US2646882A - Flotation machine - Google Patents

Description

July 28, 1953 H. FRQJS'T, JR 2,646,882

- FLOTATION MACHINE Filed Aug. 2,1950 2 Sheets-Sheet l INi ENTOR. Hildreth Frost Jr.

gmqmw ATTOR N E YS H. FROST, JR

FLOTATiON MACHINE July 28, 1953 2 Sheets-Sheet 2 Filed Aug. 2, 1950 INVENTOR. Hildreth Frost Jr.

{W Maw ATTORNEYS to be carried upwardly by the air bubbles. general, it has been deemed necessary to produce Patented July 28, 1953 UNITED STATES PATENT OFFICE 2,646,882 FLOTATION MACHINE Hildreth Frost, Jr., Denver, 0010.- Application August 2, 1950, Serial No. 177,271

13 Claims. (01. 209-470) 1 V This invention relates to flotation machines. The selective flotation of mineral particles and the like, to separate Valuable particles such as minerals, from gangue or Waste material, or vice versa, or to separate certain mineral particles from other mineral particles, has been applied not only to the separation of metal or compounds ofjgold, silver, lead, tin, zinc, molybdenum and other mineral compounds or particles, from waste rock and from each other, but also to the separation of non-metallic materials, such as NaCl from KCl. In selective flotation, the ore or other material to be treated, if not already in sufficiently fine condition, is ground or otherwise broken down into relatively small particles, mixed and carried by water or other suitable liquid, in a slurry or pulp. -To this pulp is added one or more flotation reagents, depending upon the.

characteristics or condition of the mineral or material to be separated. Thus, the flotation reagent may be a frother, such as pine oil or an alcohol frother, or a collector, such as oleic or other longchain fatty acids and compounds thereof, certain long chain amines or amine hydrochlorides, or a Xanthate, or a depressant for the gangue or other material which is to remain in the pulp, such as alkaline compounds, certain silicates, and others, or a conditioning agent,

such'as a dispersion agent, a deflocculating agent such as Na2SiO4, or a flocculating' agent'such-as lime. Other reagents, in addition to those listed above may be utilized, either alone or in combination, and since the specific flotation reagent or reagents used depend upon the particular ore or material being treated, certain reagents being more useful for specific minerals or materials to be floated or depressed, it will be understood that the reagents form no part of the present invention and any suitable flotation reagent or reagents may be utilized in using the flotation machine of this invention. 1

The pulp, either after or simultaneously with the introduction of one or more flotation reagents, is aerated, that is, air'is introduced into the pulp, to formair bubbleswhich tend to carry the mineral or other particles to be floated to the surface of the pulp, thereby forming a froth. Removal of the froth, of course, effects the re:- moval of the particles carried thereby from the pulp. An accepted theory is that the collector coats or otherwise becomes attached to the mineral particles to be removed by the froth, and enhance the tendency for the desired particles as thick a frothbed as possible, to permit the readier removal of the desired particles. It is also generally accepted that the greater the density of the pulp, the more efficient will the flotation become, based upon the particles removed in proportion to the amount of air introduced, since apparently air bubbles tend to be forced upwardly more readily in a pulp of greater density. Nevertheless, for reasons discussed below, economic reasons have often prevented advantage to be taken of the higher efilciency of flotation with a greater pulp density,

Conventional flotation machines, now commonly in use, comprise a tank in which is disposed an impeller rotated at a relatively high speed, to agitate the pulp and to assist in the introduction of air into the pulp. Numerous types of impellers have been designed, some especially to break up the air stream, which is sometimes introduced through the impeller and at other times at points adjacent thereto, and others to produce greater agitation, so as to provide a maximum contact between air and pulp. Ore particles, of course, tend to be heighly abrasive, so that wear on the impellers, with resultant replacement costs, is no small item in the operation of such machines, Abrasive wear, of course, generally increases with an increase in the density of the pulp. Also, the power requirements of the impeller generally'increase upon an increase in pulp density.- Thus, impeller wear and power requirements often require that, for the least total overall cost of operation, a pulp of lesser density be treated, even though flotation efliciency is thereby reduced. 7

