause a density build up that impedes the flotation elli-Y ciency. In addition, an appreciable amount of gangue in line sizes frequently is entrained in the ne concentrate and thus reduces the grade of concentrate.

The coarse sizes in the lower portion of the pulp body are moving under the intense action of the agitation and exert a scouring action on the liner sizes which reduces the filming effect on such particles and thereby impedes flotation. However, the usual agitation fails to make provision for loosening and distribution of the coarse strata forming in the lower portion of the cell. Even in operations where arrelatively high recovery is obtained at flotation there is a substantial amount of the valuable constituent passing from the treatment with the tailings which invites recovery if an economical method can be provided.

My invention is based on the discovery that by inducing a high degree of circulation along essentially vertical courses within a otation cell, a size segregation of pulp particles can be greatly alleviated if not completely eliminated with substantial reduction of tailings losses. In inducing such circulation I prefer to utilize a free falling movement of pulp through a downward course of substantial vertical extent which develops a high velocity movement that is highly effective in entrainment of air or other aerating gas and reduces the power requirement of the impeller due to the high velocity input of pulp. I also utilize a high velocity discharge at the bottom of this vertical course which provides a high degree of intermingling of coarser and finer sizes accompanied by intense gas release and elevating movement of the commingled solids.

Accordingly it is an object of this invention to provide a simple, efficient and economical froth flotation process in mechanical type cells which process substantially eliminates size segregation of pulp constituents in the treatment and thereby improves grade and recovery.

Another object of this invention is to provide a simple,

States Patent C) durable and economical froth flotation cell which may have a greatly increased vertical dimension as compared with conventional cells, thereby permitting large volume treatment over a small floor space and with improved flotation efficiency.

A further object of this invention is to provide a simple, eliicient and economical process which permits the circulation of a larger volume of pulp during a given flotation time and with improved grade and recovery.

Other objects reside in novel details of construction and novel combinations and arrangements of parts, all of which will be set forth in the course of the following description. Y

One of the advantages of the present invention is that it may be incorporated in machines already installed and in use as well as in new embodiments specially designed for the practice of the invention. it may be utilized in unit cell operations although it will have its greatest tially the same operation is performed in each cell although the highest eiciency will derive from the utilization of optimum dimensional relationship and operating controls.

The practice of the invention will be best understood by reference to the accompanying drawings in which a preferred embodiment of the apparatus of the present invention has been illustrated. In the drawings in both views of which like parts bear similar reference numerals:

Fig. l is an end elevation, partially broken to show arrangement of interior parts, of a flotation cell utilizing features of the present invention and represented as being empty; and t Fig. 2 is a developed section of a similar cell taken approximately on the line 2 2, Fig. 1 and with a fragmentary representation of the arrangement of adjoining cells in the series of a multiple cell machine and represented as in operating condition with flows indicated by arrows.

The machine shown in Fig. 2 comprises a three-cell arrangement in which cell C represents a rst cell of the series, cell C1 an intermediate cell, and cell C2 a last cell of a hog-trough type mechanical machine in which a suitable control (not shown) of the tailings discharge from the last cell as by overliow weir or oat valve control will control the rate of tiow through the machine. Initial feed to the machine usually is through a feed box and submerged inlet (not shown). Since these features are old and well known in the art, detailed description and illustration appears unnecessary.

Each of the cells C, C1, and C2 will comprise a front wall 12, a rear wall 13, two side walls 1d and a bottom 15. Preferably the front wall 12 inclines forwardly in its upper portion to provide an enlarged spitzkasten effect while rear wall 13 inclines inwardly as shown to crowd the froth bed toward overow lip 16 at the top of wall 12. This arrangement provides a large area near the surface of the pulp body which is out of the path of the circulating llow as will be subsequently described and assists in the collection and discharge of the froth concentrate.

Cell C1 has one or a plurality of pulp inlets 18, shown in Fig. 2 as three in number, and these inlets function as the tailings discharge of the preceding cell in the series which is the cell C of Fig. 2. The combination of feed upper surface and a plurality of sweeping vanes 28 on its` under surface.

