US2304270A - Flotation apparatus - Google Patents

Description

Dec. 8,1942. H. L. MEAD ETAL 2,304,270

- FLOTATION APPARATUS I I Filed March 8,,1940 2 Sheets-Sheet 1 Fla; 2.

Fit-'0 warn? .A/va kincriwr ATTORNEY.

Dec. 8, 1942. H. L. MEAD ETAL 2,304,270

FLOTATION APPARATUS Filed March 8, 1940 2 Sheets-Sheet 2 20 /5 /3 L I i l I i i /0 i i I w; Y

i f i i I 2 INVENTORS HAP/P) 4 M540,

4 ATTORNEY.

Patented Dec. 8, 1942 UNITED STATES PATENT' OFFICE FLOTATION APPARATUS Barry L. Mead and Ernest J. Maust, Brewster,

Fla., assignors to American Cyanamid Company, New York, N. Y., a corporation of Maine Application March 8, 1940, Serial No. 322,864

4 Claims. (01. 2b9 1s9) This invention relates to the froth flotation of ore materials and more particularly relates to improved apparatus and methods for the separation of silica fromphosphate rock by froth flotation.

The most important field of silica flotation at the present time is presented by the Florida pebble phosphate deposits wherein a finely divided siliceous gangue is present. However, up to the present timethe use of cationic reagents to effect a silica flotation has not been commercially feasible with phosphate ores due to the fact that excessive reagent costs resulted or else if the amount of reagent is reduced, the silica removal is not sufliciently complete. In the copending application Serial No. 325,011 filed March 20, 1940, patented September 8, 1942, No. 2,295,459, there is described a process of silica flotation in which the ore, such as for example, a pebble phosphate ore, is subjected to an extraordinarily complete desliming procedure removing the last traces of existing slime. These procedures have greatly improved the silica removal but encounter dimculties when applied to material such as certain phosphate rockswhich have relatively soft surfaces and which under the conditioning treatment normally preceding froth flotation, tend to disintegrate on the surface to form a small amount of a very finely divided slime. This slime, which is of the material that is not to be floated, appears to be still more deleterious in its effect on silica flotation than the original slime which is largely of a siliceous nature, often of the aluminum silicate type, and a small proportion of it will exert a greater effect than a corresponding proportion of ordinary slime.

The procedure of the present invention is effective with all siliceous ores which contain constituents that will readily yield slime in flotation machines and is particularly important in the flotation of phosphate rock where slime is readily formed and where the value .of the product is so low that mining beneflciation costs have to be kept at a minimum in order to show :any profit.

In accordance with the present invention a flotation apparatus isprovided which can not only be operated economically but which also results in the production of a highgrade phosphate product. Broadly the invention provides a method and apparatus which combines the introduction of the ore pulp after conditioning with the necessary flotation reagents, into a flotation cell below the froth area but above the zone of agitation whereupon the ore is subjected to aeration with a minimum of agitation. The

floatable portion of the ore material is immediately carried into the froth by the air bubbles and the tails or non-floatable material sinks until met by an upward flow of water from the zone of agitation and is discharged from the cell at a point immediately above the zone of agitation. During the flotation operation the major portion of the ore pulp does not come in contact with any moving mechanical parts and hence no interfering secondary slimes are produced.

The improved apparatus and method of the present invention will be made more apparent from the following detailed description when taken in connection with the accompanying drawings in which:

Fig. l is a diagrammatic vertical section through the center of the apparatus and illustrating the course of the ore pulp during operation;

Fig. 3 is an enlarged vertical section along the line 3-3 of Fig. 2.

Referring to the drawings in more detail, the flotation cell is made up of an outer shell 'or wall comprising a cylindrical side wall i and the conical bottom wall 2. The conical bottom 2 is provided with asuitable tail discharge outlet 3. A secondary cylindrical shell t is positioned inside the outer shell I, providing passage area 5 for removal of tails into conical portion 2.

An agitating and aerating mechanism 6 rests within the inner secondary shell 3. The agitating and aerating mechanism may be of any suitable type but is preferably of the Fagergren type which comprises a rotating element in the form of a squirrel cage composed of vertical staves which is surrounded partly or completely by a stator of similar construction. The rotary element is connected with a suitable air inlet 20 through which air is drawn into the pulp by coaction of the stator-rotor mechanism. The agitator mechanism 6 is so located in the inner shell l that upon rotation there will be a gentle suction action exerted on any liquid in the'pipe 1 extending from the bottom of the inner shell into the conical area of the outer shell to a point immediately above the tail discharge opening 3.

