US2350943A - Countercurrent froth flow flotation system - Google Patents

Description

June 1944- J. w. THOMPS ON ET AL 2,350,943

COUNTER CURRENT FROTH FLOW FLOTATION SYSTEM Filed March 2, 1940 4 Sheets-Sheet l .1 /4. Flam/=50 5 4.5500711 .Rtorncu 1944- J. W.QI'HOMPSON ETAL 2,350,943

COUNTER CURRENT FROTH FLOW FLOTATION SYSTEM Filed March 2, 1940 4 Sheets-Sheet a llll ll lllllll ll TTE NW 5 W5 JL 1 Gttorneg June 1944- J. w. THOMPSON ET AL COUNTER CURRENT FROTH FLOW FLOTATION SYSTEM Filed March 2, 1940 4 Sheets-Sheet 4 Ti rm? mm m mm Huh-kl Patented June 6, 1944 COUNTERCURRENT FROTH FLOW FLOTATION SYSTEM John W. Thompson and Lionel E. Booth, Salt Lake City, Utah, assignors to The Galigher Company, Salt Lake City, Utah, a corporation of Utah Application March 2, 1940, Serial No. 321,840

11 Claims.

This invention relates to a countercurrent froth flow flotation system which is advantageously applied to concentration of metallurgical pulps bymeans of flotation.

The principal objects of the invention are:

First. To produce a higher grade of concentrates by the so-called rougher cells of a flotation machine.

Second. To decrease or eliminate the amount of middling return. I

Third. To improve the metallurgical efliciency of flotation generally.

' water.

Fourth. To increase themetallurgical capacity I of flotation machines.

Fifth. To decrease or eliminate the amount of spray or wash water used in launders.

Sixth. To reduce floor space requirements.

Seventh. To allow the direct filtration of flotation concentrates.

Eighth. To simplify the cleaning and re-cleaning operations.

Ninth. In comparison with prior practice, to reduce the quantity of frothing reagent required.

The manner of attaining the objects just outlined, and some of'the resulting advantages are set forth briefly in the following paragraphs.

(a) The froth is caused to travel from the tailing end of a flotation machine unit towards the feed end and is discharged in proximity thereto. In the course of its travel from the tail- 3 ing end to the froth discharge end, the froth drops any gangue orvalueless material back into the pulp zone of the machine.

(b) A smaller amount of froth is discharged fin circulating loads a ndv because the spray and launder wash water is virtually eliminated.

fe kshort launders only are required at the pointof frothnischarge, and as a result, steep slopes can be used,'which discharge directly into a pump box or any other convenient point for retreatment. j "f f ('j)- The floor space required, is reduced because of increased cell capacity and because of the elimination of side'launders for carryingoff the froth. I r i (g) Laimders'are advantageously placed on steeper grades, thereby allowing for the direct discharge of concentrates to filters. I

(h) Rougher' froths' and-intermediate froths are advantageously discharged directly to cleaner or re-treatment cells without the use of dilution This provides for extremely compact installations.

(2') Because less froth is removed from the flotation cells, less frothing reagents are required. I According to the invention, a liquid or semiliquid such as flotation pulp, is confined as a normally static body. Different parts of the pulp body are subjected to progressively varying bubble generation, for example, by means of aeration or agitation in varying degrees, with the result that correspondingly varying masses of froth containing the valuable mineral of an ore under flotation treatment, are constantly building up on the surface of the pulp. The differences in the levels to which the froth builds up, create potential fluid heads which cause the froth to flow by gravity from the higher levels to the lower levels, and particularly to the lowest level at one end of the pulp body where the froth which carries the finished or partially finished concentrates, is advantageously discharged and saved. The less valuable materials or tailings,

on the other hand, are caused to flow counter to the flow of the froth, and are discharged at the other end of the pulp body. This is accomplished by causing the maximum degree of progressive. aeration or agitation to take place in proximity to the point of discharge of the tailings.