Other flotation machines utilize air for agitation as well as aeration, being generally known as air liftmachines, but such machines require unduly large amounts of power to compress the tremendous quantities of air necessary to provide the desired agitation, usually through relatively high velocity streams or jets of air. Such machines are generally obsolete, but many are still in use. 7

' Again, while the impellers or high velocity air jets tend to produce a greater contact between air and pulp, at the same time the churning effect thereof also has a tendency to break up larger air bubbles, or cause smallerair bubbles to drop the particles carried thereby. Also, for machines of any appreciable capacity, the distance which the froth must travel from the point at which it arrives at-the top .of the pulp, before being discharged as into a froth launder atone side of the to of the tank, may be sufficiently great that a portion of the air bubbles will have broken or been otherwise reduced in carrying capacity. rthermore, numerous air bubbles may tend, in traveling from the lower portion of a relatively deep bed of pulp to the surface, to disintegrate through expansion, so that the carrying capacity of the same is reduced or lost. In many instances, a relatively effective layer of froth can be produced on the surface of a body of pulp without undue diiiiculty, but if the layer is not removed immediately, it interferes with new bubbles coming to the surface, which tend to break up and drop the mineral particles back into the pulp. Thus, additional and expensive reagents have been deemed necessary to produce a sufficiently tough bed of froth that a suificient amount of the desired particles can be separated. As with many types of apparatus, conventional flotation machines are generally designed for a specific capacity or flow rate, and variation there- .from results in increased costs, based upon either the volume of pulp. treated or the amountof material separated, and/or a decrease. in. separation ,efliciency. Thus, for one or more of the foregoing reasons, the efficiency of prior flotation operations is generally less than desired.

' Among the objects of the present invention are to provide a novel. flotation machine by which effective flotation separation can be accomplished with relatively thin froth layers; to provide such a flotation machine which permits pulp of greater density to be treated effectively, and without unduly increasing costs; to provide such a machine which permits the removal or froth from a. relatively shallow bed of pulp; to provide such a machine by which a. larger proportion of the air bubbles may effectively carry away desired particles; to provide such a machine which permits relatively large amounts of material, as well as small amounts, to be treated without a tendency for undue decrease in efficiency; to provide such a flotation machine which does not require rapidly rotating impellers, with the power requirements and excessive replacement costs due to abrasive wear thereof; to provide such a flotation machine which does not require unduly large amounts of power, such as required by air lift machines; to provide such a flotation machine wherein the removed froth is in a better condition for subsequent use; to provide such a flotation machine whose capacity may be varied without unduly decreasing the efliciency; to provide such a letation machine which may be utilized for the flotation separation of various types of ores or other materials; to provide such a flotation machine which may be adjusted to. accommodate different materials or operating conditions; to provide such a flotation machine which may be made in any one of several different forms, particularly to accommodate different types of ores or other materials to be separated; to provide such a flotation machine which may be adjusted to accommodate variations in the thickness or other characteristics of the froth layer; and to provide such a flotation machine which involves few moving parts, is relatively simple in construction, and is economical in operation.

Additional object and the novel features of this invention will become apparent from the description which follows.

A flotation method which the flotation machine of this invention is particularly adapted to carry out, comprises the steps of establishing a downwardly flowing body of conditioned ulp, the pulp being aerated sufficiently to cause at least a relacan be handled more readily by pumping equipment and the like. The pulp may be conditioned and aerated prior to the downward flow thereof, or maybe partly aerated and/or conditioned prior thereto and airintroduced from beneath into the body of the pulp during its downward passage. Also, a series of similar steps may be utilized, with re-aeration, repulping, and/ or the addition of add-itionalreagents between the passage of-the pulp along successive downwardly inclined paths.

Flotation. machines particularly adapted to carry out the above method are illustrated in the accompanying drawings, in which:

Fig. 1 is a perspective view, in vertical section, of a portion of a flotation machine constructed in accordancewith this invention;

Fig. 2. is an enlarged fragmentary perspective View, also in vertical section, of a portion of the machine of Fig. l, with certain variations;

Fig. 3 is a diagrammatic sectional elevation of a machine similar to that of Fig. 1;

Fig. i is a fragmentary perspective section of a. portion of an alternative table bed or bottom;

and

Fig. 5 is a vertical section taken through a series of louvres, alternative to the louvres of the machine of Fig. l. T