The fins or vertical baffles 8 in the inner shell prevent the swirl of liquids in the tank that would otherwise occur when the agitation mechanism is rotated.

The inner shell 4 also contains a battle 9 extending upwardly at a slight angle around its inner periphery at a point just above the zone of agitation and slightly below the upper rim of the shell 4. Around the inner periphery of the central shell I a baffle It! extends downward at a slight angle.- The baffles 9 and I are so arranged that in operation of the flotation machine ore particles that are lifted by air bubbles are directed into the froth which overflows the upperrim of the shell I into a launder II, and

, so that the tails or ore particles not supported by the air bubbles are carried along with the flow of water through the discharge opening I2 formed by the upper rim of the shell 4 and the lower portion of the baflle ID. The launder II spirals around the outer shell I in the manner shown so that the froth containing the concentrate will flow by gravity through the discharge pipe I2 to a storage tank or the like.

A feed inlet I3 opens into a feed distributing space I 4 formed by a larger hollow member I5 surrounding a housing I6 which encases a drive shaft H of the agitator mechanism.- 6. The lower portion of the housing I6 has a flared portion I8 covering the top of the agitator mechanism. The hollow member I5 also has a flared portion I9 at its lower end so that a substantially uniform space is maintained between the housing I6 and the hollow member I5.

While the feed distributing system is preferably that shown, any method of introducing the feed into the flotation apparatus so that the feed is distributed in the aeration zone at a point above the zone of agitation and does not come in contact with the moving partsof the agitator can be employed.

From the foregoing description the use and operation of the improved flotation apparatus of the present invention will be readily understood.

We refer now specifically to Fig. l'which illustrates the course of an ore pulp when subjected to a froth flotation operation according to the present invention. The ore pulp previously conditioned with water and the necessary flotation.

reagentsis introduced through the feed pipe I3 into the feed distributing area I4 and then drops onto the flared portion I8 of the housing I6. The ore pulp spreads out in the quiescent aeration zone 2| above the agitation zone 22 and below the froth level 23. The flared member I8 prevents the ore pulp from dropping directly into the revolving agitation mechanism 6. The agitator mechanism is ,rotated at the desired speed by means of the shaft I'I driven by any suitable source of power (not shown). The speed of the agitator mechanism and the amount of air 'introduced will, of course, vary with different ore materials.

As soon as the ore pulp enters the quiescent aeration zone or bubble. column, the floatable material is immediately lifted by the air bubbles and carried into the froth. The froth carrying the concentrate overflows into the launder II and thence by gravity through the pipe I2 to a suitable storage tank. The non-floatable or dif-' flcultly floatable ore material drops through this quiescent zone until met by the upward rising flow of water from the zone of agitation. These non-floatable particles or tails are carried along by the flow of water through the tail outlet I2 and dropped through the area 4 into the conical portion of the shell 2. The tails follow along the the recirculation pipe 1. Any bubbles which contain floatable materials and which pass in the tails are drawn up through this recirculation pipe by means of the gentle suction created in this pipe by' the agitating mechanism. These particles are thus returned to the main flotation cell where they are removed in the froth.

In most instances the froth will overflow into n the launder without any mechanical assistance.

However, invsome cases it will be desirable to use a skimmer to remove the froth. When particles of the concentrate drop out of .the froth due to insufficient. aeration or other causes; they are prevented from. passing into the tails' by means of the bafll I0 which deflects them into the aeration zone and they are thus subjected to further action of the air. bubbles and again lifted into the froth. When the concentrate is being carried upward by the air bubbles the baffle 9 prevents entrance into the tail outlet I2. It is to be noted that the bulk of the ore does not come into direct contact with the moving parts of the agitating mechanism. Only a small portion of the feed ever enters the agitating mechanism. Another very small portion of the tailing product (phosphate) with a small amount of concentrate passes up the recirculating pipe to enter the agitating mechanism.