An advantage of this novel arrangement is that worthless particles or gangue, which may inadvertently be carried up through the pulp by the 3 rising froth, are promptly dropped back into" the current of ta'ilings and discarded as waste. The novel characteristics of the machine of the invention make feasible many original combinations of individual flotation multiple cell units, as will'hereinafter be more fully explained. By means of such combinations, large savings in original plant cost, in operating time and expense, and in the cost of reagents may be ef fected.

' Apparatus for practicing the invention may advantageously comprise a plurality of individual flotation cells arranged together in series to form a-niultiple cell unit in which free communication "among the constituent cells, as well as a common pulp level, are maintained, while at the sametime, 'the'cell's are operatively distinct one from Each cell is advantageously provided with its individual froth generator, and each froth generator is regulable according to the'quantity of froth required at its own particular location in the sequence of operations of the multiple cell unit as a whole. The pulp feed isintroduced into the first cell, advantageously at a point low in the pulp body, and is conducted successively through the remaining cells of the unit, until used at the taillngs end of a flotation machine,

while progressively smaller quantities of air are used in the successive cells of a series until the first cell at the head end is reached.

The froth containing the valuable minerals of an ore under treatment, progresses from the last cell towards the head end where it is discharged from cell No. 1 in the form of finished or partially finished concentrates, the latter being conducted to a cleaning flotation machine which may or may not utilize the countercurrent I froth flow feature.

In the accompanying drawings, which illustrate specific embodiments by means of which the invention is advantageously put into practice,

Fig. 1 represents in plan, a flotation machine comprising for example, four cells;

Fig. 2, a longitudinal, verticalsection taken on the line 2'-2 in Fig. 1, pipes in the background being omitted;

Fig. 3, a cross-section taken on the line 3-3 in Fig. 2;

Fig. 4, a diagrammatic plan, corresponding to Fig. 1 and serving as a nucleus around which the succeeding Figures 5 to 28 are developed;

Fig. 5, an arrangement similar to Fig. 4, but arranged for producing a better grade of concentrates withoutmiddling returns;

Figs. 6 and '7, respectively, a diagrammatic plan and corresponding front elevation showing an arrangement for re-treatment or cleaning of concentrates from multiple cell rougher units;

Figs. 8 and 9, respectively, a diagrammatic plan and corresponding front elevation operatively similar to Figs. 6 and 7, but having the cleaner cells turned through an angle of 90 degrees for straight flow of concentrates over the end of machine for the purpose of economizlng showing the manner in which cells may be added for greater capacity;

Figs. 12 and 13, respectively, diagrammatic plan and corresponding front elevation of an arrangement of cells for double cleaning treatment of metallurgical pulp;

Figs. 14 and 15, respectively, a diagrammatic plan and front elevation showing rougher cells with a drop in elevation between each group of four cells, which facilitates the control and feeding of reagents in certain cases; g

Figs. 16 and 17, respectively, a diagrammatic plan and front elevation of a cell arrangement similar to that shown in Figs. 14 and 15,,but having the cleaner cells turned through an angle of 90 degrees, for the purpose of giving the concentrates a right line flow through the machine and at the same time accomplishing an economy in floor space;

Figs. 18 and 19, respectively, a diagrammatic plan and front elevation of a cell arrangement having the advantages of operation of those shown in Figs. 16 and 17, but providing for a more compact floor disposition;

Figs. 20 and 21, respectively, a diagrammatic plan and front elevation of a cell arrangement having-operative characteristics similar to those of the arrangement in Figs. 14 and 15, but showing an especially advantageous floor arrangement;

- Figs. 22 and 23, respectively, a diagrammatic plan and front elevation of an arrangement having the advantages of that shown in Figs. 14 and 15, but in which the cleaner cells are parallel to the rougher cells, and more cleaner cells are provided for;

Figs. 24 and 25, respectively, a diagrammatic plan and front elevation of an arrangement of rougher-cells having a drop in elevation between them as in Figs. 14 and 15, but providing for double cleaning;

Figs. 26 and 27, respectively, a diagrammatic plan and front elevation, of a cell arrangement which accomplishes operative results similar to those accomplished in the arrangement of Figs. 24 and 25, but providing for a considerably more compact floor disposition; and

Fig. 28, an end elevation in diagram, viewed Referring to the drawings, Figs. 1, 2 and 3 show a flotation machine which includes much of the mechanism forming the subject of United States Patents Nos. 2,055,065 and 2,085,947, granted to Lionel E. Booth. This mechanism'has novel features which are particularly well adapted for use in combination with the present invention.