An impeller Z6V is mounted on the' A hollow column 3d issupported in a depending posi-v Y tion from the lower endiof bearing assembly 22`in` encompassing relation toshaft 21. The column 30 extends throughoutsubstantially the vertical extent of cell C1 and carries a laterally extending cover member 31 at its lower .end whichoverhangs impeller with its under surface y providing only a slight clearance with the tops of bladesV 27 onthe impeller. Y Y Y Y A plurality of pulp intake openings 33 Vare located in the upper portion of column near but below liquid level 19 and air intake openings 34 are located infV theV column above the liquid level. yIf Vtheaeration, isV to.V utilize atmospheric air the openingsr34V will be left un`.

plugged, but if an aerating gas under lpressure is used,.a ll but one of said openings will be plugged and the remain'- ing one connected as by threaded nipple with a header or, For best r`e" sults the liquid head over openings 33 should correspondV other source of gas supply (not shown).

to the showing in Fig.V l, and if a given operation produces a greater froth depth or lowering of liquid level 19, onek or more slots 40 should be inserted in guide member` 414 to provide a weir overflow above lip 16 and .thereby bring the liquid level into proper relationship with openings 33.

fraot the flow of aerating gas downwardly through said b e. t

Due to the substantial distance between the openings 33 and the impeller 26 andthe unrestricted fall of the pulp onto the impeller, such pulp attains a relatively high velocity movement before reaching the impeller which induces a high degree of gas entrainment in the cascading action. The impeller is rotated at a speed which will discharge the pulp-gas intermixture at a rate at least equal p to therate of its delivery to the impeller, and in preferred practice,l at an even higherrate. As a consequence pulp enters column 30 in a volume permitted `by the area of openings 33 collectively under the hydrostaticV head of the liquid extending to level 19`. The shield 36'prevents a vortex formation which might recirculate froth eoncen- Y trate and the circulatory action effectively retards size stratification of pulp particles.

Whenever'feed entering a given cell tends to cause such stratification' by delivering too `large a proportion of coarse sizes into the lower partof the pulp body, the` impeller Ydischarge eifec'tsa displacement action in which v a substantially. higher percentage `of ner sizes replaces the coarser sizes elevated by the Vupward sweep of pulp i through the cell. In the usual flotation cell, this elevat- An annularfbatfle 35 divides the Yupper hollow portion ofcolumn 3i) into an inner air passage andan outer pulp passage. Thisbaflie may-be of any suitablelength but should extend below the pulp intakeopenngs?, so that the entering pulp streams are diverted withoutconverging and thus fall by gravity in an unimpeded descent tothe impeller. ln order to avoid any vortex'formation at the surface which might remove aV substantial quantity ofthe froth concentrate; l provide' an annular shield 36 above openings 33. Other shapes of shield may be provided but the annular formi is simple to construct andY is easily connected. e v v As shown in Figs. 1 and 2, the cell bottom A1S maybe providedvwith a centralr aperture 42 normally closed by a plug 43 and this opening Vwill be used for draining the machine as required, or if desired, a suitable Vgas line may be connected for the supply of additional aerating gas, or

reagent. The machine illustrated has the bearing mem`l ber 22 detachably mounted on superstructure 20 so that the impeller 26 and column 30 may be installed and removed as a unit. In addition, an access opening 45 closed by a plug 46 permits separate mounting'and removal of the impeller. Also as shown, the spacing be-v tween the impeller may be varied by adjustment of bolts 48 inslots 49.

The practice of the invention in a machine such as illustrated in Fig 2 will be described. Aconditioned pulp is fed continuously toa first cell, such'as cell C, flows'` through the openings 18 to iillrthe next cell Cl-which may l ybe any number of intermediate cells, and `again passesv `through openings 13 to till a last cell Cz'gwhichghas, a .e

continuous, regulated discharge suchl as anfadjustable weir (not shown). The flow permitted by the` openings 18 provides a substantially uniform liquid level 19in all cells. The pulp will contain one portion of solids in a coarser size range and another portion of ner sizes, the

actual size distribution varying withfeach ore treated.

Each of said cells will have a circulation of the'type l `depicted in Fig. 2 in which the impeller 26 will befrotated at a peripheral speed onvt'ne order of 1600 feet per minute and all feed thereto enters through theV plurality formation occurs in the vascending pulp, column.

ing movement is Voffset byfresulting downward currents as the upper portion of the cell has no capacity `to relieve itself from the ,input of pulp. However in the present arrangement, the input and discharge capacity of the upper portion of the solids arefree to descend only within the enclosure of thelcolumn.` v

A s a`result,.a high degree of mixing Yof tine and coarse sizes accompanied `by intense gas release in tine bubble In a typical test installation: in ajcell of approximately 375 gallons capacityA and arranged substantially as shown in Figi2, it was determined that the pulp was recirculating at a'rate ofbetween'450 and 500 gallonsper minute. Average flotation time in such` installations is on the order of two minutesso the entire pulp volume recirculates ,between'two and `three times'within the dotation time period providedfor such cell. v