- The improved apparatus and process of the present invention is not limited in its usefulness to any particular type of ore material. It is, however, especially suited for the froth flotation of silica from phosphate rock and this is a preferred embodiment of the present invention. As pointed out heretofore there are some problems peculiar to the froth flotation of silica from phosphate rock using cationic reagents which the present invention overcomes to a very large extent. One of the factors which affects the efiiciency of silica flotation from phosphate rock is that slimes have a detrimental effect on the cationic reagents. The primary slimes can be removed by desliming operations prior to the flotation operation and hence avoided. There are certain ore materials, however, which after a preliminary desliming operation and which are then subjected to direct contact with the agitating mechanisms in flotation machines, developa secondary slime. In the case of phosphate rock this secondary slime has even greater detrimental effect on the cationic reagents than the primary slimes. It is particularly desirable in the separation of silica from phosphate rock to effect a clean separation and remove as much of the silica as possible, since the tails are the valuable product in this type of flotation and any silica remainingbehind greatly lowers the grade of the phosphate. The apparatus of the present invention is very efficient in the removal of silica from phosphate rock by froth flotation.

When a properly conditioned deslimed flotation feed is subjected to froth flotation accordingtothe present invention, the flotation of the silica takes place very rapidly and immediately upon admittance to the cell. The ore pulp substantially does.

nism and hence there is little opportunity for the production of secondary phosphate slimes. A complete separation is effected in a single flotation cell which is also an important advantage, since it eliminates the necessity for employing a string of flotation machine's.

Referring again specifically to Figs. 1 and 3, the operation of the improved apparatus and process will be described in connection with phosphate rock. The conditioned feed with the proper amount of water and reagent is admitted in the central portion of the flotation cell and flows uniformly out into the cell above the agitation zone as indicated by the arrows. Hence, the silica that is ready to float is lifted by the air bubbles and comes to the surface immediately and is collected in the froth. The phosphate is kept in suspension due to the circulating water in the cell and flows by gravity into the phosphate (tails) take-off zone at the periphery of the cell above the agitation zone. Very little water is taken off with the phosphate so there is an extremely low velocity at the point of takeoff of the phosphate and hence there is little tendency for the rapidly rising silica to enter the phosphate take-off zone. While the silica is being lifted by the air bubbles, direct flow of the silica is deflected from entering the phosphate take-off zone by' the inclined bafiie 9 and any silica that may fall back after reaching the surface of the cell is deflected from entering the phosphate take-01f zone by the inclined baflie Ill. The small amount of flocculated silica which does enter the phosphate take-off zone is ready to float again under the slightest pretext if given the opportunity. Hence, as the tails pass beneath the recirculation pipe I, this flocculated silica together with water and a small amount of phosphate is drawn back into the cell proper where the silica is subjected to further aeration and is collected in the froth. The recirculation pipe I, while adding substantially to the usefulness of the present apparatus is not the important element essential for its operation.

In comparative tests on a sample of phosphate rock using the same cationic reagent combination we have found that much better results were obtained employing the apparatus of the present invention in which the phosphate tails are taken ofi? above the zone of agitation rather than at a point below this zone and this is one of the important features of the invention. In this test, flotation in the cell of the present invention, the phosphate tails obtained contained 78.09% B. P. L. with only 3.35% insoluble (silica), whereas a test in a similar flotation cell but having the phosphate take-off zone at the bottom of the cell in the area of agitation resultedin phosphate tails having 75.51% BQP. L. and 6.40% insoluble (silica). The percentage recovery in both instances were about the same, However; it

is noted that a much higher grade is obtainedusing the-flotation cell of thepresent invention and a single per cent increase in-grade of phosphate rock is worth more than an 8% increase in recovery.

Comparative tests between the operation of the improved floation cell of the present invention and a standard Fagergren cell were carried out as follows. r

A sample of Florida phosphate rock was subjected to froth flotation using a 12" cell of this invention, in the presence of cationic silicaprometer and a higher alcohol hydrocarbon frother.

Thesamephosphate rock was subjected tofroth flotation in two- 12" Fagergren cells connected in series and using the same reagent combination. Test conditions were so arranged that the feed and reagents could be directed to either of the two types of flotation cell without interruption, thus assuring that cell conditions for the test were constant and that the only difference in results would be due to the type of cell employed.

. from the Fagergren cells is entirely too high to Commuson No. 1

Cationic reagent with alcohol frother as an emulsion one 12" flotation cell of the present in- .vention Feed rate: 191.6 1bs./hr.

COMPARISON No. 2

Cationic reagent with pine oil added separately i one 12" flotation cell of the present invention I Lbs/T. feed Re- B. P. L. Insol. Ratio emery Cationic Pine reagent oil Feed... 37.68 Conc. 77. 44 2. 35 2. 27 90. 5 .43 43 Tails..-" 6.44

Feed rate: 334.4 lbs/hr.