Patent No. 2,055,065 is concerned with a rotatable impeller comprising a tight walled, substantially bell-like structure along the lower circumference of which a plurality of depending teeth or lugs are spaced apart from one another. Compressed fluid, such as air, is conducted into the hollow interior of the bell, and this air is caused to bubble through the spaces between the depending teeth, into the surrounding pulp. The size of the bubbles is determined largely by the speed of rotation of the impeller, while the quantity of bubbles generated is advantageously regulated by the amount of compressed air admitted into the bell.

Patent No. 2,085,947 is concerned with peeling blades that are advantageously disposed radially around the impeller just described, in order to conduct the copious flow of bubbles from the impeller upwardly through the pulp, thereby preventing a congestion of bubbles around the impeller, and thus enhancing the efllciency thereof.

In Figs. 1,2 and 3, the numeral 40 denotes a structure embracing four successive individual cells I, 42, 43 and 44, the one at M being regarded as the head cell and the one at M, the tail cell. The pulp is advantageously introduced into head cell 4| through an inlet opening 46 located at the-bottom of a feed box 45, the inlet opening being advantageously located low in the cell structure.- In this cell, the pulp is exposed to the proper means for producing a certain desired amount of froth which rises through the pulp body 41 and into the space "-4 above the pulp surface 49. The pulp body is caused to travel successively through the cells ll, 42, 43 and 44 in the general direction of the arrow 53. During the movement of the pulp through the respective cells, it is exposed to a graduated increase in froth generation, which results in a correspondingly greater quantity of bubbles rising through the pulp from cell to cell until thelast cell is reached, where the froth production in the present example, is at the maximum. This 2,360,943 results in building a body of froth 48 which is deeper at 48-2 than it is at l8-I', whereby a fluid or hydrostatic head is created approximately along the gradient 59. The froth being extremely mobile, tends to find its fluid surface level because of gravity, and in so doing, a quantity of froth is continually being pushed in the direction of the arrow 54, from the higher froth levels to thelowest froth level, at which latter point it overflows the froth discharge weir to be disposed of as desired.

A hollow, tight-walled impeller is indicated at 56, it being rigidly mounted on a rotatable shaft 61, supported and driven in any suitable manner (not indicated). Spaced apart from one another along the lower circumference of the tightoccupied, combined with maximum performance and output of the flotation machine. For the purpose of giving at least a partial understanding of walled portion 56 of the impeller are depending lugs 55, and projecting upwardly into the interior of the impeller is a pipe 58 through which compressed air is discharged. The compressed air reaches the pipe 58 through the pipe assembly 59 from a main supply header 69, and the flow of compressed air from the header to the impeller may be controlled by a valve 6 I.

In operation, assuming the impeller to be rotating at the proper speed, which may vary from 1209 to 1900 f. p. m. and assuming the proper amount of compressed air to be flowing into the impeller, the compressed air bubbles through the spaces 62 between the lugs 01' the impeller. The incipient bubbles are clipped into extremely small bubbles which in rising through the pulp, pick up the mineral and form the froth masses. F. p. m. indicates peripheral feet per minute.

The fine bubbles which are discharged by the impeller are guided upwardly through the froth by means of the peeler blades 63, 64 and 65. it being understood that the number and arrangement of the peeler blades are not restricted by ,the showing in the present drawing, which represents merely a suggestive arrangement.

The impeller 56 and rotatable shaft 51 are duplicated at 56-I to 56-9, and ST-I to 513, respectively, in the respective cells 92 to M. The peeler blades 63 to 65 are also duplicated in the cells 42 to 44, although the duplicates are not shown in the figures.