As illustrated in Fig. 3, flotation apparatus which includes the flotation machine of this invention may comprise a conditioner C of any suitable design, into which is introduced a pulp comp-rising particles of the material to be treated, carried by water, and to which suitablereagents are added, The conditioner C may include a suitable impeller 9, and, if desired, conventional means (not shown) for introducing air into the pulp so. as to aerate the same. From the conditioner C, in which the pulp remains for a period of time normally dependent upon the diffusion rate of the. flotation reagents, the conditioned pulp passes over an outlet baffle 53 into a feed chamber 1 l, the rate of flow of conditioned pulp to chamber H being controlled by an adjustable gate. l2, or in any other suitable manner. Aeration, or additional aeration may be accomplished in feed chamber H, as by an air pipe l3 from which air is introduced into the pulp through suitable holes therein. Aeration may be accomplished in any other desired manner, as by an air inlet box for supplying air to holes in the bottom of the chamber for discharging air into the pulp, although the air inlet may be located on a side of the chamberrather than the bottom, or a plurality of air inlets may be used.

Feed chamber II is disposed at the upper end of an inclined bed or bottom M. of a table T, having side walls I5. Disposed between the side walls 15 of table '1, and in spaced relation to bottom l4 and also downwardly inclined, are an inlet bailie l5 and a plurality of froth separating baffles or louvres El, the lowermost louvre ll leading to a froth' collecting trough o launder l8. Baiiie l6 forces the pulp to flo b t the louvres l1, while successive portions'of the layer of froth formed on top of the body of pulp, passing downwardly along the table bed I 4, are intercepted by each of the louvres l1, and the collected froth flows downwardly over each louvre IT, in turn, and over the lowermost louvre intothe frothilaunder l8,'from which it may be removed through an outlet IS. The remainder of the pulp iS discharged from the lower end of the table bottom l4 into a feed chamber 20 for a second table T, constructed similarly to the table T but at a lower elevation. Table T may be consideredas a continuation of table T, while feedohamber 20 for table T comprisesa convenient placeito repulp, re-a'erate; or add additional flotation reagents to the pulp. Thus, repulping may be accomplished by a paddle shaft 21, while further aerationmay be accomplished in a manner similar to that described in connection with feed chamber H. Table T,'similar to table '1, has an inclined bottom 14' and side walls 15, while disposed between side walls l5 and in spaced relation to bottom M are inlet bafile HS and louvres l1, over the lowermost of which'the removed froth flows into a froth launder i8 for dis-charge through an outlet I9. As -before, battle it forces the pulp to flow beneath the louvres l1, whilerelatively thin, successive portions of the layer of froth on top of the body of pulp, moving down bottom [4' of table T','are intercepted by louvres I1, and the remainder of the pulp is discharged into a tailings launder 22, from which the pulp may be carried to a suitable point of disposition, or to other separators or flotation apparatus, as for the purpose of removing additional components and the like.

It will be understood, of course, that more than two tables may be utilized, with each preferably forming a continuation, as it were, of the previous table, but with provision for repulping, and aeration when desired, in the feed chamber for each successive table. A plurality of tables may, of course, be placed in multiple deck arrangement, i; e. one above the othenand operated'in either-parallel or series relation, in the latter instance a zi'g-zagarrangement being employed, if desired. When another table is to succeed table T, tailings launder 22 may be converted to a feed'chamber for the next table, with suitable provision for repulping, etc. Thus, the flotation operation may be continued until all the desired particles have been removed. The desirability of repulping between successive tables is occasioned by the tendency for stratification of the particles in the body of pulp flowing down the bottom of the'table, and the consequent tendency for heavier particles to collect in the bottom of the next feed chamber, and the upper portion of the body of pulp to contain a greater proportion of the water. It may, of course,'sometimes happen that aeration in a feed chamber will'produce sufiicient agitation for repulplng. In any event, the length of any table is preferably limited to a distance within which suflicient froth will be formed to warrant removal and/or within which stratification does not interfere un duly with flotation separation.