The flotation operation. just described has the effect of increasing Vplmtfcapat`y as a higher volume of pulp can be treatedecientlyin a shorter time than in conventional operations. A greatly improved grade and recovery is attained. impeller speeds are reduced with consequent `power savings and reduced wear. Y This was demonstrated in'a comparative test in a commercial milling operation; Threestandard cells were subjected to comparative tests Yforten day periods with size analysis of concentrateproducedV in each cell. The ten day average established that cell No. 1 had 33 percent in the plus l0() size range, cell No. 2, 31 percent plus 100 and cell No. 3, 33' percent plus' `100. Y, f e Y Theimiddl'e No. 2 cell was then modiliedto correspond with the arrangement shown in Fig. 2, cells Y1 and 3 were wasrundertalcen. The average analysis was as follows:

of openings 33 in column 30 from near but below theI l liquid level 19. This entering pulp is directed by the Aanff nular baille 35 into. gravitational fallinitially separated,`

cell No.1, 27 percent plus 100,V cell No. 2, 45 percent plus 100, and cell No. 3, '34 percentplus'lOO. The foregoing-,test results.` arercited kas typical, of the degree of concentration of thevcoarsersiz'es Ywhich can be attained in the practice of thepresent invention.

*The'maehineillustrated in the drawings is a Denver Equipment Company ho`g-troug hY type modified to em-Y body features `of the present invention. While such a Vmachine is well suited to thepracticeof my invention, it

. will be understood that other standard mechanical-type` cells may be similarly modifiedV for the practice of the invention. `Howeveigthe `invention lends itself to em-` bodiment in specially designed cells'of much greater depth than'conventional cells.' Theextension of depth apparf` Aently does not lessenmetallurgical ,efficiency and in some Vinstances may'imp'rvef it, and the resulting increase in` cell. is` substantially balanced and` f Y s cell capacity permits substantial increase in plant capacity without enlargement of plant area and no increase in operator requirements. Y

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

I claim:

l. In the froth flotation art in which a conditioned pulp is subjected to a succession of flotation treatments at progressive stages of a course of flow with arpredetermined otation time at each stage, the improvement which comprises maintaining a body of pulp of substantial vertical extent subject to continuous feed and discharge at each stage, inducing a circulatory ow within said body so as to direct an elevating component of movement to substantially all the solids in the lower portion of said body and an unimpeded gravitational fall to a substantial portion yof the solids in the upper portion of said body and below the surface thereof, supplying an aerating gas for entrainment in the pulp in said gravitational fall, and controlling the volume and velocity of pulp in said gravitational fall so as to recirculate a major part of the pulp volume during said flotation time.

2. In the froth flotation art in which aconditioned pulp is subjected to a succession of flotation treatments at progressive stages of a course of flow with a predetermined ilotation time at each stage, the improvement which comprises maintaining a body of pulp of substantial vertical extent subject to continuous feed and discharge at each stage, inducing a circulatory flow within said body so as to direct an elevating component of movement to substantially all the solids in the lower portion of said body and an unimpeded gravitational fall to a substantial portion of the solids in the upper portion of said body and below the surface thereof, supplying an aerating gas for entrainment in the pulp in said gravitational fall, controlling the volume and velocity of pulp in said gravitational fall so as to recirculate a major part of the pulp volume during said flotation time, and removing a concentrate by `overflow at a distance from said circulatory ow.

3. A processas dened in claim 1 in which the circulatory flow is directed to cause a continuous intermingling of liner and coarser sizes in the pulp.

4. In the froth liotation art in which a conditioned pulp is subjected to a succession of flotation treatments at progressive stages of a course of ow with a predetermined otation time at each stage, Vthe improvement which comprises maintaining a body of pulp of substantial vertical extent subject to continuous feed and discharge at each stage, inducing a circulatory flow within said body so as to direct an elevating component of movement to substantially all the solids in the lower portion of said body and an unimpeded gravitational fall to a substantial portion of the solids in the upper portion of said body and below the surface thereof, supplying an aerating gas for entrainment in the pulp in said lgravitational fall, and controlling the volume and velocity of pulp in said gravitational fall so as to recirculate a quantity of pulp in excess of the pulp volume of said stage during said otation time.

V5. In the froth otation art in which a conditioned pulpV is subjected to a succession of otation treatments at progressive stages of a course of flow with a predetermined flotation time at each stage, the improvement which comprises maintaining a body of pulp of substantial vertical extent subject to continuous feed and discharge at each stage, inducing a circulatory flow within said body so as to direct an elevating component of movement to substantially all the solids in the lower portion of said body and an unimpeded gravitational fall to a substantial portion of the solids in the upper portion of said body and below the surface thereof, supplying an aerating gas for entrainment in the pulp in said gravitational fall, and controlling thevolume and velocity of pulp in said gravitational fall so as to recirculate the pulp volume of said stage a plurality of times during said otation time.

References Cited in the le of this patent UNITED STATES PATENTS 1,556,083 Daman oct. 6, 192s 1,921,220 Daman Aug. 8, 1933 2,612,358 Daman -sepr. so, 1952

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