The amount of froth generated in the successive cells may advantageously be controlled or regulated by precisely varying the relativeamounts of compressed air admitted into each respective impeller, by means of valves 6| to '6I3. It is also possible to vary th generation of froth in the successive cells by varying the speeds of rotation of the respective impellers 56 to 56-3.

In order to provide .for the freeflow of the froth, as well as for the free counterflow of the tailings, it is advantageous to separate the different cells one, from another, by comparatively low baflles, such as those indicated at 67 in Figs. 1 and 2. The sidewalls '68 and 69 and endwall I9 serve to confine the froth to. the channel formed over the surface of the, pulp. and to compel the froth to be discharged at the weir 5!, as hereinbefore mentioned. The tailings stream may advantageously be discharged over ayweir II, and disposed of as desired. Both the weirs 5| and Il may consist of removableflashboards for varying the relative heights thereof.

; .'I'he multiple cell system of constructiqn is very elastic and adapts itself to an almost endless the many combinations of cells that can be advantageously made to meet difierent requirements, a few of the possible'combinations are further illustrated in diagrammatic form in Figs. 5 to 28.

The arrangement in Figs. 6 and 7 is one for positive re-treatment or re-cleaning of rougher concentrates. In this arrangement the feed enters at I6 and passes through the four rougher cells 18, discharging the tailings at 19 and the rougher concentrates at 99, from where they pass directly into the cleaner cells BI. The finished concentrates are discharged at 82, while the cleaner tailings are discharged at 83 into a pump 99, from where they are returned into the main feed '95. For convenience, the pump 94 is omitted in Fig. '7.

In Figs. 8 and 9 the arrangement is similar to that in Figs. 6 and 7, but the cleaner cells aI-I have their longitudinal dimensions at right angles to the longitudinal dimension of the rougher cells I6. The pump is indicated at 84-I, and the cleaner concentrates are discharged at 82-I, cleaner tailings at 93I.

In Figs. 10 and 11. the cleaner unit 8I-I is similar to that in Figs. 8 and 9, but the number of individual cells in the rougher unit 86, is increased for greater tonnage. Here, the feed enters at 81. The rougherconcentrates are discharged into the cleaner unit at '86, and the rougher tailings are discharged at 89. The cleaner tailings are discharged at 99 and pass into the pump 9I from where they are returned to the feed 81.

In Figs. 12 and 13, a double cleaning treatment is provided for. The feedenters at 92, and passes through the rougher unit 93, from which the concentrates pass at 94 into theflrst cleaner unit 95.

The concentrates from the first cleaner unit pass at 96 into the second cleaner unit 91. The tail ings from the two cleaner units are discharged at 99 and 99 respectively, and in combination enter the pump I99 which returns them into the,

feed 92. The finished concentrates from the second cleaner unit are discharged at It", while the total tailings are discarded from the rougher unit.

a drop in elevation between the cells is provided for. This facilitates the control and feeding of reagents in certain cases. The feed enters the first, rougher unit I93 at I96, and the concentrates from this unit are discharged at I91 into the cleaner unit m5. While the-tailingsare dis;

charged at; I98, passing into the second rougher unit I94, from where theconcentrates are,dis-.

charged at III and the tailings at-IIZ. I'he'tailings. from the cleaner unit I are discharged at.'

H3 and are passed to the pump I, being joined meanwhile by the concentrates discharged at I II,

The arrangement of cells described in conneccarded at I41.

to be returned to the feed at m. The finished concentrates are discharged at I I5.

gles to the longitudinal dimension of the rougher units HIS-l and ll4-I.

In Figs. 18 and 19, the arrangement is operatively similar to that in Figs. 16 and 17, but is more compact because the second rougher unit Il4-2 is placed in parallel with the first rougher unit I03-2 instead of being in tandem therewith as in Figs. 16 and 17.