Two 12" Fagergren cells Lbs./I. feed Re- B. P. L. Insol. Ratio Cationic Pine reagent oil Feed.-- 35.97 Cone".-. 71.67 Tails. 4. 24

Feed rate: 368.5 lbsJhr. In the above comparisons it will be noted that 'while the phosphate recovery was a little higher from the Fagergren cells the grade was much lower. The insoluble in the phosphate product come into the economical picture in phosphate flotation. In the case of improved flotation apparatus of the present invention and in which a single .cell was used,-a 92% recovery of a very high grade phosphate product was obtained.

As pointed out above, one-of the important points in flotation of silica away from phosphate is to obtain a silica-free phosphate product, or tails in this case. This is one of the outstanding advantages of the present invention over prior flotation cells and the ability to obtain economically a high grade phosphate product is the difference between the. commercial success or failure'of such a process.

Another important feature of this improved flotation cell is its freeness from sanding up.-

The silica floats out immediately and the phosphate overflows the periphery of the side walls above the zone of agitation, hence very little ma terial can remain in the cell and there is no opportunity for sanding up, whereas cells that do sand up or de elop dead areas in similar fltation cells result in failure. Also there is no opportunity for material to accumulate and be repeatedly drawn in the rotor-agitator mecha-- nism to produce secondary slimes to interfere with the silica flotation.

What we claim is:

1. In combination with a froth flotation apparatus of the aeration type including an aeration cell having located therein a stator-rotor mechanism comprising a rotating element in the form of a squirrel cage composed of staves surrounded in part, at least, by a stator of similar construction, an inverted funnel-shaped hood covering said stator-rotor mechanism and serving as an air inlet through which air is drawn into the cell by co-action of the stator-rotor mechanism, that improvement which comprises bafiie means surrounding said inverted funnelshaped hood and defining an annular space, means for introducing an ore pulp into said annular space, a plurality of radial vertical bafparatus of the aeration type including, an aeration cell having located therein a stator-rotor mechanism comprising a rotating element in the form of a squirrel cage composed of staves surrounded in part, at least, by a stator of similar construction, an inverted funnel-shaped hood covering said stator-rotor mechanism and serving as an air inlet through which air is drawn into the cell by co-action of the stator-rotor mechanism, that improvement which comprises a truncated conical baflie superposed over, and separated from, said funnel-shaped hood, said conical bafile terminating in a cylindrical sleeve surrounding and spaced from the air inlet passage, the space between the sleeve and air inlet and the space between the baffle and hood forming a passage adapted to permit the introduction'of an ore pulp, a plurality of radialbaffies disposed about the inner wall of the aeration cell and extending upwardly at least sub- I stantially to the top of the stator-rotor mechanism and outwardly to a point adjacent to, but spaced from, the outer staves of said statorrotor mechanism, an outer cell having a conical bottom surrounding the aeration cell and paratus of the aeration type including an aeration cell having located therein a stator-rotormechanism comprising a rotating element in the form of a squirrel cage composed of staves surrounded in part, at least, by a stator of similar construction, an inverted funnel-shaped hood covering said stator-rotor mechanism and serving as an air'inlet through which air is drawn into the cell by co-action of the stator-rotor mechanism, that improvement which comprises bafile means surrounding said inverted funnelshaped hood and defining an annular space, means for introducing an ore pulp into said annular space, a plurality of radial vertical bailies disposed about the inner wall of the aeration cell and extending upwardly at least substantially to the top of the stator-rotor mechanism and outwardly to a point adjacent to, but spaced from, the outer staves of said stator-rotor mechanism, an outer cell having a conical bottom surrounding the aeration cell and adapted to provide a space between the walls of the two-cells, a discharge opening in the conical bottom of the outer cell, a tailing discharge opening leading from the aeration cell into the space between the walls of the two cells, said tailing discharge opening being above the upper end of the radial vertical bafiles and a froth overflow at the upper periphcry of the outer cell.

4. A froth flotation apparatus according to claim 3 in which the aeration cell is provided with a recirculation pipe positioned at the bottom thereof immediately below the stator-rotor mechanism and extending downward into the outer cell to a point adiacent the discharge opening in the conical bottom.

HARRYJL. MEADQ ERNEST J. MAUST.

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