As illustrated in Fig. 1, the inlet baffles l6 and I6 may be provided with a curved, rearwardly and downwardly inclined upper end or lip 24, while the upper end of each of the louvres l1 and i7 is preferably provided with a rearwardly and downwardly inclined portion 25. Inlet baffle l6 and louvres I! may be substantiallyparallel to the table bottom l4, but inclined slightly upwardly with respect thereto, so as to be in substantially parallel relation themselves. However, the lowermost point of the upper end 25 of each louvre I! is preferably above the lowest point of the lower end of the respective louvre, to prevent any back flow or back wash of the pulp around the lower end of the louvre. In addition, to prevent any back flow of the removed froth into the pulp bed, the uppermost point of each louvre I1 is higher than the lowest point "of the lower and of the louvre next above; or,

"aerate the pulp therein, and assist in repulping.

As indicated previously, the holes and air box may be on a side of the feed chamber, or a plurality thereof may be utilized. If desired, for repulping an impeller or agitator of any suitable type may also be disposed in chamber 20, while additional preliminary aeration may be performed in initial feed chamber E I. The baffie J6 and louvres I! may be set in a predetermined position, and attached to the side walls 15 of table 'I', as may be inferred from Fig. '1, or the louvres may be mounted on a suitable framework by which the'inclination and/or spacing of the baffle and louvres with respect to the bottom [6 may be changed as desired, as well as the spacing between the louvres. As illustrated in Fig. 2, the bafile and louvres may be mounted on a frame which includes a bar 23 at each side, each of the louvres I! being pivotally attached, as 'bypins 29 to the'side bars 28 of the-frame. A longitudinally extending link 35 attached to each of the louvres, as by pivotal connections 31 at the lower ends of the latter, is adapted to be adjusted forwardly and rearwardly and maintainedin any desiredposition by'a set screw in a bracket 32, mounted on side bar 28, or in any other suitable manner. Thelouvre frame may alsobe adjusted in position by a set of adjusting screws, including front adjusting screws 33 and rear adjusting screws 3d,- mounted on brackets 35 on theside walls 15 of the table and connected 'to frame bars 28 by swivel brackets 36. As will be evident, rearward movement of the link 36 will cause the lower ends of the'louvres l! to be moved upwardly, thereby increasing the spacing between the louvres. Similarly, forward movement of thelink 30 will move the lower ends of the louvresdownwardly, thereby decreasing the spacing between the louvres. Upward or downward adjustment of the frame including side bars 28, may be accomplished by adjusting'screws 33 and, by which the louvres maybe adjusted bodily upwardly or downwardly, tipped from front to back or vice versa, or tipped to one side or the other. Such adjustments may bedesirable to accommodate different depths of 'thelayer of froth Which-tends to form on the top or the body" of pulp, or different depths of the pulp body; -Also, the table bottom is may be reciprocated oryibrated, as by an electrically operated vibrating mechanism (not shown) or by a reciprocating device 38 which is shown in Figs. 2 and 3 and which-includes a'crank, or a cam,

such device being similar in operating principle to vibrating or reciprocating. devices utilized in connection with jigs and, concentrating tables. If desired, the entire table may be vibrated or reciprocated, or the louvres only, to agitate the .pulp andv assist in flow of froth bubbles to the top of the downwardly flowing body of pulp.

Additional air, or air for aeration, may be supplied through the table bottom M, to provide aeration of the pulp body as it travels down along the table bottom, while, as illustrated in Fig. 4, the table bottom need: not; be smooth, but may be provided with, laterally extending corrugations or'riiiles 40, through whichair holes y extend, a. suitable. air 130x42 preferably being provided under the table bottonmso that air under pressure may be supplied to the holes 4!. 9f course, the corrugations need not extend the entire length of the table bottom, but only for a partthereof, while air also may be suppliedv to only a part of the length of, the table bottom. In case there is a tendency for a thicker layer of froth to be formed adjacent-the upper end of the bed, the spaces, 43 between the louvres may be correspondingly higher than at the lower end.

When the louvres are adjustable, as in the manner shown in Fig. 2, a suihciently close fit against the sidewalls l of the tank Tmay be provided to prevent pulpflow around the edges of the louvres, while, as in Fig. 5, a portion of the top of each louvre may be. provided with flanges or ridges l5 to tend to move the flow of the froth passing thereover toward the center, or in any other desired direction. Also, jets of water may be utilized to control the flow of removed pulp, or

tawash removed. particlesdown along the louvres.