In Figs. 20 and21, the arrangement is operatively similar to that in Figs. 14 and 15 but provides for a different disposition as to floor space. Here. the feed enters the first rougher unit III-lat HIS-3, while the tailings from the IIi4-l are discharged at second rougher unit 2-4. The finished concentrates are discharged at -3 from the cleaner unit "5-3.

- In Figs. 22 and 23 the general arrangement again is similar to that in Figs. 14 and 15, but more cells are included in the cleaner unit together with a somewhat different floor arrangement. Here, the feed enters at IIB into the first rougher unit N1, the concentrates from which pass at II8 into the cleaner unit IIS, while the ta lings pass at I2II into the second rougher unit The concentrates from the second rougher unit are discharged at I22, and are ioinedby the tailings from the cleaner unit which are discharged at I23, the two going to the pump I24 by which they are returned to the feed H6. The total finished concentrates are discharged at I25,

' and the total tailings are discarded at I26.

In Figs. 24 and 25, the arrangement provides for a drop in elevation between the two rougher units I21 and I28 for the same purpose as that in Figs. 14 and 15, but includes the double cleaning feature by means of two cleaner .units I29 and III. The feed enters at III; the concentrates from the first rougher unit I21 pass at It: into the first cleaner unit I29, while the tailings from the first rougher pass at I83 into the second roug'her unit I28. The concentrates discharged at I34 from the second rougher, are merged with the tailings discharged at Ill-4 and I29-l respectively from the two cleaner units, and at I54 are pumped back into the feed iii. The total concentrates are discharged at I35 from the first cleaner unit, and the total tailings are discharged at I36 from the second rougher unit.

. In Figs. 26 to.28, the arrangement provides for the same general operative result as attained by that in Figs. 24 and 25, but at the same time provides for conservation of fioor space. Here. the first rougher unit is indicated at I21, the second at I32, the first cleaner unit at I30, and the second cleaner unit at I40. The feed enters the first rougher at I4I, while the concentrates from this rougher enter the first cleaner unit I at I42. The tailings from the first rougher enter the second rougher at I43, while the concentrates from the second rougher leave at I, merge with the tailings from both the cleaner units and are returned by means of the pump I45 to the feed I. The total finished concentrates are discharged at I46, while the total tailings are dis- The concentrates from the first cleaner I go through the passage I44 into the second cleaner I40 and the tailings from the sec-v ond cleaner are discharged at I49.

The structure illustrated in Figs. 1 to 4, may

' of the structure.

be described as composed of the individual cells 4i to 44, or it may consistently be regarded as embracing only a single cell whose configuration is longitudinally extensive and which is provided with means for quantitatively graduated froth generation from end to end, or in which froth generators are spaced apart from one another along the longitudinal dimension with means for precisely varying the production of froth by the successive generators. If desired, the battles 51 may sometimes be omitted, which still further emphasizes the single cell viewpoint.

In any event, the distinguishing feature of the machine is always the open and substantially unobstructed passage for pulp and froth in countercurrent relation to each other from end to end various assemblies of units shown in Figs. 5 to 24, as well as to the unit shown in Figs. 1 to 4. For example, the assembly as shown in Figs. 12 and 13,,c0nsists of the three units 83, 85 and 21, where the passage through the rougher unit 93 is open and unobstructed from the end I5| to the other end I52, although including six individual impeller spaces each provided with its own impe1ierI53.

Again, in the same figures, the open passage through the first cleaner unit 95 extends from the end I54 to the other end I55, and in the second cleaner unit 91, from the end I55 to the other end I51.

Another example is the assembly in Figs. 26 to 28. Here the open passage through the first rougher I31 extends between the ends I58 and I59; the open passage through the second rougher I38, between the ends I60 and I5I; the open the ends I62 and I83; and through the second cleaner I40, between the ends I64 and I65.