The froth may also be discharged, as into side launder, from each louvre.

As will be evident from Fig. 1, wherein the flow of the main body of pulp is indicated by the solid arrows, and the flow of froth bubbles indicated by the arrows having circular appendages, the froth layer on top of the pulp tends to be forced by each upper end 25- of the louvres l'i into the space 43 between the respective louvre and the louvre or baille thereabove, the louvres, of course, being in overlapping relation. Spaces 43 may be between a e" and V in height, while the table bottom l4 may be inclined at about 5, although other spacings or angles of inclination may be. utilized. The froth removed through the uppermost space 43 flows downwardly over the top of the uppermost louvre, IT, and onto the second louvre ii, where it is joined by the: additional froth flowing through the second space 43, and, similarly down along each of the louvres until the entire collected froth flows into the froth launder I3. As will be evident, only a relatively thin layer of froth, equivalent in thickness. to the spaces 43, is removed at each louvre. The pulp body flowing down along the table-bottom I4 is, of course, preferably sufficiently deep that the froth layer on the top is forced up against the baffle or louvre thereabove, thus insuring that the desired froth will flow into each space 43. Since the body of pulp is relatively shallow, compared with present conventionalflotation machines, the froth bubbles do not need to travel a particularly great distance to reach the top of the pulp body, thus increasing the efficiency of separation. Also, since the froth layer may be removed by the successive louvres within a relatively short time after forming on top of the pulp body, the distance which; the froth bubbles .8 must travel prior to removal may be made relatively small, thereby further increasing the chiciency of separation. While probably a greater proportion. of. froth will be removed at the upper louvres, froth will. tend to continue to form beneath the -lower louvres and even a very thin layercan' be removed. -Furthermore, during travel of. the removed froth down along the louvres, the tendency for the froth bubbles to burst during such travel is; an advantage in the method and apparatus of this invention, since the liquid. formed by bursting bubbles will more readily wash removed particles down along the louvres. Also, liquid and particles collectingin froth launder 18, are morev readily handled by pumps and, the like, since the volume is reduced,

and there is less air, for a pump to handle. As

will be evident, as soon as the froth bubbles are removed-from the main body of pulp, fragility of-the bubbles is relatively immaterial, and in fact an advantage,; a u I i Since it is generallyrecognized that a higher flotation efficiency is; produced by operating with a pulp ofhigher density, it would be expected that previous flotation machines would operate more/economically with pulps of the greatest density which could be handled. However, as

indicated previously, an increase in the density of the pulp results in a'greater increase in the power requirements of a relatively high speed impeller, the increase in the power requirements being related to anexponential of the density, rather than to a linear function of the density, as apparently is the efiiciency. Thus, a point is soon reached at which any increase in density results in a greater overall cost, due to the more rapid increase in power requirements. However, with the flotation method and machine of the present invention, a pulp of considerably greater density than could be handled economically by previous flotation machines may be treated, and advantage taken of the increased flotation efficiency without unduly increasing the power requirements. Obviously, neither the table bed nor the operating louvres require power for operation, and even when the table bed and/or louvres are vibrated or agitated, the power requirements therefor will increase only in accordance with the increase in the weight of the pulp, compared with the total weight of the pulp and parts to be reciprocated, which will be a linear function having aslope less than one. 17 will be evident, of course, that the impeller in the present conditioner, when used, does not need to be a high speed impeller, but operated only at a sufficient speed that the reagents are adequately mixed. Furthermore, when aeration takes place primarily in the feed chambers, there is no necessity for aeration in the conditioner. The, repulping paddles, when used, also move relatively slowly, being utilized more as mixing paddles rather than high speed agitating paddles or impellers, as in the case of the impellers of previous flotation machines. 7 In addition to the increase in flotation separation efficiency with a pulp of higher density, the capacity of the apparatus is also increased, since with a pulp of higher density, less water must be run through the machine and consequently a, greater proportion of the total volume ofpulp passing through the machine comprises particles to be separated. A higher pulp density also tends to reduce the total amount of flotation reagents necessary, since dilution is reduced.