In the most advantageous form of the machine, the two sidewalls, such as 68 and 69 in Figs. 1 and 2, are sufllciently high so that the froth is prevented from overflowing excepting at the end weir 5|. There are times however, when it becomes desirable to discharge the froth over either one or both sidewalls. In such cases these walls are provided with removable flashboards, for example, such as those shown at I1II, I1I, I12 and I18. When these flashboards are removed, the froth may overflow at suitably graduated levels, for example, those represented by the bottom edges of the fiashboards, which in this instance follow closely the gradient 50. By removing such flashboards in various combinations thereof, almost any desired control may be exercised over the sidewall froth discharge. The sidewall discharge of froth may be carried off by any suitable means, for example, by launders "4..

The invention is characterized by the countercurrent relationship existing between the froth flow and the flow of the at-least-partially-impoverished pulp or tailings, as herelnbefore explained. It should be remembered however, that while the froth flow in this relationship is along the substantially level surface of the pulp body, the counterflow of the pulp and its suspended tailings is not likewise substantially horizontal.-

In fact, it is only the net transportative displacement of the pulp and its tailings that is horizontal, because both are subjected to the varying upwardly directed impulses in the successive bubble column zones. This variation causes many of the pulp particles, including tailings, to circulate upwardly and downwardly during the progress of this horizontal displacement.

This viewpoint applies to the at the weir ll accordingly.

The aerating mechanism of the aforementioned Patent 2,085,947 is especially well suited for use in combination with the present invention, because air or other fiuid is admitted to the impeller under pressure, usually from threefourths to one and one-half pounds per square inch. The flow of this compressed fluid through each successive impeller, is subject to accurate control, whereby the requirements of the invention for precisely differentiated generation of fluid bubbles to form froth in differential quantitles at the corresponding localities on the surface of a pulp body, are fully accomplished.

It is the ability to control the constant formation of froth at definite points and in certain predetermined quantities that makes possible the gravity flow of the froth across the surface of a pulp body in opposition to the movement of the pulp body, which in this instance is in the direction of the weir H, and occasioned by the overflow at that point. a

In ordinary flotation, froth is removed along the full length of a machine. .Since large proportions of the reagents used, are removed with the froth, the frothing properties towards the tail end of a machine are materially diminished, frequently to a point where it is diilicult to maintain a froth overflow at all at this end of the machine.

In using the countercurrent flow feature, it is to be noted that since the froth breaks down in traveling from the tail end to the head end, water composing the bubbles, together with reagents, is dropped back into the pulp body and is again carried towards the tail end .of the machine, thus using this part of reagents over and over again.

Performance of the countercurrent froth flow system compared with performance of what has heretofore been regarded as standard practice, in actual operating tests, gave results as follows:

Test N0. 1

Zn Fe Insol.

C. C. F. F. system: Percent Percent Percent Concentrates 63. 0. 2. l 'lailing 1.3 Stfiidlard practice at Silver King 1 (on centrates 63. 2 0. 8 l. 3 'Iailing 1.6

Test N0. 2

Zn Fe Insol.

C. C. F. F. system: Percent Percent Percent Concentrates a 62.6 0. Tailing 1.1 stgllllflllllld practice at Silver King i i Concentrates 63.0 0. 8 l. 6 Ta 'ng. 1.0

It will be noticed that the concentrate recova cries and tailing losses are practically the same for both the countercurrent froth flow tests and invention, are self evident. The direct savings in reagents hereinbefore dwelt upon, are in addition to the savings just enumerated.

Having fully described our invention what we claim is:

1. A method of counter-current froth-flow flotation, comprising feeding flotation pulp substantially constantly into one end of a normally static, longitudinally extended body of flotation pulp which has substantially uniform width, thereby imparting a substantially constant, and substantially unidirectional, longitudinal displacement or transition to the pulp body and causing pulp to discharge at the opposite end of the pulp body; introducing air into' the transient pulp body in graduated quantities from end to end thereof, the greatest quantity being introduced at the said pulp discharge end; and accumulating the resulting bubbles in the form of froth on the surface of the pulp body substantially in the proportion of air introduction at corresponding points along the length of the pulp body, thereby forming a hydrostatic head of froth, and causing the said froth to flow by gravity along the surface of the pulp body counter to the direction of transition of the pulp, by confining the said froth against discharge at said pulp discharge and and laterally along the length of the pulp body.

2. A method of counter-current froth-flow flotation, comprising feeding flotation pulp into one end of a normally static, longitudinally extended body of flotation pulp which has substantially uniform width, thereby imparting a substantially constant, substantially unidirectional, longitudinal displacement or transition to the pulp body and causing pulp to discharge at the opposite end of the pulp body; conducting the transient pulp one into another, the said froth generating zones extending from near the locality of feeding pulp to near the locality of discharging pulp; generating froth in the successive generating zones with increasing intensity of generation from zone to zone, the least intensity being in promixity to the locality of feeding pulp, and the greatest in proximity to the locality of discharging pulp, thereby causing froth to rise, to the surface of the pulp body in quantities which are substantialy proportional to the successive intensities of generation; and. accumulating the said froth on the surface of the pulp body as it rises, thereby forming a hydrostatic head of froth, and causing said froth to flow by'gra'vity along the surface of the pulp body counter to the'direction' of transition of the pulp, by confining the said froth against discharge at the locality'of discharging pulp and laterally along the length of the pulp body substantially up to the vicinity of said local ity of feeding pulp. I I

3. A method of counter-current froth-flow flotation, comprising maintaining a longitudinally extended body of flotation pulp having substantially uniform width; introducing air into the lower portion of the pulp body in successively graduated quantities from maximum to minimum along the length thereof and within an aerating zone which is substantially coextensive horizontally with the said pulp body, to form bubbles which rise through the pulp body and to the surface thereof in substantially correspondingly graduated quantities; continuously supplying additional pulp to the pulp body near one end thereof and continuously discharging tailings near the opposite end thereof, thereby causing the aerated pulp to fiow in a substantially continuous, substantially unidirectional longitudinal stream from the pulp inflow end of the pulp body to the tailings discharge end thereof and immediately above said aerating zone; accu-' mulating the bubbles. in the form of froth at the. surface of the pulp body substantially in the proportion of air introduction at corresponding points along the length of the pulp body, thereby forming a hydrostatic head of froth, and causing the said froth to flow by gravity along the surface of the pulp body counter to the direction of transition of the pulp, by confining the said froth against discharge at said tailings discharge end and laterally along the length of the pulp body; and discharging said froth from the surface of the pulp body near said pulp inflow end thereof.

4. A method, as recited in claim 3, wherein a minor part of the froth is discharged at a locality or localities situated between the two end extremities of the pulp body.

5. A flotation machine, comprising an elongated container adapted to hold a body of pulp; aeration means disposed in an aerating zone defined at a low level within said container and said means extending along the length thereof; pulp inflow means disposed near one end of said container; tailings outflow means disposed near the opposite end of said container; froth outflow means disposed at the upper part. of said container near said pulp inflow means; and means for effecting flow of froth along the surface of said body of pulp substantially from the tailings-outflow end of said container to the said froth discharge means, said container having its interior, above said aerating zone, substantially free and unobstructed so pulp may flow substantially horizontally, substantially unidirectionally, and longitudinally, from said pulp inflow means to said tailings outflow means and within a zone disposed above said aerating zone.

6. A flotation machine, comprising an elongated container having substantially uniform width and adapted to hold a body of pulp; aeration means disposed in an aerating zone defined at a low level within said container and said means extending along the length thereof; pulp inflow means disposed near one end of said container; tailings outflow means disposed near the opposite end of said container; froth outflow means disposed at the upper part of said container near said pulp inflow means; and means for regulating the supply of ,air to said aeration means so that said supply of air will be a maximum near the tailings-outflow end of said container and a minimum near the pulp-inflow end of said container, resulting in the building up of a hydrostatic head of froth upon the surface of the body of pulp at the tailings-outflow end.

of said container, and in the gravity flow of froth from said tailings-outflow end to said pulp-inflow end of the container during operation of said flotation machine, said container having its interior, above said aerating zone, substantially free and unobstructed so pulp may flow substantially horizontally, substantially unidirectionally, and longitudinally, from said pulp-inflow means to said tailings-outflow means and within a zone disposed above said aerating zone.