A, greater pulp density, and a consequent tendency for a more rapid froth bubble formation, will produce a sufficient froth pressure to force the bubbles between the louvres, and insure a rapid and effective removal of thefroth. Also, even with a pulp of lesser density, the froth pressure will be sufficient to force the bubbles relatively rapidly through the spaces between the louvres. Furthermore, due to the'restraining influence of the louvres above the froth, even a relatively shallow froth layer will produce sufficient pressure to force with froth through the spaces, in addition to gravity, thus causing-the machine of this invention to operate more effectively than common prior flotation machines, the froth bed of which I. generally open to the atmosphere and unrestrim ed in direction of flow. It will be evident thafi the flotation machine of this invention may be adjusted or set for any desired density or pulp capacity, since the'angle of inclination of the table bottom may be altered to accommodate different flow characteristics, rate of rise of froth bubbles, thickness of froth bed or layer, and other factors. Other variations and changes may also be made. For instance, the downwardly extending section 2| at the upper end of each louvre I1 and I1 may be inclined at diiferent angles to the respective louvre, and also need not be straight, but may be curved or have any other desired configuration, while the louvres themselves may have different configurations. In general, such a downwardly extending section is desirable to force as much of the froth layer as possible into the space between the louvres, although the vertical extent thereof may be altered for variations in froth layer depth, amount of froth layer removed, and other conditions. The lip 24 of baffles l6 and It may eX- tend downwardly for a greater distance in the feed chamber H or 20, as to form a more nearly enclosed. space for aeration, while the lip may be made adjustable, and also may have a different configuration from that shown.

The material of which the tanks, chamber, louvresand bafiies are made may be selected in accordance with the pulp to be treated. The framework of the tables may be made of wood, while the bed and side walls may be made of wood or metal, or wood covered with metal, as desired, and the bafiies and louvres, while preferably made of shaped metal, may also be made of wood or other suitable materials.

From the foregoing, it will be evident that the flotation method and machine of this invention fulfill to a marked degree the requirements and objects hereinbefore set forth. As will be evident, relatively thin froth layers can be effectively removed, the pulp body may be relatively shallow, and the froth bubbles may be removed within a short distance from their arrival at the top of the pulp body. This will permit the effective separation of particles, in a pulp wherein difliculty is encountered in producing any more than a relatively thin froth layer. As will further be evident, there need be no rapidly rotating parts, subject to constant abrasive wear, such as the impeller of the conventional flotation machines now in use, thereby decreasing power requirements as well as repair and replacement costs. Particularly by utilizing a series of tables, and repulping between the tables, the capacity of the flotation machine of this invention may be increased considerably without undue cost, while the machine may be operated at a smaller capacity without a tendency for decrease in efflciency, merely by adjusting the louvres for a supporting structures, and drives therefor, may

be eliminated. Even when the table is reciprocated, the reciprocatingmechanism is not subjected to abrasive wear, nor does it require the large amounts of power required by a high speed impeller, particularly of relatively large capacity.

Although certain variations in the embodi ments of this invention have been illustrated and described, it will be understood that additional variations and also other embodiments may ex-- ist, all without departing from the spirit and scope thereof.

What is claimed is:

1. A flotation machine comprising means for conditioning pulp; means for aerating said pulp; a table having an inclined bottom; a feed chamber for feeding said pulp to the upper end of said table bottom; and a series of inclined louvres disposed in overlapping relation and spaced above said table bottom with the highest point of the upper end of each louvre being above the lowest point of the lower end of the louvre next above;

2. A flotation machine as defined in claim 1, wherein the upper end of eachsaidlouvre is inclined rearwardly and downwardly.

3. A flotation machine comprising means for conditioning pulp; means for aerating said pulp;

a table having an inclined bottom; a feed chamber'for feeding said, pulp to the upper end of said table bottom; a series of inclined louvres disposed in overlapping relation and spaced above said table bottom with the lower end of each louvre below the upper end of the louvre next below;

and a froth discharge launder for receiving froth from the lowermost louvre.

4. A flotation machine as defined in claim 3, including means for adjusting the vertical dis tance between adjacent louvres.

5. A flotation machine as defined in claim 3,

including means for adjusting the distance between said louvre and said table bottom.