7. A flotation machine, comprising an elongated container adapted to hold a body of pulp,

said container having its lower portion partitioned off at intervals along its length transversely of its width forming individual aeration cells; mechanical aerating means disposed in the respective aeration cells; pulp inflow means disposed near one end of said container; tailings outflow means disposed near the opposite end of said container; froth outflow means disposed at the upper part of said container near said pulp inflow means; and means for effecting flow of froth along the surface of said body of pulp substantially from the tailings outflow end of said container to the said froth discharge means, said container having its interior, above said aeration cells, substantially free and unobstructed so pulp may flow substantially horizontally, substantially unidirectionally, and longitudinally, from said pulp inflow means to said tailings outflow means and within a zone disposed above said aeration cells.

8. A flotation machine, comprising an elongated container having substantially uniform width and adapted to hold a body of pulp; said container having its lower portion partitioned off at intervals along its length transversely of its width forming individual aeration cells; mechanical aerating means disposed in the respective aeration cells; pulp inflow means disposed near one end of said container; tailings outflow means disposed near the opposite end of said container; and means for regulating the extent of aeration within the respective aeration cells so that the aeration will be a maximum near the tailings outflow end of said container and a, minimum near the pulp-inflow end of said container, resulting in the building up of a hydrostatic head 'of froth upon the surface of the body of pulp at the tailings outflow end of said container and in the gravity flow of froth from said tailings outflow end to said pulp inflow end of the container during operation of said flotation machine,

said container having its interior, above said aeration cells, substantially free and unobstructed so pulp may flow substantially horizontally, substantially unidirectionally, and longitudinally, from said pulp inflow means to said tailings outflow means and within a zone disposed above said aeration cells.

9. In a flotation system, a plurality of flotation units interconnected in series arrangement to effect a single final discharge of froth, each of said flotation units comprising an elongated container for pulp. having substantially uniform width and defining along its length a lower aeration zone, an intermediate separation zone; and an upper froth transportation zone, the said separation zone and froth transportation zone extending substantially free and unobstructed along substantially the entire length. of the said container, the container having pulp inflow means and froth outflow means near one of its ends, and tailings outflow means near its opposite end, and having further, means for aerating pulp differentially substantially from end, to end of said aeration zone, the locality of greatest aeration being near the tailings outflow end of the the pulp body and within said froth transportation zone during operation of said system, whereby froth flows along said froth transportation 10 zone toward said froth outflow means under the influence of gravity, and pulp flows substantially unidirectionally counter thereto; and respective passage means connecting the said froth outflow means of each of the said flotation units, except the last, with the said pulp inflow means of the next succeeding.

10. A method of countercurrent flotation comprising, maintaining a longitudinally extended body of flotation pulp; introducing air into the lower portion of the pulp body, within an aerating zone which is substantially coextensive horizontally with the said pulp body, to form froth which rises through the pulp body and accumulates at the surface thereof; continuously supplying additional pulp to the pulp body near one end thereof, and continuously discharging tailings from the pulp body near the opposite end thereof, thereby causing the aerated pulp to flow in a substantially continuous, substantially unidirectional, longitudinal stream from the pulp inflow end of the pulp body to the tailings discharge end thereof and immediately above said aerating zone; flowing the said accumulated froth on the surface of the pulp body and along the length thereof from near said tailings discharge end of the pulp body toward the said pulp inflow end thereof; and discharging said truth from the surface of the pulp body near said pulp inflow end thereof.

11. In a flotation system, a plurality of flotation units interconnected in series arrangement to eflect a single flnai discharge of froth, each of said flotation units comprising an elongated container for pulp defining along its length a lower aeration zone, an intermediate separation zone,

15 and an upper froth transportation zone, the said units, except the last, with the said pulp inflow 9 means of the next succeeding.

JOHN W. THOIWPSON. LIONEL E. BOOTH.

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