6. A flotation machine comprising a plurality of tables, each having an inclined bottom, said tables being disposed in descending relation; a chamber for feeding pulp to the upper end of each said table; a series of inclined louvres for each said table in overlapping relation and spaced above said table bottom with the lower end of each louvre below the upper end of the louvre next below, for intercepting froth and causing removed froth to flow along said louvres; a froth discharge launder for each said table and receiving removed froth from the lowermost louvre, each said table bottom except the lowest discharging the pulp remaining into the feed chamber for the next lower table; and a tailings discharge launder receiving the pulp remaining from lowermost table.

7. A flotation machine as defined in claim 6, including repulping means in the feed chamber for each table except the uppermost.

8. A flotation machine comprising a table having an inclined bottom; means for feeding pulp to the upper end of said table; means for vibrating said table bottom; and a series of inclined louvres in horizontal and .vertical overlapping relation and spaced above said table bottom, for intercepting froth and causing said froth to flow along said louvres.

9. A flotation machine as defined in claim 8, wherein said table bottom has a series of transversely extending corrugations.

10. A flotation machine as defined in claim 9, wherein said table bottom is providedwith holes, and said aerating means includes means for supplying air to said holes.

11. A flotation machine comprising a table having side walls and an inclined bottom; means for imparting vibratory movement to said table bottom; a feed chamber disposed generally below the level of the upper end of said table bottom and connected therewith so that pulp will overflow from said feed chamber down and along said table bottom; means for discharging air into pulp in said feed chamber; a baiiie disposed above the upper end of said table bottom in spaced relation therewith, said bafiie having a curved, rearwardly and downwardly extending upper'end, for forcing pulp to flow beneath said ;bafiie and down along said table bottom; a series of louvres disposed in overlapping relation and spaced from said table, each said louvre extending beneath the louvre next above and having a downwardly and rearwardly inclined upper end for intercepting froth and forcing said "froth to flow between said louvre and the louvre next above; a frame including side bars for supporting said bafile and louvres in said frame; a pivotal connection at the upper end of each louvre for mounting said louvre on said side bars; a link extending longitudinally above and along said louvres; a pivotal connec tion between said link and the lower end of each said louvre; adjustable means for mounting said link in a desired position; adjusting screws for each end of said side bars, said adjusting screws being mounted on a side Wall-of said tank; a froth removal launder for receiving removed froth from the lowermost louvre; and means for receiving the pulp discharged from the lower end of said table bottom.

12. A flotation machine comprising a table having side walls and an inclined bottom having transversely extending corrugations and holes therethrough means for supplying air to the holes in said table bottom; a feed chamber disposed generally below't-he level of th upper end of said table bottom and connected therewithso that pulp will overflow from said feed chamber down and along said table bottom; a ba-flie disposed above the upper end of said table bottom in overlapping spaced relation therewith, said baflle having a curved, rearwardly and downwardly extending upper end, for forcing pulp to flow beneath said bafiie and down along said table bottom; a series of louvres disposed in vertical and horizontal overlapping relation and spaced from said table, each said louvre having a downwardly and rearwardly inclined upper end for intercepting froth and forcing said froth to flow between said louvre and the louvre next above, the uppermost louvre extending beneath said bafile; a f r-0th removal launder for receiving removed froth from the lowermost louvre; and means for receiving the pulp discharged from the lower end of said table bottom.

'13. A flotation machine comprising means for conditioning pulp; means for aerating said pulp; a table having a relatively gradually and downwardly inclined bottom; a feed chamber for feeding said pulp to the upper end of said table bot tom; and a series of downwardly inclined louvres disposed in overlapping relation with the highest pointof the upper end of each louvre being above the lowest point of the lower end of the louvre next above, said louvres being spaced above said table bottom at approximately equal distances and at distances which permit a relatively shallow bed of pulp to flow along said table bottom beneath said louvres while additional :froth may be for-med during such flow.

HI-LDRETl-I FROST, J R.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 247,629 Garvin Sept. 27, 1881 711,015 Stebbins Oct. 14, 1902 775,945 Ste'bbins Nov. 29, 1904 1,480,884 Dolbear Jan. 15, 1923 1,792,179 McLean Feb. 10, 1931 2,221,008 Traylo'r Nov. 12, 1940 2,267,496 Ellis et 'al. Dec. 23, 1941 2,330,875 Ellis et al. 'Oct. 5, 1943

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